Gyrocompasses have two great advantages over magnetic needle compasses: They point to the spin pole of Earth as opposed to the magnetic pole; and they are completely unaffected by the ferrous metal of a ship's hull or the magnetic fields produced by electrical currents running through nearby wires. Their main component is a motorized, fast-spinning, damped, gimballed wheel. When this wheel is not spinning exactly in the plane containing Earth's spin axis, an interaction between the angular momentum of the wheel and the angular momentum of Earth produces a restoring torque that pushes the wheel back into the true north-south orientation.
A ship's gyrocompass is mounted in a complex set of gimbals that isolate the instrument from the ever- present pitching, yawing, and rolling. Aircraft gyrocompasses are even more complicated due to the higher velocity of the plane and the speedy changes in altitude during takeoff and landing.
German scientist Hermann Anschutz-Kaempfe (1872-1931) started working on the device because he needed a compass to guide a submarine on a planned expedition underneath the north polar ice. In partnership with his cousin, Max Schuler, Anschutz- Kaempfe sold a prototype to the German Navy in 1908. Schuler found that if the pendulous suspension of the gyroscope had a period of eighty-four minutes (the period of a pendulum of length equal to Earth's radius), disturbances due to the ship's acceleration were canceled out. Elmer Sperry, the American inventor, also produced gyrocompasses, and patent disputes ensued.
