retreating blade stall
helmet fire
Thanks for your explanation of the rapid loss of rotor rpm because of low rotor inertia.
I am still trying to understand what the cause of the rotorhead separation described in NTSB report actually was. The report does'nt give any explanation. The 1996 report says that early (1980-81) separations were thought to be caused by low rotor rpm and that problem was fixed with an engine governor and raising the low rpm warning from 90 to 97 percent rpm I think it was.
But the main purpose of the report was the fact that a rotor failed at normal rpm and that fact concerned the NTSB and concerns me.
In that case it seems likely to me that the blade may have stalled because of a gust. A stalled airfoil tends to dive and could hit the tailboom under the right conditions possibly. I dont know, this is all new to me, most of my experience is fixed wing and fixed wings do not often fly normally at high angle of attack close to stall.I do fly gliders close to stall climbing in a thermal normally but that is never near the ground.
It appears that helicopters do operate at close to stall angle of attack in normal flight (at least that is what the Robinson manual says).
So do helicopter pilots need to be concerned with retreating blade stall and possible blade divergence into the the tailboom in turbulence or is the blade designed to handle retreating blade stall?
Also could a low inertia blade be more likely to diverge when hit by a strong gust?