Yes you can do "flips" or "waterfalls'. I do them regularly. With both a fun fly Pizzaz and a 1.20 size, 10 lb. World Models Ultimate Bipe. You have to have your control throw on the elevator set with at least 45 degrees of throw, or more. It helps a lot if you have flaperons mixed with the elevator to go the opposite direction of the elevator in the manuver, also at very high control throws. I don't use flaperons on the Ultimate, only the Pizzaz.

You must enter the manuver at a very slow speed, nose really high. Picture the entry of the flip as a Harrier manuever. Keep a lot of engine power in reserve. When you are ready to try the "flip", add all your power and full down elevator at the same time. You will most likely need to correct the effect of engine/prop torque with rudder. As your plane comes up the back side of the flip, reduce power to allow you to come over the top nose high and slow, then start over.

DON'T try this at low altitudes until you rae really good at it. You can spin your plane in in a heartbeat!

Silversurfer