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Landing

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LANDING GEAR

LANDING GEAR SYSTEMS Learning Objective: Identify the various types of landing gear systems used on fixed-wing and rotary-wing aircraft. Every aircraft maintained in today is equipped with a landing gear system. Most aircraft also use arresting and catapult gear. The landing gear is that portion of the aircraft that supports the weight of the aircraft while it is on the ground. The landing gear contains components that are necessary for taking off and landing the aircraft safely. Some of these com-ponents are landing gear struts that absorb landing and taxiing shocks; brakes that are used to stop and, in some cases, steer the aircraft; nosewheel steering for steering the aircraft; and in some cases, nose catapult com-ponents that provide the aircraft with carrier deck takeoff capabilities. FIXED-WING AIRCRAFT Landing gear systems in fixed-wing aircraft are similar in design. Most aircraft are equipped with the tricycle-type retractable landing gear. Some types of landing gear are actuated in different sequences and directions, but practically all are hydraulically operated and electrically controlled. With a knowledge of basic hydraulics and familiarity with the operation of actuating system components, you should be able to understand the operational and troubleshooting procedures for landing gear systems. Main Landing Gear The typical aircraft landing gear assembly consists of two main landing gears and one steerable nose landing gear. As you can see in figure

Figure 12-1.–Tricycle landing gear. is installed under each wing. Because aircraft are different in size, shape, and construction, every landing gear is specially designed. Although main landing gears are designed differently, all main gear struts are attached to strong members of the wings or fuselage so that the landing shock is distributed throughout the main body of the structure. The main gears are also equipped with brakes that are used to shorten the landing roll of the aircraft and to guide the aircraft during taxiing. Nose Landing Gear On aircraft with tricycle landing gear, the nose gear is retracted either rearward or forward into the aircraft fuselage. Generally, the nose gear consists of a single shock strut with one or two wheels attached. On most aircraft the nose gear has a steering mechanism for taxiing the aircraft. The mechanism also acts as a shimmy damper to prevent oscillation or shimmy of the nosewheel. Since the nosewheel must be centered before it can be retracted into the wheel well, a centering device aligns the strut and wheel when the weight of the aircraft is off the

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gear. Flight instruments Most aircraft have these flight instruments: Altimeter

The altimeter shows the aircraft's altitude above sea-level by measuring the difference between the pressure in a stack of aneroid capsules inside the altimeter and the atmospheric pressure obtained through the static system. It is adjustable for local barometric pressure which must be set correctly to obtain accurate altitude readings. As the aircraft ascends, the capsules expand as the static pressure drops therefore causing the altimeter to indicate a higher altitude. The opposite occurs when descending. Attitude indicator

The attitude indicator (also known as an artificial horizon) shows the aircraft's attitude relative to the horizon. From this the pilot can tell whether the wings are level and if the aircraft nose is pointing above or below the horizon. This is a primary instrument for instrument flight and is also useful in conditions of poor visibility. Pilots are trained to use other instruments in combination should this instrument or its power fail.

Schempp-Hirth Janus-C glider Instrument panel equipped for "cloud flying". The turn and bank indicator is top center. The heading indicator is replaced by a GPS-driven computer with wind and glide data, driving two electronic variometer displays to the right. Airspeed indicator

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The airspeed indicator shows the aircraft's speed (usually in knots ) relative to the surrounding air. It works by measuring the ram-air pressure in the aircraft's pitot tube. The indicated airspeed must be corrected for air density (which varies with altitude, temperature and humidity) in order to obtain the true airspeed, and for wind conditions in order to obtain the speed over the ground. Magnetic compass

The compass shows the aircraft's heading relative to magnetic north. While reliable in steady level flight it can give confusing indications when turning, climbing, descending, or accelerating due to the inclination of the Earth's magnetic field. For this reason, the heading indicator is also used for aircraft operation. For purposes of navigation it may be necessary to correct the direction indicated (which points to a magnetic pole) in order to obtain direction of true north or south (which points to the Earth's axis of rotation). Heading indicator

The heading indicator (also known as the directional gyro, or DG; sometimes also called the gyrocompass, though usually not in aviation applications) displays the aircraft's heading with respect to geographical north. Principle of operation is a spinning gyroscope, and is therefore subject to drift errors (called precession) which must be periodically corrected by calibrating the instrument to the magnetic compass. In many advanced aircraft (including almost all jet aircraft), the heading indicator is replaced by a Horizontal Situation Indicator (HSI) which provides the same heading information, but also assists with navigation Turn indicator

The turn indicator displays direction of turn and rate of turn. Internally mounted inclinometer displays 'quality' of turn, i.e. whether the turn is correctly coordinated, as opposed to an uncoordinated turn, wherein the aircraft would be in either a slip or a skid. The original turn and bank indicator was replaced in the late 1960s and early '70s by the newer turn coordinator, which is responsive to roll as well as rate of turn, the turn and bank is typically only seen in aircraft manufactured prior to that time, or in gliders manufactured in Europe. Vertical speed indicator

The VSI (also sometimes called a variometer). Senses changing air pressure, and displays that information to the pilot as a rate of climb or descent in feet per minute, meters per second or knots.

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Additional panel instruments that may not be found in smaller aircraft include: Course deviation indicator

The CDI is an avionics instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a track, which can be provided by a VOR or an Instrument Landing System. This instrument can also be integrated with the heading indicator in a horizontal situation indicator. Radio Magnetic Indicator

An RMI is generally coupled to an automatic direction finder (ADF), which provides bearing for a tuned Non-directional beacon (NDB). While simple ADF displays may have only one needle, a typical RMI has two, coupled to different ADF receivers, allowing for position fixing using one instrument. Layout

Six basic instruments in a light twin-engine airplane arranged in a "basic-T". From top left: airspeed indicator, attitude indicator, altimeter, turn coordinator, heading indicator, and vertical speed indicator Most aircraft are equipped with a standard set of flight instruments which give the pilot information about the aircraft's attitude, airspeed, and altitude. T arrangement Most aircraft built since about 1953 have four of the flight instruments located in a standardized pattern called the T arrangement. The attitude indicator is in the top center, airspeed to the left, altimeter to the right and heading indicator under the attitude indicator. The other two, turn-coordinator and vertical-speed, are usually found under the airspeed and altimeter, but are given more latitude in placement. The magnetic compass will be above the instrument panel, often on the windscreen centerpost. In newer aircraft with glass cockpit instruments the layout of the displays conform to the basic T arrangement. Basic Six In 1937 the Royal Air Force (RAF) chose a set of six essential flight instruments which would remain the standard panel used for flying in Instrument Meteorological Conditions (IMC) for

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the next 20 years. They were: airspeed indicator (knots) attitude indicator vertical speed indicator (rate of climb) altimeter directional gyro (compass) turn and bank indicator (aircraft attitude) This panel arrangement was incorporated into every RAF aircraft, from the light Tiger Moth, to the heavy Avro Lancaster, and minimized the type-conversion difficulties associated with Blind Flying, since a pilot trained on one aircraft could quickly become accustomed to any other if the instruments were identical. This Basic Six set, also known as a six pack[1], was also adopted by commercial aviation. After the Second World War the arrangement was changed to: (top row) airspeed, artificial horizon, altimeter, (bottom row) radio compass, direction indicator, vertical speed.

AIRCRAFT HARDWARE What You Need To Know By Ron Alexander The quality of our workmanship in building an airplane is very important. We all take the needed time and spend the necessary money to ensure we have a high quality airplane. We want it to not only look attractive, but also to be safe. But what about the materials that hold the airplane together the aircraft hardware? Do we try to cut expenses by using questionable bolts or used nuts? Is it really necessary to spend money on high quality aircraft hardware? Absolutely! The hardware used to assemble your airplane should be nothing but the best. Why take the time to build a perfect wing only to attach it to the fuselage with used hardware. It makes no sense. To quote the Airframe and Powerplant Mechanics General Handbook . . . "The importance of aircraft hardware is often overlooked because of its small size; however, the safe and efficient operation of any aircraft is greatly dependent upon the correct selection and use of aircraft hardware." Very well stated. The same book also provides us with a very good definition of aircraft hardware. "Aircraft hardware is the term used to describe the various types of fasteners and miscellaneous small items used in the manufacture and repair of aircraft." The subject of aircraft hardware can certainly be confusing. Thousands upon thousands of small items are used on a typical airplane. What does the custom aircraft builder really need to know about hardware? Where do you find the information? What reference is really the end authority on proper installation? What do all of those AN numbers mean and do I have to know them? What types of hardware should I really learn more about in order to build my own airplane? These questions will be answered in this series of articles on aircraft hardware. I hope to eliminate some confusion over what type of hardware to use and how to properly install it. To begin our discussion, it is absolutely imperative that you use nothing but aircraft grade hardware. Commercial grade hardware found in hardware or automotive stores is legal to use on an experimental airplane but should not be considered for even a moment. Why? Let's look at bolts as an example. Common steel bolts purchased from a hardware store are made of low carbon steel that has a low tensile strength usually in the neighborhood of 50,000 to 60,000 psi. They also bend easily and have little corrosion protection. In contrast, aircraft bolts are made from corrosion resistant steel and are heat treated to a strength in excess of 125,000 psi.

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The same comparison applies to most hardware items. So, use only aircraft quality hardware on your airplane. Save the other hardware for your tractor. If aircraft hardware is special, then there must be a standard against which it should be measured and manufactured. That standard was actually developed prior to World War 11, but became more definitive during that war. Each branch of the military originally had its own standard for hardware. As time went on these standards were consolidated and thus the term AN which means Air Force-Navy (some prefer the older term Army-Navy). Later the standards were termed MS which means Military Standard and NAS which means National Aerospace Standards. Thus, the common terms AN, MS and NAS. Together they present a universally accepted method of identification and standards for aircraft hardware. All fasteners are identified with a specification number and a series of letters and dashes identifying their size, type of material, etc. This system presents a relatively simple method of identifying and cataloging the thousands and thousands of pieces of hardware. Several pieces of hardware will have both an AN number and an MS number that are used interchangeably to identify the exact same piece. A cross reference exists that compares these two numbers. So in the end, you are able to read your plans or assembly manual and identify, by number and letter, each piece of hardware on your airplane. You can then obtain that piece and properly install it in the right place. Imagine trying to do that without a system of numbers. The specifications for each piece of hardware also define the strength, tolerance, dimensions, and finish that is applied. If you would like further information on this numbering system, you can contact the National Standards Association in Washington, DC.

FIGURE 1 Out of all the thousands of hardware pieces manufactured, which ones are important to the custom aircraft builder? The following types and categories of hardware will be discussed: Bolts Nuts Washers Screws Cotter pins and safety wire

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Rivets Turnlock fasteners Miscellaneous items such as 0-rings, crush washers, etc. Control cable hardware Fluid lines and fittings Electrical wiring and connectors Where do you find information concerning aircraft hardware? Your aircraft plans or assembly manual should provide you with a general overview of hardware used on your project. Use the hardware the aircraft designer or kit manufacturer recommends. Do not substitute with your own ideas. This can be dangerous. The manufacturer has tested the design and its safety is dependent upon the proper pieces of hardware. FAA Advisory Circular 43-13-IA is an excellent reference source. The Airframe Mechanics General Handbook also has a very good section on the selection and use of hardware. These two books are considered the primary authority on the proper use of hardware. In addition, I would recommend two other small reference books: the Standard Aircraft Handbook and the Aviation Mechanic Handbook. Both of these provide a good reference source. The Aircraft Spruce & Specialty catalog also contains good reference material on hardware. If you have any doubts about the quality of the aircraft hardware you are purchasing, request a copy of the manufacturer's specifications. These specifications along with a specific manufacturer's lot number should be available. BOLTS Bolts are used in aircraft construction in areas where high strength is needed. Where this strength is not necessary screws are substituted. Aircraft quality bolts are made from alloy steel, stainless or corrosion resistant steel, aluminum alloys and titanium. Within our industry the first two are the most common. Aircraft bolts will always have a marking on their head. If you see no markings at all on the head of a bolt, do not use it. It is probably a commercial grade bolt. The markings on bolts vary according to the manufacturer. You should see an "X" or an asterisk along with a name, etc. If you purchase a corrosion resistant (stainless steel) bolt, the head of that bolt should have one raised dash. An aluminum bolt will have two raised dashes on its head. Aluminum bolts have limited use. They should not be used in tension applications or where they will be continuously removed for maintenance or inspection. A chart of typical bolt heads is presented in Figure 1. NAS bolts have a higher tensile strength (usually about 160,000 psi) and can be identified by a cupped out head. Close tolerance bolts are machined more accurately than general purpose bolts and they are used in applications requiring a very tight fit. Close tolerance bolts can be either AN or NAS and typically have a head marking consisting of a raised or recessed triangle. The standard bolts used in aircraft construction are AN3 through AN20. Each bolt typically has a hexagon shaped head and a shank that fits into the hole. The shank is threaded on the end and the unthreaded portion of the bolt is termed the grip. The diameter of a bolt is the width of the grip. The shank of a bolt will be either drilled to accept a cotter pin or undrilled. Another option is to purchase a bolt that has the head drilled for the purpose of accepting safety wire. Clevis bolts are manufactured with a slotted head and are used for control cable applications. The size, material, etc. of a bolt is identified by an AN number. A breakdown of a typical bolt AN number follows: AN4-8A AN means the bolt is manufactured according to Air Force-Navy specs. 4 identifies the diameter of the bolt shank in 1/16" increments 8 identifies the length of the shank in 1/8" increments

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A means the shank of the bolt is undrilled (no letter here means a drilled shank) So, this particular bolt is a 1/4 inch diameter AN bolt that is 1/2 inch long measured from just under the head to the tip of the shank. The bolt also has an undrilled shank which means it cannot accept a cotter pin. Also, bolt length may vary by +1/32" to -1/64". If the letter "C" follows the AN designation (ANC) that identifies a stainless steel bolt. The letter "H" after AN (ANH) identifies a drilled head bolt. FIGURE 2: AN Aircraft Bolt Dimensions In constructing you airplane, you will not encounter many bolts larger than an AN8 (1/2 inch diameter). To add a bit more confusion, if the dash number defining the length of the bolt has two digits, the first digit is the length in whole inches and the second number the length in additional 1/8" increments. In other words, an AN514 bolt would be I- 1/2 inches long. Now that you are totally confused let me recommend a hand tool to simplify bolt selection and sizing. An AN bolt gauge is available that will assist you in identifying a bolt (click on the above link to Figure 2). If you need to determine the proper size of a bolt, the length must be sufficient to ensure no more than one thread will be inside the bolt hole. This is the grip length of the bolt and it is measured from the underneath portion of the head to the beginning of the threads (see Figure 3 below). The grip length should be equal to the material thickness that is being held by the bolt or slightly longer. A washer may be used if the bolt is slightly longer. A piece of welding rod or safety wire can be used to measure the length of the hole. In his book titled Sportplane Construction Techniques, Tony Bingelis shows a simple tool that can be made for this purpose.

FIGURE 3 It is important that you do not "over tighten" or "under tighten" a bolt or the nut attached to a bolt. Under torque or under tightening results in excessive wear of the hardware as well as the parts being held. Over tightening may cause too much stress on the bolt or nut. The best way to avoid this is to use a torque wrench. AC43-13 presents a table of torque values for nuts and bolts. It shows fine thread and coarse thread series with a minimum and maximum torque limit in inch pounds. I recommend using a torque wrench whenever possible, at least until you get an idea as to the amount of force required. Of course, critical installations should definitely be torqued to proper values. A torque wrench is not that expensive and will be a worthwhile investment for a custom builder. Basics of Bolt Installation Certain accepted practices prevail concerning the installation of hardware. A few of these

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regarding bolt installation follow: 1. In determining proper bolt length - no more than one thread should be hidden inside the bolt hole. 2. Whenever possible, bolts should be installed pointing aft and to the center of an airplane. 3. Use a torque wrench whenever possible and determine torque values based on the size of bolt. 4. Be sure bolt and nut threads are clean and dry. 5. Use smooth, even pulls when tightening. 6. Tighten the nut first - whenever possible. 7. A typical installation includes a bolt, one washer and a nut. 8. If the bolt is too long, a maximum of three washers may be used. 9. If more than three threads are protruding from the nut, the bolt may be too long and could be bottoming out on the shank. 10. Use undrilled bolts with fiber lock nuts. If you use a drilled bolt and fiber nut combination, be sure no burrs exist on the drilled hole that will cut the fiber. 11. If the bolt does not fit snugly consider the use of a close tolerance bolt. 12. Don't make a practice of cutting off a bolt that is too long to fit a hole. That can often weaken the bolt and allow corrosion in the area that is cut. AIRCRAFT NUTS Aircraft nuts usually have no identification on them but they are made from the same material as bolts. Due to the vibration of aircraft, nuts must have some form of a locking device to keep them in place. The most common ways of locking are cotter pins used in castle nuts, fiber inserts, lockwashers, and safety wire. The aircraft nuts you will most likely encounter are castle nuts, self-locking nuts, and plain nuts. Wing nuts and anchor nuts are also used. Castle Nuts AN310 and AN320 castle nuts are the most commonly used (see Figure 4). Castle nuts are fabricated from steel and are cadmium plated. Corrosion resistant castle nuts are also manufactured (AN310C and AC320C - remember, when you encounter a "C" it will designate stainless). Castle nuts are used with drilled shank bolts, clevis bolts and eye bolts. The slots in the nut accommodate a cotter pin for safetying purposes. The thinner AN320 castellated shear nut has half the tensile strength of the AN310 and is used with clevis bolts which are subject to shear stress only. The dash number following the AN310 or AN320 indicates the size bolt that the nut fits. In other words, an AN310-4 would fit a 1/4 inch bolt.

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FIGURE 4 Self-Locking Nuts Self-locking nuts, as the name implies, do not need a locking device. The most common method of locking is derived from a fiber insert. This insert has a smaller diameter than the nut itself so that when a bolt enters the nut it taps into the fiber insert producing a locking action. This fiber insert is temperature limited to 250-deg. F. The designation of these nuts is AN365 and AN364. This brings us to an example of a cross-reference MS number. An AN365 is also termed MS20365 with the AN364 being MS20364. Both of these nuts are available in stainless. The AN364 is a shear nut not to be used in tension. An all metal locking nut is used forward of the firewall and in other high temperature areas. In place of a fiber insert, the threads of a metal locking nut narrow slightly at one end to provide more friction. An AN363 is an example of this type of nut. It is capable of withstanding temperatures to 550-deg. F. The dash number following self-locking nut defines the thread size. Self-locking nuts are very popular and easy to use. They should be used on undrilled bolts. They may be used on drilled bolts if you check the hole for burrs that would damage the fiber. One disadvantage, self-locking nuts should not be used on a bolt that is connecting a moving part. Am example might be a clevis bolt used in a control cable application. Plain Aircraft Nuts Plain nuts require a locking device such as a check nut or lockwasher. They are not widely used in most aircraft. AN315 is the designation used for a plain hex nut. These nuts are also manufactured with a right hand thread and a left hand thread. The check nut used to hold a plain nut in place is an AN316. If a lockwasher is used a plain washer must be under the lockwasher to prevent damage to the surface. Other Aircraft Nuts There are a number of other aircraft nuts available. Wing nuts (AN350) are commonly used on battery connections or hose clamps where proper tightness can be obtained by hand. Anchor nuts are widely used in areas where it is difficult to access a nut. Tinnerman nuts, instrument mounting nuts, pal nuts, cap nuts, etc. are all examples of other types that are used. Basics of Aircraft Nut Installation 1. When using a castle nut, the cotter pin hole may not line up with the slots on the nut. The Mechanics General Handbook states "except in cases of highly stressed engine parts, the nut may be over tightened to permit lining up the next slot with the cotter pin hole." Common sense should prevail. Do not over tighten to an extreme, instead, remove the nut and use a different washer and then try to line the holes again. 2. A fiber nut may be reused if you are unable to tighten by hand.

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3. At least one thread should be projecting past the fiber on a fiber nut installation. 4. No self-locking nuts on moving part installations. 5. Do not use AN364 or AN365 fiber nuts in areas of high temperature - above 250' F. 6. Shear nuts are to be used only in shear loads (not tension). 7. Plain nuts require a locking device such as a lockwasher or a check nut. 8. When using a lockwasher, place a plain washer between the surface of the airplane part and the lockwasher. 9. Shear nuts and standard nuts have different torque values. 10. Use wing nuts only where hand tightness is adequate. WASHERS Finally, a hardware item that is simple. You are likely to encounter only a couple of different types of washers AN960 and AN970. The main purposes of a washer in aircraft installation are to provide a shim when needed, act as a smooth load bearing surface, and to adjust the position of castle nuts in relation to the drilled hole in a bolt. Also, remember that plain washers are used under a lockwasher to prevent damage to a surface. AN960 washers are the most common. They are manufactured in a regular thickness and a thinner thickness (one half the thickness of regular). The dash number following the AN960 indicates the size bolt for which they are used. The system is different from others we have encountered. As an example, an AN960-616 is used with a 3/8" bolt. Yet another numbering system. If you see "L" after the dash number, that means it is a thin or "light" washer. An AN960C would be - yes, a stainless washer. I can tell you are getting more familiar with the system so I will throw another wrench into the equation - an AN970 washer has a totally different dash number system. I am not even going to tell you what it is. I will tell you that an AN970 is a larger area flat washer used mainly for wood applications. The wider surface area protects the wood. There are other types of washers. I mentioned lockwashers that are made several different ways. They are often split ring, they are sometimes internal tooth and even external tooth (see Figure 5). You will also find nylon washers and finishing washers that usually have a countersunk head. So, as you can see, washers are not quite as confusing as other hardware even though we can make ft difficult if we wish.

FIGURE 5 COTTER PINS AND SAFETY WIRE The cotter pins mostly used on custom aircraft are AN380 and AN381. Cadmium plated cotter pins are AN380 and stainless are AN381. Cotter pins are used for safetying bolts, screws, nuts and other pins. You will normally use them with castle nuts. The MS number you may see is MS24665. The dash numbers indicate diameter and length of the pin. As an example,

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AN380-2-2 would be a cadmium plated pin 1/16" in diameter and 1/2" long. All supply companies will have charts showing the various sizes versus the reference number. Safety wire is also widely used. The most used sizes in diameter are .020, .032 and .041 or small variations thereof. The material is usually stainless steel or brass. The easiest method of installation is acquired by using safety wire pliers (see Figure 6). The pliers are used to twist the wire. The wire is installed so that if the nut or bolt begins to loosen it will increase the tension on the wire. Be sure you do not overtwist the wire - doing so will weaken the safety wire. Leave about 36 twists and then cut off the excess wire and bend its end so you do not snag it with your hand at a later time.

FIGURE 6 I want to emphasize the major point of this article. USE ONLY AIRCRAFT QUALITY HARDWARE. Do not assume the engineer role by using hardware types or sizes that are contrary to your plans or assembly manual. In future articles I will discuss the other hardware items including control cable installation, screws, rivets, turnlock fasteners, etc.

Aircraft SubscribeYou are in: Home › Aircraft › News Article

DATE:05/10/10 SOURCE:Flight International APU: Unsung hero of the engine world By John Croft

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Auxiliary power units (APUs) do their dull and dirty work hidden away in aircraft tailcone compartments, unlike their turbine engine brethren connected to the wings or empennage. On occasion however, the tables get turned. On a bitterly cold Thursday in January 2009, the Honeywell 131-9A APU in the tailcone of a US Airways A320 that had just departed New York's LaGuardia airport came to the rescue after the aircraft struck a flock of geese. With both CFM56 turbofans damaged and the associated electrical generators eventually knocked off line, the APU during the final seconds of the ditching provided the power needed to keep the flight controls, displays and envelope protections in place to allow the pilot to touch down in the Hudson River in control and at the lowest possible airspeed.

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APUs such as Honeywell's 331-200ER in this Continental 767 are meant to be out of sight, out of mind. Picture: Ed Croft That the APU was available so quickly was testament to a well-trained crew. During the final hearing earlier this year on the successful, fatality-free ditching, a National Transportation Safety Board official asked the captain: "According to the [cockpit voice recorder] transcript, immediately after the bird strike, you called for the ignition to 'on' and to start the APU. This was before beginning the checklist. Can you explain your decision to do this?" To which Captain Sullenberger replied: "From my experience, I knew that those two steps would be the

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most immediate help to us in this situation." That the APU was able to start and perform without question when needed was testament to the pedigree of these small compact turbine engines. The two primary manufacturers of the engines, Honeywell and Hamilton Sundstrand, continue to refine the devices and are preparing a raft of new technologies aimed at boosting reliability and "on-tail" time while decreasing emissions and fuel burn. APUs are generally used to provide cabin air on the ground, pneumatic pressure for engine starts and primary or back-up electrical power for environmental, cockpit and hydraulic systems. They use the same fuel as the aircraft's engines and generally account for about 2% of the total fuel burn on a given mission. Market leader Honeywell, whose APUs are standard on all Boeing 737NG models and have been selected as an option on 60% of Airbus A320s, is readying its most advanced APUs to date for the new Comac 919 single-aisle jet and the Airbus A350. Both APUs are derivatives of the company's popular 131-9 model, which is also on tap for the new Bombardier CSeries narrowbody line. A near-term technology focus for Honeywell has been extending the life of the gas turbine wheels in the APU by moving to a one-piece turbine wheel rather than a hub with replaceable blades. Both Honeywell and Hamilton Sundstrand use a single-spool engine architecture with a single-stage centrifugal compressor, combustors and two-stage high-pressure turbine. Overall pressure ratio is approximately 11:1 with peak temperatures in the neighbourhood of 2,000°F (1,090°C) for Honeywell's Airbus A350 design. The spool also drives an electrical generator and a compressor for pneumatic air flow to the aircraft's environmental control system and engine start system. The 131-9 typically drives a 90kV or 120kV generator and provides up to 168lb/min (76kg/min) pneumatic pressure, says Steven Chung, vice-president for marketing and product management for the APU line at Honeywell. Chung says the company has shipped more than 6,000 131-9 series APUs since 1991, when it was first developed for the McDonnell Douglas MD90.

LIFE INCREASE Honeywell says the dual-alloy one-piece turbine wheels will provide some operators with a 10-20% increase in APU life, which for the 131-9 is on average about 12,000h time before overhaul (TBO). Interim maintenance typically includes replacing certain line replaceable units

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(LRU) during the life of the APU in part due to internal wearing of valves, mating materials and springs. Replacement parts include igniter plugs and filters. "In hot climates with lots of pollution, particularly India and the Middle East, sulphur was building up on the blades and corrosion was an issue," says Mike Madsen, vice-president of airlines for Honeywell. "This change eliminates that issue." Madsen explains that the dual alloy turbine wheel is fabricated with a hub that is fused to a ring of integral blades, an optimal design that, he says, eliminates potential for certain failures, thereby decreasing removal by 10-20% in regions such as China, India and the Middle East, where APUs are operated "pretty consistently" on the ground due to a lack of land-based electrical power service. "It really attacks the potential failure modes you can experience," says Madsen. "One of the challenges you have with an APU is that it operates on the ground and ingests air that is not as clean as the air at altitude. This can lead to accelerated wear on engine." He says the one-piece design eliminates the nooks and crannies where corrosion from salts and other contaminants can begin. Like Hamilton Sundstrand, Honeywell offers an option to customers to monitor APUs in the field using temperature and vibration measured on board the aircraft at certain times and sent to the ground via the aircraft communications addressing and reporting system. "In some cases, this allows airline to change out the questionable unit with an operational APU and get the other fixed," says Madsen. Airlines in some cases own their own spares and in other cases, purchase an integrated service solutions programme, whereby Honeywell manages the spares and provides them to the carriers when a failed unit is returned. Honeywell also has a rental bank and aircraft-on-ground (AOG) units available. Madsen says about 60-70% of customers contract with Honeywell for full support of their APUs on a cost per hour basis. Along with licensed maintenance providers, customers can obtain services at the company's facilities in Germany, Singapore and at Honeywell's home base in Phoenix, Arizona. Many airlines, typically the legacy carriers, have their own APU maintenance facilities. "We are in the process of facilitating Air China, China Eastern and China Southern to do their own maintenance on APUs," says Madsen, adding that the company also has an APU maintenance facility in China.

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CARE PROGRAMME Hamilton Sundstrand offers a power-by-the-hour care programme, with the main company-owned maintenance centre in San Diego, a facility in Northern France and a sister company (Pratt & Whitney) facility in Singapore. Third-party provider, StandardAero, also performs maintenance on the units. "We set up many airlines that want to do their own in-house repair," says Danny Di Perna, vice-president and general manager of Hamilton Sundstrand Auxiliary Power Systems. "We provide them tooling and documents and we can set up the operation as turnkey if desired." A network of field service representatives help with AOG situations but Hamilton Sundstrand does not maintain a pool of spares. The company has increased its warranty up to four years or 4,000h, up from the typical three-year warranty of legacy systems. Like Honeywell, Hamilton Sundstrand's APUs are maintained on-condition and tend to last 12,000hr or more. Hamilton Sundstrand says it has 5,000 APUs in total for the commercial aircraft market in operation, including 1,600 APS3200 APUs for single-aisle aircraft. Di Perna says 60-70% of the airline customers are using the data trending service. To better keep track of APU performance and potential problems in the field, Hamilton Sundstrand is building a 253m2 (2,720ft2) customer response centre for its APUs in Windsor Locks, Connecticut. The facility will be completed later this year. Madsen says Honeywell has 20 APUs retrofitted with the dual alloy turbine wheel in the second-stage turbine slot flying as part of an evaluation - 10 on Boeing aircraft and 10 on Airbus aircraft. As of mid-September, the units had accumulated 20,000h operating time in total with no failures. Honeywell plans to have accumulated 50,000h operating time on the 20 units by mid-2011. Starting in June 2011, the company will introduce the new turbine wheels for both high-pressure stages for new and aftermarket models. For overhauls, where the existing units will receive the new turbine wheels, Honeywell says turn-time will be reduced about half a day since the single-piece wheels will be pre-balanced at the factory. Turn time in total for an APU is 20-25 days, says Madsen. Major drivers for next-generation APUs include cutting weight and improving reliability, along with reducing fuel burn and lowering emissions. Chung says goals for the Bombardier APU include a 15% reduction in overall fuel burn over a mission profile, a design driver that stems from desired sales in European markets. For the Airbus A350, Honeywell's HGT1700 APU will be its largest unit to date, delivering an equivalent power of 1,300kW (1,700shp) but cutting fuel burn and nitrogen oxide emissions with a new variable speed controller, also to be included in the APUs for the CSeries and Comac C919. The variable speed controller runs the APU at an optimal speed based on ambient temperature, altitude and bleed air or generator demands, says Honeywell's Chung. For the 131-9, the controller will vary the speed of the APU within 10% of its nominal run speed of 48,800rpm. Quieter APUs are also in demand, particularly in Europe and for East and West Coast US airports, says Chung. He says many airlines are asking for APUs that generate 3-10dB less than current international noise standards. "A lot of the noise has to do with APU emissions," says Chung. "That's where we come in with installation kits for the air inlet and exhaust to quieten it down." Other means of cutting noise include choosing blade counts for the compressor and turbines to push the noise above the audible range, he says. For the C919, Honeywell has a patented tailcone muffler design that quietens the overall noise of the APU when integrated to the aircraft. Hamilton Sundstrand is introducing its first variable speed APU to the commercial market in the Boeing 787 with its APS5000. Unlike traditional APUs, the APS5000 drives two 225kV generators only, making it the first "all-electric" APU, says Hamilton Sundstrand. "It's remarkably quiet," says Di Perna. "There's no bleed-air provided." Di Perna says testing of the APS5000 is "just about wrapping up" and certification is expected in November. Other new

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commercial aircraft wins include the ARJ21, Mitsubishi Regional Jet and Irkut MC21. Beyond the 787, Hamilton Sundstrand plans to take advances from the 787 programme into a new line of single-aisle APUs, a strategy aimed at taking market share from its competitor. Di Perna says Honeywell is dominant in the single-aisle market, with a 75-80% share compared with Hamilton Sundstrand's 20-25%. "We're trying to get 35-45% market share in the next seven years," says Di Perna. He says both companies have approximately 40% market share in military APUs and 50% each for regional aircraft.

Aircraft Procedure - Introduction Pilots are highly trained professionals who fly airplanes and helicopters to carry out a wide variety of tasks. Except on small aircraft, two pilots usually make up the cockpit crew. Generally, the most experienced pilot, the captain, is in command and supervises all other crew members. The pilot and copilot share flying and other duties, such as communicating with Air Traffic Controllers and monitoring the instruments. Some large aircraft have a third pilot—the flight engineer—who assists the other pilots by monitoring and operating many of the instruments and systems, making minor in flight repairs, and watching for other aircraft. (but nowadays this duty is performed by pair of computers) New technology can perform many flight tasks, however, and virtually all new aircraft now fly with only two pilots, who rely more heavily on computerized controls. As older, less technologically sophisticated aircraft continue to be retired from airline fleets, the number of flight engineer jobs will decrease.

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Before departure, pilots plan their flights carefully. They thoroughly check their aircraft to make sure that the engines, controls, instruments, and other systems are functioning properly. They also make sure that baggage or cargo has been loaded correctly. They confer with flight Dispatchers and aviation weather forecasters to find out about weather conditions en route and at their destination. Based on this information, they choose a route, altitude, and speed that will provide the fastest, safest, and smoothest flight. When flying under instrument flight rules—procedures governing the operation of the aircraft when there is poor visibility—the pilot in command, or the airline dispatcher, normally files an instrument flight plan with air traffic control so that the flight can be coordinated with other air traffic. Takeoff and landing are the most difficult parts of the flight, and require close coordination between the pilot and first officer. For example, as the plane accelerates for takeoff, the pilot concentrates on the runway while the first officer scans the instrument panel. To calculate the speed they must attain to become airborne, pilots consider the altitude of the airport, outside temperature, weight of the plane, and speed and direction of the wind. The moment the plane reaches takeoff speed, the first officer informs the pilot, who then pulls back on the controls to raise the nose of the plane. Unless the weather is bad, the actual flight is relatively easy. Airplane pilots, with the assistance of autopilot and the flight management computer, steer the plane along their planned route and are monitored by the air traffic control stations they pass along the way. They regularly scan the instrument panel to check their fuel supply, the condition of their engines, and the air-conditioning, hydraulic, and other systems. Pilots may request a change in altitude or route if circumstances dictate. For example, if the ride is rougher than expected, they may ask air traffic control if pilots flying at other altitudes have reported better conditions. If so, they may request an altitude change. This procedure also may be used to find a stronger tailwind or a weaker headwind to save fuel and increase speed. Pilots must rely completely on their instruments when visibility is poor. On the basis of altimeter readings, they know how high above ground they are and whether they can fly safely over mountains and other obstacles. Special navigation radios give pilots precise information that, with the help of special maps, tells them their exact position. Other very sophisticated equipment provides directions to a point just above the end of a runway and enables pilots to land completely “blind.” Here the air traffic engineers play major role to keep the ground equipment to their absolute specification for "blind" landing. Once on the ground, pilots must complete records on their flight for their organization and the FAA. report. Although flying does not involve much physical effort, the mental stress of being responsible for a safe flight, no matter what the weather, can be tiring. Pilots must be alert and quick to react if something goes wrong, particularly during takeoff and landing.

Simple lesson plan to fly Flight Plans Pilots wishing to fly under IFR rules must first file a flight plan with Air Traffic Control, before departure. Calling the Aeronautical Information Office can do this. The flight plan contains the aircraft identification, or callsign, the type of aircraft, planned speed (true airspeed, or speed across the ground without wind), requested route of flight (from VORTAC to VORTAC), planned cruising altitude, and sometimes other information such as color of aircraft, and number of people on board. We will discuss all these later and for the time being have these in mind.

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This flight plan information goes into the Air Traffic Controllers and they prepare a strip of paper called a flight progress strip. After that, controllers can review the proposed route of flight and make changes as necessary to conform to local procedures and routings. When the aircraft is ready to depart, the pilot calls either the control tower and requests clearance. The controller checks the flight strip, and clarifies the routing and any changes to the routing with the pilot, so both pilot and Air Traffic Control know the exact route the pilot will fly. The controller also tells the pilot his flight plan code number, and the pilot sets an instrument on his aircraft called a transponder to transmit this code. This beacon code transmission is picked up by radar, allowing the ATC computer to know exactly which aircraft it is, and which flight plan it corresponds to. Getting started Imagine you enter the cockpit of a parked A340 - everything is ready except that all systems are shut down. APU (Auxiliary power unit) and engines are also switched off. Now both batteries are switched on at the Overhead ELEC panel.

Overhead ELEC (electrical) panel The next thing to do is to check the APU fire warning. To do this, the TEST button on the APU fire panel is depressed and released when the fire light illuminates.

APU fire warning Now the APU is switched on by pushing the MASTER switch on the APU panel.

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APU panel When the "FLAP OPEN" message appears on the ECAM (Electrical Contactor and Management Unit) the APU start switch is depressed. When the AVAIL light illuminates, the APU bleed push button on the AIR panel is pushed to supply the air conditioning and other systems with air. Check the all panels for white lights out and turn the three IR switches to NAV for the alignment process. Refer to the following MCDU (Multifunction Control Display Unit) programming procedure. STATUS PAGE (PS) The DATA BASE validity must be checked at first, as well as the navaids and waypoints. FLIGHT PLAN Should be completed thoroughly. It includes data like: Take off runway, SID with ALT/SPD data, expected take off time, course, waypoints and the expected step climbs descents SEC FLIGHT PLAN Must be filled in when ever a specific condition is likely to happen such as take off runway change, alternative SID etc. RAD NAV (Radio and Navigation) Any required Navaids manually entered using ident. INIT Winds, expected ZFWCg (Zero Fuel Weight Center of Gravity / ZFW (Zero Fuel Center of

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Gravity), Fuel planning: The FMGS (Flight Management Guidance System) calculation the minimum required fuel this value must confirmed. After that, the DATA page is selected and the preflight data is printed out using the ACARS (Aircraft Communications Addressing and Reporting System). The printed sheet must be kept as it gives the required fuel for each waypoint of the Flight Plan. PERF (Performance) The derated climb and descents and speeds are typed in - this is necessary. Flight plan checked: MCDU: FPLN page ND (Navigation Display) in plan mode: range as required, with CSTR selected on EIS CTLE panel. ALT/SPD checked, Distance to successive waypoint is provided. The overall distance of the route is indicated in the 6th line of the MCDU Now the before Start Checklist (written on the table) can be completed. Before starting the engines, turn the beacon light on and seat belts to on. ATC communication Now check your departure time and you are ready for startup. Before that, contact the control tower (Aerodrome) for clearance for startup and pushback the aircraft to taxiway. Engine Start up The normal engine start procedure is the AUTO START procedure. In this case the FADEC prevents start malfunctions like hot start, stall etc. It recognizes all of these and takes appropriate actions for instance reducing fuel flow, cranking the engine, attempting new starts or cutting fuel flow. The air from the APU (APU bleed) allows to start 2 engines simultaneously.

The engine start up sequence is simple: 1 and 2 are started firstly to pressurize the green and blue system which supply the parking brakes and hydraulic actuators. An actuator is a little box that converts the electrical inputs to real rudder movements. The Boeing B707 for instance doesn't have this system. Engine 1 and 2 first, followed by 3 and 4. Check thrust levers idle.

Engine Start Then set IGN/START to START - now an eye must be kept on the ECAM to check if APU bleed is stable. ENG1 Master switch is set to ON followed by ENG 2 when N2 of Engine 1 has reached 10%. Now monitor and check in the right order: Start valve open (now high pressure bleed air (minimum 30psi) air is blown into the engine), N2 IGN A or B, Fuel flow, EGT OIL PRESS ignition rising. FADEC (Full Authority Digital Engine Control) closes the start valve

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when N2 reaches 50%, now monitor EGT and ENG Vibration and the engine AVAIL which illuminates when the start sequence is over. Now the same is repeated for ENG 3 and 4. When all engines are running stable set the IGN / START switch back to NORM which automatically switches the Packs back ON. If, for any reasons, there is an abnormal start DO NOT interrupt the FADEC protective and just follow the ECAM instructions if they appear. Another procedure to start the engines is the MANUAL START, which is only used in exceptional cases, like high altitude airports or subsequent low APU bleed pressure or to CRANK the engine dry prior opening the fuel flow.

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Overhead Panel Taxi When all engines are running check both left and right side for any obstacles let the tore bar to pull the aircraft on to the correct path from the apron. Again, contact the tower and get the

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clearance to enter the taxiwayan most of the time you will be asked to enter the taxiway either to runway 22 or 04 and hold short of runway. Now, smoothly move the thrust levers forward only a few centimeters as otherwise you would blow everything away that is standing behind you and therefore you do not exceed N1 40% during taxi. The APU bleed should be turned off to avoid ingestion of exhaust gases by the passengers. On straight taxiway and shallow turns the pedals are used to steer the aircraft but the hand is kept on the steering tiller is used in sharp turns. Be careful with that - it is very sensitive so move this wheel very slowly. Also, when on the ground do not start turns too early. Remember that the nose gear on the A340 is far back (4 meters), this means that the cockpit has to be over the grass in an intersection. If you turn too early the main gear can end up in the grass so make sure to over steer significantly. Slowly move the thrust lever 1 (left one) slightly forward to make a right turn and use the right lever for number 4 engine slightly forward to make a left turn. It is not recommended to use differential braking to avoid gear stress. The speed shouldn't exceed 10 knots in turns also if brake temperature exceeds 150° degrees the brake fans (not installed in all aircraft) must be switched on. Remember to taxi slowly at about 10-12 knots. You usually do not use thrust reverser during taxi and it is used on old 737-200s or MD80s but not on the newer aircrafts. Extend the flaps to 1 + F the lever is located on the center panel and you simple pull the handle up and move it down one step. Make sure the stabilizer trim is in the green range and the rudder trim at zero. Take off Here you have come most critical point of your adventure. Contact the tower again and request for take off. You will be cleared to enter the runway and takeoff. When turning onto the runway, switch on the strobes and landing lights and align the aircraft on the center line and select Auto Brake MAX on the main instrument panel (below the gear indicator)In case of an engine failure the aircraft stops automatically when the thrust levers are moved to IDLE. Then push the CONFIG test on the ECAM so as to insure that the ECAM take off check list items are all green. If everything is set the thrust levers are moved slowly to 50% N1 and when all engines are running stable at 50% move the levers the stops (TOGA). A yellow arrow appears on the PFD indicating the acceleration. Now full concentration is needed to monitor speed, engine gauge and the aircraft on the centerline. At 90 knots, the rudder has to be used to keep the aircraft aligned with the centerline as at 100 knots the nose gear steering disconnects from the nose gear. This is actually the most tricky part of the take off run and in case of an engine failure it is difficult to keep the aircraft aligned with the center line as the airspeed is still to low for an effective rudder and the nose gear steering is disconnected. This is why much attention has to be paid on the engine gauges at this stage to react as early as possible. At 140 knots smoothly move the side stick backwards to gain a pitch attitude of 8° to avoid tail strike and then to 12-15° (depending on weigh). The Autopilot is available 5 seconds after take off. CLB/CRZ/DES(Climb/ Cruise/ Descend) When a stable positive rate of climb is established the gear is selected up and thrust reduced

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to CLB at 1500feet. The flaps are retracted at 200kts but as this only a traffic pattern they are set to 1. In case of a traffic pattern, usually you maintain 1500 feet above ground. You can use the autopilot for the traffic pattern. Just press AP1 and Pull + rotate the altitude knob to 1500 and then pull it. Now select your desired heading - simply add 180° to your current heading to make a 180-degree turn to fly the downwind leg of the traffic pattern. From now on, until landing, the aircraft is under observation of the Air Traffic Control system. After departure, ATC issues altitudes, speeds, headings, and sometimes re-routes as necessary, and assumes responsibility for separating the aircraft from all known traffic. Landing Put the FLAP lever to 2 and select 160 knots airspeed. Now put the gear lever to down and the FLAP lever to 3. Select 140 knots speed. Before turning on final extend the flaps to FULL and arm the spoilers and push the Autobrake switch to Medium - you do not use Autobrake max during landing. Now the aircraft should be aligned with the runway centerline with the localizer display indicator and have an airspeed of 140 knots with the gear down and flaps set to FULL and a rate of descent of 700-800 feet per minute and a pitch angle of 4-5°(but the actual landing angle should be 3°). These parameters need to be monitored constantly - never fix your eyes on one parameter always keep all parameters in view. The PAPI will help you to establish the correct glide path. The PAPI (Precision Approach Position Indicator) consists of 4 lights which can illuminate red or white. If you see 2 red and 2 white lights than the glide path is correct - if 3 reds and 1 white is seen than slowly add power and smoothly pull the stick backwards to reduce the ROD. But most of you will know how this works either from real life or from the flight simulator. When passing 500 feet a voice message is heard indicating 500ft so monitoring altitude above ground does not have high priority. It is very important to keep the speed at 140 knots and if it is below 140kts then in most cases this will result in a hard landing if the speed is to high the aircraft will climb during the landing flare. Switch the Autopilot off by pressing the red side stick button twice and press one of the red buttons twice on the thrust levers to disengage the outthrust system. A short aural warning will be hared. Continue descent at 700 feet per minute until reaching 30 feet. Now reduce rate of descent to half and count slowly 1, 2, 3 while retarding the thrust lever to idle when the retard call is heard. Avoid push the stick forward if not absolutely necessary and this will increase the rate of descent and result in a hard landing. To make it correct always give very little side stick inputs and monitor what happens and if descending to fast pull the stick back again but always small inputs and monitor speed. Also remember a nice approach is almost a nice landing so if you monitored all parameters well a soft landing is not guaranteed. When the forward boogie touches the ground move the thrust reverser levers upwards and the spoilers will be extend automatically. Now the landing is not over at all and the nose gear has to be landed as well and if you keep it up to long it will just fall down and this is not very comfortable therefore, slowly move the side stick forward and give a little input and just see what happens. Shut down Take the next intersection and taxi to the apron. Push the spoiler lever down, retract the flaps to zero, switch off the strobes and landings lights and reduce speed to 10-12 knots. Make sure the APU is on when parking position is reached. Set parking brake and move the Engine Master switches to OFF one after another. Turn of the beacon light and seat belts. After the

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aircraft lands, the flight plan is closed, and the pilot turns off his transponder.

How do they start jet engines on airplanes? Gas turbine engines come in many shapes and sizes. One type discussed in How turbine engines work includes a normal "jet" engine on an airplane. The hot gases produced by the burning fuel drive vanes in exactly the same way that wind turns a windmill. The vanes connect to a shaft that also spins the turbine's compressor. Another type of gas turbine engine, popular in tanks and helicopters, has one set of vanes for driving the compressor, as well as a separate set of vanes that drive the output shaft. In both of these types of engines, you need to get the main shaft spinning to start the engine. This starting process normally uses an electric motor to spin the main turbine shaft. The motor is bolted to the outside of the engine and uses a shaft and gears to connect to the main shaft. The electric motor spins the main shaft until there is enough air blowing through the compressor and the combustion chamber to light the engine. Fuel starts flowing and an igniter similar to a spark plug ignites the fuel. Then fuel flow is increased to spin the engine up to its operating speed. If you have ever been at the airport and watched a big jet engine start up, you know that the blades start rotating slowly. The electric starter motor does that. Then you (sometimes) hear a pop and see smoke come out of the back of the engine. Then the engine spins up and starts producing thrust. On smaller turbine engines (especially home-built models), another way to start the engine is to simply blow air through the air intake with a hair dryer or leaf blower. This technique has the same effect of getting air moving through the combustion chamber, but does not require the complexity or weight of an attached starter motor. Besides the starter shaft, most big jet engines include another output shaft for driving things like electrical generators, air conditioning compressors, etc. needed to operate the plane and keep it comfortable. This shaft can connect to the main turbine shaft at the same point the starter does or elsewhere. Some jet airplanes have a separate turbine (sometimes in the tail cone of the plane) that does nothing but generate auxiliary power. It is more efficient to run this smaller turbine when the plane is sitting on the tarmac.

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Engine Lubrication, Part I With the correct oil friction losses in an engine are reduced to a minimum. This is done by taking into consideration circumstances as engine usage, ambient temperature, time of year and climate, location and engine design. The engine manufacturer usually recommends a certain type of oil to use regarding different circumstances.

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Landing Gear Configurations Two main types: Conventional, and Tricycle

Tricycle Has nose wheel, which may be steerable Main gear, on either side Example: Cessna Keeps aircraft level during take-off and landing The most important advantage is its ease of ground handling.

Conventional Two main wheels One tail dragger wheel Reduced drag in the air

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Reduced landing gear weight Requires more skill in ground taxiing The most important advantage is the ability to operate the aircraft over rough terrain.

Classification of Landing Gear

Main landing gear Cushions landing impact Heavily stressed area Main Landing Gear consists of the main weight-bearing structure Auxiliary landing gear includes tail wheels, skids, nose wheels, etc. Nonabsorbing Landing Gear

Includes Rigid landing gear, Shock-cord landing gear, Spring landing gear Rigid: helicopters, sailplanes. No flexing other than the structure. Shock cord system: uses “Bungee” cords Spring type uses spring steel (some Cessna’s)

Shock-Absorbing Landing Gear Dissipates landing energies by forcing fluid through a restriction This fluid generates heat, dissipated into the atmosphere Two types: Spring Oleo, and Air-Oil Oleo Spring Oleo is history by now Air Oleos are all very similar: a needle valve restricts fluid flow Air in the oleo holds the weight of the a/c on the ground Air Oleos present in both retractable and fixed gears

Fixed Gear Non retractable, usually bolted on to the structure Often uses fairings or wheel pants

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Cessna 152 Advantages: Lighter weight Less compex Least costly

Retractable Gear Designed to eliminate drag (the greatest advantage) Can be either fully or partially retractable Direction of retraction depends on airframe model Methods of retraction: hydraulic, electric, mechanical, pneumatic Critical area of aircraft maintenance for safety reasons

Hulls and Floats Can be single float, or multiple Definition may include floating hulls (ex. “Lake” aircraft) Floating hulls may only require wing tip floats Skis used for snow and ice (wood, metal, composites) Skis may use shock cord to assist angle of ski attack Skis are mounted on the same strut as tires

Landing Gear Components Exact definitions of some components will vary The Oleo strut is the widely used form of shock absorption on aircraft landing gear.

Trunnions Portion of the landing which attaches to the airframe Supported at the ends by bearings

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Landing gear traditionally extends from the center

Struts Vertical member, contains the shock absorbing mechanism Top of the strut mounts onto the trunnion Strut forms the cylinder for the oleo (“outer” cylinder) Piston is the moving portion (aka piston rod, tube or inner cylinder) Oil is forced from the lower portion of the strut to the upper Oil flow is restricted or varied according to a metering pin Final weight of a/c rests on air in the top of the strut Snubbers are used to prevent a sudden dropping of gear on takeoff Metering pin controls the flow of fluid between the chambers. The shock of landing is absorbed by the fluid being forced through a metered orifice. The metering pin gradually reduces the size of the orifice as the shock strut extends, which avoids a rapid extension after the initial shock of landing and related bounce. Chevron seals are used in shock struts to prevent the oil from escaping On nose wheel struts, a cam is built into the strut for the purpose of straightening the nose wheel before retraction. Filling a shock strut: “exercise” the strut in order to seat the seals, and remove air bubbles from the fluid. Most shock strut oil levels are checked by releasing the air, bottoming the strut, and checking to see if the oil is at the level of the filler plug. Information about shock struts: see: Manufacturer’s maintenance manual Information decal located on the strut Mfr’s overhaul manual

Torque Links Also called scissors assembly Two A-frame members Connects and aligns upper and lower cylinders

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Connects the strut cylinder to the piston Restricts extension of piston during retraction Correctly aligns axle to the strut

Trucks Located at the bottom of the strut piston Axles are mounted on the truck Trucks can tilt fore or aft to allow for a/c attitude changes

Drag Links Stabilizes landing gear longitudiannly May be hinged to allow retraction Also called a drag strut

Side Brace Links Stabilize gear laterally May be hinged to allow retraction Can be called a side strut

Overcenter Links (aka downlock mechanism) Use to apply pressure to the center pivot joint in a drag or side brace link Overcenter link is hydraulically retracted to allow gear retraction Also called a downlock, and/or a jury strut

Swivel Glands Flexible joint with internal passages Route hydraulic fluid to the wheel brakes Used where space limitation eliminate flex hoses

Shimmy Dampers

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Hydraulic snubbing unit Reduces tendency of nose wheels to oscillate

Piston type dampers Piston and rod filled with hydraulic fluid Piston has an orifice restricting speed of travel Slow movement has no restriction Large shimmy dampers incorporate temperature compensation

Vane type dampers Employ stationary vanes and rotating vanes Small passages restrict fluid movement Central shaft rotation is restricted from moving quickly

Damper Inspections Check for leakage & effectiveness of operation Check mounting bolts and hardware Most dampers are fairly reliable

Steering Systems Some a/c have free castering nose wheels; most have steerable.

Mechanical Steering Systems Uses foot power to steer the aircraft – no assistance Some types will disengage when the gear is retracted Some types have an automatic centering device when weight is off the a/c

Tail Wheel Conventional gear use the tail wheel to steer May be a castering type with no steering capabilities (rudder steers)

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May be lockable, for parking purposes

Power Steering Systems Used where large amounts of force are required to steer Controlled by pilots rudder pedals, OR By a steering wheel, OR By a combination of both Most will require a towing bypass valve which allows Ground crews to to the a/c without damaging the system

Retraction Systems Purpose: reduce drag, or adapt a/c for landing on different surfaces (consider retractable wheels on float systems)

Mechanical Systems Crank mechanism, or uses a lever pulled by the pilot This method may use a mechanical latch system to lock wheels “up” No emergency backup available for this system

Electrical Retraction Systems Uses a central motor and push-pull rods Uses microswitches to detect when gear is down/locked, or up/locked

Hydraulic Retraction Systems Most common system of retraction for most sizes of a/c Used exclusively where landing gear is too large to be retracted by other methods May use ED pumps, electric pumps, hand or wind-driven pumps

Emergency Landing Gear Systems 4 possible methods of dropping gear when hydraulics are lost:

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air bottle “blows” the gear down hand crank or ratched separate hydraulic system (may be hand pump) mechanical system which releases UP locks, and gear free-falls

Landing Gear Operation 4 main components: shock strut the wheel the brake assembly the trunnion and side/drag brace scissors (torque links) actuating cylinder down & up locks the bungee system

Using hydraulics, landing gear retraction requires greater energy than lowering Gear rotates on the trunnion pin Extending landing gear requires a release of the UP lock first, then The gear can begin free falling, slowed by the snubber in the orifice check valve Final few degrees of travel may require hydraulic pressure assistance Bungee system is used for emergency operation:

Gear doors must be operated before extension & after retraction

Landing Gear Position Indicator Systems Positive indication must be provided to the pilot that gear is down & locked Safety system includes squat switches and other microswitches Squat switches tell pilot when weight of a/c is on the wheels

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Squate switches are electrically “open” when on the ground Some a/c use warning horns: they sound when: If gear is retracted, and throttle retarded to below cruise Landing gear position indicators: show position of Landing gear May use a system of different color indicator lights

Transport Aircraft Landing Gear Systems

Corporate Jets and Dual-Wheeled Transports Most have retractable tricycle-type gear, 2 wheels on each Nose gear will probably be a dual-wheel steerable type Gear will become completely enclosed when retracted

Helicopter Landing Gear Basic skid gear is common for small & mediums Wheel gear is used on sikorsky aircraft Retractable or cushioning gear may impart ground resonance Skid tubes are replaceable, and repairable Bending and deforming limits are established, and occasionally liberal Skid protectors are available, as are “bear paws” snow shoes Ground handling wheels are bolt-on towing additions

Inspection and Maintenance of Landing Gear The following must be carefully inspected: Attachments to fuselage or wings Struts Wheels

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Brakes Actuating mechanisms for gear Hydraulic systems Gear doors

Fixed Gear Inspection Inspect for wear, deterioration, corrosion, alignment Jack up the aircraft to relieve the weight on the gear Shock cord should be inspected for age & fraying (5 years, retire) Shock Cord MIL-C-5651A. See diagram for year and quarter. Check oleos for bottoming: air charge has been lost.

Retractable Landing Gear Inspection Similar to fixed gear inspection, but add inspections for: Wear or looseness in joints or trunnions Leakage of fluids Smoothness of operation Operational check performed by jacking the airplane & operating gear Check for clearance of new tires in the wheel wells Check for operation of gear doors Check operation and adjustment of microswitches

If a oleo bottoms upon initial landing, but operates normally during taxiing, it is likely an indication of low fluid. Check your fluid levels.

Alignment of Main Gear Wheels Check for Camber and Toe-in. Camber is the tilt of the top of the wheel inboard or outboard Toe is the angling of the forward edge of the tire

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Oleo type gear often use angled shims or washers A common Toe setting is 0º, with a tolerance of ½º Some a/c may require alignment to be set while weight is on the gear. Use grease plate for this

Inspection of Floats and Skis Consider pop out floats and fixed floats (helicopters) Standard float assemblies for small a/c are sensitive to salt water Check for corrosion thoroughly Use standard sheet metal repair techniques Check for leaks See powerpoint slides for float parts familiarization diagram

Tires and Wheels

Aircraft Tire Operation Characteristics Tires for aircraft must endure higher loads and higher speeds than automobiles and trucks; the safety issue is much higher as well. Heat generation is higher in aircraft tires Rubber, the major material used, dissipates heat slowly Underinflating or overinflating increases shear forces in between the plies: tension will be higher in outer plies than in inner.

Type I tires: smooth contour Type II tires: high pressure III: low pressure IV: extra low pressure

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V: not applicable VI: low profile VII: tires are constructed for extra high pressure; jet aircraft. VIII: extra high pressure, low profile, low speed or high speed.

Types I, II, IV and VI are being phsed out.

Aircraft Tire Nomenclature Tire ply rating refers to the maximum static load and its inflation pressures Tire markings: manufacturer, country of mfr, design type, load rating, tube or tubeless, tire size, part number, ply rading Number of recaps used to be stamped on the sidewall, but not all models have provision for this. Chafers are used to protect the wheel rim-to-tire bead chafing. The most important part of an aircraft tire is the bead. A tire with smooth tread is used for very light aircraft, grass runways, and locations where braking is only used as an aid to taxiing. Ribbed tread tires are used for directional stability, good tread wear, and to allow water to escape from between the tire tread and runway. A Chine sided tire is used to deflect water or slush away from the intake of the jet engines. Double or single chine wheels exist. Inboard halves of an aircraft wheel are different from the outboard by the provisions made for mounting & securing the disk brake assembly, and the presence of fusible plugs. The fusible plug is used to prevent tire blow-out due to heat build-up. The plug has a low melting point core which melts under high temperatures which may build up during heavy braking.

Tire Structure Steel wire beads form the inner diameter Plies are diagonal layers of rubber coated nylon cord fabric Chafers protect the tire during mounting/demounting. They also provide a good seal between tire and wheel.

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Breakers are used to increase structural strength Inner liner acts as a built-in tube; prevents air from seeping through the casing plies. Beads anchor the plies and provide mounting surfaces for the wheel Tread is the surface of the tire for runway contact Most treads have groove patterns with 3 – 6 ribs, depending on size and type of service The light point on a tire is indicated by a red dot on the tire.

Tire Storage Tires should be stored vertical, in racks, in cool dry places. Ensure there are no sources of light or electrical appliances (for the ozone) nearby. Same with chemical fumes.

Tubes Made of rubber sections vulcanized together. Air valve is vulcanized to the tube for inflation/deflation Tubes can be checked for leaks by immersing in a water trough with a light inflation pressure applied.

Aircraft Wheel Construction Aircraft tires are too stiff to stretch over wheel rims. Damage will occur to the bead of the tire Split rims are used, and the two halves are sealed with an O-ring Most wheels are constructed of forged aluminum or magnesium alloys Wheels rotate on two tapered roller bearings; the cups are shrink fitted into the hub. Wheels are constructed with three fusible plugs, equally spaced around the wheel. The bead seat area is strenthened by rolling: it pre-stresses the surface Nose wheels are smaller in diameter and width than mains: rarely have brakes

Demounting and Mounting Tires Safety procedures: Deflate the tire beforee loosening the axle nut. This must occur in case the rim is cracked or the wheel bolts fail.

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Before we loosen the wheel half retaining bolts, we must deflate the tire, and remove the valve stem. Break the tire beads away using a bead breaker – do not use sharp tools Then dismantle the wheel halves & inspect the bolts Always use a safety cage when inflating a tire. Bearings are generally a tapered roller bearing in hubs. Grease seals are used to prevent foreign material from entering and contaminating the wheel bearing grease. Stuck wheel bearing? Don’t beat it to death with a hammer & punch ~ use a bearing puller. The only place to obtain proper inflation pressures is in the A/C M/M. That manual will quote pressures for the aircraft when loaded. (all-up weight) Installing tubes requires a dusting of talc into the tire for lubrication purposes. Tube should be placed so that the yellow strip (the heavy spot) is adjacent to the red dot (the light spot) on the tire. If using a tubeless tire; inspect the new tire to make sure it is a tubeless type. Install bolts and nuts ensuring they are installed in the correct direction. Use an alternating sequence to tighten. Only partially inflate the first time to allow the tire bead to seat to the wheel. A strap around the surface of the tread may be used to prevent the tire from expanding radially. Nitrogen is preferred, but not always necessary. Tires should be allowed to set for 12 to 24 hours before being installed. This allows for “growth” and natural stretch, and the air pressure to settle. Do not use soap/water installation liquids; may cause slippage of tire on the rim during landing.

Tire and Wheel Inspection Inspect outer tread while mounted on the a/c. Certain types of landing gear wear the tread unevenly (spring gear) Check for over or under-inflation, damage to sidewalls, cracks, weather checking, flat spots, chafing, thinning, valve stem movement (indicator slip marks) Dye Penetrant is not always the best answer: in some cases a crack may not show up because of the extreme pressures imposed by inflation and a/c weight. When the tire is deflated & inspected, some cracks will close up, and not show with Dye Penetrant. The most corrosion prone area of a wheel is any area which is exposed to the direct entry of moisture. This includes split lines, cavities, milled areas.

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Any fuse plugs showing deformation must be replaced. All of ‘em. The most critical areas on the wheel bolts is where the shank joins the head, or where the shank joins the threads. Pressures of a tire/wheel that is NOT installed on the a/c should read 4% below the recommended pressure. Any single burned patches on a tire tread would likely indicate hydroplaning. Wheel Installation

If the Mfr’s wheel balance weights have to be removed for any reason, you must mark their position, and replace the same weight in the same place.

Aircraft Brake Assemblies

Light a/c can use simple shoe brakes or single discs; low weight & speed

Internal Expanding Shoe Brakes Older a/c and home-builts One-way (single servo type), or Two way (dual servo) Can be similar to automotive types

Expander Tube Brakes Four parts: brake frame, expander tube, return springs, and brake blocks Older aircraft Hydraulically operated Each brake block is independent; no tendency to grap

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Single Disk Brakes One of the most popular types Disk held in the wheel by teeth or keys Linings on either side of the disk; compressions forms braking action One lining is attached to axle structure, the other moves according to hydraulic pressure May have multiple pistons (& therefore multiple linings) Cleveland is one type of popular manufacturer Removal of air requires a brake bleeder valve

Multiple Disk Brakes Used where a substantial amounf of braking force is required Typically will have multiple rotors and pistons, stator plates, a pressure plate and a torque tube (see page 9-22 in Jeppesen) Wear indicators are often included in this design

Segmented Rotor Disk Brakes Heavy duty brakes design for use with high pressure systems using power brake control valves, or power boost master cylinders Uses stationary high-friction linings with rotating rotor segments

Carbon Composite Brakes Weigh 40% less than conventional steel segmented rotor brakes. Natural gas is used in forming the brake discs to add carbon Strength does not decrease at elevated temps Carbon against carbon performs excellent as a friction material Carbon brakes can exceed 3000 degrees F

Braking Heat Energy Huge amounts of heat energy on braking Pilots figure out gross weight of aircraft to establish a ground cooling time for brakes

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Somewhat reduced by using thrust reversers

Troubleshooting Pilot reports excessive brake pedal travel. Check the brake fluid level. Which way should the chevron seals face? The inside of the chevron should face the pressure. An aircraft is reported as having excessive brake travel, but the brakes are still hard and effective. The probable cause is worn brake linings.

Aircraft Brake Systems Modern aircraft brakes are classified as single or multiple disk Mechanically operated, or hydraulically operated, or pneumatically operated Mechanical is the older smaller systems, using pulleys, cables, bell cranks. Many a/c use hydraulic system pressures to actuate their brakes. Some have an entirely independant system. Pneumatic brake systems use air only; some hydraulics use air as a backup pressure supply.

Independent Brake Systems Basic systems require a reservoir, a master cylinder actuated by pedal or handle, a brake assembly at the wheel, and all related hosing/tubing. Master cylinder is the energizing unit, usually one for each main gear wheel. Parking brakes are often a simple ratchet affair for holding the pedal or handle in place, which continues to supply pressure to the brakes. Various models of master cylinders; some mount on top of the rudder pedals. Function remains the same. Heel operated brakes or hand-brakes. Parking brake mechanism may be interrelated with the main brakes, but setting of parking brakes when hot may be an issue.

Power Boost Systems Power boost systems are used on a/c with high landing speeds. Power boost is halfway between manual brakes and power brakes. Power boost uses hydraulic pressure from the main system to the brakes via a check

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valve. May use a shuttle valve to route emergency air pressure. Larger aircraft require more braking power than can be applied through a master cylinder. Extra pressure can be exerted on the brake system by allowing hydraulic system pressures to act through a spool valve. A Brake Debooster serves the purpose of decreasing system pressure to a useable level in the brake system. It also has the effect of increasing the volume of hydraulic fluid flowing.

Power Brake Systems Used where manual and boosted brakes are not adequate. Uses a power brake control valve to direct hydraulic system pressure to the brakes. Power brake control valve is also called a brake metering valve; generally one for each main landing gear brake. Typical system has four lines to each valve; pressure, return, brakes, and automatic braking. Automatic braking is used to stop wheel rotation during retraction on take-off. Sources pressure from the landing gear UP position in hydraulic system.

Debooster Valves Used to reduce the system hydraulic pressure to a lesser pressure in the braking system. Generally exchanges High Pressure/Low Volume into Low Pressure/High Volume.

Multiple Power Brake-Actuating Systems Brake actuation systems get very complex at this level. Requires a lot of research and careful work on the AME’s part to learn these individual systems Brakes are operated by 2 independent systems. (#1, and #2) Each systems consists of daul-brake-control valves, pressure accumulators, brake-pressure transmitters and indicators, brake quantity-limiter valves, a skid-control manifold for each gear, and a parking-brake valve. All contribute the actuation of the independent cylinders in the eight main wheel brakes. Either system is capable of stopping the airplane on a maximum gross-weight landing.

Construction of Brakes Sintered brake linings are another term for metallic linings. Segmented rotor discs produce three benefits: Eliminate heat buildup in the disc

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Produce more efficient braking Allow for longer braking action. Floating calipers are used to adjust for brake lining wear. Those types of aircraft which use a large amount of fluid to operate the brakes will incorporate a power brake control valve. Carbon disk brake lining material is usedfor light weight, better wear resistance, and better heat resistance. Automatic adjusters are installed in modern systems to maintain a set clearance between the disc and brake lining. Heavy steel plates called Pressure Plates are used to act as a backing against which the linings are forced by the pistons.

Brake Temperature Certain a/c have brake temperature readouts in the cockpit Temp ranges are relative to a scale of 0 to 9 Brake temperatures can increase even after brakes have been applied and released due to heat soaking Temp values above a “5” illuminates a BRAKE TEMP light

Brake Maintenance Some types of bonded linings are not fully cured at the time they are installed. The curing process requires they be installed and then used in a moderate-to-heavy application of the brakes. BCIT students will learn more about curing processes in the a/c composites section of level 3. For routine maintenance, check indicator pins for brake pad wear. Check lugs or keys holding rotor disks Check fusible plugs in the wheels for yeilding or cracks Examine fittings for leakage Ensure you are servicing the brakes with the appropriate fluids. Inspect hoses fro swelling, leakage, sponginess Check for reports of dragging brakes, fading brakes, excessive pedal travel, pedal creep or non responsive braking. Dragging brakes? Check for air in the system, sticking valves, and weak or worn return

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springs Grabbing brakes? Check for oil or FOD on linings. Fading brakes? Check for overheated linings and glazing Excessive travel? Check for lining wear limits, lack of system fluid, air in the system, or maladjusted brakes. Pedal creep? Inspect for leaks in a master or slave cylinder

Brake Bleeding Purpose is to remove any air from the braking fluids system and all related valves and cylinders Air will cause sponginess or dragging Gravity bleeding uses a clear plastic tube, attached at one end to the bleed fitting at the brakes, and the other end is immersed in a container of fluid. Apply pressure to brakes, and open the bleed fitting. Trapped air bubbles will be removed with the fluid, and can be seen in the container. Maintain fluid levels in the reservoir. Pressure bleeding uses special tooling for the specific aircraft. Most types use a pressurized reservoir attached to the brake bleed fitting. Fluid is forced through the system back to the reservoir.

Anti-Skid Systems

Several reaons apply why anti-skid systems are in use on many modern aircraft: They prevent wheel lockup They prevent skidding They reduce the chance of hydroplaning They help reduce excessive heat build up

A successful anti-skid system will have two main features: A form of wheel sensor that can detect a change in the rate of deceleration

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A valve system that can rapidly apply and release the brakes, which will prevent a skid

The Three main Components of an anti-skid system: Wheel speed sensor(s) Control unit (computer) Control valves

Two types of wheel speed sensors are: The AC sensor, which creates a variable frequency AC current A DC unit, (basically a DC generator)

AntiSkid system operation

Antiskid systems are generally armed by a switch in the cockpit. System will utilize the squat switch to prevent current from flowing to the system during flight. System allows full pilot control over braking at speeds below 20 mph. System will perform its function when the wheel deceleration indicates an impending skid.

An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines. This article is an overview of the basic types of aircraft engines and the design concepts employed in engine development for aircraft.

A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution; and the niche application Stirling engine.

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Common features in all types There may be one or more pistons. Each piston is inside a cylinder, into which a gas is introduced, either already hot and under pressure (steam engine), or heated inside the cylinder either by ignition of a fuel air mixture (internal combustion engine) or by contact with a hot heat exchanger in the cylinder (Stirling engine). The hot gases expand, pushing the piston to the bottom of the cylinder. The piston is returned to the cylinder top (Top Dead Centre) either by a flywheel or the power from other pistons connected to the same shaft. In most types the expanded or "exhausted" gases are removed from the cylinder by this stroke. The exception is the Stirling engine, which repeatedly heats and cools the same sealed quantity of gas. In some designs the piston may be powered in both directions in the cylinder in which case it is said to be double acting.

Steam piston engine A labeled schematic diagram of a typical single cylinder, simple expansion, double-acting high pressure steam engine. Power takeoff from the engine is by way of a belt. 1 - Piston 2 - Piston rod 3 - Crosshead bearing 4 - Connecting rod 5 - Crank 6 - Eccentric valve motion 7 - Flywheel 8 - Sliding valve 9 - Centrifugal governor. In all types, the linear movement of the piston is converted to a rotating movement via a connecting rod and a crankshaft or by a swashplate. A flywheel is often used to ensure smooth rotation. The more cylinders a reciprocating engine has, generally, the more vibration-free (smoothly) it can operate. The power of a reciprocating engine is proportional to the volume of the combined pistons' displacement. A seal needs to be made between the sliding piston and the walls of the cylinder so that the high pressure gas above the piston does not leak past it and reduce the efficiency of the engine. This seal is provided by one or more piston rings. These are rings made of a hard metal which are sprung into a circular groove in the piston head. The rings fit tightly in the groove and press against the cyinder wall to form a seal. It is common for such engines to be classified by the number and alignment of cylinders and the total volume of displacement of gas by the pistons moving in the cylinders usually measured in cubic centimetres (cm³ or cc) or litres (l) or (L) (US:liter). For example for internal combustion engines, single and two-cylinder designs are common in smaller vehicles such as motorcycles, while automobiles typically have between four and eight, and locomotives, and ships may have a dozen cylinders or more. Cylinder capacities may range from 10 cm³ or less

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in model engines up to several thousand cubic centimetres in ships' engines. The compression ratio is a measure of the performance in an internal-combustion engine or a Stirling Engine. It is the ratio between the volume of the cylinder, when the piston is at the bottom of its stroke, and the volume when the piston is at the top of its stroke. The bore/stroke ratio is the ratio of the diameter of the piston, or "bore", to the length of travel within the cylinder, or "stroke". If this is around 1 the engine is said to be "square", if it is greater than 1, i.e. the bore is larger than the stroke, it is "oversquare". If it is less than 1 , i.e. the stroke is larger than the bore, it is "undersquare". Cylinders may be aligned in line, in a V configuration, horizontally opposite each other , or radially around the crankshaft. Opposed-piston engines put two pistons working at opposite ends of the same cylinder and this has been extended into triangular arrangements such as the Napier Deltic. Some designs have set the cylinders in motion around the shaft, see the Rotary engine.

Stirling piston engine Rhombic Drive Beta Stirling Engine Design showing the second displacer piston (green) within the cylinder which shunts the working gas between the hot and cold ends , but produces no power itself. Pink - Hot cylinder wall, Dark grey - Cold cylinder wall, Green - Displacer piston, Dark blue - Power piston, Light blue - Flywheels In steam engines and internal combustion engines, valves are required to allow the entry and exit of gasses at the correct time in the piston's cycle. These are worked by cams or cranks driven by the shaft of the engine. Early designs used the D slide valve but this has been largely superseded by Piston valve or Poppet valve designs. In steam engines the point in the piston cycle at which the steam inlet valve closes is called the cutoff and this can often be controlled to adjust the torque supplied by the engine. Internal combustion engines operate through a sequence of strokes which admit and remove gases to and from the cylinder. These operations are repeated cyclically and an engine is said to be 2-stroke, 4-stroke or 6-stroke depending on the number of strokes it takes to complete a cycle. In some steam engines, the cylinders may be of varying size with the smallest bore cylinder working the highest pressure steam. This is then fed through one or more, increasingly larger bore cylinders successively, to extract power from the steam at increasingly lower pressures. These engines are called Compound engines.

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History An early known example of rotary to reciprocating motion can be found in a number of Roman saw mills (dating to the 3rd to 6th century AD) in which a crank and connecting rod mechanism converted the rotary motion of the waterwheel into the linear movement of the saw blades.[1] Another early example was the reciprocating piston pump of Al-Jazari in 1206.[2] The reciprocating engine developed in Europe during the 18th century, first as the atmospheric engine then later as the steam engine. These were followed by the Stirling engine and internal combustion engine in the 19th century. Today the most common form of reciprocating engine is the internal combustion engine running on the combustion of petrol, diesel, Liquefied petroleum gas (LPG) or compressed natural gas (CNG) and used to power motor vehicles. One of the most advanced reciprocating engines ever made was the 28-cylinder, 3,500 hp (2,600 kW) Pratt & Whitney R-4360 "Wasp Major" radial engine which powered the last generation of large piston-engined planes before the jet engine and turboprop took over from 1944 onward. It had a total engine capacity of 71.5 litres (2.52 cu ft). The largest reciprocating engine in production at present, but not the largest ever built, is the Wärtsilä-Sulzer RTA96-C turbocharged two-stroke diesel engine of 2006 built by Japan’s Diesel United, Ltd. It is used to power the largest modern container ships such as the Emma Mærsk. It is five stories high (13.5 m/44 ft), 27 metres (89 ft) long, and weighs over 2,300 metric tons (2,500 short tons) in its largest 14 cylinders version producing more than 84.42 MW (114,800 bhp). Each cylinder has a capacity of 1,820 litres (64 cu ft), making a total capacity of 25,480 litres (900 cu ft) for the largest versions. Engine capacity For piston engines, an engine's capacity is the engine displacement, in other words the volume swept by all the pistons of an engine in a single movement. It is generally measured in litres (L) or cubic inches (c.i.d. or cu in or in³) for larger engines, and cubic centimetres (abbreviated cc) for smaller engines. Engines with greater capacities are more powerful and provide greater torque at lower speed (rpm) and consumption of fuel increases accordingly. Other modern non-internal combustion types Reciprocating engines that are powered by compressed air, steam or other hot gases are still used in some applications such as to drive many modern torpedoes or as pollution-free motive power. Most steam-driven applications use steam turbines, which are more efficient than piston engines.

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Jet engines Main article: jet engine

A General Electric J85-GE-17A turbojet engine. This cutaway clearly shows the 8 stages of axial compressor at the front (left side of the picture), the combustion chambers in the middle, and the two stages of turbines at the rear of the engine. The key part of a jet engine is the exhaust nozzle. This is the part which produces thrust for the jet; the hot airflow from the engine is accelerated when exiting the nozzle, creating thrust, which, in conjunction with the pressures acting inside the engine which are maintained and increased by the constriction of the nozzle, pushes the aircraft forward. The most common jet propulsion engines flown are turbojet, turbofan and rocket. Other types such as pulsejets, ramjets, scramjets and Pulse Detonation Engines have also flown. Turbojet Main article: turbojet A turbojet is a type of gas turbine engine that was originally developed for military fighters during World War II. A turbojet is the simplest of all aircraft gas turbines. It features a compressor to draw air in and compress it, a combustion section which adds fuel and ignites it, one or more turbines that extract power from the expanding exhaust gases to drive the compressor, and an exhaust nozzle which accelerates the exhaust out the back of the engine to create thrust. When turbojets were introduced, the top speed of fighter aircraft equipped

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with them was at least 100 miles per hour faster than competing piston-driven aircraft. The relative simplicity of turbojet designs lent themselves to wartime production, but the war ended before any turbojets could be mass-produced. In the years after the war, the drawbacks of the turbojet gradually became apparent. Below about Mach 2, turbojets are very fuel inefficient and create tremendous amounts of noise. The early designs also respond very slowly to power changes, a fact which killed many experienced pilots when they attempted the transition to jets. These drawbacks eventually led to the downfall of the pure turbojet, and only a handful of types are still in production. The last airliner that used turbojets was the Concorde, whose Mach 2 airspeed permitted the engine to be highly efficient. Turbofan Main article: Turbofan A turbofan engine is much the same as a turbojet, but with an enlarged fan at the front which provides thrust in much the same way as a ducted propeller, resulting in improved fuel-efficiency. Although the fan creates thrust like a propeller, the surrounding duct frees it from many of the restrictions which limit propeller performance. This operation is a more efficient way to provide thrust than simply using the jet nozzle alone and turbofans are more efficient than propellers in the trans-sonic range of aircraft speeds, and can operate in the supersonic realm. A turbofan typically has extra turbine stages to turn the fan. Turbofans were the first engines to use multiple spools; concentric shafts which are free to rotate at their own speed; in order to allow the engine to react more quickly to changing power requirements. Turbofans are coarsely split into low-bypass and high-bypass categories. Bypass air flows through the fan, but around the jet core, not mixing with fuel and burning. The ratio of this air to the amount of air flowing through the engine core is the bypass ratio. Low-bypass engines are preferred for military applications such as fighters due to high thrust-to-weight ratio, while high-bypass engines are preferred for civil use for good fuel efficiency and low noise. High-bypass turbofans are usually most efficient when the aircraft is traveling at 500 to 550 miles per hour (800 to 885 km/h), the cruise speed of most large airliners. Low-bypass turbofans can reach supersonic speeds, though normally only when fitted with afterburners. Rocket Main article: Rocket engine A few aircraft have used rocket engines for main thrust or attitude control, notably the Bell X-1 and North American X-15. Rocket engines are not used for most aircraft as the energy and propellant efficiency is very poor except at high speeds, but have been employed for short bursts of speed and takeoff. Rocket engines are very efficient only at very high speeds, although are useful because they produce very large amounts of thrust and weigh very little. Jet engines are usually used as aircraft engines for jet aircraft. They are also used for cruise missiles and unmanned aerial vehicles. In the form of rocket engines they are used for fireworks, model rocketry, spaceflight, and military missiles. Jet engines have also been used to propel high speed cars, particularly drag racers, with the all-time record held by a rocket car. A turbofan powered car ThrustSSC currently holds the land speed record. Jet engine designs are frequently modified for non-aircraft applications, as industrial gas turbines. These are used in electrical power generation, for powering water, natural gas, or oil pumps, and providing propulsion for ships and locomotives. Industrial gas turbines can create up to 50,000 shaft horsepower. Many of these engines are derived from older military turbojets such as the Pratt & Whitney J57 and J75 models. There is also a derivative of the P&W JT8D low-bypass turbofan that creates up to 35,000 HP.

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Types There are a large number of different types of jet engines, all of which achieve forward thrust from the principle of jet propulsion. Airbreathing Main article: Airbreathing jet engine Nearly all aircraft are propelled by airbreathing jet engines, and most of the airbreathing jet engines that are in use are turbofan jet engines which give good efficiency at speeds just below the speed of sound. Turbine powered Main article: Gas turbine Gas turbines are rotary engines that extract energy from a flow of combustion gas. They have an upstream compressor coupled to a downstream turbine with a combustion chamber in-between. In aircraft engines, those three core components are often called the "gas generator." There are many different variations of gas turbines, but they all use a gas generator system of some type. Turbojet Main article: Turbojet A turbojet engine is a gas turbine engine that works by compressing air with an inlet and a compressor (axial, centrifugal, or both), mixing fuel with the compressed air, burning the mixture in the combustor, and then passing the hot, high pressure air through a turbine and a nozzle. The compressor is powered by the turbine, which extracts energy from the expanding gas passing through it. The engine converts internal energy in the fuel to kinetic energy in the exhaust, producing thrust. All the air ingested by the inlet is passed through the compressor, combustor, and turbine, unlike the turbofan engine described below. Turbofan

Schematic diagram illustrating the operation of a low-bypass turbofan engine. Main article: Turbofan A turbofan engine is a gas turbine engine that is very similar to a turbojet. Like a turbojet, it uses the gas generator core (compressor, combustor, turbine) to convert internal energy in fuel to kinetic energy in the exhaust. Turbofans differ from turbojets in that they have an additional component, a fan. Like the compressor, the fan is powered by the turbine section of

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the engine. Unlike the turbojet, some of the flow accelerated by the fan bypasses the gas generator core of the engine and is exhausted through a nozzle. The bypassed flow is at lower velocities, but a higher mass, making thrust produced by the fan more efficient than thrust produced by the core. Turbofans are generally more efficient than turbojets at subsonic speeds, but they have a larger frontal area which generates more drag. There are two general types of turbofan engines, low bypass and high bypass. Low bypass turbofans have a bypass ratio of around 2:1 or less, meaning that for each kilogram of air that passes through the core of the engine, two kilograms or less of air bypass the core. Low bypass turbofans often used a mixed exhaust nozzle meaning that the bypassed flow and the core flow exit from the same nozzle. High bypass turbofans have larger bypass ratios, sometimes on the order of 5:1 or 6:1. These turbofans can produce much more thrust than low bypass turbofans or turbojets because of the large mass of air that the fan can accelerate, and are often more fuel efficient than low bypass turbofans or turbojets.[citation needed] Turboprop and turboshaft Main articles: Turboprop and Turboshaft Turboprop engines are jet engine derivatives that extract work from the hot-exhaust jet to turn a rotating shaft, which is then used to produce thrust by some other means. While not strictly jet engines in that they rely on an auxiliary mechanism to produce thrust, turboprops are very similar to other turbine-based jet engines, and are often described as such. In turboprop engines, a portion of the engines' thrust is produced by spinning a propeller, rather than relying solely on high-speed jet exhaust. As their jet thrust is augmented by a propeller, turboprops are occasionally referred to as a type of hybrid jet engine. While many turboprops generate the majority of their thrust with the propeller, the hot-jet exhaust is an important design point, and maximum thrust is obtained by matching thrust contributions of the propeller to the hot jet. Turboprops generally have better performance than turbojets or turbofans at low speeds where propeller efficiency is high, but become increasingly noisy and inefficient at high speeds. Turboshaft engines are very similar to turboprops, differing in that nearly all energy in the exhaust is extracted to spin the rotating shaft. They therefore generate little to no jet thrust. Turboshaft engines are often used to power helicopters. Propfan Main article: Propfan A propfan engine (also called "unducted fan", "open rotor", or "ultra-high bypass") is a jet engine that uses its gas generator to power an exposed fan, similar to turboprop engines. Like turboprop engines, propfans generate most of their thrust from the propeller and not the exhaust jet. The primary difference between turboprop and propfan design is that the propeller blades on a propfan are highly swept to allow them to operate at speeds around Mach 0.8, which is competitive with modern commercial turbofans. These engines have the fuel efficiency advantages of turboprops with the performance capability of commercial turbofans. While significant research and testing (including flight testing) has been conducted on propfans, no propfan engines have entered production.

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Ram powered

A schematic of a ramjet engine, where "M" is the Mach number of the airflow. Ram powered jet engines are airbreathing engines similar to gas turbine engines and they both follow the Brayton cycle. Gas turbine and ram powered engines differ, however, in how they compress the incoming airflow. Whereas gas turbine engines use axial or centrifugal compressors to compress incoming air, ram engines rely only on air compressed through the inlet or diffuser. Ram powered engines are considered the most simple type of air breathing jet engine because they can contain no moving parts. Ramjet Ramjets are the most basic type of ram powered jet engines. They consist of three sections; an inlet to compressed oncoming air, a combustor to inject and combust fuel, and a nozzle expel the hot gases and produce thrust. Ramjets require a relatively high speed to efficiently compress the oncoming air, so ramjets cannot operate at a standstill and they are most efficient at supersonic speeds. A key trait of ramjet engines is that combustion is done at subsonic speeds. The supersonic oncoming air is dramatically slowed through the inlet, where it is then combusted at the much slower, subsonic, speeds. The faster the oncoming air is, however, the less efficient it becomes to slow it to subsonic speeds. Therefore ramjet engines are limited to approximately Mach 5. Scramjet Scramjets are mechanically very similar to ramjets. Like a ramjet, they consist of an inlet, a combustor, and a nozzle. The primary difference between ramjets and scramjets is that scramjets do not slow the oncoming airflow to subsonic speeds for combustion, they use supersonic combustion instead. The name "scramjet" comes from "supersonic combusting ramjet." Since scramjets use supersonic combustion they can operate at speeds above Mach 6 where traditional ramjets are too inefficient. Another difference between ramjets and scramjets comes from how each type of engine compresses the oncoming air flow: while the inlet provides most of the compression for ramjets, the high speeds at which scramjets operate allow them to take advantage of the compression generated by shock waves, primarily oblique shocks. Very few scramjet engines have ever been built and flown. In May 2010 the Boeing X-51 set the endurance record for the longest scramjet burn at over 200 seconds.

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Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's exhaust or changing of propeller pitch so that the thrust produced is directed forward, rather than aft. This acts against the forward travel of the aircraft, providing deceleration. Thrust reversers are used by many jet aircraft to help slow down just after touch-down, reducing wear on the brakes and enabling shorter landing distances. It is also available on many propeller-driven aircraft through reversing the controllable pitch propellers to a negative angle.

Operation

Thrust reversers deployed on the outer two of the four turbofans of an Ilyushin Il-62 landing at Munich Airport Reverse thrust is typically applied immediately after touchdown, often along with spoilers, to improve deceleration early in the landing roll when residual aerodynamic lift and high speed limit the effectiveness of the friction brakes located on the landing gear. Reverse thrust is always selected manually, either using levers attached to the thrust levers, or by moving the thrust levers into a reverse thrust 'gate'. When thrust is reversed, passengers will hear a sudden increase in engine noise, particularly those seated just forward of the engines.

Thrust reverser deployed on the Pratt & Whitney JT8D-7 turbofan engine of an Aloha Airlines Boeing 737-200 landing at Honolulu, HI The early deceleration provided by reverse thrust can reduce landing roll by a third or more. Regulations dictate, however, that a plane must be able to land on a runway without the use of thrust reversers in order to be certified to land there as part of scheduled airline service.

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Once the aircraft's speed has slowed, thrust reverse is shut down to prevent the reversed airflow from raising debris in front of the engine intakes where it can be ingested, causing foreign object damage. Thrust reverse is effective at any aircraft speed, and, if circumstances require, can be used all the way to a stop, or even to provide thrust to push the aircraft backward, though aircraft tugs or towbars are more commonly used for that purpose. If the full power of reverse thrust is not desirable, thrust reverse can be operated with the throttles set at less than full power, even down to idle power, which reduces stress and wear on engine components. Reverse thrust is sometimes selected on idling engines to eliminate residual thrust, particularly in icy or slippery conditions, or where the engines' jet blast could do damage. In-flight operation Some aircraft are able to safely use reverse thrust in flight, though the majority of these are propeller-driven. Many commercial aircraft cannot use reverse thrust in flight. Exceptions include Russian and Soviet aircraft which are able to reverse thrust in flight (mostly before touchdown). In-flight use of reverse thrust has several advantages: It allows for rapid deceleration, enabling quick changes of speed; it also prevents the speed buildup normally associated with steep dives, allowing for rapid loss of altitude, which can be especially useful in hostile environments such as combat zones, and when making steep approaches to land. For example, the ATR 72 turboprop can reverse thrust in flight, should the appropriate control lock be withdrawn. The Hawker Siddeley Trident, a 120-180 seat airliner, was capable of descending at up to 10,000 ft/min (3,050 m/min) by use of the thrust reversers, though this capability was rarely used. Concorde could also use reverse thrust in the air to increase the rate of descent. Only the inboard engines are used and the engines are placed only in reverse idle when subsonic and below 30,000 ft. This will increase the rate of descent to around 10,000 fpm.[citation needed] The US Air Force's C-17A is one of the few modern aircraft that uses reverse thrust in flight. The Boeing-manufactured aircraft is capable of in-flight deployment of reverse thrust on all four engines to facilitate steep tactical descents up to 15,000 ft/min (4,600 m/min) into combat environments (this means that the aircraft's descent rate is just over 170 mph, or 274 km/h). The Saab 37 Viggen (retired in November 2005) also had the ability to use reverse thrust before landing, enabling the use of many roads constructed in Sweden to double as wartime runways. The Shuttle Training Aircraft, a highly modified Grumman Gulfstream II, uses reverse thrust in flight to help simulate the Space Shuttle aerodynamics so astronauts can practice landings. Types of aircraft Small aircraft typically do not feature reverse thrust, except in specialized applications. Conversely, large aircraft (weighing more than 12,500 lb) almost always have the ability to reverse thrust. Both reciprocating engine and turboprop aircraft can have reverse thrust, and almost all propeller aircraft with reverse thrust have the ability to set the propeller angle to flat pitch (called Beta range) which generates no forward or reverse thrust, but provides large amounts of drag. This is especially useful in aircraft with complex reciprocating or turbine engines, as it enables engine speed to be kept high as the aircraft descends, avoiding doing damage to the engines by shock cooling them.

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Controllable pitch propeller on one of the four turboprop engines of a United States Air Force Lockheed C-130 Hercules Propeller-driven aircraft Propeller-driven aircraft generate reverse thrust by changing the angle of their controllable pitch propellers so that the propellers direct their thrust forward, instead of aft as normal. Reverse thrust has been available on propeller aircraft dating back to the 1930s. Reverse thrust became available due to the development of controllable-pitch propellers, which change the angle of the propeller blades to make efficient use of engine power over a wide range of conditions. Multi-engine Early multi-engine aircraft such as the Boeing 247 and Douglas DC-2 were among the first to feature reverse thrust. As piston aircraft became heavier and more complex, reverse thrust became more important to allow them to operate from airports originally configured to handle the smaller planes of previous years. Additionally, the higher performance and greater altitude attainable by post World War II piston aircraft like the Lockheed Constellation made the ability to use flat pitch, or, in extreme cases, reverse thrust, in order to descend and slow for landing without over-cooling the engines or approaching the runway with excessive speed. Finally, the advent of turboprops like the Vickers Viscount and Lockheed Electra brought even higher speeds and cruising altitudes to the fleet, as well as increased power that could be used both for improved performance and to provide reverse thrust. Single-engine Single-engine aircraft tend to be of such limited size that the weight and complexity of reverse thrust is unwarranted. However, large single-engine aircraft like the Cessna Caravan & Pilatus Porter do have reverse thrust available, and single-engine seaplanes and flying boats tend to have reverse thrust as well. In other respects, reverse thrust on single-engine aircraft works much like that on other propeller aircraft.

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Twin radial engine Canadair CL-215 flying boat used for firefighting by the Minnesota Department of Natural Resources Seaplanes and flying boats One special application of reverse thrust comes in its use on seaplanes and flying boats. These aircraft, when landing on water, have no conventional braking method and must rely on slaloming and/or reverse thrust, as well as the drag of the water in order to slow or stop. Additionally, reverse thrust is often necessary for manoeuvring on the water, where it is used to make tight turns or even back the aircraft, such as when leaving a dock or beach. Jet aircraft On aircraft using jet engines, thrust reversal is accomplished by causing the jet blast to flow forward rather than aft. The engine does not run or rotate in reverse; instead, thrust reversers are used to block the blast and redirect it forward. Two methods are commonly used: In the target-type thrust reverser, the reverser blades angle outward, giving the general appearance of flower petals, and forcing engine thrust to flow forward. In the clamshell type, two reverser buckets are hinged so that when they deploy, they intrude into the exhaust of the engine, capturing and reorienting the jet blast. This type of reverser is usually clearly visible at the rear of the engine during use. Turbofan

Boeing C-17 creating a visible vortex while demonstrating the use of reverse thrust to push the aircraft backwards down the runway. In addition to the two types used on turbojet and low-bypass turbofan engines, a third type of thrust reverser is found on some high-bypass turbofan engines. Doors in the bypass duct are

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used to redirect the air that has been accelerated by the engine's fan section but has not passed through the combustion chamber (called bypass air) so that it provides reverse thrust. The Boeing C-17 has a rare form of the above type in which even the exhaust from the core is redirected along with the main fan's air. This gives the C-17 unrivaled stopping ability among large jet powered aircraft.

Fly-by-wire System A pilot could operate the original XFV prototype using two hand-control grips and control arms, and by shifting his or her weight from side to side. However, after applying that operations concept in the wind tunnel at the NASA AMES Research Center back in 2000, the testing team discovered that kinematic (body) movement was not going to allow the pilot sufficient control of the craft. Currently, the Springtail uses fly-by-wire controls. In theory, this system is somewhat like the drive-by-wire systems designed for concept cars such as GM's Hy-wire. The operator controls the vehicle using two joysticks, one for each hand. The left joystick controls the rpm of the ducted fans (the altitude control). The right joystick controls forward and backward vehicle speed, left and right turns (roll), and turning the vehicle on its vertical axis (yaw). This is also known as a three-degrees-of-freedom control device.

Photo courtesy trekaerospace.com Springtail EFV-4A flight test held on March 16, 2005

As the operator uses the joysticks, his or her commands are fed to an onboard computer

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system. The computer system interprets this information and moves the ducts, control vanes and other control surfaces so that the vehicle moves to accommodate the operator's commands accordingly. The impressive onboard computer also gives the Springtail a sort of autopilot function. The operator can enter GPS coordinates for the vehicle to follow so that the Springtail's onboard computer system will "drive" him or her to the programmed destination. In addition to regular flight movement, like a helicopter, the Springtail can hover in a stationary position. Hover-time really depends on wind conditions and altitude, but the average time is approximately two hours. In the case of any catastrophic failure, the aircraft would automatically deploy a parachute to safely bring the craft and pilot down. In the event of initial main parachute malfunction, there's a back-up parachute for the pilot. It's designed to deploy automatically after the pilot has unbuckled himself from the Springtail and pushed away from the machiine.

Section 1.1 - Introduction to Aircraft Hydraulics

Aircraft Hydraulics Definition Aircraft Hydraulics is a means of transmitting energy or power from one place to another efficiently. What is a hydraulics system?

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It is a system where liquid under pressure is used to transmit this energy. Hydraulics systems take engine power and converts it to hydraulic power by means of a hydraulic pump. This power can be distributed throughout the airplane by means of tubing that runs through the aircraft. Hydraulic power may be reconverted to mechanical power by means of an actuating cylinder, or turbine. (1) - A hydraulic pump converts mechanical power to hydraulic power (2) - An actuating cylinder converts hydraulic power to mechanical power (3) - Landing Gear (4) - Engine power (mechanical HP)

If an electrical system were used instead of a hydraulic system, a generator would take the place of the pump and a motor would take the place of the actuating cylinder. Advantages of Hydraulic Systems (over other systems for aircraft use) 1. It is lighter in weight than alternate existing systems. 2. It is dead beat, that is, there is an absence of sloppiness in its response to demands placed on the system. 3. It is reliable; either it works or doesn't. 4. It can be easily maintained. 5. It is not a shock hazard; it is not much of a fire hazard. 6. It can develop practically unlimited force or torque. Example: A gun turret must be able to change direction almost instantaneously. This is what is accomplished by this hydraulic system. In an electrical system, the rotating armature must come to full stop and then reverse direction or else the armature will burn out. This doesn't happen with a hydraulic system because there is no need for a motor in the hydraulic system. Example: In a landing gear the hydraulic motor can produce enough power to pull up the landing gear system without trouble even though air loads act on the system and the slip stream air is impinging against it. The actuating cylinder can change hydraulic power to linear or rotating motion. It has a reduction gear in it to reduce rotating motion to that amount which is needed. Previously, systems used to control motion by using steel cables connected by pulleys between the controlling mechanism (such as the pedals) and the controlled surface (such as the rudder). The cables were affected by expansion rates of the cables due to temperature changes. Hydraulic systems can control motion without worrying about the effect of temperature since it is a closed system (not open to the atmosphere) compared to a cable system. This means better control of the plane and less lag time between the pilot's movement to control the plane and the response by the control surface. Some Devices Operated by Hydraulic Systems in Aircraft

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1. Primary control boosters 2. Retraction and extension of landing gear 3. Sweep back and forth of wings 4. Opening and closing doors and hatchways 5. Automatic pilot and gun turrets 6. Shock absorption systems and valve lifter systems 7. Dive, landing, speed and flap brakes 8. Pitch changing mechanism, spoilers on flaps 9. Bomb bay doors and bomb displacement gears Some Devices Operated by the Hydraulic Systems in Spacecraft 1. Gimbeling of engines and thrust deflector vanes 2. Thrust reversers and launch mechanisms

LANDING GEAR, BRAKES, AND HYDRAULIC UTILITY SYSTEMS Maintenance on the landing gear and brakes, at times, requires maintenance of related systems. In this chapter, we will discuss the general landing gear systems and brake systems first, and then we will discuss various hydraulic utility systems. We will also examine drop checking procedures, troubleshooting, and the alignment and adjustment of the landing gear. The systems discussed in the following paragraphs are representative. For training purposes, we will use many values for tolerances and pressures to illustrate normal operating conditions. When actually performing the maintenance procedures discussed, you must consult the current applicable technical publications for the exact values to be used. LANDING GEAR SYSTEMS Learning Objective: Identify the various types of landing gear systems used on fixed-wing and rotary-wing aircraft. Every aircraft maintained in today is equipped with a landing gear system. Most aircraft also use arresting and catapult gear. The landing gear is that portion of the aircraft that supports the weight of the aircraft while it is on the ground. The landing gear contains components that are necessary for taking off and landing the aircraft safely. Some of these com-ponents are landing gear struts that absorb landing and taxiing shocks; brakes that are used to stop and, in some cases, steer the aircraft; nosewheel steering for steering the aircraft; and in some cases, nose catapult com-ponents that provide the aircraft with carrier deck takeoff capabilities. FIXED-WING AIRCRAFT Landing gear systems in fixed-wing aircraft are similar in design. Most aircraft are equipped with the tricycle-type retractable landing gear. Some types of landing gear are actuated in different sequences and directions, but practically all are hydraulically operated and electrically controlled. With a knowledge of basic hydraulics and familiarity with the operation of actuating system components, you should be able to understand the operational and troubleshooting procedures for landing gear systems.

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Main Landing Gear The typical aircraft landing gear assembly consists of two main landing gears and one steerable nose landing gear. As you can see in figure 12-1, a main gear

Figure 12-1.–Tricycle landing gear. is installed under each wing. Because aircraft are different in size, shape, and construction, every landing gear is specially designed. Although main landing gears are designed differently, all main gear struts are attached to strong members of the wings or fuselage so that the landing shock is distributed throughout the main body of the structure. The main gears are also equipped with brakes that are used to shorten the landing roll of the aircraft and to guide the aircraft during taxiing. Nose Landing Gear On aircraft with tricycle landing gear, the nose gear is retracted either rearward or forward into the aircraft fuselage. Generally, the nose gear consists of a single shock strut with one or two wheels attached. On most aircraft the nose gear has a steering mechanism for taxiing the aircraft. The mechanism also acts as a shimmy damper to prevent oscillation or shimmy of the nosewheel. Since the nosewheel must be centered before it can be retracted into the wheel well, a centering device aligns the strut and wheel when the weight of the aircraft is off the gear. Damping, steering, and centering devices are discussed later in this chapter.

In order to function safely and effectively all aircraft need auxiliary systems. These systems help the engines and the airframe to function as a complete unit. The different auxiliary systems can be listed as follows: fuel system electrical system hydraulic system auxiliary power unit

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environmental control system fire protection system

Part 1 You can choose to do the next section as a listening or a reading comprehension. If you prefer a listening comprehension, scroll to the end of the text and click on the gold button which says "listening comprehension". The basic units in the fuel system are the fuel tanks. These tanks contain fuel which is kerosene in the case of gas-turbine aircraft and gasoline in the case of piston powered aircraft. The fuel tanks are an integral part of the wing structure. Fuel can be gravity fed to the engines or pumped by electrically operated booster pumps. The fuel flow rate to the engines is determined by the setting of the power levers. The pipes which carry the fuel to the engines are fitted with non-return valves and also have stop cocks to cut fuel flow to the engine in the event of a fire. An important element in the fuel system is fuel filtration which uses filters to remove any contamination from the fuel before it enters the engine. The fuel is usually heated as it is being pumped to the engines to improve the combustion efficiency. Fuel loading can be by a pressurised system or by a gravity system. The pressurised system is connected underwing whilst a gravity system is connected overwing. Fuel quantity is shown by gauges which can be shown in lbs (pounds), kilograms, gallons or litres. Jet engines are more versatile than piston engines in the type of fuel that they can use. Jet engines can burn low octane fuels without significantly affecting performance. The quality of fuel used will eventually affect the engine due to carbon deposits and degradation caused by higher operating temperatures. Aviation authorities set standards of fuel quality and as often happens, the American standards are the ones which are best known. The American designation JET A1 is the most commonly used fuel in modern jet airliners. Additives in the form of anti-corrosion agents and anti-icing agents are also used.For design reasons related to the efficient use of space in the aircraft, the fuel tanks are normally built into the wings as these have the greatest area of space which cannot be used for other purposes. The wing structure is also easily adapted to carrying large amounts of liquid. The main components of the fuel system are, apart from the tanks themselves, the loading system (refuelling) and distribution (fuel feed system). Because jet engines need fuel to be delivered under pressure, pumps are necessary to ensure this pressure. These booster pumps are electrically operated and usually sit at the lowest point in the wing. Other important elements in the system are the filter system , the fuel heaters, the fuel venting system and the crossfeed system. The fuel filter system prevents the blocking of the engine fuel nozzles or fuel pipes by water, dirt or corroded pieces of the fuel tanks. Venting is needed both for liquid and gas. The gas air mixture in a partially empty tank must be able to adjust to changes in the outside pressure as the aircraft climbs and descends to prevent excessive

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pressure on the wing skin. In addition pilots must be able to dump fuel from the aircraft to lighten it in the event of an emergency landing soon after take-off. Gravity feed is used where practicable to allow the fuel to flow to the lowest point in the wing. This area contains a collector tank and is where the booster pumps are situated

Activity 1 Click the box which corresponds to the position in the wing of the these aircraft where the collector tank/booster pumps are probably situated (a or b)

Top of Form a b Bottom of Form

Top of Form a b Bottom of Form

Part2 Authentic Reading Read the following short extract from the technical data publication of the Avro 748, a small turbo-prop airliner with a relatively simple fuel system. Answer the questions which follow. Avro 748 Fuelling System Fuel is supplied to the engines from integral tanks in the outer wings. The usable capacity of these tanks is 1440 IG (1730 USG; 6546 litres). Fuel types normally used are Jet A, A-1, JP4 and JP5. Fuelling Each tank is refuelled or defuelled through underwing pressure connections directly

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accessible from ground level. The maximum refuelling rate is 90 IG/minute (108 USG, 408 litres) and the maximum defuelling rate is 60 IG/minute (72 USG; 273 litres). Provision is made for overwing gravity refuelling - enabling the aircraft to operate in areas lacking airport facilities of any kind. Fuel Feed Fuel from each tank is gravity-fed into its own collector tank. The main cell of each tank is emptied first at which point the float valves are activated and the contents of the tip cells is discharged. Two electrically driven L.P. fuel pumps are mounted in each collector box and deliver fuel into a common feed line. The fuel then passes through the L. P. cock and fuel filter to the engine HP fuel pumps. Either L.P. pump is able to supply full engine requirements and a cross-feed system allows fuel from both tanks to feed either engine. Fuel tank contents are indicated by an accurate capacitance type system, and can be physically measured on the ground by dripsticks fitted to the underside of each tank. (source British Aerospace) Top of Form Questions I . In which part of the wings are the fuel tanks situated? the outer wings the inner wings mid-wing 2. What do the letters I.G mean? international gallons indicated gallons imperial gallons 3. On which part of the wing is the gravity fuelling system? the upper wing the underside of the wing the wing tip 4. Where is a gravity fuelling system required? at large airports at military airports at small airports without facilties 5. What other type of fuelling is possible and more normal? automatic refuelling pressure refuelling

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in-flight refuelling 6. How does the fuel move from the fuel tanks to the collector tank? by gravity by high pressure pump by banking the aircraft 7. In what sequence (order) are the fuel tanks emptied? main tanks then tip tanks tip tanks then main tanks starboard wing then port wing 8. The tip tanks are activated by: the fuel filter the fuel pumps float valves 9. The collector tank pumps and the engine pumps are different because: the engine uses a high pressure pump the collector tank uses a high pressure pump the collector tank pump is not electrically driven 10. A collector tank fuel pump can: only serve its own tank serve both tanks serve both tanks and engines Bottom of Form Part3

Introduction Fuel management has become one of the most important functions of pilots on commercial flights. As fuel is by far the biggest single cost on most flights. The way in which an aircraft commander controls the use of fuel can make a big difference to the amount of fuel used on any particular flight. Aircraft designers have been trying for many years to reduce the amount of fuel which aircraft

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burn in regular use. Although the design of the engines is the biggest factor in overall fuel consumption, the design of the wings and the airframe, particularly in terms of weight and aerodynamic profile, can also influence how efficient an aircraft is. Authentic Reading MD-11/CF6 High Fuel Burn

Top of Form

Bottom of Form Read the text and answer the questions which follow. McDonnell Douglas and General Electric are examining ways of reducing fuel burn on the MD-11, after figures from the flight-test programme revealed that the aircraft is not meeting performance targets. Douglas has now completed more than 1,000h of MD-ll test flying at Yuma, Arizona, the majority with the three aircraft powered by General Electric (GE) CF6-80C2s. Performance figures show that fuel burn on the GE-powered aircraft is consistently 3%-4% above the companies' original estimates. and that the aircraft will therefore not meet its payload/range guarantees. Douglas says that the problem was noticed " . . . within recent weeks", and that early customers. including American Airlines have been notified. the company says: "Early flight-test data for the MD- 11 indicate that it is burning more fuel than predicted. We are treating it as we would treat any other flight-test finding which is of concern to the customer." American which will take delivery of its first GE-powered aircraft in January, has reportedly threatened to seek more than $7 million per aircraft per year in compensation, if the CF680C2-powered MD-l1 trijet does not meet its payload range guarantees. GE is examining various options for improving the specific fuel consumption of the engines, and Douglas is looking at the aircraft's weight and aerodynamics. "The aerodynamic performance of the aircraft in flight test has been very good and that remains the case. In thc weight area, we are a little over the predicted weight, but we have a weight reduction programme in place which will improve performance by about 0.75%, it says. The four MD -11s in the flight test programme are about 907kg (2,0001b) overweight, although more recent aircraft are coming off the production line slightly below their estimated weight. Among the options Douglas is examining for weight reduction is the replacement of the MD11's aluminium floor beams with aluminium-lithium The company says it is still on target to certificate the aircraft in October, with first deliveries following immediately.

Top of Form Questions

I . The aircraft on which most of the test flying has been done are equipped with engines from?

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Rolls Royce engines General Electric CFM

2. Can you guess who the "payload/range guarantees" have been given to. the passengers the pilots the airlines

3 . By how much did the builders of this aircraft underestimate the fuel bum? 3 to 4 % 0.75%

4. What does American Airlines plan to do about this problem? reduce the weight of its aircraft Donnell Douglas 5. What seems to be the main cause of the aircraft having a higher than planned fuel consumption? poor aerodynamic performance heavy 6. What actions is MDC taking to solve the problem? reducing the weight fitting new engines improving aerodynamic performance the airframe is too heavy the engines are too use a different fuel seek compensation form Mc

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The word hydraulic like many scientific or technical words in English was invented by using Greek words to describe some activity. In this case the Greek words hydros which simply means water and the word aulus which means a pipe were combined to make hydraulic. All this took place, not in Greece, but in France about 400 years ago when a French scientist and philosopher, Blaise Pascal was doing some research into the action of water in pipes and its effects on pressure. He discovered that it was not possible to compress water, or any other liquid. He discovered that when you tried to press down on water in a closed container, the force that you were putting onto the small area of the surface was reflected equally on all the other surfaces of the container. This was an early example of the power of amplification.

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The Principle of Hydraulics The force on the smaller piston will be magnified in proportion to the the difference in the size of the pistons. If the area of piston B is fifty times larger then the force will be amplified fifty times. A practical application of this effect is used in large aircraft. When the pilot of a 747 pulls the control wheel back to raise the elevators his small movement is magnified by the hydraulic system to make it possible for a small hand movement to move a control surface weighing hundreds of kilos. The hydraulic system of large aircraft is one if the vital systems. If the hydraulic system fails completely, then the controls become stuck and the aircraft is uncontrollable. The hydraulic system is driven by engine mounted pumps. The system works at high pressure. The hydraulic system is filled with a special fluid which is contained in a reservoir. The pressure of the hydraulic fluid is controlled by pumps and the movement of the fluid is controlled by valves. Systems can be pressurised and depressurised very rapidly. There are standby pumps for use in the event of a failure of the main pumps. There is also an emergency pressure accumulator to provide enough pressure for vital operations such as flaps, brakes and landing gear if all other systems fail. In modern airliners all hydraulic systems are duplicated or triplicated. This adds complexity but it is necessary for complete safety. The hydraulic system generates power to operate landing gear retraction and extension, nosewheel steering, wheel brakes and airstairs retraction. Authentic Reading A Description of the Hydraulic System on the BAe ATP The hydraulic system generates power to operate landing gear retraction and extension, nosewheel steering, wheel brakes and airstairs retraction. Hydraulic power is generated by two engine-driven pumps. Pressure is controlled within the system to 2450 psi (pounds per square inch). Electric depressurising valves (EDVs) provide an automatic means of depressurising both hydraulic pumps whenever the landing gear is in a retracted and locked position. The low system working pressures are designed to reduce wear

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and improve reliability. The majority of hydraulic components can be maintained "on condition". The hydraulic components, excluding the pumps, are grouped together in two main areas. These are easily accessible being in the nose gear bay and in a hydraulics servicing bay in the right hand wing fillet. The system pressure is controlled by an integral pump pressure control system that reduces pump delivery to zero when the system pressure reaches 2450 psi. Mineral based fluid is supplied to the pumps which are designated main and standby, from a reservoir, pressurised by air from the airframe de-icing system. The reservoir is divided into two halves by a central seal. This avoids complete loss of contents if there is a leak in one system. The reservoir is fitted with two detectors, one to indicate low hydraulic fluid level and the other to indicate high hydraulic fluid temperature. Associated warnings are displayed by amber HYD L0 LEVEL and HYD O'HEAT legends on the CWP. An accumulator is located in the nose wheel bay and is initially nitrogen charged. A triple pressure gauge located on the left side flight deck Instrument panel indicates pressure in the two pumping systems and the main accumulator. In the event of the integral pump pressure system failing, relief valves are located in each pumping system. Their function is to limit maximum permissible system pressure to 3,300psi. Filters are located in HP, LP and case drain systems. Blocked filter indication is provided in mechanical form on each filter housing. Under normal circumstances on the ground the main hydraulic pump pressure indicator will show 2,450 psi and the standby pump will indicate 660 psi. This condition will continue until the aircraft takes off and the aircraft weight on ground system, de-energises the standby pump solenoid and restores its pressure to 2,450 psi. When the landing gear is retracted and all uplocks have engaged, four micro-switches in the uplocks and landing gear lever energise the pump solenoids and the output of each pump falls to 660 psi. Selecting landing gear down restores the pressure to the working level of 2,450 psi until the weight on switches re-energise the standby pump solenoid as the aircraft touches down, reducing system pressure to 660psi again. Now test yourself on your knowledge of the information contained in the text. Vocabulary development. Fill in the missing words in the following sentences.

Fill in the missing words and then click the button to the right of the word to check whether your answer is correct. When you click the button you will get a message telling you whether the answer is correct or not. If the answer is correct you will be told your cumulative score and a # will appear after the answer. Otherwise you will get a 'wrong' message. You can delete a wrong answer and try again. The maximum score is 15. Use the reset button at the bottom of the test to clear all boxes and redo the test for reinforcement practice.

Top of Form 1. In this aircraft hydraulic power is used to operate: a: landing gear retraction and c: wheel d: airstairs pumps. b: nosewheel

2. Hydraulic power is supplied in this aircraft by two

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3. The hydraulic system is depressurized by electric

valves when the landing gear is retracted an

4. The system is designed to operate at low pressure for two reasons: a: to reduce b: to improve

5. When the engineer needs to service the hydraulic system he must open either (a ) the nosegear or (b) the hydraulics bay.

6. Detectors in the hydraulic fluid reservoir can detect (a) a low hydraulic level and (b) a high hydraulic fluid .

7. Pilots can check what the pressure is in the system by looking at a triple 8. If the pressure gets too high in the system a will limit the pressure. Bottom of Form

on the instrument pa

Aircraft Brake Systems. All hydraulic brake systems operate on the same basic principle. When the operator moves a brake pedal or other brake operating control, the movement is

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transmitted to a master cylinder or to a power brake control valve from which fluid pressure is delivered through connecting lines to a brake assembly connected to a wheel or shaft whose movement is to be braked. The fluid pressure acting on the brake assembly pushes brake linings Into contact with surfaces of a rotating disc. The resulting friction slows--and finally stops--the continued rotation of the wheel or shaft to which the disc is connected. When the brake pedal or brake control is returned to the off position, brake operating pressure is relieved, the brake lining loses contact with the disc, and the wheel or shaft is free to turn again. a. Wheel Brake Systems. Aircraft wheel brake systems are dual in nature in that they are composed of two identical subsystems that can be operated independently of each other to provide separate braking action for the landing gear on each side of the aircraft. Each subsystem is operated by a toe plate (brake pedal) that is hinge-mounted to the top of the aircraft rudder pedal. Since each brake pedal can be operated independently the brakes can be used for steering the aircraft. A list of components, which may be found in varying combinations to make up the different wheel brake systems, includes the following: master cylinder (or a power brake control valve), wheel brake assemblies deboosters, parking brake valves, shuttle valves, accumulators, connecting lines, and bottles charged with compressed air. The minimum number of parts which could be used to perform the function of a simple wheel brake system are a master cylinder (or a power brake control valve), a wheel brake assembly, and connecting lines. (1) Master cylinders. Master cylinders are used in some wheel brake systems as the means of transforming force applied by the of the operator foot into fluid pressure; the greater the force applied to the pedal, the higher the fluid pressure. Master cylinders fall into three general classifications: simple, compound, and powerboost. Within these classifications, there are many variations in shape, size, and design, depending on the manufacturer and on how the cylinder functions in the brake system. Brake systems incorporating simple and compound master cylinders operate independently of any other hydraulic system within the aircraft and are sometimes called independent brake systems. In brake systems using a power boost master cylinder, some of the power needed for braking is supplied by a power-driven pump. (a) Simple master cylinder. Some simple cylinders have integral reservoirs; others are connected with in-line reservoirs by means of a hose. In some designs, a push rod actuates the piston; in others a pull rod performs this function. The design shown in figure 4-148 has an integral reservoir, and the piston is actuated by a push rod. Note that the illustration shows the cylinder in released position, with the compensating valve open. This allows any thermally expanded fluid within a connected wheel brake assembly to pass freely into the reservoir and from the reservoir back into the assembly to replace fluid that may have been lost due to minor leakage. When the brake pedal is depressed, the first few thousandths of an inch of travel of the master cylinder push rod closes the compensating valve, thus trapping the fluid that lies between the underface of the piston and the wheel brake assembly. Further depression of the brake pedal moves the piston within its bore and forces fluid out of the master cylinder.

Pressure Unit Conversions Definition Pressure is a measure of the force against a surface. Pressure is usually expressed as a force per unit area. Here is a handy conversion calculator for some common

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pressure terms. The definitions of each term are in the following section. Top of Form Bottom of Form Additional Info Many of the items you will find on an MSDS come in both English (U.S. Customary System) and metric (International System or SI or cgs) units. The metric system has been adopted by almost every country except the United States. Even in the U.S., scientists and technical people use the metric system because of its ease of use. If you are unfamiliar with the terms used in these definitions, see our mass unit and distance unit conversion pages. Unit Pounds per square inch (psi, PSI, lb/in2, lb/sq in) Equivalent measurements, comments Commonly used in the U.S., but not elsewhere. Normal atmospheric pressure is 14.7 psi, which means that a column of air one square inch in area rising from the Earth's atmosphere to space weighs 14.7 pounds.

Atmosphere Normal atmospheric pressure is defined as 1 atmosphere. (atm) 1 atm = 14.6956 psi = 760 torr. Based on the original Torricelli barometer design, one atmosphere of pressure will force the column of mercury (Hg) in a mercury barometer to a height of 760 millimeters. A pressure that causes the Hg column to rise 1 millimeter is called a torr (you may still see the term 1 mm Hg used; this has been replaced by the torr. "mm Hg" is commonly used for blood pressure measurements). 1 atm = 760 torr = 14.7 psi. The bar nearly identical to the atmosphere unit. One bar = 750.062 torr = 0.9869 atm = 100,000 Pa.

Torr (torr)

Bar (bar)

There are 1,000 millibar in one bar. This unit is used by Millibar meteorologists who find it easier to refer to atmospheric (mb or mbar) pressures without using decimals. One millibar = 0.001 bar = 0.750 torr = 100 Pa. 1 pascal = a force of 1 Newton per square meter (1 Newton = the force required to accelerate 1 kilogram one meter per second per second = 1 kg.m/s2; this is actually quite logical for physicists and engineers, honest). 1 pascal = 10 dyne/cm2 = 0.01 mbar. 1 atm = 101,325 Pascals = 760 mm Hg = 760 torr = 14.7 psi. The prefix "kilo" means "1,000", so one kilopascal = 1,000 Pa. Therefore, 101.325 kPa = 1 atm = 760 torr and 100 kPa = 1 bar = 750 torr.

Pascal (Pa)

Kilopascal (kPa)

Megapascal The prefix "mega" means "1,000,000", so one megapascal (MPa) = 1,000 kPa = 1,000,000 Pa = 9.869 atm = 145 psi. The prefix "giga" means "1,000,000,000", so one gigapascal = 1,000 MPa = 1,000,000 kPa = 1,000,000,000 Pa = 9,870 atm = 10,000 bar. Pressures of several gigapascals can convert graphite to diamond or make hydrogen a metallic conductor! Such high pressures are rarely encountered in everyday life.

Gigapascal (GPa)

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Pressurized Airplanes When an airplane is flown at a high altitude, it consumes less fuel for a given airspeed than it does for the same speed at a lower altitude. In other words, the airplane is more efficient at a high altitude. In addition, bad weather and turbulence can be avoided by flying in the relatively smooth air above the storms. Airplanes which do not have pressurization and air conditioning systems are usually limited to the lower altitudes. Because of the advantages of flying at high altitudes, many modern general aviation type airplanes are being designed to operate in that environment. It is important then, that pilots transitioning to such sophisticated equipment be familiar with at least the basic operating principles. A cabin pressurization system accomplishes several functions in providing adequate passenger comfort and safety. It maintains a cabin pressure altitude of approximately 8,000 feet at the maximum designed cruising altitude of the airplane, and prevents rapid changes of cabin altitude which may be uncomfortable or injurious to passengers and crew. In addition, the pressurization system permits a reasonably fast exchange of air from inside to outside the cabin. This is necessary to eliminate odors and to remove stale air. Pressurization of the airplane cabin is now the accepted method of protecting persons against the effects of hypoxia. Within a pressurized cabin, people can be transported comfortably and safely for long periods of time, particularly if the cabin altitude is maintained at 8,000 feet or below, where the use of oxygen equipment is not required. However, the flight crew in this type of airplane must be aware of the danger of accidental loss of cabin pressure and must be prepared to meet such an emergency whenever it occurs. In this typical pressurization system, the cabin, flight compartment, and baggage compartments are incorporated into a sealed unit which is capable of containing air under a pressure higher than outside atmospheric pressure. Pressurized air is pumped into this sealed fuselage by cabin superchargers which deliver a relatively constant volume of air at all altitudes up to a designed maximum. Air is released from the fuselage by a device called an outflow valve. Since the superchargers provide a constant inflow of air to the pressurized area, the outflow valve, by regulating the air exit, is the major controlling element in the pressurization system. It is necessary to become familiar with some terms and definitions to understand the operating principles of pressurization and air conditioning systems. These are: 1. Aircraft altitude. The actual height above sea level at which the airplane is flying. 2. Ambient temperature. The temperature in the area immediately surrounding the airplane. 3. Ambient pressure. The pressure in the area immediately surrounding the airplane. 4. Cabin altitude. Used to express cabin pressure in terms of equivalent altitude above sea level. 5. Differential pressure. The difference in pressure between the pressure acting on one side of a wall and the pressure acting on the other side of the wall. In aircraft air conditioning and pressurizing systems, it is the difference between cabin pressure and atmospheric pressure. The cabin pressure control system provides cabin pressure regulation, pressure relief, vacuum relief, and the means for selecting the desired cabin altitude in the isobaric and differential range. In addition, dumping of the cabin pressure is a function of the pressure control system. A cabin pressure regulator, an outflow valve, and a safety valve are used to accomplish these functions. The cabin pressure regulator controls cabin pressure to a selected value in the isobaric range and limits cabin pressure to a preset differential value in the differential range. When the airplane reaches the altitude at which the difference between the pressure inside and outside

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the cabin is equal to the highest differential pressure for which the fuselage structure is designed and further increase in airplane altitude will result in a corresponding increase in cabin altitude. Differential control is used to prevent the maximum differential pressure, for which the fuselage was designed, from being exceeded. This differential pressure is determined by the structural strength of the cabin and often by the relationship of the cabin size to the probable areas of rupture, such as window areas and doors. The cabin air pressure safety valve is a combination pressure relief, vacuum relief, and dump valve. The pressure relief valve prevents cabin pressure from exceeding a predetermined differential pressure above ambient pressure. The vacuum relief prevents ambient pressure from exceeding cabin pressure by allowing external air to enter the cabin when ambient pressure exceeds cabin pressure. The dump valve is actuated by the cockpit control switch. When this switch is positioned to "ram," a solenoid valve opens, causing the valve to dump cabin air to atmosphere. The degree of pressurization and, therefore, the operating altitude of the aircraft are limited by several critical design factors. Primarily the fuselage is designed to withstand a particular maximum cabin differential pressure. Several instruments are used in conjunction with the pressurization controller. The cabin differential pressure gauge indicates the difference between inside and outside pressure. This gauge should be monitored to assure that the cabin does not exceed the maximum allowable differential pressure. A cabin altimeter is also provided as a check on the performance of the system. In some cases, these two instruments are combined into one. A third instrument indicates the cabin rate of climb or descent. A cabin rate of climb instrument and a cabin altimeter are illustrated in Fig. 16-15.

Decompression is defined as the inability of the airplane's pressurization system to maintain its designed pressure differential. This can be caused by a malfunction in the pressurization system or structural damage to the airplane. Physiologically, decompressions fall into two categories: 1. Explosive Decompression. Explosive decompression is defined as a change in cabin pressure faster than the lungs can decompress. Therefore, it is possible that lung damage may occur. Normally, the time required to release air from the lungs where no restrictions exist, such as masks, etc., is 0.2 seconds. Most authorities consider any decompression which occurs in less than 0.5 seconds as explosive and potentially dangerous. 2. Rapid Decompression. Rapid decompression is defined as a change in cabin pressure where the lungs can decompress faster than the cabin. Therefore there is no likelihood of lung damage. During a decompression there may be noise, and for a split second one may feel dazed. The

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cabin air will fill with fog, dust or flying debris. Fog occurs due to the rapid drop in temperature and the change of relative humidity. Normally, the ears clear automatically. Belching or passage of intestinal gas may occur. Air will rush from the mouth and nose due to the escape of air from the lungs, and may be noticed by some individuals. The primary danger of decompression is hypoxia. Unless proper utilization of oxygen equipment is accomplished quickly, unconsciousness may occur in a very short time. The period of useful consciousness is considerably shortened when a person is subjected to a rapid decompression. This is due to the rapid reduction of pressure on the body. Thus, oxygen in the lungs is exhaled rapidly. This in effect reduces the partial pressure of oxygen in the blood and thus reduces the pilot's effective performance time by 1/3 to 1/4 its normal time. It is for this reason the oxygen mask should be worn on the face when flying at very high altitudes (35,000 feet or higher). It is recommended that the crewmembers select the 100% oxygen setting on the oxygen regulator at high altitude if the airplane is equipped with a demand or pressure demand oxygen system. Another hazard is that of being tossed or blown out of the airplane if near an opening. For this reason, individuals near such openings should wear safety harnesses or seatbelts at all times when the airplane is pressurized and they are seated. Still another potential hazard on high altitude decompressions is the possibility of evolved gas decompression sicknesses. Exposure to windblast and extremely cold temperatures are other hazards one might have to face. The invention relates to a pneumatic system testing device and, more particularly, to an aircraft pneumatic system test cart. Conventional passenger aircraft have various pneumatic systems. An aircraft bleed system is an example of one such pneumatic system. The bleed system provides high air pressure during low atmospheric air pressure operating conditions. The high pressure air is used to provide air conditioning and cabin pressurization. Once the aircraft reaches high air pressure operating conditions the bleed system switches over to provide low air pressure. The switching function is carried out by the interaction of numerous air flow and temperature sensors with switching mechanisms. Such a system must be periodically maintained in order to insure safe and optimum system performance. Typical maintenance involves having the aircraft brought into a hangar and having the sensors and switches replaced. Although replacing system components in such a fashion can maintain optimal system performance, it is cost ineffective. First, keeping the aircraft out of service for a relatively long period of time creates lost revenue. Second, replacing the sensors and switches while they are still operational wastes the effective lifetime of expensive components. Indeed, replacing a component once it reaches the end of its life cycle is less costly and may be done with less frequency than replacing such a component based on a preventative maintenance schedule that is independent of the life cycle of the component. Periodically testing the pneumatic system and the system componentry would solve the problem of wasted component capacity, but such a solution does not fully obviate the problem of having the aircraft out of service and in the repair hangar during such testing. Conventional pneumatic testing equipment includes a pneumatic test box, a sensor/switch test oven, pressurized nitrogen tanks and various other items such as hoses, flex lines, electrical cords, fittings and seals. Therefore, testing the aircraft while on the tarmac is not feasible, as the necessary testing equipment is cumbersome and not easily transportable. SUMMARY OF THE INVENTION A portable aircraft pneumatic system test cart includes a cart with a mounting surface, having

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pneumatic test box and a sensor test oven disposed on the mounting surface. An advantage of the present invention is that the test cart may be transported to the aircraft for pneumatic testing, thereby minimizing aircraft out-of-service time. According to a preferred embodiment of the present invention, the test cart further includes at least one pressurized nitrogen tank.

Hydraulic systems utilize fluid to transmit force. Examples are brake systems, landing gear struts and (in more complex aircraft) flight control or landing gear actuator systems. Pneumatic systems utilize gas (usually air) to transmit force. Examples are gyroscopic instrument air systems and (in more complex aircraft) deice boot inflation systems. Since gasses are compressible, and fluids are not, hydraulic systems have a greater speed of response and transmit higher forces. Pneumatic systems are generally supplied by atmospheric air (pumped), or engine bleed air from the compressor sections of turbine engines. Hydraulic systems are supplied by on-board reservoirs and/or accumulators. Pumps are used to amplify control forces input by the pilot when higher forces are required to move an actuator. Pneumatic systems are generally lighter than hydraulic systems, due to the absence of fluid. Some notes on Aircraft hydraulic power system Aircraft hydraulics Aircraft Hydraulics is a means of transmitting energy or power from one place to another efficiently. What is hydraulic technology? In the hydraulic technology we transmit and control forces and velocities by transmitting and controlling pressure and flow. In nearly every kind of technology we use hydraulic drive and control techniques. A few examples are: mechanical engineering car technology agriculture technology earthmoving and mining technology ship building technology offshore-technology aircraft and spacecraft technology Advantages of Hydraulic Systems (over other systems for aircraft use) It is lighter in weight than alternate existing systems. It is dead beat, that is, there is an absence of sloppiness in its response to demands placed on the system. It is reliable; either it works or doesn't. It can be easily maintained. It is not a shock hazard; it is not much of a fire hazard.

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It can develop practically unlimited force or torque. Example: A gun turret must be able to change direction almost instantaneously. This is what is accomplished by this hydraulic system. In an electrical system, the rotating armature must come to full stop and then reverse direction or else the armature will burn out. This doesn't happen with a hydraulic system because there is no need for a motor in the hydraulic system. Example: In a landing gear the hydraulic motor can produce enough power to pull up the landing gear system without trouble even though air loads act on the system and the slip stream air is impinging against it. The actuating cylinder can change hydraulic power to linear or rotating motion. It has a reduction gear in it to reduce rotating motion to that amount which is needed. Previously, systems used to control motion by using steel cables connected by pulleys between the controlling mechanism (such as the pedals) and the controlled surface (such as the rudder). The cables were affected by expansion rates of the cables due to temperature changes. Hydraulic systems can control motion without worrying about the effect of temperature since it is a closed system (not open to the atmosphere) compared to a cable system. This means better control of the plane and less lag time between the pilot's movement to control the plane and the response by the control surface. Some Devices Operated by Hydraulic Systems in Aircraft Primary control boosters Retraction and extension of landing gear Sweep back and forth of wings Opening and closing doors and hatchways Automatic pilot and gun turrets Shock absorption systems and valve lifter systems Dive, landing, speed and flap brakes Pitch changing mechanism, spoilers on flaps Bomb bay doors and bomb displacement gears

A fly-by-wire (FBW) system replaces manual flight control of an aircraft with an electronic interface. The movements of flight controls are converted to electronic signals transmitted by wires (hence the fly-by-wire term), and flight control computers determine how to move the actuators at each control surface to provide the ordered response. The fly-by-wire system also allows automatic signals sent by the aircraft's computers to perform functions without the pilot's input, as in systems that automatically help stabilize the aircraft

Description A conventional fixed-wing aircraft flight control system consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. Aircraft engine controls are also considered as flight controls as they change speed. The fundamentals of aircraft controls are explained in flight dynamics. This article centers on the operating mechanisms of the flight controls. Cockpit controls

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Primary controls Generally the primary cockpit controls are arranged as follows: A control column or a control yoke attached to a column—for roll and pitch, which moves the ailerons when turned or deflected left and right, and moves the elevators when moved backwards or forwards Rudder pedals to control yaw, which move the rudder; left foot forward will move the rudder left for instance. Throttle controls to control engine speed or thrust for powered aircraft. Even when an aircraft uses different kinds of surfaces, such as a V-tail/ruddervator, flaperons, or elevons, to avoid pilot confusion the aircraft will still normally be designed so that the yoke or stick controls pitch and roll in the conventional way, as will the rudder pedals for yaw.

The Four Forces We’re going to start with the very basics here. If you have ever read anything about airplanes, even most kids’ books, you know that there are four forces that rule an airplane: Weight, Thrust, Lift and Drag, in no particular order. Weight is, well, weight. Because of gravity, the stuff that makes up an airplane (like anything else) is attracted towards the center of the earth. So weight always points straight down. You can’t ever really change weight (other than by making your plane lighter). Thrust happens because the engine of the plane pushes air and exhaust gases backwards, so air and the exhaust gases exert a forwards force on the engine (Newton’s Third Law). Sometimes, some airplanes’ engines (in some helicopters and some military aircraft) can push the air and exhaust gases in directions other than backwards, so this pushes the plane in directions other than forwards. This is true in very few, rare, unusual airplanes, as we’ll see, and even in those, thrust pushes forward nearly always. Lift is the upwards force generated by the wing (and sometimes by the fuselage, tail, and other features, in smaller amounts). It occurs because the wings divert air downwards when air is blown by them (Newton’s 3rd again). We will see why this happens. Lift is always directed upwards or just-off-upwards: for example, when an airplane makes a banked turn, some lift is generated towards the inside of the turn, pulling the plane inwards as well as up, so it turns. Drag is, simply, air resistance. It is the force the air exerts on an airplane (or anything else moving through the air, or water, or any fluid) trying to slow it down. Drag always points opposite to the direction of flight. As an airplane flies through the air, it drags some of the air forward with it, so that air pulls the airplane back (you guessed it – Newton’s 3rd again). This is in fact caused by different forces and different effects, always changing in many ways. Some of it is quite non-intuitive. For example, we will see how drag sometimes is higher at low speeds than at higher flight speeds. Controls The next three pages will go over airplane control systems, i.e. the mechanisms used by engineers and pilots to make an airplane fly in a desired direction, with a desired orentation. First we'll go over the basics: The three axes (roll, pitch, and yaw), the controls used to fly an airplane (stick and rudder), and the devices that translate inputs on those controls into

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changes in those axes (elevators, ailerons, and rudders). Then, we'll go into exceptions regarding those devices. Not every airplane has elevators, ailerons, and rudders; Some have elevons, all-moving tailplanes, wing-warping, thrust-vectoring, etc. (The page about this stuff has a really nice thrust-vectoring video which I think is one of the highlights of this website). We will then talk about trim. Trim are the mechanisms that automatically keep an airplane from turning if it is off-balance, e.g. if there is more weight on one side than on the other side, if some damage causes an assymetry in drag, or - most often - while the center of lift of a wing changes as the airplane speed changes. We will then go over stability, which is absolutely key in aircraft design. Stability is an airplane's natural tendency to return to (and stay at) smooth horizontal level flight. Airplanes whose designs are not stable can be very hard to fly (the equivalent of a unicycle, versus a tricycle). And then we'll move on to other performance-related topics like how an airplane's design affects its climbing and turning abilities.

A small notes on active control technology

Future developments on active control technology:

The following discussion is based on a presentation by Ilan Kroo entitled, Reinventing the Airplane: New Concepts for Flight in the 21st Century.

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When we think about what may appear in future aircraft designs, we might look at recent history. The look may be frightening. From first appearances, anyway, nothing has happened in the last 40 years! There are many causes of this apparent stagnation. The first is the enormous economic risk involved. Along with the investment risk, there is a liability risk which is of especially great concern to U.S. manufacturers of small aircraft. One might also argue that the commercial aircraft manufacturers are not doing too badly, so why argue with success and do something new? These issues are discussed in the previous section on the origins of aircraft. Because of the development of new technologies or processes, or because new roles and missions appear for aircraft, we expect that aircraft will indeed change. Most new aircraft will change in evolutionary ways, but more revolutionary ideas are possible too. This section will discuss several aspects of future aircraft including the following: Improving the modern airplane New configurations New roles and requirements Improving the Modern Airplane Breakthroughs in many fields have provided evolutionary improvements in performance. Although the aircraft configuration looks similar, reductions in cost by nearly a factor of 3 since the 707 have been achieved through improvements in aerodynamics, structures and materials, control systems, and (primarily) propulsion technology. Some of these areas are described in the following sections.

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Active Controls Active flight control can be used in many ways, ranging from the relatively simple angle of attack limiting found on airplanes such as the Boeing 727, to maneuver and gust load control investigated early with L-1011 aircraft, to more recent applications on the Airbus and 777 aircraft for stability augmentation. Reduced structural loads permit larger spans for a given structural weight and thus a lower induced drag. As we will see, a 10% reduction in maneuver bending load can be translated into a 3% span increase without increasing wing weight. This produces about a 6% reduction in induced drag. Reduced stability requirements permit smaller tail surfaces or reduced trim loads which often provide both drag and weight reductions. Such systems may also enable new configuration concepts, although even when applied to conventional designs, improvements in performance are achievable. In addition to performance advantages the use of these systems may be suggested for reasons of reliability, improved safety or ride quality, and reduced pilot workload, although some of the advantages

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are arguable. New Airfoil Concepts Airfoil design has improved dramatically in the past 40 years, from the transonic "peaky" sections used on aircraft in the 60's and 70's to the more aggressive supercritical sections used on today's aircraft. The figure below illustrates some of the rather different airfoil concepts used over the past several decades.

Continuing progress in airfoil design is likely in the next few years, due in part to advances in viscous computational capabilities. One example of an emerging area in airfoil design is the constructive use of separation. The examples below show the divergent trailing edge section developed for the MD-11 and a cross-section of the Aerobie, a flying ring toy that uses this unusual section to enhance the ring's stability.

Flow Near Trailing Edge of DTE Airfoil and Aerobie Cross-Section Flow Control Subtle manipulation of aircraft aerodynamics, principally the wing and fuselage boundary layers, can be used to increase performance and provide control. From laminar flow control, which seeks to reduce drag by maintaining extensive runs of laminar flow, to vortex flow control (through blowing or small vortex generators), and more recent concepts using MEMS devices or synthetic jets, the concept of controlling aerodynamic flows by making small changes in the right way is a major area of aerodynamic research. Although some of the more unusual concepts (including active control

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of turbulence) are far from practical realization, vortex control and hybrid laminar flow control are more likely possibilities. Structures Structural materials and design concepts are evolving rapidly. Despite the conservative approach taken by commercial airlines, composite materials are finally finding their way into a larger fraction of the aircraft structure. At the moment composite materials are used in empennage primary structure on commercial transports and on the small ATR-72 outer wing boxes, but it is expected that in the next 10-20 years the airlines and the FAA will be more ready to adopt this technology. New materials and processes are critical for high speed aircraft, UAV's, and military aircraft, but even for subsonic applications concepts such as stitched resin film infusion (RFI) are beginning to make cost-competitive composite applications more believable. Propulsion Propulsion is the area in which most evolutionary progress has been made in the last few decades and which will continue to improve the economics of aircraft. Very high efficiency, unbelievably large turbines are continuing to evolve, while low cost small turbine engines may well revolutionize small aircraft design in the next 20 years. Interest in very clean, low noise engines is growing for aircraft ranging from commuters and regional jets to supersonic transports. Multidisciplinary Optimization In addition to advances in disciplinary technologies, improved methods for integrating discipline-based design into a better system are being developed. The field of multidisciplinary optimization permits detailed analyses and design methods in several disciplines to be combined to best advantage for the system as a whole. The figure here shows the problem with sequential optimization of a design in individual disciplines. If the aerodynamics group assumes a certain structural design and optimizes the design with respect to aerodynamic design variables (corresponding to horizontal motion in the conceptual plot shown on the right), then the structures group finds the best design (in the vertical degree of freedom), and this process is repeated, we arrive at a converged solution, but one that is not the best solution. Conventional trade studies in 1 or 2 or several parameters are fine, but when hundreds or thousands of design degrees of freedom are available, the use of more formal optimization methods are necessary.

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Although a specific technology may provide a certain drag savings, the advantages may be amplified by exploiting these savings in a re-optimized design. The figure to the right shows how an aircraft was redesigned to incorporate active control technologies. While the reduced static margin provides small performance gains, the re-designed aircraft provides many times that advantage. Some typical estimates for fuel savings associated with "advanced" technologies are given below. Note that these are sometimes optimistic, and cannot be simply added together.

Active Control Composites Laminar Flow Improved Wing Propulsion Total

10% 20% 10% 10% 20% 70%

New Configuration Concepts Apart from evolutionary improvements in conventional aircraft, revolutionary changes are possible when the "rules" are changed. This is possible when the configuration concept iteself is changed and when new roles or requirements are introduced. The following images give some idea of the range of concepts that have been studied over the past few years, some of which are currently being pursued by NASA and industry.

Blended Wing Body

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The BWB design is intended to improve airplane efficiency through a major change in the airframe configuration. The thick centerbody accommodates passengers and cargo without the extra wetted area and weight of a fuselage. Orginally designed as a very large aircraft with as many as 800 passengers, versions of the BWB has been designed with as few as 250 passengers and more conventional twin, podded engines.

Joined Wing The joined wing design was developed principally by Dr. Julian Wolkovitch in the 1980's as an efficient structural arrangement in which the horizontal tail was used as a sturcural support for the main wing as well as a stabilizing surface. It is currently being considered for application to high altitiude long endurance UAVs.

Oblique Flying Wing One of the most unusual concepts for passenger flight is the oblique wing, studied by Robert T. Jones at NASA from 1945 through the 1990s. Theoretical considerations suggest that the concept is well suited to low drag supersonic flight, while providing a structurally efficient means of achieving variable geometry.

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New Roles and Requirements In addition to new configuration ideas, new roles and requirements for aircrafrt may lead to new aircraft concepts. Some of these are summarized below.

Pacific Rim Travel As global commerce continues to increase, the need for passenger and cargo transportation grows as well. Many have speculated that growth in pacific rim travel may be the impetus for high speed aircraft development. The figure above suggests how the time required for flight from Los Angeles to Tokyo varies with cruise Mach number. (The somewhat facetious Mach 8 aircraft requires extra time to cool off before passengers can deplane.)

Supersonic transportation (Boeing High Speed Civil Transport Concept)

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Ground Effect Cargo Tranport Concept Vehicles designed for missions other than carrying passengers include military aircraft with new constraints on radar detection (low observables), very high altitude aircraft, such as the Helios solar powered aircraft intended for atmospheric science and earth observation studies, and vehicles such as the Proteus, designed as a communications platform.

Low Observables (B2 Bomber)

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Autonomous Air Vehicles (Pathfinder: a prototype for Helios solar UAV)

Halo Autonomous Air Vehicle for Communications Services (an AeroSat) Finally a new class of air vehicles intended to provide lower cost access to space is under study. The near-term future of such designs depends on the economic health of the commercial space enterprise and it presently appears that these concepts are not likely to be seen soon.

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Access to Space Conclusions Improved understanding and analysis capabilities permit continued improvement in aircraft designs Exploiting new technologies can change the rules of the game, permitting very different solutions New objectives and constraints may require unconventional configurations Future progress requires unprecedented communication among aircraft designers, scientists, and computational specialists

System 55

FEATURES Two axis, roll & pitch autopilot

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Combines programmer, computer, annunciator and servo amplifier functions into one compact panel mount unit Heading select, VOR/LOC front and back course intercept and tracking Can be interfaced with RNAV, GPS, or LORAN systems, and all radio couplers are standard Liquid crystal display (LCD) Special approach switch allows pilot to select increased autopilot sensitivity for VOR, LORAN, or GPS approaches Vertical speed command in precise 100' increments Altitude hold, control wheel steering (CWS) and VOR/LOC/GS off course deviation warning *OPTIONS Remote Annunciator - Information Flight Director Steering Horizon - Information Directional Gyro or HSI - Information Automatic Electric Pitch Trim - Information Altitude/Vertical Speed Selector - Information Yaw Damper/Rudder Trim System - Information SPECIFICATIONS SYSTEM CURRENT REQUIREMENTS: Avg. Operating 1.0 [email protected] VDC; 0.5 Current: [email protected] VDC PROGRAMMER/COMPUTER: Power Requirements: 14/28 VDC Dimensions: 6.25" x 1.5" x 10.60"

Max. Current:

5.0 [email protected] VDC; 3.0 [email protected] VDC

Weight: 3.0 lbs. TSO: Autopilot- FAA C9c; Flight Director- FAA C52a

TURN COORDINATOR: Power 14/28 VDC Requirements: Flag RPM Detector: (operating limits) nominal RPM less 20% Weight: 1.8 lbs. ROLL SERVO: Power Requirements: 14/28 VDC Current Requirements: Weight: 2.9 lbs. Dimensions: PITCH SERVO/TRIM SENSOR: Power Requirements: 14/28 VDC Current

Flag Voltage Detector: Current Requirements: Dimensions:

(operating limits) 9.0 VDC approx. 0.3 Amp 3.275" x 3.275" x 5.62"

included in system current requirements 3.75" x 3.75" x 7.25"

included in system current

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Weight: 2.9 lbs. Requirements: Dimensions: requirements 3.75" x 3.75" x 7.25"

ALTITUDE PRESSURE TRANSDUCER: Power 10 VDC (supplied by Requirements: programmer/computer) Overpressure: 150% operating maximum

Pressure Range:

0.15 PSI absolute

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