UNIT - II INTRODUCTION TO AIRCRAFTS

T.Y. B.Tech. (Mech)Elective-I

Basic components of an Aircraft

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Contents Aircraft Components Material use in Airframe Construction Example of Material use in Airframe Construction Fuselage Structure• - Truss Type• - Pratt Truss• - Warren Truss• - Monocoque• - Semi-Monocoque Basic Structure Member Terms Wing Structure Empennage Structure Power Plant• - Wing Pod Mount• -Fuselage Mount Landing Gear Structure

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Introduction• There are thousands of designs and ideas about

aircraft which have been developed through aviation history.

• Despite this some main components became permanent in every aircraft design.

• As fix-wing aircrafts are the most common aircrafts they will be the most studied.

• The type and class of the aircraft determine how strong it must be built.

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Categories of aircraft • Airplane, • Rotorcraft, • Glider, • Lighter-than-air, • Powered-lift, • Powered Parachute, and • Weight-shift Control.

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Fixed-wing aircraft components• Airplane as an engine-driven, • fixed-wing aircraft that is supported in flight by the

dynamic reaction of air against its wings. • In advanced avionics aircraft, which refers to an

aircraft that contains a global positioning system (GPS) navigation system with a moving map display,

• In conjunction with another system, such as an autopilot.

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A. Fuselage

B. Wings

C. Empenage or Tail

D. Power Plant

E. Landing Gear or

Undercarriage

Aircraft Components

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• A rotary-wing aircraft consists of the following four major units:– 1. Fuselage– 2. Landing gear– 3. Main rotor assembly– 4. Tail rotor assembly

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STRUCTURAL STRESS• The primary factors to consider in aircraft structures are:– strength, – weight, and – reliability.

• These factors determine the requirements to be met by any material used to construct or repair the aircraft.

• Airframes must be strong and light in weight. • All materials used to construct an aircraft must be

reliable. – Reliability minimizes the possibility of dangerous and

unexpected failures.

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• Many forces and structural stresses act on an aircraft when it is flying and when it is static.

• When it is static, the force of gravity produces weight, which is supported by the landing gear.

• The landing gear absorbs the forces imposed on the aircraft by takeoffs and landings.

• During flight, any maneuver that causes acceleration or deceleration increases the forces and stresses on the wings and fuselage.

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Stresses• Aircraft structural members are designed to carry a

load or to resist stress. • In designing an aircraft, every square inch of wing

and fuselage, every rib, spar, and even each metal fitting must be considered in relation to the physical characteristics of the material of which it is made.

• Every part of the aircraft must be planned to carry the load to be imposed upon it.

• The determination of such loads is called stress analysis.

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• The term “stress” is often used interchangeably with the word “strain.” While related, they are not the same thing.

• External loads or forces cause stress. • Stress is a material’s internal resistance, or

counterforce, that opposes deformation. • The degree of deformation of a material is strain.• When a material is subjected to a load or force, that

material is deformed, – regardless of how strong the material is or how light the

load is.

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• There are five major stresses to which all aircraft are subjected.• Stresses on the wings, fuselage, and landing gear of aircraft are:

– tension, – compression, – shear, – bending, and – torsion.

• These stresses are absorbed by each component of the wing structure and transmitted to the fuselage structure.

• The empennage (tail section) absorbs the same stresses and transmits them to the fuselage.

• These stresses are known as loads, and • the study of loads is called a stress analysis. • Stresses are analyzed and considered when an aircraft is

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TENSION• Tension is the stress that resists a force that tends to pull

something apart. • The engine pulls the aircraft forward, but air resistance tries to

hold it back. • The result is tension, which stretches the aircraft.

– Yield strength - The stress a material can withstand without permanent deformation. Yield strength is the stress which will cause a permanent deformation of 0.2% of the original dimension.

– Ultimate strength - The maximum stress a material can withstand.– Breaking strength - The stress coordinate on the stress-strain curve at

the point of rupture.• The tensile strength of a material is measured in Force per square

meter and is calculated by dividing the load (N) required to pull the material apart by its cross-sectional area (mm).

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Compression• If forces acting on an aircraft move toward each other to

squeeze the material, the stress is called compression.• Compression is the stress that tends to shorten or

squeeze aircraft parts.• Compression is the opposite of tension. • Tension is pull, and compression is push. • Compression is the resistance to crushing produced by

two forces pushing toward each other in the same straight line. – For example: when an airplane is on the ground, the landing

gear struts are under a constant compression stress.

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TORSION

• Torsion is the stress that produces twisting. • While moving the aircraft forward, the engine also

tends to twist it to one side, but other aircraft components hold it on course. Thus, torsion is created. The torsion strength of a material is its resistance to twisting or torque.

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