Aircraft Engines Flashcards
Thrust
Force needed to overcome drag.
Gas Turbine Engine
Develops thrust by burning a combustible fuel-air mixture and changing energy of expanding gases into propulsive force. Has a four-cycle process.
4-Cycle Process
Intake, Compression, Combustion, and Exhaust.
Engine Sections
Air Inlet, Compressor, Diffuser, Combustion, Turbine, Exhaust, and Accessory Section.
Air Inlet
Designed to channel incoming air into the compressor with minimum energy loss from ram or drag effects.
Two Functions of Air Inlet
First, recovers as much total pressure as possible and delivers it to the front of the engine. Secondly, delivers air to the compressor inlet with a minimum of turbulence and pressure variations.
Compressor
Primary function is to supply air in sufficient quantity to produce required engine thrust(power).
Main element Of a compressor
Rotor and Stator
Rotor
Blades fixed on a spindle, compresses air at each stage and accelerated it rearward.
Stator
Stationary blades fixed within the engine, act as diffusers at each stage, partially converting high velocity to pressure.
Diffuser
Slows down and evenly spreads out the air for combustion process.
Combustion
Houses the fuel nozzles and igniter plugs.
Fuel Nozzles
Surrounds the combustion chamber and evenly sprays fuel throughout the chamber.
Turbine
Transforms a portion of the energy of the exhaust gases into mechanical energy to drive the compressor and accessories. Absorbs 60% to 80% of total pressure energy from exhaust gases.
Turbine Assembly
Located aft of the combustion chamber, consists of two basic parts; rotor and stator. Construction is similar to compressor.
Stator(TA)
“Turbine Guide Vanes”. Discharges gas at extremely high speed directly onto the rotor assembly. Converts pressure energy into mechanical energy.
Rotor(TA)
“Turbine Wheel”. Blades attached to rotating disk, which is attached to the main power-transmitting shaft of the engine.
Engine Rotor Assembly
Combination of the compressor and turbine rotors on a common shaft.
Exhaust
Direct the flow of hot gases leaving the turbine section.
Accessory
Primarily, it provides space for accessories necessary for operation and control of the engine. Generators and fluid pumps are mounted.
Fluid Pumps
Consists of Hydraulic, Oil, and fuel pumps.
Types of Jet Engines
Turbojet, Turboprop, and Turbofan.
Turbojet
Straight gas turbine engine that gets its thrust by accelerating a mass of air through the engine. All thrust produced occurs within the engine.
Advantages of Turbojet
Best at high speeds for aircraft like fighter jets.
Disadvantages of Turbojet
Cannot produce exceptionally high thrust at low altitudes and speeds.
Turboprop
Combines thrust developed by propeller and thrust produced by the exhaust gases at the exhaust nozzle. Take the max possible gas energy from gas steam. 90% converts to shaft horsepower driving propeller reduction gears and accessories. 10% produces jet thrust as gases exit exhaust nozzle.
Extension Shaft Assembly
Transmits power from the engine to the reduction gear assembly(gearbox).
Reduction Gear Assembly
Reduces high rotation speed if the turbines to a suitable propeller shaft speed. Read case is used for mounting accessories.
Advantages of Turboprop
Develop high thrust at low altitudes, ideal for lifting heavy loads off short or medium length runways.
Disadvantages of Turboprop
Propeller efficiency drops off as airspeed and altitudes increase.
Turbofan
Similar to Turboprop except that an enclosed axial flow fan replaces the geared propeller. Produce between 30% and 85% of total thrust. Fan air exhausts through fan discharge nozzle.
Advantages of Turbofan
Combines good operating efficiency and high thrust capability of the turboprop with the high speed, high altitude capability of the turbojet. Higher and more efficient cruise thrust and lower fuel consumption. Less weight, noise.
Disadvantages of Turbofan
No major disadvantages, almost always power plant for all large conventional military aircraft for this reason.
Engine Ratings
Represent thrust that an engine develops during various operating conditions such as takeoff, climb, and cruise. Manufacturer establishes rating in terms of pounds of thrust.
3 conditions which influence power input of engines
1) Temperature of Atmosphere- High Temp=Less Power/ Low Temp= More Power
2) Pressure of Atmosphere- Low Pressure=Less Power/ High Pressure=More Power
3) Bleed Air extracted from engine.
Flat Related
Refers to the ability of the engine to produce a constant maximum thrust over a wide temperature range.
