Remote compass location?

[Les]

I've just installed my new D-180 and now looking for a place to mount the remote compass. I plan to locate it in the tailcone aft of the baggage compartment, preferably as far foward as possible.

I've read the install manual and understand that I need to use a compass to look for an appropriate location. Because of the steel in the overhead sliding canopy the compass will probably need to be mounted low near the belly.

My question is will the magnetic fields of other electrical devices affect the remote compass. Specifically, I need to mount in this same general area a Whelan strobe power unit, Trio autopilot servo and and my ELT. Battery is mounted on the firewall. If there is a conflict, what distance between units would result in acceptable compass performance?

Thanks,
Les
Mustang II

 

[dynonsupport]

So magnetic field intensity falls off with the inverse cube of distance. What that means is that every little bit of distance away from ferrous metal and power helps a lot. Generally, a foot of clearance can be sufficient in some installations, but two feet tends to be better.

Any customer feedback on this one?

 

[N941WR]

Les,

I've built an RV-9 so this may or it may not help you.

In my -9 I mounted it to the top of the tailcone, one bay behind the baggage compartment.

This picture should give you an idea of how and where I mounted it: http://www.repucci.com/bill/electrical/oat%20probe%20wire%202.jpg

Never mind the overkill on the rivets.

My thinking was that any metal (tools?) that I might put in the baggage compartment will be on the floor so mounting this up top puts it further away from those types of things. The cables you see hanging in the picture are for the shoulder harness and are SS, so they shouldn’t impact the compass.

The OAT probe runs aft of the compass and is mounted in the 1/2 round bulkhead which is covered by a fiberglass fairing. It seems fairly accurate, once you get flying the cool air displaces the hot air from sitting on the ground. Kind of like the OAT gauge in my truck, you have to get moving before it reads accurately.

 

[Les]

I didn't know about the inverse cube law so that gives me something I can work with...a little bit more is a whole lot better. I can definitely get a foot separation from my strobe power pack but probably not two.

Bill, thankyou for your input too. I like where you mounted yours. Unfortunately, my Mustang sliding canopy has a steel tube cross-member right above this area so I'll have to look for another location. I will be installing my oat probe in a similar area to yours...I think on the fuse just below the horiz stab. By the way many thanks for making your wiring diagrams available...helped me alot. I have dual p-mags as you do. I'm still not sure on how to set up the switches for the pmags but thats a topic for another forum.

Thanks again,
Les

 

[funflying]

I came to the site tonight to comment on my compass, the readings I am getting, and and the location the magnetometer location. Mine is mounted in the tail area under the empenage fairing. There are a few steel bolts in this area, but the area is mostly aluminum. A fellow pilot installed his there and he thought it was working fine. But for me I have always felt the magnetic heading was usually off about twenty degrees. I have rechecked the installation for correct orientation per the instructions, and it is parallel to the wings with the plug side forward. The angle matches the mounting of the D100 in the panel. The readings and set-up on the compass rose worked fine.

I compared the heading between the D100 and the heading indicated on my tru-trak and they differ by about twenty degrees. I also see quit a difference between the heading and the track heading from the GPS. I know the track takes into account the wind adjustment, but it is usually not that much different than the course or bearing.

Anyway, any other recommended checks or ways to varify magnetic heading information?

 

[dynonsupport]

A few ways to obtain magnetic "truth":

If you are in a part of the country where land is cut up with section lines - they're usually oriented exactly North/South/East/West. Flying over them with the aircraft pointed in the direction of the lines (note that you may not track the lines over the ground if there's wind; remember, you care about what direction the airplane is pointed, not where it's going), and see how things compare.

Bringing a simple "boy scout" needle compass, or an aircraft "whiskey" compass, in the cockpit with you can be useful too. Just be aware that there are things in the cockpit, like all of the electrical things in the panel, that can affect it as well.

 

[funflying]

Thanks for the advice!! In fact one of the guys in the hangar across the row offered him whiskey compass to take up and use for varification.  I will cautious of the electrical fields, and be not so trusting of the readings received. I will also use the section lines to try and see what those tell me.

Those north/south/east/west directions would be true headings and not magnetic, correct?

 

[funflying]

Today was one of those days, the ones where the sky was hazy and stable, and when I got up there was little to no wind. Everything matched up within 1 degree so I think everything is pretty close to set as good as it's going to be. My next step is to install the new firmware and see how that looks and works. Thanks