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Flight Director/Atitude Indicator (FDAI)
Home of the 8-Ball

Copyright © 2002 by W. David Woods and Frank O'Brien. All rights reserved.
Last Revised 29 July 2010

CSM FD/AI

Command Module Flight Director/Attitude Indicator



LM-8 (Antares) FDAI

Apollo 14 Antares (LM-8) LMP's FDAI prior to installation in the spacecraft.  The Commander
had an indentical instrumenton his side of the main panel. Grumman image scanned by Paul Fjeld,
courtesy Karl Dodenhoff's  My Little Space Museum. Used with permission.
(Click  on the image for a full view of the LMP's panel.)




The following is an extract for the Apollo 8 Flight Journal, Day 1. Used with permission.

The FD/AI (Flight Director/Attitude Indicator) or "8-ball" is one of the most important instruments in the spacecraft. Designers had originally intended to give the crew three separate displays to show their attitude; one each for roll, pitch and yaw. Being pilots, the crews quickly threw out the three displays for a development of the artificial horizon familiar from aircraft instrument panels.

In an aircraft, the Earth's horizon provides an obvious reference against which the artificial horizon displays attitude. In a spacecraft, such an obvious reference may not exist so the inertial platform at the centre of the IMU (Inertial Measurement Unit) provides one - a reference that is constant relative to the stars, known as an 'inertial' reference. The basic function of the FDAI is to display the spacecraft's attitude with respect to the orientation of this platform. Pitch and yaw can be read off the ball directly; roll is shown by a pointer around the edge of the 8-ball. Three meters around the display show the rate of rotation around the three axes. Three additional orange needles in front of the ball graphically display the difference between the current and desired attitude of the spacecraft.

On a linguistic note, the name 8-ball refers to the black-colored, Number 8 ball in the game of Pool and, more specifically,  the variant called Eight Ball in which it plays a central role.

Eight Ball Rack


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