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Garmin GMU 11 install question

MikeinPhoenix

MikeinPhoenix

Well Known Member
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Probably a dumb question, but I’ll be installing a GMU 11 in the aft deck (under the horizontal stab) of my RV9A as is commonly done. The Garmin installation instructions state that the GMU 11 must be within 3.0 degrees of “level in-flight cruise attitude”.

Is there any trick to ensure that I’m within the required 3.0 degrees since I don’t know how the aircraft attitude on the ground compares to its in-flight cruise attitude.

Many thanks!

Mike
 
A couple of options:

1.) Level the aircraft in roll and pitch. Similar to what is done when weighing the aircraft on scales. Then use a small carpenters level to make sure your mounting surface is level in all directions. Probably need to make your own mounting shelf with standoffs or buy one of Stein Air's brackets.

2.) Don't physically level the aircraft. Use a digital level like the Aero Angle and zero the level in pitch using the reference datum. Then make sure your GMU shelf or bracket is level in pitch. Do the same for the roll axis by leveling the digital level with the roll datum and check that direction on the mounting shelf.

Once satisfied with one of the two methods secure your bracket. Then when installing the GMU 11 make sure the yaw axis is aligned with the centerline of the GMU and take note what direction the wire exits per Garmin installation instructions.

I put a GMU 11 on the rear spar of a Comanche forward of the aileron. The rear spar was 90 degrees to the aircraft centerline so I only had to tilt the bracket to take out the wing dihedral angle. I used a digital protractor to set the angle an drill the mounting holes. It works perfect.
 
Last edited:
It’s been a while but I’m 99% sure that the longeron on the 6/7/9 is horizontal (and the datum) for the entire length of the aircraft from the cockpit rail to the aft deck.
Therefore the aft deck is also at the same 0 deg attitude.
So no need to measure anything. Just bolt it on making sure it’s accurately aligned with the longitudinal axis and you’re good to go.
All of your calibrations for pitch are done at this 0 degree longeron attitude.
Not technically the flight attitude as that attitude will depend on airspeed / power setting and cg.
 
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