Anybody who doesn't agree that
it takes a higher rate of descent for a tiltrotor to get into VRS than a helicopter will have to argue with Ray Prouty (backed up by the empirical data gathered post-Marana accident by Tom Macdonald and team). Nobody will deny if that higher rate is exceeded in a tiltrotor than A-VRS can result in devastating consequences that a single rotor helicopter would not be vulnerable to.
Ray Prouty's comments after the accident and before it was known that the Marana V-22 entered VRS at 285ft agl at 2500+fpm ROD:
"The vortex ring explanation never made any sense to me," adds noted aerodynamicist and R&W columnist Ray Prouty. "By my calculations, the Osprey should have been coming down a lot faster than it was to get into a classic vortex ring state." The doomed MV-22, he concludes, "must have been hit by a meteorite."
It’s all part and parcel of the many "unknown unknowns" that afflict helicopters—especially revolutionary new rotorcraft like the Osprey, Prouty says. Or, as military aviators bluntly put it: the flight manuals are written in blood.
"I would say the V-22 has had some really bad luck," Prouty says.
Prouty says in the previously referenced article:
Test pilots have found that by tilting the engine nacelles forward, they can get out of this interesting situation, but the main result of the tests was to define a safe flight envelope within which they never would get into trouble.
Rotor & Wing Magazine :: Ask Ray Prouty
However, at 2500fpm ROD and 285ft agl I think few of us would disagree that it would be too late for either a tiltrotor or a helicopter to recover.
JD says:
Oh, I did want to respond to one thing Lonewolf wrote:
"I note that when checking this out, John took the bird up to 6-8000 feet."
Two reasons. First is that it isn't easy to find a fully developed VRS situation, and the second is that once found, a respectable length of recorded data is appreciated by all except the flight crew being bounced around.
John,
Would you be willing to give that a try at 2500+fpm ROD at 285ft agl?
Just curious...
thanks,
21stC