Chris, thank you for your answer.

**If 203 km/h** at weight 518 kg, ie 5080 N,

375 rrpm means blades pitch in flight = + 4.3° aerod. (more than the pitch setting because underbalancing), then according my spreadsheet: rotor drag = 454 N (less profile loss), and disk A.o.A = +5.1° Longitudinal flapping a1 = 4.2°

With 100 HP, propeller thrust = 1050 N

Difference= parasitical drag = 596 N

Because Drag = ½ ρ V² S Cd, we have **S.Cd**= 2 D/ ρ V² = **0.32 ** which is in **m²**

unrelated to the drag of a flat plate, but proximity gives a good mental picture.

Note: standard air density at 400 feet above see level is 1.17 kg/m3 .

**If 190 km/h**, then rotor drag = 485 N according my spreadsheet.

Disk A.o.A = +5.45° a1 = 3.85° Blades pitch in flight = + 4.12° aerod.

With 100 HP, propeller thrust = 1110 N

Difference= parasitical drag = 625 N

=> **S**.Cd = **0.38 m²**

Main uncertainty is the airspeed.

Other point.

In my post # 26, I mentioned that my calculation is for a 8.6 x 0.2 m rotor, without being contradicted. Yet the autorotation limit would be reached before 210 km/h.

Since you said reach 220 km/h, this means an inconsistency.

Are you sure on the cord of 0.2 m? Not more ?

This hardly changes the calculated parasitic drag, but I am curious.