Return-Path: Received: from dewey.cadwell.com ([208.26.246.18]) by ns1.olsusa.com (Post.Office MTA v3.5.3 release 223 ID# 0-70783U4500L450S0V35) with SMTP id com for ; Mon, 29 Jan 2001 13:06:20 -0500 Received: by dewey.cadwell.com with SMTP (Microsoft Exchange Server Internet Mail Connector Version 4.0.993.5) id <01C089DC.85CB2F70@dewey.cadwell.com>; Mon, 29 Jan 2001 10:16:19 -0800 Message-ID: From: Carl Cadwell To: "'lancair.list@olsusa.com'" Subject: 40 degree Wet Compass deviation Date: Mon, 29 Jan 2001 10:16:17 -0800 X-Mailing-List: lancair.list@olsusa.com Reply-To: lancair.list@olsusa.com Mime-Version: 1.0 <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> Thanks to everyone for their previous suggestions concerning mu metal shielding of the wet compass to remove 40 degrees of swing upon turning on the battery switch. Further findings: 1. The 40 degree swing of the wet compass becomes about 3 degrees upon pulling the fuse to the standby alternator. 2. The radio stack causes about 3 degrees of swing and the voltage regulator causes about 3 degrees swing in the other direction. 3. I have not run the engine yet. I can in about 2 weeks when test flights may begin. 4. When power is applied to the standby alternator, there is an electro-magnetic field that is created that is easily sensed with a screwdriver (the standard in detecting force fields!) 5. Mu metal was wrapped partially around the standby alternator and the deviation was reduced to about 30 degrees when power was applied. 6. The compass is not slaved to the mu metal placed under the compass. This was determined by rotating the compass to N, S, E and W while fastened to the mu metal and holding the mu metal stationary while rotating the compass. 7. However, placing the mu metal under the compass is not a good answer. Initially this removed most of the problem and left a few degrees error. After much playing around, the mu metal now causes about a 15 degree compass swing. I conclude that this variance may not be consistent and not to be trusted. 8. Mu metal around any of the wiring on the interior or moving any of the wires has no effect on the compass deviation. 9. There does not appear to be any large loops of wire that would set up a magnetic field. So, the questions are: 1. It appears that the magnetic field is coming from the standby alternator. Any speculation as to an alternative source? 2. Can I assume that when the engine is running and the primary alternator is functioning, then the field is not activated for the standby alternator and everything is good? 3. And if everything is good and I loose the primary alternator so the standby alternator is activated, does my compass then swing 40 degrees? 4. Has anyone with a standby alternator turned off their main alternator so that the standby alternator is active and observed the wet compass? Carl Cadwell N25CL, final paint this weekend. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>