I have a tower uproar with a very light wing loading (14oz/sq ft.). It will tumble, but it is difficult to do and requires that you enter from a hard positive snap. The inputs are as follows.

1. Hard up elevator at high speed (level or slight climb) 2. simultaneous left rudder, left aileron and full throttle 3. down elevator. Hold left ail/rudder, full throttle, and down elevator and the plane will do 2-3 flips before it loses energy and falls out of the maneuver.

The three steps should be done in a quick 1-2-3 count that takes a little less than a second. The idea is to hit the down elevator roughly when the plane passes through knife-edge attitude. The maneuver has to be done fairly violently or you will just end up with a lazy corkscrew. Heavier planes with big control surfaces can probably omit the snap entry and tumble straight from a climbing knife-edge attitude.