# Aircraft Performance Questions and Answers – Minimum Drag Speed

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This set of Aircraft Performance Multiple Choice Questions & Answers (MCQs) focuses on “Minimum Drag Speed”

1. What is the correct expression for induced drag?
a) $$\frac{ZW^2}{V^2_e}$$
b) YVe2
c) $$\frac{ZW^2}{V_e}$$
d) YVe

Explanation: The correct expression for induced drag is $$\frac{ZW^2}{V^2_e}$$ where W is weight, V is velocity, Z is constant. Induced drag is the function of lift and caused when an aircraft is moving in the air.

2. What is the correct expression for pressure drag?
a) $$\frac{ZW^2}{V^2_e}$$
b) YVe2
c) $$\frac{ZW^2}{V_e}$$
d) YVe

Explanation: The correct expression for pressure drag is YVe2 where Y is a constant and V is velocity. Pressure drag is caused due to the resultant pressure distribution over a surface of the body. It is generally occurred in turbulent flow.

3. Which of the following is correct equation?
a) D=YVee+$$\frac{ZW^2}{V^2_e}$$
b) CD=CDz-KCL2
c) D=Dz-Di
d) Vemd=$$\sqrt{\frac{ZW^2}{Y}}$$

Explanation: The correct equation is D=YVee+$$\frac{ZW^2}{V^2_e}$$ where Y is a constant, V is velocity, W is weight, V is velocity, Z is constant and D is total drag. The total drag is the sum of pressure drag and induced drag.
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4. Which of the following is the correct equation for minimum speed drag?
a) Vemd=$$\sqrt{\frac{ZW^2}{Y}}$$
b) Vemd=$$\sqrt{\frac{ZW^2}{Y}}$$
c) Vemd=$$\sqrt{\frac{ZW^2}{Y^2}}$$
d) Vemd=$$\sqrt{\frac{ZW^2}{Y^2}}$$

Explanation: The correct equation for minimum speed drag is Vemd=$$\sqrt{\frac{ZW^2}{Y}}$$ where Y is a constant, V is velocity, W is weight, Y is a constant and Vemd is minimum speed drag. Induced drag is the function of lift and caused when an aircraft is moving in the air.

5. The minimum drag speed determines the best operating speeds of aircraft with thrust producing engines.
a) True
b) False

Explanation: The minimum drag speed determines the best operating speeds of aircraft with thrust producing engines. The correct equation for minimum speed drag is Vemd=$$\sqrt{\frac{ZW^2}{Y}}$$ where Y is a constant, V is velocity, W is weight, Y is a constant and Vemd is minimum speed drag. Induced drag is the function of lift and caused when an aircraft is moving in the air.

6. The lift-dependent drag is reduced with the reduction in total drag.
a) True
b) False

Explanation: The lift-dependent drag is reduced with the reduction in total drag. Along with this the minimum air drag speed is also reduced. The total drag is the sum of pressure drag and induced drag.

7. The total drag is the sum of pressure drag and induced drag.
a) True
b) False

Explanation: The total drag is the sum of pressure drag and induced drag. The correct equation is D=YVee+$$\frac{ZW^2}{V^2_e}$$ where where Y is a constant, V is velocity, W is weight, V is velocity, Z is constant and D is total drag. The total drag is the sum of pressure drag and induced drag.

8. What is overall drag force?
a) The sum of drag force, zero-lift drag, lift-dependent drag and volume dependent wave drag
b) The sum of lift-dependent drag and volume dependent wave drag
c) The sum of drag force, lift-dependent drag and volume dependent wave drag
d) The sum of drag force, zero-lift drag and lift-dependent drag

Explanation: Overall drag force is the sum of drag force, zero-lift drag, lift-dependent drag and volume dependent wave drag. It is given that the mach number is a function of all the mentioned factors.

9. The drag polar curve is parabolic in shape for subsonic performance aircrafts.
a) True
b) False

Explanation: The drag polar curve is parabolic in shape for subsonic performance aircrafts. The drag polar curve is the graph plotted between the lift coefficient of the aircraft and the drag coefficient of the aircraft.

10. Which of the following is the correct equation for the Prandtl-Glauert factor?
a) β=$$\sqrt{1-M^2}$$
b) β=$$\sqrt{1-M}$$
c) β=$$\sqrt{M^2-1}$$
d) β=$$\sqrt{1+M^2}$$

Explanation: The correct equation for the Prandtl-Glauert factor is β=$$\sqrt{1-M^2}$$ where β is Prandtl-Glauert factor and M is mach number. This Prandtl-Glauert factor equation is applicable only in cases of subsonic airflow i.e. M<1.

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