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.

The shaft itself won't eat up power, but the various gearboxes and shaft
supports required will. Every bearing has a bit of friction; every
gearbox has a bit of drag. A long drive shaft, and the gearbox required
to let the cannon shoot through the hub, would cost more power than the
straight installation.

Whether it was enough to matter, in the case of the P-39, is another
thing. ISTR the P-39's problem was the lack of a turbocharger rather
than overall low power... the Airacobra started losing oommmmph above
12,000 feet, and it turned out that most of the combat was higher than that.

Remember, Tex Johnston won the Thompson Trophy in a P-39, and set a
speed record, besides.

Ron Wanttaja