Gas Turbine Types

Thrust Specific Fuel Consumption (TSFC)

the amount of fuel required to produce one pound of thrust

Pros of Turbojet

lightest weight per pound of thrust, higher and faster than any other engine, simple

Cons of Turbojet

Low propulsive efficiency at low speed, high TSFC at low altitude and airspeed, long takeoff roll

Turbojet engines are best suited for

high speed and high altitude flying

Turbofan Engine

A cross between turbojet and turboprop, combines propulsive thrust of exhaust gas with additional thrust generated by an inclosed fan

Bypass Ratio

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

Most fuel efficient engines have a higher

Bypass Ratio

Pros of Turbofan Engine

Greater takeoff weight, shorter takeoff distance, quieter, performs better at operational speeds and altitudes

Cons of Turbofan Engine

Limited at higher altitudes and airspeeds, heavier, larger frontal area

Turboprop Engine

couples a gas generator with a reduction gear box and propeller

Propeller Assembly (Turboprop)

Produces 90% of thrust, hydraulically controlled, constant speed, full feathering, and reversable

Reduction Gear Box (Turboprop)

Prevents propeller from reaching supersonic speeds, converts high RPM, low torque to low RPM, high torque

What happens if prop blades reach supersonic speeds

they would lose efficiency due to them slipping through the compressible airflow

Torquemeter Assembly (Turboprop)

transmit and measure power output from gas generator to gear reduction box, accurately measures torsional deflection at torque shaft

Alpha Mode (Turboprop)

flight range, PCL can move from idle to full power and sends signals to FCU for fuel flow

Beta Mode (Turboprop)

only used on the ground, PCL can move from idle to max reverse, increases maneuverability on the ground

Pros of Turboprop

high thrust at low speed; excellent takeoff, slow speed, and low altitude characteristics; superior for heavy loads on short runways

Cons of Turboprop

Heavier, more complicated, limited speeds

Turboshaft Engine

similar to turboprop, except turbine drives a shaft, used in helicopters

Reciprocating Engines

can be inline, opposed, or radial. Driven directly by a crankshaft or through a gear reduction box

Govenor

controls blade angle and propeller speed