Sikorsky Helicopters recently completed the first ground run tests of it’s S-97 Raider compound helicopter. The Raider is the latest form of Sikorsky’s X2 test program, which used a nearly-identical rotor and propeller combination to push it to a 250kt (290 mph) air speed, which is about fifty miles an hour faster than the fastest conventional helicopter, a modified Westland Lynx.
The counter-rotating rotors solve the problem that’s created when a helicopter’s rotor system exceeds the sound barrier. In a single-rotor system, once the blade passes Mach, the shockwaves induce flight characteristics that would scare the absolute hell out of the most jaded pilot. With the S-97, the propellor out back not only functions like a tail rotor on a conventional helicopter, but at speed it becomes a pusher prop and the main rotors can be slowed down to a safer speed.
Originally designed to take the place of the recently retired OH-58D Kiowa Warrior, the S-97 is being pitched as a development phase of a joint project between Sikorsky and Boeing that has been dubbed the “SB-1 Defiant” as part of the Armed Forces’ Future Vertical Lift program, which aims to create four distinct classes of aircraft that have parts commonality between airframes.
In the mid 70’s I was working @ Sikorsky as an outside contractor.
They were working on the ABC copter (advanced blade concept) and it had the same rotor setup. Very fast even without the pusher blades!
Had a problem with angle of climb. Saw one of the prototypes crash while taking off at a fairly steep angle. Fortunately no one was hurt, but the ship was pretty messed up.
Cool. A bit like the Lockheed AH-56 which was the fastest helicopter in the world as a prototype that the Army rejected.
I remember hearing something about a prototype helicopter with coaxial rotors almost 30 years ago. I wonder if this is a continuation of that?