Thanks for the replies everyone. Very interesting. I'll ask the instructors where I fly if they know about it.
Not sure I follow the distinction between VRS and SWP. Looks as though the idea is that one is what happens in (e.g.) a steep approach, where you're descending at reduced power, while the other is what happens when you try to hover OGE and don't have enough oomph to make it work (as happened to me). But it also looks as though Crab and Hawkeye are using them opposite ways round.
Aerodynamically, aren't they the same thing? The FAA Rotorcraft Flying Handbook has a section called "Vortex Ring State (Settling With Power)". The ASA book has the same section heading.
Shawn's book does make a distinction (p. 174) but then goes on to say "Vortex ring state is a more clear, precise definition". I think that what he's saying is that you can be in a situation where you don't have enough power to maintain altitude, without necessarily getting into VRS. Though if you're HOGE with no wind (or sort-of hovering with zero airspeed) then VRS must surely rapidly follow. (And he has a footnote which says "The term [SWP] is very misleading and won't be used. I'd ask you to remove it from your vocabulary.")
Last edited by n5296s; 11th Mar 2015 at 18:36.