I am designing and building my first floatplane. Can someone tell me are the wing stresses upon landing greater or the same as with a grass field? and for large scale 1/5 what design consinderations are needed to handle the extra weight of pontoons? ie. Rib spacing, thickness and material. Any info will help. Thanks all.

khart2000

Wing stresses are probably a lot LESS than landing on grass because water is not as lumpy. When I land on grass, my plane bounces all over the place on rollout when it hits clumps of grass, footprints (we have cattle that time-share the runway) and general bumps in the ground. A proper water landing is a gentle joy to behold, and probably less shocking than a pavement landing. If you crash hard enough into anything, you will break your plane, but at typical landing/takeoff speeds, water is more forgiving than pavement or Mother Earth.

If anybody has EVER adjusted wing structure to compensate for weight of floats I would be shocked. Proper floats weigh very little and contribute some lift at appreciable angles of attack. Adjusting the wing structure to compensate for floats would be like having releasable wingtip sections to compensate for the loss in weight as fuel is burned off.

When flying trainers on floats it is common to add a few elastics because of the extra weight.
Last year at a float fly a guy normally flew a cub on land without struts, but when he did on floats the wings folded.
There is some additional force because of the extra weight but I haven't heard of beefing up the spars or anything to handle that.
Today with gusty winds, I heard some loud smacks as the planes hit the water suddenly. I would guess that sound would have been louder on land and there would have been more damage.