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Pulley drive

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Old 06-25-2018, 01:12 PM
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jsbm1234
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Default Pulley drive

Hello everyone Iím Jeff and new to the forum. Iím thinking about building a gasser and using an echo 26cc engine. I see a lot of concerns are on the cg and was wondering if anyone has tried a pulley drive system like they do on some of the larger planes? Iíve done a little research and didnít find anyone using it on an airboat. I was also thinking about keeping the clutch. Any input or direction would be appreciated.
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Old 02-22-2019, 11:33 AM
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hmm interesting idear
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Old 02-22-2019, 03:59 PM
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Originally Posted by jsbm1234 View Post
Hello everyone Iím Jeff and new to the forum. Iím thinking about building a gasser and using an echo 26cc engine. I see a lot of concerns are on the cg and was wondering if anyone has tried a pulley drive system like they do on some of the larger planes? Iíve done a little research and didnít find anyone using it on an airboat. I was also thinking about keeping the clutch. Any input or direction would be appreciated.
Do you mean putting the engine down on the airboat deck and use a belt and pulley system to drive the prop hub ? Putting the engine down low might stop the boat from being top heavy. I had one drawn up at one time like that and was going to use pulleys, a belt and other parts from Small Mechanical Components: Precision Gears, Timing Belts, Gear Assemblies, Timing Belt Pulleys, Couplings, Bearings and much more - SDP/SI but never got to build it and lost the drawing.The frame for it would also be a place to connect the cage onto.
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Old 02-23-2019, 04:57 AM
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I’ve never seen anyone try this. With my background and experience with airboats, I will tell you that you’re asking for trouble using any sort of pulley drive for a few reasons. Weight, complexity, and several modes of failure are a few problems. Airboats don’t need to be complicated, and if you want even reasonable performance, you need it to be as light as possible. If you’re worried about blow overs and rolling, then you need to design the hull properly. If you build the hull so the width is 1.5X prop diameter and length 3X prop diameter, that’s an excellent base to start from. Next would be build the engine mount with some adjustability so you can dial in the CG on the fly. The base for the prop location is 33% of hull length from the transom. Depending on hull design and weight, this can change. These figures are for a basic flat bottom boat. Hydrofoils and the like are completely different animals and thus have different “bases” to work from.
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Old 03-05-2019, 06:27 PM
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Got RPM
 
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About 25 years ago I built a 48” airboat using a 4-cycle lawnmower engine in the flat bottom hull with a chain drive to a prop in an elevated pod. The prop was about a 24”x10”, can’t remember for certain. It worked, but was too heavy for any good speed. Too much weight and excessive drag from the large flat hull. I wouldn’t do it again.


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Old 03-06-2019, 03:00 AM
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Originally Posted by Got RPM View Post
About 25 years ago I built a 48Ē airboat using a 4-cycle lawnmower engine in the flat bottom hull with a chain drive to a prop in an elevated pod. The prop was about a 24Ēx10Ē, canít remember for certain. It worked, but was too heavy for any good speed. Too much weight and excessive drag from the large flat hull. I wouldnít do it again.


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A lawnmower engine would be a lot of weight. A 4 cycle trimmer engine would be a lot lighter,but still heavier than a 2 cycle engine. I drew up a plan to use a 2 cycle engine down on the deck and use a belt and pulley to transfer power to the prop hub above. I was also considering doing it with an electronic ignition to cut down on a lot of weight on the engine.I was going to use a full crank engine so it would have the pull start on the back of the engine.I wish I hadn't lost the plan as I now have a 25cc Toro trimmer engine with a full crank.
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