Aircraft gyro-compass

The technology, limits and other information

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How a gyro-compass works, what are it’s limits

     I’ve been experimenting with a few ideas, I wanted to build a steampunk artwork, that would be functional as well as aesthetically appealing. I ran across a BEECHCRAFT gyro-compass from the mid 1960’s for an incredibly low price of 10$, it even had the safety plugs from being tested installed still. I have been bouncing some ideas around, having to do mostly with a geomagnetic storm of disastrous proportions, due to a massive solar flare. An event such as this would mostl likely render magnetic compasses useless for several days, and severely damage navigation and communication satellites in orbit. My idea was to construct a portable vacuum source with a simple PWM (PulseWidthModulation) circuit to control the vacuum motor, a lead acid battery (12v), and a few other bells and whistles to make the unit operational.
     After searching the internet, I believe I have discovered the one piece of information that is not readily published on it! The amount of vacuum use in aircraft gyro navigation system. I finally went to BEECHCRAFT’s website where I sent them an e-mail on their contact form, and really wasn’t expecting much help at first, but was pleasantly surprised when a Senior field engineer contacted me back about the particular gyro-compass I had. He didn’t have full specs, but did inform me it was made by a third party company for Beechcraft, and would accurately keep a gyro lock on course at up to a 30 deg turn or bank (kinda impressive for that time). He also let me know that the instrument will operate between 4.5 and 5.5 in. Hg (inches of mercury) of vacuum, any less will lead to course error, and any more risks destroying the gyroscope (it will fly apart inside). He also let me know that I should locate an adj. vacuum purge valve to prevent exceeding 5.5 in Hg so as to prevent damage. After some work I managed to locate what I need and will post further on my project.
     A gyro-compass in an aircraft is used to maintain a directional course when flying, along with a gyro artificial horizon indicator, turn and bank indicator they all run on a vacuum created by the pitot tube on the wing of the aircraft. The pitot tube has two ports on it, one for static pressure which runs the vacuum powered instruments, and a dynamic pressure that is used with the static to tell you what you airspeed is while flying. A gyroscope spins rather fast, and has pivots at several points. Gyro’s used for navigation are even more advanced with jewel bearings (sapphire) and in some instances like on ships at sea, they actually float in containers of liquid mercury so as to offset the vibration and constant pitching of the vessel. Most gyro-compasses used in aircraft have several ports for vacuum plumbing on the back, usually an intake (needs a micro airfilter attached to protect the instrument), a vacuum port (connect to your vacuum source), and a gauge port (for monitoring the vacuum level in the instrument). More modern vacuum gyros has a small flag that flips up when the vacuum drops below a certain point to warn you of a possible course error. Gyro-compasses do need to be reset every so often when flying to adj. for mechanical errors as a result of flight, a friend of mine John who is an aircraft structure and composite technician and a light aircraft pilot says that he resets his every 30 miles or so when flying a course, or at way-points. The gyro-compass will have a kno b on the front that allows the operator to set the course heading, and by pulling the knob out or pushing in, the instrument is “CAGED” to protect it from rough turns or extreme turbulence.