To prevent a much longer debate here....perhaps a bit of ancient history being introduced might help.
A quick read of this thread done in the past right here at Rotorheads might produce a way to better frame the two competing views.
Of interest is one post made by Nick Lappos who is a very astute individual when it comes to such issues.
Vortex Ring / Settling with power (Merged)
Nick is not here to discuss the following post but it is just one of many he has contributed during other discussions of VRS and SWP.
For what it is worth....I agree with both Crab and Nick for an array of reasons.
There most certainly is a difference between SWP and VRS. and to say otherwise fails to fully consider all of the factors that affect each....and both.
I recall Nick saying in one of his posts that in some modern helicopters there is enough power in the Rotor Systems to simply climb out of VRS....although for sure I am oversimplifying what he had to say about that.
Crab and helisphere,
I can't subscribe to the updraft theory of VRS, it is just not that clean. The precise disk angle needed to enter and sustain VRS is not something that an armchair calculation is likely to prove. True VRS is a flaky thing, often needs the pilot to work at staying in the condition. I would be interested to chat with a long line pilot to see what he/she experienced in the event.
I would bet dollars to donuts that power issues are much more the issue, and I must say that few "experts" know much about the distinction between VRS and SWP to differentiate, including experienced and well intentioned government safety experts and investigators.
To my knowledge, no tests have shown anything close to a VRS case where updrafts and such have triggered any events. I believe the conditions that would create the updraft would also create enough turbulent flow to disrupt all those calculations (but that is a belief, not based on data.)
The situation is perpetuated with a thousand "VRS" demonstrations by a thousand instructors who show SWP to their sutdents. I searched youtube for VRS demos on video, and found NONE that were VRS, all were SWP.
To recap, to get VRS, you must descend at about 70% of the induced velocity, about 700 fpm, and also have about 8 knots forward velocity (straight down will not do). If you enter from lower descent rates, it is not VRS, it is SWP, and if you do nothing to correct the SWP, it can degrade to SWP.
None of the above means there is no danger, just explains what the physics of the situation is. The cure for either is about the same, once in the situation, but the cure to prevent SWP is to retain some power margin, enough to allow some vertical maneuvering while OGE. THAT is not mentioned in the typical VRS discussion, making it somewhat misleading to spin on and on about VRS, descent rates and updrafts, when most cases can be solved with adequate attention to power and weight.
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