What's the latest news of the V22 Osprey?

[JohnDixson]

Back to 21st Century

Let me explain a bit further re the questions I posed.

First, however, someone forwarded my post to Tom MacDonald and I received a very appreciated response from Tom, and it was good reconnecting after many years. I probably should mention that in 1992 or so, I instigated an attempt to offer Tom a job flying at SA, which, unfortunately for us, but probably crucial to the Bell/Boeing V-22 Team, he did not take. In his response, Tom mentioned his intention to write an in-depth SETP paper at length on the subject, saying that the 2003 paper was limited by the 20 minute presentation time allotted by the SETP at their functions.

Anyhow, as to the first question on V-22 aircraft reactions to VRS, the underlying reason for the question is that there is a separate aerodynamic situation that perhaps some may mistake for VRS, and while it is clear that some posters have very obviously encountered true VRS, some others may have mistaken what I am about to describe for VRS.

This particular phenomenon was demonstrated to me just after I joined SA in 1966, by our Sr Exp. Test Pilot Byron Graham ( I was the ad hoc copilot, but that's another story ) He was doing a 53A flight loads survey at max weight and on the card was something called a " Rough Approach ". Up and away, he slowed the machine almost to a hover, and then began a descent. At about 20 KIAS and 1500-2000 fpm, that machine went from dead smooth to an ungodly N/rev hammering. Zero pitch or roll perturbations and zero effect upon cyclic control power/sensitivity. Other than the exceedingly high vibration levels, the aircraft was hands-off stable. Byron explained the SA aero people's analysis as being that the advancing blade tip is intercepting the tip vortex from the preceding blade. So, over the years, I can say that I saw probably a couple of hundred of these events, in 4,5,6 and seven bladed models. Behavior is the same, but the indicated speed/rate of descent for the event is controlled by the blade loading, attitude ( really the CG influence ) and the behavior of the particular airspeed system of that ship ( sometimes the speed is bouncing off zero ). Some forward speed is necessary, and the descent angle is very very steep, but not quite vertical.

The second question I proposed asked whether the V-22 testing included prop pitch increases after VRS was encountered. I was asking about pitch, and do understand that the V-22 has isochronous governing, and that the prop Nr is increased automatically when in helo mode. I suspect that answer will have to wait for the longer SETP paper. My curiosity derives from thinking, based on some hand-done CT/sigma ( blade loading ) calculations that the prop rotor is already at fairly high Ct/sigma values already when coming to a hover. Just curious.

Again, thanks to whoever sent my previous post to Tom MacDonald.

Thanks,
John Dixson