I believe the waterfall is similar to the tumble called the "Endo" in the full size world. The airplane ends up translating sideways while flipping over foreward several times. To do it in a full size Extra 300 you pull the nose up 45-60 degrees, roll left 90 degrees (climbing knife edge with the left wing down), push in left rudder smoothly while feeding in a touch of left aileron and smoothly feed in full foreward stick. The yaw rate from the left rudder creates a gyroscopic reaction that "Helps" you push the nose foreward.... once it starts to go it locks in until it runs out of energy... usually 2 to 3 flips. The biggest mistake is jamming the controls in, anytime you are trying to "Harness" gyroscopic forces you need to be smooth and slow on your control inputs. When I first learned to tumble a full size Extra I tried to "jam in" the foreward stick and rudder... all I got in return was a very violent outside snap and about -6 on the G-meter. The other way to enter, which is much more pleasing to watch, is to pull to a 45-60 degree upline and start rolling to the left... after a couple rotations start feeding in left rudder and foreward stick slowly and begin to take out the left aileron... if it catches you'll get a fast roll that turns into a shoulder roll and then finally lets go and tumbles end over end.

My RC chipmunk does a pretty good tumble if I pull up and put the sticks into the top left corners... but with a small engine and wood prop it doesn't create enough gyroscopics to get a true tumble like full size planes can.

Ty