Originally Posted by davylah
By the way, before anyone mentions the Sikorsky X2, it's not a helicopter, it's a gyroplane.
Nope, it's a compound helicopter.
The Rotodyne used tip jets powering the rotor for takeoff & landing only, the X2 rotor is powered all the time and mechanically linked to the pusher prop.
Still not a true helicopter of course & isn't in the same class as far as speed records go, and it's not the fastest compound one either - it's probably the fastest prop augmented one though (it's faster than the AH-56 anyways). The Bell 533
& Lockheed XH-51
were both faster decades ago but used jet augmentation