OS40FS prop size?

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Steve - 22 Jun 2004 00:00 GMT

I'm considering using an OS40FS in a fun fly type plane, and wonder what sort
of performance I might get out of an APC 12.25 x 3.75 wide blade prop.
Anybody try this and have some RPM figures? I'd probably use 5% nitro fuel.

Thanks,

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Steve

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Steve - 23 Jun 2004 15:12 GMT

>I'm considering using an OS40FS in a fun fly type plane, and wonder what sort
>of performance I might get out of an APC 12.25 x 3.75 wide blade prop.
>Anybody try this and have some RPM figures? I'd probably use 5% nitro fuel.
>
>Thanks,

I'm still looking for this information. rcfaq.com seems to be down, and I
can't find any other source of rpm & prop sizes at the moment. The OS
Engines site lists props up to 12x7 for this engine but give no indication of
RPM.

So if anyone has this information - OS40FS RPM figures with a 12.25x3.75 prop
I'd be grateful for your help.

Thanks,

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Steve

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Dr1Driver - 23 Jun 2004 15:40 GMT

>So if anyone has this information - OS40FS RPM figures with a 12.25x3.75 prop
>I'd be grateful for your help.

For a Fun Fly-type plane, you need pull, not speed. The .40 can easily handle
an 11-4 or even a 12-4. Don't worry about the "recommended" RPMs, just
concentrate on how the plane flies.
Dr.1 Driver
"There's a Hun in the sun!"

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Steve - 23 Jun 2004 16:01 GMT

>>So if anyone has this information - OS40FS RPM figures with a 12.25x3.75 prop
>>I'd be grateful for your help.
[quoted text clipped - 3 lines]
>concentrate on how the plane flies.
>Dr.1 Driver

Sure! - but knowing the RPM I can calculate the thrust, and I figured RPM
would be the most likely figure to get. I've flown it on a .37 with an 11x4
and need a little more grunt out of the hover.
Standard muffler limits me to 12000, a pipe gave me 13400 all with an 11x4
APC. Pipe is much heavier of course and doesn't help with the balance I'm
seeking! There's no room to move anything around so adding weight to
compensate is the only option - not a good idea in this plane!

I'd just wondered whether I might do better with a 4-stroke as torque/speed
curves for 2 & 4-strokes are quite different, and sometimes the lower
absolute power from a 4-stroker can still win the day with the right prop
choice. In this case I would have a net weight loss on losing the pipe, and
might just have gained the rest in a more efficient prop at slower speed.

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Steve

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Steve - 23 Jun 2004 15:45 GMT

>>I'm considering using an OS40FS in a fun fly type plane, and wonder what sort
>>of performance I might get out of an APC 12.25 x 3.75 wide blade prop.
[quoted text clipped - 10 lines]
>
>Thanks,

OK, I think I'll give up on this. I was looking for maybe 10500 RPM, and now
I don't think I'm going to get it from this engine. I'll stick to 2-stroke
for this one.

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Steve

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Morris Lee - 23 Jun 2004 22:01 GMT

> >>I'm considering using an OS40FS in a fun fly type plane, and wonder what sort
> >>of performance I might get out of an APC 12.25 x 3.75 wide blade prop.
[quoted text clipped - 3 lines]
> I don't think I'm going to get it from this engine. I'll stick to 2-stroke
> for this one.

Good idea. 2-strokes have better power-to-weight ratios than 4-strokes.
You want to keep a fun-fly type plane as light as possible.

Morris

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Model Forum / Radio Controlled / Air Models / June 2004

OS40FS prop size?