Tuesday, October 9, 2012

Countersinking Stub Spars Begins

Realized I had not registered to vote after the move last summer so found myself waiting in a huge line registering to vote (nothing like waiting until the last day) and after that was accomplished, along with doing errands the remainder of the afternoon, was able to make a token effort to make forward progress on the RV-12.

Now that the rib attach angles are all riveted down onto the left spar (still need to do the right spar later) the next section in the plans begins with working on the stub spar. The stub spar is just behind the leading edge of the wing and extends from the root of the wings at the fuselage, outboard to a point approximately one third of the wing’s length. Because the stub spar is just aft of the wing’s leading edge, the skin rivets in this area are flush because of leading edge air flow considerations. To the best of my knowledge, this is the only place on the wing's skin where Van’s places flush rivets. So for a change, I’m actually countersinking underlying surfaces for flush rivets on the skins ... AND following the plans.

The plans suggest on making a countersink gauge by drilling a 1/4” hole in a piece of scrap aluminum. The edges of the countersunk hole are not to exceed the width of the 1/4" hole in the gauge.  One of the nice things about having a countersink cage is once the proper countersink depth is acquired, the rest of the countersunk holes end up very consistent.

In an effort not to elongate the stub spar holes during the countersinking process, decided it would be best to make a plate to secure the tip of the countersink cutter and prevent drifting.
                          Countersink centering plate held in place with Clecos and the gauge with the 1/4” hole in it.

After the plate was made it took a little bit of time trying to decide how best to secure the stub spar to countersink it. Because the stub spar flanges are on an angle, it makes securing the spar interesting. Figured out a method that appears to be working so will stick with it. There are two stub spars to machine countersink and there are lots and lots of holes. Plus all the holes in the two main spars will also require countersinking at some point, so I have hours and hours of countersinking ahead.

                                 Machine countersinking the stub spar rivet holes to 120 degrees for flush rivets.
                     Using the countersink gauge with a 1/4" hole in it to verify the width of the countersunk hole.