General question on prop sizing  
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General question on prop sizing - 6/30/2008 2:03:53 AM   
wjbender


 

Posts: 28
Joined: 7/18/2007
From: tinton falls, NJ, USA
Status: offline 		I have an OS 75 Ax and get 10,200 on an APC 13 X 8. I am running 10% Omega and a # 8 OS glow plug. engine seems to run great.

My question is: should I try a lower pitch to increase RPM and get the engine more into its power cruve? Possibly a 13 x 7

What is the ideal RPM for this engine?

Thanks
       Post #: 1

RE: General question on prop sizing - 6/30/2008 3:26:51 AM   
Rcpilot


 

Posts: 6540
Joined: 3/20/2002
From: Arvada, CO, USA
Status: offline 		13x8 sounds a little big for that engine.

I run the Tower .75 on any of the following props:
12x8, 13x5, 13x6, 13x7

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RE: General question on prop sizing - 6/30/2008 12:44:56 PM   
Harry Lagman


 

Posts: 1145
Joined: 11/19/2003
From: Auckland, NEW ZEALAND
Status: offline
quote:

ORIGINAL: wjbender

What is the ideal RPM for this engine?

Thanks



Try a few props and find out. 10,200 rpm with the APC 13 x 8 is not a bad number - about par or slightly better than an average .91 four-stroke with the same prop.

OS has tended to promote the use of larger props with its two-stroke engines of late - presumably as a "responsible corporate citizen" with respect to noise issues. One can therefore assume that OS has designed these engines to happily handle the prescribed heavier loads without deleterious effect.

There is always "the right prop" for every engine/airframe/pilot combo. Regardless of what good theorycraft may suggest and what the guys at the field might recommend, oftentimes it takes a good day at the field, a few props, a bit of patience and some experimentation to find out just what that "right prop" is.

Good luck and do report back in the interests of science

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       Post #: 3

RE: General question on prop sizing - 6/30/2008 1:12:05 PM   
Hobbsy



Posts: 10560
Joined: 12/2/2001
From: Colonial Beach, VA, USA
Status: online 		Harry, that's good stuff you said, when I got my Webra P-5 .91 people had trouble wrapping their minds around the smallest recommended prop being a 14x12, (which it turns at 8,500 on 5% nitro) and the largest a 16x8. I tried that 14x12 on a SuperTigre .90 and it only could manage 7,000 and quickly got hot. The P-5 has an absolutely huge muffler.

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