bj, the AOA sensors need to be in the free airstream as they need to give an indication of the angle of the wings of the aircraft to the airflow at any given time in flight. Hence they are normally located near the nose of the aircraft. If they (AOA sensors) were inside the aircraft they would only indicate the angle of the wings relative to the earths surface and not give any indication relative to airflow.
It's the same as the pitot tubes (airspeed sensors) and static ports (for altitude). They need to be in the free airstream to give accurate indications. Thus they are on the outside of the aircraft, usually near the nose area, where the airflow is generally undisturbed.
