This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Aircraft Propulsion”.
1. Gas turbines are used in aircraft propulsion because
a) they are light
b) they are compact
c) they have high power-to-weight ratio
d) all of the mentioned
View Answer
Explanation: These are the reasons why aircraft propulsion uses gas turbines.
2. The type of aircraft gas turbines include
a) turbojet
b) turbofan
c) turboprop
d) all of the mentioned
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Explanation: These are the types of aircraft gas turbines.
3. In the ideal case, turbine work is greater than the compressor work.
a) true
b) false
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Explanation: The turbine work is equal to the compressor work in ideal case.
4. The processes in compressor, turbine, diffuser and nozzle are
a) reversible
b) adiabatic
c) reversible and adiabatic
d) none of the mentioned
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Explanation: This is an assumption for the aircraft gas turbine.
5. The thrust developed in turbojet engine is the
a) unbalanced force
b) balanced force
c) both of the mentioned
d) none of the mentioned
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Explanation: It is caused by the difference in momentum of air entering the engine and exhaust gases leaving the engine.
6. Which of the following statement is true?
a) mass flow rates of gases at engine inlet and exit are same
b) the pressure at inlet and exit of engine are ambient pressures
c) both of the mentioned
d) none of the mentioned
View Answer
Explanation: The mass flow rates at engine exit and inlet are different because of different combustion rate of fuel.
7. The air-fuel ratio used in jet engine is very small.
a) true
b) false
View Answer
Explanation: The air-fuel ratios used in jet propulsion is usually very high.
8. When flying at high altitudes,
a) air is of less density
b) air exerts less drag force on aircraft
c) both of the mentioned
d) none of the mentioned
View Answer
Explanation: This is the reason why commercial airplanes fly at high altitudes to save fuel.
9. The propulsive efficiency is given by
a) work done by engine / propulsive power
b) propulsive power / work done by engine
c) energy input rate / propulsive power
d) propulsive power / energy input rate
View Answer
Explanation: This tells us how efficiently the energy which is released during combustion is getting converted to propulsive power.
10. We cannot use regenerators and intercoolers on aircraft engines.
a) true
b) false
View Answer
Explanation: The reason being space and weight limitations.
11. In aircraft propulsion the most widely used engine is
a) turbojet
b) turbofan
c) turboprop
d) all of the mentioned
View Answer
Explanation: In turbofan engine, turbine drives a large fan which forces air through a duct surrounding the engine.
12. The bypass ratio is the ratio of
a) mass flow rates of two streams
b) pressure ratio of inlet and exit
c) volume flow rate of inlet and exit
d) none of the mentioned
View Answer
Explanation: This is the definition of bypass ratio.
13. Increasing the bypass ratio of turbofan engine ____ thrust.
a) does not affect
b) decreases
c) increases
d) none of the mentioned
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Explanation: As the bypass ratio increases, the thrust also increases.
14. Removing the cowl from the fan gives us
a) turbojet
b) turbofan
c) turboprop
d) all of the mentioned
View Answer
Explanation: This is how we get a turboprop engine.
15. In turbofans, the bypass ratio is 5-6 and in turboprop it is as high as 100.
a) true
b) false
View Answer
Explanation: This is the main difference in turbofan and turboprop engine.
Sanfoundry Global Education & Learning Series – Thermodynamics.
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