RE: Lightening the GP Skybolt
*Cough*
Funny you should ask, I recent'y gave my old Skybolt away in that "Pay it forward" thread, and I was thinking "If I ever got another one, what would I change?"
First, this thing does NOT build tail heavy - It builds heavy - period.
I think the people with the tailweight problem are probably putting those silly little 2-strokes in a plane that should obviously have a 4-stroke in it.
So, what would I do?
First, I think I'd open up the ribs. There's a lot of balsa there that is only there so GP could sell that Wing Jig of theirs.
Next, I would cut some holes in the side like you suggested, but not two big rectangles, rather, cut some triangular holes which will keep a lot of strength. Like I did with the UltraSport I'm currently lightening - see pic)
Another biggie I would do is to use thicker stock on the tail feathers and skip the sheeting.
I think those mods would help bring the weight down without compromising the structure.
One more thing: replace any sheeting that seems particularly heavy.