Dumas Big Swamp Buggy

[420TEE]

Tunnel hull air boat. Anybody ever make one of these work? Makes a real pretty boat and with TH .46 on 15% nitro it gets up on the sponsons and hauls the mail. However steering it is another thing. Two big air rudders, no water rudder as designed by Dumas and it is nearly uncontrollable. Zigs and zags on it's own, can't keep it straight. Rudders and linkage tight, no slop. Servos work fine. Just tried a 2" brass fin on the back of the left sponson. No help. On second pass boat hung a sharp left onto the beach and snapped the brass fin rod off. Tried different linkage settings for more or less rudder throw to no avail. I guess it's too sensitive to breezes. Can't stop them. :(

[Shaun Hendricks]

You could try installing a gyro. They are common now on helicopters and planes that have sensitive controls. The gyro reacts to counter poor behavior faster than you can and it doesn't overcorrect like most human pilots.

It's probably not the solution to your problem, I have no idea what is causing the issue, but it might keep you going relatively straight. :D

[420TEE]

Shaun, Thanks but unfortunately gyros don't work in the yaw axis. At least not small, cheap ones. My feeling is a design flaw, the CG being too high with the engine and fuel tank 4-5 inches above the water, causing the boat to "chine walk" until one chine hooks the water and the boat slews to that side, overriding any rudder input I apply. I could hang a hunk of lead in the boat but that's kind of counterproductive. Oh well, as I said, it's a pretty looking boat on a shelf in my shop. :(

[Shaun Hendricks]

Primary use of gyro is Helicopter tail rotor control. Last I checked... that was yaw... :D

But if it's truely 'walking' I don't think it would help the condition.

[Axethrower64]

I have one and it may be that your servos are running too fast. Takes a soft hand and lower engine rpms for turns or she will zig zag from over correction, at least thats what my initial problems were. I think it mostly the very large rudders. If you look at the smaller swamp buggy its rudder is half the size and only one is used. I modified that one too with two rudders and she'll swap ends before you can blink once.

[420TEE]

Axethrower- Since I lasted posted two years ago I noticed on pictures of airboats on their forum that the engine thrust on most boats is parallel to the boat deck but on mine it is designed to tilt about 6 degrees up. I figured that would push the bow down causing the chine toward the front to dig in on a turn and slue the boat around. I leveled the engine with a few washers at back mount bolts. Then I could run tight turns wide open with no digging in. Design flaw. Unfortunately last winter I tried the boat on the snow. Really flew, but it hit somewhat deeper snow and the sponsons dug in like skis and no turnee. Hit the concrete base of my barn wide open. The whole engine mount stand ripped off, but the boat held together pretty well. It's fixed but I haven't run it since. :(

[hpiguy]

I've seen people install small lexan spoliers on the front to keep the nose down and help a bit.

And they also greatly increase the rudders size to move more air in the direction they want.