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Old Nov 05, 2011, 10:08 AM
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Not as Good as The Kid
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South Pasadena, FL
Joined Sep 2009
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Originally Posted by dead View Post

This is the Analysis to go along with Leespaddock's testing...
Okay, I’m on board now. Thanks, Dead, and thanks for linking my analysis. Here are some important things to remember about what I have done.

Although it has been 31 years since I had to defend an independent study, the process is the same – to use scientific standards and address the data only, with no hypotheticals, in a way that you can defend it. Good questions are things like “why did you do it this way” or “why did you not use this technique”, but if the data is addressed objectively, and without agenda, then these questions are easy to answer.

One thing to remember is that I focused on developing a prop constant (pK) from Lee's very fine data, because it provides a means for comparison. Unless I made a math error, these constants can be plugged into the Watts formula so that using the same efficiency rating (84% was linear), the prop diameter, the prop pitch, the Kv of the motor, battery cells, battery mAh, measured volts, RPM’s, and Amps, are all relative per sample, per pK. Resistance, lost Amps, heat, and the difference between measured Watts and kinetic Watts was illustrated.

This was achieved and produced for WOT and the half-throttle setting. The volts, across the board, and the difference in RPM increase from half to full, were constant enough to be statistically acceptable, keeping in mind that the RPM increase for nearly all the samples was 33% from half setting to full setting and not 50%.

I will try to review all the posts so far to see if there are any questions about the analysis that I have not answered, but I think this thread can become a very productive thread if each of us continues to contribute by recording and sharing data. My focus for now will be to try some in-flight comparisons, using video, so we can hopefully see differences during maneuvers we are used to performing, or seeing others perform.

I feel that this is an important discussion for one main reason… to get the most out of a very fine airplane. This means a balance between motor size, motor weight, Amps, heat, and flight time. For most of us, turning a bigger prop at a lower RPM with reduced prop stall and higher torque is the ultimate goal. Sometimes this is all about disk diameter and pitch, but the prop constant will also tell us about performance relative to load.

Feel free to PM me if there is a question about my analysis, but feel free to run with the data too, or duplicate the test and present different data, or try new propellers in this size class. This should be fun for some of us, but crazy boring for others. Such is life.
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