The goal in locating the SP-2 magnetometer is to place in in the location least affected by magnetic fields or ferrous metal objects. I used a hiking compass to measure needle deflection in certain areas, and I kept coming to the conclusion that the best location was halfway back on the fuselage, just a few inches under the top skin. The problem was that I didn't want to make any more holes in that area, so I decided to make a .20" thick aluminum "bridge" on which to mount it. The bridge spans between the baggage and middle bulkheads and is mounted at the same horizontal angle as the longerons. The SP-2 is mounted using heavy-duty Velcro strips and I believe it should be as free from magnetic deviation as possible.
Looking toward the tail
Looking forward past the SP-2 to the ELT antenna and baggage bulkhead
