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Comment by kens | Hacker News Reader

Any questions about this system? (I know everyone hates Twitter threads...)

Absolutely beautiful collection of machinery, though just a single brief thought about the tolerance stackup in that thing will inevitably give me nightmares for weeks.

Any idea what that stackup looks like, and how the resultant error in calculations/readings was communicated to the pilot?

The official spec had lots of maximum allowed tolerances and how to test for them. E.g. the true airspeed had to be +/- 4 knots from 150 to 300 knots and +/- 1% and less than 7 knots above that. Mach number had to be +/- 1% but no greater than 0.02 or less than 0.006 of the real Mach number.

Any idea how it compares to the hydraulic computer designed for the Pratt & Whitney J58 engine used on the SR-71 Blackbird? I saw this video (linked below) wherein a test engineer talked about the engine design. He touched a bit on the hydraulic computer (at the 6:50 mark), and I thought it was ingenious and fascinating.

https://youtu.be/MJrXUh0eZjw

I wonder how reliable those were. Additionally, since they are mechanical in nature, were they a limit to aircraft performance (seems unlikely, but figured it is worth asking).

I don't know about the reliability in practice, but the official spec called for a "reliable life of 1000 hours with reasonable servicing" and a life of 5000 hours with replacement of parts. I don't think they put a limit to aircraft performance since you're not changing altitude or speed very fast compared to the speed of a gear. The spec called for testing acceleration up to 10g.

Also, to the submitter: thanks for fixing my typo in the title. Of course I make a typo that is highly visible at the top of a popular tweet.

There is white powdery detritus around some of the components. Some sort of galvanic reaction?

https://pbs.twimg.com/media/FhUHb-6WYAAMayN?format=jpg&name=...

We're not sure what it is. There's also a resistor with leads that look like they have been attacked by fungus, but it's probably corrosion. It's unclear why just a couple of components would have this issue.

I used to work on avionics of a mostly newer vintage than this but I love this sort of technology. Thanks for sharing and if you get around to digitizing the manuals I'm sure they'd be fun to look at too.

Any plans to publish this on your blog? It's a much more elegant source of information. This also belongs there with the other great articles.

Yes, I'll get it on my blog at some point. But honestly Twitter is a lot less work and reaches a lot more people.

Second vote for a blog!

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