Variable stability demonstrator which can perform post-stall maneuver using neither gyroscope nor thrust vectoring nozzle, but foldable tailplane. Folding tailplane would move CoL forward and reduce stability, in another words, making this aircraft highly maneuverable. To perform "Cobra", reach 500 mph in level flight, fold tailplane and pull up until AOA exceed 90 degrees, then release pitch control,unfold the tailplane as soon as possible and the aircraft would return to level flight instantly, just like a slingshot. To perform "Kulbit", reach 600 mph in level flight, fold tailplane and pull up until AOA reach 180 degrees, push the stick(nose down) for a short period of time to make AOA slightly exceed 180 degrees(about 20 to 30 degrees), disengage pitch control and unfold tailplane immediately, then the aircraft would get back to level flight itself. Video:https://tieba.baidu.com/p/5555050729 Further details:https://tieba.baidu.com/p/5555050729