Drove the Rivets for the cover plate

In case I have not mentioned this previously, lets just say that I am so glad that do NOT have put up with any of this stuff for the right wing fuel tank assembly. I finally got wipe to cobwebs off of my rivet gun and used it to set the 4 rivets to secure the cover plate over the hole. Since it had been so long since I had used the rivet gun and bucking bar to set rivets, I at least did the "smart" thing and took one of my test pieces that was already drilled, deburred, and dimpled, and still have a few holes available for some test rivets.

Another thing I wanted to do was test a flexible shaft flat rivet set with the rubber cup that surrounds the flat rivet set, which s at least 1.4 inch larger in circumference than my 1 inch flat set that have been using for my build up to this point. I bought this thing because it had the red rubber cup around the edges of the metal flat set, to allow it to grab the aluminum and keep it from slipping.SO I put it in my rivet gun, and well, lets just say that its a good thing I did some tests first, before I did the real thing.

Its hard to see in the next pic, but I was less than pleased with the rubber rivet set. The main reason was that the rubber extends almost 1/16th of an inch beyond the metal rivet set surface, and this does not allow the rivet set to sit directly on the rivet head before you squeeze the trigger on the rivet gun. The result was similar to what many others have experienced with this "stock" tool. The head of the rivet does not sit flush in the dimple and allows the head to rise up, resulting in a proud and improperly set rivet.

None of the pics of the shop heads came out very well, so you'll just have to trust me when I tell you that, in addition to poorly set manufactured heads, I also discovered that my air pressure was set way to high for the rivet gun. I don't even remember the last set if rivets that I drove with the rivet gun, but they must have been AN7470AD4 rivets, because the gun pressure was turned way up. The result on my test rivets was that the shop heads were all way over driven, and the gun was barely controllable.

Once I figured out how to turn down my gun pressure again, AND I switched back to my 1 inch wide flat rivet set, I was able to get satisfactory rivets.Here is the pic showing that horribly large flat set the rubber cup, and the bucking bars, rivet gauge, and my "normal" flat set already installed on the gun. You can see how much the rubber extends beyond the actual metal part of the larger flat set.

I think I can still make this larger set work, because I do continue to have problems with the flat set sliding off the rivet. I am going to have to sand or cut off the "excess" amount of rubber so that the flat set will make better contact with the surface of the rivet. I have to try taking off a little bit of rubber at a time, and run some more tests.

Now for the fun part. As I have mentioned many times before, the key to setting good rivets is all about how well you clamp the work piece to ensure that it will not bounce, bend, or vibrate in such a way that the rivet will not end up being set correctly. If you work alone and do not have a bucking buddy to help you, you absolutely MUST keep the work secure, since one hand will be operating the rivet gun, and the other will be working the bucking bar, the work piece has to be clamped down good. SO here is the contraption that I dreamed up - all for 4 rivets on one lousy fuel tank rib:

This "contraption" is made up of 6 different clamps, and 3 different wood blocks, all strategically placed on the work bench, with the rib positioned upright on the edge of the bench, with the bottom rib flange clamped in place first, followed by all the other clamps to make this assembly as rigid as possible, so I could set the 4 cover plate rivets. Here are the remaining detailed photos, showing exactly where and how I had to set each clamp to achieve the objective:

The smaller block of wood ha to  used to ensure that the hing for the trap door could be cleared. the other clamps had to be placed carefully so that the stiffening rings would not be compromised. Every single one of these clamps was needed until I felt that the rib was stationary enough to be ready to set these rivets. Let's just say that I am glad that this is the only rib that I have to do all this work on.

And the final result, after using my standard rivet set with a piece of masking tape over the face of the set, and my "fat man" tungsten bucking bar.

At the end of it all I was pleased with the results, and my rivet gauge confirmed that the rivets were set correctly. There will be a million more of these rivets to set if and when I finally get to the point where I am riveting the skins to the wings.

With this little "project" done, I think I will turn my attention back on the Leading edge assembly, and I will remark the lines for the rivets, cut line, and nut plate locations on the LE skin, using the edge of the skin as my reference point, so that my spacing of everything from one side of the bay to the other is accurate and consistent.

I am now very close to making that dreaded cut in my LE skin.

On another note, we had our first YE rally of 2018 yesterday - flew 2 kids and one adult - had some engine issues on the third flight adn had to RTB shortly after Takeoff. Getting tired of dealing with fouled plugs on airplanes so I may renting a different one for next month's rally.

We also had our EAA Chapter 301 Founders Day Brunch and Awards Ceremony. A great time was had by all at the Mount Vernon Country Club high on top of Lookout Mountain. The Chapter is 50 years old as of the 23rd of this month, which is a pretty significant accomplishment, and we received a very nice new Chapter Banner from EAA HQ that looks really sharp.

Till next time, KPR....

Dimpled the Cover Plate for the Fuel Tank rib

Well I suppose that's a long enough break since my last post. Time for some updates. In my previous post I was trying to decide what side of the tank rib to place the cover plate over the hole in the web about half way up the width of the web. After mulling that over a bit, I decided to put it on the outboard side of the rib web instead of the rib web. My reasoning for this was that MOST of the time the wings should be level, and there is a slight dihedral angle in the wing where the tip will be just a bit higher than the root.

This, combined with a slightly positive angle of incidence of the wing while it is in sustained level flight, lead me to believe that pressure from the fuel inside the tank will be greater on the outboard sides of each rib most of the time, while the small holes at the bottom rear of each rib will allow fuel to slowly escape to the next inboard bay. Since the fuel pressure should be greater on the outboard sides of each rib due to the reasons I mentioned previously, I decided to put the cover plate on the outboard side of the hole in the rib web, so that any pressure from the fuel against that rib and the patch plate would tend to push the patch plate tighter against the rib web, keeping the fuel from entering that hole, and forcing it to go through the trap door instead, as intended.

Having finally decided where to put the plate, the next step was to dimple the holes for the rivets. This turned out to be yet another exercise in "imaginative problem solving." If you haven't guessed by now, I am documenting this entire tank rib trap door fabrication process because almost nobody documents this to the level of detail that satisfies me, and as it turns out, the steps required to complete this little side assembly are a little more involved than you might think.

First problem - decide which side to put the dimples for the 4 AN426AD3-3.5 rivets. I decided to use flush rivets for this since that should be sufficient for holing this small plate in place, and flush rivets take up less space inside the tank than an AN 470 rivet. Remember, I am trying to stuff as much fuel as possible in these tanks, so every little bit helps, even if that does seem a bit anal.

I decided to put the manufactured head of the rivet on the outboard side of the rib web. Again, this is because fuel pressure will tend to push the rivet head against the rib head, instead of pushing it away.

So I put the dimple dies in my hand squeezer and set the dimples in the over plate:

Next problem -I would need to use my C-Frame tool and table to set the dimples on the rib web. None of my yokes were long enough to reach the holes in the rib web. Then another problem cropped up. The trap door was getting in the way. In hindsight, all I had to do was remove the hinge, but stupid me likes to do everything the hard way. The rib sits awkwardly on the table because of the trap door.Another problem was that my C-Frame table had been setup with the male dimple die on the bottom and the female die on the top. With this application they would need to be reversed so that the male die is on the top and the female die is on the bottom. Why is this a problem - the female die is longer than the male die, so my table no longer sits "flush" with the dimple dies in this reversed state.

So the combination of the trap door interference and the reversed setup of the dimple dies on my C-Frame table presented some challenges:

Here you can see the female die sitting very proud of the table

And it looked like this sitting on the table as a result of the trap door interference:

So how do I get the rib to set level on the dimple dies so I can pound these dimples properly: I was not concerned about the proud dimple die situation, but I did not want the dimples to be improperly set at an angle, so leveling the rib web was a concern. My solution was to place a couple of the fuel tank access plates on the other side of the rib to level it out just enough for me to set the dimples properly.

And here are the pics with all the dimples set in both parts:

I will have to use the rivet gun and a bucking bar to set these rivets. this will be the first time I have picked up the gun in a very, very long time. I will have to do some practice rivets on some scrap first, to make sure my air pressures are set properly, and I get my timing back. I want to set all of these rivets perfectly so I can move on with other much more important tasks. This little adventure has certainly resulted way too much of a time suck on the build.




I also finally called my tech counselor Jim Elliot ad he came out for another visit to help me finalize plans for the mod to the Leading Edge. I think I now have all the info that need to be brave enough to drill the final rivet and nut plate holes in the skin and the subskin, so that I can take it off the wing spar and make that all important cutout. More on that visit and the next steps for that tomorrow.

KPR

Tech Counselor Visit and more Fuel Tank Rib Fabrication

Had a little lull over the new year holiday - cold temps, getting sick, holiday obligations - blah! Nice to get back to airplane building for a change. Picking up where I left off, per Vans input about the hinge for the trap door assembly I decided to do the same - leave the rear hinge pin bent to 90 degrees and leave a small amount of excess on the other side of the hinge without bending it or peening it, etc. The idea is that the rear hinge pin will hit up against the rear baffle plate without ever coming out of the hinge, as long as there is a sufficient amount of pin left on the other side to keep from coming out or causing the hinge to hang up.

So I straightened the bent part of the hinge pin a bit more to keep that end from binding against the eyelets of the hinge, and then I made a mark on the other end after setting the bent end along the rear flange of the rib, simulating where it would hit the rear baffle plate:

 Then I cut the hinge with the dremel tool cutting wheel and deburred the end on the scotch brite wheel:

The piece of metal sticking up one the left is actually a reinforcement plate that goes on the forward part of the most inboard and outboard ribs. In this case it served quite well as a mock baffle plate so that I could verify the length of the hinge pin was correct.

Next came the cover plate for the open hole also seen in the above pic. Vans says that with the flop tube assembly this hole also needs to be covered with a patch plate so that fuel is only allowed through the trap door location. of course this is NOT in the instructions or the plans, so it begs the question, if someone was building the kit with very little or no outside help, they would never cover up this hole. How would they know f they needed to. Vans once again fails to impress me with its lack of updates to the plans of its older models that are still being built and flown. The hole is about 1.5 inches wide, so I reasoned that a 2 inch square patch plate over this hole with 4 AN426AD3 flush rivets in each corner should doe the job. this allows me to maintain 1.4 inch edge distance at each corner of the patch plate:

I cut the plate from scrap .025 inch thick aluminum sheet and deburred it on the scotchbrite wheel. then marked the location for the plate over the hole in the rib, as well as the location for the 4 rivet holes as shown above.

After drilling the 4 rivet holes in the plate, I had to match drill the holes in the rib. So I used the clamps to secure the plate on the rib and got that all done. then I deburred all the holes:

Now I get to decide which side of the rib to mount the plate. the general idea for this is that you want to put the plate on the side of the rib that might encounter the most force due to the amount of fuel in the bay at any given time. I need to decide this because I am using flush rivets to mount this thing. It is not structural so there is no need for AN470 rivets for this, and I am also trying to minimize the amount of space taken up by things other than fuel inside the tank. A rivet seems like a minute detail, but it all adds up in the end - excess sealant, excess hardware, excess rivets, and so on...... It all means less fuel in the the tank.

Since I am using AN426 rivets I will need to dimple the skins, and I have to decide which side of the rib I want  to do this.

This past weekend I had my technical counselor Jim Elliot come out again to review my plans for the cutout of the leading edge skin. He was satisfied with my planned approach. So now I am almost ready to remove the LE and make the big cut. In the coming weeks you will finally start to see what I have been planning to do all along. To think of all the research, design work, and safety evaluations I have gone through to make this seemingly rather small mod makes my head hurt. So I'll leave it at that for now.

My big problem now is that I have the fuel tank in prep mode in my only LE cradle, so in order to take off my LE I have to figure out what to do with the fuel tank. I think I may be making another cradle this weekend to give me some flexibility with handling these big parts. Not really a big problem, just yet another one that I have to deal with on this never ending journey...

KPR