prop rpm question

: The thrust is probably 4x, like the engine's power. The advance rate makes
: the prop want to pull the airplane at 2x the speed, but again, 2x the speed
: requires 4x the power...

Check your equations. Drag force goes with the square of the velocity.
Drag power (force*velocity) therefore goes with the *cube* of velocity. So, if that's
the governing equation, 2x the speed requires 8x the power.

If you look at the operator handbooks for identical airframes with different
engine options (e.g. PA28-140/150/160/180/235, PA24-180/250/260/400), you'll see that
they almost exactly follow this cubic (i.e. cube-root) equation.

-Cory


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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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