Question

A jet fighter is designed to operate at maximum mach of 2.0. Which of the following is approximated value for empty weight fraction if rubber engine sizing is used? Given, W0 = 20000lb, AR = 5, thrust loading T.L. = 0.6 and wing loading W.L. is 25.

(a) 0.8109

(b) 0.8532

(c) 0.526

(d) 0.3562

I got this question during an online exam.

The origin of the question is Rubber-Engine Sizing in division Initial Sizing of Aircraft Design

Answer 1

Correct option is (a) 0.8109

Best explanation: Given, jet fighter with maximum Mach number Mmax = 2.0

Gross weight W0 = 20000lb, wing loading = W.L. = 25, Aspect ratio AR = 5, Thrust loading T.L. = 0.6.

For, given parameters empty weight fraction is given by,

We/W0 = [a + b*(W0^c)*(AR ^d)*(T.L.^e)*(W.L.^f)*(Mmax ^g)]*K

Now, for jet fighter a = -0.02, b = 2.16, c = -0.1, d = 0.2, e = 0.04, f = -0.1, g = 0.08, K = 1.0

We/W0 = [-0.02 + 2.16*(W0^-0.1)*(AR^0.2)*(T.L.^0.04)*(W.L. ^-0.1)*(Mmax ^0.08)]*1.0

We/W0 = [-0.02 + 2.16*(20000^-0.1)*(5^0.2)*(0.6^0.04)*(25^-0.1)*(2^0.08)]*1.0

We/W0 = -0.02+0.8309 = 0.8109.