# Aircraft Design Questions and Answers – Flight Mechanics – Gliding Flight-1

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This set of Aircraft Design Multiple Choice Questions & Answers (MCQs) focuses on “Flight Mechanics – Gliding Flight-1”.

1. For a typical gliding flight, thrust will be ________
a) zero
b) equal to the lift
c) always same as drag
d) always same as weight

Explanation: For a typical gliding flight, Thrust Will be zero. Gliding flight is often termed as unpowered flight. Lift and drag during gliding flight will be determined by using glide angle.

2. The tangent of glide angle is ________
a) equal to drag to lift ratio
b) lift to drag ratio
c) inverse of thrust
d) equal to thrust

Explanation: The tangent of glide angle is equal to the drag to lift ratio. Lift to drag ratio is called aerodynamic efficiency of the aircraft. Tangent of Glide angle is inverse of the Aerodynamic efficiency or inverse of the lift to drag ratio.

3. If aerodynamic efficiency of the glider is 20 then, found the value of corresponding glide angle.
a) 2.86 unit
b) 3.8
c) 5.6
d) 12.12

Explanation: Glide angle = arctan (1/Aerodynamic efficiency) = arctan (1/20) = 2.86 unit.

4. A typical glider has weight of 150N and has glide angle of 2.5°. Find Lift produced by the glider.
a) 149.85N
b) 150kN
c) 322N
d) 120Kn

Explanation: Lift = weight* cos (glide angle) = 150*cos (2.5°) = 149.85 N.

5. Glider with glide angle of 4.2° is gliding with gliding ratio of _____
a) 13.6
b) 12.9
c) 15
d) 25.4

Explanation: Glide ratio = 1/tan (glide angle) = 1 / tan (4.2°) = 13.6.

6. Typically, a high performance unpowered aircraft is called ________
a) sailplane
b) glider
c) jet
d) twin engine

Explanation: Typically, a high performance unpowered aircraft is termed as sailplane. A glider is crude, low performance unpowered aircraft. This is based on typical sailplane terminology.

7. Find the velocity required for maximum range. Consider a sailplane has wing loading of 110N/m2 and K/CD0 of 0.35.
a) 10.3m/s
b) 10.3mph
c) 12.5mph
d) 9.2mph

Explanation: Velocity = $$\sqrt{\frac{2*wing \,loading*\sqrt{K/CD0}}{density}}$$
= $$\sqrt{\frac{2*110*\sqrt{0.35}}{1.225}}$$
= $$\sqrt{106.24}$$ = 10.3 m/s.

8. If a glider needs to be flown at maximum range then, at which value of CL we should fly this glider? Consider CD0/K is 2.8.
a) 1.67
b) 3.2
c) 5.6
d) 2.5

Explanation: CL = [CD0/K] 0.5 = 2.80.5 = 1.67.

9. Which of the following is correct for a typical glider?
a) Drag D = W*cos (gamma)
b) Drag D = W*arcsine (gamma)
c) Drag D = W
d) Drag D = Thrust T

Explanation: Above equation is used to provide information about drag of atypical glider. Drag can be given by, Drag D = W*cos (gamma) where, D is drag, W is weight of the glider and gamma is the glide angle.

10. If my glider has lift coefficient at maximum lift to drag as 1.5 and induced drag factor K is 0.007 then, find parasite drag coefficient.
a) 0.01575
b) 0.01 N
c) 0.02N
d) 0.0157N

Explanation: Parasite drag coefficient = K*lift coefficient2 = 0.007*1.5*1.5 = 0.01575.

11. All the gliders are unpowered.
a) True
b) False

Explanation: Typically, gliders are built with zero thrust. However, in modern days there gliders which operates with some power plant. Hence, statement is not correct. Not all the gliders are unpowered, some are powered as well.

12. If a sailplane has glide ratio of 45 then, find horizontal distance travelled by this sailplane. Consider altitude loss of 1000ft.
a) 45000ft
b) 1000ft
c) 3456ft
d) 987ft

Explanation: Horizontal distance = glide ratio*altitude loss = 45*1000 = 45000ft.

13. Sink rate can be used to ____________
a) determine the time a glider may remain in the air
b) determine and estimate takeoff gross weight
d) calculate weight to thrust ratio

Explanation: The time a glider may remain in the air can be determined by using the sink rate. Sink rate is the product of aircraft velocity and sine of the glide angle. It is the vertical velocity.

14. A glider has aspect ratio of 20 and CD0 of 0.02. In order to attain maximum range, determine the value required aerodynamic efficiency. Take e as 1.
a) 28.02
b) 20
c) 30
d) 43

Explanation: Aerodynamic efficiency= 0.5*(π*e*aspect ratio/CD0)0.5
= 0.5*(π*1*20/0.02)0.5 = 28.02.

15. Determine the value of sink rate of glider which is operating with 4.2° of glide angle and has speed of 120m/s.
a) 8.78m/s
b) 9.8ms
c) 56.5ms
d) 8.7ms