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RV-8 GMU-22 mount location

P

Pman

Active Member
All,

Has anyone WITH MANUAL ELEVATOR TRIM installed the GMU-22 (magnetometer) in the aft fuselage just aft of the F-809 bulkhead...??
This is the bulkhead just aft of the static ports.

I realize some have been successful mounting their GMU-22 in this location, however, my concern is the proximity of the "manual elevator trim cable"---I'm wondering if the trim cable would interfere with the magnetometer?

Just trying to determine if anyone with manual elevator trim has been successful mounting their GMU-22 in this location?

Thanks in advance for your response.

Mike Perillo
RV8
 
I mounted there in a manual trim -9A and DID have issues. not sure if it was the manual trim or elevator horns. I never was successful degaussing and ended up building a shelf in front of the rear bulkhead. The -8 is narrower and would be more difficult to install at that location. I think im going out to the wingtip for my -8.
 
Pman said:
All,

Has anyone WITH MANUAL ELEVATOR TRIM installed the GMU-22 (magnetometer) in the aft fuselage just aft of the F-809 bulkhead...??
This is the bulkhead just aft of the static ports.

I realize some have been successful mounting their GMU-22 in this location, however, my concern is the proximity of the "manual elevator trim cable"---I'm wondering if the trim cable would interfere with the magnetometer?

Just trying to determine if anyone with manual elevator trim has been successful mounting their GMU-22 in this location?

Thanks in advance for your response.

Mike Perillo
RV8
Click to expand...

Mike, I think a tail-mounted GMU 22 in an RV-8 has a potential for problems. In my opinion, there are two better choices out there: one a dorsal shelf and the other a wingtip mount. Try doing a search if you're interested in either of these. I think the dorsal shelf is mounted just aft of the baggage compartment, maybe not as far back as what you are describing.

We used the wingtip mount in our -8 and have had zero issues. You just have to be aware of the potential for interference from the iron pipe in the leading edge of the aileron. You should be able to find the location that worked for us in the archives, otherwise let me know and I can send you a photo.

Mike, here is the thread with the wing mount photo: http://www.vansairforce.com/community/showthread.php?t=143552&highlight=gmu+wingtip+mount
 
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After a number of installs, I think the wing mount location is preferable and less likely to have issues overall than a tail mounted unit (at least in a 4/8/10). I did struggle with an RV4 install quite a bit when I mounted the GMU in the tail, the trim cable definitely was magnetized and I could not get it degaussed so I ended up moving the GMU to the wing. The wing is not perfect either as you struggle with the aileron CW along with the landing/nav/strobe lights. I was able to get it calibrated in the wing finally after degaussing the aileron CW and aileron hinge/hardware.

It's also a bit easier to install in the wing IMO as you don't have to make a mount for it back in the tail. You can buy a nice universal mount from Garmin that makes wing tip mounting a breeze.
 
+ 1, per Walt

Walt has it here with this one. Only one tip off of his post. We found that mounting the unit between the aft spar and the main spar was a good place to build a bracket and mount it there. That is just far enough away from the 4130 and the water pipe that the unit will calibrate out just fine. The problem with mounting these units anywhere is the electro static field that is sent through the airframe close to the unit if you have anything grounded close to the units. We had a landing light, strobe, marker light and a servo in the wing we used to mount the unit. We found that once we removed the local grounds for all those other devices in that wing and ran a dedicated ground for all of them back through the wing into the center section of the air frame the electrostatic field in that area went away as there was no more flow through the airframe at that vicinity. I would think this would be much the same problem with mounting the unit anywhere in the aircraft. Some of the guys like to run separate ground systems for the whole aircraft so they can keep the "EMI" as low as possible. We have found that it is not always needed to go to that length with a common Day, Night VFR aircraft system.
Just what we ran into, hope it helps, Yours, R.E.A. III #80888
 
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Guys,
Thanks for the comments and info..., it's greatly appreciated.
With the auto pilot servo in the right wing, I'll plan to install the GMU in the left wing-tip.
Also, FYI; the latest/newly revised Garmin G3X-Touch Install Manual (Revision AA, NOV 2016), added info regarding fuselage GMU installation for the RV6/8/10.
However, nothing is mentioned regarding manual or electric trim options(?). As you all know, for those RV8 builders installing "manual elevator trim", the cable routing will result in very close proximity to the GMU fuselage location.
Thanks again!

Mike Perillo
RV8
 
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Mike, I do see that a specific note was added regarding 6/8/10 installation, thanks. Why would the 6 be any different from the 7's recommended install location? That's where I'm mounting mine, I'll report back...
 
AlexPeterson said:
Mike, I do see that a specific note was added regarding 6/8/10 installation, thanks. Why would the 6 be any different from the 7's recommended install location? That's where I'm mounting mine, I'll report back...
Click to expand...

Just a point of reference: I have the GMU mounted in the tail on my RV-6 (electric trim) and have had no issues in over 3 years.

 
GMU 22 RV-8 Installation Location

Appendix Page A-3 of The Garmin Installation Manual:

"A.2.2 RV-6/8/10
In RV-6/8/10 aircraft, the GMU 22 is frequently mounted on a rigid aluminum shelf suspended between
the aft fuselage longerons, midway between the baggage bulkhead and empennage. If this location is used,
ensure that the seat belt cables and attachment hardware are not magnetized."

However, it does not address rear mounted battery and/or pitch servo. Will be installing in the left wing.
 
GMU-11 location RV-4

IMG_7669.jpg


Is this location possible to use for the GMU-11.

The Com antenna can be seen just above the shelf.
GPS antenna will be located nearby as well.

Otherwise the distance to other electronics is reasonable.
 
Regarding the above post----- "Is this location possible to use for the GMU-11.

The Com antenna can be seen just above the shelf.
GPS antenna will be located nearby as well.

Otherwise the distance to other electronics is reasonable."




Can't tell by your photo.?. However, are you installing "manual trim". If so, I can tell you when I considered mounting my GMU in the same vicinity as you have proposed, the manual trim cable (being ferrous) caused considerable magnetic disturbance..., I opted to install my GMU in the wing tip.

Best of luck, hope it works for you!

Mike
 
Hi Mike

The pictures shows the avionics rack in the baggage area on my 4

Im installing the electric elevator trim in the tail.

I can route that cable at the bottom of the fuselage using shielded cable.

However, the elevator servo (GSA28) will be mounted just below it on the elevator crank
 
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Hi Espen,

Sounds like you have a good plan......, I wasn't sure if you were planning to install the "manual" elevator trim.... Regarding the GMU, installing an electric elevator trim (with shielded wiring) is less problematic than the "manual trim cable".

Good luck, and have fun with your build!!

Mike
 
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