John, You have rediscovered what most pilots refer to as the Northerly turning error. It has everything to do with the dip angle of the earth's magnetic field. Your Airpath compass can only respond to the horizontal component (where you are located) of the three-dimensional earth magnetic field. The angle between compass pivot line and the magnetic dip angle will produce a turning force on the compass card whenever there is some relative motion such as raising or lowering the tail, or turning the aircraft in flight (banking included). In the Northern (magnetic) hemisphere, turning through Northern headings will cause the compass indication to lag behind the actual heading during the turn. Easterly or Westerly headings will indicate close to the actual heading. Southern heading turns will cause the compass to lead the actual heading. In the Southern hemisphere these Northerly and Southerly turning errors are reversed due to the opposite magnetic dip angle. At the Earth's magnetic equator the dip angle is zero and these turning errors disappear, but the pitch and bank induced errors will remain. I don't think there is any way to change the above physics in your compass. Airpath does sell compasses for use in the Southern hemisphere for $15 extra. These compasses are referred to as "south field". The manufacturer reverses the magnetic field of the compass card, and reverses the numbers on the card by 180 degrees to get the proper read out. This then will give the same Northerly turning errors indication as found in the Northern hemisphere. You can adjust your compass to compensate for local magnetic effects due to the iron in your engine or magnetic fields generated by your electrical system. That's why you should make the compass adjustments with the engine running and electrical equipment turned on as directed in the manufacturer instructions. My Dynon EFIS does not exhibit turning errors, because it senses and responds to the total Earth magnetic field vector. That includes direction and strength of the magnetic field. The Dynon electronic sensor can tell the difference between the Earth's magnetic field and induced magnetic fields produced by the aircraft installation.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD USA sidney.w...@titan.com -----Original Message----- From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net] On Behalf Of Martindale Family Sent: Monday, August 16, 2004 4:48 AM To: KRnet Subject: KR> Compass dip Folks My Airpath type dash compass seems to fluctuate through 10 degrees one way on easterly and the opposite on westerly headings when the tail is lifted on the ground to level attitude but not on north or south headings. I think this has something to do with the dip setting. Does anyone know how to change these compasses from north to south hemisphere settings. Does the card have a different slot underneath to take the pivot point? Is it easy to change? Need to know before I hack into it. John The Martindale Family 29 Jane Circuit TOORMINA NSW 2452 AUSTRALIA phone: 61 2 66584767 email: johnj...@chc.net.au _______________________________________ to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net please see other KRnet info at http://www.krnet.org/info.html
