Aircraft Engines Flashcards
What is the reciprocating engine theory of operation?
A reciprocating engine is an internal combustion device that converts the energy in fuel into mechanical energy. A compressed fuel/air charge is burned in each cylinder of the engine which pushes the pistons down. The movement of the pistons then rotates the crankshaft and transfers the rotation to the propeller. A camshaft is geared to the crankshaft to enable valves to open and close at precise times. The valves let the fuel/air mixture into each cylinder and, after the charge is burned, the valves let the exhaust gases out. Magnetos develop a high-tension current that is distributed to successive cylinders at the precise time it is advantageous to ignite the fuel air mixture.
Remember intake, compression, power, and exhaust strokes.
What is the basic radial engine design and how does it operate?
Radial engines are simply reciprocating engines with the cylinders arranged radially around a central crankcase and crankshaft. It operates like any other 4-stroke cycle reciprocating engine.
What is firing order and how is it determined?
The firing order of an engine is the sequence in which the power event occurs in the different cylinders. Provides balance and eliminates vibration. It is set by the engineers of the engine.
Why are valves adjusted on a radial engine?
Reciprocating engines with solid lifters or cam followers generally require the valve clearance to be adjusted manually by adjusting a screw and locknut. Valve clearance is needed to assure that the valve has enough clearance in the valve train to close completely. Hydraulic lifters automatically keep the valve clearance at zero.
What is the purpose of a master rod and articulating rods?
The master rod serves as the connecting link between the piston pin and the crankpin. The crankpin end contains the master rod bearing. Flanges around the large end of the master rod provide for the attachment of articulating rods. The master and articulating rod assembly is commonly used on radial engines. In radial engines, the piston in one cylinder in each row is connected to the crankshaft by the master rod. All other pistons in the row are connected to the crankshaft through the master rod via the articulating rods.
What is the purpose, function, and operation of multiple springs on a valve?
The function of the valve springs is to close the valve and to hold the valve securely on the valve seat. The purpose of having two or more valve springs on each valve is to prevent vibration and valve surging at certain speeds. The springs are arranged one inside the other and vibrate at different engine speeds. The result is rapid damping of all spring-surge vibrations.
What is propeller reduction gearing and why is it used?
Propeller reduction gearing is used to allow the engine to turn at a high RPM while keeping the propeller speed lower and efficient. The propeller is geared to the engine crankshaft in such a way as to make the propeller not turn as fast as the engine. There are three common types of reduction gearing: spur planetary, bevel planetary, and spur and pinion.
What is the basic theory of operation of a gas turbine engine?
A gas turbine engine is an internal combustion engine. Like a reciprocating engine, the functions of intake, compression, combustion, and exhaust are all required. The difference is that, in a turbine engine, these functions happen in dedicated sections of the engine and they happen continuously. Air is taken in at the front of the engine and is compressed in the compressor section. From there it is sent through a diffuser to the combustion section where fuel is discharged and combustion takes place. The energy in the fuel is released and is directed into the turbine section. Turbine wheel(s) extract the energy in the burning fuel. Depending on the engine type, the energy is converted into rotational mechanical energy to operate the engine and create thrust by turning a fan, propeller, or rotor.
What are some causes for turbine engine performance losses?
The thermal efficiency of a gas turbine engine is a prime factor in performance. This is the ratio of the net work produced by the engine to the chemical energy supplied in the fuel. The turbine inlet temperature, compression ratio, and component efficiencies are the three most important factors affecting thermal efficiency. Temperature limits must be adhered to or the turbine section can be overheated and destroyed. If the efficiency of the engine components is reduced,
then engine performance will reduce.
(Thermal efficiency and Damaged or worn components)
What is the purpose of a turbine engine diffuser?
The diffuser is the divergent section of the engine after the compressor and before the combustion section. It functions to reduce the velocity of the compressor discharge air and increase its pressure so that it can be combined with fuel and burned in the combustion section.
What type of engine is a typical Auxiliary Power Unit (APU)? What is its function and how does it operate?
A typical APU is a turboshaft gas turbine engine that is made to transfer horsepower to a shaft. The shaft turns the engine compressor from which bleed air for the aircraft is obtained. It also drives an accessory gearbox that rotates a generator. The generator supplies the aircraft with electrical power on the ground and in the air.
The APU is often operated with no personnel on the flight deck.
