Timeline for Why does Boeing 737 use 2 Inertial Reference Systems (IRS) and GPS?
Current License: CC BY-SA 3.0
12 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Aug 3, 2017 at 4:53 | comment | added | Federico | @JanHudec oh, you're right. I don't know what I was thinking yesterday evening :| | |
| Aug 2, 2017 at 22:09 | comment | added | Jan Hudec | @Federico, no, it is easiest to solve at Equator, because there the axis of rotation lies in the local horizontal plane. The methods are actually both used, because magnetometer gives magnetic heading, and that is used for heading indicator, while the gyroscopic method (gyrocompass is a gyro with attached weight so the axis is horizontal, but I expect IRS to simply spin up all axis gyros, measure the rotation and align the coordinate system accordingly) gives true heading, which is needed by the inertial navigation system. | |
| Aug 2, 2017 at 20:59 | comment | added | Federico | @JanHudec you mean that at (or very close to) the Equator it is not possible to solve it? (Earth's rotation cannot be sensed there). Could be a mix of the two approaches, personally I have seen it done mostly with magnetometers, so I can ascribe to unfamiliarity the reason why I haven't thought of what you mention. | |
| Aug 2, 2017 at 20:47 | comment | added | Jan Hudec | Actually, the "heading problem" is solved by waiting long enough to sense the rotation of Earth. Magnetometer is not particularly useful due to the varying declination. | |
| Mar 9, 2017 at 15:12 | comment | added | FreeMan | @traducerad - redundancy is what keeps the plane safe should something go wrong with a single system. I'm sure that manufacturers & airlines would love to do away with redundancy because it adds weight, complexity and cost which take away from cargo capacity, range and profit. However, they prefer to not have the bad publicity of planes falling out of the sky due to a failure in a single system. There are probably many single-system failures every day that have essentially zero impact on a flight arriving safely due to the redundant systems. | |
| Mar 9, 2017 at 14:46 | comment | added | Prodnegel | @traducerad, The use of 3 identical systems is what is known as triple redundancy. Let's say you have only have 2 systems, and 1 of them begins to show different readings than the other. How do you know which to believe? With 3 systems in total, if 1 begins to show different numbers, you will know that the 2 other ones are more than likely the "correct" ones. | |
| Mar 9, 2017 at 9:56 | vote | accept | traducerad | ||
| Mar 9, 2017 at 9:52 | comment | added | Federico | @traducerad as I said, the "voting and monitoring" one? IIRC, with two INSs, the pilots perform this function, as one uses INS R and the other uses INS L. | |
| Mar 9, 2017 at 9:47 | comment | added | traducerad | "a third system", what system compensates the difference in measurements of both systems? | |
| Mar 9, 2017 at 9:43 | comment | added | Federico | @traducerad there is usually a third system that performs what is called "voting and monitoring" | |
| Mar 9, 2017 at 9:42 | comment | added | traducerad | Thx for your answer. But if it is only for redundancy and they do not communicate amongs eacht other. How do they compensate the differences in measurements of both systems? 3 isn't that overkill? | |
| Mar 9, 2017 at 9:38 | history | answered | Federico | CC BY-SA 3.0 |