Precious Metal Pics so far : ) - RC Groups
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Mar 26, 2003, 10:24 PM
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Precious Metal Pics so far : )


I FINALLY got a digital!
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Mar 26, 2003, 10:24 PM
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.
Mar 26, 2003, 10:28 PM
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last one till I cut wing cores
Mar 26, 2003, 10:30 PM
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Mar 26, 2003, 10:49 PM
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gkamysz's Avatar
What size props will you be trying?

Greg
Mar 26, 2003, 11:12 PM
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2x6 volt 400, each geared 2.33:1 (MP Jet boxes w/ nose mounts), running 8 cells parallel to 9/4 front and 9/7 rear props.

Mark
Mar 27, 2003, 12:27 AM
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gkamysz's Avatar
9x4? Surely the flight speed of your model will be over ~30MPH pitch speed of the 9X4 prop. The difference in pitch is too great. Have you run the drive and checked the current draw of each motor?

The idea is to share the load. I think it would be best to just use the same size props. The slight difference in pitch that is required is probably not qoing to be available anyhow.

It should sound sweet though. Hope to see it at Mid-Am?

Greg
Mar 27, 2003, 04:53 AM
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I agree. 9x6 on the front and 9x7 on the back is my prediction of what you will end up with
Mar 27, 2003, 07:26 AM
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In reading some (NACA/NASA) research, and from what I have heard from people that have done CR setups, the rear prop needs AT LEAST 50% more pitch than the front prop.Running the SAME pitch is effectively useless.The idea is not to share the load, it is to accelerate air that has already been accelerated to X speed, thus, the front prop is X (4), the rear prop is X+3"(7)
.According to reading, a 9/4-9/6 combo would be the minimum...I managed to find a good LH 9/7 to try, so I actually sized the ship around the props!
Do not look so much at the front prop pitch as PITCH SPEED, look at the rear,as that is the speed at which the air will leave the rear of the prop blade, and that wil determine airspeed more.
The parallel wiring should negate any minor differences in draw, though they ought to draw very nearly the same.The ESC will only "Know" it sees a draw of the two combined motors... hopefully (Jeti 350ESC)
No, I havent put power to the thing yet...I will when it's ready to go .No need yet :O
And, if it doesn't fly, wel, theres always a nice Mega BL waiting to go in there!The spinner would be a lot easier too! I'm going to hate to make the thing!

Mark
Mar 27, 2003, 09:19 AM
RIP Azarr - "Old age is not for sissies"
Azarr's Avatar
Very nice Mark, hope we'll see it at MidAm

Azarr
www.ecubedrc.com
Mar 27, 2003, 11:59 AM
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I shall be there
Mark
Mar 27, 2003, 08:07 PM
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The naca papers I read showed the rear prop to have just a little less pitch for the rear prop. Which paper did you read?

Try this paper.

Your explanation sounds fine but if your model is flying faster than the pitch speed of the first prop, the first prop will actually slow the air not accelerate it. Because of this it will be generating no thrust and possibly drag even though it still takes power to turn the prop.

I know the ESC doesn't care what the motor curents are but measuring the individual motors current would tell you how well the load is being shared.

Greg
Last edited by gkamysz; Mar 27, 2003 at 08:09 PM.
Mar 27, 2003, 08:45 PM
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Yup, I read that one. It was published in 1937, quite a bit earlier than the paper I have that I got from a research friend of mine.
I'm going to try to get hold of the guy that owns the REAL PM and see what pitches they use.
Thanks for the help. We'll see what happens when I throw the thing to the wind!
Mark
Mar 27, 2003, 09:01 PM
Throttle,,What's that?
dirtdiver's Avatar
Thats the spirit i like to see. I always try stuff that is not supposed to work. Sometimes there right sometimes there wrong

Pat
Mar 28, 2003, 07:17 AM
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I'm still trying to find an email for Ron Bucherelli that owns the Precious Metal. I have a few feelers out....


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