I grew up flying planes and have a couple scratch builds under my wing now. But that was over a decade ago as a teenager. Now that I have big boy money I just finished my first 1/4 scale Phoenix Waco with a 7-cylinder radial engine. Yes, 16 year old me would be VERY proud of future me.

So anyways, I have it all set up for the most part, just need to set aileron weights still but otherwise I am mostly ready to go after breaking the engine in over the summer. Question is, exactly what angle determines a balanced center of gravity? Based on the Phoenix "hanging tool" type center of gravity test, it appears to be SLIGHTLY tail heavy based off of the horizontal stabilizer. The manual is pretty vague. It just says "go for it," basically.... Back in the day I would say close enough, looks good. Like it's not far off at all. But I've flown a tail heavy Sbach recently (after thinking it was close enough) and it was not the most enjoyable experience getting it back to earth safely.

So what angle determines center of gravity? Because looking at the wings you wouldn't know it's not perfect. But looking at the horizontal stab it is still a bit off. I think my brain might be playing tricks on me though. The fact I put a 90cc radial engine on a 60cc plane and it's STILL a tad tail heavy is really messing with my head. So what do you use to balance CG? I have my fuel tank directly behind the firewall and I know that will add some weight to it. And given how slowly this engine sips fuel I know I will never be landing on a completely empty tank, so that is something to consider I think too...