[HN Gopher] Reverse-Engineering the Mechanical Bendix Central Ai...
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Reverse-Engineering the Mechanical Bendix Central Air Data Computer
Author : picture
Score : 36 points
Date : 2023-10-07 16:07 UTC (6 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| OldGuyInTheClub wrote:
| I'm struggling to wrap my head around manufacturing so many parts
| to the needed tolerances and having them work under the
| temperature swings and forces seen in flight. Debugging these
| analog computers would involve a large number of engineering
| disciplines!
|
| Impressive technology and excellent article.
| Animats wrote:
| It's not that hard. All the components here are common and
| well-behaved - gears, cams, bearings, shafts, mounting plates,
| and synchros. Only the mounting plates, shafts, and cams are
| fully custom. Everything else is an off the shelf part. It's
| like designing electronics - you use standard components, but
| boards are custom for the job. Design is mostly topology plus
| constraints to make it fit and keep vibration and backlash
| under control.
|
| There are mechanical equivalents to proto boards, sort of like
| Lego gearing, but all metal. W.M. Berg used to be the main US
| maker. So you make up all the functionality on a breadboard,
| test with inputs and outputs, then rearrange for production.
|
| The mechanical design is like medium duty clockmaking. Teletype
| machines are in roughly the same scale - the parts can be
| handled without tweezers and are not too fragile. (And all
| custom, with far more levers than gears.) It's possible to go
| smaller but everything becomes more fragile and wears faster.
|
| It's roughly the same technology as naval fire direction
| computers [1], but smaller and more automated.
|
| [1] https://en.wikipedia.org/wiki/Mark_I_Fire_Control_Computer
| creer wrote:
| The synchros run the cockpit displays. Sounds like an intuitive
| match. But the computed values are also used in other systems:
| engine control, targeting, that sort of thing. Is the signaling
| to these also through the synchros? Is there some kind of
| standard signal format for these?
| creer wrote:
| Seems to be mostly synchros. With more views in the videos
| around this one:
|
| https://www.youtube.com/watch?v=bbOMHQMohc0
| kens wrote:
| The signaling is indirect. The air data computer is connected
| to another box, the air data converter. The air data converter
| is designed for a specific type of aircraft. It converts the
| synchro outputs from the air data computer into the formats
| required by the particular aircraft. These are probably synchro
| outputs as well, but might need to be scaled. (I don't think
| there is a standard.) The converter would also distribute the
| signals as needed, with a connector for each device that
| receives the data.
| andrehacker wrote:
| Ken: big fan of your and Marc's work, would be so great if you
| guys could give the Ken&Marc treatment to the "Nortronics
| NAS-14V2 Astroinertial Navigation System", The R2-D2 unit from an
| SR-71. Well, here's hoping.
| kens wrote:
| Author here for all your mechanical computer questions :-)
| mgsouth wrote:
| Based on a quick search, it looks like air impedance (the
| mysterious air density x speed of sound calculation) affects
| turbine stability. So needed for engine control?
| kens wrote:
| Thanks, that makes sense. Do you have a link that discusses
| this?
| CamperBob2 wrote:
| _I 'll point out that reverse engineering the CADC is not as
| easy as you might expect._
|
| Well, there goes that illusion. :)
|
| An amazing piece of work as usual, Ken. Thanks for sharing your
| hard-won insights on this gadget. The linear-endpoint
| wraparound hack was worth learning about all by itself. I'm
| surprised it took until 1954 before someone got around to
| patenting that, as it seems like a valuable general-purpose
| control technique. I can imagine a CORDIC-like algorithm that
| takes advantage of something similar to avoid clamping.
|
| You _have_ to find a way to power this thing up as a static
| demonstration piece.
| kens wrote:
| Thanks! We're powering up the unit piece by piece.
| CuriousMarc got a vintage pitot tube vacuum simulator so
| we'll use that to simulate the different pressures.
| dekhn wrote:
| Are the synchros in this similar to what the Rosenblatt
| Perceptron used to adjust and show weights: "This machine was
| designed for image recognition: it had an array of 400
| photocells, randomly connected to the "neurons". Weights were
| encoded in potentiometers, and weight updates during learning
| were performed by electric motors.[2]: 193 "
| kens wrote:
| I couldn't find details on the Perceptron's motors, but I
| expect they were DC motors, rotating the potentiometers
| higher or lower as needed. The synchro is useful if you have
| a rotation in one location and one to match the rotation at
| another location. But with the Perceptron, you don't have a
| specific rotational angle you want, just "more" or "less".
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(page generated 2023-10-07 23:00 UTC)