250+ TOP MCQs on Aerodynamic Relationships and Answers

Aircraft Performance Multiple Choice Questions on “Aerodynamic Relationships”.

1. The minimum drag speed is given by ___________
a) (big(frac{2W}{rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{4})
b) (big(frac{2W}{gamma rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{4})
c) (big(frac{2W}{rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{2})
d) (big(frac{2W}{gamma rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{2})
Answer: a
Clarification: The correct formula for minimum drag speed is given by (big(frac{2W}{rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{4}) where W is weight, ρ is density, K is constant, S is span area and C_Dz is coefficient of lift dependent drag.

2. The minimum drag mach number is given by ___________
a) (big(frac{2W}{rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{4})
b) (big(frac{2W}{gamma rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{4})
c) (big(frac{2W}{rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{2})
d) (big(frac{2W}{gamma rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{2})
Answer: b
Clarification: The correct formula for minimum drag mach number is given by (big(frac{2W}{gamma rho S}big)^{frac{1}{2}}big(frac{K}{C_{Dz}}big)^frac{1}{4}) where W is weight, ρ is density, K is constant, S is span area, γ is ratio of specific heats and C_Dz is coefficient of lift dependent drag.

3. At steady state flight condition
a) T>D
b) Tc) T=D
d) T≠D
Answer: c
Clarification: At steady state flight condition the thrust produced by the aircraft is same as the drag produced by the aircraft i.e. T=D. At this state the minimum power speed is given by (frac{1}{sqrt[4]{3}})=V_md where V_md is minimum drag speed.

4. Which of the following is the correct relation between minimum power speed and minimum drag speed?
a) V_mp=(frac{1}{sqrt[2]{3}})V_md
b) V_mp=(frac{1}{sqrt[4]{3}})V_md
c) V_mp=(frac{1}{sqrt[3]{3}})V_md
d) V_mp=(frac{1}{sqrt[4]{5}})V_md
Answer: b
Clarification: At steady state flight condition the thrust produced by the aircraft is same as the drag produced by the aircraft i.e. T=D. The relation between minimum drag speed and minimum power speed is given by V_mp=(frac{1}{sqrt[4]{3}})V_md where V_md is minimum drag speed and V_mp is minimum power speed.

5. What is the value of minimum power speed when minimum drag speed is 300m/s?
a) 173.21 m/s
b) 227.95 m/s
c) 134.16 m/s
d) 200.62 m/s
Answer: b
Clarification: The correct answer is 227.95 m/s. Given V_md is 300m/s. From the formula V_mp=(frac{1}{sqrt[4]{3}})V_md substitute the values.
On substituting we get, V_mp=(frac{1}{sqrt[4]{3}})*300
V_mp=227.95m/s.

6. Airspeed with minimum power speed relates to the performance of the aircraft with power producing engine.
a) True
b) False
Answer: a
Clarification: Airspeed with minimum power relates to the performance of the aircraft with power producing engine whereas minimum drag speed relates to the performance of aircraft with thrust-producing engine.

7. In a glider the engine used is thrust producing engine.
a) True
b) False
Answer: b
Clarification: Airspeed with minimum power relates to the performance of the aircraft with power producing engine whereas minimum drag speed relates to the performance of aircraft with thrust-producing engine. In a glider the engine uses both minimum power speed and minimum drag speed but does not have any engine present.

8. What is the relative airspeed of an aircraft whose airspeed and minimum drag speed are 500m/s and 150m/s?
a) 3.33
b) 0.3
c) 33.33
d) 0.333
Answer: a
Clarification: The answer is 3.33. Given, airspeed is 500m/s and minimum drag speed is 150m/s. From the formula u=(frac{V}{V_{md}}) where V is airspeed and V_md is minimum drag speed. On substituting the values we get u= (frac{500}{150})
u=3.33.

9. What will be the drag to minimum drag ratio when the relative airspeed is 3.33?
a) 5.49
b) 1.51
c) 5.59
d) 1.82
Answer: c
Clarification: The answer is 5.59. Given u=3.33. From the equation (frac{D}{D_{min}})=(frac{1}{2}big[u^2+frac{1}{u^2}big])where (frac{D}{D_{min}}) is drag to minimum drag ratio and u is relative airspeed. On substituting the values,
We get (frac{D}{D_{min}})=(frac{1}{2}big[3.33^2+frac{1}{3.33^2}big])
On solving we get (frac{D}{D_{min}})=5.59.

10. Which of the following is the correct performance equation?
a) (big[frac{lambda}{u}+τbig]+frac{1}{2}big[u^2+frac{1}{u^2}big])=E_max(big{singamma_2-frac{V}{g}big})
b) (big[frac{lambda}{u}+τbig]-frac{1}{2}big[u^2+frac{1}{u^2}big])=E_max(big{singamma_2-frac{V}{g}big})
c) (big[frac{lambda}{u}+τbig]+frac{1}{2}big[u^2+frac{1}{u^2}big])=E_max(big{singamma_2+frac{V}{g}big})
d) (big[frac{lambda}{u}+τbig]-frac{1}{2}big[u^2+frac{1}{u^2}big])=E_max(big{singamma_2+frac{V}{g}big})
Answer: d
Clarification: The correct equation is (big[frac{lambda}{u}+τbig]-frac{1}{2}big[u^2+frac{1}{u^2}big])=E_max(big{singamma_2+frac{V}{g}big}) where λ is dimensionless power, u is relative speed, τ is dimensionless thrust, E_max is maximum efficiency, sinγ₂ is horizontal component, V is airspeed and g is gravitational force.