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Peter Garrison summed up with:
"In my opinion, it is unlikely that any flap deflection has a discernible positive effect upon rate of climb, but I would be interested in seeing evidenceâ€"from actual flight test, not anecdoteâ€"to the contrary."
I do not fly with a recording variometer but I do fly with a variometer. This contribution is, in fact, anecdotal, and it may not translate to powered airplanes. But Peter did mention gliders...
I fly a rigid hang glider with inboard trailing edge (simple) flaps. On days of weak lift, I fly from thermal to thermal in as streamlined an airfoil configuration as possible, with zero degrees of flaps. Once in lift, I will set approximately 10 degrees of flaps. I Invariably notice a corresponding increase in apparent rate of climb. In the absence of lift, 10 degrees of flaps will just yield a slower rate of sink. The difference is measured in feet per minute. More flaps, up to 40 degrees, yields an increasing sink rate.
Regarding the increase in rate of climb or decrease in rate of sink, I once wondered if perhaps the 10 degrees of flaps were simply forcing the nose down into a more efficient angle of attack. This could be the case if I were chronically trimmed too slow. However, I was not able to reproduce the sink rate/rate of climb improvements simply by lowering the nose.
In case it matters, my glider has no tail, but has outboard trailing edge elevons. Airspeed at which I notice these differences is about 24 mph.
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