Gregory's ServerWith all these rotating assemblies in the attitude indicator, the wires would get tangled up. To avoid this, the indicator uses two sets of slip rings: one on the roll axis and one on the pitch axis. 4/N
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23 comments
 The three amplifiers are in a unit that attaches to the back of the attitude indicator box. Inside are three amplifier boards, a small power supply board, and an AC transformer. Here's a closeup of one of the amplifier boards. It's a bit of a mess with components stacked on other components to save room. The spider-like component in the middle is a pulse transformer. It drives the transistors on the right, one for each motor direction.  And an admirable sparsity of 10-turn pots! Says person formerly responsible for a thing called a "neutron induction computer," a design gone bad as it was a 2U rack unit containing -93- 10-turn potentiometers. Nightmare. This photo shows the attitude indicator in the F-4 cockpit. It is in the center of the control panel, below the purple radar screen. There are two sources for attitude information, selected by the primary/standby switch in the upper left. The mounting of the switch is questionable: screwed down to the console with visible wiring. While researching the use of the attitude indicator in the F-4, I came across the "nuclear store consent switch". If the plane has a nuclear bomb attached, you flip this switch from the SAFE position to the upper position (REL/ARM) to arm the bomb for release. Somehow, I was expecting something more elaborate. For more on the F-4's attitude indicator (including reverse-engineered schematic), see my blog post at https://www.righto.com/2024/09/f4-attitude-indicator.html Credits: I worked on this with @tubetime and CuriousMarc. Thanks to the collectors who provided attitude indicators and amplifiers. Aircraft photos from National Museum of the USAF: https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/196051/mcdonnell-douglas-f-4c-phantom-ii/  @kenshirriff I had trouble wrapping my head around the mechanism. There's a diagram about halfway down the Wikipedia page that helps: @kenshirriff I could have used this years ago. I was in responsible for testing the standby flight instruments for the B-2, and the "turnball" (not sure anyone else calls it that) would work once, then fail when QA came to witness. I eventually found out why from the spec (which the USAF made hard to find), and rewrote that test. As usual, a great view of interesting tech.  @kenshirriff @tubetime @yourfutureex @tubetime That's the reason that the attitude indicator is vitally important: in an aircraft, gravity can feel like a completely different direction from down. For example, see the famous video of pouring iced tea in a plane while doing a barrel roll.   @kenshirriff https://en.wikipedia.org/wiki/Permissive_action_link sound like a fine idea until you find out they were all set to 00000000 for a time. @kenshirriff @0tracas  @kenshirriff I've wanted to know how these things work for ages, I'll check this out when I have time!  @FritzAdalis The reddish-purple circle is the radar scope for the AN/APQ-120 radar system.  @kenshirriff wow, that's some workmanship. Late change in requirements leading to iffy solution? @tehstu I've seen the switch in other aircraft photos and in the manual, so it's not a one-off hack. I think the attitude indicator originally took a single input source but later planes had two inputs.  |
The attitude indicator uses 1960s-era electronics, with each angle transmitted over three wires from a synchro. The indicator uses a servo loop for each axis, using a feedback loop to rotate the motor until the shaft angle matches the input angle. A "control transformer" compares its shaft angle to the electrical input and generates an error signal. The amplifier turns the motor as needed to eliminate the error.
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