bone2156

Hi Everyone, I have been toying around with the idea for a large scale airboat for some time and just recently came across an old Homelite weed wacker at a yard sale. Seems to have good compression and pretty clean. Could not start it as I think the carb is dirty. This morning I tore it all apart for a cleaning and to soak the carb. and a bit of paint.
Done some reading on here and the net and have done the old google search for pictures. Came across one fiberglass hull that was sold on Ebay I guess. It is about 42" x 25".
I am thinking that is about the size I am shooting for. (picture attached) Will be starting out with some foam to carve the shape, seal over the foam with body filler and paint, then lay the glass.
The big question is how does one find out that the cc is for this engine. Fella I bought it from thinks it is about 15 to 18 years old, and has not been used in about 8 years. I did not see any numbers or markings on the little engine. Any help from those in the know would be greatly appreciated. Steve

1QwkSport2.5r

Easiest to measure the diameter of the piston or the diameter of the bore and measure the stroke. I use a vernier caliper to do this. To measure the stroke, set the engine at Top Dead Center and stick the end of the caliper in through the spark plug hole and read the measurement. Now do the same thing with the piston at Bottom Dead Center. With the caliper base flat against the top of the head, slide the caliper out until the end touches the piston. Alternatively, you can set the piston below TDC and with the caliper slid farther out than is needed, rotate the engine past TDC and you'll get your first measurement. This can be a little more accurate than guessing where exactly TDC is. Take the reading from BDC and subtract the reading from TDC. This gives you the stroke. Now take the bore diameter and halve it, then square the product. Multiply that number by pi (3.14159) then multiply by the stroke. If you measured in inches, your final product will be in cubic inches. To get the displacement in CCs from cubic inches, multiply your CI number by 16.38.

bone2156

I will give that a try. We'll see how good my math skills are. Thanks

bone2156

I picked up a Ryobi 31cc weed wackier today. Good compression but dirty carberator. I think I will use this for my airboat project assuming I can get it running. Questions: where do you get a prop hub for these week eater engines? I could make one, I have access to a metal lathe, but would be way easier to buy one already made. Steve

mysteryrc

Jag engines, or wackerengines.com

aspeed

If you scroll down a bit, there is lots of info on the "Engine Conversions" section for the weedwacker stuff. I have been gathering the Homies up for a while too for boats. Gotta find a nice pond here, besides Lake Erie.

Rick in Ohio

You can get your engine conversion kit from this website http://www.carrprecision.com/Pages/prod02.htm

This is where I got mine from for my weed eater motor.

I just haven't had to time this winter to build my air boat.

bone2156

Just purchased a converted Ryobi 31cc engine with prop hub off of EBay. $52.00' I think I did pretty good. Now I can start designing my airboat. I am thinking something about 42" x 24" with maybe 5" sides. After reading about conversions on here, I am going to rin an18" x 6" pusher prop. S

Rick in Ohio

That's about the same size boat I am thinking about building when I get time. I pickup a 3 blade 16x8 pusher for my weed eater motor, I did build a motor stand to test the motor out before starting the boat. Just need to get my wife's honey do list done first.

bone2156

Oh, those honey do lists always get in our way of having fun. Luckly I have a custom woodworking business and I can get away to do what
I want. Just as long as I get my chores done.
What are your plans for your hull Rick? I am planing on starting with foam to carve and sand the shape, and then a few layers of fiberglass. Then I dig out the foam. I did a tugboat hull this way. Easy to make changes or repairs. S

Rick in Ohio

I am thinking about building the hull out of very light wood then glassing it. That way I have part of the motor mount built in it. The trick will be making this boat so it don't tip over when turning so the motor placement has to be just right. My have to do some testing in the bath tub..... the wife will like that for sure.

bone2156

Don't know tons about airboat design, but I would think if the design had a rounded edge or a beveled edge on the bottom side, would that not Keep it from "hooking" and then doing a flip?
As I am going for the scale look and speed, the weight is not a major concern for me. 1/8" bending ply would work for you. Easy to form and bend for the bottom and sides. And once you glass it, it will stiffen it all up. S

Rick in Ohio

Yes I am thinking that the 1/8" ply wood and then glassing it would be the best when it comes to putting the fuel tank and the other stuff in to this boat.

Right now my wife has me building a stand for my daughter's front load washer & dryer to get it up off the floor so she don't have to bend over so far....... I new this was coming !

bone2156

They never want us to have any fun. I try not to smile to much and tell the wife what a hard day I had.

Been looking into the 2 part urethane expanding foam. You can pour it into any mold, cut it, sand it ant it wont melt when using epoxy resins.

Rick in Ohio

If you go that way keep me posted and maybe some pictures ok?

I have a little time today I may go down in the basement and start my planning and clearing a spot to build this boat. Wife will be at work today!

Rick in Ohio

Well the wife was away at work today. I setup the motor stand that I built to test run the motor, put the motor on and fuel tank .... its ready for a test maybe this weekend if it warms up a bit.

bone2156

Sweet! Your engine looks real nice. Can't wait to hear how it runs. S

Rick in Ohio

Why I built a motor stand is the prop looks to me like its a puller and not a pusher but the box it come in is saying its a pusher prop. Also if I can remember right the motor turns to the left looking at it from the front so this is why I thinking they sent me the wrong prop. When I order this prop I talk to them on the phone and told them what way the prop was to turn.

I could be wrong but I will find out when I start it up.

1QwkSport2.5r

Your prop is manufactured to turn clockwise. The leading edge (the thick edge) faces the direction the prop should turn. It will push air turning counterclockwise but less efficiently.

bone2156

Your second picture looks like a pusher prop if the engine turns counter clockwise when you are facing the hub. Do you still gave the recoil starter? You could check to see which way the engine turns using that. I think I read somewhere here that most turn counter clock wise.

aspeed

It is a pusher prop for a motor that runs counterclockwise as viewed from the propeller side. The prop should be flipped around so the flats are towards the rear of the boat. I would assume the motor is in front of the prop, at the rear of the boat.

Rick in Ohio

Yes aspeed the motor will be facing the front of the boat. with the prop to the rear. So I take it I can flip this prop around to make it work right?

When I called to order this prop I told them what way every thing was going to be and this is the prop they sent me and the paper work with the prop is saying that its a pusher. The way I have it on there now like the picture shows it just don't look right to me.

aspeed

Yes, just flip the prop around. The flat part of the prop does the pushing and the curved part is the airfoil which goes to the front. This of course assumes it turns ccw as we are looking at it from the picture.

bone2156

Rick, I checked my Weedeater motor and it turns counter clock wise. And son of a gun, we learned something new today. I thought sure you had that prop on the right way. I used to fly control line planes when I was a kid and thought I remembered which way a prop went. My 18 x 6 two blade prop will be here next week. I think I will hook it up tp my drill to see how it works best. S

bone2156

just ordered some urethane foam off of EBay. Also have a box built to pore the urethane foam in. Next is to build a hot wire foam cutter and some templates for the shape of the airboat. Like they say
"half of the fun is in the building". Going to start out with a foam block 43 x 26 x 6. Should be pretty close to my finished size. S