Backcountry Pilot • Proper magnetic compass mounting position

Proper magnetic compass mounting position

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Mon Jan 28, 2013 12:52 pm

Proper magnetic compass mounting position

Split from My 185 project in Texas -Z
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Regarding your intent to replace your windshield mag compass for a panel mounted vertical, I would STRONGLY recommend NOT! [-X I have a vertical card that the previous owner of my 185 installed on the glare-shield and it is the most almost worthless piece of junk. It has been serviced and checked and still is erroneous often. It almost sent me way off course when flying through Northern Canada. If I would have continued, it would of probably been a crash in uninhabited wilderness. I intend to remove it soon and replace it with an Airpath hanging from the windshield where it belongs away from magnetic fields from panel mounted equipment. I have much more confidence with the OEM type set up when flying in the bush. Every Boeing I've ever flown has had the mag compass mounted high above and I think that is for good reason. - Your results may vary and if you're not going to seriously fly your airplane in the bush it might not matter.....FYI-my experience only.
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Mon Jan 28, 2013 1:40 pm

Re: My 185 Project in Texas

RockHopper wrote:Regarding your intent to replace your windshield mag compass for a panel mounted vertical, I would STRONGLY recommend NOT! [-X I have a vertical card that the previous owner of my 185 installed on the glare-shield and it is the most almost worthless piece of junk. It has been serviced and checked and still is erroneous often. It almost sent me way off course when flying through Northern Canada. If I would have continued, it would of probably been a crash in uninhabited wilderness. I intend to remove it soon and replace it with an Airpath hanging from the windshield where it belongs away from magnetic fields from panel mounted equipment. I have much more confidence with the OEM type set up when flying in the bush. Every Boeing I've ever flown has had the mag compass mounted high above and I think that is for good reason. - Your results may vary and if you're not going to seriously fly your airplane in the bush it might not matter.....FYI-my experience only.


Are you saying that the only mistake was mounting the compass in the panel amidst the electronics? I had a Precision vertical card compass in my 170 that I mounted from the windshield, and it worked quite well. I've never enjoyed using a wet compass.
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Mon Jan 28, 2013 1:43 pm

Re: My 185 Project in Texas

Although I am far from an expert on anything airplane related... The first thing I tossed in my C170 was the whiskey compass. Replaced it with a PAI 700 VC Compass on the glareshield. No issues.. Was the bomb. Same thing is going in my 180. Might be different as it will be nested w/in the V Brace, but time will tell.

http://www.aircraftspruce.com/catalog/i ... ckkey=5962
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Mon Jan 28, 2013 2:56 pm

Re: My 185 Project in Texas

I have a previously installed PAI 700 in the panel of the 170A I am currently flying. With the control yoke in the normal flying position the compass is correct, when the yoke is pulled full back (elevator full up) the compass swings 30 degrees to the right do to the magnetic effect of the control column T. Just as a note the installation instructions for this compass strongly recommend not installing it in the panel. I will be moving mine to the top of the glare shield when I have a chance.

Tim
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Mon Jan 28, 2013 6:17 pm

Re: My 185 Project in Texas

Let me first state that this reply is not meant to be condescending in any way as I wish for you to be aware of the seriousness of compass error. I realize sometimes guys do mods to their panels to update, thinking that they ' re doing the correct thing. After my little ordeal, I have found that several other "Pro" bush pilots have had similar problems with the vertical card compass and refuse to use them. When your life may depend on a reliable sensitive master mag compass over 100's of miles of uninhabited country, you have to have instruments you can trust. Again, if your just bashing around in the lower 48 VFR with lots of landmarks for reference, not so much a problem and more of an irritation. -Now decide that one day you're going to make a trip up to the Northern Territories , maybe even further west to Alaska and you find yourself under a low ceiling in the mountains trying to stay in the clear with few clear distinguishable landmarks. Now that not so reliable compass may give you erroneous information that may cause you to decide to turn the wrong direction, possibly up a box canyon or just out to the middle of nowhere? Totally disorientated trying to figure out which way to turn? You and your pax lives vary well may depend on that one instrument. -Been there and done that and it's not fun at all!
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Mon Jan 28, 2013 6:31 pm

Re: My 185 Project in Texas

RockHopper wrote:Let me first state that this reply is not meant to be condescending in any way as I wish for you to be aware of the seriousness of compass error. I realize sometimes guys do mods to their panels to update, thinking that they ' re doing the correct thing. After my little ordeal, I have found that several other "Pro" bush pilots have had similar problems with the vertical card compass and refuse to use them. When your life may depend on a reliable sensitive master mag compass over 100's of miles of uninhabited country, you have to have instruments you can trust. Again, if you're just bashing around in the lower 48 VFR with lots of landmarks for reference, not so much a problem and more of an irritation. -Now decide that one day you're going to make a trip up to the Northern Territories , maybe even further west to Alaska and you find yourself under a low ceiling in the mountains trying to stay in the clear with few clear distinguishable landmarks. Now that not so reliable compass may give you erroneous information that may cause you to decide to turn the wrong direction, possibly up a box canyon or just out to the middle of nowhere? Totally disorientated trying to figure out which way to turn? You and your pax lives vary well may depend on that one instrument. -Been there and done that and it's not fun at all!
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Mon Jan 28, 2013 6:34 pm

Re: My 185 Project in Texas

Very cool info on the compass, thanks everyone. We have the VC compass mounted in a "temporary" part of the panel. We have not started the plane yet, and I never thought about the yoke affecting it.

I test both of those on Wednesday and report back.

Rob, toggle breakers sounds like a great idea! Where do you get those? And thanks.
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Mon Jan 28, 2013 10:06 pm

Re: My 185 Project in Texas

RockHopper wrote:Let me first state that this reply is not meant to be condescending in any way as I wish for you to be aware of the seriousness of compass error. I realize sometimes guys do mods to their panels to update, thinking that they ' re doing the correct thing. After my little ordeal, I have found that several other "Pro" bush pilots have had similar problems with the vertical card compass and refuse to use them. When your life may depend on a reliable sensitive master mag compass over 100's of miles of uninhabited country, you have to have instruments you can trust. Again, if your just bashing around in the lower 48 VFR with lots of landmarks for reference, not so much a problem and more of an irritation. -Now decide that one day you're going to make a trip up to the Northern Territories , maybe even further west to Alaska and you find yourself under a low ceiling in the mountains trying to stay in the clear with few clear distinguishable landmarks. Now that not so reliable compass may give you erroneous information that may cause you to decide to turn the wrong direction, possibly up a box canyon or just out to the middle of nowhere? Totally disorientated trying to figure out which way to turn? You and your pax lives vary well may depend on that one instrument. -Been there and done that and it's not fun at all!


I think you did a spectacular job of illustrating the perils of a bum compass. I'm still wondering if what you so passionately dislike is the panel mounting of compasses, or vertical card compasses altogether?

I'm glad this topic came up. Never gonna mount a compass in the panel now.
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Tue Jan 29, 2013 6:06 am

Re: My 185 Project in Texas

I have experienced precisely what Rockhopper described, on more than one occasion, in fact. I have always valued a good compass, having "grown up" in an aviation world that hadn't yet discovered GPS, and flying in a part of the world with virtually no radio nav aids.

I have used plain old whiskey compasses, many of which were useless due to mounting, interference, etc, etc.....I have met a VERY few of them that worked well.

I removed one of those and replaced it with a Hamilton Vertical Card compass in a Super Cub, mounting the Hamilton high up in the windshield to get it away from as much structure as possible. It still didnt' work well enough to suit me. I then installed on that compass a set of compensators (sold by Spruce), and that allowed the compass to swing. Still wasn't perfect, but was the best Cub compass I've ever encountered, with the exception of a goniometer.

In my C 170, the panel mounted whiskey compass was pretty directionally challenged, and I needed panel space for other stuff. I chucked the whiskey compass and installed a S.I.R.S. compass high in the windshield. THAT compass is absolutely the best I've ever come across, and I'd go there LONG before going with the vertical card compass. Not sure of the price difference, but I'll bet it's not that far apart.

Here's a link to Spruce's listing of the different SIRS compasses: http://www.aircraftspruce.com/menus/in/ ... _sirs.html

I'd get the one that sticks on glass, and mount it high in the windshield, or mount it in the original mounting location of the 185, mid high in the windshield. It should work there well.

If you are going to spend a dollar on a compass of any kind, it may as well be one that actually works, and the SIRS compasses really work, in my experience.

MTV
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Tue Jan 29, 2013 9:18 am

Re: My 185 Project in Texas

mtv wrote:In my C 170, the panel mounted whiskey compass was pretty directionally challenged, and I needed panel space for other stuff. I chucked the whiskey compass and installed a S.I.R.S. compass high in the windshield. THAT compass is absolutely the best I've ever come across, and I'd go there LONG before going with the vertical card compass. Not sure of the price difference, but I'll bet it's not that far apart.

Here's a link to Spruce's listing of the different SIRS compasses: http://www.aircraftspruce.com/menus/in/ ... _sirs.html
MTV


Our local avionics shop has a universal hatred for vertical card compasses. They recommend the SIRS to everyone big or small as the Pegasus unit is OEM on some high-dollar business jets. I like mine-
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Tue Jan 29, 2013 3:39 pm

Re: My 185 Project in Texas

I've got the Hamilton mounted on the glareshield of the Luscombe and it's really kind of laughable. I'm not sure where you would put one in this bird that would be in any way reliable. Just land once in awhile and ask where you are I guess. :D Just kidding.

EB
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Tue Jan 29, 2013 4:25 pm

Re: My 185 Project in Texas

I think you did a spectacular job of illustrating the perils of a bum compass. I'm still wondering if what you so passionately dislike is the panel mounting of compasses, or vertical card compasses ?


I have no issue with where the compass is mounted as long as it works correctly. I used to think the vertical card compass was a kinda neat improvement until I became the owner of one and have realized how fickle and unreliable it is. My 185 is setup as a true all season airplane with all the float, ski brackets, hook eyes etc, so it may have issues with magnetic fields due to all the ferrous metal. I need to replace the windshield soon, and have been seriously considering mounting a high quality compass as far up in the wind shield as possible for several reasons. The primary issue is again a reliable compass. Secondary is if the compass is up high, its out of the field of view. In the Pacific Northwest, we have lots of days where we fly under ceilings with rain showers that sometimes obscure passage ways between the mountains. We approach at an angle in a bank peering in to see if we can see through to the otherside before committing to continue. When your banked over 30 degrees and bent over trying to see, its real helpful to have a clear unobscure view to make a decision as to go or no go.
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Tue Jan 29, 2013 8:19 pm

Re: My 185 Project in Texas

This compass conversation should probably be on its on thread considering the interest it's getting, but I'm going to continue it here myself. When I told my friends I was replacing the whiskey compass with a VC compass they asked "Why? What do you use a compass for?". I explained that I used it to set my heading indicator (which my autopilot uses) and the reason I was changing was because I was tired of doing the backwards math between the whiskey compass and the heading indicator. The next question/comment was "just set the heading indicator off the GPS". That kinda left me speechless (not an easy thing to do).
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Wed Jan 30, 2013 5:33 am

Re: My 185 Project in Texas

They are the "Children of the Magenta Line".

And GPS gives you track, not heading.

But, whatever makes one happy.

Bear in mind that the Airbus 380/Boeing 777 both have a magnetic compass. Wonder why?

MTV
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Wed Jan 30, 2013 7:37 am

Re: My 185 Project in Texas

Barnstormer wrote:This compass conversation should probably be on its on thread considering the interest it's getting, but I'm going to continue it here myself. When I told my friends I was replacing the whiskey compass with a VC compass they asked "Why? What do you use a compass for?". I explained that I used it to set my heading indicator (which my autopilot uses) and the reason I was changing was because I was tired of doing the backwards math between the whiskey compass and the heading indicator. The next question/comment was "just set the heading indicator off the GPS". That kinda left me speechless (not an easy thing to do).


GPS won't help you with magnetic heading. Check out the SIRS and put the whole thing to bed. :mrgreen: :mrgreen:
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Wed Jan 30, 2013 6:33 pm

Re: Proper magnetic compass mounting position

My whiskey compass points 3 degrees west of due north whenever my alternator is charging. It is mounted on the top of the glaresheild and is too close to the engine, used to be mounted to the center rib of the windsheild. Also the plane had a genny before so the magnetic attraction of the alternator may be the problem. I don't worry about it too much around here because Tukahoe mountain is a big lump of low grade iron ore so any magnetic compass will lead you right to it. #-o
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Wed Jan 30, 2013 8:40 pm

Re: Proper magnetic compass mounting position

I've ridden with five pilots that put something next to or under the compass that skewed it noticeably... but they didn't notice. :shock:

Two of them were portable gps units laid on the top of the panel, two of them were cell phones, and one was a comm antenna for a handheld in a 2 seater ultralight that the cable was carefully routed around the windscreen to avoid obscuring vision then straight over to the compass and clipped onto the compass housing, using it as a base. #-o

Edit: Also, I had a passenger once put her camera next to my compass, and I watched the compass swing over to meet it.
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Wed Jan 30, 2013 9:08 pm

Re: Proper magnetic compass mounting position

In my citabria, my vc compass is right in the center on top of my dash. My gps is beside it and does swing it. But if I can't put my compass in the panel with the other electronics, where does one put everything so there is no interference? Should probly through the gps out and just fly by the compass, but damn the gps is nice...
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Wed Jan 30, 2013 10:16 pm

Re: Proper magnetic compass mounting position

Most of my compass problems have all come with the old wet compass - hated them.
Most of the error problems were solved with a degausing of the tube structures around it.
Most panel mount wet compasses I have used varied depending on what electrical was on or off.

Worst was in a J-5 leaving Ft. Nelson towards Anchorage under a low cloud base.
Note: The owner had just bought it out of a museum south of San Jose, my assumption was that it passed the annual OK.

We had followed I5 from Reid Hillview to Bellingham, then the roads to Hope and on north to Ft. Nelson where we decided that maybe we should check the compass before heading out since we had not been using it. Taxied over to the compass rose and the compass was basically stuck on 265 degrees even as we dragged the tail wheel around. took the compass out of the plane and walked it over to the compass rose and it worked pretty well. Ended up with the rear seat person holding it up occasionally when needed.
Worked OK. Got us there. Somehow the left vertical tube that comes down near the compass was highly magnetized. Got it fixed in Anchorage.

I do not remember the maker of the vertical card compass currently in my 170-B but it is mounted up high on the wind shield with the wiring coming down from the top frame as far from electrical fields as possible.

Love it - almost no, to very little, deviation - steadier than my heading indicator.

I have ridden in a couple of 185s with the sea plane kit bars and they those vertical compasses were each unstable and "hunted" Both of those compasses were on top of the panel cover, close between the bars.

Either way - fly safe - and know what yer flyin.

Chris C
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Thu Jan 31, 2013 7:02 am

Re: Proper magnetic compass mounting position

"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 :D had one in the glider wore it out thermaling, I use pilotage and GPS in a flight computer and paper chart.
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