Aircraft Design

Aircraft Design – An Overview

Aircraft Design Process
 Design – creating a plan or product that will satisfy a set of requirements.  Aircraft Design Process – creating an aircraft that will satisfy a given civil or military mission requirement
– Assume product details – Analyze performance – Verify if performance meets goals
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ID1100
P. SRIRAM
Department of Aerospace Engineering, IIT Madras

Example Design Requirements
 150 passengers carrying capacity
– Each passenger weight (80 kg) + baggage +?

Design Examples (Prof. RKK)
Mech. Engg. Components SubSubassemblies Modules Machines Systems Large Systems Huge / Complex Systems Bolt, Nut, Screw Brake, Gear Box Engine Bicycle Automobile Trains, Aircraft Tools Screwdriver, Spanner Multi-blade Multiscrewdriver Swiss Knife Lathe CNC Machine Robotic Assembly Line Satellite Station Online Reservations EE Resistor, Capacitor Software Small C Program

 Cruise altitude 9-12 km 9 Cruise speed about 1000 kmph  Minimum range 5000 km (Boeing 737: 110-180 passengers, cruise 110850kmph @ 10km, range 5500km) 850 kmph M ~ 0.7 at sea level, 0.85 at 10km
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Transportatio Bucket Wheel n System, Big Building Excavator

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Team Design Approach
 Why team design?
– Very complex end product – B747: 6 million parts; 75,000 drawings used

Is a team always necessary? (Burt Rutan’s designs) Rutan’
Global Flyer (2005) SpaceShip One (2004)

 Typical team composition
– design requirements – technology requirements – budgeting – scheduling

Voyager (1986)
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Beech Starship (1982)
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Lockheed Skunk Works (small team)
U-2 (1955)

Assignment
 Write a short report (single page – hand written only) on an aircraft of your choice
– Essential features – Unique / distinctive features (must have) – Some essential dates (like design initiation, prototype, first flight, service entry / retirement) – Ref: Janes All the World’s Aircraft (book), Wikipedia, World’ Airliners.net, Aircraft company web sites – Writing must be original; verbatim copying from source will get zero

SR-71 (1966)

 Due next week (Sep 8)
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Typical Design Groups
(courtesy: Prof. S.P. Viswanathan, Bell Helicopters)

Aerodynamics Group

       

Aerodynamics – overall configuration Fuselage – cabin layout, seating etc. Empennage – tail / fin, stability & control Wing – wing and associated Stress or structural – structural layout Weight & balance – distribution, c.g. location Lofting – design drawings (geometry) Production – manufacturing & assembly
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Aerodynamics Group

Aerodynamics Group

sleek, streamlined, high performance
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sleek, streamlined, high performance But where will the passengers sit?

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Fuselage Group

Fuselage Group

now, passengers can fly in luxury
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Fuselage Group

Empennage Group

now, passengers can fly in luxury But what about the Stability?
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Empennage Group

Empennage Group

excellent control and stability
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excellent control and stability But what about control forces?
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Wing Group

Wing Group

excellent lifting device
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Wing Group

Stress Group

excellent lifting device But where are the engines? pax?
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Stress Group

Stress Group

that’s a sturdy airplane
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that’s a sturdy airplane But will it fly?
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Weight & Balance Group
Balsa wood frames

Weight & Balance Group
Balsa wood frames

Ultra-light film

Ultra-light film

lightest aircraft ever built
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Weight & Balance Group
Balsa wood frames

Lofting Group

Ultra-light film

lightest aircraft ever built Did someone say 800kmph cruise?
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Lofting Group

Lofting Group

most accurate geometry specification
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most accurate geometry specification Yes, but we also need performance
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Production Group

Production Group

Least expensive to produce
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Production Group
        

Requirements of Design
Payload Flight Performance Cabin Arrangement, Comfort Fuel consumption Purchase cost Maintenance costs Life (overhaul) requirements Operational safety Noise & chemical pollution (Concorde ozone)
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Least expensive to produce But, we need simplicity & performance
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Requirements of Design
       Ground equipment compatibility (Airbus A380) Crew workload (A340, B777 ~18 hr flights) Fire Safety (90 second evacuation) Atmospheric hazards Proven technologies, materials Low manufacturing cost High operational reliability (GE90 1/50,000hrs)
– ETOPS ratings

Some Large Airplanes
 H-4 Spruce Goose
– 180 tons, 1940’s 1940’

 B747
– 330-440 tons, `60’s 330`60’

 AN225
– 640 tons, `80’s `80’

 A380
– 560-590 tons, 2000’s 5602000’

 Easy fault identification, repairs  Quick turnaround on ground (Concorde brakes)
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Airbus A380
      

Requirements of Design
Ground equipment compatibility (Airbus A380) Crew workload (A340, B777 ~18 hr flights) Fire Safety (90 second evacuation) Atmospheric hazards Proven technologies, materials Low manufacturing cost High operational reliability (GE90 1/50,000hrs)
– ETOPS ratings

 Easy fault identification, repairs  Quick turnaround on ground (Concorde brakes)
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Design Team Structure
 Group members suggest their ‘best’ best’  Chief designer has to select ‘overall best’ best’
– Goal is overall optimum design – Multi-disciplinary design / MDO Multi– What compromises to make?

Design Compromises (conflicting requirements)
 Stability vs. maneuverability
– Air pressure in tires

 Helicopter blade radius
– Low ‘r’ sturdy blade structure (given blade area) – May need higher  – Hub force proportional to 

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Evaluation of Design Choices
 When several good (acceptable) design choices are available, how do we pick the ‘right’ one? right’
– e.g. Engine placement in an airplane
 Wing mounted  Tail mounted  Fuselage embedded  Wing embedded

Wing Mounted

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Tail Mounted

Wing Embedded
B-2

DH Comet

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Fuselage Embedded
Tejas (LCA)

Multi-disciplinary optimum choice
Wing Mounted Factor Cabin Noise Maintainability Fuel Line Length Weight score 60 85 95 90 100
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Tail Mounted wtd. score

wtd. score score 95 75 50 50

HS Sea Hawk
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Team Experience Overall Score

Multi-disciplinary optimum choice
Wing Mounted Factor Cabin Noise Maintainability Fuel Line Length Team Experience Overall Score Weight score 20 30 25 25 100 60 85 95 90 Tail Mounted wtd. score 1900 2250 1250 1250 6650
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Multi-disciplinary optimum choice
Wing Mounted Factor Cabin Noise Maintainability Fuel Line Length Team Experience Overall Score Weight score 45 35 10 10 100 60 85 95 90 Tail Mounted wtd. score 4275 2625 500 500 7900
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wtd. score score 1200 2550 2375 2250 8375 95 75 50 50

wtd. score score 2700 2975 950 900 7525 95 75 50 50

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Stages (Steps) in Aircraft Design
        Preliminary Design (Configuration) Detailed Design (Ready for Production) Prototype Fabrication Ground Testing Flight Testing Redesign based on testing experience Certification / Qualification Design Modification from field experience
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Boeing 747
 60’s design, still flying 60’  Lost Military tender to Lockheed C-5 Galaxy C-

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In times of need …

Typical timescales (B747)
        1963 – concept originated 1966 – first design ready 1967 – production line launched 1968 – first plane rolls off 1969 – first flight 1970 – certified, enters service 1971 – first modified design (B747-200) (B7471986 – last B747-100 delivered B74751

(the case of the North American Aviation P51 Mustang)

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In times of need …
(the case of the North American Aviation P51 Mustang)
 1939 – war breaks out in Europe  1940 – Britain shopping for US planes
– March 1940 – NAA order for 320 planes – October 1940 – first P51 Mustang rolls off
 178 days from concept to first flight  Contractually, 120 days from order to prototype  Actually achieved in 102 days!
– (prototype had no engine, no brakes, no gun mounts)

Concorde

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Concorde Time line
    1962 – Anglo-French agreement Anglo1965 – design completed 1969 – first flight 1976 – commercial operation
– 5000+ hrs of flight testing (B747 ~1500 hrs)

Innovative Design
 Innovation (or new technology) can offer effective ‘compromise without compromise’ compromise’  Example
– Strong & Sturdy – steel structure
 Steel density 7800 kg/m3, aluminium 2700 kg/m3

 1970’s oil embargo 1970’
– Concorde ~6 p-km/ltr B747-100~15 p-km/ltr pB747p– “arrive before you leave” ” leave

– Light – balsa wood + polymer films
 Density ~ 1000 kg/m3

 Solution? New innovative material!
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 2003 retired from service

Composite Materials
 Carbon Fiber Reinforced Plastics
– As strong as steel / aluminium – Density ~ 1500 kg/m3

Designing with Imagination and Creativity
 Piston Engines  Gas Turbines
– Lighter, More Power, Lower Maintenance

 Helicopters for flexible deployment (VTOL), Airplanes for speed and efficiency Imagination and Creativity – Tilt Rotor
– Helicopter mode for flexibility – Airplane mode for speed – Took decades of development
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Example Helicopters

Helicopter Speed Limitations

Bell 206 r=5.1m, CH47 Chinook r=9.2m, 225 rpm 400 rpm blade tip speed ~ 210 m/sec

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Tilt Rotor Concept
 A significantly Different Design meant to overcome inherent deficiency of existing (helicopter) design  Helicopter Speed Limit
– Blade tip speed v=r ± forward speed v= – Advancing tip speed not to exceed Mach~1 – Retreating side speed sufficiently > 0

Bell V-22 in Helicopter Mode V-

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V-22 – airplane mode

History of Tilt Rotor – XV-3
 Bell’s Initial Tilt rotor Design Bell’ (earlier tilt wing designs)  Single-Engine Single First Flight – August 1955  More than 250 test flights over seven years.  Completed more than 100 full conversions from helicopter to fixed-wing fixedmode.  Proved feasibility of tilt rotor flight.
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XV-15 Tilt Rotor
 Contracted by the U.S. Army and NASA in 1973  Maximum GW of 15,000 lbs  2 Aircraft built and used for test and demonstration purposes  Demonstrated tilt rotor technology maturity and provided the necessary confidence that led to the most extensive U.S. government tilt rotor program.
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Current Tilt Rotor – V22
       STOL/VTOL Gross weight (lbs):57k/53k Useful load (lbs):24k/20k Internal fuel (lbs):7,700 Speed :340 kt (630kmph) Dry tank range:770 nm Passengers:24

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