05 February 2010
Dynamic Rollover in a Rotorway Exec.
What happened here? I can only guess-
This is a "Homebuilt" helicopter. You buy it in kit form and put it together from thousands of parts. Then as the builder, you are also the "Test Pilot". I believe this machine has a tail rotor that is driven by several long V-belts inside the tailcone. That tone of descending pitch you hear in the video? I think it's likely the sound of those belts beginning to slip, allowing the tail rotor rpm to slow. Obviously as the tailrotor rpm slows it becomes less and less effective, requiring the pilot to apply more and more anti-torque input to compensate.
At some point the tailrotor would reach a critical angle of attack and would stall. I think that may be what's happening here just as the helicopter is touching down. Once the tailrotor is stalled the pilot cannot stop the fuselage from turning in reaction to the torque the main rotor is applying to the fuselage, so the pilot loses control of the helicopter and gets into the phenomenon known in the helicopter realm as "dynamic rollover".
(Remember, the rotor on this thing turns opposite from most helicopters.)
Anyone got a better explanation?
Interesting video on the subject here.