Thread: Build Log Dornier Do-335
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Old Jun 13, 2011, 10:55 AM
pmullen503 is offline
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United States, WI, Fond du Lac
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Once the shells are made it's time to cover the inside and add internal structure. This is true monocoque construction; the exterior skin bears all the loads on the structure. To make the FFF stiff enough, and strong enough to carry the loads I cover both sides.

Normally, I'd cover the inside with 1/2 oz. glass cloth and epoxy (I did one set like this and send it to Stacker for eval.) but I thought I would try covering the inside with paper and WBPU. The paper covered shells are lighter (60 vs 78g each) than the fiberglass but the fiberglass covered shell is probably much stronger.

The strategy for motor and LG mounts is to spread the loads to as much skin as possible. The skin will have excellent tensile strength but not much compressive strength. The idea is to tie several formers together with bamboo or carbon fiber to spread out the loads. I use plywood for any part that has screws attached. Otherwise, foam with balsa laminated to both sides makes a very strong, yet light former material. In the nose I'll add balsa stiffeners after I cut the hatch. I still haven't figured out where everything will go in front. I like to put a FFF former every 4-5". Normally, I'd glue the sides and formers in one step but because there's so much going on and I wanted to run the wires and work out the pushrod runs, I glued the formers into one half (the longerons are there to keep the formers lined up). I ran the wires, mounted the servos and ran a flex cable for the rudder. Then I glued on the other side. When the glue is dry, I block sanded out the ripples in the FFF.

The weight at this point is 298g and it's stiff as a board. 30% of the total weight is wire, servos and pushrods.
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Last edited by pmullen503; Jun 14, 2011 at 09:11 PM.
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