Geebax
Captain
Australia
Offline
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JJB* Posted at 11-21 01:49
Airline pilot do not re-calibrate their magnetic compass during long distance flights, its confusing to read this even if it is within "" later in your text.
They simply adjust the East or West variation on a dial to the position where they are flying to get a correct True N reference point for all the other 359 headings....
"Think about this....when calibrating DJI drone users can start on any heading the calibration, just make a 360 turn (flat+nose down). SW measures the normal expected variation in magn fields though the magnetometer and if its done in a free of magn interference area calibration is succesfull. Minor deviations through a full circle are averaged. Done."
Agreed. This is a vital point in the discussion, and one that many people simply do not understand. There is no point in the compass dance where you point the aircraft in a guaranteed heading, so the whole process cannot reasonably be called a 'calibration', because when calibrating any variable you would have to tell the device under calibration that the current variable corresponds to a known value. At no point in the compass dance do you do anything that indicates where either magnetic or true north is located.
At the risk of starting another fight, and hurting even more butts, I will also suggest that local magnetic variation is a complete red-herring also. Given the very short distances over which we fly our drones, and also that we do not plot a course for them in the same sense as full sized aircraft, local magnetic variations do not matter at all. Even in the hypothetical situation where we might plot two waypoints, possibly several miles apart, the compass is only taking a relatively small and minor part in the navigational exercise between the two points. The aircraft knows where it is and where it should be, from that it can calculate a heading. It then uses the compass to turn the aircraft to that heading, and off it goes. Several times per second during the flight, the aircraft performs the same calculation, so that if the original heading was not quite correct, or wind has pushed the aircraft off course, a new heading is generated for the aircraft. as a result, tiny course corrections are being made all the time, so in fact you could have a quite large local magnetic deviation and it would make almost negligible difference to the aircraft's navigation.
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