Has anyone tried to make a reduction prop drive for a conversion engine?

My Poulan 54cc turns about 6900-7000RPM with a 22-8 prop. But that engine is rated for over 12,000RPM in the saw. Imagine the prop you could swing if the engine RPMs went up to 9000 or 10,000RPM and you could swing a 24 or 26" prop at 7500RPM!! The thrust would be unbelievable.

The reason I'm curious about this is because I don't believe that my Poulan 54 engine is -- up in the "powerband" at 7000RPM. I'll bet it makes it's best power at 9000-11000RPM.

I was thinking about a belt driven reduction drive. Remember the old Byron Mustang with the belt drive unit?

I don't know a thing about machining these kinds of parts. I would think that a gear driven drive would require some sort of lubrication system to keep things from heating up and seizing.

I know that running the engine at higher RPM's will make it wear out faster. I don't care about engine life. These conversions are so cheap-- I could build a new one every year if I had too.

i've dreamt about a belt reduction set up for years but haven't gotten around to it yet. toothed belt with nylon or alum pulleys and sealed for life bearings sandwiched between 2 aluminum plates bolted to the engine case. i have to hassle friends for machine work but anyone with the right tools could pull it off for cheap. but then you gotta buy those big ($$$) props!

dave

I was thinking about using bearings from an alternator for a car. You would have to get a shaft to fit those bearings. The bearings are permanently sealed, so lubrication wouldn't be an issue. As for the shaft; I don't know if you could use aircraft 6061 aluminum or not. Would if be strong enough or would you need a steel shaft?

You could weld a few brackets to the bearing housings or make a sandwich bracket to hold the brearings and then weld to that.

I figured a 1.3:1 ratio. With the engine at 10,000RPM, then the prop would be turning about 7700RPM. Or at 1.4:1 with 10,000RPM the prop would be turning about 7100RPM.

Check this out.

www.sdp-si.com

Lots of information. Most of it too complicated for my brain , but I thought that someone might enjoy surfing that site.

I wonder if these pulleys and bearings would hold up to the HP generated by the 54cc engine.

RCPilet,

I made a toothed belt/pulley drive for my Dornier Do-18 seaplane. The real one had an inline pusher/puller arrangement with a very narrow cowling. I decided to mount a Ryobi 31cc motor in the fuselage and run a common shaft with a prop on the front and another on the back. I bought the belt, 2 aluminum cogged pulleys and 2 sealed bearings. I made the bearing mounts from some steel tubing that I had massage to fit. I had a terrible problem with vibration and radio interference. There were so many problems that I cut it all out and went to plan B. I think I have a pic if you're interested. If I'm not mistaken, I bought all the pulleys, belt, and bearings for about $45. Just be sure to design it so there is no flex when the hp comes on.

Hi,
Try the video "La Fèrte extreme scale 2001", from Werner Krop videos, they all use reduction belts in their 240 to 300 cc engines, the models weight a lot!!! the b-29 featrured there weight over 400 pounds.
Try it.

Tato

You might check to see if Iron Bay Models is going to bring it back. Or maybe by some odd chance they have one. Ocasionaly you will see someone selling one.