Question

We can design our aircraft to cruise for 3 different lift to drag ratio. Lift to drag ratio are as follows: 10, 12 and 11.25. Now, if we want to reduce thrust required to fly then, at which value of lift to drag ratio our aircraft needs to be designed so that it can operate with minimum thrust required?

(a) 12

(b) 10

(c) 11.25

(d) 10.62

I have been asked this question in an online quiz.

This key question is from Flight Mechanics topic in division Performance and Flight Mechanics of Aircraft Design

Answer 1

The correct answer is (a) 12

Explanation: Here, we’ve been asked to choose from 3 different lift to drag ratio so that our product can operate with minimum thrust required. To have thrust required minimum at cruise we should design our aircraft with maximum value of lift to drag ratio.

From given values, 12 is the highest value available. Hence, among given choices correct choice would be 12.