Ed de C. Posted October 5 Report Posted October 5 Good evening folks - My Ovation is in for its first annual under my watch. Sure enough, the first time is painful (even after a good pre-buy). In my case, a scored engine mount due to a rubbing heat shield around the left front isolator is the $7k culprit (engine has to be pulled and mount sent out for repair due to failing allowed section thickness reduction). So be it. Now that the seats are out, I'd like to clean the carpets (vacuum cleaner and Bissel extractor). One of the A/Ps told me I don't want to bring electric motors or extension cords inside the cabin's steel cage for fear of magnetizing the cage. Apparently, the failure mode is a magnetic compass that always points North, according to the A/P. He said he's seen this condition on a couple of pre-J models, but nothing post J. My question is: should I be concerned about using this kind of equipment inside the cabin? There are plenty of other motors inside the cabin already such as the avionics fans, gear motor actuator in the belly, etc. If this is a worry, then should I worry about that $500 Tanis cabin heater I bought last winter? I'm a mechanical engineer because the voodoo electrical stuff was never intuitive to me. Best, Ed Quote
Ragsf15e Posted October 5 Report Posted October 5 6 minutes ago, Ed de C. said: Good evening folks - My Ovation is in for its first annual under my watch. Sure enough, the first time is painful (even after a good pre-buy). In my case, a scored engine mount due to a rubbing heat shield around the left front isolator is the $7k culprit (engine has to be pulled and mount sent out for repair due to failing allowed section thickness reduction). So be it. Now that the seats are out, I'd like to clean the carpets (vacuum cleaner and Bissel extractor). One of the A/Ps told me I don't want to bring electric motors or extension cords inside the cabin's steel cage for fear of magnetizing the cage. Apparently, the failure mode is a magnetic compass that always points North, according to the A/P. He said he's seen this condition on a couple of pre-J models, but nothing post J. My question is: should I be concerned about using this kind of equipment inside the cabin? There are plenty of other motors inside the cabin already such as the avionics fans, gear motor actuator in the belly, etc. If this is a worry, then should I worry about that $500 Tanis cabin heater I bought last winter? I'm a mechanical engineer because the voodoo electrical stuff was never intuitive to me. Best, Ed I studied ME as well because I kept “letting out the smoke”… that being said, I’ve heard of that condition but hadn’t heard anything specific causing it. I have used a vacuum in my F when the seats were out and nothing weird happened. Quote
MikeOH Posted October 5 Report Posted October 5 Like Rags, I've used a vacuum without issue in my 'F'. Magnetic fields fall off quickly with distance, so as long as you don't sit your shop vac on the glare shield I think you'll be fine. Even if you managed to slightly magnetize the steel tube under the vacuum, that doesn't mean the entire steel frame is suddenly magnetized. I believe (the experts can correct me) the later models (post 'F' models?) used non-magnetic tubing for the center post where the compass is mounted. Quote
EricJ Posted October 5 Report Posted October 5 7 minutes ago, MikeOH said: I believe (the experts can correct me) the later models (post 'F' models?) used non-magnetic tubing for the center post where the compass is mounted. The center windscreen post in the J model, and I think every model after, is stainless and non-magnetic. It's not a terrible idea to be careful regarding making efforts to avoid magnetizing things in airplanes, which is why a lot of places use air tools instead of electric for things like drills, rivet guns, etc. It's unlikely that occasional use of a vacuum cleaner or something like that is going to do much damage. 1 Quote
GeeBee Posted October 5 Report Posted October 5 Most the magnetized truss structures I have seen come from welding on them. In the PA-18 community you see it when someone welds float fittings on or repairs a weld. Quote
Hank Posted October 5 Report Posted October 5 I generally set a small shop vac on the wing, then the hose can reach just about everywhere except the baggage area. 1 Quote
buddy Posted October 5 Report Posted October 5 I never had a problem using my battery powered vac. Quote
DCarlton Posted October 5 Report Posted October 5 There's a very very old Mooney Service Bulletin that covers this exact topic. I'll see if I have it in my files. I'm starting to suspect a problem with my compass readings. 1 Quote
1980Mooney Posted October 5 Report Posted October 5 14 hours ago, Ed de C. said: Good evening folks - My Ovation is in for its first annual under my watch. Sure enough, the first time is painful (even after a good pre-buy). In my case, a scored engine mount due to a rubbing heat shield around the left front isolator is the $7k culprit (engine has to be pulled and mount sent out for repair due to failing allowed section thickness reduction). So be it. Now that the seats are out, I'd like to clean the carpets (vacuum cleaner and Bissel extractor). One of the A/Ps told me I don't want to bring electric motors or extension cords inside the cabin's steel cage for fear of magnetizing the cage. Apparently, the failure mode is a magnetic compass that always points North, according to the A/P. He said he's seen this condition on a couple of pre-J models, but nothing post J. My question is: should I be concerned about using this kind of equipment inside the cabin? There are plenty of other motors inside the cabin already such as the avionics fans, gear motor actuator in the belly, etc. If this is a worry, then should I worry about that $500 Tanis cabin heater I bought last winter? I'm a mechanical engineer because the voodoo electrical stuff was never intuitive to me. Best, Ed Been discussed before. Everyone in old topic below says an AC cord cannot magnetize anything because it keeps alternating and reversing fields. DC power cords will magnetize the steel frame. Your 28v wires either zip tied across or along the tubing are more likely to cause magnetism. In 25 years of the same plane, I have had corded vacuums, lights, power tools in the cabin - sometimes for long periods like while replacing cabin insulation. One especially humid Gulf Coast winter in a crap hanger without sealed concrete I had a low wattage incandescent light with a small fan running continuously in the cabin for a while. Never a problem. As @Hank says, a canister on the wing with a hose may work better given the limited space. Also the motor heat blowing into the cabin is unbearable most times. I generally also just set on the wing. 1 Quote
1980Mooney Posted October 5 Report Posted October 5 30 minutes ago, DCarlton said: There's a very very old Mooney Service Bulletin that covers this exact topic. I'll see if I have it in my files. I'm starting to suspect a problem with my compass readings. Are you talking about this? https://mooney.com/wp-content/uploads/2020/12/SBM20-150A.pdf Quote
EricJ Posted October 5 Report Posted October 5 4 hours ago, 1980Mooney said: Been discussed before. Everyone in old topic below says an AC cord cannot magnetize anything because it keeps alternating and reversing fields. DC power cords will magnetize the steel frame. Your 28v wires either zip tied across or along the tubing are more likely to cause magnetism. With AC if the source happens to be shut off or disconnected near the peak of a cycle it can still leave some residual magnetism. If it is left on and slowly drawn away, it will leave everything in a reasonably random state (i.e., not magnetized), which is how a degausser works. DC is definitely worse for potentially leaving residual magnetism, so battery powered stuff isn't necessarily better from that perspective. It's all pretty low probability stuff, but the probabilities aren't zero, and it's annoying to have to go degauss something so some shops just use air tools to avoid any issues. For an owner, the occassional vacuum cleaner or drill or whatever is unlikely to cause any big problems, but being careful still isn't a bad idea. The main areas to be careful around are the magnetometer, if installed, wherever it is installed, and the compass, wherever it is installed. Other than that it's not as likely that any localized residual magnetism will cause an issue, like in the cabin, gear, etc. The only other place I recall that is sensitive to magnetism is the hydraulic lifters, where you're warned to resist the temptation to pull them out of their hole with a magnet, because residual magnetization of the check ball may be sufficient to keep it from seating. 1 Quote
PT20J Posted October 5 Report Posted October 5 As @EricJ said, DC is more likely to magnetize the structure than AC. Nothing draws more current than the starter and the wire from the battery in my J runs along the left side tubing. Since that doesn’t seem to cause a problem, I wouldn’t worry about a vacuum cleaner. Still, I find it much easier to use a shop vac with a long hose in the cramped space of the cabin. 1 Quote
MatthiasArnold Posted October 5 Report Posted October 5 3 hours ago, 1980Mooney said: Been discussed before. Everyone in old topic below says an AC cord cannot magnetize anything because it keeps alternating and reversing fields. DC power cords will magnetize the steel frame. Your 28v wires either zip tied across or along the tubing are more likely to cause magnetism. AC current does not magnetize - and according to the report even decent DC currents are no real world factor .. BTW I‘m one of these strange electrical engineers .. 2 Quote
GeeBee Posted October 6 Report Posted October 6 just install a degaussing ring around your airplane. 2 Quote
dkkim73 Posted October 7 Report Posted October 7 On 10/5/2024 at 6:01 PM, GeeBee said: just install a degaussing ring around your airplane. Is that a super hard core ADF installation? Quote
GeeBee Posted October 7 Report Posted October 7 10 hours ago, dkkim73 said: Is that a super hard core ADF installation? Believe it or not, the British created it to trip magnetic sea mines the Germans planted. It had its own gasoline powered generator in the bomb bay. It worked really good. So good, the Germans gave up on magnetic sea mines in the Channel. Quote
N201MKTurbo Posted October 7 Report Posted October 7 1 hour ago, GeeBee said: Believe it or not, the British created it to trip magnetic sea mines the Germans planted. It had its own gasoline powered generator in the bomb bay. It worked really good. So good, the Germans gave up on magnetic sea mines in the Channel. That sounds like a fun job. Just fly low over the ocean and BOOM. I imagine in most cases it would be BOOM, BOOM, BOOM! Any idea how low they flew? Quote
N201MKTurbo Posted October 7 Report Posted October 7 So, they flew between 35 and 60 feet AGL (ASL) and no faster than 135 MPH. Any lower and it blew up the plane any higher and it didn't work. The first try they were too low and it blew the hatches off the plane. 1 Quote
A64Pilot Posted October 7 Report Posted October 7 (edited) For years I built Crop Dusters that were fully 4130 steel tube fuselages. We had to degauss them with a big electric magnet that plugged into the wall, so AC current. In the Army we had to degauss steel parts after they were magnetic particle inspected, we didn’t use a magnet attached to the part, we put the part in a device that put AC current though it making the part itself a magnet and we had to demagnetize it after inspection, used a little thing that looked like a cheap compress that indicated a plus or minus needle reading detecting a magnetic field, looked like something that came out of a Cracker Jack box but it worked https://www.globaltestsupply.com/product/parker-mg-25-20-magnetic-field-indicator?gad_source=1&gbraid=0AAAAAD39hO_xgspCwwlD12AmHdAnR_dYI&gclid=EAIaIQobChMI5aHKpLX8iAMVvaBaBR1NXwDzEAQYCCABEgKOsfD_BwE So I’m not so sure the statement that AC current can’t magnetize is correct. Lightning can magnetize everything steel in an entire airframe, had that happen to one AH-64. Army did not condemn the transmission etc which surprised me. One thing I was sure of those components would never get a chip light. When I was a contract welder in the oil field one of the things we built was cattle guards from old worn out drill pipe, for some reason it was most often very magnetic and hard as hell to weld, the Arc would be moved around by the magnetic field. I think the friction of it being spun against the ground magnetized it? To combat that we would put several wraps of the welding lead around the pipe, if it didn’t work you wrapped the lead the other direction. Our Welders were DC, some AC, both were affected. However in my opinion there is a nearly zero chance that a Vacuum cleaner could magnetize anything, not that my opinion is worth much. Edited October 7 by A64Pilot Quote
carusoam Posted October 8 Report Posted October 8 hey all…! I don’t know what did it… but, my old M20C was fully magnetized… it ended my first attempt at IFR training… right at making turns using the mag compass… if you remember ANDS… accelerate North, Decelerate South… the magnetized cage added another sticking point that slowed the magnet, until it broke free, and accelerated to the next position… Pretty much made the mag compass useless for making turns in instrument conditions… people used to make demagnetizers out of used CRT screen parts… decent instrument shops probably have one… lately, people don’t remember CRT screens much any more… as far as vacuum cleaners and mag fields goes… leave the electric motors outside and bring the hose inside… most modern devices are built with some intelligence involved…all kinds of shielding to keep them from annoying your cell phone. mom’s 50 year old vac cleaner throws off enough sparking electric noise and ozone… it’s best left outside the hangar… The newer Mooneys got a larger diameter center tube, made of SS… and the mag compass is also glare shield mounted a bit far away from the center post… I’m only a retired chemical engineer… my work processes back in the day used 500hp DC motors and had computer controls all around them… both simple PC and hardened industrial controllers… Quote
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