SmithCreek, unfortunately I have no way of knowing how much weight I saved, but I can tell you I did drill holes pretty much everywhere structural integrity wouldn't be compromised. An example are the wing spars, which IMO are way over-designed on this plane. I therefore drilled 5/32" holes vertically thru the spars every 1/2" or so for the last (outer) 3 rib bays.

Other than the holes, I try to go easy on the epoxy, using it only where absolutely necessary, like landing gear block mounts, firewall, wing joining, stab&fin mounting. Everything else was glued with either thin or medium CA.

Graybeard, I now have about 10 flights on the CG Extra and have experimented a little with props and C of G. I have settled on a C of G at the back of the recommended range, which allows me to fly inverted with only a little fwd pressure on the stick. The OS 110 seems to like the APC 15X6 best for this plane. Vertical penetration is pretty decent, but not unlimited. Still, it allows for all "classic" maneuvers this plane was designed for. Landing approaches are a joy, the plane coming in on a nice flat approach with no tip stalling tendencies. Compared to other aerobats I've flown over the years (the Caps and Gilles, most notoriously....) this Extra is a pu$$ycat.

A little on the engine. I think OS really got the design right on this one. Those hoping for 120 class power will be a little disappointed, because truthfully, the engine is not a powerhouse. What it IS, is a very easy-handling and clean running lightweight engine. It weighs virtually the same as the old OS 91 4-stroker, but produces more power. The lack of a crankcase breather (the oil is recirculated internally) helps keep the plane much cleaner than other 4-stroke engines. I ran one tank on the ground, then just flew a few flights 500 rpm on the rich side. The engine never stumbled and the only adjustment required was to close the low speed needle about 1/4 turn. Idle can be set very low and transition is excellent. Nitro is very expensive in Europe, but the OS runs just fine on the 5% nitro, 18% oil fuel I feed all my other engines.