Fox, if you're still reading into this thread despite the attempts to hijack it off track then you will find that at around 41 inch span the wing loading to shoot for will be in the 7 to 8 oz/square foot range for spirited performance. It'll fly at up to 10 oz/sq ft but you won't get much fun out of it and the power off glide will suffer.

So with that sort of wing loading in mind you can find out what your target weight should be. Just divide the wing area in sq inches by 144 (that's 144 sq inches/sq foot) to find the number of sq feet of wing area and then multiply that by 8 oz/sq foot to find the target weight you should be building for. From there it's up to you to find out the fixed weight of the equipment and from there what is left for the structure.