Question

If all the other factors remain unchanged and only aerodynamic efficiency of the aircraft is doubled then, what will be the cruise segment fuel weight fraction?

(a) Will increase

(b) Will decrease

(c) Will remain same

(d) Will be independent of aerodynamic efficiency

I had been asked this question by my school principal while I was bunking the class.

This is a very interesting question from Conceptual Sketch Sizing in portion Conceptual Sketch Sizing of Aircraft Design

Answer 1

The correct option is (a) Will increase

Easy explanation: Cruise phase fuel fraction is determined by using range formula as follows:

Wn/Wn-1 = \(e^{\left(-\frac{R*C}{V*\frac{L}{D}}\right)}\)

Now if we double the value of aerodynamic efficiency the denominator will increase which in turn increases fuel fraction during cruise.