Engines Ch.4

Front 1

Identify the components of a turbojet engine

Back 1

Addition of an Inlet and Exhaust section to the basic gas generator

Front 2

Define thrust specific fuel consumption (TSFC)

Back 2

amount of fuel required to produce one pound of thrust

Front 3

Describe the operation of a turbojet engine

Back 3

Derives its thrust by highly accelerating a small mass of air through the engine. All the air entering the inlet moves through the gas generator. The turbine section of the gas generator extracts only the necessary power from the hot gas stream (75% of the total heat energy) to drive the compressor and accessories. The remaining energy is used for thrust by accelerating the gases out the exhaust section.

Front 4

Compare the propulsive efficiencies of a turbjet, turbofan, and turboprop

Back 4

Turbojet: smaller pe than turbofan at high speeds
turbofan: larger pe than turbojet at high speeds
turboprop: highest pe at low airspeeds but then rapidly decreasing pe as velocity increases to high speeds

Front 5

Compare TSFC of a turbojet with the turbofan

Back 5

Turbofan has a lower TSFC than turbojet

Front 6

Describe the characteristics of a turbojet engine

Back 6

Advantages:
Lightest specific weight
Higher and faster than any other engine

Disadvantages:
Low propulsive efficiency at low forward speeds
Relatively high TSFC at low altitude and low airspeeds
Long takeoff roll required

Best suited for high speed and high altitude flights

Front 7

Identify the components of a turbofan engine

Back 7

Combines the propulsive thrust of the exhaust gases from gas generator with additional thrust that is generated by utilizing a duct-enclosed fan.

Front 8

Describe the basic operation of a turbofan engine

Back 8

Fans that have larger cross section than front of compressor. Allows a relatively large mass of air to bypass the gas generator. On average the bypassed air can produce between 30-60% of the total thrust of a turbofan engine. This fan, driven by the gas generator, provides additional thrust by accelerating a fairly large mass of air around the gas generator. This airflow that goes around the generator is called bypassed or ducted air.

Front 9

Describe the characteristics of a turbofan engine

Back 9

Advantages:
Higher thrust at low airspeeds
Lower TSFC
Shorter Takeoff distance
Considerable noise reduction, 10 to 20% over the turbojet

Disadvantages:
Higher specific weight
Larger frontal area
Inefficient at higher altitudes

Front 10

State the average percentage of total thrust produced by the fan

Back 10

40-70% of total thrust

Front 11

Explain how the fan is driven by the turbine section

Back 11

A free or power turbine which is a turbine aft of the gas generator turbines and is not connected to the gas generator, may drive the fan.
Or, attach the fan directly to the compressor, driven by the gas generator.

Front 12

Define bypass ratio

Back 12

The amount of air that bypasses the gas generator in comparison with the amount of air that passes through the gas generator.

Front 13

Expalin how bypass ratio affects a turbofan engine's TSFC

Back 13

A higher bypass ratio yields a lower TSFC. Inversely related.