Originally Posted by
The Sultan
I once witnessed (from extremely close range) an AH-1W running on the ground at 100% rpm release an internal main rotor blade weight due to a decade old manufacturing error. When the weight departed it:
1. Blew the end of the blade off,
2. Snapped the main transmission horizontally in half,
3. As the rotor/top case exited the still attached controls put in full pitch,
4. The aircraft was lifted 6’ or so by the control tubes which then failed dropping the fuselage back to the ground,
5. The now unattached rotor climbed 80’ before loosing energy and crashing down in front of the airframe.
The magnitude of the unbalance was so large the xmsn was snapped within one revolution of the rotor so no large 1/rev forces were transmitted to the fuselage. The only fuselage damage was to the cross tubes on one side. The pilot commented that he heard a bang, the aircraft smoothly lifted before falling back to the ground. The airframe was refurbished and returned to service.
if the weight had been less and not immediately snapped the xmsn case, the excessive 1/rev would probably have broken the pilot’s neck and damaged at least the tailboom.
So back to this thread. It is plausible a failure in a blade caused excessive 1/rev which buckled the tailboom and put in full tail rotor pitch through the still connected controls tubes causing the observed yaw. Then a combination of 1/rev loads and aero forces caused the rotor/xmsn/nodal beam to depart with the rotor appearing to fly away intact.
Won’t know until we see both blades.
The video I watched showed what appeared to be the entire main rotor system autorotating to the surface, complete with the top of the gearbox casing. I doubt it would have done that if there were significant out of balance forces.