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Here is an explanation of the original problem with the Osprey...

"The mishap investigation, having ruled out all other possibilities, soon focused on the extremely high rate of descent at low altitude as the primary cause of the accident. It was concluded that during the descent, the aircraft entered an aerodynamic condition called vortex ring state (VRS)."
LtCol Gross explained that VRS is an aerodynamic condition in which the tangential airspeed at the rotor is small (associated with low forward airspeed) and the airspeed perpendicular to the rotor is high (associated with powered rate of descent). VRS typically becomes a concern below 40 knots forward airspeed at high rates of descent. To reach this condition, power must be applied during the steep descent. In layman's terms, when the induced velocity equals the vertical velocity, VRS may occur, causing a reduction in rotor lift or increased sink rate. VRS can occur as a rotorcraft settles down through its own vortex field at slow forward airspeeds.
When they knew where the VRS boundary was located, how the aircraft responded during VRS, and the proper recovery procedures and techniques, their focus turned toward avoidance of VRS. The engineers made two changes to the avionics displays that increased the pilot's situational awareness during low-speed, high-rate-of-descent flight.
With their test effort behind them, the Integrated Test Team at Naval Air Station Patuxent River, Navy and Marine Corps test pilot facility, is confident they fully understand the location of the VRS boundary for the tilt-rotor, the aircraft roll-off characteristics during steady maneuvers within the boundary, and the immediate and effective recovery procedures. They have developed avionics warnings to aid pilots in avoiding high rates of descent at low airspeed and the fleet has a better understanding of the capabilities of the MV-22 Osprey and will be confident to fly in harm's way knowing vortex ring state never will be encountered again.
Lieutenant Colonel Gross was the government flight test director for the MV-22 program from August 2002 to August 2004 and participated in several test flights. He currently is assigned to the V-22 Joint Program Office at Patuxent River, Maryland. He would like to acknowledge Tom Macdonald's and MV-22 lead government engineer Ray Dagenhart's contributions to his article in Proceedings.
http://www.military.com/Opinions/0,,Hayden_101304,00.html

Thanks for your post #11. That is the first I have ever read anything about what the testers did SPECIFICALLY to tackle this problem. Most other reports (I've read) just glossed over it and said they altered the flight parameters.

Thanks for that. I was wondering "wither the Osprey" just the other day (I have a fascination with military aerial equipment).

Very helpful, very useful, very interesting.

"Testing defined an operational envelope for the aircraft and demonstrated flight regimes free from vortex ring state (VRS). Tests also probed deeply into fully developed VRS to determine precise flight conditions where it may be encountered, and to confirm the ability of the V-22 to recover from the condition. The ability to tilt the nacelles proved to be a powerful and (in every case) reliable means for rapidly regaining aerodynamic function of the rotors, even when operating in VRS beyond the point of having sufficient controllability. Results for steady-state HROD conditions are presented and the methods for testing are described. In an operational sense, the test results show that the V-22 has a significantly higher rate of descent margin for avoiding VRS with respect to the published NATOPS limitation than conventional low-disk loading helicopters. Furthermore, dynamic maneuver testing of the V-22 showed that VRS cannot be initiated outside the steady-state VRS boundary. Simple engineering analysis is used to show that the V-22's steady-state VRS boundary is predictable by simple methods that work for conventional helicopters. High blade twist, and the side-by-side rotor configuration of the V-22 do not play a significant role in defining the VRS boundary." (emphasis added)

V-22 HIGH RATE OF DESCENT (HROD) TEST PROCEDURES AND LONG RECORD ANALYSIS