1950s Fighter Jet Air Computer Shows What Analog Could Do

Imagine you’re a young engineer whose boss drops by one morning with a sheaf of complicated fluid dynamics equations. “We need you to design a system to solve these equations for the latest fighter jet,” bossman intones, and although you groan as you recall the hell of your fluid dynamics courses, you realize that it should be easy enough to whip up a program to do the job. But then you remember that it’s like 1950, and that digital computers — at least ones that can fit in an airplane — haven’t been invented yet, and that you’re going to have to do this the hard way.

The scenario is obviously contrived, but this peek inside the Bendix MG-1 Central Air Data Computer reveals the engineer’s nightmare fuel that was needed to accomplish some pretty complex computations in a severely resource-constrained environment. As [Ken Shirriff] explains, this particular device was used aboard USAF fighter aircraft in the mid-50s, when the complexities of supersonic flight were beginning to outpace the instrumentation needed to safely fly in that regime. Thanks to the way air behaves near the speed of sound, a simple pitot tube system for measuring airspeed was no longer enough; analog computers like the MG-1 were designed to deal with these changes and integrate them into a host of other measurements critical to the pilot.

To be fair, [Ken] doesn’t do a teardown here, at least in the traditional sense. We completely understand that — this machine is literally stuffed full of a mind-boggling number of gears, cams, levers, differentials, shafts, and pneumatics. Taking it apart with the intention of getting it back together again would be a nightmare. But we do get some really beautiful shots of the innards, which reveal a lot about how it worked. Of particular interest are the torque-amplifying servo mechanism used in the pressure transducers, and the warped-plate cams used to finely adjust some of the functions the machine computes.

If it all sounds a bit hard to understand, you’re right — it’s a complex device. But [Ken] does his usual great job of breaking it down into digestible pieces. And luckily, partner-in-crime [CuriousMarc] has a companion video if you need some visual help. You might also want to read up on synchros, since this device uses a ton of them too.

39 thoughts on “1950s Fighter Jet Air Computer Shows What Analog Could Do

      1. There were vacuum tube op amp made circa 1960. They weren’t small. Philbrick made them (and others). Bob Please used to write about them and how Philbrick wrote many articles about solving analog equations using them. I think the model was KA1.
        M Walter

        1. I used to have an opamp module. Solid state, but the size of a box of matches.

          The schematics I’ve seen of tube opamps keeps it minimum.. Even the uA702, I think the first IC opamp, has.minimal circuitry.

    1. The control computers for torpedos are similarly fascinating, as it encapsulates calculations for range, speed and angle and so on. If only the technology wasn’t so destructive and costing lives, this leaves a bad aftertaste to it.

      1. Sorry to burst your fragile bubble, but a majority of our technology that is used for the betterment of mankind has come from the war machine complex. This includes the first computers and medical services that save lives today. You are always welcome to live off the grid and not partake of the technology or medical services and feel better about yourself.

      2. Why? The simple truth is that they are just tools. How they are used is completely determined by people. Do you think that Ukraine should just take them over and kill the current leadership? Maybe Poland and the Baltic states should do the same.
        The simple truth is that there are people and groups of people that will take whatever advantage they can. I say this as someone that works in the defense industry. My coworkers and myself are working hard to supply Ukraine and other NATO nations. Right now I am on a civilian space project which is great but I can tell you this. None of us were cheering like people at a sporting event. We know all too well what modern weapons can do.
        If we ever get to a world at piece I promise we will be really happy and glad to work on space probes and other projects but until then we have to keep making weapons.
        It is nice to have the luxury to sit in a safe nation and not want war or weapons all without any real negative impact but some of us don’t have that luxury. I don’t begrudge you being uncomfortable with weapons. Only a fool wouldn’t be but thinking that some how makes you more ethical or moral than others you are just fooling yourself.

  1. Interesting to compare that to a LaCoste and Romberg Gravimeter, c1980, which was, I think, essentially a mechanical computer that “monitored” the apparent mass of a fixed weight on a ship that was simultaneously moving forward, pitching, rolling and rising and falling. It used missile gyros rotating at something like 30k rpm +, presumably to detect the movement and compensate for it – I didn’t understand how that worked either 😂

  2. I’ve taken apart some old military stuff, but nothing as complex as this (R390A radios were close). I’d like to know more about how this sort of thing was designed. They didn’t have 3D CAD software at that time, so did they use the actual components or dummy copies to play with and figure out the physical arrangement of the parts? Was it designed to fit the final enclosure from the start, of did they breadboard the whole thing to get it working and then spend months/years figuring out how to fold the whole thing to fit in the can? How many of the parts were made to spec for this device vs how many were off-the-shelf?

    1. Up until the early 1980’s, it was a regular thing that a company/bureau would design a fighter around the predicted size of the new, highest performance radar array available, and then it wouldn’t end up fitting and they’d have to downgrade the design until the new one fit. Designs were everyone doing their best guess and trying to fit, and a LOT of the time, it didn’t, and they ended up with weird lumps and expanded nose cones as they tried to fit the equipment into the airframe.
      At least in the US, the military seemed to take absolute delight in designing all new hardware for everything. I have a box of custom bolts for Titan missiles from 1957. If you look at the contemporary computational equipment, like the guts of a 1950’s Marchant 10/11 digit calculator, the gear trains have a similar level of complexity. (Each digit of display has two separate tiny planetary gearsets to drive the display.) They were really good at designing custom geartrains and fitting them using paper layout/blueprints. But I bet that aside from fasteners, all the other material in this was custom designed for this specific computer. The trend towards using off the shelf hardware for military designs didn’t really seem to get going until the mid-1990’s.

  3. I worked on 70’s kit (Jaguar GR1) and loved fault finding/rectification because you could actually get a soldering iron and fix stuff.
    I’d have been over the moon to be given something like this to play with!

  4. The linked article makes reference to some us military planes, including the F-101 and the F-111.
    This looks strange about the F-111 because it saw development during the 60′ and so had more advanced computing technologies than found on the F-101 which was 10 years older.

    Talking about the F-101 : I live in the French Alps and ten years ago went on some remote mountain where a R/F-101 Woodoo once crashed during the early 60′. Although most parts were removed, there was still a lot of miscellaneous debris including the landing gear, part of a turbine, etc. But no sensible part and no analog computer !
    I recovered a few small parts including the remain of one of the landing gear doors, recognizable by the red paint on one side.
    It crashed on April 12, 1963.



  5. I worked for an Engineer in the Seattle area back in the early 1980s: owned WOODFORD Aerospace. He was part of the Air Force Team that evolved the Gyroscopic navigation for Military aircraft (Read B-52s/B-70s/ FB 111s). Seriously Complex electro mechanical devices.

  6. A few thoughts come to mind…
    Designed when slide rules and log tables were state of art for calculation.
    Early 50’s USAF navigation computers had a high precision 3D cam to compensate for magnetic north. Every month, they made a new one.
    Before integrated circuit technology developed, fluidics promised smaller and more reliable operation than gear mechanism like this.
    On a less serious note, perhaps the Antikythera mechanism was Icarus’s flight computer?…

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