Question

Why is blade element theory preferred over momentum theory for designing a propeller?

(a) Assumes flow inside stream tube as constant

(b) Neglects span wise flow

(c) Model thrust lag

(d) Account for varying blade geometry

I had been asked this question in unit test.

The above asked question is from Blade Element Theory in portion Helicopter Dynamics of Aerodynamics

Answer 1

Correct answer is (d) Account for varying blade geometry

Easy explanation: There are several reasons why blade element theory is preferred over momentum theory. It can account for varying blade geometry, allows torque estimation, allows non-linearities for example lift curve to be modelled. The other points are some of the disadvantages.