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Inside the Apollo "8-Ball" FDAI (Flight Director / Attitude Indicator)

20 hours ago
https://www.righto.com/2025/06/inside-apollo-fdai.html
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  • #Spacecraft
  • #Avionics
  • #Apollo
  • The FDAI (Flight Director / Attitude Indicator) was a crucial instrument in Apollo missions, showing spacecraft orientation via a rotating '8-ball'.
  • The FDAI displayed attitude from multiple sources, including the Inertial Measurement Unit and the Abort Guidance System, with inputs selected by switches.
  • The ball mechanism inside the FDAI rotates along three axes (roll, pitch, yaw) using motors and slip rings to prevent wiring tangles.
  • Synchros and servo loops controlled the FDAI, with feedback mechanisms ensuring accurate positioning of the ball and needles.
  • The FDAI evolved from aircraft indicators to spaceflight, used in Gemini, Apollo, and modified for the Space Shuttle simulator.
  • Bill Lear and Lear Siegler played key roles in developing the FDAI, with innovations from the X-15 to the Space Shuttle.
  • The Apollo FDAI differed from the Shuttle's ADI in electrical inputs, lighting, and feedback mechanisms, with the latter being more advanced.
  • The FDAI's design history reflects incremental changes, repurposing older mechanisms while adapting to new spaceflight requirements.
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