It’s been 3 months since my last post. I’ve been working on the tail cone a lot but I’ve just been slacking on blog updates so I figured I should get caught up with a quick summary of all the work I’ve done.
I finished up getting the tail cone parts assembled and match drilled. When I started to take everything apart I noticed that a lot of the holes in the bulkhead flanges were enlarged and oval shaped. I noticed when I was final drilling them that the holes in the flanges weren’t lining up perfectly but I thought I was doing a good enough job of getting them aligned before I drilled them. That turned out to not be the case. I had the option of building little doublers for the flanges with enlarged holes but since there were so many of them I just decided to replace the bulkheads. That lead to a lot of time wasted with waiting for the parts to get here, deburring them, reassembling the tail cone to final drill them all again, and then take it all apart again.
Then I noticed on the bottom skin that I did a really bad job when I was match drilling the stiffeners. Quite a few holes in the skin were enlarged but luckily the stiffeners all seemed to be ok. Support at Van’s didn’t think the holes looked too bad in the pictures I sent them and thought I could probably just build on without doing anything with them. However, I didn’t like how large some of them were so I decided to re-drill the worst of them for 1/8″ rivets. Luckily it’s the bottom skin so no one will really notice the different size rivets unless they go looking for them.
Once everything was finally deburred and dimpled, the weather was getting colder so it took a while to find warm enough days to get the priming done. I’ve started using PPG Omni epoxy primer instead of the Stewart Systems stuff. I really like it. I can get it locally and it sprays much easier than the SS epoxy primer leaving a nice smooth finish. The cured primer doesn’t hold up as well to solvents as the SS stuff does but it’s good enough for me.
I’m finally at the point where I’ve riveted the tail cone bulkheads and frames together and I’m assembling the tail cone to start riveting the skins.
Also, back in October I received my wing kit! Now I just need to finish up with the tail cone so I can get to the wings.
I spent a couple days match drilling the longerons. Overall I think that went pretty well but I did drill one hole that didn’t match up with the bulkhead flange hole on the other side of the longeron. I stopped the drill before it went all the way through the flange and was able to shift the flange into the proper position. I believe the hole I drilled was straight and in the right spot but the I think flange was shifted a little bit away from where it should have been. Unfortunately, I won’t know how bad the damage is until I get it all disassembled and can really look at it. I’m sure I’ll be sending a photo to Van’s to see what I should do about it.
I’ve finally finished drilling the stiffeners in the left side skin. I counted something like 86 holes in one stiffener, so for both sides that’s around 500 holes total. There was one quick step where I got to attach a couple small stiffeners and match drill them with an angle bracket that I had to fabricate. After that it was time to insert the longerons and the aft deck, get everything clamped properly into place, and then get back to match drilling.
After I got all of the stiffeners drilled in the right side of the tail cone, the next step was to flip it over an attach a couple bulkhead pieces and the left skin. This turned out to be really difficult. Putting the bulkheads on was easy, and putting the skin on started off easy, but once we were trying to cleco the skin to the bulkheads things didn’t line up. I was wondering if I needed to shape the flanges on the bulkheads to make them fit the curve at the bottom of the side skins a little better because this is how well they fit the curve at first:
It turned out that I just needed to start with clecoing different spots and use a little force.
Here’s the section that gave me trouble so that you can follow along with the part numbers that I’m going to mention:
I managed to get everything together by attaching the F-1011, F-1012, and F-1079 completely to the bottom and right skins (This is how it will go together if you follow the plans, but by the time I finally got everything to go together I had already attached the left skin and then removed the bulkheads and F-1079 to try to re-position them). Then I clecoed F-1079 to the left skin to make sure that piece was lined up. At this point, the holes in F-1011 didn’t really line up well with the holes in the left skin but I was able to start wedging clecos into the holes in the bottom flanges of the bulkhead. It was really stressful because the holes weren’t perfectly lined up so the clecos were initially sitting at awkward angles to the skin but that was enough to help line up the next hole close enough for me to get a cleco in. I just kept working my way up the side of the bulkhead inserting clecos and eventually all of the clecos working together pulled the part into the proper position in the skin.
The flanges still just don’t really fit the curve at the bottom of the tail cone though so it is causing the flanges to bend upwards a little bit and not sit properly on the skin:
I checked with builder support and it sounds like there isn’t much to be done here except to make sure that the flanges are in contact with the skin when I rivet the parts together. The suggestions to do that were to try bending the flanges in the opposite direction a tiny bit to pre-load them a little and/or to use an o-ring taped to the bucking bar that will fit around the rivet to push the flange down with the bucking bar. We’ll see how that goes when I get to that step.
I’ve put in quite a few hours on the tail cone since my last update. We also went to Airventure for the first time and that gave me a ton of motivation to work on the plane.
One of the first things I had to do when I started working on it again was to mark all of the stiffeners with lines that are used to line them up with holes on the tail cone skins to match drill them. Each stiffener gets a line near each end that is perpendicular to the direction of the stiffener. Those are easy to do since they are short lines. You also have to draw a line down the entire length of the stiffener that is 5/16″ away from the edge. This could have been really tough if I hadn’t already seen other builder logs where they made a little tool for marking the line at the proper distance. I think some have used a scrap piece of the J-channel stiffener but I used a small piece of a hinge that I had leftover after trimming the trim tab hinges down to size. There’s a couple holes in it because I needed 2 tries to get the hole drilled in the perfect spot, but it worked really well. I just put it right on the flat side of the stiffener and braced the eyelets against the edge to hold it in the right position, then stuck a marker in the hole and drew the line across the entire stiffener all at once. It made this task so much easier, quicker, and more accurate than it could have been.
After that was done I did some quick deburring on the bottom and right tail cone skins and then got to work clecoing things together and getting the stiffeners lined up. You start by clecoing some frames to the bottom skin and then slide in a few stiffeners using the lines you drew to properly position the stiffeners. Then it’s time to start match drilling the skin holes into the stiffeners. The bottom skin went fairly quickly because it was easy to reach around and re-position the stiffener if it wasn’t quite lined up where I wanted it to be.
Once you’re done with the stiffeners on the bottom, you slide the assembly to the edge of your saw horses and cleco on the right skin. Slide in the stiffeners and continue match drilling. This was more difficult though because, for two of the stiffeners, my arms aren’t long enough to reach under and into the tail cone to re-position them if they aren’t lining up the way I want them to. This meant I had to constantly get up from my stool, go around to the other side and do my best to position them where they needed to be without actually seeing if it was lining up on the other side, and then try to hold it in place with some gorilla tape while I went back around to drill it. Sometimes I had to go back around and shift the stiffener multiple times before I was happy with where it was. Drilling one full stiffener on the right side took me about an hour and forty five minutes total. Eventually though you do finish and get to flip it over to put the left skin on and match drill the stiffeners on that side.
I haven’t been able to put the left skin on yet though because there are a couple frame pieces that go in at the very end of the tail first. I was working on match drilling an angle piece that I had to fabricate with one of those frames and make a really bad hole because I didn’t have everything properly secured. It probably would have been fine to use either the way it was or with a little fix built in, but I did almost the exact same thing on the next hole I drilled. This was enough for me to decide to just replace it. While I wait for those parts I’ve just been working on other small pieces on the tail cone that I can do without needing the tail cone to have the left skin on it. Still, it is really exciting having such a big part partially assembled in the workshop! When I actually start riveting it all together I’m going to have to do it in the garage because the tail cone won’t fit through the door to the work shop.
I’ve put about 14 more hours into the tail cone since my last tail cone post but I don’t really have any photos to show for it. Since then I’ve rebuilt the tie down block and match drilled it to its bulkhead. I actually did end up ordering a different tap off Amazon which allowed me to tap the hole a little bit farther. I also ordered the tie down eye bolts to make sure I was doing a good job tapping the hole and I was a little concerned about how much wiggle room the bolt had. I did some research on the forums and asked around and it seems like this is pretty normal so I’m not going to worry about it.
I spent a ton of time deburring (more like trying to polish with a tiny file) the little flange relief cuts which I think has finally driven me crazy enough to stop. I asked another builder how much time he spent deburring those spots and he said not much at all. So I think from now on all I’m going to do with those is make sure they don’t have any notches from the tools that were used to cut them out at the factory, and remove any burs that might scratch other parts.
I’ve cut a few angle pieces down to size and deburred them and I’ve also cut the long J-channel stiffeners down to size and have started deburring them. At the end of those stiffeners you have to cut them at a 45 degree angle. As far as I can tell this is just to provide clearance around the bulkheads that they connect to at those ends so I didn’t worry about being too precise with them. I set the miter gauge on my band saw to 45 degrees and just kind of eyeballed it. I’ve held a couple up to the bulkheads they will attach to and I think they will work out just fine. If I need to trim them down a little more later then it won’t be too much trouble to do.
And here is the only photo I have from all those hours of work. This is after I cut them down to the proper lengths but before I put the 45 degree cut on the ends.
I’m a little late in writing this post, but on 7/8/18 I finally finished the elevators! Well, they’re finished for now anyway. They still need safety wire to hold the trim tab hinge pin on and the fairings installed but those will come at a later step.
When it came time to roll the leading edges, I was a little concerned because of the different sections and the way they were positioned on the elevator. With the rudder, I just used a long PVC pipe and let it extend past the end of the elevator and rolled it from there. With the tip rib on one end of the elevator and the elevator horn on the other end this wasn’t really an option. I did some searching on the forums and found this tool here: http://www.vansairforce.com/community/showthread.php?t=126571
Basically, you get a closet rod that is 1.25″ in diameter and a couple 7/8″ sockets and you JB Weld them into the ends of the closet rod. Then you can just attach a socket wrench at either end and crank away on that to roll the edges. It worked really well and was actually pretty easy to make. I cut the closet rod down to 26.5″ which was the perfect size to be able to do the small outermost section of the skin, then the middle section, and then the innermost section without it bumping into any other rolled skins or the horns.
I was wondering if cutting the lead counterweights was going to be a problem because another builder told me that he ruined his band saw blade attempting to cut his. So I started with my hack saw and I quickly decided that it was going to be too much work to do it that way so I decided to give the band saw a try and if it ruined the blade then oh well. Luckily it worked really well and the blade still seems nice and sharp and not loaded with lead. It didn’t cut very fast through the lead though so I did have to be careful about the weights getting too hot to hold. In the end, I didn’t do a perfect job cutting them down to size and even had to do a little trimming to get them to clear some rivet heads when I was bolting them on to the elevators, but I think they will be fine.
Oh, also before I did any of the things I just wrote about, I had to finish the rivets close to the trailing edge of the tip rib on each of the elevators. These rivets are in a really narrow spot and I hate it when I have to set rivets like this. Probably the only way to set these rivets is to do kind of a modified back rivet. You set the part on your back rivet plate with the rivet in the hole, and then you have to place something on top of the rivet that will stick out far enough for you to hit with the rivet gun. Even though other builders make this look pretty easy, I’ve never had much luck with it. I’ve tried the flat side of a screw driver, I bought a crow bar thinking the end of that would be narrow enough to get in there but I wasn’t happy with that either. After watching a Hints For Homebuilders video on the EAA website I went out and bought a 2″x3/16″ steel bar. I cut a short section off of it, trimmed the corners off to make it narrower on one end, and then ground it down on one side to make it thinner at that narrow end I just made. This only kind of worked. Maybe I didn’t have my rivet gun set to a high enough pressure but the rivets took one heck of a beating and didn’t fully set. Luckily it was able to set them enough that I was able to get my thin nose squeezer in there to finish them off. Here is what the tool looked like:
I saw Justin do this on his blog and couldn’t wait until I could do the same thing with my elevators 🙂