I thought quadrocopters were so unstable that flying one without a PD controller, or better a full PID, would lead to a crash within seconds. A Helicopter, poss

I thought quadrocopters were so unstable that flying one without a PD controller, or better a full PID, would lead to a crash within seconds. A Helicopter, possibly only of the counterrotating coaxial variant, should not be affected by this instability, I think.