A guide to flying with floats

Model Airplane News, Sep 2000 by Onorato, Jim

I have found that the easiest way to make float attachments is to use a flat board to represent the top of the floats and then to block up the fuselage in the appropriate position above the board. I then draw two parallel lines on the board making the distance between them equal to the spread between the float centerlines, and then I draw a centerline between them. Next, I draw two lines across and perpendicular to the first lines with the distance between them being equal to the distance between points C and D. The points of which these lines intersect the first two parallel lines are the locations of the four mounting points on the struts. Attach the strut-mounting blocks to these points with the crossbars installed in the mounting blocks. Now, on the float, I carefully measure the distance from the step to the attachment point for the front strut, and I use this measurement to position and draw another perpendicular line on the board-the "step" line. Last, I draw one more line 1/2 inch in front of the step line and mark it "CG." Now I block up the fuselage over the centerline at the height needed to keep the propeller 2 inches above the board. The plane's CG should be directly above the "CG" line, and the plane's datum line should be at 1 1/2 degrees positive angle relative to the top surface of the board. I generally make saddles out of 2-inch-thick Styrofoam to support the fuselage in the proper position. These are free-standing and can easily be cut to shape.

Once all this has been done, determine the height of the forward strut by measuring the perpendicular distance from point A on the fuselage to the forward crossbar. (This is not the distance between A and C.)

I then draw the front strut to use as a pattern to make the front music-- wire strut. The strut should be bound to the crossbar with copper wire and silver-soldered. Next, attach the strut to the fuselage and the building board and reblock the fuselage over the board. If the strut didn't come out exactly according to the pattern, just reposition the fuselage to get things lined up properly, and remeasure to obtain the correct height of the rear strut. After making the rear strut, attach it to the fuselage and board, and make sure everything is positioned properly. If necessary, use shims to make minor adjustments.

Finally, measure the length of the diagonal braces, bend them and silver-solder them between the top of the forward strut and the bottom of the rear strut. By now, it should be obvious that this process would be much easier if the positions of the strutmounting points on the float were adjustable.

The thickness of the wire used for the struts depends on the size of the airplane. The smallest plane I have on floats is that .40size Sig Cub; that one has 1/8-inch wire for all of the support structure. The largest is a 1/4-scale Cub (I told you I like Cubs), and that one has 3/16-inch crossbars and 5/32-inch struts and diagonal bracing. It also has 1/4x1-inch plywood crossbars under the wire ones for additional rigidity.