introduction to aircraft design - i

Introduction to Aircraft DesignIntroduction to Aircraft Design

-- T. G. A. SimhaT. G. A. Simha

Reference:The Elements of Aircraft Preliminary Design – Roger D. Schaufele

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I gratefully acknowledge the support of my colleagues at PLES.

My special thanks are to- Mr. Sunder Singh- Mr. Ravi Prakash Singh- Mr. Vijay Sekhar Kandavalli

for preparing this presentation.

- T. G. A. Simha

Acknowledgement

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L749A Sukhoi-T4

X48BC130

Aircrafts

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Contents:

Introduction to Aircraft Design• Specification• Design Drivers• Stages of aircraft Development• Design Methodologies• Weight estimate• Preliminary Wing Design• Fuselage Design• Design of Empennage• Power Plant• Aircraft 3 View

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Aircraft Uses

• Civil• Military

• Civil Types- Basic Trainer - Commuter- Transport - Air Taxi- Cargo - Logistics (Ambulance, rescue, fire-fighting)- Business - Sports- Personal Transport

• Military Types- Basic and Advanced Trainers - Fighters – Air superiority- Bombers- Deep penetration - Cargo and Troop Carriers- Anti shipping and Anti submarine - Naval, Marines- Tankers - Surveillance and Electronic warfare- Air Patrol and Observation - Counter Insurgency

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Specifications

Intended use of the aircraft leads to specification

• Specification of role – Purpose, Payload• Power plant specification – Number and type• Performance specification – Speed, Range, Altitude, Take off, Landing • Mission Specification – Payload range, Military• Certification specification – FAR PART etc.

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Example of Specifications

• Charles Lindberg – Spirit of St. Lois, Feb 03.1927.

“Can you construct whirlwind engine plane capable of flying non-stop between New York and Paris. Stop. If so please state cost and delivery date.”

• US Army Signal Corps Mission Specification – Dec 23.1907- To carry two persons of about 350 lbs.- To fly 125 miles.- The speed at least 40 mph.- To be quickly assembled and disassembled.- To be assembled and fly in 1 hour.- Other features.

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US Army Signal Corps Mission Specification for 1st US Military Airplane

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US Army Signal Corps Mission Specification for 1st US Military Airplane

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Mission Specification for Short Range Jet Transport

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Mission Specification for Short Range Jet Transport

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Mission Specification for Military Attack Aircraft

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Mission Specification for Military Attack Aircraft

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Main Design Drivers

• Mission requirement- Payload - Range- Performance

• Life- In service life

• Cost- Acquisition cost- Operation and Maintenance cost- Life cycle cost

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The Design Problem

Mission Requirements

Performance Evaluation

Aircraft Drag Estimate

Aircraft Weight Estimate

Aircraft Sizing

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Stages of Aircraft Development

• Conceptual Stage- Technology Option- Aircraft Configuration – Alternatives- Preliminary Sizing- Development Testing

• Preliminary Design- Aircraft Sizing- Three View – Geometry- Preliminary Structural Layouts- Revised estimates- Additional testing- Systems Definition

• Detailed Design- Detail Structural Design- Detail System Installations – Design- Drawings for Manufacture

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Aircraft Development Process

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Design Methodologies

• Design depends on good and accurate prediction of aircraft aerodynamic parameters and weight.

• Traditionally statistical and empirical methods are used – Data from similar aircrafts.• Over 100 years of experience.• State of the art -

- Computer simulation- Multidisciplinary optimization- Computational fluid dynamics- Finite Element Method etc.

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Weight Estimate

Wto = Wempty + Wpayload + Wfuel

Where,Wto – Take off weight

Wpayload – Payload (Passenger + cargo)Wempty – Aircraft empty weight (operational)Wfuel – Fuel weight

These may be expressed as fractions(Wempty / Wto ), (Wpayload / Wto ), (Wfuel / Wto )

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Weight Estimate – Fuel Weight

The weight fractions are estimated using statistical data.

Fuel Weight fraction

Range - N. milesa - Knotsc – specific fuel consumptionL/D – Lift to Drag Ratio

Add additional fuel fractions for taxi, take off etc. The fuel fraction range 20-50%.

DL

caRange

WW

cruisef

iln

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Weight Estimate – Empty Weight

Estimated using statistical data

Wempty – Typically 30-45% of Wto

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Weight Estimate – Empty Weight

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Weight Estimate – Empty Weight

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Weight Estimate - Payload

• Estimate based on number of passengers and cargo space.• Weight of passenger + baggage (205 lbs – 215 lbs per passenger).• Cargo weight – 10 lbs per cubic feet.

Total weight, Wto = Wempty + Wpayload + Wfuel

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Some Weight Data

Spirit of St. Louis

Rutan Voyager

Concorde Boeing 747

Empty Weight 2,535 (0.494)

2,448 (.252)

172,500 (.443)

392,032 (.450)

Payload 0 0 21,000 (.054)

88,410 (.102)

Fuel weight 2,600 (.506)

7,247 (.748)

195,500 (.503)

389,558 (0.448)

Total Weight 5,135 (1.0)

9,695(1.0)

389,000 (1.0)

870,000 (1.0)

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Weight Breakdown of MWE

The breakup of manufacturers empty weight – Statistical methods

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Typical Breakdown of MWE

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Weight and BalanceThe center of gravity needs to be establishedEstimated using detail breakdown of weights

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Preliminary Wing Design

Wing Parameters

• Wing area• Sweep• Thickness ratio• Aspect ratio• Taper ratio• High lift devices• Control surface• Aerofoil design

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Estimate Of Wing Area

Wing area S significantly influences:• Cruise speed and altitude• Take off field length• Landing approach speed• Wing internal fuel

W - Weight of A/CCL – Lift coefficientq – Dynamic pressure

qCWSL *

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Estimate Of Wing Area

Wing Area is estimated for different conditions.

Based on cruise:CL : 0.4 to 0.55 for commercial jetsq : Corresponds to Vc at cruise altitude

Based on Landing approach speedApproach speed 120-150 knots commercial jetsCLmax 1.8 to 3.0

Based on Wing LoadingWing loading W/S : 80-120 lbs/s.ft for jet transport

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Typical Values

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Example of Wing Area - Estimate

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Estimate Of Wing Area

Wing Area is selected using the graph S vs W

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Wing Sweep, Thickness and Aspect Ratios

Wing Sweep:• Increase Drag Divergence Mach No. MDIV

• Aerofoil shape and thickness ratio influences MDIV

• Sweep Angle is determined using charts for the desired cruise Mach No.Sweep Angle : 0-35 degThickness Ratio : 10-15%• Airfoil Selection

- Standard NACA series- Designed by CFD

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Wing Aspect Ratio and Taper Ratio

SbAR

2

root

tip

CC

And

AR is a compromise between high L/D and structural weight.

High AR High L/D High Wing Weight

influences cruise effiency and stall characteristics.AR : 7 – 9.5 Jet transport

: 0.4 – 0.2 Jet transport

Military Aircraft:AR : 2.4 – 5.0 Jet transport

: 0.5 – 0.2 Jet transport

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Typical Wing Geometry

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Fuselage Design

Fuselage accommodates:• Pilots and Crew• Passengers• Baggage and Cargo• Engine • Utilities such as gallies etc.

Generally fuselage consists of three sectionsNose , Centre and Tail Cone

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Fuselage Design

Basic Design Parameters:• Fuselage cross section• Fuselage cabin length

For Military Aircraft:• Cockpit and vision• Airduct and engine installation

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Fuselage Cross Section

Short range unpressurised aircraft – Rectangular cross section.Long range pressurised aircraft – Circular / Double bubble.

Choice of number of seats abreast• Single Aisle• Twin Aisle• Wide bodied

Choice of class• Economy• Business• First class

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Passenger Compartment Cross Sections – Business Jets

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Passenger Compartment Cross Sections – Twin Aisle Jet Transports

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Passenger Compartment Arrangements of Business Jets

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Passenger Cabin Layouts of Long Range Jet Transports

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Fuselage Design

Nose and Tail Cone:

• Generally faired aerodynamic shapes.

• Typical L/D ratios- Nose section : 1.5 – 2

- Vision over the nose 10-20 Deg

- Tail section 2.5 to 3

- Upsweep 3 to 6 deg.

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Design of Empennage

Empennage consists of:

• Horizontal tail with Elevator

• Vertical Tail / Fin with Rudder

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Design of Horizontal Tail

The horizontal tail provides stability and control of the aircraft.

Stability of aircraft depends on location of• Centre of Gravity of aircraft• Aerodynamic Centre of aircraft

Aircraft is stable when C.G. is forward of aerodynamic centre.

H.T. sized to provide the required C.G. range of the a/c.

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Definitions:Tail Volume coefficient:SW Wing AreaSH Horizontal tail ArealH Distance of 25mac of HT from 0.25 mac wingCW m.a.c – wingFuselage Volume Coefficient:

Wfus Maximum fuselage widthLfus Fuselage length

Horizontal Tail Design

WW

HH

CSlS

WW

fusfus

CSLW 2

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Horizontal Tail Volume Diagram

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Horizontal Tail DesignThe area required is obtained from a chart

Horizontal Tail Design

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Horizontal Tail Area

Required Volume Coefficient = VH % per 1% mac X C.G Range Required

Horizontal Tail Area = Required Volume XH

WW

lCS .

Horizontal Tail Design

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Vertical Tail provides

•Directional Stability•Directional Control – To hold side slip-one engine failed case.

Vertical Tail Design

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Definitions:Vertical Tail Volume:

SV Vertical Tail AreaS Wing ArealV Distance from 0.25CW to 0.25 CV

bw Wing Span

Fuselage Volume Parameter =Hfus Maximum Fuselage HeightLfus Fuselage length

W

vvV b

lXSSV

W

fusfus

bSLH

.

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Vertical Tail Design

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The vertical tail area is obtained from a chart

Vertical Tail Design

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Detailing the Empennage:Once the Area is estimated geometric features• Aspect Ratio• Sweep• Elevator/Rudder Chord ratio• Thickness Ratio

Aircraft Design

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Typical Geometric parameters- Empennage

Aircraft Design

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Aircraft Design

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Aircraft Design

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Definition of Engine Requirements:Power Plants:

• Piston Engine -propeller (low speed)• Turbo-Prop (medium Speed)• Turbo-Jet (High Speed)

The Engine Parameters:• Power/Thrust• Weight• Fuel Consumption• Number of Engines

Generally Number of engines- specified• Design Option• Safety and Redundancy

Aircraft Design

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Aircraft Performance – Determined by the Engine• Take off Field length (Max power)• Operational rate of climb (0.9 max)• Cruise performance (0.8 max)

Engine Thrust/Power required is obtained from design charts

Aircraft Performance

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Aircraft Design

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Aircraft Design

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Aircraft Design

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Final Aircraft configuration – Three view drawingConsiderations:

Fuselage• Cabin Arrangement• Windows/doors/emergency exits• Gallies and Services• Cargo handling

Wing• Wing- Fuselage fairing• Low/Mid/High Wing• Wing location along the longitudinal axis• Location of Engines

• Location of Undercarriage

Aircraft Configuration

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Considerations (Contd..)

Engine• Location• Air duct requirement• Exhaust

Empennage• Location of HT and VT• T Tail configuration

Aircraft Configuration

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Typical 3-View Layout Drawing – Regional Turbofan

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INTRODUCTION TO AIRFRAME DESIGN

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Airframe Design Drivers

• Static Strength• Life and Durability• Aero elastic performance• Weight• Manufacturing and maintenance• Cost

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Evolution of Airframe Technology

Structural Type Truss Stressed Skin Stressed Skin

Materials Wood fabric AluminiumComposites,

Advanced Alloys like Titanium

Technology Static StrengthFatigue and

Damage Tolerance

Aero-elasticity