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Old August 29th 07, 01:57 AM posted to rec.aviation.rotorcraft
Stefan L.
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Default zero airspeed fulldown autorotation

Hello,

I would like to discuss some interesting info and thoughts.

I know that there are helicopters that can do an auto to the ground
perfectly soft with no airspeed and no flare.
I know somebody who did it in an R44.
Then I heard somebody telling about one in a R22 with two persons,
piloted - of course - by TT. I couldn't believe and neither could any
colleague.

But I did some quick calculations and if there is no big mistake, it is
theoretically easily possible. Of course there is the timing issue ;-) I
don't want to try it.

I took the 100HPsec (rotor energy at 104%) out of the R22 flight
training guide and converted them to 74 kJ.

The kinetic energy in a 1200lbs R22 descending at 1500ft/min translates
to only 16kJ. Even at 1370lbs and 2000 ft/min it is still less than half
(namely 31 kJ) of the energy in the rotor at 104%!!!

Of course you cannot get out 100% of the rotor energy, only down to
about 80% at sea level and aerodynamic efficiency is bad. But hey, you
can go up to 110% and at 1200lbs it is only 16 kJ, less than a quarter
of the rotor energy.

I do not want to have anyone try it, but has anyone here ever done such
a thing in any helicopter?

I'm NOT talking about the dead man's curve!!!
I'm talking about a perfectly established auto with zero airspeed at
high rotor rpm which needs several hundred feet for establishing!
There is no way to assume one could do it after an engine failure in
300ft AGL at 20kts!!!