FFS this again! I get the feeling that either modern day helicopter pilots get less and less training in these areas or FI's are more dumbed down than before and don't understand it themselves. Other than CFIT, I would argue that these two phenomenon's alone - are one of the biggest causes leading to a crash.
STILL this subject rears its ugly head. One would have thought that over the years almost all 'experienced' helo drivers are acquainted with the issues, done their own research or spoken to someone who fully understands it. Probably the best "experienced practitioners" for flirting with IVRS - are long liners and cattle musterers, who can sense these states almost instinctively if they live long enough!
For the "Nth" time and for as long as it takes to educate the lumpen proletariat, here it is all over again:
http://www.pprune.org/rotorheads/116...merged-14.html
Go straight to
post 261 by Nick Lappos who used to be Chief Test Pilot for Sikorsky. This is 'probably' the closest anyone will get to trying to illustrate the difference between VRS and SWP.
In a nutshell and K.I.S.S:
VRS: This requires a descent (usually >70% of the induced flow). It requires a LOW fwd speed and finally it requires application of power (You cannot have VRS in auto). 3 FACTORS.
SWP: Descent needed, Velocity (vertical or fwd), Application of power. 3 FACTORS.
To the ignorant (and I chose that word carefully), they appear similar. Far from it.
What then is the difference (drum roll):
VRS is an AERODYNAMIC phenomenon - it is to do with developing blade stall/induced flow/big green arrow movements/vortices.
SWP is a PERFORMANCE phenomenon - it is to do with the engine(s) NOT providing enough power to arrest the 3 defining factors.
Both require height to recover. Fully developed VRS requires 1000's of feet. Let no-one be in any doubt about that.
SWP requires a tiny fraction of this amount.
{Tail rotor effectiveness (TRE): diminished as it enters dirty air from the main rotors during VRS.}
Of course if mother earth chooses to intervene during the recovery phase............
See you all here again in 2021......
