Types of Landing Gear

 TYPES OF LANDING GEAR
  Conventional Tricycle

CONVENTIONAL LANDING GEAR
Consists of two wheels forward of the aircraft's center of gravity and a third small wheel at the tail. This type of landing gear is most often seen in older general aviation airplanes. The two main wheels are fastened to the fuselage by struts. Without a wheel at the nose of the plane, it easily pitches over if brakes are applied too soon. Because the tailwheel is castered--free to move in any direction--the plane is very difficult to control when landing or taking off.        Two main wheels One tail dragger wheel

ADVANTAGE
The ability to operate the aircraft over rough terrain. Due to its smaller size the tailwheel has less parasite drag than a nosewheel. Tailwheels are less expensive to buy and maintain than a nosewheel. If a tailwheel fails on landing, the damage to the aircraft will be minimal. Reduced landing gear weight

DISADVANTAGE
    
Requires more skill in ground taxiing

Suffer from poorer forward visibility on the ground. Conventional geared aircraft are much more susceptible to ground looping. Nose high attitude on the ground, propeller powered taildraggers are more adversely affected. Aircraft lack sufficient rudder authority in some flight regimes.

EXAMPLES OF TAILWHEEL AIRCRAFT:
       Cessna 170 de Havilland Canada DHC-2 Beaver Denny Kitfox Grumman Ag Cat Maule M-5 Piper J-3 Cub Vans RV-4

TRICYCLE LANDING GEAR
The landing gear on small aircraft consists of three wheels: two main wheels (one located on each side of the fuselage) and a third wheel positioned either at the front or rear of the airplane. Landing gear employing a rear-mounted wheel is called conventional landing gear. Airplanes with conventional landing gear are often referred to as tailwheel airplanes. When the third wheel is located on the nose, it is called a nosewheel, and the design is referred to as a tricycle gear. A steerable nosewheel or tailwheel permits the airplane to be controlled throughout all operations while on the ground.  Has nose wheel, which may be steerable.  Main gear, on either side.

ADVANTAGE


Keeps aircraft level during take-off and landing.  Its ease of ground handling.  It allows more forceful application of the brakes during landings at high speeds without causing the aircraft to nose over.  It permits better forward visibility for the pilot during takeoff, landing, and taxiing.  It tends to prevent ground looping (swerving) by providing more directional stability during ground operation since the aircraft’s center of gravity (CG) is forward of the main wheels. The forward CG keeps the airplane moving forward in a straight line rather than ground looping.

DISADVANTAGE
       Greater summary mass of struts due to the bigger height of the nose strut hence bending moment which is forced onto it by additional load from forces of inertia. Smaller permeability. The nose strut is reloaded because of inertia forces action and its foot-pressure on ground is increased also during running. Considerably larger volumes in a fuselage indispensable for retracting the nose strut. It is especially difficult when engine is positioned inside of a fuselage nose part. Longitudinal instability during movement of aircraft along an aerodrome with an elevated front support during take-off run. Danger of emergency or even catastrophes during damage or breaking of front support. Possibility of appearance of self-energizing oscillations has freely orienting wheels of a front support. Such oscillations are called ³shimmy.´The means for elimination of this phenomenon will result in complicating and in weight increase of a structure

EXAMPLES OF NOSEWHEEL AIRCRAFT:
    Cessna 150 Cessna 172 Cessna 182 Piper PA-22 Tripacer

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CLASSIFICATION OF 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.

MAIN LANDING GEAR
   

NON-ABSORBING 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 Cessna 152 Advantages:  Lighter weight  Less complex  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

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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

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