Originally Posted by
212man
Yes, but it wasn’t trailing!
Yes, I meant 'trailing' in the traditional sense of the blade profile.
But I am curious how that blade would have behaved in this incident. A brief search of the internet found a discussion on aerofoils flying in reverse (
https://aviation.stackexchange.com/q...lown-backwards). It drifted off topic but there was a useful plot of the lift on various aerofoils with AoA ranging from <0 to +180 degrees. So the data approaching 180 degrees gives an appreciation of lift vs AoA of an aerofoil flying in reverse. While a NACA 0012 profile has a fairly linear L vs AoA range up to around +/-10 degrees in forward flight, the linear range of L vs AoA in reverse flight seems less at only around +/-7 degrees:
But I doubt it was the L vs AoA characteristics that resulted in the description of the blade behaviour provided by Smokeyboy (#8). Lift on a wing is typically centred at around the quarter chord from the leading edge. When flying in reverse, that would remain the case but it is now located near what should have been the trailing edge and so no longer close to the axis of rotation in pitch of the blade. Once RRPM increased enough, or with some collective added, the outer tip of that rotor probably twisted into a higher AoA until the stored energy in the twisted blade 'let go' and made the blade tips twist back in the opposite direction. I guess it could be described as an aerofoil flutter behaviour(?). The sudden change in lift at the rotor tip (with no further control input required) could explain the blade flying up first then down before taking out the tail boom.