Scott & Tanya Card RV9A build log (N4822C)

I made some home made jack screws to help keep the wings straight on the wing stand. The main spars want to sag a lot under their own weight in the middle. I made two jack screws for each wing out of a 4×4 and 3/8″ threaded rod with nuts and fender washers. I drilled a hole in the ends of the 4×4s to fit the threaded rod into, then a washer and a nut. It is a pretty cool setup. Some fishing line clecoed to the spar to show straightness lined up with the rivet holes and adjustment of the jack screws was easy. Next is to align and clamp the rear spars to be sure I assemble things without building a twist into the wings.

 

  

  

  

 

After all of the wing main ribs were primed, we could get to work riveting the ribs to the main spar and rear spar. First the rear spar doublers had to be riveted on. The only trick here was figuring out which holes to leave open.

Here is a side note about how I kept the ribs in order through pre-assembly, priming, and final assembly: As I did with the empennage parts, when taking the ribs apart after pre-assembly and match drilling, I took them off in order and defined a measurement datum on the ribs. I picked the forward most edge of the rib. Then, I made a very small single punch mark in the rib with an automatic center punch. This punch mark was made a measured distance from the forward edge of the rib (my datum). Each successive ordered rib got a similar punch mark slightly further from the datum (about 1/8″ further). This way, we didn’t have to worry about order identification. All we had to do after primer was to put the increasing punch mark distances in order. Once they were in order, we put a little piece of tape on the rib with the rib number for final assembly. This is my general method for parts identification. The punch marks that I use are so small that you really need to know where to look for it in order to find the mark. I usually make note on the plans as to where to find the identification punch marks.

I used a double offset rivet set to drive the main spar rivets. The manufactured head goes on the rib side. Tanya did a perfect job bucking the other side which I had taped off to protect the spar against scratching. I drove these rivets with about 65lbs. of air pressure. Thicker material seems to equal higher pressure. I did struggle (meaning I didn’t fully succeed) to keep from banging up the rivet heads with the set. I drilled out a couple of rivets because I beat the crap out of the head with the gun. I also left a couple that don’t look very pretty but will be fine. Don’t get me wrong, most of the rivets look totally fine (pictures always make them look worse). I always seem to struggle with the double offset rivet set. It isn’t very square or true. I am thinking about ordering another one from somebody else to see if it is any better.

I waited to rivet the rear spar to the ribs until the ribs were riveted to the main spar. This is the way to go, as Dan C. found out and thankfully made my life easier. You very much want to be able to get into the rib and deflect it a bit when driving the rivets. This would have been very difficult with the rear spar already on. The temptation was very much there as I was itching to do some riveting before Tanya was ready to help.

Both main wing skeletons are now riveted together and back up on the wing stand. Now it is an exercise in alignment so hopefully as skins start to go on, we end up with straight and true wings.

 

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

 

With this round of parts etching and alodining we have made a number of improvements.

We used a dip bath to acid etch the parts. Previously our acid etch method was to take our cleaned parts out to the driveway and spray the acid etch solution onto the part from a simple squeeze spray bottle, scrub with a scotchbrite pad, and rinse with the hose. All this while working on the ground with rubber gloves on made for a miserable experience.

What we did this time was to mix up a batch of the acid etch solution (1 part PPG DX-533 / 3 parts water) of about two cups of acid and six cups of water. This was sufficient to cover the bottom of the dip bath. Then we dropped one rib at a time into the acid bath and scrubbed all surfaces with a scotchbrite pad. This was done on top of the bench in the well ventilated garage. It was much easier to dunk the part with full solution saturation and scrub, dunk and scrub, etc. Actually Tanya acid etched all of the wing ribs. After each rib or part was done in the acid scrub bath, we dunked it into a nearby trashcan full of water on the driveway, then sprayed it off with the hose and hung it up to dry.

To hang all of this stuff up to dry, we put clecos into the main spars which were up on the stands and hung the parts on the clecos. This was Tanya’s idea and it worked great. We used this for all steps including to hang up to dry after primer.

Alodining was a similar setup and process except without the scrubbing. I put 1.5 gallons of alodine (actually PPG DX-503) in the same bath fixture. This was just enough to fully cover a main rib by about 3/4″. Once the rib was done in the bath, it went to a fresh trashcan full of water. No need to spray off with the hose after the water dunk. And, hang up to dry.

For the rear spars, I etched them with the solution sprayed from a bottle. I also sprayed the alodine on them and washed it off. They sure didn’t come out very good, but that should be expected when you’re spraying alodine from a spray bottle. It just isn’t the same as dipping but there was no way I was making a twelve foot long dip setup.

After the alodined parts dried for a day, we setup the primer spray booth and shot primer. Since my last large primer batch, I bought a new Devillbis HVLP primer spray gun. I was not very happy with the results from the cheep Harbor Freight gun that I was using on the empennage parts. The $250+ that I spent on the new gun was, with out a doubt, worth every penny for me. It is so much easier to use and produces fantastic results with ease. I could go on about the gun because the difference in results is so great, but I’ll just leave it at that. Suffice to say, the new primer gun rocks!

 

  

  

  

  

  

  

  

  

  

 

For acid etching and alodining all of the wing ribs and various parts, I made up a simple dip bath. I used this same method on some of the longer parts on the horizontal stabilizer and was very pleased with the results. This was the first time that we used the same idea for acid etching though and we’ll acid etch in a bath, as opposed to the spray bottle method, from now on.

The bath is just some 1×6 pine boards screwed together real quick. Note that I didn’t bother to put a bottom on it, the bench top sufficed just fine. Then I lined the resulting box with two layers of 6mil plastic. I bought a large roll of this stuff at Home Depot early in construction and I use it for all kinds of stuff when things get messy. I stapled the plastic to the top edge to keep it in place and help it stay down in the box. I didn’t do this when I did the horizontal stabilizer. It makes a big difference as the plastic wants to come out of the bottom corners of the box and no longer conform to the flat bottomed box. After the lining was in place, I clamped one edge of the bath to the bench top to help stabilize it. This was another improvement in my process.