Propeller Efficiency

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

Sure, the air will swirl around some as it leaves the prop. It
has to, since there is no such thing as a drag-free propeller. But
it's manageable. Anyone who thinks he can design a better propeller or
airplane or anything else is well advised to do his research first so
as to avoid spending vast sums of money making the same mistakes
dozens of other guys have already made. If the OP, who is a PPL
student and has been known to "know better than the experts" in the
past, wishes to design and build himself a phenomenally new and
successful airplane or flying car, he'll have a pretty hard time doing
it. There are hundreds, maybe thousands worldwide, of aeronautical
engineers who know the limits of the physics and materials involved
and they are often employed at very good salaries by huge aircraft
manufacturers who wish to save even a few percent on fuel consumption,
drag, safety risks and other costs just to give themselves a
perceptible advantage over the competition. Any large improvement at
this point is going to require some new technologies that don't exist
yet. Better to spend the time discovering those new technologies.
There are many garages and barns and landfills full of pointless
efforts at designing a new airplane. Most successful new designs are
variations on the same old theme we've had for a long time now.

Dan