1949 Gyroscope Spins Up Again

[Curious Marc] has an Apollo-era gyroscope but isn’t quite ready to put it through this paces without some practice. So he borrowed a 1949 vintage Sperry C5 gyro and did some experiments with it using a 3-phase power supply he plans to use on the other gyro.

There is a little bit of troubleshooting and a lot of gorgeous close up shots of these electromechanical marvels. They sure are noisy, though.

[Marc] wanted a gyro testing table that can control the orientation of a gyro under test. He went the auction route to get a pretty expensive piece of gear for a relatively low price but without the expensive software. In a stroke of luck, he managed to score the required software from the vendor who was intrigued by his project. It looked to us like a table like this wouldn’t be that hard to build from scratch, either.

We are interested in what [Marc] will do with his gyros next. It is hard to imagine that gyros have come from this sort of device to a tiny IC inertial measurement unit that can fit in a phone. Imagine packing the Sperry unit on your next walking robot or self-balancing unicycle.

Need a refresher on how gyro’s work? We got that, too. It even covers the modern kind.

10 thoughts on “1949 Gyroscope Spins Up Again

  1. I have heard alot of small planes starting up and there is usually this high pitched whine that builds up and smoothes out as the plane starts up. I always assumed it was a pump or some other mechanism involved with running/starting the engine. Now I’m wondering if all that racket was just the gyros in the dash spoiling up.

    I’ll have to ask next time I’m near one starting up.

    1. @jack324 says: “I have heard alot of small planes starting up and there is usually this high pitched whine that builds up and smoothes out as the plane starts up. I always assumed it was a pump or some other mechanism involved with running/starting the engine. Now I’m wondering if all that racket was just the gyros in the dash spoiling up.”

      Yes, the whine you hear is from the vacuum pump(s). Excerpting [1]: “In an aircraft, the vacuum source is often used to power gyroscopes in the various flight instruments.”

      1. Vacuum Pump – Applications


      1. Correction, the whine you hear may also be electric gyros spinning up. One way to know if the whine is electric or vacuum driven is to note when the whine begins. If the whine begins before the engine is running it is most likely coming from one or more electric powered instruments running on battery power. If the whine begins after the engine starts it is most likely coming from a vacuum powered instrument because the vacuum pump is directly driven off of the engine. The reason for this is that proper aircraft design tries to avoid any single points of failure. If electric power fails electric powered instruments will fail, but enough vacuum powered instruments will remain working to allow the aircraft to be safely flown with a partial panel of instruments. And obviously the reverse is true, if vacuum power is lost, you will be left with enough electric powered instruments to safely fly on a partial panel. In today’s ‘glass cockpit’ approach to aircraft design where everything is electronic, there is an argument that says the electronics are so reliable vacuum-powered redundancy is not needed. [Until it is ;-( ]

    2. The noise you hear is definitely the electric gyros spooling up.

      Small aircraft tend to have three gyro based instruments. The artificial horizon, heading indicator and the turn coordinator.

      For redundancy the AI and HI are powered via a vacuum pump and the TC is powered electrically. This way you still have some form of attitude indication if you lose either the vacuum pump or the electrical system.

      More modern aircraft have all electric attitude instrumentation and replace the AI and HI with battery backed up solid state instruments.

  2. “They sure are noisy, though.”

    No, that sound is the best thing ever as you power up the instruments in an airplane – it means the fun is about to start. Problem is you usually power the instruments on after engine start so you don’t hear it unless you’re setting the radios/getting ATIS or something on the ground.

    Second best is as you power down – kill the instrument bus then shut off the engine, and listen to to the gyros spool down for minutes as you get ready to get out of a (usually) cramped, sweaty cockpit.

    Glass cockpits offer a lot of advantages, but they’re dead silent unless they’re giving you an alert/warning/status report – no visceral connection to the century of aviation that precedes them.

  3. Years ago I was given a directional gyro out of a friend’s WWII Harvard, which had been replaced for some reason or other. I fitted an air tools quick disconnect to the back and ran it up on an air compressor. Oh boy did it make some noise!
    Perhaps that could have been the reason for replacement, I don’t know. One thing is the complexity of it is a whole lot less than the beautiful electric example Marc demonstrated.

  4. The gyro in my Piper Warrior runs on vacuum and yes that’s what you hear spooling up.
    If you want a good example of the best of class, check into the gyrocompasses they use in large maritime vessels.
    It’s kind of like a gyroscope but it isn’t. It gyroscopically determines true north without a magnet. A primary navigation device. $$$$.

  5. Very interesting, thank you [Curious Marc]. I’m no expert but on a gyrocompass I am not used to seeing push-to-cage and twist to calibrate on the same knob, I usually see two separate knobs so there is near zero chance using one will interfere with the other. Also push-to-cage seems a little odd, I’ve seen spring-loaded pull-to-cage more often. I wonder why they chose electric auto-erection instead of faster, simpler, and more reliable pendulous vanes.[1] I don’t think it’s because the gyro is electric powered instead of vacuum, electric gyros often use pendulous vanes too.[2] Beware – I have read warnings from experts on these old instruments that when the radioactive glow paint on the instrument card breaks down, it leaves a radioactive dust behind that is very harmful if inhaled, even in tiny amounts.

    * References:

    1. Pendulous Vanes | Pilot Tutorial


    2. Flat Earth – A look inside the Artificial Horizon – Pendulous Vanes. [This is an electric powered gyrocompass, not vacuum.]


Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.