Question

A helicopter of gross weight W with rotor diameter D hovers at Sea level achieving a figure of merit M using momentum theory calculate the % of change in actual rotor power at 1 KM above sea level at same M density change 8% per KM may be assumed near sea level

Answer 1

P=vT

$But \ v=\sqrt{\frac{T}{2\rho a}}$

Thus $P=\sqrt{\frac{T}{2\rho a}}*T$

$$ $∆P=\frac{P'-P}{P}$

$P'=\sqrt{\frac{1000T}{2*1.08\rho a}}*T$

$∆P=\frac{(\sqrt{\frac{1000T}{2*1.08\rho a}}*T)-\sqrt{\frac{T}{2\rho a}}*T}{\sqrt{\frac{T}{2\rho a}}*T}$

=30.42-1=29.42

=29.42%