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Cake day: August 19th, 2023

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  • First, they have to align on the ground. You initialize them with your current known position (usually by GPS or your known airport/gate spot). Then, you wait for them to synchronize with the Earth’s rotation. If you’re far north, like in Alaska, this could take half an hour. If you’re close to the equator, it could take 5 minutes. Once they’re ready, from that point, any movement you make, it will know where you are and where you’ve been.

    If you spin up a gyro and begin moving around, it will maintain it’s starting position. You can use this deflection to calculate direction. If you know how fast you are going and for how long, you’ll have your position.

    Mechanical gyros drift. It’s the nature of a world with friction. Newer IRUs use laser gyros, so the only real drift they have comes from extremely minute rounding errors.




  • Yes. Most of commercial navigation systems rely on the IRUs as a primary source of position data, and they’ll usually have 3 of them. VHF is used by the crew to confirm that the aircraft is on track by referencing VOR stations, though these are slowly being phased out due to GPS.

    That being said, a single traditional IRU can have up to 2km of drift over a 2 hr flight (at which point it’s removed from service and replaced). When used in combination with two other IRUs, the error is dramatically reduced. Traditional IRUs are gyroscopically mechanical in nature and do not talk to GPS.

    Now, that being said, the new standard is called an ADIRU (ADvanced IRU), which ties in with GPS and features laser gyros. They’re extremely accurate and have essentially zero drift, plus multiple redundant components within each unit.