# Aircraft Performance Questions and Answers – Aircraft Force Systems

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

1. Inertial forces from the mass of the aircraft and its acceleration.
a) True
b) False

Explanation: Inertial forces from the mass of the aircraft and its acceleration. The inertial forces act in the velocity axis system. Inertial forces are a result of gravitational forces, aerodynamic forces and propulsive forces. Numerically it is given by Fa+Fg+Fp=Fi.

2. Gravitational force is the product of mass of the aircraft and its acceleration.
a) True
b) False

Explanation: Gravitational force is the product of mass of the aircraft and its acceleration. It is represented by Fg. It is described as the downward pulling force of the earth. It is also referred as W=mg. It can also be written as Fg=mg=W.

3. The aerodynamic forces arise from the relative motion between the aircraft and the air mass in which it is flying.
a) True
b) False

Explanation: The aerodynamic forces arise from the relative motion between the aircraft and the air mass in which it is flying. It is represented by Fa. The aerodynamic forces include lift, weight, drag and thrust.

4. In which of the following terms the forces of aircraft must be considered?
a) Aircraft weight, flight mach number, altitude
b) Aircraft weight, airspeed, altitude, temperature
c) Aircraft weight, flight mach number, temperature
d) Aircraft weight, airspeed, altitude

Explanation: An aircraft forces are described in terms of aircraft weight, flight mach number, altitude rather than in terms of aircraft weight, airspeed, altitude, temperature. In this the altitude becomes a basic variable of the aerodynamic forces.

5. Which of the following are the forces that are concerned with the performance of an aircraft?
a) Lift, drag, weight
b) Lift, drag, side force
c) Lift, drag
d) Lift, drag, weight, side force

Explanation: Lift, drag, side force are the forces that are concerned with the performance of an aircraft. The lift and drag forces play a crucial role in the performance of an aircraft.
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6. Which of the following is the correct formula for reynolds number?
a) Re=$$\frac{\rho Vl}{\mu}$$
b) Re=$$\frac{PVl}{\mu}$$
c) Re=$$\frac{\rho \mu l}{V}$$
d) Re=$$\frac{\rho Vl}{P}$$

Explanation: The correct formula for reynolds number is given by Re=$$\frac{\rho Vl}{\mu}$$ where Re is Reynolds number, ρ is density of the fluid, V is the velocity of the fluid, l is the length of the fluid and μ is the dynamic viscosity of the fluid.

7. The range of Re in the typical flight is ___________
a) 106 to 109
b) 105 to 109
c) 106 to 108
d) 106 to 1010

Explanation: The range of Re in the typical flight is 106 to 109. The mathematical formula for reynolds number is given by Re=$$\frac{\rho Vl}{\mu}$$ where Re is Reynolds number, ρ is density of the fluid, V is the velocity of the fluid, l is the length of the fluid and μ is the dynamic viscosity of the fluid.

8. What is the range of mach number for a conventional aircraft?
a) 0 to 3.2
b) 0 to 2.2
c) 0 to 4.2
d) 0 to 1.2

Explanation: 0 to 2.2 the range of mach number for a conventional aircraft. The values of mach number can increase beyond 2.2 but arise a special case of problems. To avoid any kind of troubles an aircraft must always fly at a mach number below 2.2.

9. What is the critical mach number for most subsonic aircraft?
a) Around 0.8
b) Around 2
c) Around 1
d) Around 1.5

Explanation: For most subsonic aircraft the critical mach number occurs typically at mach number 0.8. At this mach number the local flow at points on the aircraft becomes supersonic and shock waves begin to form.

10. In transonic region the mach number affects the aerodynamic characteristics.
a) True
b) False

Explanation: In transonic region the mach number affects the aerodynamic characteristics. Transonic region is a region in which the mach number ranges from 0.8 to 1.2. It depends on the airspeed of the aircraft and temperature of surroundings.

11. Below the mach number 0.5 the flow is considered as incompressible flow.
a) True
b) False

Explanation: Below the mach number 0.5 the flow is considered as incompressible flow. In the region 0.5 < M < 0.8 the flow becomes compressible and significant but leads to small changes in the lift and drag characteristics.

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