What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

GRT efis installation questions

gerrychuck

Well Known Member
I am currently in the middle of (gradually) installing a used GRT HX efis. I have fabricated a mount for the AHRS behind the baggage compartment, and plan to mount the magnetometer on the shelf in the tail. Couple of questions for those who have gone before:

-What is the consensus on the magnetometer placement? I know some people have had difficulty with the mag in the tail and have gone to the wingtip, but others have had no problem in the back. The only wiring in the neighbourhood is a single cable running down the left side of the compartment to the elevator trim motor. Strobes and nav lighting is all in the wingtips, so no other electricals in the vicinity.
-What is the best mounting method for the mag? I have seen people using both brass screws (maybe difficult to source?) and velcro strips. Leaning toward the velcro at the moment, primarily to make fine tuning position adjustment easier.

-I bought a complete prebuilt harness from Steinair, which should make the wiring connections fairly simple, but....this means I have a harness with big serial connectors on both ends, making running the wires a bit of a challenge; needs a pretty big hole through anything it needs to penetrate, although I should be able to partially disassemble the connector to allow it to go through a relatively small hole without having to re-pin it. Any ideas on routing the wire harness from behind the baggage compartment up to the panel appreciated. My current idea is to cut a slot in the bottom of the flange that the back wall of the baggage compartment screws into, then run the cable inside the side covers through the baggage compartment, through the cover plate in the side bulkhead that sits right in front of the flat actuator mechanism, forward along the floor/sidewall junction through the cockpit, under the cover over the spar and control linkages, and out the front of that cover and up behind the panel. Whew. I am really trying to manage without drilling or cutting any new holes through anything remotely structural.

Thanks in advance for any thoughts.
 
Gerry - the "right" answer is to buy some D-Sub pin insertion/extraction tools and learn how to use them. Then de-pin the connectors going to the remote parts of the airplane after carefully taking note of which wire went into which socket in the connector.

This really isn't difficult. For the magnetometer, if you have the new digital one, it's four wires, or about 5 minutes work to de-pin the connector and about the same to re-pin it when you've got the wires routed. The AHARS is a few more pins, depending on which variation you have.

No matter how you cut it, the right way is to do it like the pro's and route only the wires, not the connectors, through the aircraft structure, then re-attach the connectors once you have the wires properly run.

BTW, Stein also sells the insertion/extraction tools and I think he has a "how to" video on youtube. It really isn't a big deal - far easier than learning how to rivet.
 
Presumably the ?single cable? to the trim motor is actually a pair of wires. As long as the pair are close to each other they should not be an issue. How close are the rudder cables? Or steel cables for the shoulder harness?
My AHRS and magnetometer are on a shelf behind the baggage area in my -10; works fine.
 
My old style analog magnetometer has worked fine on the empenage deck for 6 years.
Mount it with non magnetic hardware. Velcro is silly. What holds the velcro to the airframe? Adhesive? ALL of the common adhesives (including velcro) have failed in the places I tried to use them. Do you want your magnetometer flopping around where it can jam something?
 
My installations

On my RV7a, 11 years ago I mounted the AHRS in he front left corner between subpanel and firewall as my neighbor had done. I mounted the magnetometer in the left wingtip. This has worked very well.

On my RV10, 8 years ago I mounted the AHRS on a shelf behind baggage wall and the magnetometer higher between shelf and wall. That has worked also.
 
Magnetometer

We just did a Skyview upgrade to our RV7. Mounted a remote magnetometer on the shelf in the tail and the ADHRS in the right front corner behind the panel. All works perfectly.
 
UikqYVVm.jpg
[/IMG]


This is where I mounted my magnetometer during a recent upgrade. I made a shelf to get the mag up and away from the moving rudder cables. As you can see, I put it in a ziplock bag, then used large zip ties to secure it. Its very secure, and in an area that lends itself to inspection at annual. So far no troubles. One thing that you can do is download an app to your cell phone that detects magnetic interference. Place your phone in the area you intend to place your magnetometer and power up wire runs and move controls etc to see if any of it is an issue. The one I used is called magnetmeter.

I agree with removing pins from connectors to route wires. Its really not the difficult with the right tool.
 
Wires should have little to no impact on the operation of the magnetometer(s) provided they are shielded wiring to them. Since you have the harness from Stein, then I would say you will not see any interference from strobe wiring or the like. I have run all of my wires through the center tunnel section with no interference from any of them.

Where you could see interference would be in mounting the magnetometer(s) near steel components. That would include the slider canopy (if you have a slider). In my case, I had initially built a bracket directly behind the baggage bulkhead.


It was not until I powered up the GRT's that I discovered the metal frame of the slider, when in the open position, sent my instruments into a "tizzy". I had to move the brackets one more bulkhead back into the tail cone. Have had no problems in 8 years in that position.

 
Last edited:
Wing tip for magnetometer

I had serious electro-magnetic interference every time I keyed my radio when the magnetometer was located on the shelf below the rudder. There is a test you can do before securing the magnetometer to any location to evaluate electro-magnetic interference. Go to General Settings and watch the counter when you key your radio and/or turn on equipment. If the act of keying the mike or turning on equipment causes a rapid counter change then that location for the magnetometer is not a good choice.

On my panel I have two different EFIS systems. Primary is my GRT Horizon WS system. Backup is a Dynon D10A. When I bought the RV both EFIS systems were negatively impacted by electro-magnetic interference (the GRT more than the Dynon) because both magnetometers were located on the shelf below the rudder which was just a few feet from my comm antenna. GRT strongly recommended I move both magnetometers to the wing tip (away the high emission equipment). When I did that both EFIS systems significantly improved their heading reliability.

Good luck. I also recommend non-magnetic material be used to secure your magnetometers. I built aluminum shelves and mounted them to my wing tip rib and secured the magnetometers with nylon screws and nuts. Keep them as far away from your wing tip lights as possible due to some possible interference. As Steve said shielded wire is best for this purpose. I ran my wire through blue flex tubing (and secured that with plastic strips) I bought at Lowe?s to protect the wire from chafing. Good luck.
 
My GRT legacy magnetometer is on the empennage shelf as others have done. My local Ace hardware had all the brass screws I needed, those are also pretty easy to find from lots of sources on line including my fave vendor, McMaster-Carr (might not be an option in Canada). My comm antenna is on the belly forward of the wing spar, which may explain interference from radio transmissions was a non-issue in my case.

As others have written, get a D-sub de-pinning tool and remove the pins from the connector shell. Only proper way to do it. You'll want the red/white pin tool, for example this one:
https://www.steinair.com/product/insertionremoval-tool-for-standard-d-sub-pins-mil-spec/
 
Last edited:
Thanks so much to everyone who took the time to respond; all the feedback is hugely appreciated. I am sure that the advice to de-pin and re-pin connectors is the proper thing to do. I just haven't done it before so I was gunshy. Thank you for steering me firmly in the direction I clearly needed to go. I will have to pin the connector from a gray code converter to my transponder, and perhaps from the efis to my Trutrak autopilot as well, so I was going to have to get one of the pinning tools anyway. I think I was just scared to mess up the fine work done by Stein! My setup is a legacy magnetometer and AHRS, so there shouldn't be too many pins to fuss with.

In addition, once I'm down to just the wires, I will be able to run them through a piece of plastic conduit that runs under the baggage compartment and cockpit floor from the bottom of the back baggage wall bulkhead. The builder put one in each side, with one currently unused and waiting to be given a purpose in life.

Magnetometer: I think I will still try to use the empennage shelf to start with, as it is so much easier than the other options and so easily accessed for inspections. I totally see the logic in what rzbill said about velcro and will use solid fasteners.
I have already installed magnet-meter on my phone and will check for interference (thanks for that tip painless). If there are problems with interference, I may try RVbySDI's solution before going to the wingtip; I have already fabbed a very similar shelf for the AHRS and still have some 1/8" aluminum lying around, so that option could be done pretty easily and keep the wiring run to the AHRS very simple.

Thanks again to everybody for the help; you have really helped clarify things for me and made some decisions much easier.
 
Wires should have little to no impact on the operation of the magnetometer(s) provided they are shielded wiring to them.

Strictly speaking, the braided shield does little to ?shield? magnetic fields. What is important is that the shield (or even better, a second wire twisted with the first) carries all of the return current, so you get equal but opposite fields generated, which add to zero. This won?t work if some current can bypass the shield, e.g., it is important that the device does not/cannot use the airframe as a conductor to return to ground.
 
Strictly speaking, the braided shield does little to ?shield? magnetic fields. What is important is that the shield (or even better, a second wire twisted with the first) carries all of the return current, so you get equal but opposite fields generated, which add to zero. This won?t work if some current can bypass the shield, e.g., it is important that the device does not/cannot use the airframe as a conductor to return to ground.
Bob,
Just to clarify my point, I was referring to the shielded wires capability of preventing electrical interference to the actual wiring if the shielded magnetometer wires are routed near other wires (shielded or not) such as a strobe light wire, etc. I was not necessarily thinking about the shielded wires preventing an adverse effect on the magnetometers themselves if they were in close proximity to the magnetometers. Never the less, in my build, I did feel it important to make sure there was nothing electrical, mechanical or metallurgical that would come in close proximity to the actual magnetometers.
 
Gerry,
Let me also clarify what I meant by checking your ?counter.?

In the general setup menu of your EFIS there is a serial port that shows ?AHRS-1/Air Data Computer #1.? That serial port is where your EFIS gets its Attitude, Heading Reference System information. Look at that serial port ?input counter? after you have temporarily placed your magnetometer where you want to place it. Then key your mic, turn on electrical equipment like your transponder, strobe lights, etc. - any thing that might emit an electromagnetic pulse.

If your serial port counter rapidly increases then your AHRS system, which your magnetometer is a sub part of, is getting electrical interference that will effect your heading reference over time. The counter is always changing numbers but what your looking for is a rapid change in numbers because you did something else electronically.

I?m not sure any iPhone app will give you the same level of AHRS interference information that your serial port counter will because this is directly reading what?s being transmitted to your EFIS.

If the input counter rate of change stays consistent then that location will probably work okay.
 
I am sure that the advice to de-pin and re-pin connectors is the proper thing to do. I just haven't done it before so I was gunshy.

I'm just finishing up the wiring phase and got the typical WTFO education with dsubs. FWIW, really watch Steins video a couple of times. It frustrated the heck out of me trying to get pins out.....until I finally realized I was using the wrong end of the pinning tool. One end is a half circle, the other a near complete circle. The half is used to insert, the near complete is for retracting as it encompases the wire then slides into the dsub hole. There are two dsub "teeth" 180deg from each other deep in the hole and are in line with the long axis of the dsub. Sometimes you need to wiggle the extractor to get it past the teeth, or maybe turn it 90 degrees, then back to the long axis. Took me an hour of frustration to figure that out. Then it was a breeze. Buy two metal extractors (not the plastic ones) cause they'll get bent up while youre learning the "touch".
 
I?m not sure any iPhone app will give you the same level of AHRS interference information that your serial port counter will because this is directly reading what?s being transmitted to your EFIS.

My reference to using an app for location of the magnetometer comes from a suggestion made by GRT in their installation instructions. Its more like a way to screen for any magnetic interference prior to making a decision where to locate the magnetometer.
 
I used the free Droid Sense for my android phone. Propped the phone up right beside the rudder/elevator cables and moved them about with no change in the sensed magnetic fields. Then I moved the phone to where I was hoping to mount the two magnetometers and taped it in place, once again moving all the control surfaces. No change in the Droid Sense magnetic field measurements. Installed the magnetometers and they are fine.

GRT's recommendation to use a phone-based app to sense magnetic fields proved a cheap and effective means for me to ensure I had not chosen an inappropriate mounting location for the magnetometers.
 
Gerry,
Let me also clarify what I meant by checking your ?counter.?

In the general setup menu of your EFIS there is a serial port that shows ?AHRS-1/Air Data Computer #1.? That serial port is where your EFIS gets its Attitude, Heading Reference System information. Look at that serial port ?input counter? after you have temporarily placed your magnetometer where you want to place it. Then key your mic, turn on electrical equipment like your transponder, strobe lights, etc. - any thing that might emit an electromagnetic pulse.

If your serial port counter rapidly increases then your AHRS system, which your magnetometer is a sub part of, is getting electrical interference that will effect your heading reference over time. The counter is always changing numbers but what your looking for is a rapid change in numbers because you did something else electronically.

I?m not sure any iPhone app will give you the same level of AHRS interference information that your serial port counter will because this is directly reading what?s being transmitted to your EFIS.

If the input counter rate of change stays consistent then that location will probably work okay.


Gotcha. Thanks.


I'm just finishing up the wiring phase and got the typical WTFO education with dsubs. FWIW, really watch Steins video a couple of times. It frustrated the heck out of me trying to get pins out.....until I finally realized I was using the wrong end of the pinning tool. One end is a half circle, the other a near complete circle. The half is used to insert, the near complete is for retracting as it encompases the wire then slides into the dsub hole. There are two dsub "teeth" 180deg from each other deep in the hole and are in line with the long axis of the dsub. Sometimes you need to wiggle the extractor to get it past the teeth, or maybe turn it 90 degrees, then back to the long axis. Took me an hour of frustration to figure that out. Then it was a breeze. Buy two metal extractors (not the plastic ones) cause they'll get bent up while youre learning the "touch".


Good tips. Thank you. I have 1 tool on order; sounds like a second isn't a bad idea.


I used the free Droid Sense for my android phone. Propped the phone up right beside the rudder/elevator cables and moved them about with no change in the sensed magnetic fields. Then I moved the phone to where I was hoping to mount the two magnetometers and taped it in place, once again moving all the control surfaces. No change in the Droid Sense magnetic field measurements. Installed the magnetometers and they are fine.

GRT's recommendation to use a phone-based app to sense magnetic fields proved a cheap and effective means for me to ensure I had not chosen an inappropriate mounting location for the magnetometers.


Thanks!
 
Back
Top