Mart,
I'm a bit confused because your spreadsheet looks like just momentum theory with the assumption of 0.7 FM. I don't understand how this proves Leishman's 0.5 FM wrong?
There are four forms, One is Momentum Theory. The FORM: Flight Hovering says at the top 'Combined Momentum & Blade Element Theory w/ Empirical Corrections'
Yes you are correct in that the Figure of Merit only applies to the FORM: Momentum Theory. If a FM of .5 had been used the HP by Momentum Theory would be 15 hp * 2 rotors = 30 hp. However, I have been questioning Leishman's low FM of 0.5, particularly when Momentum Theory includes the 10% power loss of a tail rotor, which does not exist on the Cornu.
Discussing the Blade Element Theory;
Due to Cornu's large cutout and wide chord, I felt that his helicopter's aerodynamic performance might also be considered as four small hang-glider wings. In addition, Cornu's the mechanical driving of the '4 wings' would be more efficient than the aerodynamic transmission from the propeller to the wings on a hang glider.
This assumption of mine may be wrong. It appears that the top speed of a modern empowered hang-glider is 90 fps, and the speed of a sailplane is somewhere around 150 fps. whereas at 0.75R on Cornu's 'wings' (blades) the speed at 24 hp would be 180 fps. Of course, a hovering Cornu does not need to consider the parasitic drag of the pilot and engine etc.
Another piece of information is the ongoing work on the Ultralight Side-by-side Electrotor.
This page shows the power calculations using the same Prouty algorithms. It is showing that it will require about 22 hp to lift 550 lbs.
All very interesting.
Dave