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A Thought…

Talent hits a target that no one else can hit. Genius hits a target no one else can see.

   — Arthur Schopenhauer

Mechanical analog computers

Posted on 2017-Mar-27 at 15:27:02 (last update on 2022-Jul-05 at 11:32:00) by Phil

In addition to the topic on Babbage’s Difference Engine and Analytic Engine, there have been mechanical analog computers since at least the early 20th century. These finely crafted devices were used, among other places, in naval gunnery directors to calculate where to point and elevate a gun to hit a distant target. Fire-control teams had to input ship and target headings and speeds, air temperature and humidity, wind speed and direction, and shell size and propellant charge (initial speed of the shell). Even the Coriolis Effect had to be taken into account at long ranges. In return, the machine would tell them the azimuth and altitude needed to hit the target.

The famed Norden Bombsight (as well as) also took many of these factors into account, to tell a bombardier how far ahead of the target to release the bombs (and how much to the side the bomber should be to allow for crosswinds). It was hardly top secret, being quite famous among the public, although aircraft crews were to make sure the device was destroyed before bailing out and saving themselves. The problem was, the Norden required a clear view of the target (difficult over Europe, with frequent clouds, ground smoke, and fog) and a knowledge of all the winds at various levels down to ground level. Thus, it rarely lived up to the hype about being able to put a bomb into a barrel. In addition, Norden insisted on hiring European craftsmen to build the things, and it turned out that several were Nazi agents who passed the plans along to Berlin before the US even entered the war! The Luftwaffe evaluated the Norden, but decided it wasn’t enough of an improvement over their existing bombsights, to build it themselves.

Discussion of other specialized mechanical calculating devices for specific purposes (as opposed to slide rules or small calculators) is welcome here. Circular slide rules with specialized scales (like the one used in Dr. Strangelove to calculate radiation exposure) aren’t all that interesting.

Posted on 2017-May-17 at 13:36:06 (last update on 2021-Mar-13 at 12:03:10) by Phil

Let’s not forget the famed Antikythera Mechanism (1) and Antikythera Mechanism (2) a 2000 or so year old orrery/astronomical calculator.

An article on Ars Technica about the internals of, and reconstructions of, the Antikythera Mechanism.

Posted on 2018-May-02 at 21:17:04 (last update on 2022-Jun-19 at 21:56:00) by Phil

Another great analog computer was the US Navy Torpedo Data Computer for its submarines. A good documentary on Navy Fire Control computers in WWII, includes some material on the TDC (although it covers mechanical analog computing). As usual with analog computers, it was built to do one thing and do it well. It was not a general purpose computer like your laptop machine.

The TDC was shown in action in USS Cod SS 224, Part 2. USS Cod SS 224, Part 1 is available.

The History Guy, in a video on the development of the transistor (Transistors and Forgotten History), shows a TDC in more detail, but not the workings, except that they were electronically-assisted mechanical. He also shows Colossus at Bletchley Park, but mistakenly says it was for decoding Enigma (it was actually for “Fish”).

Some of the basic math problems to be solved by the TDC are shown in Drachinifel’s The Drydock #88. Click the link in the comments section to go to 4:09:32 WW2 Torpedo Fire Control for Submarines.

Posted on 2018-Nov-09 at 17:27:53 by Phil

I’m not sure if the Friden STW10 mechanical calculator is internally analog or digital, but here’s a fun video about trying to make it divide by zero, and going crazy. Now, what’s that “DIV STOP” button for? I would imagine it’s well-worn on some units!

Posted on 2019-Dec-22 at 12:50:10 (last update on 2022-Sep-11 at 14:10:00) by Phil

An article on the Boeing B-29 Superfortress and its General Electric model 2CFR55B1 centralized fire-control system. Pretty amazing stuff for 1943 vintage. It was visually controlled (not by radar), but multiple gun turrets could be controlled from one of several control stations, for redundancy and flexibility. All a gunner had to do was keep the enemy fighter in the sights, and the computers did the rest of figuring exactly where to aim the guns.

A B-29 gunner’s training film shows that the gunner not only had to center the target in the sight; he also had to tell the range by inputting the target’s wingspan (once), and (continually) adjusting the reticle as the range changed. Here’s another video that shows more of the fire-control system.

Posted on 2019-Dec-22 at 13:21:26 (last update on 2020-Jul-30 at 21:50:22) by Phil

There’s also the Curta calculator (article) that could fit in your hand and was quite popular until the advent of small electronic pocket-sized calculators. Note that this device was a calculator and not a programmable computer, but still a neat piece of gear. Be sure to watch Adam Savage’s presentation on a 3D printed replica. The story of its inventor, Curt Herzstark, is one of amazing survival in the Buchenwald concentration camp.

There are a number of videos on the construction and theory of the Curta, including this and this. I seem to recall an article in Smithsonian Magazine a few years back, but it doesn’t seem to be online, although much of the material is in the Wikipedia article.

Posted on 2021-May-10 at 14:47:57 by Phil

A thread on slide rules in general, with some digressions into other calculating devices.

Posted on 2021-Sep-18 at 18:21:29 by Phil

A presentation in Greg’s Airplanes and Automobiles on the FW-190’s Kommandogerät engine control computer for the BMW-801 radial engine. This is a hydraulic (oil) geared mechanical computer to control throttle, mixture, propeller pitch, tweaking ignition timing, and supercharger speed selection all from one control lever (go slow/go fast). This was a useful thing, as a fighter pilot who doesn’t have to pay so much attention to all the individual controls (found on other aircraft) can spend more time looking around the sky for targets or threats, and can be more effective (and more likely to survive).


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