Question

We need to design a supersonic fighter with afterburner which has maximum Mach number of 1.8. If thrust at takeoff is 10000 unit and bypass ratio is 0.71 then, find ratio of length to the diameter for this engine.

(a) 4.9

(b) 1.8

(c) 2

(d) 3.4

I got this question by my school teacher while I was bunking the class.

The doubt is from Propulsion in division Propulsion and Fuel System Integration of Aircraft Design

Answer 1

The correct option is (a) 4.9

To elaborate: Given, Mach number M = 1.8, thrust T = 10000 unit, BPR = 0.71.

Now, Ratio of length to diameter is given by,

L/D = 10.625*T^-0.1*M^0.2*e ^0.04*BPR = 10.625*10000^-0.1*1.8^0.2*e ^0.04*0.71

Hence, L/D = 10.625*0.3981*1.1247*1.028 = 4.9.