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Old Dec 27, 2012, 04:41 PM
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United States, NJ, Frenchtown
Joined Mar 2003
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Question
Will the BP Hobby ....H2217-4 3500 KV do this ?

Never did a high speed pusher with a prop this small.......Are these numbers, prop speed & thrust, close to being real ?

Thank you
Rich
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Old Dec 27, 2012, 05:03 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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The numbers don't look terribly off, but I would put the big red rubber "ABSOLUTELY NOT" stamp on this one since the poor GWS prop is liable to explode at those RPMs.

The Graupner CAMSpeed 3x3 would be a much better choice...

But still no.

You'll definitely want to run less RPMs and a bigger prop on that plane. You've cranked the RPMs and pitchspeed up real high, but in doing so you sacrificed so much thrust that the plane would most likely fly like a glider with a screaming noisemaker attached to it. Where are you mounting the prop and motor on a U2, and what sort of flying are you planning to do with it? If possible, I'd recommend a Suppo (BP) 2217/8 1100Kv motor swinging a 9x7 folder on 3S.

If you absolutely must run a small, fast prop on four cells, the 2217/6 1500Kv with a 5.5x4.5 would be a better choice. 3" props are firmly outside reality for most non-tiny planes.
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Old Dec 27, 2012, 05:17 PM
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The motor & prop have a very flat efficiency curve as power is reduced.

This setup is strictly to get the slow U2 glider up high enough to find a thermal & glide down. Then back up again.
The 340 continous watts to use a EDF are out.

Will buy a GWS HD 3" X 3" & test it out on the test stand for scream of 39,000 rpms . Ok with a U2
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Old Dec 28, 2012, 09:02 AM
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Chattanooga, Tennessee, United States
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That GWS HD 3x3 will probably explode long before you get it to 39,000...to avoid injuring someone, use a carbon prop for such high RPM.
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Old Dec 28, 2012, 09:08 AM
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Thank you Phil.

I am taking off my prop testing Flack Jacket.

Rich

I have wound up a APC E that high. I think it was a 5" for the GWS F-15 pusher.
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