GPS HDG and TRACK TRUE incorrect?
Bart_BE
Guest
Hello everyone,
I was calculating (manually, not in flight simulator) the heading that I should follow to fly from Cork Airport to Shannon Airport in Ireland. I have a very recent low-air map of Ireland. The heading that I had to maintain according to my protractor was 343°. In flight simulator, however, when I make a flight plan to fly from Cork (EICK, runway 35) to Shannon (EINN) airport, the flight plan and nav log tells me I should maintain heading 350°. This is incorrect. I know it's not an issue with the software as I've recently done a format of my hard drive and reinstalled only Windows XP Pro, the drivers and Flight Sim 2004. Could someone be so kind to try the same thing with his own flight simulator?
Another problem is with the wind: if I set custom weather and I take 20KTS wind coming from 310° then in my nav log from Cork to Shannon, flight simulator still tells me that I have to maintain 350°, instead of the log displaying the wind correction (if I calculate this with protractor and flight computer on the map, taking the speed of the King Air into account, my calculations tell me I should make a 2° wind correction to the left, in other words fly 341° to arrive in Shannon in a little over 10 minutes time). Did anyone else notice flight simulator not taking wind into account? I know that the wind has been set because I can feel crosswind during take-off. I'm doing it correctly I think, I make one wind layer that goes up to 5000FT and I take a BeechCraft King Air to fly the course at 4500FT.
Has anyone else noticed problems like these? I haven't tried it with other maps yet, but I have a low-air map of Belgium too and I'm gonna try that out sometime too.
Thanks,
Bart
4 Answers
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Don Wood
Guest
I am not familiar with the area you are flying in but I suspect the situation here may be one of magnetic variation. Map and chart directions are plotted in "true" numbers of degrees (i.e., 343 degrees true). Flight instruments measure magnetic direction. A correction must be made from the map heading to get the heading you need to fly to achieve a particular course and that is called magnetic variation.
Mag. Var. is not constant. In some places, it can be close to zero. In others, it can be more than 15 degrees, plus or minus. Plotting charts usually show lines of magnetic variation and, along the border of the chart, show the amount of correction that must be applied. In your situation, I would not be surprised to find the Mag. Var. for the area you are flying to be seven degrees.
Don hit the nail on the head I think, mag variation for Cork is about 6* so add a tolerence for errors with the protractor and a roundup by FS you get the 350* steer. What are the upper winds you have programmed in for the flight? (direction/strength)
Bart_BE2
Guest
Hey guys, thanks for answering so soon,
I also thought about magnetic variation, but you've got variation and deviation, the variation is identical for a certain place on the planet, but every airplane has its own deviation due to instrument placing etc. so the heading should be different depending on which aircraft you're flying and it doesn't seem to be... I'm definitely going to have a look on my map tonight, I believe the magnetic variation is somewhat 3 to 4 degrees, but to be honest, and you're right, I didn't take that into account.
As far as the wind is concerned: I just took one layer of wind (from 0 to 5000 feet) and I took wind 310/20 (coming from 310 degrees, 20 knots strong). I can feel the crosswind on the runway when I take off, but the heading in my nav plan remains 350 degrees, despite the fact that a correction to the left should be made. It doesn't matter which wind I set, whether I set 0 knots or 20 knots, my nav plan always instructs me to fly 350°, and yeah, if I fly 350° then I get there, but it's not really the way it should be if you know what I mean. Am I doing something wrong with the wind here? Should I set multiple layers instead of just one big one?
Cheers,
Bart
Deviation will be zero for flight sim models which is why I did not mention it. Aircraft have a deviation card on/next to the compass and these are checked on the annuals...I think! Anyway they are certainly checked after hard landings, equipment changes. Having looked on my recent VFR charts (gotta stay legal) which sadly cuts off at Dublin which is 5.5W therefore +5.5 (West is best East is least as an easy way to remember) I expect Cork to be at least this if not +6. Variation changes from place to place Stansted for example is only 2.5W and is not a million miles from Cork. Also remember you need to align the HSI with the compass every so often during flight (15 mins) due to drift/wander. As for the wind I do not have an answer. Use real world weather and see if this affects calculations or try a stronger wind at 90* ie a crosswind.
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