Marty,
I have heard of putting the prop, motor and torque meter on a stand, winding
it up and writing down torque at measured intervals of time during
unwinding. Very hard to get accurate numbers in the initial power burst. This
produces a nice curve, but no useful information for flight. Static thrust may be
used to estimate initial acceleration on takeoff. It does not even give an
estimate of motor run time in flight, because the torque and RPM of the prop
depend on the forward speed through the air.
Proper assessment of propeller characteristics requires having air moving by
the prop in the range of flight speeds. It requires measuring torque,
thrust, airspeed and RPM. It doesn't hurt if you can measure airspeed inside and
outside the slipstream, but the airspeed is not uniform within the
slipstream, so that can be complicated.
Measuring static thrust of a prop is like measuring the force on an airfoil
perpendicular to the airstream. It does not tell you anything useful about
the prop at flight speeds. Advance ratio is the ratio of forward speed to
circumferential speed. It and blade angle determine the attack angle of each
chord of the propeller blade. It is analogous to attack angle of a wing.
Measuring a propeller without measuring airspeed and RPM is like measuring the
forces on a wing without measuring attack angle. The information is useless.
"(What I NEED, more than anything else, is the time to work on the concept!)"
Yes!
Gary Hinze
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http://www.aol.com.
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Received on Mon Apr 30 2007 - 13:10:00 CEST