Hi Dave
Go along with you - the cheapest performance upgrade is a lighter model!
However, you can go too far. On a structure like you describe, I'd use 1/8" square spruce for the fuselage longerons and wing main spars, with 1/8" square balsa for the fuselage uprights, diagonals and cross-members. The spruce I use is all bought at either hobby stores, craft stores or mail order - I don't have the equipment or skill to make up my own.
Reckon you can go too far with lightness, as above. Wind is a fact of life and if your model is more tossed around by it than flying through it, you're probably not having a lot of fun. I tend to go out less in wind as years pass, but I've moved to Chicago and have learned that it's not called the 'Windy City' just because of its blow-hard politicians. My latest 9.5oz 36" span model is not going to get out flying all that much, I fear...
The photographs are of my 51" 'Great Big Sportster' that I designed by scaling up a 25.5" span rubber powered design by Chuck Wenlock and putting a minimally altered rubber model style framework in the outlines.
The model weighed 25oz with rudder/ele/motor control, a small outrunner and a 3S LiPo around 1200Ma. The majority of the framework is 1/8" square spruce and balsa, as above, some minimal 1/8" balsa sheet in the fuselage nose, 1/16" ribs, a minimum of ply - firewall, UC and wing mount with the thickest thing on the model being the 3/16" strip wing LE. The wing TE looks hefty, but I used two pieces of 1/16" balsa sheet in a 'V' arrangement, so it looks like the carved from solid sheet TE the 'full sized' version had, but was far lighter.
It was a handy enough model for any wind I'd be flying it in, but was a solid and resilient structure that was no bother in use.
Hope that helps
Dereck
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