# Aircraft Performance Questions and Answers – Cruising Performance – Aircraft with Mixed Power Plants

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This set of Aircraft Performance Multiple Choice Questions & Answers (MCQs) focuses on “Cruising Performance – Aircraft with Mixed Power Plants”.

1. What is a turboprop?
a) It is a combination of turbojet and ramjet
b) It is a combination of turbojet and turbofan
c) It is a combination of turbojet and scramjet
d) It is a combination of turbojet and propeller engine

Explanation: Turbo-prop is a combination of turbojet and propeller engine. The power-plants used in turboprop are mixed power-plants i.e. it is a combination of both thrust producing engine and power producing engine.

2. The residual energy is converted into __________
a) power
b) thrust
c) lift
d) drag

Explanation: The residual energy in the exhaust is converted into thrust by the exhaust nozzle. The shaft power is converted into thrust through the propeller. This way the cruise performance characteristics of an aircraft wiith mixed power-plants lies between that of aircraft with pure thrust or pure power-producing plants.

3. What is the range of thrust producing engine?
a) RT=$$\big[\frac{V_{mdi}}{C_T}E_{max}\big]\big\{\frac{2u^4}{u^4+1}\big\}$$lnω
b) RT=$$\big[\frac{V_{mdi}}{C_T}\big]\big\{\frac{2u^3}{u^4+1}\big\}$$lnω
c) RT=$$\big[\frac{V_{mdi}}{C_T}E_{max}\big]\big\{\frac{2u^3}{u^4+1}\big\}$$lnω
d) RT=$$\big[\frac{V_{mdi}}{C_T}E_{max}\big]\big\{\frac{u^3}{u^4+1}\big\}$$lnω

Explanation: The correct equation for range of thrust producing engine is given by the equation RT=$$\big[\frac{V_{mdi}}{C_T}E_{max}\big]\big\{\frac{2u^3}{u^4+1}\big\}$$lnω where V is true airspeed, C is specific fuel consumption, Emax is endurance and ω is fuel ratio.
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4. What is the range of the power producing engine?
a) RP=$$\big[\frac{\eta}{C_P}E_{max}\big]\big\{\frac{2u^2}{u^4+1}\big\}$$lnω
b) RP=$$\big[\frac{\eta}{C_P}E_{max}\big]\big\{\frac{2u^3}{u^4+1}\big\}$$lnω
c) RP=$$\big[\frac{\eta}{C_P}\big]\big\{\frac{2u^2}{u^4+1}\big\}$$lnω
d) RP=$$\big[\frac{V_{mdi}}{C_P}E_{max}\big]\big\{\frac{2u^3}{u^4+1}\big\}$$lnω

Explanation: The correct equation for range of thrust producing engine is given by the equation RP=$$\big[\frac{\eta}{C_P}E_{max}\big]\big\{\frac{2u^2}{u^4+1}\big\}$$lnω where V is true airspeed, C is specific fuel consumption, Emax is endurance, η is propeller efficiency and ω is fuel ratio.

5. What is the range formula for mixed power-plant?
a) R=Emax$$\big[Π\frac{\eta}{C_P}+(1+Π)\frac{uV_{md}}{C_T}\big]\big\{\frac{2u^2}{u^4-1}\big\}$$lnω
b) R=Emax$$\big[Π\frac{\eta}{C_P}+(1-Π)\frac{uV_{md}}{C_T}\big]\big\{\frac{2u^2}{u^4-1}\big\}$$lnω
c) R=Emax$$\big[Π\frac{\eta}{C_P}+(1-Π)\frac{uV_{md}}{C_T}\big]\big\{\frac{2u^2}{u^4+1}\big\}$$lnω
d) R=Emax$$\big[Π\frac{\eta}{C_P}+(1+Π)\frac{uV_{md}}{C_T}\big]\big\{\frac{2u^2}{u^4+1}\big\}$$lnω

Explanation: The range formula for mixed power-plant is given by the equation R=Emax$$\big[Π\frac{\eta}{C_P}+(1-Π)\frac{uV_{md}}{C_T}\big]\big\{\frac{2u^2}{u^4+1}\big\}$$lnω where Π is the proportion of thrust derived from the shaft power in the overall thrust of the power-plant, CT, CP are the specific fuel consumption of thrust producing and power producing engines, Emax is endurance and V is true airspeed.

6. What is the full form of ESHP?
a) Equivalent shaft horsepower
b) Equal shaft horsepower
c) Engine shaft horsepower
d) Endurance shaft horsepower

Explanation: ESPH stands for Equivalent shaft horsepower. It is the combination of thrust output with the shaft power output to give the total output in power form as if the engine was a pure power producing engine.

7. ESPH is the combination of thrust output and shaft power output.
a) True
b) False

Explanation: ESPH stands for Equivalent shaft horsepower. It is the combination of thrust output with the shaft power output to give the total output in power form as if the engine was a pure power producing engine.

8. The proportions of thrust and power are independent of speed and engine output.
a) True
b) False

Explanation: The proportions of thrust and power are independent of speed and engine output. So there is a need for the calculations of each combination of engine power setting and aircraft speed.

9. The calculations in turboprop aircraft are done in a continuous function.
a) True
b) False

Explanation: The calculations in turboprop aircraft are done in a point to point manner and not in a continuous function. This is because the proportions of thrust and power are independent of speed and engine output. So there is a need for the calculations of each combination of engine power setting and aircraft speed.

10. The expression of range and endurance is written in terms of endurance factor and relative speed function.
a) True
b) False

Explanation: The expression of range and endurance is written in terms of endurance factor and relative speed function. This helps in easy calculations and understanding of cruising performance. This also helps in analyzing the effects of drag characteristics and specific fuel consumption.

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