"Now assume an increase in torque which doubles the rotational speed, the
new relative airflow (the new hypotenuse angle) is at 10.31 degrees so the angle
of the airflow relative to the propeller blade (the angle of attack) has
increased by 20-10.31= 9.69 degrees."
John,
You are assuming that the increase in torque will not also produce an
increase in airspeed. Torque is proportional with the square of rotational speed
which is proportional with thrust, which is equal to drag, which is
proportional to velocity squared. It would seem that everything would happen faster,
but the angles would remain the same. The prop will turn faster in proportion
to a faster airspeed. Of course, other things will change, too, disturbing
the simple assumptions made here. Lift will increase in proportion to the
square of speed, but weight will remain the same, so the plane will climb,
producing changes in attack angle and attitude. More of the prop thrust will
directly counter gravity. Drag may be less than thrust. Velocity may not
increase in proportion to torque. Blade attack angle may then increase, although
by a much smaller amount than your theory assumes.
Gary Hinze
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Received on Mon Apr 16 2007 - 04:58:20 CEST