Consider a $4-$bladed conventional helicopter with a blade chord of $21$ inches, rotor diameter of $53$ ft $,$ an empty weight of $11,300lb,$ and a maximum gross weight of $16,800lb.$ Cruise speed is $150$ kts at $4000$ ft at standard atmospheric conditions. Rotor rotation is $4\mathrm{.}3$ Hz$.$ Power available is via two turboshaft engines with $1,560$ shaft $hp$ each. For these problems, use rotor "ideal" assumptions for use with Momentum Theory.

$4.$ The helicopter travels at an advance ratio of $=0\mathrm{.}368.$ Assuming a circular fuselage with frontal radius of $4$ ft $,$ what is the power ratio needed?