Before I get started about the stiffeners, here is a pic showing the quick change chuck and several collets with different bits and reamers in them:
The small dimples near the root of the collet are the recessed holes where the ball bearings in the chuck lock it in place. The nice thing about this tool set is that they give you 3 each #40 and #30 sized collets, so you can mount a drill bit in one, a reamer in another one, and a clearance or pilot bit in another one. then all you have to do is change the collet when you need a different tool. The only thing I don't like about it much is that it takes two different sized wrenches to tighten the bits in each collet.But since you should only have to do that every once in a while it's not that big of a deal.
Now on the stiffeners. I never thought I would get as much done on these as I did today. especially after attending the annual Parade of Lights in downtown Denver last night and hitting a couple of bars afterward. Was a fun night, but a really late one as well.
Preparing stiffeners always means cutting the basic parts from specially prepared aluminum angle that is pre-punched at the factory with a system of guide holes, notches, and grooves. These locations are then used to mark the positions where 90 degree angle cuts are made to separate each stiffener from the angle stock, and then t make the angular tapered cuts on one side that are designed to reduce stress concentrations and diffuse them across the entire part. I commented further about these when I did the rudder and the elevators long ago. The process for the making the fuel tank stiffeners is exactly the same.
Since I use a Dremel cutoff wheel to separate each stiffener from the common 3-4 foot long piece of aluminum angle, Safety is paramount. There are all sorts of ways to hurt yourself badly when making these parts. I ALWAYS where ear muffs AND safety goggles when I fab these parts.
Here is how I started out - Two clamps securing the first of 4 separate angles that must be cut to produce all of the stiffeners for each fuel tank. You can also see the dremel tool with the flex shaft and the cutting wheel in the distance on the floor.
Lines have been drawn by connecting all the notches. Then you use these as guides for making the rough cut of each stiffener. Then you start cutting. I extended the angle out from the edge of the bench far enough to allow room for the dremel tool to make the angular cuts as well as the separation cuts. As you cut each stiffener you remove the clamps, move the angle a bit more, and cut the next one, then wash, rinse, repeat.
Here is shot of the smallest of the stiffeners after cutting. Lots of sharp and raggedy edges on these, so be careful when you pick them up from the floor
When you get to the very last stiffener on the supplied angle, you need to reposition it to a different orientation on the bench so you can cut the last angle on the end. All I had to do was clamp it to the other edge at the corner of my work bench:
And here are all the individual stiffeners immediately after cutting them from the angle
And here is the dangerous mess that it leaves on the floor. Be sure that you don't do this job in your bare or stocking feet. You should also know that even though I wear the safety goggles, you have to get used to being pelted by metal particles when using a dremel cutoff wheel. It just happens, so you just need to deal with it. Nothing is large enough to puncture the skin, but you definitely feel it when they hit your face. So eye protection is absolutely necessary.
Trust me, those remnants are all razor sharp. I have never found a good use for any of this scrap metal, so the best place for this stuff is in the aluminum recycling bin.
After they are all cut, then next steps is to debur all the edges on the scotchbrite wheel. There are 6 bays per fuel tank, and two stiffeners on the bottom skin per bay, for a total of 12 stiffeners per fuel tank, or 24 total. So it takes a while to get all the edges nice and smooth, but when you do, you end up with a stack that looks like this:
Each of these four sets of stiffeners, marked T711 A through D, are different lengths. the longer ones are either 8 inches, just under 8 inches by varying amounts. So it is important to make sure that you cut and trim them as closely as possible to the expected dimensions, and even more important to label them properly, since they need to go in the proper bay of the fuel tank. The T711B stiffeners are place in 3 of the 6 bays in each tank, so there are more of them than the any other stiffener. All others will consist of a total of 4 stiffeners each for the A,C, and D parts.
The next step is clecoing them to the bottom of the fuel tank. Vans shows the basic orientaion of each one, which is to have the flange with the rivet holes facing forward, and the "stiffening" angle toward the rear of the tank. However, then they have a note somewhere on the plans that states that it is OK to change the orientation of the stiffeners by reversing them to make it easier to apply the proseal and back rivet them in place. Here are the pics with each stiffener clecoed in place:
Next step is to match drill the rivet holes for each stiffener and debur them. Then I need to start masking them with electrical tape and start getting my proseal routine, supplies, and procedures in order. Then the fuel filler port and fuel sump drain flange need to be positioned and drilled into the skin. So it was a good day at the factory since I was able to fab all of the tank stiffeners. This tank is rapidly getting to a point where it will be ready for the "goop" and riveting pretty soon.
KPR
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