The Comant CI-105 blade transponder antenna is attached to the fusalage with 2 lock washers and 2 nuts. I decided to fabricate a reinforcing plate from .032 aluminum sheet. I happened to find a template on the internet for the CI-105 that would work out perfect. I printed out a scale copy and used that to fabricate the 2 plates. The plate are 4" wide and 5 3/8" long. I cut out the template and placed it over the aluminum sheet and marked all the rivet and mounting holes. I drilled out the 2 mounting holes to #12 and all the rivet holes to #40. The BNC connector hole I drilled to 5/8" using my step drill. I repeated the process for the 2nd plate and deburred all the holes. I decided to mount the transponder antenna just aft of the baggage compartment bulkhead and toward the right edge near the stringer. I placed the plate on the floor and made a rough location mark. Then I marked a parallel line using the center of the fusalage as a guide. I placed the plate parallel to the line and drilled my first #40 hole. I placed a cleco in the hole and continued drilling the remaining rivet holes. I also drilled the mounting holes and the BNC connector holes. I deburred the holes and checked the fit of the antenna. Last, using my rivet dimple set with the nail holes and my hand squeezer, I dimpled all the rivet holes in the skin. Later I will machine countersink the reinforcing plates, clean and prime.
