Chapter 3 – Airplane Propulsion Introduction to Aeronautics Quick Notes (PTU) :-
Requirement of Power to Fly :-
An aircraft is nothing without a source power which makes it to move forward.this power is provided by airplane propulsion system. These power plants are called aircraft engines.These engines propel (to throw ) aircraft in forward direction with the help of their thrust.When aircraft moves forward at high speed aerodynamic forces get generated.These forces are lift and drag which acts on aircraft.Lift acts vertically upwards and drag acts horizontally apposite to motion of aircraft.lift make aircraft to fly in air.Drag tries to stop the forward motion of aircraft.But its magnitude is not so high and quite lower than that of engine thrust.Hence power requirement is very necessary for a airplane or any other aircraft.
Balance of Forces :-
Different kinds of forces acts on aircraft when it starts moving on grounds with the help of airplane propulsion system. There are basic four fundamental forces acts on aircraft in moving condition.
Thrust is the major force produced by airplane propulsion system i.e. aircraft engines. This forces is used to propel aircraft in forward direction. When aircraft engines throw mass of air or exhaust in backward direction with some force, according to newton’s 3rd law a force with same magnitude propel aircraft in opposite direction. This is thrust force. When aircraft moves forward, aerodynamic forces acts on aircraft. These aerodynamic forces are lift and drag. Lift helps aircraft to fly in air and it acts vertically upward. Drag tries to stop forward motion of aircraft. It acts horizontally in opposite direction to thrust. Weight is force due to gravitational pull of earth and is vertically downwards.
Various Means of Producing Power for Forward Flight:-
There are several ways by which power is used to propel aircraft forward.
- Piston Engines
- Gas-turbine Engines
- Rocket engines
- Ram-jet and Scram-jet engines
- Launching system
Piston Engines :-
Piston engine is kind of airplane propulsion system.It is a internal combustion engine.It uses rich gasoline air mixture as fuel.This airplane propulsion system is also known as Reciprocating engine.This name is given to piston engine as a piston moves up and down i.e. reciprocates to produce power.It works on Otto cycle.A fresh fuel-air mixture enters in cylinder where it is compressed by piston to very high pressure.Here spark is produced by spark plug which burn this mixture at constant volume.High temperature gases pushes piston engine with very high power which is transferred to crank by connecting rod and then to fly wheel.
Major parts of pistons engine are:-
- Inlet valve
- Outlet/Exhaust valve
- Spark plug
- Connecting rod
- Crank Shaft
- Fly wheel
Four Stokes in Piston Engine:-
- Inlet Stroke/Suction Stroke
- Compression Stroke
- Power Stroke
- Exhaust Stroke
some topics like jet propulsion, thrust equation, turbojet, turbofan, ramjet engines are in link given below
Location of Engines:-
- Piston engine are used with propeller and are generally in old aircraft. These are mounted very forward on fuselage.
- Jet Engines are mounted under the wings.Some time at tail portion of fuselage.
- Jet engines are also mounted on both side of fuselage near wing.
Propeller and its uses :-
Propeller basically is a type of fan and one important of airplane propulsion system.It convert rotational motion into thrust.Hence this power is used to propel aircraft.This is done by pressure difference produced forward and rare portion of blade.Blades of propeller is made up of airfoils.This difference in pressure can be understood by Bernoulli equation.
Uses of propeller
Propeller is very common part in airplane Propulsion system .Some example of uses in airplane propulsion are
- Propeller is used with piston engine for production of thrust.
- In turboprop engine propeller is used to produce major thrust.
- Propeller is major cause of thrust generation in helicopters as rotor.
- tail rotor of helicopter is also a propeller.
Basically rocket engine a non-air breathing engine.It has fuel and oxidizer inside the tanks of rocket. itself.this engine is completely in non-contact of external air.This fuel and oxidizer comes in combustion chamber through different pipes.Here combustion occur. Hot gas comes out from convergent-divergent nozzles with very high velocity.Which is used as thrust for forward motion.There are some kinds of rocket engines.
- Liquid propellant rocket engine
- Solid propellant rocket engine