This set of Aircraft Design Questions and Answers for Experienced people focuses on “Configuration Layout – Wing/Tail Layout and Loft-2”.
1. As a designer, our task is to design wing layout such that the location of MAC from root chord or centre line is at 8ft. Find the appropriate value of the wingspan if wing is rectangular.
a) 28m
b) 50ft
c) 32ft
d) 32m
View Answer
Explanation: Given, rectangular wing.
MAC location y = 8ft. As wing is rectangular taper ratio t =1.
Wingspan b = (6*y*(1+ t)) / (1+t+t2) = 6*8*(1+1) / (1+1+12) = 6*8*2/3 = 32ft.
2. A fighter jet is flying with wing span of 90ft. If mean aerodynamic chord MAC is at 30ft from tip chord then, to design such wing which type of planform should I use?
a) Rectangular
b) Delta
c) Square
d) Triangle
View Answer
Explanation: Given, wing span b=90ft, location of MAC from tip = 30ft
Location of MAC from root y = b/2 – 30ft = 90/2 – 30 = 45-30 = 15ft.
To find planform let’s find taper ratio first from y.
Location of MAC is given as, y = (b/6)*(1+t+t2) / (1+t). …. (1)
From given options, let’s consider delta wing first.
Delta wing has taper ratio near to none. Let’s consider taper ratio to be zero for idle case.
Hence, by substituting value of taper ratio in eq (1),
Y = (90/6)*1+0+0/1+0 = 90/6 = 15ft.
This value is same as we found earlier from given data. Hence, wing planform is delta.
3. An unstable A/C configuration is a typical wing-aft tail body. IF MAC is 4m then, what would be the approximated location of the CG?
a) 7m
b) 5m
c) 6m
d) 2m
View Answer
Explanation: Typical location Cg for an unstable wing = 50% of MAC = 50% of 4 = 0.5*4 = 2m.
4. Following diagram represents?
a) LEX
b) Rounded wingtip
c) Midline tip
d) Blended tip
View Answer
Explanation: Wings can have different wingtip shapes. Above figure is showing a typical rounded wingtip. A smoothly rounded tip allows air to flow easily around tip. LEX stand for leading edge extension.
5. Following diagram represents?
a) Rounded tip
b) T.e. extension
c) T.e. kick
d) Straight tip
View Answer
Explanation: Above figure is often termed as trailing edge kick. A straightened out trailing edge will increase the flap chord. It also reduces induced drag. Rounded tip will permit air to flow around tip easily.
6. As a designer, our job is to design a wing which has root chord Cr as 1m. What should be the approximate radius of fillet?
a) 1m
b) 0.1m
c) 2m
d) 2.1m
View Answer
Explanation: typically fillet radius can be approximated as 10% of the root chord.
Hence, radius = 10% of Cr = 10% of 1 = 0.1*1 = 0.1m.
7. Following diagram represents?
a) T-tail arrangement
b) Wing chamfer
c) Wing fillet
d) Wing drag
View Answer
Explanation: Wing fillets are arcs as shown in figure. Wing fillets are used to improve smoothness of the root of the airfoil as shown. This will result in improvement of aerodynamic efficiency. A typical fillet is a circular arc.
8. Which of the following is correct?
a) Linear interpolation is only used for flat wrap surfaces
b) Flat surfaces can only be generated by using linear interpolation
c) Linear interpolation will never give flat surface
d) We can generate flat wrap surface by using linear interpolation method
View Answer
Explanation: A flat wrap surface has same tangent angles for different conic curves. When linear interpolation method is used, it does not always provide constant cross-sections or c/s with same tangent angles. Hence, it may or may not produce flat wrap. We can generate flat wrap by providing some constraints as well.
9. Determine the corrections or otherwise of the following assertion [A] and reason [R]:
Assertion [A]: To generate new airfoil, we use spanwise line instead of chord line in flat wrap interpolation technique.
Reason[R]: Chordwise line will generate flat structure from curves having different values of tangent angle.
a) Both [A] and [R] are true but [R] is not the correct reason for [A]
b) Both [A] and [R] are true and [R] is the correct reason for [A]
c) Both [A] and [R] are false
d) [A] is true but [R] is false
View Answer
Explanation: In order to provide flat wrapping to wing, it is required to interpolate between airfoil coordinates with same tangent angle or slope. Chordwise lines are affected by wing twist. So, it will not generate flat structure from curves with different tangent angles. Hence, a spanwise line is used for flat wrap interpolation.
10. At maximum thickness point, fillet is in ____________
a) purely in hp
b) purely vertical plane
c) plane at an angle of less than 20° always
d) plane at 45° always
View Answer
Explanation: Fillet arcs will be normal to wing surface only at the maximum thickness point. At any other section it is not perpendicular to surface. Hence, at maximum thickness point, fillet is in pure vertical plane.
11. Fillet radius is typically more at rear of the aircraft.
a) True
b) False
View Answer
Explanation: Fillet arcs can be of constant radius or can be of varying radius. Typically, at rear of an a/c fillet arc radius is more. This will result in reduction of the flow separation.
12. Wing planform is always elliptic.
a) False
b) True
View Answer
Explanation: Wing planform is shape generate when viewed from top. Elliptic wings are more efficient in terms of lifting properties. However to manufacture it is also difficult. Hence, wing planform is not always elliptic rather it will be selected according to mission requirements.
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