What do we mean by "Roll Stability". I hold that there is no such thing-in the sense that there is static and dynamic pitch stability. Resistance to roll is a function of roll damping (-1/Lp). But any stability (in that I mean a tendency to revert to the original state once disturbed) is provided by the roll mode. Who would want an aircraft that when rolled -and the the control centred- then the bank reverted to zero?. Seems like a Helo autostab-but thats different. Many aircraft have a neutral or divergent roll mode- but are not considered "unstable". I've flown quite a few of them-F4, F3, Hunter, -how about the change in sign of the Lv function in the Hawk with alpha?! Do we consider the Hawk to be unstable?