Was digging through some old pix and came across these. This was an attempt to buid a foam wing with substantially less foam than in a normal cored wing. I'm showing it here just to show even crazy ideas have a place.
The first attempt was to build a wing with normal ribs only made of foam. My friend Mark Bambrick framed one up with 1/2" foam ribs, a foam LE and TE and foam flpas. Got it all cut and it was not too bad. It was certainly light, but even the 1/2" ribs got pretty snaky to work with. Of course, after it was sheeted it was fine.
Shown here is the third attempt, attempt #2 was actually used in the Eclipse Mk 2 that I campaigned from 1981-1983. The approach used here was to build an eggcrate of 1/4" foam ribs, then add foam then wood LE and TE plus foam flaps. Egg crate spacing was about 2.5" so even at 1/4" thick the foam did not snake around too much. This is not a true geodesic wing but by angling the crate diagonally I got good support for the sheeting and some nice structural stiffness.
Pix 1 shows assmbly of the basic eggcrate. These pieces slipped together and glued with a drop of titebond just at the intersection.
Pix 2 shows the foam LE, TE & flaps installed, then the whole thing was cut like a normal foam wing. Then the rib joints were all re-glued at all the intersections using a thin nosed glue gun and Titebond. The wing core is interstion at this pint. It weighs scarcely 1 oz ut cannot support its own weight in bending. However it is EXTREMELY stiff in torsion due to the diagonal rib orientation.
Pix 3 shows the core to which have been added wood edges and the landing gear platform. I really liked installing these triangluar LG platforms as they were well braced to the sheeting and LE. The core is shown resting on the Eclipse 2 which had the same style wing structure.
Pix 4 shows the all-up weight for the wing ready for sheeting with all its wood edges, LG platform & wire installed at just under 3 oz. Of this the foam was barely 1 oz, and the rest of the weight was wood and wire.
Unfortunately the wing in the pix met its demise at the next step - sheeting. On Eclipse 2 I used epoxy on the ribs to attach the sheeting. It was durable, strong and stable, but I thought I could do lighter!
For the wing in the pix I prepared the sheeting in the regular way, but then I covered one side of the sheeting with "OO" silkspan attached with thin cA. After sanding out the covered side, I flipped that over and sanded the inner balsa surface away so the skin with covering was .060. It was thus thin with a hard shell finish readdy for a sealing coat and filler. Then the mistake: I tried saving some weight using titebond to attach the sheeting to the ribs. Unfortunately the the silkspan & CA covering had formed a vapor barrier and there was no where for the water from the titebond to cure out. As a result the sheeting buckled badly...
If I was ever to try this again I think I would forego the sheeting. I would add a spar top/bottom and capstrip the rib strips using foam safe CA. Would make for an interesting look and should still be light and strong...