Drum dia and torque

Bob Johnson wrote:
Hi Bill --

Today we towed in light wind and so turned 2300 engine RPM in the climb. The
454 c.i. torque/hp curves show the engine was generating about 430 lb-ft
torque and 200 hp at these revs.

Now here is where I tend to go off the rails. Just 75 hp is required to lift
a 1100 lb sailplane 1700 ft in 45 sec.

I know there are some aerodynamic and mechanical losses but it's hard to
believe they amount to some 125 hp.

The 200 hp rating is at full throttle - is that what you were doing? If
it is using an automatic transmission with an unlocked torque converter,
that could account for a lot of horse power. There is also the drag and
weight of the wire. I suspect wire drag is substantial when it's 2000'
long, but not enough to account for the 125 horses. The glider wings are
working at 2 G or so, which doubles the drag. Start adding these up, and
there are a lot of potential losses. Also, your engine may not be
running at it's rating.


--
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Eric Greenwell
Washington State
USA