Engineer to Degauss aircraft in Yorkshire
 

Good evening Ppruners, following on from me asking what could cause a compass to be not working as it should be it turns out it needs to be degaussed, this was the conclusion after a brand new compass was put in the cockpit and it had the same error. The problem is that we are struggling to get the maintenance outfit on the airfield to sort it, I have no idea why this hasn't been sorted and they are just leaving it. I was wondering if anyone knew of anyone who could sort this out for us, as it's been dragging on for way too long!
Any pointers would be great.

Cheers, Jim:ok:

I had a similar problem with my RV-6A. when the control column was pushed towards the panel the compass swang wildly

It didn't matter that if you made that huge input in flight you would be through VNE in a couple of seconds and that if you just kept the control inputs to normal flight range there was no effect on the compass, the engineer insisted that it was cured.

in the end I purchased one of these items and just stroked it up and down the stick a few times and then suddenly "ping" the compass was not affected.

WERA Screwdriver & Tool Magnetiser / Demagnetiser,0300 | eBay

I hope that your problem can be solved as easily.

As DV says...it could just be one ferrous component causing problems.

In a previous life I used to build new a/c,when compass swing time came along we sometimes had problems with magnetic 'hotspots' affecting either the main flux detector or the E2 standby compass.

We used a magnetic field detector...


http://i695.photobucket.com/albums/v...dindicator.jpg


But I also used an E2 compass sometimes...just moving it around the cockpit to see where the largest swing was (keeping the E2 orientation constant).

Sometimes we had (say) a magnetised tailplane or occasionally something like a magnetised Ejection seat gun :)...but it can obviously be any ferrous component

quite a few smartphones have magnetic field sensors built in, you could probably find the offending item with one of those.

After the comment from Twiddle I had a look for a suitable app and there are loads! They apparently work by detecting the localised magnetic variation by using the inbuild compass. My test detected that there is a strong magnetic field around my laptop!!

Finally making headway!
 

Well, I have finally been put in touch with a company based at Robin Hood Airport, or Doncaster if you prefer like I do. They generally deal with the big metal but I'm guessing it's all the same principals. I tried the smart phone application but I don't know how much I trust it, as I can get a reading and move around but when I get back to the same point the reading can be different. I did try it in the aircraft though and the cockpit seemed to pick up the same amount of magnetism as outside, whereas in the engine bay it went ballistic! But I don't know enough as to what is magnetic that shouldn't be etc, and if I could have picked a reading up from the mags

The earths magnetic field is very weak. So weak, that holding a compass near another compass will give you a deviation already.

Instead of using a vague iPhone app which may or may not work, why not simply use any old handheld compass and move it about the cockpit and engine bay? You can get compasses as gimmicks in children's toy stores these days for next to nothing and they'll probably work just fine for this purpose.

In fact, with an actual compass it'll probably be the North or South indicator which will point straight to the offending item. Like a magnet drawn to it - and in fact that's exactly what's happening.

Many years ago there was a Gardan Horizon in our hangar with the same compass problem. The sparkies ended up wrapping the fuselage with linked mains extension leads and plugging in a couple of 2kw electric heaters for a few hours in an attempt at degaussing. It didn't work and I can't recall what happened next.
G-AYOL if anyone knows (withdrawn from use in 1984).

just fly it under some high-tension powerlines (remove your mag . compass first! )
that'll cure the bugger :}

May kill you too! but that's another issue...


On a serious note, degaussing requires a powerful AC field to be gradually weakened.....usual method is to put a large electromagnet near the item to be degaussed, switch on then move slowly away until the emitted field is too weak to affect the subject -matter.

Maybe a scrapyard with a crane-mounted magnet would do it?

DC is no good, it straightens the magnetic "grain" of the subject-matter and weakening the field doesn't affect that alignment....AC "stirs" the poles and as the field weakens, leaves the magnetic structure randomly orientated.


Hope this helps!

Shirley if you want to degauss a whole airframe then you must remove all instrumentation that uses any sort of magnetic sensor or driver - and in particular the compass - otherwise you'll demagnetise the lot. Radio speakers and headsets 'may' survive but varios, moving coil meters and similar will likely be irrevocably stuffed. I'm in the process of scheming a giant set of helmholtz coils to degauss a K13 [classic steel tube glider] fuselage to get rid of gross compass errors, although for one of the club fleet this was more easily achieved by moving the radio speaker from it's mount next to the compass :eek: !

Jim

Instrumentation taken out
 

Thanks for all the input gents, yes Jim everything is getting whipped out tomorrow and there will be one of sherburns engineers with him. The bill could be a big one.

Cheers, Jim

Bo####ks
 

The lads came to test everything with a magnetometer and found nothing magnetised! So sadly back to stage one, which is a royal pain in the arse. We have decided to fit a suppressor/filter on the alternator to try and chalk that one off, so I will hopefully see if that cures it tomorrow, as we realised that the engineer never fitted a suppressor on the new alternator since the last one went faulty. I have done some research with my friend Google and seem to think that it's some sort of electrical problem, bit of a head scratcher!

Cheers, Jim:ok:

just remember that if you have lots of "extra" wire and bundle it up into a neat coil,-----you'll have an electromagnet.

The spaghetti behind the instrument panel should only be sufficiently long to reach it's termination without sharp angles or strain and should allow the connected item to be readily-withdrawn from the panel for maintenance /disconnection.


Can't you set small "correcting" magnets to reduce the errors?

a good Yachtsman's book should give you the info...try the old-fashioned public library!

SteveF said: Many years ago there was a Gardan Horizon in our hangar with the same compass problem. The sparkies ended up wrapping the fuselage with linked mains extension leads and plugging in a couple of 2kw electric heaters for a few hours in an attempt at degaussing. It didn't work and I can't recall what happened next.
G-AYOL if anyone knows (withdrawn from use in 1984).End quote

Bumping an old thread.

G-AYOL was the first GA I flew in as a kid. Family friend on Jersey owned it and I'd get to passenger (ok he let me fly it in the air) from Jersey to Shoreham. All I knew back then was keep it on a particular heading...nearest thing we had to autopilot in 1970's I guess.

My entire Supercub was turned into a magnet!
 

Thats right, in a container, crossing the Atlantic Ocean on a freighter to the UK, and vibrating gently as it spent five or six days ON THE SAME COURSE,
the entire airframe was magnetised. Had to remove the instruments entirely, found a place in mid panel where the compass worked OK Any degaussing of the entire airframe would have been prohibitively expensive.

We had persistent problems with gyro/mag compass errors on our R22 fleet. Problem traced to sensor down in the bottom of the instrument panel affected by the steel yaw pedals. Pedals degaused but errors returned after fairly short time. Eventually had to raise a mod to relocate the sensor.

Had problems with the compass on a steel framed aeroplane. Used a hand compass to determine from where the problem was coming and then used the £8 device bought from Amazon to deal with the magnetised area. Took about 30 seconds.

The current was limited due to the heaters, and rightly so. If you can do it again, connect the coils to a high powered AC welder at a couple hundred Amperes, slowly reducing the current after turn-on.