Engine Vocabulary

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 aircraft accessories mounted to the accessory gearbox.


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.


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 turbofan engines. 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.


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 2700ºF.


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.


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.


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 aircraft application. 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.


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 supplies approximately 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.

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 removes energy from the combustion gases to turn the high-pressure compressor and accessory gearbox.


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.


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.


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. The combination of the hot air and cold air are expelled and produce an exhaust, which causes a forward thrust.


(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 Boom

When 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 a plane is going at the speed of sound it is traveling at Mach 1.


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.


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 forward fan.


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.


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.


This speed of flight includes most of the commercial flights that carry passengers and cargo. Transonic speed is 350 - 750 MPH.


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.


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 1,100ºF to 1,300ºF. 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.


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.


A 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 increasing the total air-mass flow and reducing the velocity within the same total energy supply.


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