ORIGINAL: pimmnz
Mark,
Seems to me you are going around this from the wrong end... The UPF on p8 is 25%, 90" and weighs just under 16lb. Uses a fully articulated, sprung u/c etc, etc... and flies with good aerobatics on a ST G2300 and Bolly 19x8. At 20% you should be aiming for a flying weight of around 10-12lb. With a similar size/power model engine it would almost do unlimited vertical. Re-visit the drawings you have, find some fullsize structural drawings and the start removing that which is un-necessary. If it ain't there it won't weigh anything, and can't break. Those full size designers have done all the hard work for you and just copying them really does work. The UPF space frame is 1/4 sq balsa, and the model has been flying for six years now. Durability is not a problem.
Evan.
I don't have any drawings (yet), I am going from the weight mentioned by Stickbuilder. I am not too concerned with aerobatics, this will be a scale project to use for relaxed flying and some scale aerobatics such as big loops, rolls, a spin or two, etc. The wilder stuff can be done with other planes... I have always been a light builder, so it won't be a tank, but I am more concerned with the look and easy flying for this one.
Mark