Question

An A/C is cruising with thrust to weight of 0.9. If A/C is powered by prop engine then, find maximum lift to drag?

(a) 1.11

(b) 2.11

(c) 3.12

(d) 4.221

The question was posed to me during a job interview.

The origin of the question is Thrust Weight Ratio-2 in division Thrust-Weight Ratio and Wing Loading of Aircraft Design

Answer 1

Right choice is (a) 1.11

For explanation: Given, thrust loading at cruise T.L. = 0.9, prop aircraft.

For prop aircraft maximum L/D = Cruise L/D

Hence, T.L. = D/L.

Hence, cruise L/D = 1/(T/W) = 1/0.9 = 1.11.