View Full Version : Airfields with a compass Rose in south east
I need to calibrate my EFIS compass so require an airfield with a compass Rose in south east, any ideas?
Cheers
We calibrated our EFIS compass by taping a Silva compass to the wing & rotating the aircraft through the cardinal points. We checked the heading using a sighting compass from behind the aircraft.
You can check your calibration by taxiiing in a straight line and seeing if your GPS track & EFIS heading are the same (Check whether your GPS track is shown magnetic or true - ours shows a Mag tack - but if true you'd expect a difference of the magnetic variation).
stickandrudderman
30th Sep 2011, 23:25
I used the compass on my i phone as a start, and it turned out not to need any further adjustment.:ok:
goldeneaglepilot
1st Oct 2011, 07:05
Might be an idea to try to borrow a Landing compass and set it up in the same way as you would for a compass swing. No need for a ground based compass rose then.
I used similar methods already, but there must be a slight inaccuracy as when I am cruising it shows a 30 kt cross wind whichever direction I am flying!
The manufacturer says it's probably the compass calibration so I want to get it perfect so I can eliminate it
Cheers
Dave
John R81
1st Oct 2011, 08:40
Redhill has one. Visible on the Google Earth view of the airfield, the circle NW of the threshold of 08L. Just ask TWR for permission to use - no problem. You might want to call ahead (all details in Pooley's or here Welcome to Redhill Aerodrome (http://www.redhillaerodrome.com/)) as I believe there is a charge for use of any ground area.
BISH-BASH-BOSH
1st Oct 2011, 18:16
Cambridge has one.
Crikey, I used to do compass swings back in the day, landing compass and compass swing form at the ready....jeez that brings back memories. 4 point for error and 8 point for accuracy. Now I'm a pilot I know that I was wasting my time on those extra 1/2 degree errors I spent so much time on.
Deeday
1st Oct 2011, 19:13
I saw some markings on the tarmac at Blackbushe, yesterday, that looked like a (rather faint) compass rose. It was on the run-up checks area to the south of the taxyway.
Surely a compass swing is done mostly with a person outside the aircraft, with a handheld compass, telling the one inside (sitting there with the engine running, electrics on etc as per a normal cruise config) which way to turn, etc.
It isn't immediately obvious to me how a single person, in the cockpit, is going to know when the aircraft is accurately lined up with ground markings.
Swinging a compass to half a degree is indeed pointless but it is good to have a fairly accurate one when doing old-style (as in JAA IR training) instrument procedures, where you fly wind corrected headings. If your compass / HSI is say 5 degrees out (which is pretty common) these procedures are harder.
No the way it's done is for the guy in the a/c to turn onto his cardinals using his instruments. The guy outside with the landing compass then calculates the error on the a/c instruments. So say you lined up on 360 using your HSI, the guy outside measures your heading and finds that it's actually 358. You then do your other three cardinals and calculate the error (it's not even all the way around). All the pilot has to do is line up the a/c accurately, the techy does all the calculating and adjusting. You adjust the flux detector which is usually somewhere in the wing by physically turning it and then you do an eight point check swing and then calculate your compass card errors, being as a compass swing never actually removes all errors.
Well that's how I used to do them, it's probably done by computers these days.
OK I see what you mean.
It comes down to the same thing in the end.
On a modern EHSI, one method is that you place the aircraft on the cardinals (using the outsider to tell you which way to turn to be lined up) and then you enter into the EHSI config which cardinal you are on, and repeat this for the four cardinals, and it computes the correction internally.
Whereas a mag compass has to be done iteratively.
I am still looking for a method which uses GPS track, in flight. In calm air it is trivial of course, but one almost never has that. I intuitively know that a method can be developed which corrects for the wind, and I posted some stuff on it here some months ago, but nothing came of it. It would be the most accurate way to do it.
It is fairly obvious how to check a compass against a GPS on some heading (usually not a heading of your choice), by discovering the wind aloft (pretty easy with a GPS) and then flying along that heading, and then heading = GPS track.
But developing a general formula for doing the four cardinals eludes my brain...
I bet it would not be far different in principle to the triangular-track method of calibrating the ASI. Fly the four cardinals, and on each one you note the TAS, GS and the track, and plug those values into a formula and you get the actual headings flown.
Don't swing an aircraft compass over a hard surface unless it is approved for the purpose. Concrete usually has iron bars in it that make results meaningless. Tarmac is often over a concrete base.
500 above
3rd Oct 2011, 17:01
White Waltham has one.
Don't swing an aircraft compass over a hard surface unless it is approved for the purpose. Concrete usually has iron bars in it that make results meaningless. Tarmac is often over a concrete base.
Indeed, obviously compass swings should only be carried out on a compass swing pan.