M3

My Feedback: (25)

When adding floats to a plane, how do you ensure a properly balanced plane? I have added floats to three planes, two of which flew well (obviously good luck), one didn't fly at all.

I am getting ready to add floats to a SIG SE and would like to makes sure I don't overlook something when positioning the floats.

tpstorey

Mark the CG location you are happy with as a land based plane i.e. where the plane hangs level.

Now add the floats with the step directly below the marked CG. Slightly behind is okay too.

Now hang the plane by the marked CG location and add weight to the front or back of the floats to level the plane. Adding the weight to the floats rather than to the plane allows you to switch back and forth between land and water (including snow don't forget) with out adding and removing weight. Of course, if you're really lucky, you won't need to add any.

For other important considerations check out
http://www.flyinglindy.homestead.com/skisandfloats.html
I followed Chuck Cunningham's articles years ago and my first attempt, and everyone since then, has worked beautifully.

M3

My Feedback: (25)

So, if the step is too far back from the CG, the plane would fly too tail heavy, correct? I think this was the case with my SIG Racsal 40. It simply would not fly correctly and I gave up (after a near miss with a neighbor's boat house).

FLYBOY

My Feedback: (11)

The step has nothing to do with CG. He basically said, put the step about where the CG on the plane is and then ballance the whole thing again. If you put floats on it and the cg was correct before, it may not be now. Add the weights to the floats so you don't mess up the plane, then you can take them off, or put them on and not worry about the CG any more.

tpstorey

Not exactly. We're talking about two different things that need to come together correctly, sorta like high and low needle valves that can throw each other off.

1. For a plane to fly well, it needs to have the CG in the correct position (usually 25 to 33% behind the mean aerodynamic chord). It doesn't matter what's hanging on the plane when it's flying. Could be floats, could be skis, could be wheels, could be a small child. The CG needs to be correct for FLIGHT.

2. For a float plane to take off easily from water, the step needs to be located under or slightly behind the CG.

Here are the two ways people often go wrong.

1. A person wants to add floats to a plane so they slap them on with the step under the correct CG for flight. They don't then check to see if the CG is still in the correct place. Often it has moved back, the plane is now tail heavy and either won't get off the water because the step is not under the CG, or it gets off the water and flies terribly because it is tail heavy.

2. The other thing that happens is people attach the floats without concern for the step, but rather in the place that balances the plane on the correct CG. This often puts the step far forward. The plane would fly fine if it could get off the water (the CG is in the correct place for flight), but the step is not in the right place for taking off from water. (In fact, these planes will most likely fly fine off of snow because the step doesn't matter on snow. The floats are just acting like big skis.)


Follow the directions in my first post and the CG AND step will both be in the right place.

M3

My Feedback: (25)

"They don't then check to see if the CG is still in the correct place. Often it has moved back, the plane is now tail heavy and either won't get off the water because the step is not under the CG, or it gets off the water and flies terribly because it is tail heavy. "[QUOTE]

OK, so basically once I have a plane flying correctly and then add floats, I need to make sure that the plane balances at the original CG WITH the floats installed, making sure the float step is lined up with the CG.

I thought I read in the GP 40 size float kit instructions that when installing floats, the CG should be moved back 1/2 inch from normal land flying. Does this sound right?

tpstorey

You put it all together in one nice sentence. That's it, exactly.

Moving the CG back will make the plane more responsive/tail heavy. I don't know why they would want you to move the CG back. I've never heard of float instructions saying that. Are you sure they didn't say something like "put the step of the float 1/2 inch behind the CG"? That would make more sense, but I could be wrong.

M3

My Feedback: (25)

I built the floats a while ago and there's always that chance (sometimes a pretty good chance) that I was rushing to finish and get out to the lake to fly and read the instructions wrong. I'll look at them today.

Any comments on floats on a mid-low wing plane like the SIG Somethin' Extra?

JimCasey

My Feedback: (1)

Comments on floats with a low-wing plane:

The arrangement works fine.
Relative advantages: Low-wingers tend to be more stable than high-wing planes when taxiing in windy conditions. There's not as big a problem of the wind getting under the upwind wing and flipping the plane over. The low wing plane cannot tip as far before the wingtip hits the water, which stops it from tipping more. The low-wing plane also generally has less dihedral than a high-winger so less wind gets under the upwind wing for that reason, too. Several guys in my club fly Astro-Hogs on floats, and they're super.

Relative disadvantages:
1.The wing usually has to be installed/removed through a birdcage formed by the float-mounting struts, so it's a little tedious to attach/detach the wing & servo wires.
Japanese pattern floatplanes have the floats mounted to the wings and not the fuselage, so removing the wing is the same as if the plane had wheels.

2.When a low-wing plane DOES blow over, the fuselage gets more water in it. High wingers tend to float on the wing keeping the interior of the fuselage dryer. Low-wingers float on the wing, too, after the fuselage fills up with water.