Question

What is the formula for the helix angle?

(a) Φ=tan^-1\(\frac {V_0}{V_E}\)

(b) Φ=sin^-1\(\frac {V_0}{V_E}\)

(c) Φ=cos^-1\(\frac {V_0}{V_E}\)

(d) Φ=tan^-1\(\frac {V_E}{V_0}\)

This question was addressed to me during an internship interview.

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

Answer 1

Correct choice is (a) Φ=tan^-1\(\frac {V_0}{V_E}\)

To explain: According to blade element theory, When the propeller rotates and advances, the tip traces out helix. Along with this the trailing vortex also traces helix. This angle is measured between the direction of the flow and plane of rotation and is computed using the formula:

Φ=tan^-1\(\frac {V_0}{V_E}\)

Where, V0 is the forward airspeed of the aircraft

VE is the effective resultant velocity.