Not true. A well done paint job (on a sport model) - especially using dope can be as light or lighter than Monokote. Generally the reason people think paint is heavy is because they start out with sub-standard wood work and then cake on primer and paint trying to conceal things that could have been resolved by sanding.

But I agree that for most people paint is heavier because of what I just said. My point is that it's not a universal truth - just happens more often than not.

When you get to scale, on the other hand, there are a lot of things contributing to the weight other than paint. On scale models, flying qualities are considered secondary.

PS. I agree that painting a trainer probably isn't the best thing to do. Just makes you cry more when you crash it. I silked and doped my trainer and crashed it on top of a school. It exploded.