Question

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) Delta

(b) Rectangular

(c) Square

(d) Triangle

I have been asked this question during an online interview.

Origin of the question is Configuration Layout in section Configuration Layout and Loft of Aircraft Design

Answer 1

Right choice is (a) Delta

The best 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+t^2) / (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.