In 1933, Wiley Post became the first person to fly solo around the world. It might not have been possible without this Sperry Gyroscope autopilot, which allowed him to simultaneously fly and navigate.”Mechanical Mike,” as the Sperry autopilot was called,  incorporated two gyroscopes and operated upon compressed air and hydraulic pressure. It was a “three-axis” autopilot, that is, one gyroscope sensed pitch  changes and roll (bank) changes by the aircraft, and the other gyroscope sensed heading  changes (yaw). The air compressor and the hydraulic pump were engine powered. The gyro scopes were driven by compressed air. Compressed air was also used to correct changes of  aircraft attitudes in relation to pitch, bank, or yaw, through a system of small air ducts and  semilunar plates. Attitude changes of the aircraft, produced pressure differentials in airflow in the ducts ending near the discs. The result was a proportional change in air valves that was transmitted to the appropriate hydraulic system which, in turn, moved the proper-control surface (elevator for pitch, aileron for bank, and rudder for yaw). The autopilot, which Post called “Mechanical Mike,” required no electrical power and functioned very well.
Credit: Photo by Eric Long, National Air and Space Museum, Smithsonian Institution (NASM 2012-01350)

1933 – “Mechanical Mike” Sperry Autopilot