crodenb

I have started my first build of an airboat, posting pictures, and would like any comments or suggestions. Progress has been alittle slow as I am using pictures, from the many post, as my building plan. The boat is 24 X 12 X 2 and I am planning on using an OS 40 or 45 for power, as a pusher. My next step is the cage. Thanks in advance for any comments or suggestions...

arcdude

Welcome Crodenb, good start on your boat, I haven't built that particular style of boat but I can offer what knowledge I do have and hopefully it'll help you out a bit. First off the motor mount looks a little suspect, is that 1/8th" plywood that you used for the uprights? The frame you made for the sides of the motor mount looks to be about 3/4" wide which won't be strong enough if that is 1/8 " ply and it should be fastened either by bolts or screws into the main frame inside the hull. If you go back to the main page of the airboat section up near the top you'll see a thread entitled Carbon 'Selph Inflicted' SI3-60 to see what your particular mount should look like strength wise, it doesn't have to be carbon but in the least it should be 1/4" aircraft plywood and I'm sure Jeremy will be happy to answer any questions you may have. The other immediate concern I'd have is the frame around the outside, there should be frame work around the edges where one outer sheet meets another which can be installed between the frame members all around the perimeter, not sure if that makes sense? Good luck on your build, great start!

crodenb

Thanks Arcdude, I appreciate the information, I was concerned about the mount and the structural strength, I will put another piece up the sides, and I had the plane of bolting the entire mount into the frame work just prior to putting the expoxy in it and closing up the deck. I have cut 1/8" sides just haven't put them on, I may put some stringers in between the main frame and outside just to be safe. Thanks again and will post pictures of progress soon...

Jeremy_H

I share the mount concerns, but two other things spring to mind.

Cooling can be a problem with pushers on airboat's it seems. My twin has the front engine providing cooling, but test showed that full throttle for more than a few seconds with the pusher running alone caused overheats. Aeroplane pushers are moving through the air much faster, we are at generally lower speeds so the flow is not there so much. It's easy to think that the incoming air must be fast to be able to replace the air moved by the prop, but it's pretty slow going in. I'd run some bench tests to make sure I think, as soon as possible in case an engine reversal is on the cards.

Exhausts can be a problem on pushers, what did you have in mind there?

One other note is I see there's a wooden prop on there. I know it's just a dry assembly, but just to check, please don't use wooden props on RC airboats. They can't take the occasional water impact and can shatter. Once you've witnessed the sound of a prop hitting water at full chat you'll get an idea of how wise this is

Boat's looking great so far, I'm interested to see how the bottom skin is going to finish at the bow, I note you appear have different curves on the two outside frames, or is it just that you've not glued the skin to those just yet?

crodenb

Jeremy_H, thanks for the suggestions. The overheating problem I have had before on a outboard tunnel, even with water cooling, figured it was the high nitro fuel, and that I was running it to lean, so I am planning on using a 10% fuel with a high oil content, I have even considered a water cooling system, but haven't really designed one yet, I may see if I can come up with a marine head for the engine and go that route. As far as the wooden prop its for building purpose, I am not a wooden prop fan, going to use master air screw prop, in a 10 X 6 size. The exhaust I think I have worked out, I have a pitts muffler, and extension, which offsets it. The bottom skin and sides are for in the progress mode, I am going to work on that. I have been searching for a really good picture of the front so I can get some ideas of the designs and structural support issue. I am building a lot from memory of my youth living on the St. Johns river, and full size airboats.

Thanks for the suggestions and comments -- Carl

l8rg8r

Greetings nice air boat build I was going to build one myself but found one I liked for sale and bought it it has a os 60 and spins a 12x10 prop it is a pusher I haven't experienced any over heating after 10 + min of on and off full throttle running I am getting temps of 210-220 at the glow plug I'm running odonnels 20 0/0 It's a k&s pacer 34"long 15" wide

arcdude

Congrats on the nice find, hope your planning on completing your own build? There is nothing that"ll put a bigger smile on your face than running your own creation

crodenb

Thanks for info on the over heating issue, I haven't had much time this summer to build, work has kept me on the road, I am currently working on the cage and rudder assy, I am using aluminum tubing, after I get it done and welded, I'll get pictures posted. I have been considering a steel gage, but not sure about the size of stock to use.