Where do you balance an airboat????

[randall1959]

I just built an airboat out of an old wave board. It works well except when I give it full throttle and the nose bounces on the water terribly. Is it that I need to add weight to the bow? I'm guess that's the problem, because it works fine at slow speeds but porpoises terribly at higher speeds. Any help is appreciated.

[rpage]

wow that rocks! nice job! I had built an airboat some 20 years ago and I had the same problem with the bouce at high speeds. I did add weight as you suggest. But I mainly do planes now and am just looking into boats again. I am sure a boat builder could answer this for sure.

Again, nice job! Looks like a blast! :D

[randall1959]

And I had this unused engine and radio gear left lying around so I decided to do some experimenting when I found the wake board at the garage sale. The radio gear is all 27mhz stuff so no problems shooting down big rc planes. I'm not sure what it weighs but I'd say around ten lb or so. That sounds kinda heavy but if I could just get the nose down I think it will have more than enough speed to be lots of fun :D Tonight I moved the pod forward about four inches, along with the "cockpit". I also added some down thrust to the engine and put it back on the charger to try again tomorrow. I'll keep everyone posted on what develops.

[Lewist]

by giving the engine downthrust you will lift the nose, it you give the engine upthrust it will try and lift the rear of the board therefore lowering the front.. and picking the back up giving more speed!

[zenchal26]

quick fix trim tabs

[randall1959]

First, I cut off the transom so it's square across the back. The rear of the boat was tapered up and I think that caused it to "rock" back at higher speeds. I think this is built into a wake board so that you can turn quickly. Second, I added a trim tab across the bottom. Now the bow stays right on the water and this thing goes like a bat outta you know where.... :D Now I've added on board video and it's a blast watching it slice through the cat tails from the drivers seat........ :D

[speedchaser]

I like the fact that your prop doesn't look too oversized for the board and yet seems to really wack it - you can tell by the wake... What type motor do you use - and does it turn well on the air rudder?

[randall1959]

As long as the wind isn't ripping like it did yesterday, when I flipped it over backwards... :eek: It will turn on a dime. Actually when the photo was taken I had it running at half throttle, and operating the camera myself. I have a Thunder Tiger 61 pro on it with a 12X6 prop. Lately I've been using an APC 12X6 to get a little more speed. It's a little heavy at 16lb but I think sometimes the weight aids in making it stable at higher speeds.

[Minimole]

Sorry for kinda changing the subject, but i hope to build my own electric airboat soon, and was just wondering, in all the picks of air boats ive seen so far, it seems all the stuff is at the back, so doesnt that mean it leans way back in the water, or is there something i dont understand? When im planning and building my boat, should i have all the stuff at the back, or more centrelized?

Thanks, Duane :D :D

[randall1959]

Most rc airboats balance at a point 1/3 forward from the transom. I think the thrust being above the boat tends to keep the bow down.

[Minimole]

Excuse the stupidity, but what is the transom? (Im a heli and car guy...)

So its OK to have like the electronics and battery and motor and all that at the back? Where do you all put it all? Pics?

Thanks, Duane :D :D

[randall1959]

That's the back end of the boat. My boat has all the electronics in the pod at the rear of the boat. some put the electronics, like the receiver and the batter pack and all that in a water tight case on the deck of the boat to keep it from being top heavy and wanting to flip over. Don't worry about "stupid" questions. The only "stupid" questions are the ones we DON'T ask....... :D

[dougmontgomery]

In my opinion, your boat regardless of the cg or thrust angle is going to try to fly.....soon as you develope enough speed and you hit a few wave to get the air beneath the hull,You have such a huge bottom surface it will act like a wing unless you put some kind of canard that will force the bow down at high speeds. Take it for what it is worth.

[tdonily]

Some years ago (VERY early 90's or earlier), RC Boat Modeler had an article on building an airboat from scratch. One of the models the author created started out as an old pair of airplane floats. This "cat" platform had an air rudder, but needed the use of a water rudder to aid in steering. But as you've mentioned with the buildup of air under the hull, his catamaran setup allowed a huge amount of air under the tunnel of the craft and when given enough power, totally left the surface of the water. To the height of 15 feet. His remedy for the problem was to add downforce fins to the bow of the boat to keep it firmly planted on the water. Also, I found a website that's dedicated to "Unusual" R/C craft which does cover some design ideas of airboats. It is: http://home.wanadoo.nl/stuipsmulders/Frameset_index1.htm
Makes for an interesting read.