Sikorsky X2 coaxial heli developments.

[riff_raff]

X2 rotor speeds

"No clutches, guys. The whole drive system is tied together, rotors and prop shaft."

NickLappos,

So if I understand you correctly, you're saying the X2 TD drivetrain is a single, fixed gear ratio. With rotor speed changes effected only through engine throttling (ie. like V-22), and torque split controlled through rotor and prop blade pitch settings?

It's not that a multi-speed geared rotorcraft transmission can't be made to work with a conventional friction clutch for shifting. Boeing's (unmanned) A160 uses such a system, as did the Bell XV-3 (I believe). Although neither has been/was shifted during flight on a regular basis due to safety concerns.

You also say that the ABC TD could slow the rotor to 82% via engine speed throttling, which sounds like the engine guys (Pratt?) were being very conservative, even with mid-70's turbine engine technology. I'd guess that a modern turboshaft engine with variable compressor geometry, digital FADEC and a well sorted combustor could probably run satisfactorily at 70% engine speed or less.

Would something like a 100% to 70% speed range be satisfactory for what the X2 wants to do?

Thanks for the input.
riff_raff