Thermodynamics Questions and Answers – Aircraft Propulsion 2021

Thermodynamics Questions and Answers – Aircraft Propulsion 2021

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Aircraft Propulsion”.

A propulsion system is a machine that generates thrust in order to propel a vehicle forward. Thrust is typically developed on aeroplanes by employing Newton’s third law of action and reaction. The engine accelerates a gas, or working fluid, and the reaction to this acceleration creates a force on the engine. Now, MIT researchers have performed their own tests and discovered that ionic thrusters could be a much more powerful means of propulsion than traditional jet engines. They discovered that ionic wind generates 110 newtons of thrust per kilowatt, compared to 2 newtons per kilowatt for a jet engine.

1. In aircraft propulsion the most widely used engine is
a) turbojet
b) turbofan
c) turboprop
d) all of the mentioned

Answer: b
Explanation: A turbine drives a large fan in a turbofan engine, which pushes air through a duct surrounding the engine.

2. 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

Answer: a
Explanation: This is how bypass ratio is described.

3. Increasing the bypass ratio of turbofan engine ____ thrust.
a) does not affect
b) decreases
c) increases
d) none of the mentioned

Answer: c
Explanation: As the bypass ratio rises, the thrust rises with it.

4. Removing the cowl from the fan gives us
a) turbojet
b) turbofan
c) turboprop
d) all of the mentioned
View Answer

Answer: c
Explanation: This is how a turboprop engine is obtained.

5. In turbofans, the bypass ratio is 5-6 and in turboprop it is as high as 100.
a) true
b) false

Answer: a
Explanation: The biggest difference between a turbofan and a turboprop engine is this.

6. 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

Answer: d
Explanation: These are the reasons why gas turbines are used in aircraft propulsion.

7. The type of aircraft gas turbines include
a) turbojet
b) turbofan
c) turboprop
d) all of the mentioned

Answer: d
Explanation: These are the different types of gas turbines used in aircraft.

8. In the ideal case, turbine work is greater than the compressor work.
a) true
b) false

Answer: b
Explanation: In an ideal situation, the turbine function equals the compressor work.

9. The processes in compressor, turbine, diffuser and nozzle are
a) reversible
b) adiabatic
c) reversible and adiabatic
d) none of the mentioned

Answer: c
Explanation: For the aircraft gas turbine, this is an assumption.

10. The thrust developed in turbojet engine is the
a) unbalanced force
b) balanced force
c) both of the mentioned
d) none of the mentioned
View Answer

Answer: a
Explanation: The difference in momentum between air entering the engine and exhaust gases exiting the engine causes it.

11. 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

Answer: b
Explanation: Because of the different combustion rates of gasoline, the mass flow rates at the engine exit and inlet are different.

12. The air-fuel ratio used in jet engine is very small.
a) true
b) false

Answer: b
Explanation: In jet propulsion, the air-fuel ratio is usually very high.

13. 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

Answer: c
Explanation: This is why, in order to conserve fuel, commercial aircraft travel at high altitudes.

14. 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

Answer: d
Explanation: This metric indicates how effectively the energy released during combustion is converted to propellant fuel.

15. We cannot use regenerators and intercoolers on aircraft engines.
a) true
b) false

Answer: a
Explanation: The explanation for this is due to space and weight restrictions.
The power portion of an aircraft propulsion system is the aircraft engine, also known as an aero engine. The majority of aircraft engines are piston or gas turbine engines, but a few have been rocket-powered, and many small UAVs have used electric motors in recent years. The presence of four engines increases the aircraft’s capacity, enabling it to be used as a passenger, freighter, or military aircraft. Many of the first purpose-built jet airliners had four engines, including the world’s first commercial jetliner, the De Havilland Comet.

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