Aircraft Structures I Chapter-1

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AIRCRAFT STRUCTURES

AIRCRAFT STRUCTURES



 INTRODUCTIONINTRODUCTION



 PRINCIPA PRINCIPA LL AIRCRAFT AIRCRAFT COCOMMPONPONEENTNTSS OFOF

FIX

FIXEEDD W W INGING ((FFunction, material andunction, material and construction )

construction )

-- FFuselageuselage -- WWiinngg

-- EmEmpepennnnagagee

-- FFlight control surfacelight control surface -- LaLandndining gg gearear

-- PPower plant structureower plant structure -- DDoors and windowsoors and windows

AIRCRAFT STRUCTURES

AIRCRAFT STRUCTURES



 INTRODUCTIONINTRODUCTION



 PRINCIPA PRINCIPA LL AIRCRAFT AIRCRAFT COCOMMPONPONEENTNTSS OFOF

FIX

FIXEEDD W W INGING ((FFunction, material andunction, material and construction )

construction )

-- FFuselageuselage -- WWiinngg

-- EmEmpepennnnagagee

-- FFlight control surfacelight control surface -- LaLandndining gg gearear

-- PPower plant structureower plant structure -- DDoors and windowsoors and windows

Objective

 To understand the structural components of  aircraft and the stresses imposed on those

INTRODUCTION

 DEFINITION

1. AIRCRAFT

 A _{ny structure, machine which is designed to be}

supported in the air either by dynamic reaction  with the air or by it¶s own buoyancy.

 A irframe

  basic assembled structure of any aircraft (except

that of lighter than air aircraft) or rocket necessary  to support the aerodynamic and inertia loads

imposed by the weight of the vehicle and its contents.

 Includes the fuselage, wings, tail boom, nacelle,

cowling, fairings, stabilizers, control surfaces and landing gear.

B

rief History of Aircraft Construction

 Early dreamers

 Greek myth ± Daedalus with his son Icarus, flew 

inth on Crete where they were imprisoned by King Minos. Ignoring Daedalus¶s warning, Icarus flew too close to the sun. His wings melted and he plunged into the sea. Fall of I ca oration. All rights reserved.

 Leonardo Da Vinci made suggestive drawings of  the orinthopter, a parachute and a helicopter

 The Montogolfier brothers made their hot air  balloon from linen cloth lined with paper and

 Otto Lilienthal made about 2000

successful flights  with gliders made

of willow wands and waxed cotton in the 1890¶s

 The Wright brothers made their

successful flight in

1903, at Kitty hawk, north Carolina

 The early flying machines produced by the

 Wright brothers, and others had wings made of   bent wooden ribs covered with fabric and a body 

of open framework made of strips of bamboo held together with piano wire.

 The next generation of airplanes before the first  world war were built with a wood truss and had  wings braced with struts and wires.

 The Welded thin walled steel tubing truss came as a major breakthrough in the later years of the first world war replacing the wood.

 The stressed skin construction were the skin

carries all of the structural loads was developed and widely used in the 1920¶s and 1930¶s

 Thin sheets of wood veneer were molded in to a ply wood structure forming the fuselage

 Laminated wooden rings were built at critical

locations to provide attachment points for the  wing, engine and landing gear

 The wood was later replaced with aluminum alloy 

sheets which were riveted into thin sheet metal formers.

 The development of pressurized transport jet aircraft created new challenges in aircraft

structure design

 In 1954, two de Havilland comets vanished during flight suffering damages caused by pressurization loads around rectangular cutouts

 A new system of fail safe construction was developed  where doublers are installed at strategic locations and

CLASSIFICATION OF AIRCRAFT

1. LIGHTER TH AN AIR 

Lighter than Air

 Supported in the air by their own buoyancy 

 A .Balloons: - non-porous spherical bags filled with light air

- Gas filled

- Hot A ir

B. A irships :- are engine driven and can be Steered.

ng structure; the pressure of the buoyant gas maintains the bag¶s shape. Blimps are rarely used for their original purpose of transportation, but their hovering capabilities, high v rosoft Corporation. All ri ghts reserved.

Heavier than Air

 Supported in the air by the dynamic reaction of  the aircraft structure with the air

 Can be classified as

1. Fixed wing aircraft

 Have pairs of fixed wings to generate lift

forward movement of the wing through the air generates lift

 Monoplane - has a single pair of fixed wings

 Biplane ± has two pairs of wings  Sea plane ± lands on water surface

 A mphibian ± can land both on water surface and on land.

2. R otary Wing

 A rotating airfoil shaped wing generates lift

 Main Structural Components of fixed wing aircraft  T_{he fuselage}  The wing  The landing gear  The stabilizers

 These structural components are an assembly of  structural members

 The structural members are designed to carry  loads or resist stress

Stress- The internal force of a material to resist

B

asic Stresses

 Tension

 Compression

Tension ²

is the stress that resists a force that tends to pull a material apart

Compression ²

Shear-is a stress that resShear-ists the force tending to slide one layer of material over an adjacent layer

2. Combination stresses

Bending ± is a combination of tension and compression

B

asic requirements to be met by

aircraft structures

 High aerodynamic cleanness

 Low weight of construction with necessary  strength and stiffness

 Simplicity of operation

 Ensuring high reliability combat survivability  and flight safety 

The Fuselage

 The main body of the aircraft on which the  wings, tail, and landing gear are attached. Purpose

 Provides space for cargo, controls, accessories, passengers and other equipment

R 

_equirements

 Convenience for accommodating the crew, passenger, equipment and cargoes,

 Sufficient bending and torsional stiffness.

 Must be strong and light in weight

 Must be streamlined

 Must be air conditioned or ventilated

 _{Must be pressurized if the aircraft flies at high}

altitudes

Types of Construction

 Three general types :- depending upon the method by which stresses transmitted to the structure

1. Truss

2. Monocoque

Truss

Truss



 A A rigid frame work of bars, beams, rods, tubesrigid frame work of bars, beams, rods, tubes and wires.

and wires. TThe members are joined together by he members are joined together by  riveting or welding



 Longitudinal longeroLongitudinal longerons are the ns are the primary loadprimary load

carrying members

carrying members 

 Lateral bracing is placed at Lateral bracing is placed at regular intervals.regular intervals. TThehe

frame work is covered with fabric, wood,

frame work is covered with fabric, wood,

aluminum or fiberglass

There are two types of

There are two types of

truss

truss

construction

construction

1

1.. PPratt trussratt truss

  Vertical and diagonal members connect the Vertical and diagonal members connect the

longerons

longerons

 TThe diagonal members can be wires (carry only he diagonal members can be wires (carry only 

tension) or rigid tubing (can carry both tension

tension) or rigid tubing (can carry both tension

and compression)

2. Warren truss

 _{The longerons are connected only with}

diagonal members Material

Stressed Skin Construction

 A ll the loads are carried in the outside skin

 Can be built in a clean, smooth and efficient aerodynamic shape

Full Monocoque

 Is a metal tube or cone without internal structural members

 Formers can be used to give shape

 R elies on the strength of the skin to carry  stresses

Semi Monocoque

 Has additional longitudinal members

(Longerons and stringers) to reinforce the skin

 The skin is riveted to stringers which in turn are riveted to the formers

The Structure includes

1.Skin (plating)- aluminum alloy, titanium, and stainless steel 2. Longitudinal Members      Stringers      Longerons 3. Vertical members      Frames or formers       bulkheads

The Wing

Purpose

 Produces lift

 Provides attachment points for the landing gear, engines and the aileron

WINGS

 Wing is essentially a beam which gathers and

transmits all the aerodynamic loads to the central fuselage attachment

Requirements

 Minimum possible drag

 Minimum value of product (Cl-S)

 Maximum aerodynamic quality 

D_esign

 Depends on the intended use, size, weight and speed of the aircraft

WING TYPES

 S_{traight wing :}

 If the leading edge of a wing is perpendicular to the airflow, it is called a straight wing

 S _{wept wing :}

 If the leading edge of a wing meets the airflow  at an angle, it is called a swept wing

TYPICAL WING FORMS

Rectangle (Wright brothers) Triangle (Concorde) S=40¶ C=6¶ S=42.5¶ C_r =90.75¶ Trapezoid (F18) Trapezoid (Boeing 747) Compound (Space shuttle) S=13¶ C_r =15¶ C_t=6¶ _CS=81.3¶ r =54.3¶ C_t=13.3¶ 7.2¶ 60¶ 35.7¶ 9.8¶ 30.5¶

PARTS OF A WING

 _{Wing box}  Fixed leading edge  Fixed trailing edge  Ailerons  S_poilers  _Flaps  S_lats

WING TERMINOLOGY

 Leading edge is the portion of the wing front of the front spar 

 Trailing edge is the portion of the wing back of rear spar 

 The chord _{is the distance between the leading edge and trailing edge}

 Wing box is portion of the wing between the front spar and rear spar 

 Ribs are the airfoil shaped members from leading edge to trailing edge

 Span is the distance between the root and tip of the wing

 Aspect ratio AR = B2 _/A

Leading edge

Trailing edge Tip

Root

Types of wing construction

Based on number of spars

 Mono spar

 T wo spar

Based on how they are supported

1. Cantilever- doesn¶t need external support 2. Semi cantilever- needs external support

Based on how stresses are transmitted

 Truss

Truss type

 T_{he spars are separated by compression}

members

 T_{he truss is held together with high}

strength steel wires. The compression

members carr y the compressive stresses,  while the drag and anti-drag wires carr y 

the tensile forces. The structure carries

the entire load. The skin is usually not a

S

_{tressed skin}

 A metal skin is riveted to stringers and ribs

 T_{he stringers are also riveted to the skin}

and the ribs

Sandwich (bonded honeycomb)

 Metal bonded honeycomb

 Fiber glass

Wing Configuration

 Low wing  High wing  Mid Wing  Dihedral wing  Gull wing

Tail unit

 The empennage

 Includes the tail boom, vertical stabilizer, and the

The stabilizers

 Horizontal stabilizer

Horizontal sta

Horizontal sta

b

b

ilizer

ilizer

P

Purpose-urpose- provides longitudinal stability and controlprovides longitudinal stability and control

P

Provides attarovides attachment point for chment point for the elevatorthe elevator

C

Constonstructiruction-on- simisimilar to tlar to the winhe wingg

x

x TTrussruss x

x Stressed skinStressed skin x

V

_ertical

S

_tabilizer

 Purpose

 provides directional stability and control

- Provides attachment point for the rudder

- Construction

- similar to the horizontal stabilizer

- Location ±

 Control Surface

 A re hinged or moveable surfaces to control the

P

rimary control surfaces

1.The elevator 2.The ailerons

 C

ombination control surface

R 

uddervators (V-tail) ± functions as a

rudder and elevator

Elevons- serves the functions of the elevator

and aileron

F

laperons- functions as a flap and aileron

Stabilator- a hinged moveable horizontal

stabilizer which can be used for pith

Tabs

Function- provides a means of trimming the aircraft

 A _{ssists the pilot to move the main control surface}

Location- hinged at the trailing edge of the main control surfaces

 Construction

 Corrugated skin

 _{Bonded honeycomb}

Types

 T_{rim tabs}

 S_{er vo tabs}

 Balance tabs

uxiliary control surfaces

1.Trailing edge flaps 2.Leading edge flaps

3.Leading edge slats

 T _y pes  Plain flap  Fowler flap  S_{plit flap}  S_{egmented flap}  _Construction

 Fabric covered truss

 S_{tressed skin}

 Location

 usually hinged or mounted on the trailing

edge of the wings

 Can be actuated mechanically, hydraulically or electrically 

S

_{poilers and}

S

_{peed Brakes}

 Purpose

 to reduce lift

 _{to increase drag}

 to aid the aileron in lateral control

 _{to reduce speed of the aircraft during}

L

_{eading edge flaps}

 Purpose

 increase the camber of the wing and provide greater lift at lower airspeeds

 Location

 usually hinged on the leading edge

 normally flush with the lower surface of the wing

 Can be actuated mechanically, electrically or hydraulically 

4. L

_{eading Edge}

S

_lats

 Purpose

 to reduce the stalling speed and increase lift at lower airspeeds

 Location

 mounted on the leading edge of the wing

 Construction

 similar to trailing edge flaps

 Operation

 normally flush with the wing leading edge

  When extended move forward and open a slot to allow air flow and prevent stalling

The

L

_{anding Gear (Under Carriage)}

 Purpose

 supports the aircraft during ground operations

 Dampens vibrations while towing and taxing

 Cushions the landing impact

 Location- is attached to the fuselage or the wing

 Can be fixed or retractable

 Extending and retracting systems

 Mechanical

 Electrical



 Has shock absorbers to cushion the landingHas shock absorbers to cushion the landing

impact and dampen vibrations

impact and dampen vibrations



 _{Shock chordShock chord}



 Spring gearSpring gear



 Spring oleoSpring oleo



 S_{kis are used for take off and landing on}

snow or ice

 Floats are used for those aircraft which can take off and land on water surfaces

Float

 A completely enclosed water tight structure attached to an aircraft to provide buoyancy and stability while landing on water surfaces.

L

_{anding gear arrangement}

- Conventional has two main wheels and one tail  wheel

T

T

ricycle

ricycle

landi

landi

ng

ng

gear

gear



 TT _{wo main wheels (aft of the wo main wheels (aft of the CG)CG) and aand a}

nose wheel

nose wheel 

 Widely  Widely uused on modesed on moderrn ain airprplaneslanes 

 Advantages Advantages



 Allows mo Allows morre foe forrcef cef uul al apppplication of thelication of the

 b

 brrakes with oakes with ouut nosing ovet nosing overr



 _{OffeOfferrs bettes betterr visibility visibility} 



N

_{acelles or Pods}

 A re streamlined enclosures used to cover the engines

 T_{he structure consists of skin, cowling,}

structural members, the fire wall and engine mounts

The cowling

 Is the removable covering of the engines found on areas, which need regular

The engine mount

 Is the f rame that supports the engine and attaches it to the f uselage or the wing

 Can made f rom welded steel tu bing or formed sheet metal

M

_ain

S

_{tructural Components of A}

Helicopter

 T_{he f uselage}  T_{he main rotor}  T_{he tail rotor}  T_{he landing gear}

The fuselage

 Has similar features as the fuselage of fixed wing aircraft

The main rotor

 is the component that produces lift