Thank you all for your help. I think you are right Tom that it is the CG problem. Not that something is shifting during flight, but that I balance my planes on my fingers rather then putting them on the jig. That way I can't see the side of the plane and it could be balanced with tail slightly down. I also use the mid setting for my CG, if I the plan say 90-100mm I go for the mid point which is 95mm. So I build the balancing jig and will go and rebalance my entire fleet. That's the only thing I can find at the moment, so thank you all again.