Question about Belt/Chain drive systems

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Othman

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Aug 23, 2004
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Ottawa, ON, Canada
Hello everyone. I am looking for some pros and cons about belt drives and/or chain drives for a prop shaft that is offset from the engine shaft by approximately 1 to 2 ft. Keep in mind this is for low horsepower use (<80hp).

A nice wide belt seems like a good approach to me, kind of like what you might see on a motorcycle belt drive. With the long offset length, I would tend to worry about the belt flopping around at certain speeds.

I don’t have much experience with these kinds of systems, and I hope you guys can help me out with some ideas.

Thanks very much.
 

wsimpso1

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Well, cog belts and chains are used numerous places. Cog belts in propeller speed reducers, motorcycle final and primary drives, machine tools, etc. Silent chains are used in many of the same places, and are also used extensively in automatic transmissions and 4x4 transfer drives. So, I know that they can work.

There are a number of standard cog and chain sizes for machine tools and other stuff, but a transfer drive robbed from a 4x4 might give you a bunch of what you want...

As to what limitations they have, I imagine that they will have a critical speed or frequency above which you would enter resonance and a speedy self destruction would follow.

The comment I got was go find suppliers in the Thomas Register (online) or do a 'net search. That will send you on the way to their technical assistence folks, and you get to figure it out from there.

Be prepared for having to build an engine, drive and propeller and test it on a stand. An ignition timing light might do great - run through the entire speed range with the strobe triggered by either the main coil or by one of the spark plugs and look for the strobed image of any components or the belt to go fuzzy looking.

Remember the critical stuff when designing your bearings and output shaft, like the fact that the prop bearing set's most extreme loading comes under highest inertia propeller yawing and pitching at it most severe rates.
 

orion

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A couple of other items to consider:

With chain systems, the entire enclosed assembly will most likely be substantially heavier than that which you can achieve with a cog belt - this is especially true when you look at seperating the pulleys by the distances you mention. The chain will also need forced lubrication.

Cog belts however need very precise alignment, cooling air flow, and protection from foreign matter. Depending on power and type of belt, cog belt systems can also be somewhat noisier than the chain counterparts.

A well designed chain system will be virtually bullet-proof. Cog belts on the other hand will need more frequent inspections, as well as periodic replacement.

Both systems can be designed to significantly alleviate issues of torsional feedback/vibration however each has inherent oscillation (vibratory) characteristics, which should be well accounted for in the design process (usually a proper dampened idler will fix any such issues).

For the best chain based reduction drive, look for a fine pitch "silent" chain design as this type of chain geometry will be capable of the highest surface speeds with the least amount of noise, and will have some of the highest strength ratings (per inch of width). In designing with a chain system, make sure to use the design guidelines presented by the manufacturer, including all the proper safety factors.

There are several belt options. The original is the HTD belt by Uniroyal (I think it's Gates now), but today there are at least three or four others that will fit the bill. In order to get the best performance, you want to avoid Nylon reinforced belts since the Nylon chord will stretch somewhat as the belt warms up. The best reinforcement seems to still be Kevlar.

In all cases though, when looking for components and/or technical help, do not mention "airplane" in any form as this will usually cause the phone line to disconnect rather abruptly. The airplane industry is so avoided by these suppliers that Gates, for instance, forbade any of their dealers to help or support any such project. If any are caught doing so, they can be subject to loosing their distributorship, be subject to fines, or even legal action.
 

Othman

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Ottawa, ON, Canada
Thanks for the good information, I appreciate the help.

Just to paint a bigger picture for you guys, the propulsion configuration I'm considering is sort of like the Wright Flyer. The engine centrally mounted, with a transmission to drive two outboard propellers.

I know, sounds like a weird thing to do, but I have my reasons to go that way.

I think I would like to stay away from chains because of the weight and lubrication issues.

Just to bounce an idea of you guys, I was thinking that I would run multiple belts to each shaft (say 2 or 3 thinner belts, rather than one fatty). My rational for that is safety... they would share the load, and if one breaks the others will pick up the "slack", and you'll live to fly another day.

more comments are welcome :)

Thanks again.
 

whirlybomber

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sydney, australia
not to rain on your parade as it were, but if one of your belts lets go in a multiple belt setup, then there is a good chance some of it will ge caught in the other ones, and shorten their remaining life span.....
 

Othman

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Ottawa, ON, Canada
Good point. A broken belt may slip into the sheave of its neighbouring belt and dislodge it... but on the other hand, it may not.

I found good reference material on the Gates website. As you mentioned Orion, they specifically say that their products cannot be used on aircraft. I'll keep that in mind if I ever call their technical help department. I hate it when they ask "so what is it for anyway? what are you building?"
 

orion

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There's a number of things you can mention that are similar to airplanes in application, but not actually airplanes - airboats, industrial fans, wind tunnel equipment, etc. The people on the other end of the line though are not dumb so really watch your words. If you talk about airboats, and then mention 200 mph speeds, they just might figure it out. :gig:
 

cj357

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Oct 6, 2004
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Wisconsin
Using multiple belts is not a bad idea. In fact there was a certified helicopter that used that set up.

Chris
 

pylon500

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Dec 26, 2003
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Taree Airport Australia
G'Day Othman,
If you are trying to use belts to drive remote props, maybe you could take a look at some of the latest motor-gliders.
These guys are using single HTD belts to drive props at least three feet away from the engine crank. :eek:
Also their mounting arms are being made from composite which in turn become the belt protectors.
I'll try to include a picture of one, but it may have to be sideways!!:rolleyes:
Arthur.
 

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