Man where has the time gone! Been dealing with a back injury that then led to other medical problems that basically left me immobile, and then we got slammed for the past 4 days with massive non-stop monsoon rains that prevented me from venturing out into the garage except to make sure that the cars were not floating away. The sun finally came out today and I am also able to walk again,so of course it was time to get out to the factory again.
I should also mention that Airventure began this past Monday. It is bitter pill for me to swallow that I was not able to attend this year for a number of reasons, but I found some relief in the fact that EAA has done a wonderful job of providing several streaming opportunities for both video and sound for the airshows and other events during the week, so I haves pent a great deal of time online this past week taking in as much as I can. There is so much to report about all this that I will devote an entire post to it later on.
I received another order from Vans with some more ribs, more Z-brackets, and my first two tubes of Proseal. Mike Rettig has a mixing tool and the pneumatic delivery tool that I can use to dispense it so I will get with him when I am ready and borrow those items to seal the tanks.
In the mean time I have reached a point in the normal build instructions where the next step is to attach the assembled fuel tank to the wing, cinch down the tank skins to the wing spar and the adjoining LE, verify there are no gaps between the main wing skins, LE, and fuel tank, and final drill the holes for the nut plates through the fuel tank skin and the joiner plate.
This is where I deviate from the normal build process to complete the LE modification I have been planning for a very long time now. Instead, I performed the following steps:
1. Fluted, straightened, edge deburred, and filed down the Rib LE bumps to an additional 408-1 left and right rib. These ribs will replace the W709 ribs adjacent to the first 408 rib. IOW the first two inboard ribs for my LE skin will both be 408 ribs instead of the normal 408 inboard followed by W709 rib design.
2. I have struggled trying to decide between a couple of different methods for drilling the holes in the second hole-less 408 rib. My choices were basically to measure and pre-drill at least one hole in the rear flange of the rib based on measurements taken from the other 408 ribs that have already been drilled, or to position it similar to the first one and back-drill the holes through the back side of the wing spar just as I did for the other one.
After much debate with myself about how best to do this,I decided to take the measurements and attempt to drill the center hole of the rear rib flange based on those measurements, so I can alt least have a starting reference point that is attached to the wing spar while I figure out how to assemble the rest of it. Some measurements of interest for this are:
408 rib rear flange length - 4 and 7/16ths inches
Center of rear flange - 2 and 7/32 inches
Center hole location - 3/16 inches from the outer edge of the flange. I marked both this line AND the min edge distance line on the rear flange.
I marked the center hole location with a sharpee, then center punched and pilot drilled with a #40 drill bit. I was right on the money - unfortunately the wrong money with this hole. DAMMIT! I marked the min edge distance location instead of the 3/16th inch location for the center hole, so now my rear flange center hole is at max edge distance for the rib, and is 1/16 inch off from where the hole was drilled in the other 408 ribs. I basically said screw it, realizing that with the rear flange holes a bit further out from the web should create a better situation for the rib flanges centering up in the holes in the LE skin, so I went ahead and drilled the final hole to #30. If I need to I will order yet another 408 rib and do it all over again. What a pain.
I removed the existing W709 rib to be replaced with the new 408 rib while leaving the LE skin on the wing spar. I then replaced it with the 408 rib and clecoed the center hole in place. I then spent some time checking the alignment of the rib flanges by locating the reference line I drew on the flanges with the holes in the LE skin, and they seem to be OK,even after offsetting the rear flange hole by 1/16th of an inch. So I think I will continue using this rib and back drill the remaining rear flange holes once I have it squared up with the wing spar and wing skin. That will require a post of its own to describe how I do this, since the original method I described in a previous post cannot be used since this rib is inside the LE skin and is not on the outer edge. I have a plan for this that I will share in another post. I will basically remove the LE skin so that this rib is exposed so I can clamp it down against the wing spar. Having at least one hole already drilled in the rear flange of this rib makes this possible. Vans, are you paying attention?
SO why all this fuss over the rear flange of the 408 rib. Well, to put it simply, this is hard part of this entire process. It is difficult because the rear flange of this rib is notably shorter than the flange on the 409 rib, and the hole patterns in the wing spar are also different for the same reason. The only hole that aligns between the 408 and 709 ribs is the center hole. This is why the location of the center hole in the rear flange of the 408 rib is so critical. I am going to have to devise a hole pattern and possibly drill some additional holes in the wing spar web to ensure that the rear flange of the 408 rib has the proper support. I have not finalized the dimensions of this final hole pattern, but I can probably use the same pre-drilled holes to either side of the center hole, but will have to add some more holes to distribute the load on the rear flange correctly. If I use these additonal predrilled holes the hole pattern will not be the same as it is for the original 408 rib, so I have some decisions to make here.
One other thing I figured out today is the length dimension of my revised joiner plate. The original plate is 1.5 inches wide by 36.5 inches long and .032 inches thick. I realized that since my new joiner plate will be approximately 12 inches wide, I need to account for the change in the shape of the wing spar between the 2 ribs. The spar bar ends about half way in between the original 408 rib and the 709 rib that I am replacing with another 408 rib. I also realized that the final hole spacing in the LE skin is a bit different for the 709 rib location than it is for the 408 rib location.
Long story short, the length of part of my new joiner plate will need to be 36.5 inches for the first 5.75 inches of width, and then change to 36.75 inches after that in order to account for the increased LE skin hole spacing from 1 inch for the 408 rib to 1.25 inches for the 709 (and my second 408 rib). If I want the new joiner plate to connect to each of the most rearward rivet holes in the LE skin for both ribs, I will need to adjust the length of the new plate accordingly. I also need to be mindful of the clearance between the skin and the end of the tie down attach bracket for now. Truth is that much of this will get trimmed away so that only a portion remains over each rib flange similar to the original joiner plate dimensions for the rear side of the LE.
Another dimension I need to record is that the distance between rear rib flange rivet holes between the original 408 rib and the 709 rib that I am replacing is 10 inches on hole centers. The spacing between each 709 rib from that point moving outward to the outboard edge of the LE is 10.5 inches. So the spacing after this second rib is different. This is important because it basically prevents me from using the LE wing skin for one method of securing and drilling this new rib that I had been planning. Had the spacing between all the ribs been the same, I would have been able to use this method, but since this is not the case I am not even going to elaborate on how I was going to do this.
That's about it for now. Too busy measuring stuff to take pics so will try to do that tomorrow. Upcoming tasks include cutting the .032 x 12 inch wide by 42 inch long piece of aluminum to initial length measurements described above, and preparing to bend this to shape against the 408 ribs. Hopefully that will go reasonably well but will not be as easy as the smaller 1.5 inch wide strip was.
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