No, but seriously, go back and rework your numbers BrianC. You should get a rotor radius of 193.2' using momentum theory with 0.4HP HOGE (I think you have a units error somewhere).
Solve for radius:
[tex]R=\frac{T^{3/2}}{\sqrt{2 \rho \pi } P} [/tex]
T = 300 lbs (Airplane plus pilot)
[tex]\rho[/tex] = 0.002 slug/ft^3
P = 0.4 HP * 550
