Originally Posted by Nick Lappos
Why just recips? Because the recip engine is so heavy for its power that a recip helo typically spent 10 to 13% of its max gross weight on the engine (vice 4% for a turbine), so it has to pinch pennies when it comes to power, or it won't carry any payload. A turbine helo has way too much blade chord for hover (it throws away power) because it needs that chord for higher speed forward flight.
Nick, i remember hearing somewhere than Kaman were the first to switch over to turbine helicopters. Then again their machines always are sold on efficiency, so they are probably using low chord blades. I don't think i've ever seen any real attempt at fairing intermeshing masts for low drag either.
Were S69 ABC blades designed with lower than normal chord? I imagine that X2 will demonstrate that rigid rotor counterrotators have good efficiency potential at all airspeeds, by simply avoiding retreating blade stall. This would especially be the case if the design is eventually able to beep down RRPM at high speed.
Mart