AIR FRAME

AIR FRAME

INTRODUCTION

Aircraft :- All types of air supported vehicles are called as aircraft.

(OR)It is a man made contrivance

(device) which can fly in the air.

Air Frame :- An aircraft without engine is called airframe.

Types Of aircrafts

According to Weight :-

Lighter than air Aircraft :-Ex:- Balloons, Airships.

Heavier than air Aircraft :-Ex:- Gliders, Helicopters,

Aeroplane.

According to number of Wings :-

Mono Planes (One wing on each side of the fuselage is fitted).

Bi Planes (Two set of wings fitted on each side of the fuselage).

Mono plane Aircraft :-

Bi – Plane Aircraft :-

According to number of Engines :-Single engine aeroplane

Multi engine aeroplane.

According to type of engines :-Propeller driven aeroplane

Jet Planes.

Single Engine Aircraft :-

Multi Engine Aircraft :-

Propeller Driven Aircraft :-

Jet Aircrafts :-

According to Speed :

Subsonic (with a speed below that of sound).

Sonic (with a speed equal to that of sound).

Supersonic (with a speed more than that of sound).

Other Classifications :-

Land Planes (which can take-off from and can land on ground).

Sea planes (which can take-off from and can land on sea).

Amphibians (which can take-off from and can land on both ground and sea).

Land Plane:-

Sea Plane :-

Sea Plane :-

Sea Plane :-

Major Structural Components Of A/C

Fuselage Main plane / Wings Aileron Flaps Elevators Fin Rudder Air Brakes Under carriage Engine

Aircraft :-

FUSELAGE :-

The fuselage is the main structure or body of the aircraft.

Fuselage provides attachment for the main planes, tail unit and in many cases for engines and under carriage.

It also provides space for cargo, passengers and other equipment.

This contains the cockpit from where the pilot controls the aircraft.

MAIN PLANE / WINGS :-

The function of the main plane is to provide sufficient lift and to support the weight of the aircraft in flight.

Therefore the main plane must be of an aerofoil section.

The construction of the main plane must be strong enough to transfer this lift to the fuselage.

AILERON :-

The ailerons are the control surfaces hinged on the aircraft’s wing structure to form a movable section of the wing trailing edge near the wing tip.

The surface controls the rolling movement of the aircraft.

The ailerons are always connected so as to move in opposite direction.

The ailerons are operated by the control column from the cockpit.

FLAPS :-

Flaps are usually fitted on the trailing edge on the underside close to the fuselage.

Flaps are made movable downwards to various degrees and are used for different stages of flight.

When flaps are extended, augments lift and increases drag beyond certain degree of their extension.

ELEVATOR :-

The elevators are pair of control surfaces hinged to the rear spar of the tail plane and are connected to the control column.

Elevators are normally coupled together to operate as a one unit.

The forward movement of the control column moves the elevator downwards and vice versa.

Elevators controls the aircraft about the lateral axis, i.e pitching movement.( Nose up and down attitude)

FIN :-

Fin gives directional stability by increasing the keel surface.

The fin is separately fastened to the fuselage tail bay or is built integral with the fuselage tail bay.

The fin gives attachment points for the rudder

RUDDER :-

The rudder is hinged to the rear of the fin is connected to the rudder bar.

Rudder is a movable vertical surface for controlling the motion of aircraft about the normal axis.

Rudder give directional stability to the aircraft. Rudder is connected to the rudder bar of pedals in the cockpit

by means of cables, number of pulleys and fairleads.

AIR BRAKES :-

An air brake is an integral part of the aircraft. It can be extended to increase the drag of an aircraft

at will. The effectiveness of airbrakes increases with the

speed of the aircraft. Air brakes are operated hydraulically and controlled

by a micro switch from the cockpit.

UNDER CARRIAGE :-

The under carriage may be located either under the fuselage, center section or under main planes.

The under carriage supports the weight of the aircraft on the ground.

It allows landing and take-off. The under carriage absorbs shocks when aircraft

lands.

ENGINE :-

The engine is accommodated in the nacelle on the wings or in the fuselage.

It gives power to the aircraft.

FUSELAGE

FUSELAGE

The fuselage is the main structure or body of the aircraft.

Fuselage provides attachment for the main plane, tail unit and in many cases for engines and under carriage.

It also provides space for the cargo, control accessories, passengers and other equipment.

In single engine aircraft it houses the power plant. A fuselage must resist the bending and twisting

forces acting on it.

Bending Force :- A up and down bending force due to tail and elevator loads and tail wheel load while taxing.

Twisting Force :- A twisting force due to rudder and fin loads acting of the centre line.

Materials used in fuselage :-

A wide range of materials used in airframe for fuselage construction are steel, aluminium, magnesium, titanium, wood, fabric, glass, plastic and rubber.

Types of fuselage construction

Fabric covered fuselage

Stressed Skin

Monocoque Construction

Fabric Covered Fuselage:-

A fabric covered tubular structure used for fuselage construction.

This is one of the cheapest and most widely used.

This is commonly used for small, light weight aircrafts.

Stressed skin construction :-

Stressed skin is used on frames and stringers.

The stringers seen alongside fuselage while the frames are made and fitted across it.

The skin is attached to stringers and frames with rivets.

Monocoque Construction:-

The word monocoque is a French word meaning a single shell. In practice there is no pure monocoque construction.

The true monocoque construction uses frame assemblies and bulk heads to give shape of the fuselage, but the skin carries the primary stress.

The main problem in monocoque construction is maintaining enough strength while keeping the weight within allowable limit.

MAIN PLANES

Main Planes (OR) Wings

The function of the main plane is to provide sufficient lift to the aircraft.

The main plane / wing supports the weight of the aircraft in flight.

The main plane must be of an aerofoil section.

The construction of the main plane must be strong enough to transfer the lift to the fuselage.

Bi Planes :- They are made of two set of main planes.

Braced Monoplanes :- Bracing struts are used from fuselage to a point approx half way along the wing.

Cantilever Main planes:- All external bracing and support is eliminated which results in the need of deep wing spars and a result thick wings.

Bi – Plane Aircraft :

Braced Monoplane Aircraft :

Cantilever Monoplane :

Forces acting on Main Plane :-

The main plane must be able to resist the following forces acting on it i.e.

Bending Twisting Shear

Bending :- Up and down bending force due to the lift and weight, and a backward bending force due to drag.

Twisting :- Twisting is due to lift and weight being unevenly distributed and also due to the action of ailerons and flaps.

Shear :- A vertical shear force due to lift and weight, and also horizontally backwards shear force due to drag.

AILERON, ELEVATOR & RUDDER

Primary control surfaces

Elevators

Aileron

Rudder

ELEVATOR :-

The elevators area pair of control surfaces hinged to the rear spar of the tail plane and are connected to the control column.

Elevators are normally coupled together to operate as a one unit.

The forward movement of the control column moves the elevator downwards and vice versa.

Elevators controls the aircraft about the lateral axis, i.e pitching movement.( Nose up and down attitude)

Elevators Operation:-

Elevators are linked to the control column, movement of the control column forward lowers the elevators, thus increasing the lift on the tail plane. This increased lift on the tail plane lowers the nose of the aircraft result in a dive. Similarly elevators up results in a climb. The elevators are operated by the control column , control column forward – elevators down, control column back – elevators up.

AILERON :-

The ailerons are the control surfaces hinged on the aircraft’s wing structure to form a movable section of the wing trailing edge near the wing tip.

The surface controls the rolling movement of the aircraft.

The ailerons are always connected so as to move in opposite direction.

The ailerons are operated by the control column from the cockpit.

Aileron Operation :-

Ailerons are always connected so as to move in opposite direction, thus assisting each in causing the aeroplane to bank. The ailerons are operated by the control column, control column to left port aileron up, starboard aileron down aileron banks to port. The unequal wing lift on each side of the aircraft produces a roll, which will continue until the pilot centralizes the control column.

RUDDER :-

The rudder is hinged to the rear of the fin is connected to the rudder bar.

Rudder is a movable vertical surface for controlling the motion of aircraft about the normal axis.

Rudder give directional stability to the aircraft. Rudder is connected to the rudder bar of pedals in

the cockpit by means of cables, number of pulleys and fairleads.

Rudder Operation:-

Rudder is connected to the rudder bar of pedals in the cockpit by means of cables, which passes through a number of pulleys and fairleads. Pushing the right rudder pedal forward will cause the rudder to move to the right i.e. the tail will be pushed to left tending the nose of the aircraft to go towards the right. The opposite effect is obtained when the left pedal is pushed forward.

Movements of primary control surfaces

Elevators - Pitching Movement

Ailerons - Rolling Movements

Rudder - Yawing Movements

UNDER CARRIAGE

Types of Under carriages

Fixed Under carriage

Retractable Under carriage

Nose Wheel Under carriage

Tail Wheel Under carriage

Fixed Undercarriage :-

In fixed undercarriage the undercarriage remains fixed through out the flight (even after take-off)

Most of the training aircrafts have this type of under carriage.

This type of undercarriage is not fitted to modern high-speed aircrafts.

FIXED UNDERCARRIAGE

Retractable Undercarriage :-

In this type of undercarriage the undercarriage retracts / folds inside the fuselage or wings after take-off, by operating a control liver from the cockpit.

This type of undercarriage eliminates the air resistance.

Most of the modern and high-speed aircrafts have this type of undercarriage only.

RETRACTABLE UNDERCARRIAGE

Tail Wheel Type Undercarriage :-

In tail wheel type undercarriage the undercarriage unit consists of two main wheels and a tail wheel.

We will find this type of wheel arrangement in very old aircrafts.

Tail Wheel Undercarriage :

TAILWHEEL UNDERCARRIAGES

Nose Wheel Undercarriage :-

In this type of undercarriage the undercarriage unit consists of one nose wheel and two main wheel arrangement.

This arrangement is used on most of the modern aircrafts because it has several advantages.

NOSE WHEEL UNDER CARRIAGE

Bogie Undercarriage:-

With the increase in size and weight of the aircraft the design has to overcome many difficulties, one of which is undercarriage arrangement.

Due to wings being reduced in thickness, leaves less room for the stowage of undercarriage when retracted.

Hence the necessity came for multi wheel arrangement.

This type of multi wheel arrangement is known as “Bogie undercarriage”.

BOGIE UNDERCARRIAGE

Advantages of Under Carriages

To support the weight of the aircraft on ground. To absorb the shocks when aircraft lands. To Provide smooth taxyng by absorbing minor

shocks. It gives minimum rolling friction during take off. The u/c gives large braking effect. To withstand the side loads of cross wind take off

and landing.

Tyres :-

The main function of aircraft tyres is to support and cushion the aircraft while at rest or moving on the ground.

Tyres are made with special care to withstand a variety of stress, strain and wear occurring during different phases of aircraft operation.

The wear while braking is much greater than the wear which occurs at the touch down point.

The aircraft tyre consists of (a) inner tube and (b) outer cover.

While the inner tube retains the air the later provides the strength to contain the same and ensure protection of the inner tube.

The tyres are made from materials containing cotton, nylon, metallic wiring, and rubber compound under specified conditions.

Tyre Creep

All tyres when first fitted to their wheels tend to move slightly as they settle down on their rims.

After the initial settle down there is a tendency for the movement to continue , which if allowed will result in a broken/torn valve body.

To prevent this all tyres are marked with paint to coincide with their respective positions with the wheel rim.

The independent rotation of tyre over the wheel is called “tyre creep”

FLAPS & SLATS

Flaps

Flaps are the part of leading edge or trailing edge of an aerofoil, which are made movable downwards.

By this the aerofoil becomes more cambered thus resulting in an increased lift coefficient.

Increased camber can be obtained by turning down either the leading or the trailing edges or the both.

In most of the aircrafts only the trailing edge flaps are used.

Flaps are made movable to various degrees and are used for different stages of flight.

Types of flaps :-

Variable camber (or) Simple flaps Slotted Flaps Split Flaps Fowler Flaps Jet Flaps Zap Flaps

Slats :-

The slat is a small auxiliary aerofoil of highly cambered section which is normally fitted to the leading edge of a wing along the span.

The effectiveness of slats depends upon the coverage of leading edge of the wing by the slat and the chord of the slat.

Disadvantages of Slats :-

(i) High nose attitude on landing resulting in the need of a long under carriage.

(ii) Pilots visibility on landing is reduced. (iii) Unnecessary extra drag during normal

flight. (iv) Sudden changes in trim when automatic

slats comes into operation.

Advantages of Flaps over Slats :-

(i) Flaps reduce the stalling speed without having a nose up attitude.

(ii) Pilots visibility on landing is not reduced. (iii) Flaps can be put up when not required,

as such do not give unnecessary drag during normal flight.

Materials Used In Construction

Basic Constructional Requirements Of Airframe:

The aircraft construction should be such that its airframe must be able to provide:

(i) Smooth skin of the required aerodynamic form.

(ii) Sufficient strength to withstand aerodynamic, landing and handling loads.

(iii) Sufficient stiffness to retain its correct shape under all loads.

(iv) Mounting points for engine, armament, fuel tanks, equipment etc.

(v) Protection of aircrew and radio gear, cooling for engines and electrical gear.

(vi) Sufficient breakdown points for easy dismantling for transportation.

(vii) The design itself should be cheap and easy for production and repairs.

Materials used in Airframe:-

Wide range of materials used in airframe construction.

(Metallic & Non metallic)

Steel, Wood, Fabric, Glass, Lead

The most commonly used are alloys of Aluminum, Magnesium and Titanium.

Types of construction and Materials:-

In order to achieve a satisfactory combination of all the above constructional requirements, the aircraft structures are made of wood, metal and fabric or combination of them.

Wood:- Wooden structures have had a day for themselves. However , there were certain disadvantages such heaviness, in adequate strength / weight ratios, highly inflammability etc..

Wooden structure were also susceptible to climatic conditions and were easily attacked by insets etc.

Ex:- Mosquito aircrafts.

Metal :- Metal structures have a very high strength weight ratio and has taken the place of wood in modern aircraft construction.

A metal structure can be manufactured in any quantity maintaining the quality control. It does not easily get distorted due to temperature/climatic changes and are proof against inset attack.

It may rust or corrode at times but will not burn easily.

Composite Construction :- In this type metal is used for main strength member and wood is used for less important and less loaded members.

Thus the good quality of each materials are used and their faults partly avoided.

TYPES OF AIRFRAME

Classification Of Structure :-

Primary Structure

Secondary Structure

Tertiary Structure

Primary Structure :-

This parts of the airframe are highly stressed and if damaged may cause failure of aircraft and loss of life.

Ex :- Spars, Longerons, Engine Mountings & Stressed Skin.

Identification :- Coloured Red or Shown White.

Secondary Structure :-

This parts of the air frame are highly stressed, but if damaged will not cause failure of aircraft or life of aircrew.

Ex :- Flooring, Guns, Ammunition, Oxygen Bottles.

Identification :- Coloured Yellow or Shown hatched.

Tertiary Structure :-

They are lightly stressed parts.

Ex:- Fairings, Wheel Shields, Brackets etc..

Identification :- Coloured Green or Shown Stippled.

Types of Structure Construction :-

Stressed skin construction Monocoque construction Box Spar construction D – Spar construction.

Stressed skin construction :-

This stressed skin construction consists of a hollow shell of metal plates or ply wood.

which are strong enough to carry the loads imposed on it.

Stiffened internally by longerons and stringers.

This type of construction is also known as semi monocoque construction.

Monocoque Construction :-

If the skin sheet metal is of sufficient strength and rigidity, a single sheet can be used to cover the wing without the actual support or spars.

Aircraft structures made according to this method are known as monocoque construction.

Box- Spar construction :-

Here the skin of the upper and lower surfaces of the wing joints the front and rear spars together in the form of a box.

Leading and trailing edges are separately attached to the wing to complete the structure.

D – Spar construction :-

In this form of construction the spar is placed at or as near as possible to the point of maximum thickness of the wing and skin of the leading edge is rigidly attached to it, to form a D – Type shape.