[HN Gopher] Inside the Apollo "8-Ball" FDAI (Flight Director / A...
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Inside the Apollo "8-Ball" FDAI (Flight Director / Attitude
Indicator)
Author : zdw
Score : 107 points
Date : 2025-06-14 15:43 UTC (7 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| kens wrote:
| Author here for your Apollo questions :-)
| johng wrote:
| I mainly remember this because he refers to it as the 'frappin
| 8 ball' in the Apollo 13 movie, if my memory serves.
| mcpeepants wrote:
| same here, he sure does
| kens wrote:
| Yes, in the movie, Lovell says "What's the frappin'
| attitude?" as the 8-ball rolls out of control. The actual
| Apollo 13 transcript has nothing like that, interestingly
| enough.
|
| Links: https://archive.org/details/apollo1319959231994/page/n
| 92/mod... https://www.nasa.gov/wp-
| content/uploads/static/history/alsj/...
| rbanffy wrote:
| I remember a similar thing from the, IIRC, F-104.
| _dwt wrote:
| Great article. I'd never thought about a spacecraft ADI having
| a third axis. Sadly, a nitpick - Bill Lear's F-5 autopilot was
| not, as far as I can tell, in any way connected to the Northrop
| F-5 fighter jet.
| kens wrote:
| Thanks. You are correct about the F-5 autopilot, so I fixed
| that. It turns out that it was used in planes such as the
| C-47, C-60, C-45, and B-26, but is unrelated to the F-5.
| garaetjjte wrote:
| >The Command Module for Apollo used a completely different FDAI
| (flight director-attitude indicator) that was built by
| Honeywell.
|
| That's surprising. Was there any requirement that necessitated
| them to be different parts, or it's just because different
| suppliers were chosen by Grumman/North American?
| jschveibinz wrote:
| Back in the day, this would be have been a good homework
| assignment for an EE analog controls class.
| chiph wrote:
| kens - Are the collectors of the output transistors on the
| amplifier boards connected to the metal can? I can see from the
| photo that the heatsinks don't touch (there's a gap between them
| for the capacitors). Did they use nylon screws to prevent an
| electrical path through the frame?
| kens wrote:
| Unfortunately, I don't have the FDAI handy to check this.
| CamperBob2 wrote:
| For TO-5 bipolars, it was common for the collector to be
| connected to the case. I wouldn't say that's universally true
| but I don't recall any exceptions off the top of my head.
| WillAdams wrote:
| This was actually mentioned in a recent talk by Freya Holmer ---
| I believe this one:
|
| https://www.youtube.com/watch?v=hUlvxaQBW78
| wafflemaker wrote:
| That's a 'kunst' of UI (a gem?). One look and you instantly know
| the orientation of your craft.
|
| As an amateur astro-pilot (1000h in KSP and 200+ in Flight of
| Nova, both flight simulators with realistic orbital mechanics)
| I'd like to say that in modern cockpit of the fusion propelled
| ships in FoA, the one thing I'm missing from Apollo-style flight
| instruments of KSP is the Nav-Ball.
|
| The jet-fighter-like "ladder" style attitude meter can't be read
| with just one look. You need to focus to see the numbers next to
| the ladder steps. And then another look at the compass for a full
| reading. 3s of focus (away from controlling the ship) vs. 0.5
| (that your subconscious has most likely already interialized).
|
| To put that 3s into perspective, according to ship readings,
| Apollo 11 had <20s fuel left when it touched down on the moon.
| johnsutor wrote:
| Brings me back to playing Kerbal Space Program
| timewizard wrote:
| I wonder if that simulator was OV-095 at SAIL.
|
| https://spaceflightblunders.wordpress.com/2017/03/31/ov-095-...
|
| EDIT: Ah. It almost certainly was:
|
| https://www.superstock.com/asset/oct-astronauts-frederick-ri...
| kens wrote:
| There are many different Shuttle simulators. The simulator
| photo in my post is one of the Shuttle Mission Simulators
| (SMS), now at Stafford Museum in Oklahoma. The Shuttle Avionics
| Integration Laboratory (SAIL) is a different simulator for
| avionics testing (rather than astronaut training) and is
| currently in Houston.
| jart wrote:
| Ken once again proves he's one of the greatest publishers on
| Hacker News.
| dmd wrote:
| The strong impression I always get from the entire Apollo program
| is "they didn't know it couldn't be done at the level of
| technology available, so they did it anyway".
| jsrcout wrote:
| > 3. The FDAI's signals are more complicated than I described
| above. Among > other things, the IMU's gimbal angles use a
| different coordinate system from > the FDAI, so an
| electromechanical unit called GASTA (Gimbal Angle Sequence
| > Transformation Assembly) used resolvers and motors to convert
| the > coordinates.
|
| I'm so glad I work in software.
| userbinator wrote:
| 1960s technology, designed and made in the USA. It seems that
| people back then were far more clever at making do with what they
| had.
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