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Old 2nd Feb 2007, 12:47
  #15 (permalink)  
FH1100 Pilot
 
Join Date: Nov 2006
Location: Pensacola, Florida
Posts: 770
Received 29 Likes on 14 Posts
Couple of things...

1) VRS is not always about absolute rate-of-descent of the airframe. Remember the V-22 crash in Marana, Arizona that killed all those Marines? It wasn't that the ship was descending vertically so fast. In fact, the pilot still had "forward" airspeed. But this is deceptive. He also had the nacelles tilted backward (which I believe NATOPS now prohibit) as he was trying to decel/descend and maintain position on Lead, who'd screwed up the approach (and subsequently hard-landed his machine, a fact that was overshadowed by the crash of #2). It was this "apparent" RoD that the proprotors were seeing that caused them to start to go into VRS, evidenced by the roll instability the pilot experienced just before one of the proprotors "let go" into full VRS, putting the aircraft into unrecoverable A-VRS at which point it rolled pretty much inverted and crashed.

2) We need to be careful when we speak in absolutes. Although I generally do not like to disagree with Nick, when it comes to the absolute RoD's needed to induce VRS, one image sticks in my mind: That amateur video of the Canadian Sea King hovering around at the airshow in upstate New York. One minute he's hovering there, pretty as you please, camera steady on him. Next thing you know, it's falling like a wet turkey, blades coned up like a ballerina, tips nearly touching. (I wish I could find the full video that was shown on the local news the day it happened. The truncated clip that we see in the archival footage just doesn't give the complete story.)

I think that maybe nature doesn't always cooperate with our pat theories and "rules." I think that maybe a sudden gust...an updraft through the rotor can make it "think" that the whole aircraft is in a rate of descent. When that happens, if all the other stars are lined up correctly, boom-crash!

Downwind quick-stops to termination? Yikes, there's a scary thought!
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