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Old 12-11-2007, 03:06 AM
Look out for that tree!!!
Larry3215's Avatar
Join Date: Mar 2006
Location: Gig Harbor, Wa USA
Posts: 7,061

I dont think there is any real need for the sponsons to stick out that far. Its an esthetic thing more than anything else.

As far as going to 1/2" blue foam for the center panels. Im not sure.

Ive havent worked much with the blue foam. I know its pretty stiff but I dont know how well it would hold up to the bending stresses the the center joint would have to take if you eliminated the under brace.

As the design stands now, a really hard landing will crack the 6mm foam on either side of that joint where the center brace glues on. Even running on rough ground in cold weather can crack the joint.

If you didnt have the center under brace the forces acting on the cneter joint at the top of the V would be several time stronger because of the leverage effect.

Keep in mind, that center section has to resist the bending forces created by the weight of the entire plane when ever you hit the ground. The center under brace reduces the leverage on the joints and spreads the bending forces over 2 joints instead of a single center joint. The under brace also changes the forces acting on the center joint to compression forces instead of tension forces.

On the other hand - it would be simple enough to do test glue up of some 1/2" blue foam if you have any and see how it hold up.

The 1/2" blue foam would certainly be stiffer in twisting.

I would be tempted to keep the same construction techniques that Im using now, but make a 200% - 300% sized version out of the 1/2 blue foam. Say 4 or 5 feet long by 3 or 4 feet wide

That would be cool

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