Fluting and straightening the ribs

These are fluting pliers and the resulting fluted rib. What is fluting you may ask? This is a process where small crimps are made in the flange of each rib to help bring the flanges to 90 degrees perpendicular to the web or main flat part of the rib, and to correct the bow in the web or flat part of the rib that results from bending the top and bottomflanges of each rib. The process of attempting to bend two 90 degree flanges on a thin piece of aluminum causes the larger flat part of the metal to bow in one direction. Fluting the flanges is necessary to straighten the bow in the metal by counter-acting the bending moment that occurs. Easier to see than to explain. Since I have already straightened all the flanges and fluted all the HS ribs, I will try to show a pic of the Vertical Stab ribs later on so you can see how pronounced the bow really is, and how fluting works to straighten it out. It really does work nicely.

HS 404 and 405 Continued - marking the rivet hole locations

SO these are the marks for the rivet holes that ensure that they have enough edge distance. 4 holes are required for the main rib flange, while only two are required for the flange on the nose rib. The whole point of the exercise of clamping the two rib sections together was to determine where the edges of the flange of the nose rib will line up with the flange on the main rib as shown in this pic. It is otherwise difficult to figure out where these holes go since the front spar fits in between the two ribs.

The vertical lines represent the edges of the trimmed flange of the nose rib and where it will be positioned in relationship to the main rib once positioned on the other side of the front spar. This allowed me to "transfer" the position of the shorter flange of the nose rib onto the larger flange of the main rib so that I can better determine where the center rivet holes needed to be drilled to maintain proper edge distance. Van's wants everyone to locate these holes themselves, so they do not pre-drill any of the holes in either flange.

This was a major pain in the ass to figure out, but I am confident that all the holes are now properly marked. Basically the marks all represent rivet hole locations that 1/4 inch away from all edges of each flange in each rib. The distance needs to be 2x the diameter of the rivet used. IN this case, they are 1/8 inch thick rivets, so 2x 1/8 inch is 1/4 inch to meet minimum edge distance.

HS 404 and 405 rib flange aligment continued.....Mounting hole alignment shown

A better shot showing the two forming holes underneath the clamp that I used to alig the two rib sections. Alslo shows the finished front rib after the nibbling and edge smoothing was completed.

Also don't forget to radius the inside corners where the flange is trimmed or nibbled away. Another thing to notice from this pic is the reference line drawn with a sharpie next to the area that has been trimmed away. Always perform major trimming or cutting so that you are not quite to the final trim line. Then perform final sanding, trimming, or grinding up to the established trim line. It's always easier to trim a little more metal away than it is to replace it after it's gone! Many builders have had to order new parts here, either due to improper trimming, or because they mess up the edge distance when trimming the flange or marking and drilling the holes. Thanks to Ron Duren's posts about these problems in his site, I was able to avoid this problem, and my finished parts all came out fine.

HS 404 adn HS 405 Rib flanges aligned and clamped, and center lines marked

Not a very clear pic, but it shows the alignment of the two rib sections.

Drilling holes correctly in the HS 404 and HS 405 flanges - my method

This is the source of great controversy, discussion, and advice as to how to go about marking and drilling the holes for the rivets that end up attaching this main rib to the front spar and subsequently to the nose rib - sort of a 3 layer sandwich of thin alumimum that must be solidly attached by riveting them all together. The controversy revolves around measuring and marking the holes to be drilled, while maintaining proper edge distance from the material. Setting a rivet too close to the edge can cause cracks or failures in the part, so this does have to be done correctly.
After spending lots of time reading and studying the plans, I had an epiphony of sorts. Realizing that the front spar is just the middle layer of the sandwich, the real challenge was to get the rivet holes of the ribs in the right spot, while making sure that the two rib pieces line up correctly. I also realized that the mounting holes in each rib that are used when forming each part appear to be in alignment with each other. As shown here, I simply clamped the two pieces together, lining up the two forming holes as closely as possible, while checking the outer edges to ensure they also were aligned.

I also used two pieces of aluminum from the trim bundle and placed them on both sides of the ribs where the flanges join to further ensure that the ribs are in proper alignment. Then youn really need to pay attention to the lovely drawing in the plans, which, much to my disappointment, is a bit too small to properly show all of the detail regarding how the edge distance and marks for each hole are determined. Be careful, and spend quality time here to fully understand how each set of refernce lines for each rivet hole are determined. Posts on VAF also very clearly discuss this problem.

More nibbling......

Your's truly nibbling away at the rib.

Nibbler tool

The nibbler tool, and some scrap aluminum showing my less than great cuts made with the dremel cutoff wheel, and the rib undergoing the trim...