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Old Jan 14, 2009, 03:13 AM
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Bruce Abbot's test data is now included on www.flybrushless.com

Thanks again Bruce for allowing me to add it to the site.

Enjoy,
Robert
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Old Jan 14, 2009, 02:28 PM
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Robert

A possible enhancement to the tabulated data in Flybrushless.

If efflux velocity was included allong with each static thrust value, then the power injected into the slipstream by the prop [SS power] could be evaluated.

This power, divided by the battery output power would give the overall efficiency of the motor+prop combination.

Strictly speaking, this power value [SS power] is correct only for the static case [zero flying speed], as for all the other static measurements.

With experience factored in, just two numbers [SS power and efflux velocity], would be a sufficient description of a power train to match it to a model.
Last edited by peterangus; Jan 14, 2009 at 02:33 PM.
Old Jan 14, 2009, 02:56 PM
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How do you measure efflux velocity accurately - I've tried the Eagle Tree pitot tube airspeed indicator, but the results are nowhere near consistent - I can't determine exactly where to place the tube to get accurate results (both in terms of distance from the hub in relation to prop diameter, and how far behind the prop). I've also tried a Kestrel, but again, where do you place it (without it seriously interfering with the air flow).
Old Jan 14, 2009, 02:59 PM
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Sorry but I'm not familiar with the the efflux velocity (I will look it up later), but is this something that has to be measured or can it be calculated from the existing data?

I'm always looking for ways to improve the site. I have considered adding a calculation to predict the current/rpm for a given prop/voltage. Similar to what Drive Calculator does, but at lot simpler (and most likely less accurate). However I'm not sure if this is a road I should go down since others are doing it.

Robert
Old Jan 14, 2009, 03:11 PM
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Robert - it has to be measured - I don't understand all the intricacies, but I think, basically, it gives you a way of comparing the air speed off the prop (and from equations, the amount of power "injected into the slipstream") with the calculated pitch speed at a certain rpm.
Old Jan 14, 2009, 03:42 PM
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Interesting thing happened this morning.
I went to the Web site and tried a list of motors that I've created for something, probably about 30 outrunners in all in the 143g to 170g weight range, and not one of them had data on the site.
Seems to me that all the motors with data entries are tiny.
Just an observation.
Old Jan 14, 2009, 04:06 PM
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Ken,

I did a search on my site and there are only 7 motors on my site that have weights between 143-170 grams.
http://www.flybrushless.com/search/a...weight/143:170

Of those the only one with any prop data is GPS C35-48-B

I can only show the data I have, and so far I only have test data from Phil (Dr Kiwi) and Bruce Abbot. I think I also have a few results from MicroDan. I am working on a way to share data with Drive Calculator and PeakEff.com.

In the mean time if you have any data you would like to add to the site please feel free to. If you already have a lot of test data stored in an excel file, database, etc send me a PM and I can import it for you. That's what I did for Phil's data.

Thanks,
Robert
Old Jan 14, 2009, 04:12 PM
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Also none of the Neu motors have any test data for them. I just pulled all of the ones with kv,rm, and io off of their site.

I will get around to adding others later, but for now I'm spending more of my time working on the site rather then adding motors.

Robert
Old Jan 14, 2009, 04:55 PM
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Dr K

I produced the attached plot using a HUGER wind meter.

As you see, the velocity varies from point to point. A reasonable average value to record would be 95% of the highest value that can be found.

Best if the prop is tested in "pusher" config, with no centrebody to confuse things.

The presence of the meter should have zero effect on the upstream flow [ie, upstream of the meter].
Old Jan 14, 2009, 05:08 PM
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Quote:
Originally Posted by Ken Myers
Interesting thing happened this morning.
I went to the Web site and tried a list of motors that I've created for something, probably about 30 outrunners in all in the 143g to 170g weight range, and not one of them had data on the site.
Seems to me that all the motors with data entries are tiny.
Just an observation.
In my case it is because I don't have a test rig like Louis Fourdan's - my set-up is limited to about 400W or so, so I simply cannot test monsters!

You obviously have a different vision for "tiny" motors... "Tiny" to me is <10g, small is up to 30g, medium is in the 50-70g range - I think of anything over 100g as really big!
Old Jan 14, 2009, 05:14 PM
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Thanks for the diagram, Ken - Excellent work! I'll have to see if I can get some comparable figures.
Old Jan 18, 2009, 03:40 PM
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Here is a very-compact way to present a large ammount of propeller data from static tests.

For any prop listed, just four numbers provide.... static thrust.... efflux speed......efflux power..... and shaft power .......at any rpm.

C/B is the efficiency of the prop acting as a static fan.
Last edited by peterangus; Jan 18, 2009 at 03:58 PM.
Old Jan 18, 2009, 04:09 PM
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Now all we need is a complete list of props, each with all four constants given!

I can measure Static Thrust and Shaft Power (is that simply Power-in?), and thus get A and B, but I can't measure Efflux Power or Efflux Speed... so C and D are beyond me.
Old Jan 18, 2009, 07:35 PM
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Hi
Some comments
a) Thrust versus (rpm/1000) exponent could be around 2.05 .. 2.10 for a better regression
b) Same versus Power in, possible exponent 3.05 .. 3.10
c) Power shaft = Power In - iron losses - copper losses - ESC losses
Louis
Old Jan 18, 2009, 11:30 PM
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I'm fine with adding in constants for props to my database. The only hard part there is telling me what they are (it would also be nice to know what they mean).

Robert


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