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Old 5th Sep 2003, 11:15
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NickLappos
 
Join Date: Apr 2003
Location: USA
Age: 73
Posts: 3,012
The only way to tell what the stall margin of the rotor is uses the Coefficient of thrust to solidity ratio. This factors in the tip speed (a very important contributer).

Coefficient of thrust divided by solidity. Ct is thrust divided by density, disk area and tip speed squared. Solidity is the total blade area divided by the disk area.

R-22 values (assume thrust is equal to weight):

Disk area 496 sq feet
radius 12.58 feet
Tip speed 676 feet per second
chord 0.6 feet
Max gross weight 1370 pounds

For a gross weight R-22, Ct/sigma is .084, which is very normal for a typical helo (a Black Hawk is about .08). The rotor begins to stall at about .17 and is fully stalled at about .20.

Conclusion, the R22 rotor is very normally loaded, and not near stall in normal conditions.

The referenced R22 paper warns that the conclusion about stall based on a computer analysis that is somewhat flakey (as I think it is) especially when such programs are not backed by flight test data:

http://www.ntsb.gov/publictn/1996/SIR9603.pdf

Last edited by NickLappos; 5th Sep 2003 at 11:44.
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