Aircraft Configuration

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Why airplane look like they do

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总体设计流程

设计要求与目标 （Level 0）

总体布局

客舱布局

优选主要参数：W, T, S, A, Λ

分析模型：统计数据＋经验公式

初始方案（三面草图）

部件外形初步设计

飞机特性分析与评估

总体参数敏感性分析与优化

分析模型：分析模型＋经验修正

初步方案（三面图）

分系统定义与总体布置

几何、重量、气动、推进、性能、

操稳、DOC、环保性、……

分析模型：数值模型＋试验

总体方案（数字样机）

部件外形详细设计

多学科评估与优化

几何、结构、重量、气动、性能、

飞行品质、DOC、环保性、……

总体方案冻结

Level 1 Level 2 Level 3

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Outline

• What is aircraft configuration

• Conventional configuration

– Layout characteristics

– Variations of basic configuration

• Alternative configuration

• Creativity and configuration design

• Special considerations

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What Is Aircraft Configuration

• Definition of configuration

– Arrangement of parts or elements

• Definition of aircraft configuration

– Arrangement of primary aircraft components, such as

• Powerplant or propulsion system layout

• Wing layout

• Empennage layout

• Landing gear layout

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What is conventional configuration

• A cantilever monoplane wing

• Separate vertical and horizontal tail surface

• A discrete fuselage used to provide volume

and continuity to the airframe

• A retractable tricycle landing gear

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Layout Characteristics of

Conventional Configuration

• Powerplant location

• Air intakes

• Vertical location of the wing

• Empennage

• Landing gear

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Powerplant location

• Nose location – propeller propulsion

– For aircraft with a single tractor propeller engine

– Advantages

• Propeller clearance

• Self-contained and independent of the rest of the aircraft

– Disadvantages

• Poor visibility

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Powerplant location

• Fuselage center/aft buried location

– For single and twin engine military jet trainer and

combat types

– Advantages

• Compact overall layout

– Disadvantages

• Difficult maintenance access and engine removal

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Powerplant location

• Wing-mounted powerplants

– For majority of larger aircraft

– Advantages

• Reduction of structure weight

• Compact: fuselage is shorter

• Access for Engine maintenance

is convenient

• Easy control of center of gravity

– Disadvantage

• Opposite of advantage of rear

fuselage podded powerplants

C-130

C919

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Powerplant location

• Rear fuselage podded powerplants – For business jet and

moderately large transport

– Advantages • Clean wing: CL is higher

• Easy control when one of engines fails

• Landing gear is shorter

• Less noise in the cabin

• Lower drag

– Disadvantage • Opposite of advantage of wing-

mounted powerplants

Hawker

Horizon

Citation X

ARJ21-700

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Powerplant location

• Upper or lower podded powerplant

– For some unmanned aircraft

To simplified

fuselage layout

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Air intakes

• Pitot (nose) intake – Advantages

• Compact

– Disadvantage • Excessive length

• Occupying an undesirably large part of the fuselage volume

lighting

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Air intakes

• Side intake above wing

– For low-wing trainer/attacker

– Advantages

• Minimum intake length /Low volume requirement

– Disadvantage

• Flow distortion

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Air intakes

• Side intakes below wing

– Located below a mid to high wing

– More common layout than above-wing intakes

– Advantages

• Enhance flow at high angles of attack by extending the

wing leading edge above intakes

Flying Leopard Su-27

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Air intakes

• Ventral intakes

– Advantage

• For high performance fighter where high angle of attack

manoeuvrability is important

– Disadvantage

• Concern about the probability of debris ingestion during

ground operation

歼10

F-16

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Air intakes

• Upper fuselage, dorsal intakes

– For transport with three engines or stealthy aircraft

– Not recommended

• Operate only at low angle of attack

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Vertical location of the wing

• High wing (上单翼)

• Mid-wing (中单翼 )

• Low wing (下单翼 )

运-8

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Vertical location of the wing

• The choice of wing location is a

compromise between:

– aerodynamic

– Structure

– operational considerations

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The vertical location of the wing

• Aerodynamic considerations

– Mid wing

• Lowest interference drag

• Advantageous for a supersonic aircraft.

– Low wing

• Enable the flap to be continuous

– High wing

• Beneficial in having an efficient spanwise lift

distribution

• Low drag due to lift

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The vertical location of the wing

• Structure considerations

– The desirability of having an uninterrupted

wing structure has a substantial impact on

the vertical location of wing.

• A high wing or low wing has an advantage over

a mid wing.

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The vertical location of the wing

• Operational issues

– Clearance

• High wing is advantageous

– Passenger appeal

• High wing is advantageous

– Crashworthiness

• Low wing is advantageous

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Comparisons of Vertical Location of the Wing

High wing Mid-wing Low wing

Interference

drag 2 1* 3

Lateral stability 1 2 3

Visibility from

cabin 1 2 3

Landing gear

weight 3** 2 1

Structure layout 1 3 1

Installing engine 1 2 3

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Why low-wing configuration for passenger jet

• The beams of wing can be

continuous across the

fuselage under the floor.

• Landing gears are short.

• Easy access for engine

maintenance

• Crashworthiness

consideration

A320

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Why high-wing configuration for military transports

• Operation requirement

– Floor of the fuselage must

be close to the ground

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Summary of the vertical location of wing

• High wing

– Freight aircraft

– Smaller propeller-powered transport aircraft

– Some light aircraft, especially single-

engines types

– Some combat aircraft, including V/STOL

types

– Unmanned aircraft

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Summary of the vertical location of wing

• Mid wing

– Some high performance combat types

– Weapons system aircraft with a long

internal weapons bay

– Possibly multi-deck transport aircraft

• Low wing

– Majority of passenger transport aircraft

– Some light single- and twin-engine trainers

– Some combat aircraft, including those

which use of canard configuration

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Empennage

• The basic configuration for the tail

surface

– A horizontal fixed tailplane (Stabilizer )+

Elevator

– A vertical fixed fin + Rudder

– A dorsal fairing

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Empennage

• Variations on the basic arrangment

– Variable incidence tailplane

• To adjust the pitch trim of the aircraft especially when

deployment of the high lift device introduce significant

pitching moment increments

– All moving tailplane

• Used as the primary pitch control with the elevator.

• Offering significant advantage at transonic and supersonic

speed, because effectiveness of conventional trailing edge

control is much reduced.

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Empennage

• Vertical position of horizontal tail

– The horizontal tail is within the wing downwash

which has the effect of reducing the effectiveness

as a stabilizer.

– The degree of this reduction is a function of the

vertical location of the tail relative to the wing

– Possible location

• “T” tail

• High mounted

• Low mounted

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Empennage

• Considerations of Vertical position of horizontal tail

– Less interference of downwash from the wing

– Easy for structure layout

Location high middle low “T” Very high

Structure weight

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Examples of Horizontal Tail Position

米格15

波音717

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Landing Gear

• Three type of layout

– Tail wheel

– Tricycle

– Bicycle

Tricycle is used

most commonly

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Landing Gear

• Fixed or retractable ?

– when V < 150 （kts）, fixed landing gear

– when V > 150 （ kts ）,retractable

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Landing Gear

• Load allocation

– Nose leg: 6-14% of mass

– Main leg: ~ 45% of mass

(each)

• Lateral disposition of

main wheels

– Must preclude any

tendency to overturn

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Landing Gear

The landing gear of Boeing-747 and C-5A

More legs and wheels are needed for very large airplanes

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Examples of Landing Gear

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Variations of Basic Configuration

• Braced wing

– Advantage: reduction in structure mass

– Disadvantage: drag penalty

– Be used on small aircraft flying at low speed

Can be used on large transport ?

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Sweep

• Why sweep

– Primary reason

• To delay the onset of compressibility drag

– Other reasons

• To facilitate landing gear and stowage behind the

primary wing structure

• To enhance static longitudinal stability

F-86

轰六

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Sweep

• Why forwards sweep ? – Advantage: beneficial in achieving higher

maximum lift

– Disadvantage: prone to aeroelastic divergence

VFW Hansa Jet

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Sweep

• Sweep angle

– The amount of sweep should be the minimum

required for aerodynamic reasons.

– Large sweep angle are required to maintain

subsonic leading edge flow when an aircraft is

flying supersonically.

– A low span detla wing becomes advantageous.

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Winglet (Wing Tip Fins)

• To reduce drag during cruise by

effectively increasing the wing span

A330

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Twin booms

• What is twin booms configuration – Twin booms extending aft

• Why is twin booms configuration used ? – Provision for pusher propeller for a general aviation or

unmanned aircraft where engine mass is such that it must be

located close to the center of gravity of the aircraft.

– To give unrestricted access for a rear freighthold

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Landing gear variations

• Tailwheel layout (后三点) – Advantage

• Simple and light

– Disadvantages • Ground manoeuvring is more difficult

• Poor visibility

• Take-off and landing is more complex

– Suggestion • Limited to light aircraft where operational penalties are

accepted in exchange for simplicity.

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Landing gear variations

• Bicycle layout (自行车式) – Advantage

• An uncluttered wing and a long fuselage free from landing gear components

– Disadvantages

• The highly loaded nose leg

– ground manoeuvring and rotation at take-off difficult

– Need for a special landing techniques to avoid extreme nose leg loads during touch down and braking

– Suggestion

• Should not be used unless there is no acceptable option

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Alternative Configurations

• Alternative configuration should be considered only: – If a clear advantage is identified

– If the corresponding disadvantage is presented

• Typical unconventional configurations – Biplane

– Butterfly tail

– Tailless layout / Flying wing

– Variable sweep

– Canard layout

– Three surface configuration

– Jointed Wing Configurations

– Double Fuselage Configurations

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Biplane

• Used in the earliest day of aeronautics – Large wing area was required

– Drag penalty became unacceptable when speed increased

• Nowadays can be used in aerobatic aircraft and MAV – Low wing loading

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Butterfly Tail

• The horizontal and vertical tail surface are combined into a pair of inclined surface.

• Advantage – Smaller total surface area and less interference drag

• Disadvantage – Cross-coupling of stability and control characteristics

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Tailless layout / Flying wing

• Advantage

– Low observability

– Low drag

• Disadvantage

– Longitudinal control is limited.

– The need to keep the center of gravity movement

within a small range.

– Because of lateral stability and control problem, a

vertical fin is often needed.

– A rudimentary fuselage is often required for

payload volume.

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Tailless layout / Flying wing

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Variable Sweep

• Highly swept wings can posses poor low speed aerodynamic

characteristics.

• Variable sweep configurations try to overcome this problem by

matching the sweep angle to the ideal at given flight speed.

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Canard Layout

• Advantage – Canard trim forces are generally in the same

direction as those on the wing • Trimmed maximum lift coefficient is higher

• Better trimmed lift-to-drag ratios

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Canard Layout

• Design consideration

– Airflow from the canard interferes with wing, and it is

essential to match the layout geometry to achieve the best

overall result.

– The canard must stall before the wing with flaps up as well

as down, otherwise uncontrollable pitch-up can occur.

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Canard Layout

• Three variations

– Long coupled

• A small canard is located sufficiently for ahead of the

wing that the interference effects are small.

• Beneficial both in terms of cruise trim drag and at low

speed, especially take-off rotation

– Short coupled with delta wing

• A canard is placed just ahead of the wing

• Careful location of the two components enables the lift

effectiveness of the pair to exceed that of sum of their

isolated values

– Canard with forward swept wing

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Examples of Canard Layout

歼-10B 台风战斗机

X-29 旅行者

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AD-100 and AD-200

Design for Stall Prevention

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Why canard for Long EZ

• Amateurs fly it !

– It is essential to prevent the airplane to be stalled

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Why canard for Proteus

Unique Configuration Adapts to many Mission Requirements

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Three surface configuration

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Jointed Wing Configurations

• Lower structure weight because of improved stiffness in torsion and bending

• Built-in direct lift and direct side-force capability

• Reduced induced drag

• Reduced transonic and supersonic wave drag as well as improved area ruling

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Double Fuselage Configurations

世界上翼展最大的飞机（平流

层发射系统），该飞机首飞于

2019年4月13日。

南航本科毕业设计项目（2006年）

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Wing In Ground

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Considerations of Configuration Design

• General comments

– No logical procedure to produce an unique

configuration

– Can be radically different configurations

with similar mission performance

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An example of radically different configurations

with similar mission performance

Vulcan B-47

Wto 81.6 T 79 T

payload 9.5 T 10 T

Vmax 1038 km/h 1050 km/h

range 7650 km 6500 km

AVRO Vulcan:

- tailless

- delta wing

- 4 engines

Boeing B-47:

- conventional

- sweep wing

- 6 engines

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Considerations of Configuration Design

• Considerations

– Technical aspects

– Marketing aspects

– Emotional and styling considerations

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Technical Considerations

• It is nearly always desirable to place the

fuel c.g., the payload c.g., and empty

weight c.g., at same longitudinal

location.

– This consideration has a major influence

on the relative placement of those airplane

components, which primarily affect the

overall c.g. location.

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Technical Considerations

• The critical Mach number of the wing of a

subsonic airplane should be selected

such that the airplane does not cruise too

far into the drag rise.

– This requirement means that wing sweep

angle, airfoil type and airfoil thickness ratio

must be chosen in such a way to avoid

excessive drag rise at cruise Mach numbers.

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Technical Considerations

• The critical Mach number of the wing

should always be lower than the critical

Mach number of stabilizing or control

surfaces.

– This requirement means that the thickness

ratio, sweep angle and aspect ratio of

stabilizing or control surfaces must be

selected to yield critical Mach number

greater than that of the wing.

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Technical Considerations

• The integration of major components

such as nacelle on the wing, wing on

fuselage and so on needs to be done so

that interference drag is minimized.

– Ideally this means that any connecting,

intersecting items should intersect at as

close as possible to 90 degrees.

– If it is not possible to do this, extensive

fairings are needed to avoid interference

drag penalties.

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Technical Considerations

• Major intersecting structure components

should be arranged to avoid duplication

of special heavy structure.

– Think “structure synergism”

• Low weight airplane structures come about only

by judiciously combining multiple functions into

major structure elements.

• For example:

– In high wing transport with fuselage mounted main

landing gear, it is desirable to attach the landing gear

to the same fuselage frame which are used to attach

the wing.

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Technical Considerations

• In deciding on the location of the major

airplane components:

– Think “Light”

– Think “Simple”

– Think “Accessibility”

– Think “Maintainability”

– Think “Cost”

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Procedure for Configuration Design

• Collect the data and document related to aircraft

you design

• Write down possible configurations

• Conduct comparative study and trade studies of

those possible configuration

• Make a decision to select one of them

• Draw a preliminary three-view of configuration

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An Example

General Aviation Aircraft AD-600

• Collect the data and document related to aircraft you design – There are a lot of data for many kinds of airplane

in the book “Airplane Design part 2” by Roskam.

Airplane payload

(lbs)

Take-off

weight (lbs)

speed

(kts)

range

(n.m)

Beech Duke B60 1300 6775 239 1,080

Beech Baron M58 1500 5400 200 1200

Cessna T303 1650 5150 196 1000

Piper PA-44-180 1250 3800 168 725

AD-600* 1250 7900 250 1000

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An Example

General Aviation Aircraft AD-600

• The possible configurations

– Conventional (Beech Duke B60 and more others)

– Canard（Beech Starship）

– Three surface （Piaggio Avanti）

Beech Duke B60 Beech Starship Piaggio Avanti

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An Example

General Aviation Aircraft AD-600

• Comparative study and trade studies

– Conventional or unconventional ?

– Powerplant location ?

– Vertical location of the wing

• Low-wing, mid-wing or high wing ?

– Empennage

• “T” tail, high mounted or low mounted ?

– Landing gear

• Tricycle, Tailwheel or bicycle ?

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An Example

General Aviation Aircraft AD-600

• Make a decision

– Conventional

– “T” tail

– Wing

• Unswept

• High wing

– Powerlpant

• Two wing-mounted powerplants, pusher layout

– Less cabin noise

– Beneficial for stability

– Landing gear

• Tricycle

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A preliminary three-view of configuration