Question

When is the blade element theory applicable?

(a) When solidity is much greater than 1

(b) When solidity is much lesser than 1

(c) When solidity is equal to 1

(d) When solidity is equal to 0

This question was addressed to me in a job interview.

My doubt is from Blade Element Theory in chapter Helicopter Dynamics of Aerodynamics

Answer 1

Right option is (b) When solidity is much lesser than 1

Best explanation: In order to make sure that the blade element theory is applicable, there are certain conditions that have to be met. First being that the spacing to the chord ratio should be high.

\(\frac {s}{c}\) >> !

And solidity should be much lesser than 1. Solidity is defined by:

σ=\(\frac {Bc}{πr}\)

Where, B is number of blades

C is the chord length

R is the radius