Guys, I'm not quite sure that "stalled prop" is correct terminology. I
think "slippage" might be more approprite. I don't think that there
something unusual happening, other than the prop is trying to push (and
pull in) more air than is available in a static position. It's similar to a
slipping clutch that finally stops slipping when the car speed matches the
engine speed. The prop is just running at a very low efficiency when
standing still.

I believe Ed's new engine is making more hp than the old one, and thus, is
able to spin the prop at a higher rpm. As was suggested, he should watch
his t/o roll rpms to see if it goes up, or drop off a little. I had a
similar problem in that I had to throttle back on t/o, or risk
overreving/overboosting because the prop was slipping a lot. When he's
flying he will be able to tell if he needs a different prop (more pitch,
etc). You'd only change the prop now if your rpms are too low which would
indicate too much pitch/too little hp.

Chuck Harbert

I am convinced that "stalled" is the more proper term. You do not say that your
wing has "slipped" when you fall out of the sky.  At static operation the angle
of attack on the prop sections is a function of the blade angle, and the stream
velocity thru the prop. At static that angle on most props is over the classic 15
degree stall angle, in the inboard steeper part of the prop. With our props
pitched so we can strive for those nice top speeds near 200 mph, this represents
quite a large portion of the inner section of the prop. The stalled portion is
reduced as foward speed is increased, and more of the prop becomes effective.
This may, or may not be perceptible to the pilot. This same efffect in marine
props is improperly called "cavitation", and is more pronounced because the
smaller props are more "twisted" to higher angles. - Vance

Vance is correct. As the airspeed increases, the effective (relative) angle of attack of 

the blades decreases and more of the air flow over blade reattaches and the blade becomes more effective.
This should be appearant during high taxi tests. The RPMs will sag as the prop becomes effective. If the static thrust is known for this prop/RPM, there would be the same thrust at the same RPM now. The higher RPM may produce less thrust now with a higher portion of the blade stalled. Once up to speed everything gets way better. Lynn E. Hanover

Lynn E. Hanover

 
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