Tuesday, September 11, 2012

Tail Cone Dimple Mania Completed With Noodle Bridge

The original plan was to prime today but decided to just forge ahead and continue dimpling the remainder of the tail cone components and have that task completed in total. The left and right F-1279 upper tail cone skins proved to be quite a challenge and took approximately two hours each to dimple (twice as long as the other skins). The biggest issue being the F-1279 skins are totally curved and also taper from fore to aft making it necessary to continually make adjustments to the way the skin was propped up to keep the holes in the skins square with the C-frame’s dimple dies. Nothing hard really, just time consuming to have to constantly check to make sure the C-frame was perfectly perpendicular to every hole being dimpled and adjust accordingly.
                                               Making use of tall items with mass that were in the shop to help
                                               hold the F-1279 skin in position for dimpling with the C-frame.

Decided to finish up with all the dimpling and moved ahead dimpling the F1278 tail cone top skin. Not all the holes receive dimples … the holes for the triangular plate used for mounting the vertical stabilizer’s forward skin do not need to be dimpled, nor do the seven holes aft of the mounting plate for the vertical stabilizer. I elected to dimple the four top holes that go into the fuselage frame for consistency but they will not be seen and could just as well be the standard LP4-3 pop rivet.
                                               Vertical stabilizer mounting plate slot and mounting area for the
                                               triangular plate used to mount the vertical stabilizer’s forward skin.

For being a flat piece of metal, dimpling was quite easy and very fast but the F-1278 top skin has its own unique challenges. Because it does not have any bent edges or J stiffeners built in, it is very floppy and just droops over the bench at an alarming angle. I did not want to join the two work benches just for one piece of aluminum, so once again found the pool noodles quite useful to support the skin hanging over the edge of the work bench.
                                Pool noodles used to make a bridge to support the F-1278 top skin during dimpling.

Return from the future: The portion of the top skin between the F-1210 far aft fuselage frame and the aft bulkhead the plans say to add extra break really needs it … especially the last 12” to 14”. If you are planning on dimpling your RV-12 for flush rivets as I am doing, hold off on dimpling the F-1278 top skin until the top skin is test fit onto the tail cone assembly. Once dimpled, you can not add more break.