Originally Posted by
Wycombe
I recall an awful accident at Oxford in the early 90's when a light aircraft (PA28, I think) was flipped on short finals by the downwash from a large helicopter (S61, I think, which was operating shuttles from there as it was British Grand Prix weekend).
Here is a link to an AAIB report for a PA-28 crash on short final believed caused by wake turbulence from an S-76 in 2009, for interested parties.
I have only a university aerospace engineering degree and yes, rotor blades flap - as I recall, to mitigate dissymmetry of lift as the aircraft moves - but is there a limit to the hinge angle, which, if exceeded, could cause the helicopter to roll anyway?
Could a wake vortex act on the rotor and fuselage independently? I suppose there must be a distance at which the vortex diameter is about the same as the length from the rotor head to the fuselage, so the top of the vortex could grab the rotor and the bottom the fuselage? Although I suspect this distance would be so close to the landing aeroplane that the helicopter pilot would have bigger problems anyway.
Edit: after a quick research, no, don't think so. I just read a paper where the vortex core was measured and it's only about a foot across for a 757 / a bit more for an MD-11. Presumably the velocity outside of the core rapidly decays to a point that wouldn't bother a helicopter