That branch of engineering concerned primarily with the special problems of flight and other modes of transportation involving a heavy reliance on aerodynamics or fluid mechanics. The main emphasis is on airplane and missile flight, but aeronautical engineers work in many related fields such as hydrofoils, which have many problems in common with aircraft wings, and with such devices as air-cushion vehicles, which make use of airflow around the base to lift the vehicle a few feet off the ground, whereupon it is propelled forward by use of propellers or gas turbines.