ORIGINAL: dick Hanson
flaps don't push -or pull - they are just reshaping the wing - changing it's angle of attack
Bingo... for the most part. But altering the camber can change the pitching moment. On some models with barely adequite tail volume this can result in odd elevator needs to balance the new angle of incidence and pitching moments.
Anyway, full span flaperons is a bad idea. Do a search for many past threads about this and the adverse yaw that occurs.