Originally Posted by
Lonewolf_50
if the main rotor mast bent while at flight RPM, in powered flight, at some point between the top of the transmission case and the rotor hub, that would probably create some vibrations and loads that the attach points aren't built to withstand. I an not sure what would initiate such a bend..
Just to add, I've found if a 206 mast is under power it will either twist or shear vs bend.
Originally Posted by
ferry pilot
And how many of those hours were flown with these blades and in conditions that could induce them to bounce?
You'll find that 63 year service history does apply as Bell blades were known to "bounce" as well. However, there are a couple other differences between the Electra whirl mode vibrations and this helicopter. For one is the difference in the cycle rate of the "h
armonic vibration coupling," to use your term, between the Electra and a 206 or any other helicopter. While the Electra destructive wing flutter happened over a period of flights or time, any similar "coupling" or bounce would have destroyed this 206 within that single event and probably within the 6 bounces. Its somewhat similar when a helicopter goes into ground resonance where the "h
armonic vibration coupling" can and will self-disassemble the helicopter within a dozen or less blade rotations. The other difference, the "bounce" discussed here is induced by the pilot which in turn is usually due to a system discrepancy like an improper collective minimum friction setting vs a design issue like with the Electra. Because of the destructive nature of "harmonic vibration coupling" in helicopters, any design flaws are usually worked out long before the aircraft is even flying.