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Airboat Engine Question

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Old 03-20-2016, 06:37 PM
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Hi there. I am just starting to build an airboat I found plans for online and had a couple of quick questions regarding it. Firstly, I believe, the plans are drawn for a pusher set-up like the real thing. If I do this, how does one start the engine, as the rudders will be located behind the engine in which I would like to ask how to start the engine. Or, secondly, is there and problems with swapping my engine around and making it a standard tractor/puller set-up. I personally would like to swap it so it faces forward, as it would make it a lot easier to start for me, and I would honestly prefer it. Thank you.
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Old 03-20-2016, 07:23 PM
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Tractor engines are a more efficient setup and allows a larger range of props. You just need to position the engine such that it balances well. Not a difficult task provided you allow for some fore/aft movement of the engine. Set the prop at 30% of hull length measured from the transom to start with.
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Old 03-20-2016, 07:36 PM
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Thank you. So if I understand this correctly, the prop should be located at approximately 30% of the total length measured from the transom. In my case, 24" long hull would put the line of my prop at approximately 8" from the back of the boat. Thanks again.
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Old 03-21-2016, 02:36 AM
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Quote:
Originally Posted by NEW222 View Post
Thank you. So if I understand this correctly, the prop should be located at approximately 30% of the total length measured from the transom. In my case, 24" long hull would put the line of my prop at approximately 8" from the back of the boat. Thanks again.
That's just a starting point. Allow for a couple inches of movement fore/aft for balancing. What size engine are you working with and what prop are you planning to use?
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Old 03-21-2016, 12:30 PM
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I just bought an older MDS 6.5 cc or .40 ci engine for the build. The prop that is recommended is a 10 x 6. I may have to modify the engine mounts to accept the prop, but will mock one up before cutting. I will also have to wait for a couple of weeks till I go to the US to pick up a mini table saw.
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Old 03-21-2016, 03:33 PM
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Quote:
Originally Posted by NEW222 View Post
I just bought an older MDS 6.5 cc or .40 ci engine for the build. The prop that is recommended is a 10 x 6. I may have to modify the engine mounts to accept the prop, but will mock one up before cutting. I will also have to wait for a couple of weeks till I go to the US to pick up a mini table saw.
I am not sure how much experience you have with airboats, but generally you prop an airboat a bit lighter than an airplane. You may find it necessary to try a 9x6 or 10x5 prop. The general basis for hull sizing is loosely based on prop size - length of hull roughly 3X prop diameter and 1.5X prop diameter for hull width. Build light if you can - balsa or liteply framework and as thin of sheeting as you can. Reinforce the hull where the engine stand will go. It's bad news if the engine removes itsel from the hull while you try to drive it.
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Old 03-21-2016, 04:53 PM
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Thank you again. I have honestly ZERO experience with airboats. I have built a foam version of the Lil Swamp Buggy, and that is it. And to add to that, I have not yet tested it as it is starting to warm up here now, and will hopefully get to it while on holidays in a couple of weeks. The maiden will be on grass. The airboat I will be building is approximately 24" long by 14" wide. I believe that the plans I downloaded here were by Mr Cajun Gator, but am unsure, hence why I am still trying to get a the plans he had offered a few years ago before starting the one I have plans for. Thank you for the tip of engine mounting. I was wng the older MDS engine cheap for this application. Anyways, thanks again, and I will more than likely have a few questions along the way of my build. For the time being, here is one of my current airboat.
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Old 03-21-2016, 04:54 PM
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And another
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Old 03-21-2016, 04:57 PM
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Ok, and please allow me to ask another question. When assembling my airboat, the big one, I will be using 1/8" Baltic Birch Plywood. Once it is cut and the framework is ready to be assembled, what is the glue best used for this application? Also, what is the recommended glue for gluing the bottom, top, and / or side sheeting on with. I do plan on putting a coat of polyester resin on the framework, and joints before installing the top deck.

P.S. I really like the look of the airboat you have pictured in your avatar, whatever it is.
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Old 03-21-2016, 06:33 PM
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Quote:
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Ok, and please allow me to ask another question. When assembling my airboat, the big one, I will be using 1/8" Baltic Birch Plywood. Once it is cut and the framework is ready to be assembled, what is the glue best used for this application? Also, what is the recommended glue for gluing the bottom, top, and / or side sheeting on with. I do plan on putting a coat of polyester resin on the framework, and joints before installing the top deck.

P.S. I really like the look of the airboat you have pictured in your avatar, whatever it is.
I use regular 2-part epoxy for all assembly of the framework, sheeting, and final sealing of the sheeting. Typically I use 15 minute and 30 minute for assembling framework and gluing the sheeting on and 60 minute finishing resin for sealing the outer sheeting. The last build I did (Selph Inflicted tapered flat bottom .40 series) I used the finishing resin for the outer skin sealing except I thinned it down a little bit - about 20% with clean methanol. Acetone will also work. Thinning the resin (after mixing both parts well) allows a thinner coat that penetrates better. Doing three thinned coats seems to work better than two un-thinned coats. I sand each coat smooth after curing with 150 grit sandpaper and wipe clean thoroughly with acetone twice. This removes the parafin layer that deposits as the resin cures. I don't know if polyester does the same thing or not.

If you look through the airboat forum, you'll find several of my build threads. The boat in my avatar is the "Kamikaze" airboat designed by Hooty301. That boat weighs about 8 pounds RTR and was originally built for a K&B .65, and later used with an ST S90 and now an Enya R120-4C. It's 39"L X 18" wide. There's videos of it on YouTube as well as my other boats. I think I've built 9 boats total now.
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Old 03-24-2016, 10:52 AM
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I did this up as a bit of a guide some time back may help (keep in mind things change depending on design)
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Old 03-24-2016, 05:51 PM
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Thank you. That is a real nice guide. Just seen it and printed it out.
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