On 08/05/2013 01:38 AM, Михаил Сойтанен wrote: > In nav.dat file VORs have slave variation. As > I understand, slave variation of VOR depends on magnetic variation at he > location. Does Flightgear use this slave variation, or it computes magnetic > variation "on the fly"? > Do we need to track magnetic variation change every year and manually edit > nav.dat for it?
Executive summary: VOR alignment in nav.dat should reflect the VOR alignment as reported in the Airport/Facility Directory ... which is generally *not* the same as the actual local magnetic variation. I would expect Robin's xplane data files to track this properly in most cases, since they are routinely rebuilt from official data. ============= In the real world, VOR alignment is controlled by whomever owns and operates the VOR. It gets changed only on special occasions. There are three things to consider: a) The path through space of the actual electromagnetic VOR radials; b) The airways as plotted on the charts, typically defined in terms of VOR radials; c) The actual local magnetic variation. For obvious reasons, there needs to be very little discrepancy between (a) and (b). The discrepancy between (c) and (a), or between (c) and (b), is much less tightly controlled. Back in the days before GPS, pilots typically would not notice a discrepancy of this kind, even if it was rather large. If you decide to go looking for such discrepancies, they are easy enough to find, by finding the VOR's alignment (i.e. nominal magnetic variation) as documented in the Airport/Facility Directory and cross-checking it against the current local magnetic variation. As a less-precise version of the same idea, you can look at the orientation of the charted compass rose and compare it against the local magnetic variation. Nowadays, however, it is fairly easy for pilots to detect such a discrepancy, even if they weren't looking for it, by cross-checking a VOR radial against the GPS bearing-to-station. This is a predictable source of confusion for pilots working toward their instrument rating. Changing VOR alignment requires revising the charts, so they don't do it more often than necessary. FAA standards say they are "supposed" to re-align VORs to keep them within 1 degree of the actual magnetic variation, but this effort is chronically underfunded and it is easy to find VORs that are mis-aligned by more than a degree, sometimes quite a bit more. Bottom line: The VOR alignment in nav.dat should track the VOR alignment as documented in the A/FD. It should not track the actual local magnetic variation. ------------------------------------------------------------------------------ Get your SQL database under version control now! Version control is standard for application code, but databases havent caught up. So what steps can you take to put your SQL databases under version control? Why should you start doing it? Read more to find out. http://pubads.g.doubleclick.net/gampad/clk?id=49501711&iu=/4140/ostg.clktrk _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
