Reverse-engineering the mechanical Bendix Central Air Data Computer #Aviation #History @kenshirriff

Ken Shirriff takes a look at an analog computer used in US fighter planes in the 1950s:

How did fighter planes in the 1950s perform calculations before compact digital computers were available? The Bendix Central Air Data Computer (CADC) is an electromechanical analog computer that used gears and cams for its mathematics. It was used in military planes such as the F-101 and the F-111 fighters, and the B-58 bomber to compute airspeed, Mach number, and other “air data”.

As you approach the speed of sound, the fluid dynamics of air changes and the calculations become very complicated. With the development of supersonic fighter planes in the 1950s, simple mechanical instruments were no longer sufficient. Instead, an analog computer calculated the “air data” (airspeed, air density, Mach number, and so forth) from the pressure measurements.

Each value in the CADC is indicated by the rotational position of a shaft. Compact electric motors rotated the shafts, controlled by magnetic amplifier servos. Gears, cams, and differentials performed computations, with the results indicated by more rotations. Devices called synchros converted the rotations to electrical outputs that controlled other aircraft systems. The CADC is said to contain 46 synchros, 511 gears, 820 ball bearings, and a total of 2,781 major parts (but I haven’t counted). These components are crammed into a compact cylinder: 15 inches long and weighing 28.7 pounds.

See Ken’s detailed reverse engineering of this device in his blog post here.


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