Thanks mate for the help.Iam pretty sure the c of g is right but where exactly do you measure it from on a biplane. The prop came prefitted but I checked that and it can only go on one way.On my other model I held the fuse around the c of g to launch it and that seemed to work well.On a low wing aircraft you can't do that and I've been holding the fuse just behind the wing trailing edge.Could this be the problem?