1QwkSport2.5r

I was inspired by a gentleman on another forum that originally designed and built this boat. I was fascinated by the design and the fact its all wood, AND he posted part of his drawings to build it.. Here's what he calls the "Kamikazee"

This thing is 32"L x 18"W, weighs 6#10oz RTR with wet rudder only, and K&B Sportster .65 engine. Top speed 25-30mph.


Here's a 2 minute video of my boat running.
http://s153.photobucket.com/albums/s...t=MVI_0222.mp4

Got RPM

Really nice boat! I like the natural wood look, and it seems to run well too. What do you have planned for the next one?




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1QwkSport2.5r

Thank you! The boat seems to go pretty good but the engine needs an attitude adjustment. I have a few things I need to try to get the transition cleaned up.. it loads up in the low RPMS. (Came from a Military Mig27 drone kit) At 1:11 in the video you can hear it sputter a little bit. I think the hole in the idle disk is too big.

Next project is an Outrigger Hydro. Balsa/Birch construction with some aluminum for engine stand and boom tubes. I'll be running a TT .46 Pro until I can afford a real screamer.

I'm Legal v8 on RCAW, I know we've exchanged words over there about the Hydro subject/upcoming project.

hyper701

nice one mate, i started my first airboat build yesterday, its a cajun gator puller, and i will be runing a os la-40. how do you like the wet rudder set up?? does it create much drag??

1QwkSport2.5r

The wet rudder is the way to go running on water. The steering is far more precise. If you watched the video I posted in the 1st post, This boat will almost turn on a dime with just a wet rudder. Drag is minimal from what I can tell. I made it from 1/8" aluminum sheet metal and used a grinder and dremel to sharpen the edges. I'm going to modify the rudder a little bit to add a "breakaway" mechanism. This is so if you hit something it pops the rudder up and goes over the obstruction instead of bending/breaking the rudder.

Running that OS 40LA engine, I'd run a fuel with at least 20% oil - the more castor the better.

I'll be posting pics of my second airboat within the next week. Outrigger Hydrofoil running with a Thunder Tiger .46 Pro. Should be a good setup.

hyper701

Been running the la40 for a few years now in my plane. I will be running a top flight 10x6 prop, so im hopeing to get 35 mph+ out of this boat. Cant decide weahter to go with a wet rudder or twin air ones. I have a 50mm stainless rudder in the shed that would b perfect, but i love the way airboats drift around corners with air rudders.

1QwkSport2.5r

If that Top Flight prop is wood, don't use it on the boat. Wood props will shatter if they hit water.

hyper701

yea, did not think of that, thanks for the warning!! think iv got another prop in my flight box, will have to dig it out. also iv decided to go with the dual air rudder set-up.

1QwkSport2.5r

try it out with the air rudders, but you may find the turning radius to be quite wide, especially at low speeds.. steering is diminished the slower you go. If you design it right, it should work pretty well but keep the wet rudder as an option. It will make a significant difference is performance.

Got RPM

With good piloting skills and a flat bottomed boat you'd be surprised how well one can maneuver an airboat at relatively slow speeds. It isn't the speed of the boat that determines how well an air rudder works - it is the speed of the prop blast passing the rudders that changes the boat's direction. A skilled pilot can turn a stopped airboat around almost in its own length. All it takes are rudders that are large enough for the hull's weight and a skilled finger on the throttle.

All that said, a water rudder does provide for better control, particularly for a beginning driver. It eliminates the sliding turns that some like so much, but it does make driving the airboat more like driving a car.


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1QwkSport2.5r

I suppose that is possible.. I guess I'd rather have a little tighter control since most of the places I run at have lots of weeds and trees around the shoreline.. I have air rudders made and have had them mounted but everyone said "wet rudder only" so I didnt put them back on after mock-up. I think I over-built my boat and the air rudders may add to much weight as it is right now.. would have to balance the front a bit do it doesnt sit too low in the water.

Thanks for the insight - I kinda figured air rudders would have to be pretty large to get that kind of control from them.. Every other airboat running air rudders only slid a lot more and I guess I don't care for that too much.. who knows.. I might change my mind when winter hits and I run on snow.

On a side note - I made a few slight mods to my wood boat - I noticed a small vibration in my engine stand. (prop is zero balanced) Turns out the plywood is still a little warped so I added a thin piece of foam double stick tape to put between the top plate and the legs of the stand. No more vibration. I also moved the engine forward 1/4" to see if it will not sit as deep in the water in the back. The baffle was pulled from the muffler in hopes of curing the transition condition. I'm going to go run it once it warms up a bit more and GPS it with a few different props and see what happens.. I havent done any tuning with props yet as I've been trying to get used to it and get the engine running right.

1QwkSport2.5r

I ran the Flatty today for a couple tanks of fuel. I took the 12x8 off and put a 12x6 on to see if it would run any different/better. Top speed improved 2-4mph I'm guessing (it looked much faster than before). I didnt want to GPS it since the water had a little chop to it. I'm gonna duct tape the GPS to it sometime this week and run each prop to see what gives me the best speed. Then its gonna get a better rudder and a better servo. I'll try to grab another video soon.

1QwkSport2.5r

So I guessed a little wrong.. I went and ran the boat today, and this time I stuck my GPS on the boat and ran 3 different props. I got 20.0mph on the 11x7, 22.1mph on 12x6, and 24.9mph on the 12x8 prop. The 12x6 sounded faster, but actually wasnt. I didn't bother running the 11x6 because I know it would be less than 20mph given the RPMS can't counteract the lack of thrust. Overall, I'm pretty happy with these numbers. The boat as-is is 6lbs 10oz, the GPS weighs 8.75oz so that adds up to 7lbs 2.75oz with the GPS on-board and wet rudder only. I'm going to see if I can shave some weight off by switching fuel tanks and grab a couple 13" props in low pitch numbers and see if that gives me any more top end. This boat given its weight might end up being a candidate for dual engines if I can get the throttle controls adjusted to pull 2 carbs.

1QwkSport2.5r

I got 30.3MPH with 13x5 prop and 15% nitro. Not too shabby.. I think there's more to be had from the old K&B...

1QwkSport2.5r

I tried out the air rudders on this boat this past weekend since I hadn't done it yet, and the engine has been running like a big turd... So I ran it in the yard for a tank of fuel. It runs in grass excellently, except it slides too well... A wise man once said (not quoted word for word) "An object in motion stays in motion until another force acts upon it".. My boat was in motion until a TREE acted upon it, thus bringing it to a complete stop. The damage to the boat is relatively minor, however my pride took a hit to the gut... Here's what it looks like:



Of course it had to hit *between* 2 support ribs, 1 (center of boat) being 1/4" plywood so it kinda taco'ed the front a little bit. I squirted about .25-.33oz of epoxy into the inside of the damaged area and now its solid again. I just need to fill the dented areas with some wood filler and recoat the boat with Epoxy Finishing resin. Needless to say, I won't run the airboats in the front yard anymore.

(I was really bummin' after this happened, but at least I didn't totally destroy it..)

1QwkSport2.5r

Well, I've reached the speed threshold at which the bow lifts and flips. The last time I ran it I didn't have the gps on it, but at 30mph it is planted pretty well so I'm guessing it has hitting 33-34mph. I think I need to add some ballast to the front. I think I can get this thing to hit close to 37-38 with a 13x7 apc and some weight. . I have a 13x6 on it now. I'm thinking about adding a turn fin on both sides of the transom too.

1QwkSport2.5r

Ran this boat out in the snow today.. It slid too far and I couldnt catch it.. It tried jumping the driveway. Scoreboard: Driveway 1, Kamikaze 0..




I slid into the fence in the back yard putting a crack in the top/front that I have to patch... I have some 'glass cloth I'm going to lay on the whole bottom and the front 2-3" on the top. I'll patch the holes and fill them in and hopefully make it float again soon..

1QwkSport2.5r

Since the bottom of the hull seems to be prone to getting holes in it from random objects, I'm fiberglassing the bottom. I found a link someone posted about laying plastic sheeting over wet epoxy resin/fiber cloth to get a seamless finish without having to sand and polish the surface, or add another coat of resin. ( http://duckworksmagazine.com/03/r/ar...ass/bottom.htm ) I figured I'd give it a go. Here's the cloth laid out and cut so I have an inch or so extra all around

Resin and cloth down (11:00pm 4/14)

Plastic sheeting down over wet resin (11:19pm 4/14)

Once the resin is set, I'll pull the plastic sheet off and grab one more picture. The plastic sheeting wont stretch and conform to the hull like the cloth will so on the next layer I'll make a few cuts in the plastic to get a layer without any resin pockets or air bubbles.

1QwkSport2.5r

Here's a pic with the plastic sheeting pulled off. I have to sand the ripples out from the plastic, but it wont be as hard as it seems. (Plastic was a little too thin, I think..)
(1:32am 4/15)

Here's all of the excess cloth and resin trimmed from edges. (1:45am 4/15)


I would think if I didnt have the compound bends on the bow that the plastic would have laid flatter. The cloth would conform to the hull far better than the plastic would, and I think thicker plastic would be worse. When I put the second layer of cloth down, I'm going to cut a few slits into the plastic by the bow so I can manipulate it a little and prevent the ripples.

This is a lot easier than I thought it would be. Its just time consuming. Then again, most of the time involved is waiting for the epoxy to set up.

Altered1

It does look good!

Does this film look thicker ?  - something with a bit of 'body' to hold down the epoxy?

http://duckworksmagazine.com/03/r/ar...owpeelclsp.jpg

1QwkSport2.5r

I think the film is thicker, but only to a degree. I couldnt find the kind of film used in that link. Best I could find was a polyester blend that was .007" thick which is about the same as the plastic sheeting I used. I have some other sheeting thats thicker (4mil as opposed to .35mil) that I should try, I'll just have to make more slits for the bow's curves.

In the link, there is what I think is a typo about the thickness of the polyester sheeting which is said to be .030". My feeling is .030" thick polyester isn't going to come on a roll because it'd be too rigid.

1QwkSport2.5r

I did a small test using the 4mil plastic sheeting I have and it peeled right off leaving a nice smooth surface, so I'll be using the thicker plastic on the second layer of cloth. I probably dont need to do a second layer of cloth, but I am going to since I have the material. I'm going to toughen up the bow with a couple small strips of fiberglass too.

I'm going to try my hand at making a set of adjustable trim tabs to hopefully get a smoother top speed. At speeds over 30mph it porpoises a bit.

DJLaPalme

You can use Plan Protector, which is a thick plastic that comes on a roll like Monocote. You should be able to get it at your LHS. A friend of mine uses it to put fiberglass on his airplanes and it does a great job. I've used it too and it is perfect for an airboat hull. Just remember to let it FULLY CURE before trying to remove it. Dennis

1QwkSport2.5r

Well, I tried out the thicker 4mil plastic. On a surface with curves in only one direction (like a bow rake on a typical flat bottom boat) it would work well and would give a glass finish. Compound curves on the other hand, not so much. I had to make a few cuts on each side to get the sheeting to lay down w/o having another part lift up. I think I'll have to hybridize my method in the future to incorporate either 1 kind of sheeting that bends/forms or use two different kinds of plastic overlapping each other. I have more 'glass work to do on the hull so I'll keep trying different things.

1QwkSport2.5r

Pulled the sheeting off. The pics dont really show it all that well, but you cant see any of the "weave" where the sheeting was laid down. The finish it left requires very little sanding and no filling. Compound curves = thinner sheeting, non-compound curves = thicker sheeting. I hard rubber roller would probably work better to get the resin to settle "flat" vs. my old credit card scraping on the sheeting to remove air bubbles and even the resin.