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tmoushon(at)gmail.com
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 Posted: Sun Aug 07, 2016 4:58 am Post subject: "Magnetic Anomaly" - Degauss rear seatbelt cables |
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Recommendation: Degauss the rear seat cables before installation.
Like many others, I mounted my GMU22 Garmin magnetometer in the top center of the tail section, aft of the cargo bay bulkhead and my installation passed the interference test. That said, for my first 20 flight hours or so, I frequently experienced (1 or two per flight) a "magnetic anomaly" on my Garmin G3X touch. It was suggested that I check the rear seatbelt cables for magnetism using a cheap auto dashboard compass. Before removing the cables, I moved the auto compass along the cable and found areas on the cable that made the compass spin like a top. My good friend lent me an old (1978) Radio Shack hand held degausser. I removed the cables from the plane and took them home (did NOT want the degausser anywhere near the aircraft). On my workbench, I moved the degausser along each cable (2-30second passes)....and retested using the auto compass. The cables now did not move the needle at all. The cables were reinstalled with an extra washer at the longeron to prevent the cable from moving at the yoke. I have had 9 flights now without any "magnetic anomalies"... I have closed this issue.
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bhoppe2
Joined: 09 Apr 2015
Posts: 15
Location: Nolensville, TN
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| Posted: Sun Aug 07, 2016 7:42 am Post subject: Re: |
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I had the same problem with the magnetometer mounted in my RV-10 tailcone using the SteinAir bracket. A cheap magnetic compass would swing when moved along the outside of the tailcone. At first, I presumed the AN bolts were magnetized, but they were not. I replaced them with SS bolts just to be safe. The rear seat shoulder harness cables were the problem. I demagnetized them with an old Radio Shack 100w soldering gun. I replaced the soldering tip with a 3-turn coil of 10 gauge wire and passed the cables through the hole in that makeshift coil. It worked like a charm. No more problems with the G3X compass.
A friend recently tried to move his wet compass to the top of the windshield in his Cessna Skymaster, but he could not get it adjusted. We used that same soldering gun to demagnetize the overhead structure, but only using the side of the case of the soldering gun. It fixed his problem, too.
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Bruce Hoppe |
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hotwheels
Joined: 01 Jun 2007
Posts: 240
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| Posted: Mon Aug 08, 2016 11:29 am Post subject: Re: |
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You replaced AN bolts with SS? Which ones? I don't think SS are rated for carrying much, if any, structural load...
Regards,
Jay
[quote="bhoppe2"]I had the same problem with the magnetometer mounted in my RV-10 tailcone using the SteinAir bracket. A cheap magnetic compass would swing when moved along the outside of the tailcone. At first, I presumed the AN bolts were magnetized, but they were not. I replaced them with SS bolts just to be safe. The rear seat shoulder harness cables were the problem. I demagnetized them with an old Radio Shack 100w soldering gun. I replaced the soldering tip with a 3-turn coil of 10 gauge wire and passed the cables through the hole in that makeshift coil. It worked like a charm. No more problems with the G3X compass.
A friend recently tried to move his wet compass to the top of the windshield in his Cessna Skymaster, but he could not get it adjusted. We used that same soldering gun to demagnetize the overhead structure, but only using the side of the case of the soldering gun. It fixed his problem, too.[/quote]
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Kellym
Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ
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| Posted: Mon Aug 08, 2016 12:29 pm Post subject: "Magnetic Anomaly" - Degauss rear seatbelt cables |
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You can buy AN3C or AN4C bolts. I'd have to look up what the difference
in shear and tension strengths is. I suspect that for shoulder belt
anchor that is drilled through aluminum angle there isn't a big
difference, and that is almost all in shear.
On 8/8/2016 12:29 PM, hotwheels wrote:
| Quote: |
You replaced AN bolts with SS? Which ones? I don't think SS are rated for carrying much, if any, structural load...
Regards,
Jay
| bhoppe2 wrote: | I had the same problem with the magnetometer mounted in my RV-10 tailcone using the SteinAir bracket. A cheap magnetic compass would swing when moved along the outside of the tailcone. At first, I presumed the AN bolts were magnetized, but they were not. I replaced them with SS bolts just to be safe. The rear seat shoulder harness cables were the problem. I demagnetized them with an old Radio Shack 100w soldering gun. I replaced the soldering tip with a 3-turn coil of 10 gauge wire and passed the cables through the hole in that makeshift coil. It worked like a charm. No more problems with the G3X compass.
A friend recently tried to move his wet compass to the top of the windshield in his Cessna Skymaster, but he could not get it adjusted. We used that same soldering gun to demagnetize the overhead structure, but only using the side of the case of the soldering gun. It fixed his problem, too. |
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=459337#459337
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Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
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