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Old Aug 11, 2007, 04:54 PM
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Mount Pleasant, SC
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Help!
Airboat Question

I've started building an Airboat roughly based on some simple plans I found on the Cajun Airboat web site. I've scaled and modified the hull design to my liking and have been using
'door skin" as the wood for the hull. Overall hull dimension is 15" wide and 26" long. The area on plane once it is up to speed will be ~12 inches wide. I've done some preliminary weight checks and it looks like the total weight will be nearly 5 pounds with an 8 cell sub C battery and a 600 size electric motor.

My question is will the 600 size motor be enough power to get any kind of speed with a 5 pound airboat? I have in my parts box a couple of Magnetic Mayhem motors that the idea of a twin pusher setup might be fun. Anyway, what sort of thrust and prop speed does a 5 pound airboat need to be fun?

I already know more power the better but how much is enough?

Thanks in advance for any ideas and comments.
Palmettoflyer
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Old Aug 11, 2007, 08:22 PM
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I am a fan of the Magnetic Mayhem motors, but would reserve one to upgrade if present one is a bit puny. You are into virgin territory as far as power needed so it will be a cut and try operation.
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Old Aug 11, 2007, 10:30 PM
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I agree with Captlee you are indeed in uncharted territory on this one. Only trial and error will solve this problem. Please post the results so that others can learn!
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Old Aug 11, 2007, 10:44 PM
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I would try a reduction gearbox and use it to spin a larger prop, slower.
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Old Aug 12, 2007, 08:42 PM
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Thanks for the encouragement to push on. I do have a few items Iíd like to test as possible power candidates. Here are a few pictures of where my airboat project is now. I need to make a few basic decisions before going much further. However, I know all to well that Iíll want to modify the power system after it is built. A little fore thought at this point in the build will let me test various combination. You see in the pictures that I have a Kyosho Endoplasm 16 turn motor connected to a Great Planes gear box. This was my first thought but I believe it will be too much thrust and not enough prop speed. A better combination might be the Magnetic Mayhem in the gear box. I have gears to run either a 2.5:1 or 5:1 gear ratio. As you said, only some testing will show the best. In hind sight, I would have built the boat about 2 inches smaller in width and length. Anyway, Iíll finish up the hull to the point where I can wet test some motor combinations and see what works best. By the way, Iím trying to avoid using brushless motors around water. Iíve found brushed motors are a lot more tolerant to getting wet. When a brushless motor is dunked, the ESC goes into overload with the change cause by water in the motor. When a brushed motor is dunked, Iíve always just washed it out with denatured alcohol and keep on running. In fact, Iíve driven an upside down airboat back to the dock before.

Iím not intended to do a build thread here but Iíll keep posting pics as it progresses and I have some motor data.
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Old Aug 12, 2007, 10:35 PM
Grumpa Tom
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A build thread is mandatory! As are lots of pictures! Carry on.
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Old Aug 13, 2007, 03:56 AM
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Quote:
Originally Posted by Kmot
A build thread is mandatory! As are lots of pictures! Carry on.
I'll be more than happy to post progress as it comes. My day job, family and extreme summer heat tend to slow my work.

This is my first attempt using "door skin" ply as a model building material. Normally, I build airplanes and as light as possible. My only experience with airboats is a small 15Ē x 8Ē design that resembled a block more than a boat. It was powered with a speed 300 motor system and was a hoot. Biggest lesson learned was to keep the vertical CG as low as possible. This design will have the heavy 8 cell battery all the way down inside the hull and the hull itself is turning out to be a weight item itself. I keep pondering if I should start trying to lighten up the structure or not?
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Old Aug 13, 2007, 09:36 AM
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Before this thread goes too far, I want to thank and give credit to my source of inspiration for this build. Cajun Gator RC Airboats is a great web site and Harold McNett has some really nice pictures and information available. The plans I used are from his 24" simple design. I made some minor changes like moving the motor mount from a tractor to a pusher and enlarged the overall design to 26" length.

Cajun Gator RC Airboats
http://cajungatorairboats.com/

Cajun Gator 24" simple plans
http://cajungatorairboats.com/v-web/...topic.php?t=54
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Old Aug 13, 2007, 10:42 AM
Grumpa Tom
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Quote:
I keep pondering if I should start trying to lighten up the structure or not?
Just a WAG, but since this is an airboat, I would think that as long as you have a bit of thrust the hull will come up on plane like any other good hull and then you will be skimming along the water?
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Old Aug 13, 2007, 11:36 AM
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From what little I know about airboats, the speed range is pretty wide. Of course, more thrust would get it up on plane faster but at the penatly of top end speed. Tonight I'll try to set up a Magnetic Mayhem motor in the gear box and see what numbers I can get with the 2.5:1 ratio and maybe a 12" prop. All my MM motors are reverse timed so I'll have to figure out retiming too.
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Old Aug 13, 2007, 01:08 PM
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Just pickup the Reverse version of the magnetic mayhem motor, it works better or use the standard version if you have reverse ones on hand. Been using them in pairs on gearboxes for twin screw boats and like them fine. 2.5 to 1 is a good choice for underwater screw in speedy type scale boats. Talked to Kyosho and found out the reverse version is wound in reverse so retime will not give full power, besides a twin prop airboat might be in your future.
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Old Feb 29, 2008, 09:31 PM
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Hey Guys,
I'm back with an update. Hard to believe it has been 6 months since I was searching for advice here. I've got a bunch of pictures to post and then I'll come back with some of the spec. details as a follow up. Overall, the project has been a success!
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Old Feb 29, 2008, 09:51 PM
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Yesterday, we did get the boat to a respectable size pond and gave the boat a good shake down. The performance is pretty good but I'm planning to tweak it just a bit. The motor is a Kyosho Endoplasma with a Great Planes 3:1 gear box swinging a 11x8 APC prop. Battery used was a 8 cell 3600 mAh. I'm thinking a 9 or 10 cell battery will give it a tad bit more speed. I do have a video of the test run if I can figure out how to post video in RCGroups.

Thanks to all for the help getting started.

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