RE: OS .75AX users please post prop sizes  
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RE: OS .75AX users please post prop sizes - 2/17/2008 7:58:26 PM   
sevans16


 

Posts: 313
Joined: 11/16/2006
From: Las Vegas, NV, USA
Status: offline 		I am running a 13x8 with no heat problems and plenty of RPM. I have not tached it though. OS Manual calls for a 13x8-10. I just want a go fast hotrod.

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(in reply to Cyclic Hardover)
       Post #: 26

RE: OS .75AX users please post prop sizes - 2/17/2008 8:17:53 PM   
asmund


 

Posts: 1907
Joined: 11/20/2005
From: Floroe, NORWAY
Status: offline 		Based on my tach readings on my Tower 75, my guess is that you get about 10000 rpm on that 13-8 if it is an APC, which is to low for the engine to produce its best hp. If you want to go fast you also need rpm`s and not just the biggest prop you can find. A 12-8 will be faster in your 50 size plane because the 12" diameter is plenty for such a small plane and it will turn alot more rpm`s with the same pitch (8) and your plane will go faster.
As a general rule OS ALWAYS recommends to large propellers for their engines, this is only because they want to keep noise down
Lug the engine down with a too large propeller and it will not produce its max horsepower and you will not be able to go as fast as you could have been.

You need to get yourself a tachometer to learn what prop sizes your engine will turn well

(in reply to sevans16)
       Post #: 27

RE: OS .75AX users please post prop sizes - 2/17/2008 8:29:14 PM   
CustomPC


 

Posts: 349
Joined: 4/19/2004
From: SydneyNSW, AUSTRALIA
Status: offline 		APC 13x8 gets 10,900 on my .75AX

(in reply to asmund)
       Post #: 28

RE: OS .75AX users please post prop sizes - 2/17/2008 8:43:35 PM   
asmund


 

Posts: 1907
Joined: 11/20/2005
From: Floroe, NORWAY
Status: offline 		Not bad, that is better than the Tower 75 But what I wrote previously still applies, it will be faster with a 12-8, as long as it`s not a really draggy plane.
12-12 is just trying to kill the engine.

Sevans16. If you are this hungry for maximum speed you really should have bought the 91 FX instead. It will turn the same prop faster, or turn a bigger prop just as fast and it is basically almost the same engine when considering the weight and physical size.

< Message edited by asmund -- 2/17/2008 8:44:21 PM >

(in reply to CustomPC)
       Post #: 29

RE: OS .75AX users please post prop sizes - 5/10/2008 2:25:54 PM   
enephel


 

Posts: 157
Joined: 3/20/2004
From: Clinton, OH, USA
Status: offline 		OS .55AX spins a 12X7 no problem. I would think the .75 would handle the extra pitch to 12.

Some OS 1.20AX owners are running a 17X6 at 9600. That rivals a Saito 1.50!

(in reply to asmund)
       Post #: 30

RE: OS .75AX users please post prop sizes - 5/10/2008 2:33:45 PM   
enephel


 

Posts: 157
Joined: 3/20/2004
From: Clinton, OH, USA
Status: offline 		One thing that I'm concerned about is OS lists the .75AX at 19.4oz. They list the 1.20AX at 21oz. These two engines can't possibly be within two ounces of one another.

(in reply to enephel)
       Post #: 31

RE: OS .75AX users please post prop sizes - 5/10/2008 4:22:05 PM   
liquid_TR



Posts: 510
Joined: 4/8/2007
From: ISTANBUL, TURKEY
Status: offline 		well as far as the "designed to run bigger props" comment goes for the 55AX, Im running mine all stock, 15% omega fuel with a 9x9 APC at 15400 rpm and 9x8 APC around 16K rpm.. Very nice performance IMO without a tuned pipe or a tuned muffler..

Ive also got the 120AX, but im running it at 9100 rpm with a 17x6 JXF for 3D. Note that this engine is rated max HP @ 9000 rpm and max usable advertised as 9500.

Now the 55AX is advertised as 17k and 75AX also 16K. So I see no reason not to run smaller props on the 75AX such as 10x9 11x8 12x7 or 13x6 to gain RPM and total power output..

15x6 APC on a .75 2 stroke?? come on!..

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LiQuid TR

(in reply to enephel)
       Post #: 32

RE: OS .75AX users please post prop sizes - 5/31/2008 1:51:07 AM   
fx777


 

Posts: 46
Joined: 1/3/2007
From: Hollywood, FL, USA
Status: offline 		I have an aero-works 540T, 60" wing span, rated for 61 two stroke engine. I put the 75 AX in with a 13 6 APC, run most of the time at half throttle. It tacs at approximately 11,800 with Powermaster 15%. At full throttle it is very fast and has great acceleration. Transition from idle is great, no hesitation, and very low extended idle. Love the engine and am puting one in the Skylark 70 next.

(in reply to liquid_TR)
       Post #: 33

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