g4368744

My control surfaces (elevators) become unresponsive soon after passing mach 1, and again at around mach 1.4 or later. In both cases, control is restored spontaneously as I pass some critical velocity. What causes this? Seems to happen when the airflow over the elevators (and flaps) becomes supersonic, but it works afterwards. If I change the wing sweep will I be able to change this speed? Also, for the last part of atmospheric climb out the airplane gets less stable on the roll axis, and needs constant corrections to stay level. I read that SR-71 pilots experienced the same thing. What causes this?