The spread tow sheet looks like an awesome option. I'm not 100% sure its necessary. I was also considering another variant using EPP covered with flexible fiberglass (speedglass ???) with a semi flexible resin (types used in archery equipment). To allow to a very slippery strong and resilient wing. It would be interesting to get your thoughts on this. Carbon spar and reinforcing strips could be used to stiffen the central section of the wing and pick up the forces acting in tension and compression travelling through the wing in higher g situations. But allowing for the edges of the wing to have higher impact durability for landings, and other situations. Because now with just strengthening components of the whole wing you are just moving around the weak point in attempt to control it, vs allowing the wing to absorb and dissapate some of the forces acting on it.
Flex is the enemy of good DLG's. Any flexure whatsoever costs launch height and invites flutter. 1.7 oz Kevlar is cheap enough ($30/sq yd, 1 yd will cover an entire DLG) and provides pretty good impact resistance. Bear in mind that the leading edge needs glass atop the Kevlar (never, ever, ever sand Kevlar unless you like being angry at yourself) so you can sand to a good finish there. There are some threads on rcgroups which address various strategies for doing leading edges. 0.060" cf rods make good wing spars (2 pairs out to half span, one pair extending to the tips) on Kevlar covered wings. If you're concerned about the expense of epoxy, try ACP's Ez Lam. If you want an outer layer, use 1.5 oz glass or lighter. It's pretty cheap stuff.
The whipit is the "PZ Champ" of the DLG world -- enough to see what a DLG is like, and fun to play with regardless, but if you want to fly the big ships with high hand launches and really low sink rates, it doesn't take much time to learn what you need from the whipit . . . and that's where things get complicated and/or expensive . . .
I see it more as the Gentle Lady of the DLG world--very good performing aircraft in the hands of an experienced pilot, lets you fly literally anywhere, super portable, inexpensive, thermals off of literally anything, and has decent wind penetration. What it lacks is launch performance. That problem, however, may soon be solved by the after market world. I hear a CW20 covered molded wing (and tails) may soon be available for the Whipit for less than $100:
http://www.rcgroups.com/forums/showthread.php?t=2581273&page=17
