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Old Apr 21, 2005, 08:56 AM
Molded Hotliner Destroyer
Magnum9's Avatar
Perth, Australia
Joined Jul 2004
1,726 Posts
General rule on prop diameter vs pitch to maintain current?

As I have no test equipment to check amp draw, is there a general rule for maintaining the same amp draw? As a rough example if I am running a 12x6 prop on a geared brushless setup, would a 11x8 and a 13x4.7 both draw similar current, or are there too many variables for such a simple theory?
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Old Apr 21, 2005, 09:18 AM
jrb
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Edina, MN, USA
Joined Oct 1999
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From RCM years ago: 2 * D + P.

2 * 10 + 6 = 26 = 2 * 9 + 8 =

2 * 12 + 6 = 30 = 2 * 11 + 8 = 2 * 13 + 4
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Old Apr 21, 2005, 10:41 AM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Quote:
Originally Posted by jrb
From RCM years ago: 2 * D + P.

2 * 10 + 6 = 26 = 2 * 9 + 8 =

2 * 12 + 6 = 30 = 2 * 11 + 8 = 2 * 13 + 4
That is a fairly close quick and easy calculation and is most likely plenty close enough considering that props vary greatly.
A more accurate equation is Dia to the power of 4 times pitch.

10X6: 10X10X10X10X6=60,000
9 X8 : 9X9X9X9X8= 52,488

From MA many,many years ago.

Charles
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Old Apr 22, 2005, 05:40 AM
Molded Hotliner Destroyer
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Perth, Australia
Joined Jul 2004
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Thanks guys. Looks like my guess of go down 1 inch on my diameter and up 2 inches on pitch, or up 1 and down 2 was pretty close.
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Old Apr 22, 2005, 06:05 AM
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East Anglia, UK
Joined Sep 2002
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Yup. 7x6=8x4 as far as draw goes, more or less
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Old Apr 22, 2005, 08:57 AM
Motors beat engines!
Milwaukee Wisconsin, United States
Joined Feb 2001
4,564 Posts
If you've got a tach, just make sure your new prop rpm is at least the same or higher than the old prop rpm. If its exactly the same, your amps are exactly the same.
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