I've built the old Goldberg kit, best flying plane I've ever owned.

However, the U/C is too weak and bends on even the gentlest landing. After trying expensive spring steel 5mm wire, (which broke), I'm now fabricating a carbon fibre/kevlar U/C. The attachment area for the U/C can also do with some re-inforcing. (Don't ya hate the use of lite-ply for undercarriage doublers!!)

Mine flies great on an OS91Fx. Other planes with bigger engines seem to fly worse with the weight. Mine is very light, and the OS is a light engine. It will knife edge loop all day.

Steve