Aircraft Design MCQ – Selection of Thrust-Weight and Wing Loading
1 - Question
Low wing loading increases __________
a) weight and cost of aircraft
b) weight only
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 - Question
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
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 - Question
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.
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*3∗ᴨ∗AR∗e∗CD0−−−−−−−−−−−−−−−−√ 32 = 20*3∗ᴨ∗AR∗0.6∗0.06−−−−−−−−−−−−−−−−−√ 1.6= 3∗ᴨ∗AR∗0.6∗0.06−−−−−−−−−−−−−−−−−√ Hence, by squaring the aspect ratio AR, AR = 7.54
4 - Question
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.
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 - Question
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?
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.
6 - Question
If climb gradient is G, then which of the following is correct?
a) T/W ≥ G + 2*CD0ᴨ∗e∗AR−−−−−√
b) T/W ≥ G + 4*CD0ᴨ∗e∗AR−−−−−√
c) T/W ≥ G – 2*CD0ᴨ∗e∗AR−−−−−√
d) T/W ≥ G – 4*CD0ᴨ∗e∗AR−−−−−√
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*CD0ᴨ∗e∗AR−−−−−√.
7 - Question
For jet aircraft, thrust loading is greater than the climb gradient.
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 - Question
After estimating thrust and wing loading, we can proceed to the initial sizing.
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 - Question
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
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 = 2∗(WS)/(ρ∗CL)−−−−−−−−−−−−−−√ = 2∗2/1.225−−−−−−−−−√ = 1.80m/s.
10 - Question
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?
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.