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Archive for November, 2010

Preparing to Close the Left Tank – 1.0 hr

November 29, 2010 Leave a comment

Monday Nov 29, 2010

Well the last week saw no progress on the wings since it was Thanksgiving and we were out of town. So tonight was the first time back in the shop since last Tuesday. It is about time to close up the left tank by installing the baffle and that is a major milestone so tonight I began final preparations.

That includes bending the fuel vent line to the high point of the tank as seen here.

It also includes buffing up the surfaces of the baffle which will be sealed including the edges of the flanges and along each of the rib lines as you can see here.

I also inspected all of the rib seals to make sure there are no obvious leak points and all rivets are covered in sealant. It looks good. I hope there are no leaks but I won’t know until I seal up the baffle and access cover and perform a leak check. I’m praying for a leak-free tank.

I also ground down the nozzle of an old blind rivet tool I had so be able to pull the blind rivets on the T-712 Z-brackets. I’ll get a picture of that tomorrow.

Categories: Fuel Tanks, Wings

Tank Rib Riveting Part 4 – 6 hrs

November 23, 2010 Leave a comment

Tuesday Nov 23, 2010

Hooray, I finished riveting the ribs into the left tank skin today. I started with the center rib with the help of Denise, then I installed the inboard rib. For the record, here were the inboard rib steps:

1.  Insert the fuel tank vent line through all the outboard ribs (snap bushings installed).

2.  Clean mating surfaces of the inboard rib, skins, T-405 and T-410 with MEK.

3.  Apply sealant to the flanges and cleco the rib into the skin.

4. Rivet the rib to the skin starting at the leading edge and working toward the trailing edge using the pneumatic squeezer.

5. Apply a fillet around the interior and exterior edges and make a cap of sealant over each rivet.

6. Apply a layer of sealant to the mating surfaces of the T-410 and T-405 and cleco the parts to the tank rib.

7.  Set the rivets using a cup set with snap socs.

8.  Apply a fillet around the interior and exterior edges of T410 and T-405 and make a cap of sealant over each rivet inside and outside.

9.  Clean the flop tube fitting with MEK. Apply sealant and install the flop tube fitting and torque to 115 in-lbs.

10. Apply a fillet of sealant around the AN fitting.

11.  Clean the vent line fitting with MEK. Apply sealant and install the vent line fitting and torque to 50-65 in-lbs.

12.  Mate the vent line nut and torque to 50 in-lbs.

13.  Apply a fillet of sealant around the vent line fitting and around the vent line nut to seal the threads.

Here is the end result. No clecos!

In this photo you can see the inboard rib and the installed flop tube.

On the inside you can see the diagonal anti-hangup bracket and the vent line mated to the fitting. This tank is just about ready to be closed up by the aft baffle.

Categories: Fuel Tanks, Wings

Tank Rib Riveting Part 3 – 6.5 hrs

November 22, 2010 Leave a comment

Monday Nov 22, 2010

Three more ribs riveted into the left tank today. I started working early this morning on the outboard rib because I could squeeze all those rivets without any help. Then I completed two more of the inner ribs with the help of Denise. I found that if she drove the rivet gun while I bucked on the first six to eight rivets on each side (starting at the leading edge) I could easily finish the rest solo. That tied her up less so she could get other things done.

Here is a shot of the outboard rib. I used electrical tape to mask off the area where the doubler to the leading edge slides in.

Here is the current status of the left tank. Notice that only two ribs have clecos at this point. The rest are fully riveted. Slowly but surely.

Categories: Fuel Tanks, Wings

Tank Rib Riveting Part 2 – 1 hr

November 21, 2010 Leave a comment

Sunday Nov 21, 2010

Not a lot of time to build today. I just had time to rivet the T410 reinforcement plate to the left tank outboard rib. The instructions say to do this after the rib is riveted to the skin but it is much more accessible before the rib is installed and I don’ t see anything that will be negatively affected if I do this now. I hope that turns out to be true.

I cleaned the areas of the parts that were to be bonded first. Then mixed up about 15 grams of sealant and buttered it onto the surface of the reinforcement plate, mated the parts and cleco’d every other hole. Then I squeezed the rivets. I cleaned up the excess sealant and added a bit over each rivet head.

Here is the reinforcement plate after riveting and sealing rivet heads.

Here is the inside of the rib. The seventh blob is an extra tooling hole in the rib that must get sealed up in this process.

Categories: Fuel Tanks, Wings

Started Riveting Tank Ribs – 4 hrs

November 20, 2010 Leave a comment

Saturday Nov 20, 2010

This morning I started riveting ribs into the left tank skin with the help of my wife Denise. There are seven ribs on each tank and it really helps to have one person driving the rivet gun and one bucking rivets on the inner five ribs. The two end ribs can be squeezed so I can do that solo.

The process went better than I had feared. I was a little anxious about this step because of the ProSeal mess and the fact that reworking rivets in ProSeal is kind of a mess. We managed to keep the ProSeal contained and only had to drill out one rivet. As recommended in the instructions I prepared all the tools and parts before starting. I also cut out about 50 2×2 inch squares of paper towel to use to clean up ProSeal along the way. I mixed 33 grams of sealant (30 grams white + 3 grams black) for each rib and that was enough to butter up the flange, dab a dot on each rivet dimple, and fillet around the flanges after setting all the rivets. I also had enough to make a seal cap over the rivets on one of the two ribs installed today. Here is a view of the first rib installed. The fillet has been made around the perimeter of the flange but there are no caps on the rivet heads yet.

Here is the other side of the rib with the fillet installed. I used a syringe like a caulk gun to lay down the fillet.

Here is the second rib installed with the fillet and each rivet head sealed.

That’s two down and five more ribs to go on this tank. Then there is the other tank to do also. Looking forward to being done with ProSeal.

Categories: Fuel Tanks, Wings

Rivet Fuel Sender Reinforcement Rings – 1.5 hrs

November 14, 2010 Leave a comment

Sunday Nov 14, 2010

The business for today was to rivet the reinforcement rings and nut plates to the tank baffles. ProSeal is probably not necessary for these parts because the fuel level sender will be installed with ProSeal later but I decided to seal them anyway. Duh!

The process was fairly straightforward with no surprises. I scuffed with scotch-brite all the surfaces, cleaned with MEK, etc, etc. The photo below shows one of the two with rivets set but before I applied ProSeal over the nut plate rivets.

And here is one of the two after sealing it all up with ProSeal. I did not have any clean syringes so its a bit messier than my earlier attempts. The other reinforcement ring looks much the same.

That’s all I completed on the wings today because I had a broken sprinkler pipe that I spent a good part of the afternoon fixing while I had sunlight. Life sometimes gets in the way of building.

Categories: Fuel Tanks, Wings

Misc Fuel Tank Riveting – 2.5 hrs

November 13, 2010 Leave a comment

Saturday Nov 13, 2010

I passed my written test for my private pilot certificate today with a score of 95. I guess I could have done better. Now I just have to complete that check ride and I’ll be legal.

On the building front, I riveted a few miscellaneous items on the left tank ribs in preparation for starting to rivet the ribs into the skin. First was the flop tube anti-hangup bracket on the access cover. The two z-brackets need to be sealed or they will leak of course. Here you can see the z-brackets riveted on first with ProSeal.

Then the top strip was riveted on. No sealant required here.

Next was the tooling hole on the outboard rib. I ordered a few AN470AD6 rivets from Vans for this purpose. They were too long so I cut one down to about 3/16 inch. After scuffing and cleaning everything I applied sealant to the rib around the hole and inserted the rivet. Since my squeezer won’t handle an AD6 rivet I put the factory head on my anvil and wacked the shop head a few times with a hammer to set the rivet. It turned out better than I expected. Then I applied the usual fillets and caps to seal it up good. Here is the factory head side.

Here is the shop head side.

Then I riveted the flop tube anti-rotation bracket to the inboard rib. This was straightforward and I was able to squeeze both rivets.

Categories: Fuel Tanks, Wings

Riveting Fuel Cap and Drain Flanges – 2 hrs

November 13, 2010 Leave a comment

Friday Nov 12, 2010

Work has kept me out of the shop this week. So when Friday night came I was ready to get something done on the fuel tanks. My objective tonight was to rivet the fuel cap and drain flanges to the left tank skin. I did a check fit of the fuel cap flange to the skin and found that the machined countersinks were too small. I made them to fit the rivet heads, not the dimples in the skin. So first step was to enlarge the countersinks accordingly. Here you can see the flange with the new larger countersinks.

Then I did the whole sealing routine; cleaning parts and rivets, mixing sealant, spreading it on the flange surface and clecoing the flange to the skin. I did not forget to install the fuel vent line clip. Good boy. Then I went around the circle and riveted it up with a flush set and tungsten bucking bar. I used -4.5 rivets on the thinnest part of the flange and -5 rivets every where else.

Here is the inside of the flange after I applied a fillet all around and sealant caps on the rivet shop heads.

The fuel drain flange was easier. I could squeeze all these rivets with a 3 inch yoke.

On the inside I made sure to leave gaps between the sealant caps to allow water to flow easily into the drain.

Categories: Fuel Tanks, Wings

A Riveting Discovery – 7 hrs

November 7, 2010 Leave a comment

Sunday Nov 7, 2010

I began installing skin stiffeners on the left tank on Tuesday, Nov 2. I laid out all the tools and supplies I needed, used MEK to clean the rivets and surfaces that were going to be sealed, and then began mixing the noxious tank sealant. Man that stuff stinks up the garage.

As recommended in the instructions, I planned to back rivet the stiffeners. So I applied a dab of sealant to the skin dimples, inserted the rivets and applied rivet tape to hold them in. Then I put the skin down on my back rivet plate, spread sealant on the faying surface of the stiffeners and joined the parts. I shot the rivets at about 25 psi.

The first thing I noticed is that the rivets seemed to set a little shorter than I expected although the sealant that squeezed out made it hard to tell. When I flipped the skin over I found that the rivet heads were not flush down in the dimples. They were all about 0.010 proud of the surface – or so I thought. Needless to say I was not happy. Here is the skin with one whole row of stiffeners installed in this first step.

Here is a closeup of a few of the rivet heads. It’s hard to tell in the photo but if you run your finger across the heads of the rivets you can feel that the heads are  slightly high. The back rivets I set on the empennage were nice and smooth. You can hardly feel the heads if you run you finger across them, so that is what I expected here. I tried driving the rivets again with a swivel flush set from the head side and that improved some of them a little but I was still not satisfied with them.

The following journey played out over several days. I posted a question on the Van’s Air Force forum and got some useful responses but no clear cause or cure. Some said it was not a big deal and to just move on. But I tried a number of things to fix the problem. I checked my tank dimple dies. I tried pressing down harder with the back rivet set. I tried eliminating the rivet tape. I tried setting one with the flush set and a bucking bar. None of those things helped. Then I made a few sample dimples on some scrap 0.032 thick material and I discovered that the dimples on this relatively thick material are not as well formed as dimples in thinner material. What I mean is they create a larger diameter deformed zone that is about twice the diameter of the rivet head. When I put a straight edge across the dimple with a rivet in it I could see that the rivet head was actually lower than the overall level of the skin. When I put the straight edge on the tank skin I found that with only a few exceptions the rivet heads are actually flush with the overall surface, but they are slightly elevated relative to the skin right at the edge of the rivet head.

So what was happening is the dimple makes a depression that is about 0.010 deeper than the head of the rivet. When I press down on the back rivet set the rivet drops to the surface of the back rivet plate which is about 0.010 lower than it should be to be fully flush against the dimple. The pictures below illustrate. The red line is the skin and the extended contour of the dimple. The black line is the stiffener. In the top view the rivet is pushed all the way up into the dimple against the skin. That’s where I want it to set. In the bottom view the rivet has dropped about 0.010 so the head is flush with the back rivet plate. This is where it is actually being set so you can easily feel the edge of the rivet if you run your finger across the skin.

In the middle of the night I came up with the idea of making rivet dots out of 0.016 thick aluminum to place on the heads of the rivets when setting. The objective is to keep the rivet flush against the dimple when back riveting. Here is a photo of one of the dots held on a rivet head with rivet tape. I tried this initially when driving a few rivets on one stiffener. It worked beautifully. All rivets were tight up against the dimple and there were no marks on the skin or other issues. They are very smooth when you apply the finger test.

So I made enough dots to back rivet a whole stiffener in one setup.

I completed the rest of the stiffeners with this process with great results. I also went back and drilled out and replaced the worst rivets on the first row of stiffeners where I discovered the problem. Bottom line is this process worked out well for me. I am now happy with the look and feel of these rivets. I will probably try using the standard dimple die set on one of the ribs on the other tank to see if the deeper tank dies are part of the root cause of this problem. If so I will report that. If not I will continue to use this process.

Here is the complete set of stiffeners installed on the left tank skin.

I used some large plastic syringes to apply the sealant caps over the shop heads of the rivets and fillets along the edges of the stiffeners. This worked well for me and allowed me to control the sticky sealant better than using a spatula. Here is a closeup of the sealant “caps” on one of the stiffeners.

Categories: Fuel Tanks, Wings

Dimpling Rib Flanges – 1 hr

November 1, 2010 Leave a comment

Monday Nov 1, 2010

I was hoping to start riveting stiffeners onto the left tank skin tonight but there was limited time and I didn’t want to rush it so I finished dimpling the flanges of the ribs for the left tank instead. Maybe I’ll mix my first batch of tank sealant tomorrow.

Categories: Fuel Tanks, Wings