Just an insight but to do better waterfalls this is what i suggest. set-up ur engine so that response is tight and you have instantaneous response. Try low pitch large diameter props!!! its easier to balance a plane hanging on the prop with it!! With the plane flying level pull up to hang the plane on the prop. You can if you wish start your waterfall at this point but I however achieved impressive results by allowing the plane to tail slide a little and "FLOP" (forward for down flip or Up for up flip) as the nose passes 45deg. on that flop quickly add elevator and power!!!!! This method makes it flip faster and eliminates the need for corrections!!!! However ive only tried it on smaller 3d capable planes 30-60 size but i see no reason that it wont work on you large scale aircraft.