7 x 7
Who cares about overstressing the aircraft when you are in a life or death situation with a suicidal hijacker?
You don't necessarily have to do "aerobatics" but know how to do the zero g bit.
Perhaps it would be worth fitting accelerometers ('g' meters) is airline aircraft.
I just cannot see how sealing the flight deck off from the cabin is ever really going to work....but perhaps one day!