Sikorsky X2 coaxial heli developments.

[Dave_Jackson]

Mart,

Thanks for the reply.

IMHO, IMFU's concern about efficiency is valid. Why add the aerodynamic power loss of the propeller, plus the mechanical power loss of the powertrain to drive the main rotors when they can be driven directly from the airflow?

John mentions the feathering of the propeller. In addition, Sikorsky might have found it wise to insert an overrunning clutch in the propeller's powertrain for safety. This will preclude back-driving the rotors.


Prouty state that "One of the problems inherent in the compound helicopter configuration is that when entering autorotation at high speed the wings tend to produce so much lift that the rotor is starved for for the necessary thrust to keep it spinning.".....
.... the pilot could reduce the pitch of the propeller - thus converting it into a windmill that could extract energy out of the passing airstream. This could keep the entire drive system turning until the aircraft had slowed down to about 80 knots, at which speed it was put into conventional autorotation.

It would appear that this problem only exists because of the wings. I speculate, that this may only be applicable to the X2 if Sikorsky has a future intention of locating small wings under the large root cutout area of the new 'reverse taper' blades, to improve the craft's high speed performance.


Since we are limited to speculation;
I speculate that significant technical information on the X2 may be a long time in coming, if at all. Unlike the original coaxial-ABC, this project is not funded by the government and there may be little incentive on the part of Sikorsky to divulge much more than information for marketing purposes.
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PS. You may wish to reassess you last statement regarding coaxials and yaw control.


Dave