Finally Priming Some Wing Ribs!

2.75 cans of NAPA 7220 primer and a small but potent amount of acetone later, I almost have all of the left wing main ribs primed. The final stage of the cleaning process was the acetone. This is where you have to be careful when you are dealing with a lot of similar looking parts. Up to this point I have been very careful to keep all the left and right wing parts together by labeling them with my blue Sharpee pen, in the proper order that they were fitted to the wing spar and drilled for riveting. There are 28 of these ribs in total, and it is important to keep the installation order in tact all the way through the priming process.

The only problem is, once you get to the acetone cleaning stage, you will remove any Sharpee markings or labels that you have written on each part to keep them properly organized. This is where I get the most worried that I will mix up the sequence of the ribs. Once the markings are erased from the metal the only way to tell which one is which is to remember the order in which you stack them. Then,when the time comes to lay them out for pirming, you REALLY need to have a method in mind to keep track of the parts. I chose to lay the ribs on my new priming table from a top to bottom, left to right fashion. The following pic is taken from the opposite direction from the reference position I use to keep track of the parts, so the number 1 most inboard wing rib is actually on the bottom right of this pic:

 

It became apparent rather quickly that my new table will only hold 12 of the 13 additional ribs I needed to prime. I already primed the two end ribs. Regardless, the new table did what I expected it to do, and it was nice to be able to setup a lot of parts for priming all at once. I have found that the key to doing something like this is to be prepared to do the entire job in one session. That means allowing enough time to prime one side, drying, then flipping them over and priming the other side - all in one single work session. That way you do not forget the order that the parts are set on the table. I have also found that in cases where you are dealing with lots of parts for both left and right side assemblies, it is best to do one side and finish the entire process for those parts, before trying to work on any of the parts for the other side. This prevents me from mixing up the left and right side parts. Everyone has their own method to handle this, but it is always the last step in the process prior to actually being able to rivet things together. As such it is a very important part of the entire preparation process that you must figure out ahead of time to avoid confusion, or worse yet, the possibility of riveting the wrong part in the wrong place later on.

Here is a shot of the smaller table I have used in the past with the 13th rib:

And here is a pic of the fully primed end ribs for both wings with the support angles reattached. I set the angles on the workbench and then set the front flanges on the bench next to each angle bracket to ensure that the support angles would be flush with the flanges of the rib to make sure that the attach bracket is as straight and true to the orientation of the rib as possible. This becomes important when checking the wing assembly for any twist or bend while it is on the wing stand. I wanted to make sure that a slight angle to the support angle bracket would not introduce any unwanted twist to wing, so the support angle and the forward flange of the rib needed to be flush with each other.

These end ribs will not be riveted to the main wing spar initially since the leading edge rib on the end must also be riveted in assembly with the main rib. All the other LE ribs are offset from the main ribs just a bit to aid in riveting. I have not attached them to the wing spars yet because I also have some minor scratches and dings in the main wing spar that need to be dressed, smoothed, cleaned and primed. After consulting with Vans about these a long time ago, they decided that these were most likely just surface scratches from shipping, and as long as I don't need to remove much material from the spar web I should be able to fix them and move on. I will admit, however, that the recent loss of our EAA Chapter 43 president in his plane has given me cause for some concern about my wing spars. It appears that this accident may have been been the result of a catostrophic wing spar failure, but we are still waiting for the NTSB reports.

I need to get some more primer tomorrow so I can continue with the right wing ribs. I also did some research to confirm something about the riveting process for the main ribs to the wing spars. It seems that the Vans instructions simply tell you to rivet the ribs to both spars when the time comes. Others have cautioned that it is easier to rivet only to the the main wing spar first, so that you can spread the ribs out to get a standard straight rivet set into position while lightly bending the rib flange out of the way of the rivet gun. If you rivet the ribs to the rear spar as you go, you no longer have the capability to spread the forward flanges out as described, making a bit harder to rivet the ribs together - especially the ones nearest the root, which are much closer together to support the added weight and loads of the pilot and passenger entering and exiting the airplane.

This has certainly been a long time coming, and it felt good to get back to working on the plane, especially when you know you are getting close to being able to rivet things together. I can't say that I enjoy putting on the chemical breathing mask every time I have to do this, or breathing acetone fumes, but in the end it is just part of the process of building an airplane so you just have to accept it and move on.