Monthly Archives: March 2017

Spring cleaning: cobwebs and corrosion

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It’s time to attach the tail cone to the fuselage which means a museum piece can be ceremoniously lowered from the ceiling and brought back into production.  The last work was done over two years ago on the tail cone and it’s been in storage, basements, and garages since then.  Unfortunately, moisture left its mark with some heavy filiform corrosion on the bulkhead and bottom skin.


The tail kit components had this elsewhere when I purchased it, but never this bad.  On the bulkhead, I dug in with the angle grinder and 3M pads and made quick work of the nasty stuff.  Fortunately, it wasn’t too deep in the metal and it all came off easily.  The bottom skin is a bit trickier with the DuPont primer on it.  I didn’t do a great job priming this and did it after assembly so there were areas the corrosion was actually underneath the primer.  I’m not quite done getting that part cleaned up, as evident in the picture.

The biggest concern, out of it all, is the thin line of white corrosion along the ribs holding the battery tray (ignore the white flakes in the background, I haven’t finished vacuuming).  The surfaces between those two parts aren’t primed and I’m suspicious that there is corrosion between the two.  


I spent a good amount of time with a flash light and inspection mirror going over the rest of the tail cone.  It’s the only area like this and I don’t want to risk long term issues.  I concluded that the right thing to do is to drill out the rivets and clean these areas up properly.  It’ll be easy to do now and I’ll combine this with the custom equipment tray that I’ll be putting in to replace the battery tray.  Once this is complete, we’ll move on to attach the tail cone.

Pop goes the rivets

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Section 29 has proven to be a lot of work but the results are more than worth it.  With the help of the Mrs. again, the four side skins are riveted on now and I’m pretty happy with the results of the bending.  I was able to get the new engine mount bracket drilled and riveted to the firewall with better results this time.  After the side skins were on, I was able to get the front floor panels on.  These are pop riveted onto the structure and I’m glad I’m not building the entire airplane with pop rivets.  They are almost more work than bucking.


The landing gear mounts had to be finessed into place and led to a bit of a panic attack on my part.  While bolting them in, I realized the spacers for the two long bolts weren’t fitting quite right.  After a lot of measuring, I determined the spars were a bit too far apart according to the plans.  If the spars are off, this could be a huge concern.  After a post on VAF and a call to Van’s, I figured out that I didn’t remove the vinyl from the spacers and also didn’t insert the right spacers into the spar during construction.  I lucked out though and the spars are only .002″ off after its all said and done. That was close enough for me and Van’s so I pressed on with as it was.  Adding a thin washer fixed the spacers and the other two for the right side was cut a 1/32″ longer.


I also made up a couple of doublers for the comm antennas mounting on the belly.  I’ll be using Comant CI-122 VHF antennas and went ahead and installed nut plates since there won’t be acces from inside once the baggage compartment floor is in.  The doublers will tie into one of the baggage compartment floor ribs.  I will make two more doublers for the Delta Pop ADSB and transponder antennas which will go in the tunnel.


A lot of riveting evenings later, the skins are on and I’m ready to move on to the steps and pretty soon the tail cone.  

Some woodworking required

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Once everything was match drilled and after the mistakes were handled, prepping began on the many pieces assembled over the past week.  Edge deburring is my least favorite and takes a lot of time and effort, especially on these formed pieces.  But it is important and accomplished after a few nights of work.  Dimpling and priming the skins went quickly and riveting won’t be too far behind.

One interesting part of the build is the special tools that are required.  The latest one is a bending aid made of wood used as a clamping block for the side skins.  Each of four skins needs a rounded bend placed in them to transition from the tail cone / firewall to the more boxy part of the fuselage.  While I could have made it on the table saw at home, I elected to enlist a fellow aviator with a wood working shop rivaling the New Yankee workshop by Norm.

Just like most projects, preparation is 75% of the work but we set all the tools up and made the block of wood into the trapezoid shape required.  When put in use, it took a lot of grunting to get the skins bent.  A rolling and bending motion is used to form them and I was pretty lucky with getting a good result with the first attempt at each one.


A couple of oops

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Mistakes are inevitable and I uncovered a couple of them back to back.  With the longerons fitted and finessed, the other structure went together pretty easily.  More bending was required as four forward channels required a good twist using the vise and a strong arm.  There are also quite a few other pieces that fit along the side forward of the spar.


A lot of match drilling comes next, as the longerons need holes drilled for the sill and skins.  A drilling template is used to drill holes for the rudder pedals and is where the first mistake was uncovered.  The longerons are not an exact science, so the guide didn’t line up perfectly.  A quick email to Van’s gave me guidance to line the template up with the edge of the longeron and all was well.  


Unfortunately the next mistake was not as easy to correct.  The engine mount brackets tie into the twisted channels and get drilled using the holes on the flange already riveted to the firewall.  I realized that three of the holes weren’t in the flange completely.  This is a major component providing support for not only the engine but the landing gear and forward fuselage, so certainly a cause for concern.


Van’s stated that it’s pretty common to have thin edge distance on these but all holes did need to be in the flange.  What I don’t understand and never got any response from is why the holes didn’t line up.  The mount is welded from the factory and cannot be bent or adjusted by the builder in the direction that is needed to correct the issue.  Replacement was my only option so an order to  Van’s was placed.  I am proud of my skills at removing the rivets, as I did not want to mess up the firewall.  All went well, though, and I’m just waiting for the replacement part to come in.

Longerons take a long time

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It took quite a while to prep all the pieces, but after a lot of boring tedious work, it’s ready to put the two pieces of bread together and bang some rivets.  The wife came out in her steel toed shoes for safety and was kind enough to lay on the cold floor while I manned the bucking bar.  The work went quickly and we only had to drill out one rivet!


With the bottom of the fuse complete, the sidewalls are next and involve a bit more metal working than anything thus far in the project.  The main support pieces on the sides are made up of longerons which are formed from a 3/4″ angle iron that is 1/8″ thick.  The plans call for putting it a vise and smacking with a rubber mallet, using a bending jig to ensure the proper curve is met.  Another builder used a neat trick of putting a few nickels in the vice and using it as a manual bending machine.  I decided to give it a shot and was pretty happy with the result.  However, it took forever to get these four pieces done.  As soon as you got the lateral curve set, the vertical plane would be wrong.  So it was a laborious process of bending and rebending.


I did stall at this point for some time due to home improvement projects, back to back drill weekends, and a few other things going on.  But taking a weekend getaway in the DA-40 and running into a fellow 10 builder randomly rejuvenated my building motivation and I finally finished destroying nickels in my vise.  Taking a long break isn’t always the best for the project, as I realized that the first longeron I tackled after getting back to the build was done wrong.  Fortunately I was able to correct the wrong curve and didn’t mess it up beyond repair.  I confused my template labeling and used the wrong side of the template so had an incorrect curve.  Next up is to put them in place and start working on more of the structural component for the side skins.