We've spent the last three work sessions completing some very time consuming projects. There hasn't been a lot to show for the hours we've spent at the hangar, but I'll bring you up to speed on what's been happening.
After we finished with the stiffeners, we got to move onto the longerons. A longeron is just another structural component in the tail cone and fuselage. In this case, it's a long "L" shaped piece of aluminum that runs the entire length of the tail cone. Wikipedia tells me that there honestly isn't much difference between a longeron and a stringer (the long pieces of aluminum we worked on last week). They serve exactly the same function, but longerons tend to be a bit heftier than stringers. Also, the word "longeron" is much more fun to say.
The longerons had to be notched so they wouldn't rub against some of the other structural components of the tail cone. The notches have to be cut in a very specific location, which required a bunch of careful measuring and remeasuring. Then we drilled some small pilot holes before drilling the final 1/4" holes.
I mostly stood around the took pictures during this process. As I saw the spirals of razor sharp metal that Mike was creating as he drilled the big holes, I realized I wasn't wearing my safety glasses. You definitely wouldn't want something like this to fly into your eye!
Once the holes were drilled, we marked out the additional area that needed to be removed. Mike removed most of it with a saw and we finished up with a file.
Everything went smoothly, but since we were very careful during this process it took us about an hour to finish two notches. Now we will just hope that they are in the right place. We won't really know until we put everything together.
The next task we had to complete was bending the longerons so they line up with the edges of the tail cone skins. There is a 2° angle in the skins that we had to try to match. You can just barely see the angle in this picture.
To bend the longerons, we used the old "preload" technique from my last post. Or, as I prefer to call it, push on the metal and whack it with a hammer.
This is quite a bit harder than it looks. The "L" shape of longerons means that they have a tendency to bend in two directions instead of just one. In this particular set of pictures, that means the longeron is bending away from Mike as he whacks it with a hammer, but is also bending down toward the floor. The whole thing is a process of trying to get the 2° bend in the direction you want and then remove the extra bend that you didn't want. We got it figured out eventually, as you can see in the bottom pictures. It took forever to bend the first longeron, and about five minutes to do the second one.
The final prep task we had to finish was draw a line down the length of the J-channel stringers we previously cut. This line has to be precisely 5/16" from the edge. The problem we had to solve is how to draw a line exactly 5/16" from the edge all the way down an 8 foot long piece of oddly shaped aluminum. Mike, of course, had a clever solution that I, of course, thought was ridiculous at first. I'm pretty sure when Mike described his idea I laughed, mostly because I didn't even remotely understand what we were trying to do.
Mike's idea was to create a jig with a hole drilled in it.
You put a marker through the hole and very carefully slide the jig down the length of the stringer.
It was pretty awkward to use because the only flat surface in the J-channel is where we need to draw the line. I eventually got the bright idea to rest the J-channel on the miter box Mike built to trim the ends off the stringers and that worked much better.
These lines will eventually be used to make sure the stringers are in the right place while Mike drills holes. By centering the line in the middle of the predrilled holes in the skins, you can make sure that your stringer is in the perfect location.
With these last pieces finished, we are ready to begin construction of the tail cone!