The Bendix MG-1 Central Air Data Computer (see Parts 1, 2, and 3 for details) needed to convert the air temperature measured at the static air data probe to a rotation in order to use it as an input to the gears and cams of the mechanical computer that calculated altitude, air speed, Mach number, and other flight data for the supersonic fighter aircraft in which it was installed. How do you do that? Bendix engineers devised a clever servomechanism which used feedback to adjust a potentiometer to match the resistance of a temperature-variable resistor, then input its angular position to the gear train. The servomechanism was built with magnetic amplifier, a component, now largely forgotten, which allowed controlling a (potentially large) AC current with a small DC analogue signal.
In the process, the restoration team discovers that a thermal imaging camera accessory for smartphones can be a surprisingly useful addition to a reverse engineer’s armamentarium.