# Aircraft Performance Questions and Answers – Drag Force

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

1. Total drag is the sum of ______________
a) lift dependent drag and lift independent drag
b) lift dependent drag, lift independent drag and volume dependent wave drag
c) lift dependent drag and volume dependent wave drag
d) volume dependent wave drag and lift independent drag

Explanation: Total drag is the sum of lift dependent drag, lift independent drag and volume dependent wave drag. Also, in high subsonic mach number a value dependent wave drag is induced.

2. In high subsonic mach number a value dependent wave drag is not induced.
a) True
b) False

Explanation: In high subsonic mach number a value dependent wave drag is induced. The components that act on the aircraft moving at high subsonic mach number are lift dependent drag, lift independent drag and volume dependent wave drag.

3. Which of the following is the correct relation between lift dependent drag, lift independent drag and drag coefficient?
a) CD=CDz+KCL2
b) CD=CDz-KCL2
c) CD=CDz*KCL2
d) CD=CDz/KCL2

Explanation: The correct relation between lift dependent drag, lift independent drag and drag coefficient is CD=CDz+KCL2 where CD is drag coefficient, CDz is lift independent drag, CL is lift independent drag and K is a constant.

4. There are three types of drag.
a) True
b) False

Explanation: There are three types of drag. They are parasitic drag which is further divided into form drag and skin friction drag. The second kind of drag is lift-induced drag and third type of drag is wave drag.

5. Which of the following are the two types of lift independent drag?
a) surface friction drag and profile drag
b) induced drag and profile drag
c) surface friction drag and induced drag
d) parasitic drag and induced drag

Explanation: Lift independent drag is divided into two types. They are the surface friction drag and the profile drag. Surface friction drag corresponds to 75% of the lift independent drag whereas the profile drag leads to 25% of the lift independent drag.
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6. Surface friction drag corresponds to 35% of the lift independent drag whereas the profile drag leads to 65% of the lift independent drag.
a) True
b) False

Explanation: Lift independent drag is divided into two types. They are the surface friction drag and the profile drag. Surface friction drag corresponds to 75% of the lift independent drag whereas the profile drag leads to 25% of the lift independent drag.

7. The surface friction drag coefficient is not effected by reynold’s number effect.
a) True
b) False

Explanation: The surface friction drag coefficient is effected by reynold’s number effect. This effect results in the variation of surface friction drag coefficient and mach number. Surface friction drag coefficient decreases slightly as the increase in mach number.

8. How is the zero-lift drag force related to atmospheric pressure?
a) The zero-lift drag force is directly proportional to atmospheric pressure
b) The zero-lift drag force is indirectly proportional to atmospheric pressure
c) The zero-lift drag force is twice multiple to atmospheric pressure
d)The zero-lift drag force is half divided to atmospheric pressure

Explanation: The zero-lift drag force is directly proportional to atmospheric pressure i.e. the zero-lift drag force increases as the increase in atmospheric pressure. This is because the drag force is directly proportional to the dynamic pressure.

9. The drag force is directly proportional to the dynamic pressure.
a) True
b) False

Explanation: The drag force is directly proportional to the dynamic pressure. This results in the effect of zero-lift drag force. The zero-lift drag force is directly proportional to atmospheric pressure i.e. the zero-lift drag force increases as the increase in atmospheric pressure.

10. The zero-lift drag force will decrease with decrease respect to altitude.
a) True
b) False

Explanation: The zero-lift drag force will decrease with increase respect to altitude. This is due to atmospheric pressure varying with respect to altitude. Also the zero-lift drag force increases as the increase in atmospheric pressure.

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