This set of Aircraft Design Interview Questions and Answers for freshers focuses on “Wing Geometry-2”.
1. For high aspect ratio strength of the wing tip vortex is low.
Explanation: Wing tip of high aspect ratio wing is far from root as compared to low aspect ratio wing. The wing affected by higher ratio will be less and the strength of tip vortex will be less as well.
2. If aspect ratio of wing is 8 and S=0.1m2 then, what will be the span of wing?
Explanation: Given, wing Aspect ratio AR=8, S=0.1m2
Aspect ratio = span square/ reference area
8 = span square / 0.1
Span square = 8*0.1 = 0.8
Hence, span = 0.89m.
Explanation: High aspect ratio will give higher value of maximum lift coefficient. As shown in figure for -1, maximum lift coefficient is highest and hence, aspect ratio of 1 will be highest. Similarly for -3 it is lowest and hence, aspect ratio of 3 will be minimum.
4. Let’s consider an aircraft has statistically determined aspect ratio of 8.1. Aircraft has canard which gives contribution of 10% for total lift. Determine the aspect ratio of wing.
Explanation: Given, Aspect ratio statistically ARst = 8.1
Canard contribution = 10%
Here, total lift is not produced by the wing only. Canard is also responsible for it as well.
Hence, wing contribution = total lift – lift by canard = 100% – 10% = 90% = 0.9.
Now, aspect ratio of the wing is given by,
ARw = ARst / wing contribution = 8.1 / 0.9 = 9.
5. An aircraft with elliptic wing planform has parasite drag coefficient as 0.6. Lift coefficient of wing is 0.25 and aspect ratio is 7.5. If induced drag co-efficient is 0.0235 then, find total drag coefficient for the wing.
Explanation: Given, parasite drag co-efficient = 0.6, induced drag coefficient = 0.0235
Total drag coefficient = Parasitic drag coefficient + induced drag coefficient = 0.6+0.0235 = 0.06235.
6. An aircraft with elliptic wing planform has parasite drag coefficient as 0.9. Lift coefficient of wing is 1.8 and aspect ratio is 8.5. Find total drag coefficient for the wing.
Explanation: Given, elliptic wing, parasite drag coefficient CD0 = 0.9
Lift coefficient CL = 1.8, Aspect ratio AR=8.5
Now, Total drag coefficient = Parasitic drag coefficient (CD0) + induced drag coefficient (CDi)
CDi = CL*CL / (ᴨ*e*AR) = 1.8*1.8 / (ᴨ*1*8.5) = 0.121
Hence, Total drag coefficient = CD0 + CDi = 0.9 + 0.121 = 1.021.
7. Wing sweep is used to ____
a) increase critical mach number
b) decrease critical mach number
c) increase lofting
d) increase drafting
Explanation: If wing is at some finite angle from fuselage reference line then it is called wing is sweep by that much degree. Main function of sweep is to increase critical mach number. Lofting is skin modelling and drafting is drawing phenomena.
8. Canard pusher aircraft uses wing sweep to change location of aerodynamic centre.
Explanation: Canard pusher aircrafts are heavier at rearward part. At tail weight is more. By sweeping the wing we can alter the location of aerodynamic center for balance.
9. The ratio of tip and root chord is called ____
a) taper ratio
c) aspect ratio
Explanation: Taper ratio is the ratio of tip chord of wing to root chord of the wing. Aspect ratio is square of span divided by area. Sweep is angle between wing and fuselage reference line.
10. If root chord is 2m and tip chord is 0.9m then, find taper ratio.
Explanation: Taper ratio is defined as,
Taper ratio = tip chord/root chord = 0.9/2 = 0.45.
11. What is the function of wing twist?
a) To improve stall characteristics at tip
b) To reduce lift by tail
c) To provide lofting
d) To increase engine thrust
Explanation: Wing twist is used to delay the stall at tip typically. Wing twist can be used to rearrange the lift distribution of the wing. Lofting is skin modelling.
12. Excessive dihedral can produce _____
a) dutch roll
d) deflection at nose
Explanation: Dihedral is upward deflection of wing. It is used to provide roll stability. If excessive dihedral is provided then, it will lead to dutch roll; continuous side to side motion involving yaw and roll.
13. Determine the corrections or otherwise of the following assertion [A] and reason [R]:
Assertion [A]: In general, wing twist should not be more than 6°.
Reason[R]: Wing twist is used to improve stall properties at tip.
a) Both [A] and [R] are true and [R] is the correct reason for [A]
b) Both [A] and [R] are true but [R] is not the correct reason for [A]
c) [A] is true but [R] is false
d) [A] is false but [R] is true
Explanation: Wing twist can optimize the wing lift at a particular lift coefficient. At any different lift coefficient wing twist will not provide 100% accuracy. Wing twist is also used to improve stall at tip.
Sanfoundry Global Education & Learning Series – Aircraft Design.
To practice all areas of Aircraft Design for Interviews, here is complete set of 1000+ Multiple Choice Questions and Answers.