Rusty's CX4 Build Log: Leading Edge, Lower Wing Skins and Rear Spar

It's been a while since I've posted, but I've been busy on the right wing.

Since my last post, I was able to:

Add nylon hose for tip lights or maybe a leading edge landing light down the road
Drill and rivet the leading edge
Mount the lower wing skins
Fabricate and rivet the rear spar and reinforcement
Cut one of the top skins and mark drill holes on it

Leading Edge

The leading edge was a little difficult to work with. but I was able to bend it and attach it on my own. For some reason I had a hard time picking where to space the rivets. I just looked at pictures and counted how many rivets other builders had, and that seemed to help. You can see the lines on the sheet in the image below. This picture also show the hose I added to run wires through if I want to add lighting later. I kept it toward the leading edge so it would be easier to add a landing light in the leading edge if I ever felt like it.

I drilled the skins, and marked the center line down the rib to help me align the rib with the hole when matching drilling. In the picture above, you can see the holes drilled and the center line on the first rib.

Clamping a 2x4 at the base of the leading edge helped to hold it in place. Then I could add one on the other side to test the fit. I used the broom handle to align the ribs with the holes I drilled in the skins. Seemed to work well.

Everything riveted in place. I left two holes on the top and bottom of the wing root rib empty to maybe use as the screw holes for the wing gap fairing that will need to be added later. I haven't thought through that whole process yet, but you can see the missing rivets below. Also, don't forget to leave the out board rib alone (no rivets) so you can attach the wing tips. I got "rivet happy" and had to drill some out.

Trailing Section

So this is a little bit out of order. I actually drilled and test fit the rear ribs before attaching the leading edge skin. Rivets are pretty permanent, so it seemed safer (I don't think it makes much of a difference).

The Dremel with a flexible extension is almost a requirement when drilling the ribs if you want to get a nice perpendicular hole.

I used the rib alignment jig mentioned in the build manual (make sure your tooling holes on the ribs are all in the same place. If they are not 100% perfect, you might want to try the method I used to align the nose ribs in an earlier post).

Test fitting the lower wing skins...

Wing skins bent. I bent them over the straightest 2x4 I found. Worked okay, but I bought the recommended 3" steel angle since for bends.

More test fitting above, and below with the rear spar (1x1 angle 1/8" thick).

I marked and drilled the lower skins. Much easier since there is no fluting on the bottom of the rib flanges. The two bottom skins overlap each other. Since the wing tip is higher than the wing root once installed on the plan, I decided to make the outboard panel overlap the root panel. My thought was to keep water out of the wing when tied down.

Hole Duplicator
For the overlapping section, I made a hole duplicator so that both skins and the wing rib would all be match drilled. It is a very easy tool to make and uses two 42 blind rivets and one solid rivet from the spars. Worked great. Just match drill the lower skin and the rib, then use the duplicator by sticking the solid rivet in the hole and drill the top skin. Now all three pieces are perfectly match drilled.

To make one...Drill two matched holes in two .040 scrap pieces for BSBS-42 rivets. Rivet the pieces together. Then drill a third #30 hole in the opposite end once they are riveted together. Add a 470-4-7 rivet as a drill guide in the third hole. Here are some pics.

Below is the riveted wing so far. I should have done the top skin first as the manual recommends. My wing is very straight, but I can see how you would use the lower skin to adjust any warping you have. I'll do the left wing in that order.

Drilling and riveting the lower spar (again, manual is right. You should do this last). That's a lot of holes!

Rear Spar

Not much here to show. Just drilling a lot of holes. Make sure your wing is straight and level so you don't add any warping.

Rear spar reinforcement. Bolt direction is opposite of plans. I'm not sure if I'll regret this later, but I saw others do it this way on planes that have been flying for a while.