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What Prop to use???

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Old 05-08-2008, 06:24 AM
  #1  
speed367
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Default What Prop to use???

I just got a Seagull Ultimate that requires a 91 to 1.25 engine I bought a OS91 II 4 stroke and was looking for a prop for it. The user guide that came with the motor said to use a 11x11-12 or a 12x10-12 or a 15x6 or a 16x6. I dont know what prop to use and in addition to that my local hobby shop doesnt carry any of these except for the 15x6 will this be ok? I looked in a master screw book and didnt see any of these othere props either. For the first time in my RC life I have no idea what to do.................Please help!!!![] Im really concerned that the plane will be very sluggish and hard to handle if the prop is too big and I really dont want to loose this plane before im able to enjoy it.

chuck (speed367)
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Old 05-08-2008, 06:34 AM
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Default RE: What Prop to use???

I would think the 15-6 would be good, the others would be for faster aircraft.
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Old 05-08-2008, 08:22 AM
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Default RE: What Prop to use???

I have the engine on a Great Planes Super Skybolt biplane.

I really like the MA K Series 14x6, Graupner Super Nylon 14x7 and MA Schimitar 15x6. All three props give great performance.
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Old 05-08-2008, 09:23 AM
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mrbassman
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Default RE: What Prop to use???

What's the rpm operating range? You choose a prop that will not have you go over the high rpm limit which is set by the manufacturer. This could take some trial and error and you might end up with a few props that you may or may not use.
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Old 05-08-2008, 11:52 AM
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Default RE: What Prop to use???

A 14-6 should be fine on a .91 four stroke, likely better than the 15-6.
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Old 05-08-2008, 12:19 PM
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Default RE: What Prop to use???

My brother and I have OS and Magnum 91 four strokes on the following that are currently flying:
Big Stik 60
PT-60
Super Sportster 60
Hog Bipe
Astro Hog
...and more in various stages of completion

It has been our experience that a typical 14x6 usually puts them in the 9,500 to 10,300 RPM range depending on weather, nitro percentage, and the variations from one engine to the next. They seem to perform well with a 14x6 on our planes and that's really all we use on them.
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Old 05-08-2008, 12:26 PM
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carrellh
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Default RE: What Prop to use???

I know some people run 13x8, 12x10, 12x12, etc with these engines on slippery planes.
I read on RCU that people are happy with 15x6 and 16x6 on their 91 four strokes.

I think starting with a 14x6 would be very safe for the engine and the plane. After flying it for a whikle you can always experiment a little.
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Old 05-08-2008, 02:43 PM
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Default RE: What Prop to use???

Hi!
That's Great Planes sea plane with the engine up on the fin ..right!
I would run a APC 14x6 on that plane.
15x6 is a tad too big! Anything smaller is not going to work. Avoid Master Airscrew black coloured props! Their scimitar series is rather good though.
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Old 05-09-2008, 06:10 AM
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speed367
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Default RE: What Prop to use???

Thanks for the info all. I guess it is going to be a trial a error thing. Ill start with the 15x6 (because thats all my hobby shop has) and ill let you all know this weekend if im smiling or if im repairing . Im just hoping that the prop will give me enough power to pull out of any little problems that might arise, but what the heck building them is as much fun as flying them in my book......

thanks all
chuck
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