Gregory's ServerThe Bendix Central Air Data Computer (CADC) is an amazing electromechanical device that computed airspeed, altitude, and other "air data" for fighter planes such as the F-104 and F-111. Digital computers weren't good enough in 1955, so the CADC used gears, cams and synchros.🧵
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By using logarithms, multiplication could be done with addition. Specially-shaped cams converted to logs and back. Other cams implemented functions; 20 adjustment screws warped a metal plate to the exact shape needed. The process starts with pressure measurements. Pressure transducers (black domes) convert pressure to rotation. Inside, bellows rotate a sensor shaft. This drives a servo feedback loop with magnetic amplifiers and a motor rotating the output shaft, outputting the log pressure. The pressure signals go to differentials (circle-X symbols). Then cams (CCD) apply various functions. Finally, synchro transmitters generate 3-phase electrical outputs that drive pilot instruments, weapons systems, and so forth. Temperature is important because it affects air density. A platinum probe measures temperature through varying resistance. Another servo feedback system produces temperature rotations. The CADC is modular: temperature is this wedge-shaped module. Synchros convert a rotation into three electrical signals. Connecting the three wires to another synchro reproduces the rotation at a remote location, e.g. pilot instruments. Numerous synchros provide outputs from the CADC. I wrote a blog post about the Bendix Central Air Data Computer with more details and photos: https://www.righto.com/2023/02/bendix-central-air-data-computer-cadc.html  @kenshirriff The use of the pressure and temperature servo loops to magnify weak physical phenomenon into something strong enough to turn downstream components is quite interesting.   Riley S. Faelan, thankfully, back then, people had the notion of a product being complete and not needing any further work. @grishka @kenshirriff: Which is why the field-retrimmable cam surfaces were laden with field-retrimmable screws instead of being factory-cast out of a thermoplastic such as bakelite, right? @kenshirriff how has reverse-engineering this mechanical device compared to your normal electronics reversing process? Fascinating thread. @bitsplusatoms It's really tricky to see which gears are connected, especially when they are way in the middle of the device!   |
This analog computer performed complicated calculations using lots of gears. How did this work? Shafts rotated and their angles indicated values. The main component is a differential gear mechanism, performing addition or subtraction.