From: Doug Jones (random@qnet.com)
Date: Thu Dec 28 2000 - 19:58:02 MST
Spike Jones wrote:
>
>
> Hey Doug, Im glad you weighed in on this one. Every time I look
> at the Osprey I think how cool it would be if that concept could
> be made to work. Since you are aerodynamics cluey, help me
> out here. It always looked to me like if the pilot rotates the props
> to horizontal with too much forward speed they would lose lift
> the craft could go auger helplessly into the ground with both
> engines screaming. Wouldn't ya have flow separations all over
> the place? So then there would be a craft that could only be
> operated safely by computer, eh?
Doing a transition at high speed is probably not recommended by the
manufacturer, but I doubt that the consequences are so drastic. The
retreating blades might stall, but the wings would still support the
aircraft while airspeed would bleed off quickly. The vibration would be
hard on the aircraft and pax, though.
The problem in the Marine crash earlier this year was vortex ring
interaction- any helicopter can get sucked in by this, when the descent
rate is the same as the downwash velocity and circulation closes. You
lose lift and plummet, also called settling under power. Dual rotor
helicopters tend to have this happen to only one rotor at a time, so
tandem rotors birds pitch up or down violently, and side-by-side
vehicles roll over. This is followed by a very bad day and funerals.
The most recent crash may have been a simple CFIT error- controlled
flight into terrain. Night nap of the earth flying is not forgiving...
> I thought of a maneuver that might make it safer to land, altho
> it might not be so comfortable to the passengers: as the pilot
> approaches the landing, she would pull it up vertical and hold
> it until the upward velocity reached zero, with the nose straight
> up. Then keeping the props horizontal, the pilot rotates the
> fuselage to horizontal, and gradually settles to the deck, thereby
> avoiding the risk of what has evidently crunched two ospreys:
> lost lift because of rotating with too much forward velocity.
>
> Wouldnt that work? spike
No need- the usual transition is done after slowing to a speed where the
wings can still support the aircraft, and the rotors can also. Why add
drama if the transition can be done simply?
Sure, the V-22 does have some advantages over convntional helicopters-
but the operability and price are not worth it.
-- Doug Jones
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