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Old Nov 13, 2011, 12:28 AM
vienquach is offline
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Quote:
Originally Posted by Aeroplayin View Post
Also, the mechanical formula tells us the amount of power in Watts it takes to turn a 15x8 propeller with a 1.08 pK 5,760 RPMs, which was the APC's RPM reading at half-throttle from Lee's data. So it takes 338 Watts to do this, while it takes 1,100 more Watts to go from 5,760 RPMs to 8,560. That's 338W to produce the first 5,760 RPMs and 1,100W to generate the remaining 2800 RPMs.

So for the APC prop, that's 17 RPMs per Watt for the first half of the throttle curve and 2.5 RPMs per Watt for part-2. When I have some time, I'll run the numbers for the rest of the prop samples from Lee's data so we can compare to the reproduced data that should be coming soon.
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 ...

Vien
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