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Old Nov 13, 2011, 08:59 AM
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South Pasadena, FL
Joined Sep 2009
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Originally Posted by vienquach View Post
I prefer to have the thrust, watt, and RPM data for the whole throttle range instead of just 50% and WOT. Also, you need to consider prop stall (flow seperation) as well when you run close to WOT static.

From my own experience, the thrust / watt curve is very close to linear, so I need about 55% of max watt to get about 50% of max thrust. One professor at my school also did several static thrust measurements with expensive sensor and transducer also observed close to linear behavior of thrust vs. watt.

In your data, the relation is pretty much different from linear, well, you only have 2 data points. Would be much better if you have at least 5-6 data points to predict the relation.

338 W gives 5760 RPM ...

Remember two things about this data.... throttle is a setting and not a measure instance, as Lee’s readings may have come from, but the near-exact reading (5760 and 5790) were coincidental only, but speak volumes.

Second, my data is an ad hoc field collection as opposed to Lee's controlled system method. As you know, to complete this analysis, we wanted to take the subjectively observed comments from contributors, who were providing conflicting, or actually contradictory interpretations, and put the Xoar and APC props to the test in the field. The final information that I will provide is video evidence so that the reader can look at the data, and the hover-to-punch-out visual and come to their own conclusions.

Additionally, prop stall, or the pitch distortion, is something we cannot measure or observe, but can be (possibly) interpreted from the data.

Lee and I have both challenges everyone to contribute in a productive way, and if you feel there is contrary evidence, either measured or visual, here is the place to provide it. I'd love to see a near-linear curve from real-time data since it seems you have access to the tools to provide it. Unfortunately, the currently collected data "is what it is" unless Lee can run the numbers again at more data points, but for now, my data seems to support his non-linear performance.

The best I can do is have two other people there to observe the readings, so even if the tools are poorly calibrated, a relative relationship should be acceptable since I doubt three of us made a mistake reading and documenting the data.

We invite everyone’s contradicting data, or contradictory analysis, but I prefer that we don’t become dismissive about this data’s relevancy, or contradict it by referring to data collected by someone else for other purposes, as we cannot satisfy the need for trust and accuracy of everyone, or prepare results with tools that you feel are more accurate. I’m not challenging people to engage, but I do request it if someone fees there is significant cognitive dissonance in our findings.

So this begs the question… can you use the tools at your disposal to prepare a cure like this using these props, and these prop sizes, on these motors?
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