When you get around to learning how to do loops and such with your trainer plane, an out of balance wing can make a big difference. Even when you get out of shape and pull out of a dive and it rolls out when you give up elev. could be an out of balance wing. If a wing is out of balance by 1 oz., then you do a 10G pullout, that 1 oz suddenly becomes 10 oz. Turn the wing upside down and prop it up at the centre . Put enough stick on weights on the bottom tip to balance it. On some planes, for a more permanent setup find some nails about 4 in. long. Drill a hole the size of the nail and glue in enough nails to balance it. I put together a Sig Cap 231EX and one ail weighed twice as much as the other. It was so far out I had to build another aileron to match, although this is an extreme.