I used a Radio Shack video tape eraser costing all of 20 bucks to degausse the V brace when I modified the engine mount to accept a larger engine on my 701. The welding on the mount caused magnetism that followed up the V brace which bolts through the firewall directly to the rear of the mount and affected the wet compass enough to make south read west. I stroked the tape eraser over the mount and V brace, one directional pass only, and it was gone. I get a very slight movement in the vertical card compass on the panel of the Tundra when I move the stick in the full forward position and left or right, but not when in left or right at the neutral position as in flight. It is there though.

Degaussing can work,but often it has to be repeated periodically, and unless you can degaussing the entire airframe, sometimes it just doesn't work. Ive seen that tried with a cub after all welding was complete and within a few months, the wet compass pointed to the airframe, not north.

For the vertical card compasses, these compensators worked reasonably well in some installations: http://www.aircraftspruce.com/catalog/i ... nsator.php

Positioned mid or high in windshield, the SIRS compass works very well.

MTV

Glidergeek wrote:"And GPS gives you track, not heading"
Agreed check compass while taxiing,(unless your skidding sideways) am using a Vertical card in the Skywagon mounted half way up the center strip with a brass screw and nut on the windshield works great never been lost yet had one in the glider wore it out thermaling, I use pilotage and GPS in a flight computer and paper chart.

Just curious, do you have a seaplane brace in your windscreen or other steel fittings nearby?

RockHopper wrote:

Glidergeek wrote:"And GPS gives you track, not heading"
Agreed check compass while taxiing,(unless your skidding sideways) am using a Vertical card in the Skywagon mounted half way up the center strip with a brass screw and nut on the windshield works great never been lost yet had one in the glider wore it out thermaling, I use pilotage and GPS in a flight computer and paper chart.

Just curious, do you have a seaplane brace in your windscreen or other steel fittings nearby?

No brace and the closest ferrous metal would be the T yoke I think, my radios are in a center stack above that, a KA134 on top of 2-KX125's, transponder is down low by my right knee. Flew out to a dry lake bed and taxied around on the 4 cardinal headings and adjusted it using the GPS with engine on and off and electrons flowing and not. Is good enough for government work.

I installed a VC on the glare shield of a 185 once. We had the same swing problems as stated here. We finally took some "MU Metal" and shielded the area under the VC, and that helped...but didn't cure it. We went to a SIRS compass and as stated above, no more problems! They go in every plane I rebuild now.

When I got my first 185, down in Honduras, I flew it back with nothing working in the panel but the wet compass. Well by the time I was over the jungle in the Yucatan, I noticed that the screws holding the compass face into the holder where steel not brass. When I got tot ht coast on the other side, I went to IFR (follow roads) it was way off in certain headings. When I finished off that aircraft, I put the Vertical Card Compass in. Worked just fine until Hurricane Andrew destroyed the airplane.

In my present 185 I put the Sirs compass, very much like the one that comes with the Twin Otter. Easy to read.

One commenter asked why the 777 has a wet compass, it is the law, required equipment. In Canada and Alaska above certain latitudes, the compass is rather worthless, it starts to dip severely to the ground, due to the orientation to the pole. We usually went to free gyro mode to do surveys, and set the gyro manually to true north then. So parts of the Aleutians will have a 40° compass swing in 60 miles from local rock formations distorting the field.

dogpilot wrote:When I got my first 185, down in Honduras, I flew it back with nothing working in the panel but the wet compass. Well by the time I was over the jungle in the Yucatan, I noticed that the screws holding the compass face into the holder where steel not brass. When I got tot ht coast on the other side, I went to IFR (follow roads) it was way off in certain headings. When I finished off that aircraft, I put the Vertical Card Compass in. Worked just fine until Hurricane Andrew destroyed the airplane.

In my present 185 I put the Sirs compass, very much like the one that comes with the Twin Otter. Easy to read.

One commenter asked why the 777 has a wet compass, it is the law, required equipment. In Canada and Alaska above certain latitudes, the compass is rather worthless, it starts to dip severely to the ground, due to the orientation to the pole. We usually went to free gyro mode to do surveys, and set the gyro manually to true north then. So parts of the Aleutians will have a 40° compass swing in 60 miles from local rock formations distorting the field.

Hmmm in the middle of the dry lake I did notice it spun like crazy looks like the sirs compass is a bit cheaper too.

Sounds like the answer to mag compass issues in the Skywagon, is to degauss all the steel parts and install a SRS up high in the wind screen using brass hardware. I'd sure like to have an acurate compass that I can trust. I think I'm going to order up a SIRS compass and try it out mounting it up high on my old wind shield. Drilling a few holes in the old one before I change it out won't hurt anything if it doesn't work out.

RockHopper wrote:Sounds like the answer to mag compass issues in the Skywagon, is to degauss all the steel parts and install a SRS up high in the wind screen using brass hardware. I'd sure like to have an acurate compass that I can trust. I think I'm going to order up a SIRS compass and try it out mounting it up high on my old wind shield. Drilling a few holes in the old one before I change it out won't hurt anything if it doesn't work out.

You don't have to drill ANY holes to mount a SIRS compass. They make one that has a mount that adheres to the windshield. I was a little skeptical as to how well that stickum really works, fully expecting a compass to knock me on the noggin some day, but so far it hasn't in quite a few hours. They do make several mounting styles, though if you prefer something bolted in place, but I have a one piece windshield, and stuck it on the plexi high in the center. No problems.

MTV

Thought I'd provide an update on the my decision to replace my windshield mounted whiskey compass with a vertical card compass, and then move it to the panel on the right side. I've flown with it over there for a couple of months now and am very pleased. It gets no interference from anything, stays as steady and true as a compass can, and now I've attached something useful to the old compass windshield mount - an iPad mini mount. The perfect spot.

To be completely truthful I did have the VC compass swing wildly once. The petrified anchor tie wraps inside the engine cowling that guide the taxi/landing light wires broke and the wires laid against the exhaust pipe and welded themselves to it. For a couple of seconds there while the MaxPulse was wig wagging so was the compass - then the circuit breaker popped and the wires separated. New wires and tie wraps got the lights working again but the ordeal left the MaxPulse "confused". Off was no longer off, taxi light position was now off, and the rest of the positions were mixed up. New MaxPulse switch fixed that.

I just had a new SIRS compass installed during this month's annual, and I'm anxious to swing it and see if it works better than the old Airpath, which was wearing out, leaking, and changing its orientation after only a month or two after being swung. Howmsomever, that'll have to wait for my prop to come back from the prop shop--it's been leaking oil slightly for several years, and the leaks just got too big to ignore any longer. Airplanes = never ending maintenance.

Cary

If you fly them they break, if you don't fly them they break even more.

I must admit, if you take you time, the Sirs compass compensated to be the closest compass I have ever put in any aircraft. Most headings are right on, or a max 1° out after swinging and adjusting. Of course, it is only as good as the master compass or compass rose your using. Finding a compass rose is becoming challenging.

We have one at GXY. Of course, ya look like a damn fool to the folks in the restaurant, as you taxi around in circles doing the swinging!

Cary

On the compass interference issue:
Years ago, loaded the a/c with core samples in Northern Canada. Bad enough the compass is not as reliable as down South but for 15 minutes I didn't know whether I was coming or going (pre GPS). Used the sun and tables to set gyro then realized that the cores were probably magnetized as the compass was extremely erratic. That was it as I later found out from the rock hound (geologist).
Just to illustrate how some things catch you...unaware.

When we do compass swings, we put the helicopter in a SOP "standard configuration" with all electronics, lights, etc run up like for a mission, which is then written on the back of the deviation card in case someone forgets what config it was swung in. And even then, depending on which leg a pilot wears their survival knife, which pocket they carry a camera in, and which way they hold their mouth when they fly can change the error from what we mark on the card after adjustments are made. A red coffee stirrer-straw bitten flat does pretty good for compass adjustments BTW - regular screwdrivers make the process a pita!

Random factoid, an uncorrelated mag compass swing is one of the six indications we use to show the DC gen has successfully come on-line.

Finally got my airplane back after having it overheat a couple of weeks ago, and took the time to swing the new SIRS compass. Definitely worth the purchase.

On all points, with all avionics and all strobes on, it's right on--no deviation at all. Flipping on the pitot heat causes a deviation of between 6 and 10 degrees, and flipping on the AOA heat adds another couple degrees to that deviation. Turning on the landing lights causes a deviation of less than 5 degrees for a moment while the HID ballasts warm up, but then it goes back to no deviation.

I was never able to get the Airpath to have no deviation, although it wasn't a lot--but it kept changing over relatively short time spans without any changes in the equipment in the airplane, so that either I lived with an inaccurate compass or had to regularly re-swing it--and besides, it was leaking. I'm hoping that the SIRS is less vulnerable to changes.

Cary

mtv wrote:best Cub compass I've ever encountered, with the exception of a goniometer.

My Doc' has one of those for checking my goni. What's that got to do with compass's?

If I am ever on an airliner that has to use the compass to arrive safely... I will just shoot myself.
Oh, that's right, I can't.
Now the serious comment. Vertical card is pretty good, when you find the right spot. Never had one leak kerosene on me.