It used to be that Army flight school included, in the second half of the curriculum at Ft Rucker, a demonstration of " settling with power ", which, when one listened to the verbal description, was their understanding of VRS. The demonstrations were usually unsuccessful: only a few of the students in my class had the eye opening experience. I wasn't one, as my instructor, who was an ace in all other things, set the H-19 up in a vertical descent and I received one of those: " do you feel that....there it is.....we are on the edge of it...." recitations, while in the back of my mind I was thinking, " feel what ? ". Two months later I was out of flight school at the Test Board at Rucker in a "lead the fleet " UH-1D with 44' main blades, by myself, and after a few tries I finally got that vehicle into a real VRS event.
The point of the story, is that it is very, very hard to get a single rotored machine ( my only experience in this subject area ) into this aerodynamic situation.
Rotary Wing history seems to prove that to be the case.
- Does the logging community have a history of VRS induced accidents?
- Does the military heavy lift and artillery haulers have a history of VRS incidents?
- Does the special ops community have a history of VRS accidents?
- In all of the military H/V testing ( less the V-22 ), and FAA H/V and Cat A testing done all over the world by various manufacturers, has the VRS situation been encountered and reported?
The list could go on, and one would expect, based upon the protestations of the V-22 community that ALL helicopters are subject to VRS if within the dreaded 40/800 boundary, that there would have been accident fields of aluminum shards all over the world, accompanied by the type of FAA and military safety symposiums associated with the current EMS accident situation.
That hasn't been the case, as the entire current VRS discussion has been initiated by the V-22 community following the 2000 Marana accident. Well it should, as far as the V-22 is concerned.If the V-22 manufacturers and operators, based upon their testing, choose to impose a flight limitation, they are correct in doing so.
On the other hand, I have not seen nor read any evidence that justifies applying the V-22 flight limitation to other flying machines.
Two other related observations:
1. One aspect of the V-22 vs single rotored helicopters in VRS to ponder is why the V-22 apparently "rolls off" and cannot be controlled, whereas the single rotored vehicle remains controllable in VRS. I know the latter to be true, and assume the former based upon the accident details that were in the press.
2. Osprey Driver wrote"
"If you can power out of it, then by definition, it wasn't VRS. The only exception, I would think, is if the additional power aggravated the VRS to such an extent that one continued to descend through the bad air and managed to get into better air below."
Never having attempted to exit VRS in that manner, I can't comment from experience, but in the well-known Ray Prouty book, if one looks at figure 2.7 ( page 105 ), there is an analytical argument that says one can, with a slight "predicted" additional power( 10-12 % ) required to overcome what he refers to as a "settling with power" region.
Thanks,
John Dixson