Gregory's ServerFighter planes of the 1950s used the Bendix Central Air Data Computer, an electromechanical analog computer that computed with gears. In this thread, I look inside its pressure transducers that converted pressure readings to shaft rotations that turned the gears. 1/13
Ken Shirriff
8 comments
Ken Shirriff
Inside the CADC, two sealed black domes hold the pressure sensors. Each sensor has a stack of associated electronics boards. The boards are amplifiers that drive the motors that turn the gears. 3/13
Ken Shirriff
As the pressure changed, metal bellows inside the dome expanded, rotating a shaft. But these rotations were too weak to turn all the gears of the CADC, so a motorized servo loop amplified the rotations. 4/13
Ken Shirriff
This diagram shows the servo loop. A sensitive inductive pickup detected the rotation and generated an error signal that went to an amplifier. The motor rotated to counteract the bellows motion. When the error signal was 0, the output shaft rotation matched the pressure. 5/13
Ken Shirriff
The amplifier took three boards: transistors in conjunction with magnetic amplifiers (yellow units). Transistors weren't good enough at the time to drive the motors directly, so transistors controlled the magnetic amplifiers, which drove the motors. 6/13
Paul Evans
@kenshirriff I don't think I've ever seen (or otherwise would ever see) such a label as "CAUTION: DO NOT BLOW IN TUBES" on any piece of equipment. I wonder what the danger is - are the pressure sensors really that sensitive to damage? 
Roy Ridin' With Biden #BLM 🇺🇸
@kenshirriff so it's just a blowtorch with a slide rule spackled on to it? |
An aircraft has a pressure port to measure the static air pressure and a pitot tube to measure the total pressure due to speed. These were connected by tubes to the front of the CADC. 2/13