Chapter 1 Flashcards
The working theory of a gas turbine engine is according to
Newton’s 3rd law
The thrust force generated is according to
Newton’s 2nd law
The compressor in a running gas turbine engine is turned by the
Compressor turbine
What is thrust?
What is generated by?
How is it generated?
the force that propels an object in one direction
the force generated by the engine to propel the aircraft forward
thrust is generated through the reaction of the accelerating mass of air
What are the main modules of a gas turbine engine?
Inlet
Compressor
Combustion Chamber
Turbine
Exhaust
What are the main functions of a compressor in a gas turbine engine?
add energy to the gas
increase the pressure of the gas
increase the temperature of the gas
What are the main functions of the combustion chamber?
add energy to the gas
increase the velocity of the gas
increase the temperature of the gas
What turns the turbine in a gas turbine engine?
the hot air from the combustion chamber
What can be said about the pressure of the gas in the combustion chamber?
pressure is constant in the combustion chamber
What are the main functions of the turbine in a gas turbine engine?
The turbine extracts energy from the hot gases exiting the combustion chamber.
The turbine will then turn the compressor
What can be said about the gas’s velocity, temperature, and pressure at the turbine stage of the gas turbine engine?
velocity increases
temperature and pressure decreases
What happens at the exhaust of a gas turbine engine?
the remaining air that exits the exhaust will produce thrust
What equation can be to explain the effects of a convergent/divergent passage at subsonic flow?
mass flow rate equation
mass flow rate = density x area x velocity
In a convergent passage at supersonic airflow, what can be said about the changes in velocity and pressure?
velocity decrease
pressure increase
In a divergent passage at supersonic airflow, what can be said about the changes in velocity and pressure?
velocity increase
pressure decrease
Which part of the engine is where the pressure is the highest?
combustion chamber/compressor outlet
which part of the engine holds the highest temperature?
the turbine inlet temperature
which part of the engine is the highest stress region in terms of temperature and pressure?
turbine inlet temperature
what are the two types of thrust producing gas turbine engines?
turbojet engine
turbofan engine
what are the two types of torque producing gas turbine engines?
turbo-shaft engine
turboprop engine
how do turbojet engines produce thrust?
by accelerating a small mass of air to a very high velocity to product thrust
how do turboprop engines produce thrust?
by giving a small acceleration to a big mass of air to produce thrust
Why is a reduction gearbox needed in a turboprop engine?
the propeller in a turboprop engine needs to rotate at a lower RPM than the turbine, thus a reduction gearbox is used. This is to ensure the velocity does not exceed M1.0 to prevent the blade from stalling.
a free turbine is a turbine that is?
A free turbine is not mechanically connected with the compressor
what is meant by a 3 stage axial flow compressor?
the compressor has 3 stages.
Axial means the air goes in and comes out linearly, in the same direction
what is meant by a centrifugal compressor?
it is a compressor whereby :
air goes in linearly
air goes out diagonally usually at a 90 degree angle
What is the airworthiness standard chapter for aircraft engine in FAR
FAR Part 33
describe an air-breathing gas turbine engine
an engine that uses atmospheric air as a working fluid
What is inlet momentum drag (ram drag)?
inlet momentum drag (ram drag) is the difference between gross thrust and net thrust
What causes inlet momentum drag(ram drag)?
- inlet momentum drag(ram drag) is caused by the momentum of the mass of air entering the engine inlet
- inlet momentum drag(ram drag) is caused by the increasing speed of air that enters the engine inlet
inlet momentum drag(ram drag) causes ?
reduced thrust
For aviation applications, turboshaft engines are only used on?
APU & helicopters
What is the main purpose of the turbofan engine?
to turn the fan.
Compare the propulsive efficiency of turbojet turboprop and turbofan engines
- turbojet engines have low propulsive efficiency at low altitudes and low airspeed. its propulsive efficiency will increase with an increase in altitude and airspeed because it is best used at high altitude and high airspeed
- turboprop engines have high propulsive efficiency at low altitudes and low airspeed. Its propulsive efficiency will decrease rapidly with an increase in altitude and airspeed
- turbofan engines have low propulsive efficiency at low altitudes and low airspeed. Its propulsive efficiency will increase with an increase in altitude and airspeed up to sonic speed
compare the thrust-specific fuel consumption (TSFC) of turbojet, turboprop, and turbofan engines.
- turbojet engines have relatively high TSFC at low altitudes and low airspeed however its TSFC will decrease with an increase in altitude and airspeed.
- turboprop engines have low TSFC at low altitudes and low airspeed however its TSFC will increase with an increase in altitude and airspeed.
- the TSFC of a turbofan engine falls in between a turbojet engine and a turboprop engine.
compare the takeoff roll between turbojet engine and turboprop engine
turbojet engine requires a longer takeoff roll
turboprop engine requires a shorter takeoff roll
compare the frontal area between turbojet and turboprop engines
turbojet - smaller frontal area, reduced ground clearance issues
turboprop - large frontal area, requires longer landing gear
describe propulsive efficiency
it refers to the fuel consumption vs thrust produced by the engine
what is (TSFC)?
It refers to thrust-specific fuel consumption. it measures the fuel efficiency of an engine design with respect to its thrust output.
LOW TSFC = high efficiency
HIGH TSFC = low efficiency
What are the advantages of a gas turbine engine over a reciprocating engine?
V.F.F.L.A.S.H.
Very High power to weight ratio
far less vibration
fewer moving parts
low lubricating oil cost and consumption
ability to generate higher thrust
smaller in size
high operation speeds
what are the disadvantages of gas turbine engines compared to a reciprocating engine?
C.U.M.D.
Cost is much greater - stronger and more heat resistant materials required
usually less fuel-efficient, especially at idle
machining operations are more complex
delayed response to changes in power settings
