On 12/10/2010 07:36, Rick Cavallaro wrote:

1) The prop *will be* 100% efficient in transferring its energy to the
air - there's no other choice.

ummm... yes... but... and I hate to point this out to someone who knows
_lots_ more about this that I do...

snip
That's right. But keep in mind, its output power *must* equal it's
input power. So if you don't like the definition given, you have to
think of another somewhat arbitrary definition. For example, you
could say that only the velocity added along the axis of the prop
counts as being approved output energy - while the swirl velocity is
wasted energy. But then we could have this same debate about how much
energy the prop "really" added to the air. The point being - without
some sort of "arbitrary" definition of prop efficiency, the prop will
always be 100% efficient.


Add to the swirl, the localised turbulence around the blades, especially
the tip - and heat from plain old skin friction. Now I'm pretty sure
_you_ know all that, but others won't.

Andy