Aircraft Design Questions and Answers – Selection of Thrust-Weight and Wing Loading

This set of Aircraft Design online test focuses on “Selection of Thrust-Weight and Wing Loading”.

1. Low wing loading increases __________
a) weight and cost of aircraft
b) weight only
c) lofting
d) drafting
View Answer

Answer: a
Explanation: Low wing loading shows larger wings are used. Larger wing will increase weight and as wing is large material requirement will increase as well. This will affect the cost parameter.

2. For estimated value of the thrust loading, we got three different values of wing loading. As a designer typically which wing loading should be considered?
a) Lowest among all three
b) Highest among all three
c) Any value
d) Always take average
View Answer

Answer: a
Explanation: In general, we chose the lowest among all the values. This is done if and only if the lowest value can satisfy almost every mission phase requirement; from take-off to land. If it does not satisfy then, we should estimate another value.

3. What should be the aspect ratio (AR) of the prop aircraft if it is designed to work with maximum loiter wing loading of 32, CD0 = 0.06, dynamic pressure of 20 unit and Oswald efficiency as 0.6.
a) 7.54
b) 8.54
c) 7.65
d) 9.65
View Answer

Answer: a
Explanation: Given, Wing loading for maximum loiter W/S = 32, CD0 = 0.06,
q = 20unit, Oswald efficiency e=0.6.
Wing loading at maximum loiter is,
W/S = q*\(\sqrt{3*ᴨ*AR*e*CD0}\)
32 = 20*\(\sqrt{3*ᴨ*AR*0.6*0.06}\)
1.6= \(\sqrt{3*ᴨ*AR*0.6*0.06}\)
Hence, by squaring the aspect ratio AR,
AR = 7.54

4. What should be the load factor if, lift coefficient is designed as 2.1 and aircraft is operating at dynamic pressure q as 20 Pa. Given W/s =12.
a) 3.5
b) 5.5
c) 3.25
d) 4.5
View Answer

Answer: a
Explanation: Given, W/S = 12, lift co-efficient CL = 2.1 and q=20Pa
Now load factor n is given by, n = q*CL / (W/S) = 20*2.1/12 = 3.5.

5. A designer is designing an aircraft which has climb gradient of 1.5 and has drag of 20N. If it weighs 220kg then, determine thrust to weight ratio?
a) 0.097
b) 0.87
c) 20
d) 220
View Answer

Answer: a
Explanation: Given, climb gradient G = 1.5, Drag D = 20N, Weight W=220kg.
Now thrust to weight ratio in terms of G is given by,
T/W = (G+D)/W = (1.5+20)/220 = 0.097.

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6. If climb gradient is G, then which of the following is correct?
a) T/W ≥ G + 2*\(\sqrt{\frac{CD0}{ᴨ*e*AR}}\)
b) T/W ≥ G + 4*\(\sqrt{\frac{CD0}{ᴨ*e*AR}}\)
c) T/W ≥ G – 2*\(\sqrt{\frac{CD0}{ᴨ*e*AR}}\)
d) T/W ≥ G – 4*\(\sqrt{\frac{CD0}{ᴨ*e*AR}}\)
View Answer

Answer: a
Explanation: Climb gradient is defined as the ratio between vertical distance and horizontal distance travelled during climb. For positive wing loading, thrust loading should follow following condition. T/W ≥ G + 2*\(\sqrt{\frac{CD0}{ᴨ*e*AR}}\).

7. For jet aircraft, thrust loading is greater than the climb gradient.
a) True
b) False
View Answer

Answer: a
Explanation: For finite wing loading value of thrust loading should be greater than the climbing gradient. If it is not greater than the climb gradient then, it will result in either negative or imaginary values or both.

8. After estimating thrust and wing loading, we can proceed to the initial sizing.
a) True
b) False
View Answer

Answer: a
Explanation: Wing loading and thrust loading are very important parameter for designer. They will affect the number of crucial performance parameter of an aircraft. If adequate estimation is not done prior to the initial sizing, then it can affect the actual layout and performance of an aircraft.

9. An aircraft is to be designed to have max lift coefficient as 2.8 and at q=10Pa. If maximum load factor n=5 then, what will be the stall speed?
a) 1.80m/s
b) 1.80mph
c) 2.80mph
d) 2.80m/s
View Answer

Answer: a
Explanation: Given, lift coefficient = 2.8, q=10Pa, n=5
Since density is not given we will take as sea level.
Load factor n = q*CL/(W/S)
(W/S)/CL = q/n = 10/5 = 2.
Now, stall speed V is given by,
V = \(\sqrt{2*(\frac{W}{S})/(\rho*CL)}\)
= \(\sqrt{2*2/1.225}\) = 1.80m/s.

10. An aircraft has lift to drag ratio during cruise as 2.5 and load factor as 1.2. Which value of thrust loading should be selected?
a) 0.48
b) 0.58
c) 0.38
d) 0.28
View Answer

Answer: a
Explanation: Given, load factor n=1.2, lift to drag L/D = 2.5
Now, n at cruise is given by, n = (T/W)*(L/D).
Hence, T/w is given as,
T/W = n / (L/D) = 1.2/2.5 = 0.48.

Sanfoundry Global Education & Learning Series – Aircraft Design.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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