Originally Posted by
nigelh
I would still however like to see a proper comparison of the two techniques, as it may be that the pilot doesnt have the room infront and below to pole forwards and dive due to obstacles .
I regularly teach both techniques in R44s, and less frequently in B206 and R66. My typical recovery is from sink rates of 1000-1700 feet per minute. I have been in VRS in an R22 that pegged the VSI, but I guess I'm not good enough to nail the downwash as well as that pilot could; I've never been able to peg the VSI myself - I tend to fly out of it before I can get those kinds of sink rates.
I'll also mention that a while back Nick mentioned that sink rate to achieve VRS varies with disk loading (which affects downwash velocity) thus a light disk loaded machine like most pistons will be in VRS at a lower sink rate - he had calculated that the R44 was in VRS @ 800 ft/min. So we have the issue that the least experienced pilots are flying the machines that are the easiest to get into VRS.
In any case, I do indeed see quicker recovery using Vuichard than traditional... typically 40-50 feet vs 150 feet. It is quite abrupt - it's like hitting a speed bump as it shoves you out of the downwash. It's also slightly less comfortable for student pilots because you then have to recover from sideways flight which can be disorienting for a low time student pilot.
The traditional method also has a problem for low time pilots in Robinsons - we spend a lot of time teaching them not to do aggressive cyclic pushes in order to avoid low gee, so it feels weird for them to do an aggressive cyclic push in that situation. This can cause very slow recoveries from VRS..
My suspicion all along is that the faster recovery I see with Vuichard is because I'm not lowering the collective, the way I am with the traditional technique. It would be interesting to understand what Vuichard would do with a deeply stalled rotor system, however in 30 years of teaching probably tens of thousands of recoveries from VRS, I've never felt any indication that the cyclic was losing effectiveness. So it might be that if I did the forward recovery without lowering collective I would see the same 40 feet (but I'm somewhat skeptical that I would).
Of course, we shouldn't be recovering from fully developed VRS anyway, because what the heck were you doing all that time the sink rate was increasing??? My general advice to new pilots is that if they are on approach and they feel that sinking feeling down around ETL speeds, they should simply go around - chances are fair that they had a tailwind or otherwise screwed up the approach. If you detect it while you're right around ETL speed, you don't have to gain very many knots of airspeed to be flying again.
If it's an OGE hover it's a little different, but in that case you're presumably trying to hold a specific altitude, so it's pretty obvious when you start to sink... long before you hit VRS you should have fixed the sink rate...