Here are some images of the glue up stage of the center wing. I am using Aeropoxy as I spent some time collecting data on the strength of various glues and decided on its use for this center section. As per Sam's suggestion I am gluing up the center wing components with epoxy (Aeropoxy) but will use Titebond III to attach the skin when I get to it. I see little use for the epoxy on the skin as the Titebond absorbs deeper in balsa and, is the case with most wood glues, the glue joint is stronger than the wood. However, I would use epoxy if I had a plywood to plywood connection.
I have found that I can reuse the Aeropoxy nozzles by blowing the epoxy out on to wax paper with my air compressor and then cleaning them with Acetone and then blowing them dry with the compressor. I try and leave a small area to glue with the left over material on the wax paper. Although more expensive, I find Aeropoxy to be easier to use such as by using your finger to create a nice corner fillet and it does not gum up your hand like regular epoxy does. Additionally, it is best to wait until the end of the day and then do all your gluing at once as the setup time is recommended to be 24 hours. I find the glue is hard to the touch in about three hours but I leave it over night to be sure I have a good bond.
I used a square to position the ribs, but also measured from the center line of W1 out each side to make sure I was an equal distance for each rib. Yes there was a difference and sometime more than I would have thought. I believe that the wing is square and true. My supplies from PCM came up missing the triangle pieces so it was a 50 mile round trip to get them from the hobby shop. However, it was a good excuse to pickup many of the additional hardware items I needed for the wing. I also used a spruce spare for the bottom slot just in front of the triangle, this wing should be very strong.
I also used Sam's recommendation on extending the cardboard tube through W4, I had the tube length so I just drilled and sanded out an additional hole. Also the plywood leading edge looked like a great idea so I replaced the balsa ones with plywood. The PCM kit came with a 1/4" W1 but I had some 1/2" stock so I used it and recut W1, again something I noticed on Sam's build.
When I first saw the plan I wonder about the thickness of the N1 and N1s stock so when Sam said he was going with 1/2" I thought it sounded much better. On N1 and N1s I intend to drill through, and besides gluing them to the box, I will have two bolts and nylock nuts per piece. You might be able to make out the lines on the pieces where the bolts will go through to the box, small cutouts will be cut in the outside curve to allow the bolt and washer to set flat. I believe that this will kill any chance of vibration shaking these parts loose.
I bought 24 ounce fuel tanks, but if someone suggests a larger tank I will use that suggestion, never have used DA 50s I just guessed on the size based on the fuel used by my smaller gas engines. I also picked up the mid size Hi Tech 81 servos for the throttles and the chokes and will get them mounted before I skin.
I finally found the small cardboard tubes and they are rocket body tubes, I checked prices and the hobby shop was less expensive than ordering them due to shipping. The 1/2" size is D5 and the only small problem is that they are only 18" long so for long runs they will have to be spliced together.