Question

Which of the following is correct?

(a) Thrust required is minimum if L/D is maximum during cruise

(b) Thrust required is minimum if L/D is minimum for cruise

(c) Power required is minimum if L/D is maximum

(d) Thrust required is maximum if L/D is maximum during steady state

This question was addressed to me in final exam.

Origin of the question is Flight Mechanics topic in division Performance and Flight Mechanics of Aircraft Design

Answer 1

Correct answer is (a) Thrust required is minimum if L/D is maximum during cruise

Easiest explanation: At steady level flight or in cruise, thrust loading or thrust to weight ratio is inversely proportional lift to drag ratio. Hence thrust required will be minimum of lift to drag ratio is maximum.