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Lower Pitched Prop on OS 46FX

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Old 03-25-2011, 07:46 AM
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PatrickCurry
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Default Lower Pitched Prop on OS 46FX

I've got several OS 46FX engines that I've been running 11x6 & 11x7 props on. I wanted to try the "more thrust and less speed" thing so switched to an 11x4 prop. Running it up on the ground it was making somewhat of a high pitched sound so we tached it and it was running about 15K on the ground. I've flown the plane several times and it makes a really cool high pitched sound that echos off the trees when I'm flying and short of shooting the back off a muffler on a high speed pass, there *seems* to be no ill results. When I looked in my OS manual however, they recommend the higher pitched props. Will running too low a pitch prop harm this engine as long as I'm not running too lean and am in the recommended RPM range? I'm running Omega 10% fuel. Thanks!
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Old 03-25-2011, 01:39 PM
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Default RE: Lower Pitched Prop on OS 46FX


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ORIGINAL: PatrickCurry

I've got several OS 46FX engines that I've been running 11x6 & 11x7 props on. I wanted to try the ''more thrust and less speed'' thing so switched to an 11x4 prop. Running it up on the ground it was making somewhat of a high pitched sound so we tached it and it was running about 15K on the ground. I've flown the plane several times and it makes a really cool high pitched sound that echos off the trees when I'm flying and short of shooting the back off a muffler on a high speed pass, there *seems* to be no ill results. When I looked in my OS manual however, they recommend the higher pitched props. Will running too low a pitch prop harm this engine as long as I'm not running too lean and am in the recommended RPM range? I'm running Omega 10% fuel. Thanks!
Patrick- I'd probably try a 12X4 and see if I could get that rpm down without sacrificing thrust. I know most manufacturer's list some pretty high max rpm's for their engines but my philosophy is not to try to get those #'s but rather keep things more reasonable below 12,500. If you are going to run up in the 14-15K range better make sure you oil content is at or above what the manufacturer recommends.
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Old 03-25-2011, 01:41 PM
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Default RE: Lower Pitched Prop on OS 46FX

Whoops....my bad. I didn't realize Patrick had posted this on the OS forum. My apologies. Wait for the response from Bax.
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Old 03-28-2011, 07:00 AM
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Default RE: Lower Pitched Prop on OS 46FX

The 11 x 4 prop would be considered rather small. 11 x 6 would be about as "small" as we'd use. A 10 x 7 or 8 would also be good. Tach the engine on the ground when it's at full throttle and leaned to just rich of peak RPM. If you're turning between 12,000 and 13,000 RPM, you're good.

3D flyers like to use the APC LP12338 12.25X3.75 SPORT PROP. This is good for 3D and allows the engine to turn up enough to give you a reasonable level-flight speed, but also give you good pulling power for vertical climbouts. You don't usually run this propeller if you're doing a lot of full-throttle operation.

The larger props mentioned in the instructions will make the engine run at much-lower RPM and give you a very low noise profile. That's because most model clubs in Japan have very strict noise regulation. Let the engine turn into the 12's, and you'll have more performance with the penalty of more noise.
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Old 03-28-2011, 07:12 AM
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Default RE: Lower Pitched Prop on OS 46FX

Yeah, I was turning around 15,000 on the ground....  I'll go back to the 11x6 because I don't want to damage the engine..... But the sound was so cool!   Thanks Bill.
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