I think a V belt would slip too much and have to be too tight.

A cog belt would require less Horsepower and put less strain on everything.

I know it makes sense to use a timing belt! But all the successful reduction systems use a v belt! I hear that at an idle the belts get destroyed quickly. There must be a reason why they use a v belt instead. Maybe if the propeller hits grass or bugs in the air it could destroy the belt. But if that was the case what about the old sunbeam lawnmower! With the 2 blades cutting grass with timing belt’s, and an electric motor in between! I had one and it went threw belts at least once a year. Maybe that’s why lawn tractors use v belts and they last a long time. If any one knows why let me know. I still haven’t heard from gates belts I think I will have to email them. again

Instead of a belt system, what about a planetary gearbox system, like on a kavan electric starter?

Weight may be an issue, but if you could use delrin/plastic gears, maybe get the weight down?

just a thought

billrad

I don't think plastic gears would ever work well. The power pulses are hard on a drive system. Rotax, which supplies the engines for probably 80% of the Ultralights flying in the world uses a gearbox reduction unit, but it has a dampening system to deal with the power pulses. Even at that, if the engine idles too low you can hear the gearbox chatter.

Cogged belts, (timing belts) were also used on Ultralight airplanes, but were mostly abandoned in favor of "V" belts whenever belt reductions are still used. A "V" belt must be run much tighter than a cogged belt, but it will last longer. There is really no reason to use a cogged belt.

AV8TOR

Plastic gears work very well in helicopters. A .91 sized heli in hard 3d use, is propably more often transmitting 3 horsepower through the gears, than your biplanes ever will see:-)

Lars

The problem with a gear is! There needs an idler gear so the prop will turn in direction of the engine. Or the engine can be mounted backwards. Gears need to be meshed properly with shims, or they will destroy them self’s! if set up wrong even with little hp! i think v belt is the way to go.

you could use belts from Gates. Toni uses gates polyflex belts on his unit. Look at pae 60 of his catalogue

I did some diging around. Gates is the only place to get them. Any belt bigger and you need bigger pullyes and thats more weight. I havent done anything yet because i need a hobby latne and I am out of funds. But when luck comes my way. I will let you know what i have done and how it works.

Anyone been doing any work on a reduction drive since the last post almost two years ago? I think I may have a go at making a unit for the Stihl 65cc 4-stroke.

Happy New Year to all!!

J

Who sells coarse pitch props? A quarter scale WW-1 prop would be about 24". To get usable speed at 3000 rpm we would be looking at about a 20-24 pitch.

Mick Reeves has a 36 x 20 prop, and there are some other props available, mostly from Europe. You may get some sticker shock when you see the prices, though ( I know I sure did).

J

Anyway, what I am looking to do is to make a drive unit to turn a four-bladed prop in the 30" to 36" diameter range with a Stihl 65 for a 1/3 scale Siemens-Schuckert DIII.
I don't think it will be impossible to do, but it might be more difficult than I envision .Space inside the cowl is not a big concern and weight is not a huge concern either, at least for this project.

J

Does anyone know off the top of their head how much more power a four-bladed prop requires? For example if I have a two- bladed 32x20 and a four-bladed 32x20, how much more power would I need to turn the same RPM? I'm pretty sure I have the info somewhere but it is in storage in a box that I'm not sure the location of.

TIA,
J