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GMU-11 Installation Location?

David Carter

Well Known Member
Patron
Hi,

After lurking here for at least a decade, I recently purchased a flying RV-7A with a steam-gauge "4-pack" (no AI or DG) & TruTrak Vision AP. I'm planning to install a pair of G5s & a GMU-11 for now, with plans to move to a G3X panel later.

I've searched the forums, but haven't located any definitive advice on where & how to mount the GMU-11. For those of you who have done this, where did you mount it? Pictures would be a great help.

If mounting in the wing, how did you deal with mounting alignment in the yaw axis? (Pitch axis alignment seems easy.)

Thanks for any & all advice!
 
I usually make a shelf between the longerons 1 or 2 bulkheads back from the rear baggage wall.
 
Under Vertical Stabilizer

I mounted mine under ther vertical Stabilizer just right of center. Works perfect with no errors in the calibration or interference tests.
 
I mounted mine under ther vertical Stabilizer just right of center. Works perfect with no errors in the calibration or interference tests.

Surprising. You have a tailwheel, tailwheel spring, tailwheel weldment, steel elevator horns, plus hardware back there.

Can I send you money for a lottery ticket? ;-)
 
Left wingtip. Passes the internal testing with flying colors. I used a Garmin general purpose mount which allows for angle adjustment. I chose this location to keep as forward a CG as possible. It?s not much but every little bit helps.
 
Left wingtip. Passes the internal testing with flying colors. I used a Garmin general purpose mount which allows for angle adjustment. I chose this location to keep as forward a CG as possible. It?s not much but every little bit helps.

That's a really good point. My plane is already light in the front (fixed-pitch prop), and anything I can do to keep CG forward is a win.

Any particular reason for left rather than right?

Do you happen to know the Garmin part number for that mount?
 
I've had good luck with the wing locations but I've also had no trouble with the RV7 rear deck location of the GMU22 on the A models.

I also prefer to avoid the pitot heat wiring so i generally use the RH wing. With the GMU using the CAN bus it looks like an easier install by just extending the CAN bus from the right wing roll servo.
 
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Wing tip install question

My gmu11 arrives today. Why don?t strobe lights and aileron heim joints cause a problem in the wing ?
 
Hi,

After lurking here for at least a decade, I recently purchased a flying RV-7A with a steam-gauge "4-pack" (no AI or DG) & TruTrak Vision AP. I'm planning to install a pair of G5s & a GMU-11 for now, with plans to move to a G3X panel later.

I've searched the forums, but haven't located any definitive advice on where & how to mount the GMU-11. For those of you who have done this, where did you mount it? Pictures would be a great help.

If mounting in the wing, how did you deal with mounting alignment in the yaw axis? (Pitch axis alignment seems easy.)

Thanks for any & all advice!

I just completed a GMU11 installation in two RV-8s and both calibrated successfully the first time. I bolted the GMU11 with the supplied SS bolts to a scrap piece of .063 aluminum, and then pop riveted the aluminum mounting plate over the 4" hole in the aft fuselage deck below the vertical stabilizer. It is easy to draw a centerline on the .063 mounting plate and then mount the GMU11 centered on that line. Then draw a center line on the aft fuselage deck. Simply line up the centerline on the mounting plate with the aft deck and pop rivet it in using aluminum rivets.

It helps to have a 90 degree angle drill to drill the holes in the aft deck under the vertical stabilizer.

For what it's worth: The Doll has a GMU44 mounted in the aft deck in that 4 inch hole, and has been working well there for years. The horns and tailwheel spring have no effect on the Doll's instillation. The aft deck is already level with the aircraft in flight. Access to the magnetometer only requires removing the empennage fairing. Running the wiring is easy through the fuselage. IMHO, running the wiring through a mounted wing is more problematic. Good luck with your choice.
 
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Skid accuracy question

does mounting the GMU-11 in a wing or the HS stabiliser deck make the skid response more sensitive compared to mounting it more toward the forward part of the fuse ? The reason for the question is MGL encouraged mounting the SP7 module ( my RV3) under the seat of the pilot to get the best AHRS response.
 
Here is how my Dynon AD-AHRS is mounted in my -7A. The magnetometer is built-in.

x9nH19rl.jpg
 
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does mounting the GMU-11 in a wing or the HS stabiliser deck make the skid response more sensitive compared to mounting it more toward the forward part of the fuse ? The reason for the question is MGL encouraged mounting the SP7 module ( my RV3) under the seat of the pilot to get the best AHRS response.

The GMU units are magnetometer (heading info) only, the ADAHRS is mounted seperately.
 
That's a really good point. My plane is already light in the front (fixed-pitch prop), and anything I can do to keep CG forward is a win.

Any particular reason for left rather than right?

Do you happen to know the Garmin part number for that mount?

My right wing has the roll servo and a wingtip VOR antenna. My left has the pitot heat. There was no problem with the pitot heat as it is fairly far from the magnetometer. Also, I have wingtip lighting (all led) and again, no effect.

In the first 125 hrs, I have seen no anomalies.
 
After reading this in the Garmin 3X_Touch_Install Manual (available on their website), They recommend either aft fuselage or wing location. (if that info is helpful.)

A.2 Van?s Aircraft
A.2.1 RV-7/9
The typical GMU magnetometer mounting location in RV-7/9 aircraft is in the aft fuselage, on the aft deck (F-714), just ahead of the horizontal stabilizer and just aft of the F-709 bulkhead. This location provides a level pitch and roll reference, and acceptable separation from excessive magnetic disturbances in typical RV-7/9 aircraft.
The wingtip can be used as an alternate GMU magnetometer mounting location for RV aircraft. Ensure adequate separation from steel aileron counterweights, transmitting antennas, and lighting fixtures, and
follow the wingtip light wiring guidance for in Section 14.4 or Section 15.4.

More details on installation: can be found in Chapter 14, GMU 11 Installation of the G3X Touch manual.
 
Does the big steel counterweight running in the aileron leading edge in an RV8 cause a problem? I checked the wingtip location on mine today, and a handheld compass swung 60 degrees off when held near the aileron front!
At the midpoint between aft baggage bulkhead and HS mounting holes, there was a 5 degree swing caused by the Garmin pitch servo mount. The only place I?ve found to be completely error free is the tip of the elevator or the VS.
I can get an 8mm conduit down the leading edge of the hs without difficulty, so I was thinking of using this as my location. Any thoughts?
 
They don't cause a problem generally if you run a twisted pair of the positive and ground, which cancels the magnetic field (right hand rule). I literally just took the two wires and twisted them together by hand. Not complicated. You should do this for any power wires running out to the tip. I have mine in the left wing tip on a bracket right at the mainspar and it works great.
I'll dig up a picture of my bracket and post it later. I went with the tip as it ment less wires running through my baggage tunnel (which was near capacity with other wires) and also kept my CG forward.
Tom.
RV-7
 
Sorry, can't find the picture of the bracket. It's not complicated. Just a lightweight braced structure that I bolted in place to the last wing rib using non magnetic instrument screws (I think they were bronze or something like that).

Tom.
 
Has anyone mounted it on the aft deck with the Antisplat VS stainless steel mod? I don?t know if there?s enough steel in that area to cause an error.
 
I?m thinking about mounting my GMU-11 on the aft deck. Does anyone have any pics that show this arrangement?

I'm planning on doing the same. I've searched all over and couldn't find any pics of a GMU-11 mounted there. I've seen several pictures of GMU-22s, however, mounted on a plate sitting on top of one the holes in the deck (links to their respective posts).
Brian Chesteen
Doug Reeves
Bobby Hester

Went out earlier this week to take a look, and I don't see any reason why the GMU-11 wouldn't work in the same spot. Probably a bit further aft than where it is sitting in the pic to leave a little more room for the connector. Or maybe even right on the centerline?

2uqzwp0.jpg
 
SteinAir appears to offer a "aft deck mount" specifically for the GMU 11, which they claim "works particularly well for the RV7 and RV9". Perhaps they ship with an installation manual with pictures of their setup. Not sure I understand what the advantage of this mount is vs. just attaching directly to the aft deck.

Aft-Deck-5-600x600.jpg
 
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Ryan,

I saw that. I've just ordered an LRU Kit from Stein. So far I'm not sure of the advantage of the bracket over just a flat sheet for mounting the GMU-11. Once I get my GMU-11 I'll move it around a little to see how everything fits and then decide.

BTW, I did ask Stein if he had any pics of that bracket in use and he couldn't find any.
 
Just for reference, here's my install under the vertical stabilizer in my RV-8.



Drawing the centerline is obviously much easier if the stab is removed.

The little shelf you can buy from Spruce and Stein would probably have helped me here if I had know about it. I had run an electric trim wire through the 4" hole in the stabilizer for the initial build and now I had to move that wire so the plate would lay flat for the GMU11. That move required me to rewire the AMP plug (seen in the background) to my electric trim which was a real pain (I hate removing those pins). That process took longer than the GMU 11 installation.

Chris
 
Maybe use a digital compass? Make sure it's pointed in the same direction and try different locations inside the airplane, comparing it to outside the airplane.
 
IIRC, the installation instructions for the G5/ GMU11 have you connect the two together, power up the units and then move the GMU11 around to different locations while moving the control surfaces to find an acceptable spot.
 
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