100HP Build

**Cajun_Ag** · 01-05-2010, 05:23 PM

Lately i've been trying to design a reduction drive. If the picture is attached you can see there is not much in the way of mounting choices for any kind of plate type system used on the briggs etc engines. Also the drive shaft is only 7/8-1" in diameter and 1" long. The gates engineering program for the drive indicates a belt tension of ~810# which in my mind seems like alot for a 1" dia shaft to support. I'm considering having a sleeve machined that will thread onto the existing shaft to both lengthen it by 2-3" & increase the diameter to 1-3/4" (the max bushing dia of the pulley hub chosen).

What is the shaft dia for a rotax engine that uses these type reductions?

**Duane Scarborough** · 01-05-2010, 09:56 PM

Cajun_Ag,

Most of the Rotax reductions are gear reductions, I think. At least the Rotax aircraft reductions that I've seen are. That doesn't mean a belt reduction would be the wrong way to go. In my opinion, belts are THE way to go.

810# seems awfully high for belt tension. Maybe you need to check into that a bit further.

Here's a couple photos of the Arrow Prop reduction on my engine.

Notice that this is short coupled. If I was building one myself, from scratch, I'd mount the engine down very low, with a jackshaft up above the engine, and longer belts. But since I was not building it from scratch, I used a proven design, that was readily available.

I'll look around for an example of what I mean....

Duane

Edit: Here's a link to a youtube video where the guy did this. It's not the best example, but gets the idea across, I think. And it is an amusing video....

http://www.youtube.com/watch?v=i3T7ZQvadnc

BTW, I think it was sold a LONG time ago. The very first airboat that I ever saw used a Corvair engine and a similar redrive, with VERY long belts.

**Cajun_Ag** · 01-06-2010, 11:26 AM

The gates belts website has a design program that you can use. The output is attached & notice the chosen belt requires 861# of belt pull. As I understand it the HTD timing belt design causes it to naturally want to climb out of the pulley. I believe I have to go with this type of belt due to the amount of HP it can handle at minimal belt width.

**Duane Scarborough** · 01-06-2010, 06:19 PM

Cajun_Ag,

Look again at the section called Tension. The deflection distance and force are what you'd use to tension the belt.

The 810# number is, I believe, the force that the pulling side of the belt would be under at that RPM and HP.

I agree that sounds like a lot for a 1 inch shaft to deal with. I wonder about that much side load on the bearings too. I'll run those numbers by a mechanical engineer friend to see what he thinks.

Duane

**Cajun_Ag** · 01-07-2010, 11:17 AM

Duane if your right. Your my new best friend!!

**Duane Scarborough** · 01-07-2010, 06:42 PM

Cajun_Ag,

I showed that sheet to my mechanical engineer friend, and he agrees with what I said last night.

He said that those numbers looked correct, IF it was an electric motor.

Gates, and other belt manufacturers de-rate belts if they are to be used on internal combustion engines. That belt choice MAY be O.K., but he suggested that you check into the de-rating a bit more.

The service factor shown was 1.1, and an internal combustion engine should have a service factor more like 1.8, or 2.0.

What that means is you may need a little more belt. Rick suggested going to a 3" wide belt, and see how the numbers look like then.

Duane

**buster** · 01-07-2010, 07:44 PM

I don't know exactly how this applies to your situation, but I once had a Gates rep. tell me that a belt driving a propeller has an easy life. No clutching, no shock loading, not many contaminates, etc. He never mentioned anything about the internal combustion engine to me.

I think that would mean you should not need to de-rate it all that much. JMO

Dave

**Duane Scarborough** · 01-07-2010, 08:00 PM

Dave,

You may be absolutely correct. I sure hope so. After all, the "load" is not going to be changing suddenly. Well, I guess it would change pretty quick under acceleration, but nothing like revving the engine and then popping the clutch on a motorcycle.

Cajun_Ag,

Why don't you try contacting a Gates rep, and running the idea by him?

Duane

**Cajun_Ag** · 02-26-2010, 02:21 PM

We've made a little progress on the engine. I built an engine stand and we've pretty much sorted out the wiring and eliminated what wasn't needed. I found a 66" powerfin prop on ebay with 5 blade & 4 blade hubs. I've bought both pulley's to give me a 2.86:1 reduction and have the hub 99% drawn up and already bought the 7.25"diax4.85" 6061 aluminum rod. I'm looking through all the people I know with access to a lathe to get it machined now. Boy the big ticket items really slow down a project.

**Duane Scarborough** · 02-26-2010, 06:47 PM

Cajun_Ag,

YooHoo ! I was watching that Prop on EBAY, and wondered who bought it. It was way more Prop than I could use, so I didn't bother to bid on it. You got a decent deal, I think.

The big ticket items DO slow a project down a lot. The good / bad news is that after you've got the big ticket items, you get to start looking for the nickel and dime, impossible to find things.

Maybe that's where the folks on this forum can help, in locating those things.

Good luck with it, and keep us informed.

Thanks,

Duane

**chuckitt** · 02-26-2010, 07:01 PM

Hey Cajun, I got 6 prop dowel bushings that are 5/8 dia. outside and for 3/8 fine thread bolts. If the dowel holes in your prop hub are 5/8 inch they will work and your prop adapter can be machined for them to be pressed in. If you need them, they are $ 5.00 ea. Just let me know. My # is 352-330-1015.
Thanks, Chuck

**Cajun_Ag** · 03-01-2010, 09:13 AM

Originally Posted by Duane Scarborough

Cajun_Ag,

YooHoo ! I was watching that Prop on EBAY, and wondered who bought it. It was way more Prop than I could use, so I didn't bother to bid on it. You got a decent deal, I think.

The big ticket items DO slow a project down a lot. The good / bad news is that after you've got the big ticket items, you get to start looking for the nickel and dime, impossible to find things.

Maybe that's where the folks on this forum can help, in locating those things.

Good luck with it, and keep us informed.

Thanks,

Duane

I think it may be more than I need also, but the 4 blade hub should be about perfect. My 3 blade E series (thinest they make) for my bowfishing boat was 600+ so far about 200 more I got this one.

**Cajun_Ag** · 03-12-2010, 11:03 AM

Thanks Chuck I'm not sure at this point if I need them.

I couldn't find a hull close or have one built for less than $3500 which is about $1000 more than I wanted to spend. I got a bid for the Al and it was ~1600 all broken out just needed welding together. So I bought a spoolgun for my welder and will teach myself to weld AL. Needless to say this will be yet another delay, but the if I get proficient at welding Al then that's a huge bonus in the future.