On Nov 3, 9:52*pm, a wrote:
On Nov 3, 8:51*pm, brian whatcott wrote:



Ricky wrote:
A question for the physics-minded among us, or for anyone who just has
the answer.

I have heard the Airacobra was underpowered and that got me to
thinking;
Does having an engine at the middle of the fuselage (in any plane for
that matter, like the XP-58) and connected by a long shaft contribute
to a loss of power delivered to the propeller? In other words; would
there be more power delivered the closer the engine is to the prop?
Does the shaft "eat up" power in any way? I am a mechanic and pilot
and fairly knowlegable about a/c physics & aerodynamics but this has
me stumped.

Thanks in advance for your ponderings and/or solution!

Ricky

It's a question often asked in connection with long shafts.
The elastic angular compliance can be a positive help with vibrations,
which are absorbed by a quill shaft. But a shaft drive train that's
curved takes pillow blocks to support the curve, and these bearings take
some (small) power on their own account. Otherwise, air drag, and
bearing drag apart, there's no loss in a long quill shaft.

Brian W

I had a ME design a centrifuge application with the shaft running well
above its critical speed a bunch of years ago, but don't remember the
tradeoffs that led me to accept that embodiment. *It was not an
aviation application in any event. I did find the observation about
wind profiles around a pusher imposing design constraints -- I'd have
thought that far aft winds in the disk would be fairly uniform except
at high angles of attack.

Have you a sense of the improvement of thrust, if any, *a given engine
might have wing mounted vs nose mounted? There's less to blow against
but the wind does extend to well past the prop disk so some of that
air near the outside diameter is compromised by the wing. I'm thinking
of an application where one wants the maximum endurance at fairly low
speeds. That around the world airplane that came out of Scaled
Composites might hold the answer.

Opps, not built by scaled composites after all. Interesting that the
rear engine was the one that ran all of the time, so that was the more
efficient location (but what does Rutan know?).