View Single Post
  #3  
Old 01-24-2017, 10:19 PM
KatieB's Avatar
KatieB KatieB is offline
 
Join Date: Jun 2010
Location: Belton, MO
Posts: 1,145
Default Magnetometer Installation

One of the quirks of the Garmin installation is its super-sensitive magnetic field sensor. Like the GRT systems, the Garmin magnetometer does much more than function as a compass—it provides data to the ADAHRS as part of the calculation of the attitude of the aircraft in space. If you ask me how it does this, my answer will always be “PFM”—that is, Pure F-ing Magic.

There is a list in the installation manual of things that the magnetometer cannot be near. Basically, it’s servo motors, current-carrying wires, control cables, ferrous metals, and anything that’s been magnetized. In a plane as tiny as the RV-3, it’s a real challenge to find an interference-free spot for it. The wingtip is often recommended, but it is awfully close to the steel aileron counterweights and the wires for the LED tip lights. The tail shelf “aft deck” under the vertical stab is also a recommended location for RV’s, but in mine, it would place the magnetometer within a foot of the steel tail spring mount—and I know for a fact that it’s magnetized because I’ve poked around with a magnet so many times over the past 6 years to fish out dropped nuts and washers! It’s also susceptible to water damage from rain dripping inside the tail fairing at our great air shows. So, that’s out.

Here's the shelf after I bent the support flanges. It's just a piece of .032 out of the trim bundle from the empennage kit.
[IMG]2016-12-17_03-31-03 by jabiruchick, on Flickr[/IMG]

And the neat little mounting ring Garmin supplies with the Magnetometer...
2016-12-17_03-31-47 by jabiruchick, on Flickr

There is one place where the nearest sources of interference are the rudder cables and trim cable… and it’s halfway down the tail cone, between the longerons and a reasonable distance behind the pitch servo. I read on here and in the Garmin installation manual that some RV-8 builders mount their magnetometer on a shelf suspended across the longerons in this location. So, that’s what I did. Let me tell you, if you have a chance to install this thing before you rivet your top turtledeck skin on, DO IT! There are two mechanics at our shop and me, a halfway-wannabe mechanic, and despite the fact that I'm a well-fed Midwestern girl, I'm the only one that remotely fits back there. If I couldn’t do it, nobody could! So I did. With more grunting and swearing than a well-behaved woman would ever do. But nobody has ever accused me of being well-behaved.

[IMG]2016-12-17_03-32-01 by jabiruchick, on Flickr[/IMG]

Here it is in its new home. The camera angle makes the whole thing look a little scatty-wompus, but I assure you it's all straight.

[IMG]0114171458 by jabiruchick, on Flickr[/IMG]
__________________
Katie Bosman
EAA Homebuilt Aircraft Council
Rebuilt most of SNF tornado victim RV-3B Tony Boy II (had to sell him, but he's flying!)
VAF Dues Paid 2021!
Thoughts & opinions expressed here are my own, and not those of my employer.

Last edited by KatieB : 01-24-2017 at 10:23 PM.
Reply With Quote