Apr 21, 2005, 08:56 AM Molded Hotliner Destroyer Perth, Australia Joined Jul 2004 1,741 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?
 Apr 21, 2005, 09:18 AM Member Edina, MN, USA Joined Oct 1999 11,841 Posts From RCM years ago: 2 * D + P. 2 * 10 + 6 = 26 = 2 * 9 + 8 = 2 * 12 + 6 = 30 = 2 * 11 + 8 = 2 * 13 + 4
Apr 21, 2005, 10:41 AM
Southern Pride
Haralson County GA. USA
Joined Oct 2004
35,074 Posts
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
 Apr 22, 2005, 05:40 AM Molded Hotliner Destroyer Perth, Australia Joined Jul 2004 1,741 Posts 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.
 Apr 22, 2005, 06:05 AM Registered User East Anglia, UK Joined Sep 2002 29,713 Posts Yup. 7x6=8x4 as far as draw goes, more or less
 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.