# Aircraft Performance Questions and Answers – Cruise Method 3

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This set of Aircraft Performance Multiple Choice Questions & Answers (MCQs) focuses on “Cruise Method 3”.

1. Which factor must be reduced in cruise method 3?
a) Mach number
b) Angle of attack
c) Altitude
d) Temperature

Explanation: The factor that must be reduced in cruise method 3 (also known as constant mach number and constant altitude method) is angle of attack. Also the ratio of weight to lift coefficient and relative airspeed are kept constant i.e. W/CL ratio and u are constant throughout the method.

2. Which of the following indicates the range formula in cruise method 3?
a) R=$$\frac{1}{C}\Big(\frac{2}{\rho SC_L}\Big)^{\frac{1}{2}}\int_{W_i}^{W_f}\frac{dW}{W^{\frac{1}{2}}}$$
b) R=$$\Big(\frac{2}{\rho SC_L}\Big)^{\frac{1}{2}}\frac{L}{D}\int_{W_i}^{W_f}\frac{dW}{W^{\frac{1}{2}}}$$
c) R=$$\Big[\frac{V_{mdi}}{C}E_{max}\Big]2u_i\Big\{tan^{-1}\Big[\frac{1}{u_{i}^2}\Big]+tan^{-1}\Big[\frac{1}{\omega u_{i}^2}\Big]\Big\}$$
d) R=$$\Big[\frac{V_{mdi}}{C}E_{max}\Big]2u_i\Big\{tan^{-1}\Big[\frac{1}{u_{i}^2}\Big]-tan^{-1}\Big[\frac{1}{\omega u_{i}^2}\Big]\Big\}$$

Explanation: The correct equation of cruise method 3 is R=$$\Big[\frac{V_{mdi}}{C}E_{max}\Big]2u_i\Big\{tan^{-1}\Big[\frac{1}{u_{i}^2}\Big]-tan^{-1}\Big[\frac{1}{\omega u_{i}^2}\Big]\Big\}$$ where R is range of the cruise, C is specific fuel consumption, Emax is endurance, Vmdi is relative airspeed and ω is fuel ratio.

3. Which of the following is the correct integrated range equation of cruise method 3?
a) R=$$\frac{1}{C}\Big(\frac{2W_i}{S\rho}\Big)^{\frac{1}{2}}\frac{C_L}{C_D}2\Big(1-\omega^{\frac{-1}{2}}\Big)$$
b) R=$$\frac{V}{C}\int_{W_i}^{W_f}\frac{dW}{D}$$
c) R=$$\Big[\frac{V_{mdi}}{C}E_{max}\Big]2u_i\Big\{tan^{-1}\Big[\frac{1}{u_{i}^2}\Big]-tan^{-1}\Big[\frac{1}{\omega u_{i}^2}\Big]\Big\}$$
d) R=$$\frac{1}{C}\Big(\frac{2W_i}{S\rho}\Big)^{\frac{1}{2}}\frac{C_{L}^{0.5}}{C_D}2\Big(1-\omega^{\frac{-1}{2}}\Big)$$

Explanation: The correct equation of cruise method 3 is R=$$\frac{V}{C}\int_{W_i}^{W_f}\frac{dW}{D}$$ where R is range, V is velocity, C is specific fuel consumption, D drag and Wf, Wiare final and initial weights.
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4. Cruise method 3 is also known as ____________
a) constant angle of attack and variable mach number
b) constant angle of attack and constant mach number
c) constant angle of attack and constant altitude number
d) constant mach number and constant altitude number

Explanation: Cruise method 3 also known as constant altitude and constant mach number method. In cruise method 3 altitude, mach number and relative airspeed are kept constant i.e. M, u and h are constant throughout the method.

5. Which factor is not a constant factor in cruise method 3?
a) Mach number
b) Angle of attack
c) Altitude
d) Relative air speed

Explanation: The factor that must be reduced in cruise method 3 (also known as constant angle of attack and constant altitude method) is angle of attack. Also the ratio of weight to lift coefficient and relative airspeed are kept constant i.e. W/CL ratio and u are constant throughout the method.

6. The range factor of cruise method 3 is identical to that of cruise method 1.
a) True
b) False

Explanation: In cruise method 3 the range factor is given by R=$$\Big[\frac{V_{mdi}}{C}E_{max}\Big]2u_i\Big\{tan^{-1}\Big[\frac{1}{u_{i}^2}\Big]-tan^{-1}\Big[\frac{1}{\omega u_{i}^2}\Big]\Big\}$$ where $$\Big[\frac{V_{mdi}}{C}E_{max}\Big]$$ is range factor and range pf aircraft is function of the range factor of the aircraft.

7. The endurance of cruise method 3 is identical to that of cruise method 1.
a) True
b) False

Explanation: The endurance of cruise method 3 is not identical to that of cruise method 1. E=$$\Big[\frac{E_{max}}{C}\Big]2\Big\{tan^{-1}\Big[\frac{1}{u_{i}^2}\Big]-tan^{-1}\Big[\frac{1}{\omega u_{i}^2}\Big]\Big\}$$where where V is true airspeed, C is specific fuel consumption, Emax is endurance, u is relative airspeed and ω is fuel ratio.

8. Which of the following is a reason of disadvantage of cruise method 3?
a) Increased mach number
b) Fuel saving
c) Increased time of flight
d) Increased weight of aircraft

Explanation: The disadvantage of cruise method 3 is that to compensate the weight of aircraft the mach number and relative airspeed are decreased and there is an increase in the time of flight thus does not making any fuel saving.

9. In which of the following cases cruise method 3 is used?
a) Commercial aircraft
b) Fighter aircraft
c) Military
d) Patrol and surveillance

Explanation: Cruise method 3 is used mainly for patrol and surveillance purposes as there is more endurance and time of flight and short range which is best suitable for the surveillance purpose. Rather than cruise method 3 we use cruise method 2.

10. In Cruise method 3 endurance is more concentrated than distance travelled.
a) True
b) False

Explanation: In cruise method 3 endurance is not much concentrated rather distance travelled is concentrated. This is the reason which makes this cruise method 3 best suitable for patrol and surveillance purposes which mainly prefer more endurance and time of flight.

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