View Full Version : How do you know if your floats can support your plane?

02-17-2008, 04:10 PM

I did have skis on my GWS beaver but suddenly its 50degrees raining and 30-40mph winds. But im assuming that the snow will melt by then and the creek will be plenty high. My last floats i have built from walmart foam board worked well in supporting it, but the design was not good. When i went for WOT to take off teh floats kept wanting to submerge and my prop was getting hit by watter. So how is the float suppose to be designed in the front to break the water evenly? ANd also is there a proper scale in size like if your plane is 30in long then the floats should be 25? Im going to build these out of polystyrene foam.


02-17-2008, 04:43 PM
Here you go.....


Based on your pic - there are a few things that will need some tweaking to work well.

Pay careful attention to placement of the step - that is super critical for getting the plane off the water (no small task). Yours is FAR FAR to aft....

Chuck Cunningham is one of the long time good design guys sadly he is no longer with us, but his smarts live on.


02-17-2008, 04:50 PM
Hey im a cunningham myself. But i dont think im related to him though. It would be sweet.

02-17-2008, 05:00 PM
Alright i did a measurement of how far the back of my prop is to my leading edge of elevator(part that moves) and i got 23.5in or 24 rounding off. Is there a specific width of these floats as in how far apart? And what do you mean by step? And also is there a specific place you put those wave breakers i guess you call em where the front of your float is shapped like a boat hull but it has these lines sticing out that shoves the waves to the side.

02-17-2008, 05:45 PM
He talks about spread of the floats being about the same as landing gear (read that article carefully).

The Step is the notch in the floats where it drops to the rear portion of the float. That is a CRITICAL float element as you can not have the drag of the entire float in the water. Once at speed only the portion just forward of the step is actually in the water.

Wave breakers are called chines. Where they go is dependent upon how you float hull design kicks up the water. If done right you do not need them at all.


02-17-2008, 06:14 PM
I think these are too tiny i just built, my lengt is 24in so 75% is 18. Here are pics i placed the landing gear where i think it should aproximately go. I think i got the step thing wrong.

02-17-2008, 06:15 PM
ooopss sorry.
Yeah i dont think these will support my plane's weight.

Well i tested them and they do in fact float i just have to balance it right now.

02-19-2008, 06:00 PM
Yep too small...

You might want to take your design from existing floats and go from there rather than starting from scratch.



02-19-2008, 06:27 PM
Your step shape is wrong. It should be sharp and vertical, not angled and radiused like yours.

I had great luck with these plans:

02-19-2008, 07:02 PM
Thanks for the link. They are small but they did hold up my Beaver the only problem is that they kept submerging at full speed. And prop was getting hit by water.

02-19-2008, 07:39 PM
Thanks for the link. They are small but they did hold up my Beaver the only problem is that they kept submerging at full speed. And prop was getting hit by water.

Well ... see ... simply "supporting" the plane is minimum functionality. What the floats do when the plane is actually moving is the most important thing.

The shape of your floats, and their general dimensions is actually pretty critical. Other critical factors are the position of the step, and the angle of incidence between the float and wing. These sweet spot of these last two variables will vary by plane and will require some trial and error.

The position and shape of the step both in relation to the float itself and where it is in relationship to the CG of the plane will dictate how easily you'll get off the water. The amount your floats stick out past your prop will have an effect on how likely your plane is to nose over and/or splash water on the prop. Also, the shape of the bottom and sides of the floats will determine where the bow wave is, and whether it can splash at all on the prop or if perhaps it's behind the prop once you're on step.

LOTS of factors. You'll do yourself some favors by starting with a design that's proven to work fairly well, and then tweak it for your application.

If you've got the floats otherwise dialed in, but you're still splashing the prop too much, then you need to add chines to deflect the water away from the prop.

02-19-2008, 07:56 PM
Well here is my second attemptt, tehse are 18in long my cub here is 22in long. I didnt do the V thing on the bottom of them because im going to use them for snow use for now, i dont really have a "lake' to try it on or pond, i just have a creek and since i have no rudder and its frozen it wont work for me. So these will be snow floats. What do you think? sorry the pics suck i droped my cam in teh creek. Its dead.

02-19-2008, 08:26 PM
THAT looks far more convincing. You don't even HAVE to do the V for the water. Some people prefer flat bottomed floats.

Both shapes have pluses and minuses. I went for the Vee myself. If I think of it, I'll post some pics of my floats when I get home tonight.

02-19-2008, 09:02 PM
Cool! Thanks. Im kinda shocked at the moment from an exploding nimh battery.

02-20-2008, 07:30 AM
GA92: Another critical element in protecting the prop from spray,and keeping the model from rocking too far forward when throttle is applied, is the length of float extending forward of the prop. I think the formula is something like 1/4 of the prop dia. in inches should equal the float length forward of the prop arc. So a 10" prop should have at least 2.5" of float extending forward of it. I scratch built a set of foam floats for a 72" Beaver, using the rules pointed out by the responders in this thread, and they worked well, after some minor adjustments to suit my particular plane.

02-20-2008, 03:21 PM
Wow i never heard of this before, yeah ive got the going forward part but not the spray part out of the way yet.