Louis & Helen Darvassey/Stan-Z rotorblades

[phantom]

the blade that came apart at the trailing edge sounds like it hit the water first. water strike will cause things to happen that unless they have experience with them can send investagators in the wrong direction looking for causes that were never there in the first place.
bensen hydrocopters could go divergent in pitch with any rotor if you were not flying them slightly to very far behind the power curve.

norm

[Jerry_Forest]

Kevin, these blades must have been an early version because they had rivets along the trailing edge. Three or four rivets held, three or four didn't, etc. along the whole length. I don't know if they were bonded as well. The CofG of the blade cross-section was some amount aft of the 1/4 chord or centre-of-lift point. This would make the blade succeptible to unstable torsional oscillation.

It could go unstable on its own or be induced by a gust or some other transient. Then it twists or vibrates at its torsional natural frequency (or harmonic) and literally "explodes". The forensic evidence indicates that this is what happened to one blade. The dynamic forces would be catastrophic on the rotor and airframe.