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Accessory Drive

The accessory drive section is attached to the outside bottom or side of the engine and

is where all the mechanically-driven components are mounted to the engine. This

section takes mechanical energy from the engine to power the engine and aircraftaccessories mounted to the accessory gearbox.

Afterburner

The afterburner is an assembly aft of the turbine section that supplies atomized fuel into

the exhaust airflow to increase exhaust temperature and pressure. Afterburners use

large quantities of fuel, and thus are used for short periods of time only. Afterburners

are used on turbojet engines to increase thrust for short periods of time during takeoff,

climb and supersonic flight. Very few commercial aircraft use afterburners. Afterburners

are usually on military aircraft only.Augmentor

Augmentors are afterburners on low-bypass turbofan engines. Core airflow and bypass

(fan) airflow are mixed aft of the turbines, in the exhaust. Fuel nozzles supply atomized

fuel into the airflow and an igniter ignites the fuel/air mixture. Augmentors are used on

low-bypass turbofan engines to increase thrust for short periods during takeoff, climb,

and combat flight.

Augmentor Exhaust Nozzles

Augmentor exhaust nozzles make up the aft end of augmented low-bypass turbofanengines. It has a flame holder, fuel nozzles, an igniter, and a variable exhaust nozzle.

The fuel nozzles supply atomized fuel into the exhaust airflow and the igniter makes the

fuel/air mixture burn. Augmentor exhaust nozzles are used on low-bypass turbofan

engines to increase thrust.

Combustor

In the combustor, compressed air generated by the compressor is mixed with fuel and

then ignited. Nozzles spray fuel into the stream of air and the mixture of air and fuel is

ignited providing an extremely hot and powerful airflow. The fuel burns with the oxygen

in the compressed air, producing hot expanding gases. The inside of the combustor is

often made of ceramic materials to provide a heat-resistant chamber. Temperatures in

the combustor can reach 2700F.

Compressor


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The compressor is the first component in the core of the engine. It is made up of a

series of fans with many blades and is attached to the shaft. The compressor squeezes

air that enters it into progressively smaller areas, resulting in an increase in the air

pressure. The result is an increase in the energy potential of the air. The compressed

air is then forced into the combustion chamber.Convergent-Divergent Exhaust Nozzle

A variable convergent-divergent (C-D) exhaust nozzle (Iris) is made up of flaps that

interlock. The C-D exhaust nozzle is automatically controlled to improve subsonic and

supersonic flight of jet aircraft.

As the exhaust nozzle converges, the exhaust gases are subsonic. As the exhaust

nozzle diverges the gases become supersonic. Supersonic flight requires a C-D

exhaust nozzle. A variable C-D exhaust nozzle is used on modern supersonic aircraft. A

variable C-D exhaust nozzle is more efficient than a fixed C-D exhaust nozzle.Core

The core engine module is aft of the fan module and forward of the turbine stator case

and is made up of three components: compressor rotor and stator, combustion liner and

Stage 1 HPT nozzle. The core is responsible for supplying approximately 20 percent of

the total engine thrust and the torque for operation of all accessories.

Exhaust

The exhaust section is located behind the turbine section and at the rear of the engine.

It is made up of either a fixed or variable nozzle assembly, depending on the aircraftapplication. The exhaust section directs the exhaust gases aft and further accelerates

the exhaust gases to produce forward thrust. Variable nozzles are usually found on

military engines while fixed are typically associated with commercial turbofans.

Fan

The fan is the first component on the engine. The spinning fan sucks in large quantities

of air. Most blades of the fan are made of titanium. It then speeds this air up and splits it

into two parts. One part continues through the "core" or center of the engine, where it is

acted upon by the other engine components. The fan module typically suppliesapproximately 80 percent of the engine thrust.

The second part "bypasses" the core of the engine. It goes through a duct that

surrounds the core to the back of the engine where it produces much of the force that

propels the airplane forward. This cooler air helps to quiet the engine as well as adding

thrust to the engine.


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Gas Turbine

Another term for an aircraft engine.

High-Pressure Turbine (HPT)

The HPT module is aft of the compressor rear frame and forward of the LPT stator

case. The HPT module is made up of the HPT rotor and HPT stator and is removesenergy from the combustion gases to turn the high-pressure compressor and accessory

gearbox.

Inlet

The inlet sends air to the forward end of the compressor. The inlet is aerodynamically

designed to insure a smooth, evenly distributed airflow into the engine.

Laws of Motion

Sir Isaac Newton proposed three laws of motion.

1. If an object is not moving, it will not start moving by itself. If an object is

moving, it will not stop or change direction unless something pushes it.

2. Objects will move farther and faster when they are pushed harder.

3. When an object is pushed in one direction, there is always a resistance of the

same size in the opposite direction.

Lift

A force that pushes objects upward.Low-Pressure Turbine (LPT)

The LPT module is the in the rear of the engine, aft of the HPT stator case. LPT

components include the LPT rotor, LPT nozzle stator case and turbine rear frame. The

LPT removes energy from the combustion gases to drive the low-pressure compressor

(N1) rotor assembly.

Mach 1

Breaking the speed of sound. Mach 1 is equivalent to 760 miles per hour.

Nozzle

The nozzle is the exhaust duct of the engine. This is the engine part that actually

produces the thrust for the plane. The energy depleted airflow that passed the turbine,

in addition to the colder air that bypassed the engine core, produces a force when

exiting the nozzle that acts to propel the engine, and therefore the airplane, forward.


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The combination of the hot air and cold air are expelled and produce an exhaust, which

causes a forward thrust.

Propulsion

(as a field of study in relation to Aeronautics) is the study of how to design an engine

that will provide the thrust that is needed for a plane to take off and fly through the air.

Regimes of Flight

The ranges of speed that airplanes fly. Subsonic: 100-350 MPH. Transonic: 350-750

MPH. Supersonic:760-3500 MPH. Hypersonic: 3500-7000 MPH

Shock Wave

A series of air waves that form in front of a fast moving plane. In order to travel faster

than sound the plane must push through these waves. This creates a sonic boom.

Sonic BoomWhen a plane pushes through a shockwave it creates a sonic boom. The noise is the

result of breaking through the airwaves that form in front of a fast moving plane. The

sonic boom sounds when the plane is going faster than 760 MPH.

Sound Waves

Sound is made up of molecules of air that move. When they push together they form

sound waves.

Speed of Sound

When a plane travels faster than 760 a sound barrier forms in front of the plane. If aplane is going at the speed of sound it is traveling at Mach 1.

Subsonic

Subsonic is a speed of 100-350 MPH. Small planes such as crop dusters and

seaplanes are examples of planes that travel at this speed.

Suck-Squeeze-Bang-Blow

The term that is generally used to describe the operation of a jet engine. The fan sucks

in the air, the compressor squeezes the air down, the combustor ignites the mixture

(bang) and the turbine blows the air out the back creating thrust and turning the forwardfan.

Supersonic

Planes that travel faster than Mach 1 (or the speed of sound) are traveling at supersonic

speeds. An example is the commercial Concorde. The aircraft's speed averages more

than 760 miles per hour.


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Thrust

The forward force that pushes the engine and, therefore, the airplane forward. Sir Isaac

Newton discovered that for "every action there is an equal and opposite reaction."

Aircraft engine use this principle.

Thrust Reverser

Thrust reversers serve as an aircraft's main brakes on landing. There are three types of

thrust reversers: translating cowl, clam shell and turboprop reverse pitch. All three

literally reverse the engines thrust by closing in when deployed by the pilot pushing the

air out the front of the engine rather than the back. This motion decreases the speed of

the aircraft and is the loud noise you hear when landing.

Transonic

This speed of flight includes most of the commercial flights that carry passengers and

cargo. Transonic speed is 350 - 750 MPH.

Turbine

Located behind the combustor, the turbine section uses energy in the rapidly moving,

hot gases coming out of the combustion section to turn a shaft to drive the compressor

and other engine accessories.

Turbojet

Air taken in from an opening in the front of the engine is compressed up to 3 to 12 times

its original pressure in compressor. Fuel is added to the air and burned in a combustion

chamber to raise the temperature of the fluid mixture to about 1,100F to1,300F. The resulting hot air is passed through a turbine, which drives the

compressor. If the turbine and compressor are efficient, the pressure at the turbine

discharge will be nearly twice the atmospheric pressure, and this excess pressure is

sent to the nozzle to produce a high-velocity stream of gas which produces a thrust.

Substantial increases in thrust can be obtained by employing an afterburner. It is a

second combustion chamber positioned after the turbine and before the nozzle. The

afterburner increases the temperature of the gas ahead of the nozzle. The result of this

increase in temperature is an increase of about 40 percent in thrust at takeoff and a

much larger percentage at high speeds once the plane is in the air.

The turbojet engine is a reaction engine. In a reaction engine, expanding gases push

hard against the front of the engine. The turbojet sucks in air and compresses or

squeezes it. The gases flow through the turbine and make it spin. These gases bounce

back and shoot our of the rear of the exhaust, pushing the plane forward.


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Turboprop

A turboprop is a jet engine attached to a propeller. The turbine at the back is turned by

the hot gases generated by the engine, and this turns a shaft that drives the propeller. A

variety of smaller aircraft are powered by turboprops.

Like the turbojet, the turboprop engine consists of a compressor, combustion chamber,and turbine, the air and gas pressure is used to run the turbine, which then creates

power to drive the compressor. Compared with a turbojet engine, the turboprop has

better propulsion efficiency at flight speeds below about 500 miles per hour. Modern

turboprop engines are equipped with propellers that have a smaller diameter but a

larger number of blades for efficient operation at much higher flight speeds. To

accommodate the higher flight speeds, the blades are scimitar-shaped with swept-back

leading edges at the blade tips. Engines featuring such propellers are called propfans.

TurbofanA turbofan engine has a large fan at the front, which sucks in air. Most of the air flows

around the outside of the engine, making it quieter and giving more thrust at low

speeds. Most of today's airliners are powered by turbofans. In a turbojet all the air

entering the intake passes through the gas generator, which is composed of the

compressor, combustion chamber, and turbine. In a turbofan engine only a portion of

the incoming air goes into the combustion chamber. The remainder passes through a

fan, or low-pressure compressor, and is ejected directly as a "cold" jet or mixed with the

gas-generator exhaust to produce a "hot" jet. The objective of this sort of bypass system

is to increase thrust without increasing fuel consumption. It achieves this by increasingthe total air-mass flow and reducing the velocity within the same total energy supply.

Turboshaft

This is another form of gas-turbine engine that operates much like a turboprop system.

It does not drive a propeller. Instead, it provides power for a helicopter rotor. The

turboshaft engine is designed so that the speed of the helicopter rotor is independent of

the rotating speed of the gas generator. This permits the rotor speed to be kept constant

even when the speed of the generator is varied to modulate the amount of power

produced.Vectoring

Vectoring is the procedure that makes the exhaust nozzle structure turn to make

forward, vertical or side-to-side thrust. Vectoring supplies the directional thrust

necessary for vertical take off and landing (VTOL) and short take off and landing


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(STOL) military aircraft. Vectoring also gives aircraft a better rate of climb and increases

control during flight.

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