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Old 04-26-2018, 07:12 AM
Danny King's Avatar
Danny King Danny King is offline
Join Date: Dec 2004
Location: Southlake, Texas
Posts: 593

Originally Posted by David Carter View Post

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.
Danny King
Beautiful Doll 80434 TT 1600 hours
I0360 A1B6 200 HP
Christen Inverted Oil
First Flight 12 July 2000
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Last edited by Danny King : 04-26-2018 at 07:47 AM.
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Old 04-26-2018, 07:58 AM
Larry DeCamp's Avatar
Larry DeCamp Larry DeCamp is online now
Join Date: Apr 2010
Location: Clinton, Indiana
Posts: 790
Default 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.
Larry DeCamp
RV-3B flying w/ carb / Pmags / Catto 2b / Steam
RV-4 fastback w/ Superior XP360/AFP/G3X/CPI/Catto3b
Clinton, IN
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Old 04-26-2018, 08:03 AM
Raymo's Avatar
Raymo Raymo is offline
Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 1,966

Here is how my Dynon AD-AHRS is mounted in my -7A. The magnetometer is built-in.

RV-7A - Slider - N495KL - First flt 27 Jan 17
O-360-A4M w/ AFP FM-150 FI, Dual PMags, Vetterman Trombone Exh, SkyTech starter, BandC Alt (PP failed after 226 hrs)
Catto 3 blade NLE, FlightLines Interior, James cowl, plenum & intake, Anti-Splat -14 seat mod and nose gear support
All lines by TSFlightLines

"The object of the game, gentlemen, is not to cheat death: the object is not to let him play."
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Last edited by Raymo : 04-26-2018 at 09:23 AM.
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Old 04-26-2018, 08:26 AM
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Walt Walt is offline
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,092

Originally Posted by Larry DeCamp View Post
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.
Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
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RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
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Old 04-26-2018, 09:51 AM
StickNRudder StickNRudder is offline
Join Date: Apr 2015
Location: Tustin, CA
Posts: 38

Originally Posted by David Carter View Post
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.
Rick Woods
N5427W == Jack, Hank, Barbara, and Rick Woods.
Flying, but not done, never done.
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Old 04-26-2018, 04:33 PM
Alien Alien is offline
Join Date: Jan 2017
Location: Seabrook, TX
Posts: 2

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 Vanís 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.
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Old 12-29-2018, 02:36 AM
Huskyhipdoc Huskyhipdoc is offline
Join Date: Feb 2018
Location: Cornwall, UK
Posts: 23

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 Iíve 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?
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Old 05-02-2019, 09:19 AM
rapid_ascent rapid_ascent is offline
Join Date: Mar 2008
Location: Dublin, CA
Posts: 975

Iím thinking about mounting my GMU-11 on the aft deck. Does anyone have any pics that show this arrangement?
Ray Tonks
2018 Donation Paid
RV-7 Fuselage in progress
* Rolled the Fuselage
RV-7 SB Wings
* Both Wings fully skinned
* Fuel Tanks Complete - No leaks finally
* Ailerons Complete
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RV-7 Empennage - Complete (a little fiberglass work left)
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Old 05-02-2019, 02:44 PM
tgmillso tgmillso is offline
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 678

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.
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Old 05-02-2019, 05:14 PM
tgmillso tgmillso is offline
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 678

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).

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