Today was perhaps a good example of how quickly things can move along in the assembly process if all the parts are made (like a kit, instead of scratch building as we are) and if we don’t mess around thinking too hard about stuff.
Tim was busy until around 1:30 and I had a load of issues to attend to with regard to work (I so much for vacation but at least I could take care of it without leaving home). The morning was spent catching up on email and getting things prepped for dinner (gotta keep the “sweetie” happy). After all that it was almost 12:30 before I got into the garage to even turn on the heat. I was in the garage actually doing something by time Tim arrive. I had been on a conference call and simple kept my headset on while on mute and listening in as i drilled holes in the skin to finish the top side match drilling.
When Tim arrived i had the match drilling pretty much done and while I pulled out the bottom skin Tim cleaned up the rear spar trailing edge to file off any alignment error between the skin and the spar.
We flipped the wing over and Tim aligned the bell crank brackets to the upper skin while I worked to level the then skin by supporting each of the four corners with blocks and shims to insure the wing was flat (not having any wash out or pitch variation from root to tip.
The process of squaring and leveling the wing (as mentioned earlier) can be done a couple different ways but the bottom line is that (in my view) you need to have an image in your mind of the process you are involved in. I spent a good part of my youth working for my “old man” building houses and even did it for a few years before and during my college years. The process of squaring a wall so that when you stand it up it will be plump is very similar to assembling a wing to be square and not have any wash out. For me it is almost an intuitive process that I know most framing carpenters would find easy.
The process can be broken down into two primary steps. The first skin must set the wing with regard to square (which is not terribly hard but a bit of a challenge to find a reference). The second step, once the wing is held square by the first skin, is to insure it is flat (no wash out).
To square the wing it is also a good idea to have it close to level, although not necessary to be exact, it will be needed on the second side skinning so the procedure is good practice. Once level it is easiest to find four points that define a parallelogram. The first two points on the skin are the wing station 22-3/4″ center line at the center of the main spar and the trailing edge of rear spare at the same 22-3/4″. These two points will be marked on the upper and lower skin as the intersection of the center line (where the holes are drilled) and the edge of the skin. If you cut our skin carefully (as you should) the final width should match the plans and the skin should be square (don’t trust factory cut sheets of aluminum to be square). Even though the root and the wing tip have very irregular contours, the center line of the first rib in from each end (rib #1 and rib #12) should form a perfect rectangle on the wing skin. The second two points are the same position on theT #12 rib. The key characteristics of a rectangle is that each of the opposite sides is the same length and the angles where the adjacent sides intersect should form 90 degree angles. The wing skin when laying flat provides a perfect pattern to align the wing box. The only task that remains is to identify the reference point that make a rectangle on the skin, and mark them on the wing box.
To really describe the above process i need to generate a picture or some sort of graphical layout. maybe that will be a task for later.
Once the wing is held square by the skin on one side of the wing, attaching the second side will give the wing 3 dimensional rigidity. Holding the wing flat, or vertical and planar, when skinning the second side will insure that there is no wash out in the final wing structure.
If all of the wording above is confusing, I hope it is because of my poor explanation and not the readers inability to understand the concept of square and flat. Otherwise, you are doomed.
The bottom line for the night. The bottom skin is fully match drilled and the inspection hole is cut. Tomorrow I need to determine if I want to add the fwd ribs and skin or updrill the aft ribs. it probably does not matter but immediately after the leading edge is skinned I will proceed to cutting in the landing light for the left wing. That could happen tomorrow…