Service Bulletin 12-11-09 Part 2: Landing Gear Beef-up

After the RV-12 fleet started to accumulate a significant number of hours, several suffered wrinkled side skin following hard landings.  Close inspection revealed cracks propagating from the bolt holes in the  center-section channel which allow attachment of the landing gear legs.  The Mothership

developed a beef-up kit for the side skins (previously covered in a blog post) and a kit to substantially strengthen the landing gear attachment.  The kit consists of thicker aluminum and steel plates (shown in the pic at left) which go between the U-shaped bracket (U-1202) and the center section.  The T-shaped aluminum piece (T-1204V) on top of the center-section web is a drill guide with two #30 holes, which the builder was to use to match-drill through the web and the steel and aluminum plates below the web (U-1202C-B and U-1202D-B).  These #30 holes were then to be enlarged to 1/4 inch.  Happily, since I purchased my finish kit in 2016, the U-1202 parts already had the 1/4-inch holes drilled (my experience with match drilling holes has been less than enjoyable).  I only needed to drill the holes in the web.  The problem was that the holes I drilled in the web had to be perfectly aligned with the already-drilled holes in the other parts.  This wasn't an issue with the original beef-up kit since all the holes were drilled together and were automatically aligned.  Past experience using thin aluminum sheet with #30 holes as a drill guide showed that it's quite easy to "hog out" the original holes, causing the holes which are supposed to match the original to be off center.  I had visions of screwing up the center-section channel, which is the main structural member in the fuselage.  These 1/4-inch holes needed to be dead-nuts perfect.

To reduce the chance of misalignment, I ordered additional drill guides from Van's (they're cheap) so I could use stacks of three.  This allowed me to use a #30 transfer punch to accurately center punch the hole in the web and reduce the tendency for the #30 drill to walk off center during the drilling of the #30 pilot hole.  As instructed in the build manual, I used the reflection of the drill bit in the shiny drill guide to keep the #30 bit perpendicular to the web.  I then repeated the process with the 1/4-inch bit.

I won't know how well the holes align until I bolt on the gear.