# Aircraft Performance Questions and Answers – Thrust Producing Power Plant – 2

This set of Aircraft Performance Questions and Answers for Experienced people focuses on “Thrust Producing Power Plant – 2”.

1. What is thrust drag accounting?
a) Allocation of flow forces to the airframe drag
b) Allocation of flow forces to the wave drag
c) Allocation of flow forces to the induced drag
d) Allocation of flow forces to the parasitic drag

Explanation: The allocation of flow forces to the airframe drag or to the propulsive thrust is known as the thrust drag. It is important to distinguish these force contributions else there results a wrong estimation of the aircraft performance.

2. The net thrust of the powerplant is affected by ____________
a) pressure and temperature
b) altitude andtemperature
c) temperature and mach number
d) mach number and altitude

Explanation: The net thrust of the powerplant is affected by mach number and altitude. As it is not possible to postulate precise function that will relate thrust and mach number and altitude, we develop simple relations that give us the characteristic variation of thrust along with the changes in mach number and altitude.

3. Which of the following is the correct equation for net thrust?
a) FN=ṁ(Vj+V)
b) FN=(Vj-V)
c) FN=ṁ(Vj-V)
d) FN=ṁ(V-Vj)

Explanation: The equation for net thrust is given by FN=ṁ(Vj-V) where FN is net thrust, ṁ is mass flow rate, Vj is exit velocity and V is inlet velocity. In other words the net propulsive force is the difference between the stream force entering and leaving the engine.

4. What is the net thrust of the jet engine if the mass flow rate is 500kg/s, exit velocity is 1000m/s and inlet velocity is 600m/s?
a) 400kN
b) 600kN
c) 500kN
d) 200kN

Explanation: The answer is 200Kn. Given ṁ=500kg/s, Vj=1000m/s and V=600m/s. Substitute the values in the formula, FN=ṁ(Vj-V).
On substituting FN=500 (1000– 600)
On solving FN=20000N.

5. How is thrust related to altitude of an aircraft?
a) Thrust is directly proportional
b) Thrust is indirectly proportional
c) They are independent of each other
d) Thrust increases square of altitude

Explanation: The relation between altitude of an aircraft and thrust is that the thrust is indirectly proportional to the altitude of an aircraft i.e. thrust decreases as there is an increase in the altitude, similarly the thrust increases as there is decrease in the altitude.

6. The velocity of the engine exhaust flow is a function of the temperature of the exhaust gas.
a) True
b) False

Explanation: The velocity of the engine exhaust flow is a function of the temperature of the exhaust gas and this can be determined by the throttle setting. For any given engine thrust setting the exhaust gas velocity can be considered constant.

7. What will be the net thrust when momentum drag is 50N and gross thrust is 400N?
a) 450N
b) 8N
c) 350N
d) 350kN

Explanation: The answer is 350N. Given FG is 400N and Dm is 50N. From the formula, FN=FG-Dm we can find net thrust. Substitute the given values, FN= 400-50.
On solving FN=50N.

Sanfoundry Global Education & Learning Series – Aircraft Performance.

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