Interference with Whiskey Compass

When Whiskey Compass placed anywhere near front cockpit it will not read accurately. Any thoughts on how to make it read correctly?? Thanks.

Degauss, Swing it and EFIS

I guess there is some info missing, like what brand of compass?, where in the cockpit do you want to mount the compass?

Many times steel gets magnetized. You can "degauss" the steel, especially the front canopy frame and roll bar. The things that affect it will be the steel and electrical wires.

The next thing I am thinking of is have you swung the compass yet. All compasses are inaccurate more or less on differnt headings. I am sure you are familiar with a compass correction card that you see on all compass.


I am curious do you have another magnetic indicating instrument in the form of an EFIS. After going around this topic a couple of times you don't NEED a wwet compass if you a Dynon EFIS-10 for example. I emphasize NEED. Many feel they want a back up, but if you do have an electronic indicator, like an EFIS, you do not need an additional WET compass.

Part 23 does get more spacific in that it requires a non electrical magnetic indicator, but part 23 does not apply to us. Part 91 only mentions for VFR and IFR flight a magnetic indication, it can be electronic or not.

With a GPS in my plane I really don't pay much attention to the compass, since the GPS gives a TRACK up heading. Also with a Dynon EFIS with remote mag sensor I do not have a wet compass at all. With GPS I "track the track". The absolute heading is not important, at least VFR. I do pilotage but rarely do much dead reckoning.

Don't get me wrong you MUST have a compass or heading indicator of some kind, but don't plan on a perfect heading in all directions with a jelly jar compass. With the EFIS, remote magnetometers and corrections automatically made by the EFIS. heading is very accurate.

I am sure some RV-8'er will tell you where they mounted it. On my RV-4 I put it in the panel and it was reasonably accurate except when transmitting on the Comm. If you are having some wild compass swings, you may have some metal magnetized. Also around the compass make sure to use non-ferrous metal.



George

Whiskey compass

Did you use a magnetic tip screwdriver to mount it?
Tom

whiskey compass interference

There is not presently a whiskey compass in the aircraft. Too much interference. The aircraft is equipped with an Advanced Flight Systems ACS 2002 Engine Monitor, which is an older version of the AFS AF 2500. A pedestal mounted compass has been placed, (not mounted) on the glareshield and is not even close. A panel mounted has been tried with unsatisfactor results. Brands tried unknown. The aircraft is equipped with a King, panel mounted GPS. I would prefer to mount the compass in the panel. Thanks to all for your help.

Repeat: ID steel parts, Degauss and Swing

bamadude said:

There is not presently a whiskey compass in the aircraft. Too much interference.......A pedestal mounted compass has been placed, (not mounted) on the glareshield and is not even close. A panel mounted has been tried with unsatisfactory results. Brands tried unknown. I would prefer to mount the compass in the panel. Thanks to all for your help.

Click to expand...

Look Dude: you got to do the steps. If you want it in the panel than put it there, but make sure there are no electrical instruments adjacent. Altimeter, airspeed, VSI are fine. Vac instruments, ATT/DG, MAP, OK. Worse are motors (T&B) and next are avionics like Com's.

I don't know what you mean "not even close" means. You have not qualified how bad the interference is, but it matters little until you try to at least swing it.

It will not be correct until you follow the steps:

DID DEGAUSS THE ROLL BAR/CANOPY FRAME?

DID YOU SWING IT?

DID YOU ASSURE NO STEEL NEAR IT?

USE NON-FERROUS METAL TO MOUNT AND ADJUST COMPASS


Look I mentioned you need to degauss the roll bar. This is common. You need to ID any steel or ferrous material in the area. Than you need to makes sure it is not magnetized (degauss). Once that is done this you install the compass, with brass or stainless steel screws and swing it. After you do that let me know how it comes out.

Here is how to swing the compass:
http://www.airstuff.com/compass.html

Here are some tips:

You NEED to swing it (with a brass screw drive, and may take a few tries)

Use a magnet and find all the steel any where near the panel/cockpit. Than use a small handheld pocket hiking compass. Move it around and see if you can find the magnetized parts. (A real Magnetometer or gaussmeter), http://www.trifield.com/gauss_meter.htm A little hand held passive one sells for like $50, http://i24.ebayimg.com/02/i/05/c5/32/d7_2.JPG

My guess its the big steel items like the canopy bow, engine mount and maybe the engine crank. Any steel bolt/washer can be a magnet. Yes the engine is a magnet, however it is fairly far away, but you can account for it with the correction magnets. Look a steel ship has a compass. How? With real big correction magnets.

You (likely) have to Degauss the steel in the cockpit area. I think Bob N. of aeroelectric has a degaussing coil he lends out, I think? Google the subject and degaussing and compass swing. Good Luck I am out of ideas.


Sacramento Sky Ranch rents out their degauss-er for $75.

Here is their article. Magnetism of steel is a real thing. Trust me degaussing helps.
http://www.sacskyranch.com/degauss.htm

Here are pictures of the steps (hit next near the picture, the movies did not work well for me)
http://www.sacskyranch.com/degaussi.htm

More info
http://www.kilohotel.com/rv8/article.php?story=20040303210952285

Steel Boats and the physics of magnetic compasses
http://pollux.nss.nga.mil/NAV_PUBS/APN/Chapt-06.pdf


COMPASS TYPE
I had an electronic compass I tried in my car, which is of course all steel. It had electronic swinging. You drove around in a big circle twice in 30-60 seconds and pushed some buttons and it corrected itself. It worked OK for a week or so, but I got tired of it. It seemed to get out of calibration and got sick of going in circles to calibrate it, which some times I had to repeat two/three times to get right. I did not replace the battery when it died.

One of those electronic compasses may work for you. However if you are mounting a compass in your plane spend the bucks and get a good one or a surplus WWII airpath. Some people use car compasses. Boat compasses are kind of big and they are not cheap. I would not know how a boat compass would work.



SWING
You have to be level if its a tail dragger and ideal engine running and electrical on. That can be hard to do. You need people holding the tail up with the engine running. You can compromise and have the engine off and the the tail up, or the engine running and tail down. Always have the electrical equipment on. The idea is to represent the typical (cruise)condition. Like I said my RV-4 compass swing wild when I transmitted. I just ignored the compass when I transmitted.

click me to enlarge

Look if you install it and your swing gets you within +/-5 to 10 degrees on all cardinal headings N,S,E,W, and NE, NW, SE, SW you are doing OK. It is what it is. Just average out the error with correction magnets and live with it.

I am sorry you are having problems but degauss, swing and use an aircraft quality compass with a S-N and E-W compensating adjustment. I am done. Good luck.

There is one possibility is check the Magnetic Geological anomalies at your airport. It does little good to swing a compass in an area of magnetic disturbance. Chances are you are OK, but you can check it out. Sometimes the sectional will show Mag disturbances or the AFD (Airport Facilities Directory) will mention magnetic anomalies at an airport. These can be like 20 degrees!
http://www.ngdc.noaa.gov/seg/geomag/jsp/IGRF.jsp
http://geomag.usgs.gov/
http://science.nasa.gov/headlines/y2003/29dec_magneticfield.htm


It will never be perfect but as long as your compass does not think you left wing tip is the North Pole you will be fine.

George

Definitely degauss

bamadude said:

There is not presently a whiskey compass in the aircraft. Too much interference. The aircraft is equipped with an Advanced Flight Systems ACS 2002 Engine Monitor, which is an older version of the AFS AF 2500. A pedestal mounted compass has been placed, (not mounted) on the glareshield and is not even close. A panel mounted has been tried with unsatisfactor results. Brands tried unknown. The aircraft is equipped with a King, panel mounted GPS. I would prefer to mount the compass in the panel. Thanks to all for your help.

Click to expand...

Bamadude,
I stuck a whiskey compass in the panel of my 8a and it was waaayyy off initially. It even changed when the canopy was closed vs. open. After degaussing the rollbar and canopy frame twice each, it was pretty close. Then, you can swing it as gmcjetpilot recommended and make the correction card. Oh, and mount it using stainless steel hardware.

Compass SWING per AC 43.13-1B, Chap12, Sec 3, Par 12-37

Here is the official FAA ACCEPTABLE PRACTICE. They sound like they know what they are writing about. It is very complete. (note used OCR to convert so some error may occure. Ref original text if in doubt.)


9/27/01 AC 43.13-1B CHG 1

SECTION 3. GROUND OPERATIONAL CHECKS FOR AVIONICS EQUIPMENT (NON ELECTRICAL)

12-37. COMPASS SWING must be performed whenever any ferrous component of the system (i.e. flux valve compensator, or Standby Compass) is installed, removed, repaired, or a new compass is installed. The magnetic compass can be checked for accuracy by using a compass rose located on an airport. The compass swing is normally effected by placing the aircraft on various magnetic headings and comparing the deviations with those on the deviation cards. Refer to CFR14, 23.1327, 14 CFR 23.1547, and the equipment or aircraft manufacturer?s manual.

a. A compass swing must be performed on the following occasions:

(1) When the accuracy of the compass is suspected.

(2) After any cockpit modification or major replacement involving ferrous metal.

(3) Whenever a compass has been subjected to a shock; for example, after a hard landing or turbulence.

(4) After aircraft has passed through a severe electrical storm.

(5) After lighting strike.

(6) Whenever a change is made to the electrical system.

(7) Whenever a change of cargo is likely to affect the compass.

(8) When an aircraft operation is changed to a different geographic location with a major change in magnetic deviation. (e.g., from Miami, Florida to Fairbanks, Alaska.)

(9) After aircraft has been parked on one heading for over a year.

(10) When flux valves are replaced.


b. Precautions.

(1) The magnetic compass must be checked for accuracy in a location free of steel structures, underground pipes or cables, or equipment that produces magnetic fields.

(2) Personnel engaged in the compensation of the compass shall remove all magnetic or ferrous material from their possession.

(3) Use only nonmagnetic tools when adjusting the compass.

(4) Position the aircraft at least 100 yards from any metal object.

(5) All equipment in the aircraft having any magnetic effect on the compass must be secured in the position occupied in normal flight.



c. Compass Swing Procedures.

(1) Have the aircraft taxied to the NORTH (0?) radial on the Compass Rose. Use a hairline sight compass (a reverse reading compass with a gun sight arrangement mounted on top of it) to place the aircraft in the general vicinity. With the aircraft facing North and the person in the cockpit running the engine(s) at 1000 rpm, a mechanic, standing approximately 30 feet in front of the aircraft and facing South, ?shoots? or aligns the master compass with the aircraft center line. Using hand signals, the mechanic signals the person in the cockpit to make additional adjustments to align the aircraft with the master compass. Once aligned on the heading, the person in the cockpit runs the engine(s) to approximately 1,700 rpm to duplicate the aircraft?s magnetic field and then the person reads the compass.


NOTE:

(1) For conventional gear aircraft, the mechanic will have to position the magnetic compass in the straight and level position or mount the tail of the aircraft on a moveable dolly to simulate a straight and level cruise configuration. (2) Remember the hairline sight compass is only intended to be used as a general piece of test equipment.

(2) If the aircraft compass is not in alignment with the magnetic North of the master compass, correct the error by making small adjustments to the North-South brass adjustment screw with a nonmetallic screw driver (made out of brass stock, or stainless steel welding rod). Adjust the N-S compensator screw until the compass reads North (0?). Turn the aircraft until it is aligned with the East-West, pointing East. Adjust the E-W compensator screw until it reads 90?. Continue by turning the aircraft South 180? and adjust the N-S screw to remove one-half of the South?s heading error. This will throw the North off, but the total North-South should be divided equally between the two headings. Turn the aircraft until it is heading West 270?, and adjust the E-W screw on the compensator to remove one-half of the West error. This should divide equally the total E-W error. The engine(s) should be running.

(3) With the aircraft heading West, start your calibration card here and record the magnetic heading of 270? and the compass reading with the avionics/electrical systems on then off. Turn the aircraft to align with each of the lines on the compass rose and record the com pass reading every 30?. There should be not more than a plus or minus 10? difference between any of the compass? heading and the magnetic heading of the aircraft.

(4) If the compass cannot be adjusted to meet the requirements, install another one.

NOTE:
A common error that affects the compass? accuracy is the mounting of a compass or instruments on or in the instrument panel using steel machine screws/nuts rather than brass hardware, magnetized control yoke, structural tubing, and improperly routed electrical wiring, which can cause unreasonable compass error.

(5) If the aircraft has an electrical system, two complete compass checks should be performed, one with minimum electrical equipment operating and the other with all electrical accessories on (e.g. radios, navigation, radar, and lights). If the compass readings are not identical, the mechanic should make up two separate compass correction cards, one with all the equipment on and one with the equipment off.

(6) When the compass is satisfactorily swung, fill out the calibration card properly and put it in the holder in full view for the pilot?s reference.

Standby (wet) Compass. Adjustment compensation of the Standby Compass also be accomplished by using the ?compass swing? method.

Page 12-13 & 12-14
AC 43.13-1B CHG 1
9/27/01

Whiskey Compass Interference

gmcjetpilot and all: Thank you very much for the excellent guidance. With the info provided, I should be able to solve my problem. Again, thanks to all.