Weight & Balance with floats?

Okay, this is probably a dumb question, but it is new to me. I'm just finishing up my Javron Cub - started the engine this week. We should be good for a first flight in 7-10 days.

I built up up a set of Clamar amphibious floats that I plan to install as soon as we've flown off the test time on wheels. While I have a good sense of the W&B on wheels, I don't even know how to think about it on floats. Do we re-weigh the plane? Do planes typically get a gross weight bump up for float operations? Where would I find data to create the new templates?

I'm sure this is extremely well-trodden ground, but I'd love the forum experts to help with some guidance. Thanks very much!

When we installed the Clamars on my 2+2 we put it on the scales. Hopefully your Gross is set high enough so you can still carry full fuel and a good size load given the floats will add 300-400 lbs. Attempted to attach a W&B spreadsheet but the .xlsx appears to be an "invalid file".

What part of W&B do you not understand? Empty, loaded, flying characteristics??? The calculations are no different. It will be a good idea to weight it after the float installation is complete unless you can get accurate weight and arm information for every little part which you install. Most of us, except for Bill Rusk aren't that capable. Even he weighs it when done. You will find that the empty CG will move forward, particularly since you are using amphibs. A gross weight bump up is dependent on a number of different things depending on the particular airplane. In your case just pick a number and flight test to it just as you are doing on wheels. Any related items which need to be installed in the fuselage should be placed as far aft as is practical for CG purposes. Do not be reluctant to install ballast if needed for best flight performance. I know ballast is a dirty word for those who are weight nuts, and most of us are, however when properly located it makes a tremendous improvement in handling.

Do you have stock Piper shaped/sized wings or extended wings? If you have extended you will likely find that the addition of a ventral fin will give you better stability.

Never seen a floatplane weighed or looked at a W&B worksheet for one. Where's the best place to put the scales-- at the spreader bars?

hotrod180 said:

Never seen a floatplane weighed or looked at a W&B worksheet for one. Where's the best place to put the scales-- at the spreader bars?

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Generally for an amphib just use the wheels as you would on a wheel plane. On straight floats use any points which are convenient for the type of scales which you have. Just make sure that you have measured the correct distance from the datum. I used a tension scale hanging from a hoist to the lifting rings on the front spar and a sensitive bathroom scale under the tail post.