Here is a view of a center rib after installation of the stiffeners.
After fabricating the stiffeners, I started to shoot them on.
This view shows two of the center ribs after cutting the lightning holes. In this picture, the closest rib has the lightning holes flanged as well.
Ok, the rib has been formed and fluted, next I placed the rib on the edge of the table and gently straightened the edges using the rubber mallet with strikes to the lower portion of the flanges (to maintain the proper outer dimensions) until I've obtained a 90 degree flange. The last step is to check for rib straightness and make any minor corrections to the fluting as necessary. I say corrections to the fluting because the fluting will cause the rib to bend one way or the other.
To correctly place my flutes, I first identified the location of the future rivet installations by referring to the information available on the drawings where it stipulates a 1.5" typical spacing. I located this data on the backing board itself and then simply marked the spaces between the rivet locations as my flute locations. (I utilized the backing board as the marks would be visible after the rib had been formed.) Once the rib flanges have been bent over, I simple transferred the marks from the backing board to the newly formed rib. For the actual flutes, my philosophy is to use the minimal amount necessary to do the job. As shown in the photo, I started out fluting every other mark, and for me this worked quite well. Another tip: take your time and ease up on the proper amount of fluting, a little patience will be rewarded!
Now it is time to start on the center ribs themselves. I layed out and cut the ribs using the same techniques previously discussed, then bent the rib flanges using the form blocks shown at the top of this page. It is hard to see in this photo but due to the curvature along the top of the rib, the rib is now bowed and will require fluting to straighten it out.
For the center ribs, I made the same type of form blocks and layout guide as the nose ribs and I included all of the necessary holes for the two "types" of lightning holes located at the aft end of the rib (the inboard ribs have a different lightning hole cutout pattern than the outboard ribs do).
There are a total of 22 center ribs required, with 8 of them being fabricated from .032" 2024T3 aluminum and the remainder constructed form .025" 2024T3 aluminum. The thicker ribs will be installed in the inboard section of the wings, surrounding the fuel tanks and forming part of the wing root. Aside from the material thickness, there are also two different lightning hole patterns which must be cut into the proper ribs. In essence, the inboard ribs (.032" ) will receive two separate holes in the rib's aft-most position while the rest of the ribs (.025") have an oval hole in that location. There are also 4 smaller ribs which will be installed between the false spare and the rear spar. These are fabricated from .032" 2024T3 and have the two-hole pattern just as the inboard ribs do.