Autos and blade loading

[Spaced]

Just wondering at what point an auto becomes impossible with reguard to blade or disk loading.
From what Ive read the V-22 has some sort of auto capabilty although the desent rate is around 4-600ft/min.
Out of some sort of deranged madness I visited Mollers skycar site, which he stated that over 30lb/ft^2 autorotation is impossible.
Is that right?
Any thoughts apreciated.

[sycamore]

These figures are approximate for the V-22, and assuming an average blade chord of 2.5 ft, give a total rotor area of 2268sq.ft, and a blade area of appx 270 sq.ft,. At a MAUW of 57000 lb. that is appx 25 lb/sq.ft for area loading and about 211 lb/sq.ft blade loading.
For a Long-ranger at 4200 lb the figures are 4 lb, and 108 lb/sq.ft.
Be a bit like kissing a ducks arse at the flare!!!.
Syc.:yuk:

[Grainger]

Spaced: I think you'll find that's 4-6 thousand ft/min. :eek: :eek: :eek:

I think I'd rather take my chances on the bricks they'll be overtaking on the way down...

[NickLappos]

Rate of descent in autorotation is determined by the disk loading, so the heavier the rotor disk is loaded, the faster the bird comes down. The cyclic flare is the only way to slow that ROD, and this flare is also less effective at high disk loading, so the effect is doubly harmful.

In addition, the collective pitch pull at the bottom relies on rotor inertia to provide the power to cushion the touchdown, and a small rotor like those on tilt rotors has about half the inertia of a helicopter. This makes that final few feet a real problem.

I am told that the V-22 comes down like a brick in auto (the 4600 feet per minute sounds about right) and the cyclic flare is not very effective, so the auto is really a controlled crash. The V-22 is intended to come down in airplane mode, and just shed the blades on landing. Of course, its wings are highly loaded, so the touchdown speed in airplane mode should be 130 knots or so (!!)

The loading of the blades are not much of a factor here, that is more important for the maneuvering thrust capability of the rotor.

[46Driver]

4600 ft per minute? Makes me curious what a CH-53E comes down at. First time I saw the big Sikorsky doing an auto, it looked Wile E Coyote dropping the ACME anvil. If an Osprey comes down faster than a 53,..........

[NickLappos]

46 Driver,

You are astute! The 53E has a disk loading of about 14 lbs/ft2, and it comes down at about 2800 feet per minute!

It does have a pretty good flare, and lots of rotor inertia, so it can autorotate. One of the old time Sikorsky test pilots, a real pro and former Marine named Jack Peterson, autorotated the 53E during its initial trials back in the mid 1970's. he made a soft landing a about 25 to 30 knots as I recall.

[Arm out the window]

Great metaphor there, 46 Driver! Maybe the tilt rotor would look a bit like Wile E Coyote after hitting the ground at the end of an auto, too; that is, all concertina-ed up.