Attached Flange on the back of the Firewall

Click to enlarge

I did find some time on Christmas eve to go back and create and attach the flange on the back side of the firewall. I was looking at some other builders' photos and discovered that I had forgotten to do this. This process was very easy to do. I stuck the .75"x.75"x.0625" angle up to the back side of the firewall and marked the places on this angle where the firewall had flange cuts. Then, using a #40 drill bit, I drilled holes at these locations on the mounting side of the angle. I then used my band saw to cut slots up to these holes so I could bend the angle to match the contour of the firewall edge. Be careful not to take too much material out of the mounting side of the angle. You don't need to, as you do not bend the angle much to get it to take the shape of the firewall edge.

Finishing Touches on Top Skin

I did work on the airplane this past weekend, but didn't take any pictures. I pulled the rivets on the top skin. Before I did, I remembered that I will be putting the side skin under the top skin, which is not what the plans call for. So, before pulling the rivets I had to go back and crease the edge so it will make a nice fit when I do pull the rivets along the rear stringer. I also may make my temporary angles which are holding the F8 & F9 bulkheads tops in place permanent. They seem to be holding everything in place nicely. I still have time to decide.

I also started cutting the lower skin. I think I will do it in 3 parts.

I am having knee surgery this Friday, so building will come to a stop for a while.

Fitting the rear fuselage top skin. - Part2

While my wife toiled away at preparing a great Thanksgiving meal, I worked on my CX4 project. It was time to put the trimmed top skin back on and drill the holes in the stringer. Before I put the skin back on, I marked out the hole locations in the stringer and then drilled them with a #40 drill. This way I could replace the skin and hold it tight to the stringer with the straps and 1"x2" boards, reach up underneath and use the previously drilled holes as guides for drilling the skin. This technique worked great.

Click on image to enlarge

I occassionally drilled a little deeper into the 1"x2" board and used a cleco to temporarily secure things.

One of my concerns leading into drilling these holes was how to secure the stringer where it butts against the forward longeron. If you remember, I chose to do my splice differently than the plans call for. I'm doing this splice from the outside with screws instead of the inside with consunk rivets. So, at this point I have to undo my splice to drill my holes. This means that nothing is holding the two peices together where the stringer butts against the forward longeron. So, I carefully held the stringer and skin in place with a clamp and twisted it inward (because the top skin wants to bow outward) until everything lined up and then drill the first hole nearest my splice and installed a cleco.  I also used a couple of wood clamps after this first hole was drilled to twist everything into alignment. This really wasn't as hard has it sounds. Just take care and drill that first hole carefully. Everything else falls into place after that.

So, once all the holes are drilled, you can remove the clecos from the underside, loosen the straps and clamps carefully and install clecos on the outside. It is one of those times you can look at your project and see that you have accomplished something of significance.

By this time, the turkey was done and I had one more thing to be thankful for!

Fitting the rear fuselage top skin.

With the rear bulkheads in place, it was time to start fitting the rear top skin. The key is to pre-drill the bulk heads where you want the rivets to go. Once the holes were drilled in the bulkheads, I used my Dremel tool and drilled the skin from underneath using the bulkhead holes as guides. I started with just the centerline holes and put cleco's in them.

Click on image to enlarge

Then I clamped a 1"x2" board to each side edge and then use some straps to pull the skin down tight. Looking underneath, I was concerned about the gaps I saw near the top of the bulkheads. After a conversation with Dave Thatcher, I proceded with drilling holes and installing cleco's. What I did was, I loosened the straps until the skin laid nicely near the tops of the bulkheads and drilled the holes and installed more cleco's. Then I would draw the straps tighter and repeat the process.

I am pleased with the outcome as the gaps I was concerned with just went away using this procedure. As I tighten the strap closer to the stringer, I then used the clamps holding the 1"x2" board in place to clap it to the stringer.

Once all the holes were drilled, I then drilled them to 1/8" size and marked the oversized skin for trimming along the stringer and the F6 & F10 bulkheads.  I have now removed the skin for trimming and while it is off, I will predrill the holes in the stringer. I will also debur all the holes. Hopefully, I will be able to finish the installation over the Thanksgiving weekend.

Installing F8 & F9 Bulkheads

I finally spent time working on my project yesterday. I worked on locating and installing the F8 & F9 bulkheads. I used an 8 foot piece of 1"x2" square alum. tubing as a straight edge and placed it on top of F6 & F10 bulkheads to determine the height of F8 & F9 bulkheads. I had already used this square tubing to make sure F10 was level with F6.

Click on image to enlarge

The photo above shows the assembled bulkheads, but I assembled them after the next step I'm about to describe.  I had to figure out a way to get the tops of the bulkheads to stay in position while I attached the skin. I had assembled my bulkheads by laying them on the plans. I temporarily assembled them with cleco's, but found that they were too tall to fit between the square tubing and the 2"x4". So what I did was I disassembled the top of the bulkheads and clamped them to the underside of the square tubing. I located them in a postion where the top skin would transition nicely onto the side stringer (I use a scrap peice of .020 alum. for this). I then used some scrap 1/16"x3/4" angle as temporary "holders" to keep the top bulkhead piece in place where I wanted it. Once I had drilled holes and cleco'd everything in place, I could disassemble everything and begin to figure out how to attach the remaining side and bottom bulkhead pieces, which I kept assembled.

I had to trim my side pieces so I could raise the bottoms to the correct height. I slid them between the temporary mounting angle and the face of the bulkhead and then aligned everything the way I wanted it. Then drilled holes and cleco'd things together.

Take note of the hole in the left side piece. This is the hole that the elevator push rod tube is suppose to go through. Again, I drilled this hole by placing this piece on the plans and locating it's position. As I said before, the bulkheads didn't fit until they were trimmed down. I only trimmed from the top on both side pieces on both the F8 & F10 bulkhead (instead of trimming a little off the top and a little off the bottom of these pieces), so at this point, I don't know if this hole is in the correct position. I'll let you know when we get to installing this push rod tube. If I had to do it over, it might be better to drill this hole later on.

I did try to pull the top skin down over the top pieces before attaching the side and bottom pieces, but I didn't feel comfortable in doing so. I'm now ready to try this again. Till next time...

Too much football

Between watching football, and my son playing football, I haven't had much time to work on my CX4 project. I did pull some rivets to finish my rear stringer lengthening and it's installation, but that's about all. I ordered some screws for the forward splice between the forward longeron and the rear stringer. I think I'm ready to start the installation of the top rear skin. I'll do a trial fit soon.

Get that seat back height correct!

For many of you, this is your first project. This is mine as well. Mistakes happen. Here's another example of one I made and corrected.

I assembled the section between the firewall to F6 (seatback) and then started on assembling the fuselage. I didn't pay close attention to the height of the seat back. I had assembled it by placing it on the plans. But the builder needs to keep in mind that there are many areas of adjustment before proceeding. My seat back height was too high, but I didn't realize it. I proceeded to set up my 2x4 on my work bench by locating the F10 bulkhead position and then leveling the top of F10 to the top of F6. Thinking I had things where they ought to be, I notched F10 for the 3/4" stringer angle. I did the port side 1st. But when I got to the starboard side I could see that I was going to cut into the large hole that F10 has for which the elevator control passes through. Since I bought my bulkheads from Peter Beck, I called him to discuss this hole location. He immediately recognized that I had an issue with my set up. After some discussion and measuring, we determined that I had not set my F6 top to 6" above the forward longerons.

So what I had to do is lower the seatback top and reposition my 2x4 so I could relevel my F10 top with the lowered height of F6 top. Now everything was where it needed to be. In the photos below you can see I simply repaired the 1st notch I had cut on the port side of F10 and continued with my building.

Click on photos to enlarge

Tool for bending forward upper longeron.

I need to take a couple of steps back to show you how I bent the upper longeron to match the angle of the rear stringer that runs from behind F6, all the way back to F12. You can't really bend the upper longeron until it is mounted in place because you don't know the angle to which to bend it. Here is the tool I made to bend mine.

Click on photos to enlarge

I used a scrap 2x4 and cut a slot at one end of it just wide and deep enough to fit the upper longeron into. My 2x4 just happened to be 27" long, but it gave me enough leverage to bend the forward longeron inward.

It is important to have bulkhead F10 in place and notched for the 3/4"x1/16" angles, making sure they are level with the top of the forward longeron. Then temporarily mount the 3/4"x1/16" stringer and bend the forward longeron inward until the angle matches the stringer. A second pair of hands is nice to hold the stringer while you bend the longeron, but not required.

Mounted F12 to Stringers

Click on photos to enlarge

I continued work on attaching the stringers today. This is tedious work because it requires you to assemble and then unassemble the peices several times before you have what you want. I used a scrap peice of the 1/16" angle as a shelf to attach the stringers to. I attached this to the front side of F10 as shown in the photo above. The angle makes it easy to level the stringers at F10 side to side. The stringers will be held in place with one 1/8" rivet attached vertically through this shelf. Due to lack of space to drill the vertical rivet hole, I figured out the appropriate location of the vertical rivet hole and dismounted the angle and drilled it 1st. Then I remounted it and put the stringer back in place and used a Sharpie to transfer where the hole was to the stringer. Then unassembled everything and carefully drilled the hole in the stringer. Then I went to the other side and did the same thing. Very tedious!

Next I attached F12 to the stringers. I was having trouble figuring out the horizontal distance F12 is from F10. The plans have the distance from F10 as it is laid out on your 2x4, but I had to cut the end of the board off because it interfered with F12. So my measurement was gone also. I finally found it on Sheet #3 (Rudder & Fin Assembly) where it indicates "about" 17 3/4" between the front and rear fin spars. Well, these spars mount to bulkheads F10 and F12 respectfully. Not very clear if you ask me. I trimmed my stringers so that I achieved this distance. In lue of a countersunk rivet to mount F12 to the stringer, I will leave the cleco in place until it is time to put the side skin on where I will use a "hole finder" and use this hole to attach the skin as well. I have to remember to use a long rivet here.

It might be time to replace some clecos for rivets and then some top skin.

Stringer splice to go beyond 8 foot stock length.

Click on images to enlarge.

I didn't get much done this Labor Day weekend. We had a family wedding to attend. I wanted to get something done so I worked on lengthening the stringer past the standard shipping length of 8 feet. I cut off 36" and added 41" which puts the splice between F9 & F 10. I'll let you know what my final length is when I install F12. I'm leaving the cleco's in place until I know for sure I have enough length to work with.


I used a 5" piece of 3/4" x 1/16" aluminum angle (same material as the stringer) for the splice. You have to round off the outside corner edge to get it to fit inside the 6061-T6 aluminum angle due to the inside radius. I used an aggressive file to knock off the corner edge and then used sand paper to give a nice radius until it matched perfectly with the inside radius. I will use 1/8" rivets to secure from the top only, so as to save the side rail for attaching the skin to.

While talking to Dave Thatcher on the phone on "what I do next", he reminded me that there are two anchor nuts that hold the front fin spar to F10 which get mounted later on to the front side of F10. He said not to rivet the side skin on until I have mounted these nut plates. I leave little notes like the one above to help remind me of these things!

 Click on photos to enlarge.

Because C3 thru C6 protruded out the bottom slightly, I had to modify my bottom skin flange just outside of ribs C3 & C6 as you see in the photo above. Basically I cut a small wedge out of the flange so I could get the skin to angle upward towards ribs C1 & C2 on one side and ribs C7 & C8 on the other side.

 Then I attached a piece of bent aluminum to extend the C2 & C7 rib flange down to the skin as shown in this photo.

Other ways to fix the problem were discussed, like tearing out the seat pan & ribs C3 thru C6 and redoing them, but I opted for this fix. I discussed with Peter Beck why ribs C3 thru C6 might have been longer in the rear and he was going to review his forms. There are some trimming involved with these ribs anyway and, had I followed the plans and laid the wings directly on the floor, or placed a flat piece of plywood between the 2x4's I used to raise my structure off the floor, I would have just had to trim the ribs C3 thru C6 from the top side to make the seat pan fit correctly. Had I known what was happening, I would have chosen to do this.

All in all, if I had not mentioned this to you, you would never have known about this mistake as it is on the bottom of the airplane where no one will see it.

Seat Pan Mistake & Correction

Another mistake I made that I would like to communicate had to do with the center section. The plans say to lay the center section spar on a flat level surface and attach the wings and create the rear center section spar. Then you are to attach the ribs C1 thru C8. Well, my garage floor in flat and level so I used it. However, what I did next sort of got me in trouble. I was having trouble working with a wrench when everything was laying flat on the floor, so I placed two 2x4's under the wings to raise everything up off the floor so the wrench would work better. When I went to install my ribs, I made them fit the top of the front & rear spars. Well, ribs C3 thru C6 were slightly taller in the rear than ribs C1 & C2 and C7 & C8. This made ribs C3 thru C6 protrude out the bottom by about 3/16". I didn't discover this until I flip the center section over to put on the bottom skin.

See next post for how I corrected for this mistake.

Here is the reworked wing tip.

Click on photo to enlarge

As you can see from this photo, my first attempt at the leading edge of my left wing tip did not have a satisfactory result. What I decide to do is to start on my right wing and try to figure out how to do it correctly. Then I came back and redid this wing tip. The trick is to roll this with a different radius at each end.

Trying to get the wing tip skin to mate well with the wing skin was a bugger as well. I had a neighbor help me with this process. He held things in place while I drilled the holes. This was truely a trial an error process for me. I hope filler will hide my poor workmanship. Most who have seen these corners say I'm being too hard on myself. You be the judge.

Next came the center wing tip rib. I had to reshape it to get it to fit properly. I was concerned that the other wing tip was going to be different from this wing tip, but as it turned out, I had to make these changes on both wing tip structures. So, whether they are different from the plans, the important thing is, THEY ARE A LIKE!

Wing tips were a problem

Click on photo to enlarge

 I have now uploaded my CX4 build photos for everyone to review and since I'm starting this blog after I have started, I will try to pick a couple of issues that gave me trouble. One of these was the wing tip structure. I had several issues that challenged my building abilities.

First was fitting the rear wing tip spar. I should point out that I bought Peter Beck's spars/center section and his bulkhead and rib kits. I personally thing Peter has a good product and if this is how you want to get a head start on your project, I would recommend his kits. As you can see in this photo, the rear spar had to be positioned in a different position than called for in the plans. No big deal really, just do it. I have found this similar issues throughout the build process. I guess it's just part of "scratch building" from plans. Dave Thatcher has been a great help with dealing with these types of things.

First Post

Why blog? Well, I have been the editor of the Quickie Builders Association newsletter, Q-Talk, for nearly 5 years now and the newsletter seems to be as relevant today as a typewriter in the age of computers and the Internet. After 20 plus years and 5 editors, the Q-Talk newsletter will come to an end this December. I believe the Internet has replaced it. Yahoo Groups allows you to discuss any subject or ask any question to other like minded people and get a response almost instantly. The newsletter used to be the means by which this type of information got communicated. By the time I publish the newsletter now, a topic is old. The newsletter used to be the archive of all the information that was known about our little airplanes. It was always strongly suggested that you buy all the back copies to inform yourself about what had come & gone with this particular airplane design, before you started your project. Now you are asked to search the Yahoo Groups email archive to get yourself up to speed. Searching the Yahoo Groups archives is way easier than trying to remember what issue a brake mount modification was in.

Also, instead of writing an article about an issue you have overcome with your project and then sending it to the newsletter editor, guys started their own blogs to record their journey with their airplane. And this is the reason I started this blog. Not only for me to record my journey, but to document my build process for those future builders.