Propeller Efficiency

On Apr 16, 3:05*am, wrote:
On Apr 15, 3:53 am, WingFlaps wrote:





On Apr 15, 3:11 pm, wrote: On Apr 13, 8:20 pm, WingFlaps wrote:

Does anyone have any idea of the ratio between thrust power and churn
power?

Less than 80%. Look in Wiki for discussion of losses.

* * * Wiki isn't so accurate. The figure for max efficiency is in the
range of 85 to 87%, depending on AOA and a bunch of other stuff. The
Wright Brother's propeller on their Flyer had an efficiency of 83%
because they understood that it was a rotating airfoil rather than
some sort of paddlewheel.
* * * For prop math, see this: *http://www.epi-eng.com/propeller_tec..._propeller.htm

There's nothing like theoretical efficiency calculations to impress.
I'll say it again, real props struggle to achieve 80%. Now Dan, before
you jump down my throat, note that of these calculations in your ref.
did not include vortex tip losses and most don't even consider
friction and never compressibility (which is major problem *as the tip
goes near or supersonic). Basing efficiency purely on slip doesn't
work for real airscrews and the washout is nearly always _wrong_.

Cheers

*Those calculations are more than theoretical. We know, in foot-pounds
per minute, what an engine produces, and we can take that directly to
the acceleration of the airplane or its cruise speed versus drag, and
come up with an efficiency figure.

And the answer is TADA less than 80%....

Cheers