Aircraft Design Configuration

V11 – December 2008 Based on similar Powepoint presentation elaborated by Prof. Derek Bay, Cranfield

Configuration - Overview 

Conventional Configurations Variations regarding powerplant & intake location, vertical wing position, tail unit layout and landing gear.



Unconventional Layouts Biplanes, variable sweep, canard designs, twin booms, multi-hulls, span-loaders, joined wing and blended wing body designs.



Special Configuration Issues Short Take-Off & Vertical Landing, stealth, waterborne operations, engine installation.



Cases Studies P-51 Mustang, Mitsubishi Zero, Chance-Vought Corsair.

Configuration Overview Ugly is Most of Time not Good

3

Conventional Configuration      

Cantilevered monoplane wing. Separate horizontal and vertical tail surfaces. Control via ailerons, elevators and rudder. Discrete fuselage to provide volume and continuity to airframe. Retractable tricycle landing gear. Minimum number of powerplants needed to meet power and operational requirements.

Overall Configuration Variations

Wing Configuration Variations

Conventional Configuration Examples

Boeing 747

Boeing F-18 

Embraer Legacy

Some Successful Unusual Conventional Configurations

Convair B-36

Lockheed Constellation

Boeing 727

8

Some Successful Unconventional Configurations Lockheed P-38

Avro Lancaster

SAAB Draken

Conventional Configuration Within the category of conventional aircraft there are many variations from the standard to be considered:     

Powerplant Location – nose, wing podded, rear fuselage podded, internal. Intake Location – nose, side, ventral, dorsal. Wing Vertical Location – high, low, mid. Tail Unit Arrangements – variable incidence, all-moving, T-tail, multi-finned, butterfly. Tricycle Landing Gear Configuration – numbers of legs, bogeys and wheels.

10

Powerplant Location Nose-Mounted 

Most logical position for any single tractor propeller engine aircraft. Piper Arrow

Embraer T-27 Tucano



Advantages include – symmetry of layout, good propeller clearance, access and maintainability.

Powerplant Location Nose-Mounted: Chance-Vought F4U Corsair

The F4U incorporated the largest engine available at the time, the 2,000 hp (1,490 kW) 18cylinder Pratt & Whitney R-2800 Double Wasp radial. To extract as much power as possible, a relatively large, 13 ft, 4 inch (4.06 m) Hamilton Standard Hydromatic three-blade propeller was used. To accommodate a folding wing, the designers considered retracting the main landing gear rearward, but for the chord of wing selected, it was difficult to fit undercarriage struts long enough to provide sufficient clearance for the large propeller. Their solution was an inverted gull wing, a similar layout to the one used by Germany's Stuka dive bomber, considerably shortening the length of the main gear legs The anhedral of the wing's centersection also permitted the wing and fuselage to meet at the optimum angle for minimizing drag, without the need for wing root fairings. Offsetting these benefits, the bent wing was more difficult to construct and would weigh more than a straight one.

Powerplant Location Wing-Mounted (Outer Wing) 

Many uses:  Large aircraft with propellers, turbojets or turbofans.  For jets/fans, these will be podded and mounted onto

under-wing pylons.  For props, these will be mounted directly onto the wing structure. 

Advantages include:    

Versatility – use of alternative engines. Compact overall layout. Inertial relief – reducing required wing structural mass. Ease of access for maintenance.

Powerplant Location Wing-Mounted (not directly in wing) – cont. 

Also several drawbacks and necessary considerations:  Ground clearance may be a problem in which case high wings may be used (with tall landing gear) or possibly top-wing mounting (e.g. BAe 748) with aerodynamic penalty.  Spanwise location – should depend on propeller diameter or statistical analysis of fan burst trajectory and impact on neighbor.  Typical values are 30% and 55% semi-span for a 4engine design; large values give big engine-out yaw problems and larger rudder sizes.

Powerplant Location Over/Under-wing Mounted - Examples

Lockheed Constellation

Sukhoi Superjet 100

 VFW 614

Powerplant Location Integrated into Wing Embraer EMB-120 Brasília

Grumman Tracker

16

Powerplant Location Buried in wings Some aircraft have housed the powerplants in the wing root area with significant structural disadvantages.

B-1 Lancer DeHavilland Comet

Powerplant Location Rear Fuselage-Podded 



Used on many moderate sized transport aircraft of the past and also many modern small business jet aircraft. Advantages Reduced engine-out yaw



smaller rudder size.

Disadvantages Rearwards movement of CG stability problems. Structural acoustic fatigue. Difficult to inspect during turn around time.

Powerplant Location Rear Fuselage Podded - Examples

A-10 Thunderbolt

Vickers VC-10

Embraer ERJ 145

Powerplant Location Middle of Fuselage

Heinkel He 162

Powerplant Location Example of Aircraft Engine Located Above the Fuselage Due to the PiperJet’s unique engine installation in the tail, ground personnel can walk around the aircraft without being exposed to its jet blast. With the engine thrust line well above the aircraft’s center of gravity, Piper engineers are working on developing a system that automatically compensates horizontal stabilizer position for the changing pitching moments introduced through changes in engine power. 21

Powerplant Location Example of Aircraft Engine Located Above the Fuselage

McDonnell Douglas DC-10 22

Powerplant Location Wing-Podded

vs. Fuselage-Podded

Ground Clearance Possible problem

Good

Internal Noise Fair

Good

Acoustic Fatigue Possible problem for wing & flaps

Possible problem for fuselage

Crash Safety Good

Possible problem 23

Powerplant Location Wing-Podded

vs. Fuselage-Podded

In/on/under the Wing At Rear Fuselage Propulsive Efficiency Good

OK if well positioned

Longitudinal Stability Good

Problems due to aft CG & short tail arm

Tip Stall Good

Possible problem

Asymmetric Thrust Poor

Good

24

Powerplant Location Wing-Podded

vs. Fuselage-Podded Weight

Good

Poor

Engine Maintenance Good

High off ground

Wing Aerodynamic Efficiency Problems from cut-outs

Very good

Fuel Feeds to Engines & Wing Anti-Icing Good

Ducts and lines through cabin

25

Powerplant Location Internally Housed Used on many single and twin turbojet/turbofan engine aircraft such as military trainers and fighters.  Advantages 

 Compact layout.  Reduced drag.



Disadvantages  Engine removal and maintenance problems.  Structural acoustic fatigue due to jet efflux.  Jet pipe length minimized by moving engine rearwards

but this affects CG, stability and control.

26

Powerplant Location Internally Housed - Examples

McDonnell-Douglas A-4 Skyhawk

SAAB Gripen

Sepecat Jaguar

27

Powerplant Location Internally Housed - Installation

28

Intake Location Nose Intake 

Used on many early jet fighters with mid-fuselage mounted engines.



Requires use of long inlet ducts and jet pipes – gives low flow distortion but high total pressure losses.



No need for boundary layer diverters.



Occupies large amount of internal volume.



Only small radome may be housed in shock cone center-body.

Intake Location Examples of Aircraft with Nose Intakes

English Electric Lightning

MiG-19 Farmer

MiG-21 Fishbed 30

Intake Location Side Intake (Below Wing) 

Used on the majority of modern high-wing strike and combat aircraft designs.



Leaves the nose area free for radar equipment installation.



The wing is often extended above the intakes to improve high- performance.



Flow diverters are needed to accommodate fuselage boundary layer growth.

31

Intake Location Examples of Side Intakes (Below Wing)

Tornado ADV

Dassault Breguet F1 Mirage 32

Intake Location Side Intake (Above Wing) 

Used on many low-wing design trainer and combat aircraft.



Wings may be used to shield the intakes and reduce the maneuvering .



Any sharps bends have to be avoided to prevent flow distortions.



Short intake lengths are possible with low overall volume requirements.

33

Intake Location Examples of Side Intakes (Above Wing)

F-4 Phantom

BAe Hawk 100

T45A Goshawk 34

Intake Location Ventral Intake Situated on underside of fuselage - an increasingly common position for high performance combat aircraft. 

Gives very good high-

maneuverability.



Prone to FOD and debris ingestion.



Complicates nose wheel positioning/stowage.



Restricts carriage of under-fuselage stores.



Low flow distortion and pressure losses into intake.

35

Intake Location Examples of Aircraft with Ventral Intakes

Eurofighter 2000

F-16 Fighting Falcon

36

Intake Location Dorsal Intake Situated on top-side of fuselage. 

Only tends to be used on 3-engine airliners with 3rd engine buried in the rear fuselage/fin area with a few exceptions.



Gives poor performance at high- due to separated flow ahead of intake.

37

Intake Location Examples of Aircraft with Dorsal Intakes

Cirrus Jet

Lockheed L1011 Tristar

 North American YF-107 38

Vertical Location of Wing High Wing 

Gives an efficient spanwise lift distribution leading to low lift-induced drag.



Improves lateral static stability.



Preferred for most freight and military transport aircraft:  Low floor line for easy loading & unloading.

 Good all-round vehicular access when on ground.  Wing fuel load away from ground when landing with failed

landing gear.  Good ground clearance for powerplants, especially props.

39

Vertical Wing Location Examples of High-Wing Aircraft

Grumman Mallard Boeing C-17

Lockheed C-130 Hercules Alenia G-222 40

Vertical Location of Wing Low Wing 

Improves lateral maneuverability.



Preferred for most passenger transport aircraft:  Wing structure conveniently passes below floor.  Volume free fore and aft of wing structure for cargo

holds, luggage and landing gear stowage.  Minimizes landing gear length and mass.  Wing provides buoyancy when ditching into water

and also a platform for emergency evacuation.

41

Wing Location Examples of Low Wing Aircraft

Boeing 777

Boeing 737

Airbus A380 Falcon 2000

Tail Unit (Empennage) Conventional Layout 



Approximately 70% of aircraft in service have a “conventional” arrangement comprising separate fixed horizontal stabilizer and vertical fin surfaces for stability and moving elevator and rudder sections attached to fixed surfaces for control. This is the simplest solution & provides optimum overall performance in the majority of cases. 43

Tail Unit (Empennage) Examples of Aircraft with Conventional Tail Units

Boeing 737 Boeing 777

Airbus A380

44

Conventional Primary Control Surfaces

45

Tail Unit (Empennage) Variable Incidence Tailplane 

Here the forward (main) section of the horizontal surface is not fixed but is capable of rotation through a small range of angles of attack.



As such, it is generally used to adjust pitch trim rather than using the conventional elevators.



It is especially useful for countering the effects of significant pitching moment increments caused by deployment of powerful high lift devices.



Elevators are still used for pitch control. 46

Tail Unit (Empennage) Aircraft with Variable Incidence Tailplanes

Boeing 757-200

Sabre

Vought F-8 Crusader

Dassault Falcon 20 47

Tail Unit (Empennage) All-Moving (Slab) Tailplane  

  

Whole of the horizontal tailplane surface is used for both pitch control and trim (with no separate hinged elevator). This offers significant advantages at transonic and supersonic speeds when effectiveness of conventional trailing edge surfaces is dramatically reduced. Universally adopted for supersonic fighter designs. Most also use differential movement of opposite sides to improve roll rate (then known as tailerons). Powered controls are necessary due to the large control force requirements.

48

Tail Unit (Empennage) Examples of Aircraft with Slab Tailplanes

Tornado GR1

F-5 Tiger

A5 Vigilante

A7 Corsair 49

Tail Unit (Empennage) T-Tail  

Horizontal tailplane mounted on top of fin. Often used on large high-mounted sweptwing designs and also smaller low-wing aircraft.

Lockheed C-5A Galaxy Douglas DC-9

Beechcraft Duchess 50

Tail Unit (Empennage) T-Tail - Advantages 





Provides substantial “end-plating” effect to fin, improving its effectiveness and reducing the fin size requirement. Lifts the horizontal tail clear of any propwash & the wing wake during cruise flight, therefore reducing buffet and fatigue. Allows engines to be mounted on the aftfuselage, if required. 51

Tail Unit (Empennage) T-Tail - Disadvantages Gives a large mass penalty to the empennage due to the higher loading and aeroelastic effects.  Increased likelihood of “deep stall” – puts tail in wake of stalled wing, making recovery difficult or even impossible. 

C-9 Nightingale Lockheed C-141 Starlifter 52

Tail Unit (Empennage) Multi-Finned 

 

If fin-sizing exercise results in large single fin dimensions then sometimes preferable to use two (or more) smaller fins instead. Allowed Constellation to operate from existing hangars. Also produces desirable “end-plating” effect to horizontal tailplane, reducing its size requirements. 53

Tail Unit (Empennage) Multi-Finned – Further Comments Fins have to be positioned far enough apart so that undesirable mutual aerodynamic interference effects are not too severe.  If fins are positioned in slipstream of propellers rudder performance is improved at low speeds.  Difficult to avoid fin stall at high sideslip angles.  Not generally used nowadays for single-boom layout transport aircraft. 

54

Tail Unit (Empennage) Examples of Multi-Fin Transports/Bombers

Lockheed Constellation

Avro Lancaster

B-24 Liberator

Lockheed A-29

55

Tail Unit (Empennage) Twin Fin Fighter Aircraft  Twin fins nowadays more associated with supersonic fighters.  More compatible with twin-engine aircraft (F14/F15/F18) than single (F16) due to “engine-out” sizing considerations.  Special benefit of supersonic application is that interference effect disappears providing fin Mach lines do not intersect.  Can also provide infrared shielding of engine exhaust to improve stealth, especially if canted (F22).  Resultant reduced fin height improves aeroelastic behavior. 56

Tail Unit (Empennage) Examples of Twin-Fin Fighters

MiG-29 Fulcrum

F-14 Tomcat

F-15 Eagle

F-18 Hornet 57

Tail Unit (Empennage) V-Tail In this case the conventional tail surfaces are combined into a pair of inclined surfaces.  The separate roles of the tailplane/elevator and fin/rudder are combined.  Advantages include: 

 Less interference drag; smaller total surface area;

improved stealth characteristics. 

Disadvantages include:  Cross-coupling of stability/control characteristics; handling

difficulties; need for fully automatic flight control system.

58

Tail Unit (Empennage) Examples of V-Tail Aircraft

Lockheed F-117 Nighthawk Beech Bonanza 59

Tail Unit (Empennage) Horizontal Positioning 



Surfaces should generally be positioned as far aft as possible to maximize the tail moment arm. Restrictions on this may be caused by engine-induced structural fatigue (e.g. F-5).

60

Landing Gear Layout Tricycle Gear Configuration 

The most conventional, comprising:  Pair of main legs behind aircraft CG.  Single nose leg ahead of CG.



Each leg incorporates:  Shock absorber to dissipate vertical landing

energy.  Single or two side-by-side wheels or multiple bogie arrangement. 

Only main wheels are generally fitted with brakes. 61

Landing Gear Layout Tricycle Gear Configuration – Further Comments Only the nose wheel is usually steered for ground maneuvering.  For effective steering, nose leg should support between 6 and 10% of the aircraft mass.  Provision must be made for attachment and stowage of landing gear units.  Lateral positioning (track) dictated by need to prevent overturning during ground maneuvering – mainly a function of height of CG, track distance & shock absorber characteristics. 

62

Landing Gear Layout Examples of Tricycle Landing Gear Aircraft

Douglas A4-F Skyhawk

Cessna 172N

Hawker Hunter

BAe Hawk 63

Landing Gear Layout Tricycle Gear Configuration – Number of Wheels As the aircraft mass increases, operations from runways of given strength dictate need for more wheels to spread the load – many possible variants:    

Two-axle bogie Three-axle bogie Three or four main legs Multiple legs on single axes

64

Landing Gear Layout Two-Axle Bogie  



The main legs are split into two-axle bogies, with usually two wheels per axle. Such as arrangement is generally necessary if the aircraft mass is between about 90 and 200 tones. It is common to many civil and military transport aircraft types.

65

Landing Gear Layout Examples of Aircraft with Two-Axle Bogies

Airbus A310 Airbus A330

Boeing C-135

66

Landing Gear Layout Three-Axle Bogie 

For very large aircraft (e.g. > 210 tones), the load has to be spread even further – one option is to use a 3-axle bogie arrangement.

On the Boeing 777, the extra axle is put in the centre of the bogie.

On the C-5 the extra axle is put sideby-side with the rear axle – the aircraft has 28 wheels in total! Both have main bogie steering to reduce turn radius & tyre scrubbing. 67

Landing Gear Layout Three-Axle Bogie Aircraft  C-5 Galaxy

 Boeing 777

68

Landing Gear Layout Three Main Legs Some large aircraft use an additional main leg to spread the load, e.g. Airbus A-340: 2-wheel nose gear and 3 main gear, each of double-wheel 2bogie – 14 wheels in total.

69

Landing Gear Layout Four Main Legs 



This will generally be the case for very large civil transports (> 300 tones) with low wing designs (e.g. Boeing 747). It poses significant problems for airframe attachment & stowage.

70

Landing Gear Layout Four Main Legs – Boeing 747

71

Landing Gear Layout Multiple Main Legs with Single Axles 

Good option for heavy high wing military transports with retraction into fuselage blisters. The Antonov An-124 Condor has 24 wheels: two side-by-side, 2-wheel nose legs, and ten main legs (5 each side), each with 2 wheels. 72

Landing Gear Layout Tail Wheel Configuration 



Here the two main wheels are located forward of the CG and a tail wheel or skid provides the third support point. This is a simpler, lighter and cheaper design than a tricycle layout but has significant disadvantages:  Difficult ground maneuvering and take-off/landing due to

inhibited visibility. 

This was the norm for many early aircraft but its application is nowadays limited to simple light aircraft where emphasis is on simplicity and low cost – often with fixed (rather than retractable) legs. 73

Landing Gear Layout Examples of Tail-Wheel Aircraft

Curtiss P-6 Hawk

Hawker Sea Fury

DHC-1 Chipmunk 74

Landing Gear Layout Single Main Gear Leg 

Sometimes advantageous to concentrate the main load into a single main leg rather than two.

BAe Harrier



For Harrier, a tricycle main units would be difficult to accommodate in he fuselage (because of powerplant) or wing (because of wing trailing edge controls and underwing pylons).

Ground roll stability obtained from pair of lightweight , lightly-loaded outriggers, located near to wing tips. 75

Landing Gear Layout Bicycle Configuration 





This is a specialized form of the single main leg configuration but with the rear leg significantly further back. This results in the nose leg carrying a similar proportion of the mass as the rear leg. Advantage is an uncluttered wing and long length of available fuselage space (e.g. for a bomb bay). 76

Landing Gear Layout Bicycle Configuration – Further Comments 

Disadvantages are:  Highly loaded nose leg makes ground maneuvering very

difficult.  Specialized landing technique needed, especially if in cross-winds.  Outriggers needed for ground roll stability. 

The configuration is not recommended unless there is no viable alternative. 77

Landing Gear Layout Aircraft with Bicycle Configurations

Boeing B47E Stratojet

B-52 Stratofortress

Landing Gear Layout Design Constraints

Unconventional Configurations Biplane The norm for the first 30 years of aviation. Early airfoils were very thin requiring external bracing so that biplanes gave best structural efficiency.  Many penalties of use, especially at higher speeds – increased total mass, drag and aerodynamic interference.  Aerodynamics and materials advances have led to increased wing loadings (W/S) so that biplanes are mostly redundant nowadays – main exception is aerobatics aircraft where low W/S is an advantage and specialized aircraft such as crop-sprayers.  

80

Unconventional Configurations Biplanes

Pitts S1-S Antonov An-2 81

Unconventional Configurations Variable Sweep (Swing-Wing) 

Design Problem:  High sweep usually needed for

transonic/supersonic speed designs but this affects low speed performance.  Possible solution is to use variable sweep wings. 

This gives a better matched performance over a wide speed range and offers an aircraft multi-role capabilities over subsonic and supersonic speed ranges. 82

Unconventional Configurations Variable Sweep - Disadvantages    

Increased mass over conventional design due to heavy actuation system. Increased system complexity and costs. Increased drag due to interaction between fixed and moving parts of the wing. Trim and stability/control problems due to movements of aerodynamic centre and CG. 83

Unconventional Configurations Variable Sweep Aircraft

MiG-23 General Dynamics F-111

F-14 Tomcat

84

Unconventional Configurations Canard Layout  The conventional aft horizontal tailplane is replaced by a foreplane (or canard) while the main wing is then moved rearwards for stability purposes.  Two main categories:  Lifting canard – canard provides substantial lift

as well as longitudinal trim and control.  Control canard - longitudinal trim and control only. 

This is not a new idea – the original Wright Flyer was a control canard configuration. 85

Unconventional Configurations Canard Layout – Configuration Advantages  Negligible trim drag penalty, usually a download on the rear tail surface on a conventional layout.  More rapid pitching maneuver response as initial change is in required direction.  Possible layout advantage (e.g. aft-located wing passes behind the cabin).  Better provision for escape from “pitch-up” (associated with tip-stall on highly swept wings). 86

Unconventional Configurations Canard Layout – Configuration Disadvantages  Airflow interference from the canard over the main wing surface.  Increased pitching moment effect with wing flap deployment due to large moment arm – so sophisticated high lift devices may not be used with consequent lowspeed performance penalty.

87

Unconventional Configurations Long-Coupled Canard Layout  Small canard located far enough forward so that interference effects are small.  Particularly suited to long-range supersonic aircraft designs (bombers, transports, etc.).  Foreplane effect is beneficial for cruise trim drag reduction and at low speed, particularly for take-off rotation. 88

Unconventional Configurations Long-Coupled Canard Layout Aircraft Examples

Tu-144 Concordski

Rockwell B-70 Valkyrie

89

Unconventional Configurations Short-Coupled Canard Layout  Foreplane placed just ahead of (& usually above) wing.  Careful location enables lift effectiveness of pair to exceed that of sum of isolated lifting surfaces.  Most applicable to high agility combat aircraft designs.

Dassault Rafale

Saab Gripen 90

Unconventional Configurations Canard with Forward Sweep  Rearward sweep usually preferable as it gives better compromise of aerodynamic characteristics – especially stability/control.  Forward swept wings also more prone to aeroleastic divergence – overcome with associated mass penalty.  Method could give overall layout advantages, e.g. by allowing wing carrythrough structure to pass through rear of aircraft and avoid main section. 91

Unconventional Configurations Canard With Forward Sweep – Aircraft Examples

Su-47 Berkut

Grumman X-29A

92

Unconventional Configurations Employs both a foreplane and a tailplane. Advantages  Stabilizing effect of tailplane.  Favorable trim & control functionality of foreplane. Disadvantages  Fuselage mass penalty.  Increased interference drag and also skin friction due to increased total wetted surface area. 93

Unconventional Configurations Three Surface Aircraft

Piaggio Avanti

94

Unconventional Configurations Twin-Boom Layout Aircraft  Several possible reasons for being adopted:  Allows engine to be mounted close to CG –

particularly pusher-prop types & early jets.  Over-riding requirement for aircraft to have unrestricted access to rear of freight hold.  Visibility for rear gunner/bomber crew.  

Results in use of twin fins. Disadvantages include: increased wing mass, increased interference drag and less usable volume. 95

Unconventional Configurations Twin-Boom Layout Aircraft Cessna C337 Skymaster

Northrop P-61 Black Widow

Armstrong-Whitworth Argosy 96

Unconventional Configurations Span-Loaders  Closely related to flying wing designs whereby the payload held in main wing box structure.  Small central fuselage pod sometimes used to house flight deck and central services. Advantages  Spreads the payload across the wing, rather than the

fuselage.  This gives inertial relief to the wing structure.  Most of aircraft then comprises wing (with higher lift/drag than conventional fuselage).  Gives typical 10% reduction in take-off mass. 97

Unconventional Configurations Span-Loaders - Disadvantages  Difficult emergency passenger evacuation procedures.  Structural layout problems.  Fuel location.  Pressurization of wing section.  Increased moments of inertia leading to poor roll rates.  Complicated flight control system.

Rockwell Delta Spanloader

98

Unconventional Configurations Flying Wing (Blended Wing-Body) Layout  Similar to spanloaders – optimum aerodynamic solution sought - wing is most efficient means of lift generation so fuselage is dispensed with altogether. Advantages  As for spanloader – inertial relief of wing gives lower

wing structure mass and lower costs.  Potential for increased passenger cabin volume and improved comfort levels.  Major opportunity for using laminar flow technology – easier to apply to wing than a fuselage. 99

Unconventional Configurations BWB Aircraft - Disadvantages  Passenger wariness of unconventional (more feasible to military & cargo transports).  Unfamiliar structural layout & design.  Complex aerodynamic interference effects.

Boeing Concept for a BWB Airliner

Northrop B-2 Spirit Bomber 100

Unconventional Configurations Braced-Wing Airliner

101

Unconventional Configurations Braced-Wing Airliner • The tight coupling between structures and aerodynamics requires the extensive use of MDO to make it work • The strut allows a thinner wing without a weight penalty and also a higher aspect ratio, and less induced drag • Reduced t/c allows less sweep without a higher wave drag penalty • Reduced sweep leads to even lower wing weight • Reduced sweep allows for some natural laminar flow and thus reduced skin friction drag

102

Unconventional Configurations Braced-Wing Airliner Study

Conventional reference airplane

Source: AIAA Paper 2000-0420 103

Unconventional Configurations Braced-Wing Airliner Study

Source: AIAA Paper 2000-0420 104

Special Configuration Issues  An

aircraft’s specifications and requirements may include some special provision which could then have a dominant influence over the resultant configuration.  These include:  Short Take-Off & Vertical Landing (STOVL).  Stealth.  Waterborne Operations. 105

Special Configuration Issues STOL & STOVL Aircraft 

Short Take-Off (& Vertical) Landing Aircraft.



Two classes of military aircraft sometimes have a need for STOL or STOVL capabilities.  Freight.  Combat.

106

Special Configuration Issues Military Freight STOL Airlifters 

Often required to operate to and from airstrips of short length and poor surface strength.



No major effect upon configuration selection (unless tiltrotor/wing technology adopted) but increased emphasis on:  High installed thrust.  Complex high lift devices and wing technology.  Low tire pressures.



Several civil variants also developed with perceived need.

Special Configuration Issues Examples of STOL Airlifters

DHC Dash 7

Kawasaki NAL Asuka

Breguet 941 Boeing YC-14

108

Special Configuration Issues V/STOL Airlifters – Tilt-Wing

Vertol VZ-2A Canadair CL-84 Dynavert

Special Configuration Issues V/STOL Airlifters – Tilt-Rotor

Bell XV-15

Bell-Boeing V-22 Osprey 110

Special Configuration Issues STOVL Combat Aircraft 

For vertical landing the available vertical thrust component must exceed the landing weight.



Logical to also use this component for short take-off.



STOVL thrust component provided by downward deflection of exhaust gases of forward flight propulsion unit(s).



Impractical to locate this thrust component immediately below CG at all times so additional thrust provision needed for balance. 111

Special Configuration Issues STOVL Combat Aircraft – Further Comments 

Three standard methods available for providing vertical thrust component:  Vectored bypass flow.  Separate vertical lift engine.  Remotely driven lift engines (using main

powerplant as energy source). 

All methods require separate low-speed control capability, usually using reaction jets supplied with bleed air from main engine compressor. 112

Special Configurational Issues STOVL Fighter – Vectored Bypass Flow RR Pegasus engine has 4 nozzles, each rotating to vector efflux as required – rear two exhaust hot gases and front two exhaust colder bypass air from behind fan.  Results in compact system, though bulky and also has to be located about aircraft CG.  Several thrust augmentation methods are available (e.g. plenum chamber burning where fuel is burnt in bypass air) but cause problems (e.g. hot gas ingestion & ground erosion). 

113

Special Configuration Issues STOVL Fighter – Vectored Bypass Flow

Rolls Royce Pegasus BAe Harrier 114

Special Configuration Issues STOVL Fighter – Vertical Lift Engines 

Uses one or more dedicated lift engines in addition to deflected thrust from cruise engine.



Allows engine to be located more conveniently to aft of aircraft with lift engines forwards, giving more design flexibility.



Disadvantage is extra mass of lift engine – worthless in forward flight mode.

Yak-141 Freestyle

115

Special Configuration Issues STOVL Fighter Remotely Driven Lift Fans Lift fan driven remotely from main cruise engine by either mechanical shaft drive (as in X-35 JSF) or gas drive.  Mechanical drive places restrictions on fuselage layout.  Compressed gas drive is bulky and relatively inefficient.  Total effective fuselage volume likely to be more than for other two possible methods. 

Lockheed Martin X-35 JSF

116

Special Configuration Issues Stealth  

Increasingly important for modern combat aircraft designs. Final configuration depends heavily on overall priority of stealth against performance. B-2: Stealth is primary design driver F-22: high performance levels with stealth B-2 Spirit F-22 Raptor

117

Special Configuration Issues Stealth – General Observations 

  

   

Foreplanes best avoided. Internal powerplants & weapons. Intakes with long curved ducts. Exhausts must be shielded. Avoid surfaces positioned at right angles to each other (e.g. use inclined fins). Minimize discontinuities in shape/surface. Surface edges parallel to each other. Difficulties with cockpit transparencies – use of unmanned vehicles advantageous. 118

Special Configuration Issues Waterborne Aircraft Very common in the early days of aviation. Can operate from anywhere with a large stretch of reasonably calm water.  Became less popular due to:  

 More airfields available after WW2.  Trend for using higher wing loadings ○ Results in higher take-off & landing speeds and high water

resistance forces.

Use nowadays restricted to small aircraft operating in coastal regions or in remote locations with many lakes & rivers.  Two basic categories – float planes & flying boats. 

119

Seaplanes

Special Configuration Issues 120

Special Configuration Issues Waterborne Aircraft – Float Planes 

   

Conventional landing gear replaced by large floats. Invariably propeller-driven. Usually direct conversions from landbased types. Usually only applicable to small aircraft (12 tones max). Air drag of floats is high and gives large tail download trim requirement.

DeHavilland Beaver

Cessna LC-126

Special Configuration Issues Waterborne Aircraft – Flying Boats  Usually larger than float planes.  Fuselage used as a hull for waterborne operations.  Wing tip floats or fuselage sponsons used to provide waterborne roll stability.  Some types also have conventional retractable landing gear and are then amphibious.

Boeing 314 Clipper

Consolidated OA-10 Catalina 122

Configuration Issues: Engine Installation Torque Counteraction

123

Configuration Issues: Powerplant Installation

Flow pattern before and behind the wing, showing angle of attack at intake of podded (dotted) and rear-mounted engines

124

Configuration Issues: Powerplant Installation Left - Airflow laterally disturbed due to the presence A of the fuselage Below - Airflow vertically disturbed due to the presence of the wing

Airflow is strongly disturbed by the presence of the airplane. Engine incidences must be properly adjusted to the local flow to avoid inlet distortion and even separation in the intake.

125

Powerplant Installation

Powerplant Installation Rotor Burst Containment

APU

Engine

Thank You!