I built a twin 26" span Lear Jet last year, at just over 6oz AUW. Actually could have lightened the formers a bit more, but did spice them in sections, to take advantage of continuous grain strength. The method for reducing formers was to use formers made from balsa splints at mid former location, as free flighters do. After gluing in place, the perimeter is carefully sanded to a round shape. Without the r/c gear, this model could have easily been built a bit lighter as a rubber powered model, with a prop on the nose. The main spar is 1/32" sheet shear webbed.
Flight:
https://www.youtube.com/watch?v=sQk1QhpGCsA
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