Wings – N249DA

Riveting the Wing Skins

So now that the fuel tank and leading edge is on the wing, now it is time to add the top skins. We started with the inboard top skin and wing walk doubler. In the first picture below you can see five ribs very close to each other. The large number of ribs in a small area designed to disperse the weight of a passenger or pilot while entering or exiting the aircraft. There is an extra piece of skin in between the ribs and the actual skin to help with the dispersement.

After getting the skins in place and clekoed in place my dad and I began riveting. He was on the inside, and I was on the outside. Once the inboard skin was on, we put on the outboard and continued.

We started close to the middle and worked our way to the outsides. Once both the inboard and outboard skins were attached, a J stiffener was added down the middle. This helps to add stiffness to the structure. Finally, the top skin was completely riveted to the structure. This was a big moment. I was also surprised how rigid the structure was.

Now that this is all done, time to do it all again to the other wing!

Finishing Leading Edges and Creating the Front of the Wing

Now that the tanks are finished, time to rivet the leading edges so they can be added to the spars. Most of the work was already completed before the leading edges were primed. They were just clecoed back in place, and then riveted. This went pretty easily, and next it is on to putting the tanks and leading edges on the wing spar.

So next was putting the tanks and leading edges on the main spar. First the leading edge goes on. Then the tank is added. This helps to ensure there is no sag in the spar when the main skins go on.

This is super exciting! Great progress, even though it is hot outside in Texas now. it really starts to look like a part of an airplane now. Next will be the main wings skins.

The Tank Continues

So the tank was almost ready for testing. The last major part to put on was the back baffle. This is really tricky because there are several ribs which all have to line up. Once everything is lined up, the side of the baffle is riveted to the tank skin.

The last step was to add the tank attach brackets to the back of the baffle. This is done with pull rivets since you cannot access the inside of the tank very easily. Now the structure of the tank is complete. Time to close out the last few items. This included the plumbing for the fuel vent and fuel pickup, and the access plate.

Once this was completed, it is time to test the tank. I ordered the test kit from Van’s. After testing there was only two leaks on one tank, and no leaks on the other. Overall, very happy with how it turned out!

The Tank Work Continues

So now that the all the drilling and dimpling work is finished on the tank, it is time to put it together. Because the tank needs to be water-tight, sealant is used to achieve that. It is a two part sealant that has to mixed at a ratio of 10:1. This stuff stinks, and is super sticky! A thin coat of sealant is applied to parts prior to riveting. Then a nice fillet is applied around the parts, and all of the rivets are incapsulated to prevent fuel from leaking out. The goal is to seal the tank from the inside out. First to be install were the filler neck, drain flange, and the stiffeners.

Next was time for the actual ribs of the tank. Again sealant was used to to ensure a water-tight seal. But you have to be careful, because if you use too much sealant, you can alter the shape of the tank, and it may not fit correctly. So I think this is more of an art form than a science. But in the end, I got through it. I’m sure its on the neatest job, but the most important question is will it leak?

Now I will not know if the tank will leak until it cures completely. That may take an additional 2-3 weeks from today (04/18/2021). I will for sure update the status when I know it. With all the ribs in, there are a few more items to take care of in the tank. The first is the vent line. This ensures that there is not a suction on the tank. Additionally, the fuel pickup tube is added to the tank. Finally, the Fuel Level Senders is added as well. Now to get the other tank to this point.

More Tank Work

Now that the tanks have been fitted, there are a few more pieces that need to be made for the tank. The first is the Tank Attach Bracket. This piece will attach the tank to the fuselage of the airplane. It helps to distribute the weight. It starts out with a piece of angle aluminum (Looks like an “L”). I used a templed included with the instructions to trace it onto the aluminum and then used a band saw to cut it out.

Then, using the same pattern, I drilled several holes as instructed. Finally, the bracket is match drilled to the rib. It is key to remember where your fingers are. I nearly drilled my finger while match drilling. Luckily, it barely grazed my finger, but I started paying attention a lot more.

Next up is a modification to the inboard rib of the tank. It comes as a solid piece of metal. A large hole is cut out of it, and a doubler ring and special cover is used to cover the hole. The doubler ring allows for nut plates to be attached to hold on the cover. The cover holds two important items.

First, it holds the fuel level sender. This lets the pilot know how much fuel is in the tank. Secondly, it holds the fitting for the fuel pickup tube. This takes fuel from the tank, and attaches it to the fuel line from the fuselage.

The final two things I will cover are the fuel cap and drain valve. Not a lot of anything going on here. Parts are already made, just match drill them to the skin. I will say that the fuel cap piece had a cool feature. When it was designed, the lip around the cap holder, was designed to be different thicknesses. This is to account for the bend in the fuel tank skin. So you can see that in the middle picture, the thickness changes as you go around the lip.

Finally the drain valve is used to drain the tanks if it is ever needed. This also is the lowest point of the tank. Aviation fuel is less dense than water, so the water will sink to the bottom, and thus the lowest point of the tank. Part of the pre-flight check is to take a sample from each tank to ensure that no water has contaminated the fuel.

Up next, we start to rivet the tank, and I will talk about my new “best friend”, tank sealant.

Fitting Leading Edges and Tanks

So, now that we have the structure together and the skins on the it, the time has come to fit the fuel tanks and the leading edges. This is the first time that I really got an understanding for how the wing will look and the size. I was surprised. The first step was to attach the leading edge to the spar. this is done by attaching the ribs of the leading edge to the web of the spar (photo one below). Once in place and secured, a splice strip allows the tank to be screwed into it. This means the tank will be screwed into the leading edge.

After leading edge was on, the tank is fitted. It is secured to the spar. Below are pictures of the left wing with both the tank and leading edges on. Big accomplishment.

One big factor is how well these two parts line up. They are both made off the wing, and at this point, it would be very difficult to change the shape. Luckily, both the left and the right sets line up very closely, and I deemed it acceptable.

The last little step in attaching the tank for fit, is to drill the attach holes into the “Z” attach brackets. Since you want these to fit perfectly, the center (of three) holes is drilled before going on the spar, but once there the other two are matched drilled. This ensures a perfect fit. Next up will be more fuel tank work!

Fitting the Skins to the Wings

So now that the structure for the wing has been riveted together, the structure is moved to the wing stand. This stand rolls and allows me to move it around the garage. Even with this stand, I am able to park my truck in the garage each night. The skins are cleoced to the structure. There are two skins for the top and two for the bottom.

Once the skins are on, they are match drilled to the ribs. This is more “normal” work. On the top skin, a stiffener is ran the entire length of the wing. This has a special “J” shape, and helps to provide rigidity to the structure. These come without any holes, so you draw a line down the center and use that to help keep it centered while you match drill it to the skin.

Riveting the Right Wing Structure

So now it is time to start riveting the ribs to the main spar. This is a nerve-racking time. The spars are very expensive, and something that you do not want to mess up. So I took my time, and made sure that I was ready for every rivet. There are a total of 14 ribs to be riveted, so it takes a little while. Each rib had 5-6 rivets. Once I started to get into a rhythm, it went very well. Overall, I only had to replace two rivets.

After the ribs are riveted to the main spar, they are then riveted to the rear spar. This is much easier, as a different tool can be used. The entire process is then repeated on the right side.

Start of the Fuel Tanks

So similarly to the leading edges, the fuel tanks have a skin that is held in shape by a set of internal ribs. There are a few differences between the two. The first is the fuel tanks have additional stiffeners along the bottom of the skins. This are very similar to what was made and used on the rudder and elevators. Next, the ribs have a cutout on the bottom corners. This is to allow fuel to drain to the pickup so it can go to the engine, and it also allows water to drain to the lowest point, which has a quick drain. This drain is checked before every flight to ensure no water is in the fuel. The rest of the assembly went together just like the leading edge.

Since the leading edge ribs attach directly to the spar, the fuel tank has to have a back baffle to help create a water-tight tank. The baffle has attach brackets which attach the baffle and tank to the spar. These are made from a “Z” channel that is supplied. Once the tank is together, the attach brackets are temporarily attached to the baffle with blind rivets. The issue is the web of the channel is so close, most rivet pullers do not fit into the area. So, a quick trip to a local tool shop resulted in an inexpensive rivet puller. It was then ground down with a grinding wheel until it fit, and it still functioned! This was then used to pull the rivets, and finish this part of the tank build.

Also, I’m trying something new. I’ve been saving time-lapses of my work to help prove to the FAA that I am the primary builder of this airplane. I have put several parts together in videos, and I plan to start sharing them with the blog posts. So feel free to check them out.

Leading Edges

So while waiting to prime the main ribs, the next step was to begin the leading edges. These go on the outboard front of the wing. The main spar and ribs are behind it, and the fuel tank is to the inboard side of it. To start, a cradle is built to hold the skin in shape while you are working on the leading edge. A rib was traced onto some plywood to ensure the right shape was cut out. Then two of them were screwed to some 2x2s to make the cradle. I then decided to add a third holder in the middle. Overall, this was a simple, yet effective design.

After the cradle was built, I started to work on prepping the ribs to be put in the skin. Once all of the ribs were ready, I started to cleco the ribs to the skin. This was very frustrating. Even with the cradle, the skin is not shaped perfectly, so it takes some time to ensure everything lines up. Eventually it all worked out. And this had to be done for the left and right sides.

One difference in the leading edges is a stall warner is on the left leading edge. A stall is a loss of lift over the wing, normally due to a high nose up attitude. So, the stall warner is a device that helps to alert a pilot they are approaching a critical nose up attitude. There are newer technologies that help keep pilots aware, but I decided to also install the stall warner in my plane. There is a special bracket that goes in the left leading edge to hold some of the electronics. Then a small metal piece sticks out of the leading edge and when the air flowing over it lifts it, the stall warner goes off in the cockpit. This addition took maybe an extra 30 minutes, but I believe it is worth it. After that was installed, everything was disassembled. Then came the normal demurring, scuffing, dimpling, and priming.