Engines 4: Gas Turbine and Reciprocating Engine Types Flashcards
Thrust Specific Fuel Consumption
The amount of fuel required to produce one pound of thrust
What are the four gas turbine engine types?
Turbojet
Turbofan
Turboprop
Turboshaft
What are the components of a turbojet engine?
Inlet
Compressor
Burner/Combustion Chamber
Turbine
Exhaust Nozzle
How does a turbojet produce thrust?
By accelerating a small mass of air through the engine and expanding the gasses leaving through the exhaust nozzle
What determines the propulsive efficiency of an engine?
By how efficient the propelling mechanism is at converting kinetic energy to propulsive force
What are the advantages of a turbojet engine?
- Best high speed performance
- Best high altitude performance
What are the disadvantages of a turbojet engine?
- Highest Thrust Specific Fuel Consumption
- Longest takeoff rolls
What are the components of a turbofan engine?
Fan
Compressor
Burner/Combustion Chamber
Turbine
Exhaust nozzle
How does a turbofan produce thrust?
By accelerating a large air mass through the fan
How much thrust is produced by the fan on a low bypass turbofan engine?
30%
How much thrust is produced by the fan on a high bypass turbofan engine?
60%
How much thrust is produced by the gas generator exhaust gases on a low bypass turbofan engine?
70%
How much thrust is produced by the gas generator exhaust gases on a high bypass turbofan engine?
40%
What is bypass air?
Airflow that enters the fan and goes around the gas generator part of the turbofan engine
What are the advantages of a turbofan engine?
- Better thrust specific fuel consumption than a turbojet
- Shorter takeoff distances
- Can lift heavier loads
What are the disadvantages of a turbofan engine?
- Large frontal area
- Slower speeds
- Cannot reach higher altitudes like turbojet
What are the components of a turboprop engine?
Propeller assembly (includes the pitch change/dome assembly)
Torquemeter assembly
Gas generator with a reduction Gear Box
How much thrust is produced by the prop on a turboprop engine?
90%
The majority of the thrust from a turboprop comes from the prop
What is the purpose of the reduction gear box in a turboprop engine?
- To ensure that the propeller remains subsonic
- To convert from high RPMs/low torque to low RPMs/high torque
If the propeller went supersonic, it would then become very inefficient in the compressible air
What is the purpose of the torquemeter in a turboprop engine?
To transmit and measure power output from the gas generator
What is the purpose of the propeller in a turboprop engine?
To convert engine power output into forward thrust
How does a turboprop produce thrust?
By accelerating a large mass of air to a moderate speed with a propeller
What are the two major components in a torquemeter assembly?
- Torque shaft (inner shaft)
- Reference shaft (outer shaft)
The torque shaft is connected to the reduction gear box and is the one actually providing torque to the prop
The reference shaft is fixed and doesnt move
What are the advantages of a turboprop engine?
- Low thrust specific fuel consumption
- High thrust at low airspeeds
- Can lift heavy loads off short runways
What are the disadvantages of a turboprop engine?
- Heavy and complicated
- Limited to 450knots
What are the components of a turboshaft engine?
Gas generator
Free turbine/power turbine
What is a free turbine?
A turbine not connected to the compressor and located behind the gas generator
How can a fan on a turbofan engine be driven?
Through the gas generator turbine or a free turbine
What is the purpose of the gas generator in a turboshaft engine?
To provide exhaust gas to drive the free turbine
What is the purpose of the free/power turbine in a turboshaft engine?
It converts the energy from the gas generator into mechanical energy to drive the rotors
Where does all the thrust come from in a turboshaft engine?
The free/power turbine
There is negligible (or 0%) thrust from the exhaust gases
What are the basic components of a reciprocating engine?
Crankshaft
Cylinder
Pistons
Connecting rods
Valves
Valve-operating system
Crankcase
What are the two methods of driving a propeller in a reciprocating engine?
Direct drive (through the crankshaft)
Through a reduction gear box
Bypass Ratio
The ratio of bypass air to air entering the gas generator
How does the bypass ratio affect the performance of a turbofan engine?
The higher the bypass ratio, the more fuel efficient the engine is
