Tiedown Fabrication

I actually fabricated some parts from the plans tonight.  This section of the plans has us fabricate the tiedown brackets that bolt to the main spar and help secure the aileron bell cranks as well.  There was a good bit of fabrication from raw materials so it was pretty much, but just a bit slower than I usually work.  I started off by tapping the holes in the AEX tie down stock for a 3/8 x16 threaded eye bolt. I had to actually run out to Ace hardware and pickup a tap and tap handle to get this done, so I did that while I was grabbing some dinner.  The plans calls for us to go 1″ of depth, so I wrapped some tape around the tap to mark 1″, and clamped the AEX stock to my work bench to start the process.

Almost finished with tapping this one

I have done this process before on other projects, so I lubed up the tap with some Boelube and slowly worked the tap into the AEX stock making sure it was straight.  I gave it a few twists into the metal, and then backed the tap out to clear some of the chips. I kept repeating this advance and retreat process until I had the full 1″ of depth as called for in the plans, and then did the second piece of AEX stock for the other wing.  The reason I did this first was so that if I messed up tapping the metal, I could just flip the piece around and use the other end, since both ends are identical.  Once I was happy with the threads I trimmed the 1/32″ of an inch that Vans calls for in the plans.  I am not sure why we need to take the AEX stock down from 7 and 16/32″ to 7 and 15/32″ using a bandsaw very carefully and then finishing it on the bench grinder.

New threads are kind of hard to see in this photo, but they are there!

Next up was to fabricate 4 spacers to fit between the tie down bracket and the main spar. These are called W-726 and the plans has a full size drawing of what they are supposed to look like, so they are easy to make from the AB4-187×1.25 stock.  I measured them out for 2″ on my bandsaw and cut them out.  The next process was to mark the center and then drill the lightening hole using the drill press and a 1″ bi-metal hole cutter.

After I had the lightening holes done on all 4 of these parts, I was happy with them and moved on to finishing their edges.  I ran them on the bench grinder to round the corners, and then deburred the edges nice and smooth on the scotchbrite wheel.  Then I deburred the lightening hole to make it smooth. They were ready to be match drilled with the tiedown bracket and main spar.

This next part required a bit of measuring, squaring up and clamping to make sure everything was perfect.  We first start out by drilling an index hole in the AEX tie down stock to be used to help guide it onto the main spar for easier back drilling.  The plans calls out the dimensions, I marked it up and drilled it on the drill press to make sure it was perfectly square, and then repeated the process for the other tiedown.

Then I used masking tape to hold the spacers on the main spars while I positioned the tiedown bracket and squared it up with the spar web using a square, using the index bolt to help with alignment.  Then I clamped it all down and back drilled everything using a #12 drill bit.

Once I was happy with the left side, I repeated this same process for the right. As I drilled a hole, I would stick a AN3-7 bolt into the holes to make sure nothing moved during drilling.  There is some tight tolerances here, and it holes the aileron bell crank, so its pretty vital this is done right. The next step is to drill for the 4 nutplates that secure the W-726 spacer blocks to the AEX tie down bracket.  This is pretty clever, as Vans has us put the nutplates on the tiedown bracket and then rivet the spacers to the bracket, that way if you never need to replace the nutplate for any reason, its as simple as just removing the entire bracket and replacing it on the bench instead of having to drill the main spar!  See below:

So, theres a couple ways of drilling these nutplates.  The route I chose was simple, and didn’t require any special tools.  I simply took a couple of AN3-6A bolts and ran them into the tiedown bracket and spacers and threaded on a nutplate to use as a jig for my drill holes.  This nutplate would be sacrificial, since its going to drill all 8 of them, but there are extras. Once I drilled the first hole, I clecoed the nutplate and used the bolt and drilled the second hole.

Yes, this nutplate is on backwards, but it doest matter since I am just using it as as drilling jig!!!


Once all the mounting holes were drilled for the nutplates, it was time to countersink the backs if the W-726 spacers for the flush rivets.  We use flush rivets here because these spacers need to sit flat against the main spar with no interference on this side.  I chucked up my microstop with a #30 pilot countersink and then countersunk all the holes in the spacers.

Notice my “CS” marking so I know which side to countersink 🙂

After I had all the holes drilled, it was time to go back and deburr every hole (except for the ones we countersunk, duh!).  I deburred the holes in the tiedown bracket, the spacers and the spars.  I also deburred the edges of the AEX tiedown stock as well and rounded the corners to prevent cuts and scrapes in the future, using the bench grinder and scotchbrite wheel.

In the plans, Vans tells us to go ahead and rivet these spacers onto the Tiedown brackets but doesn’t mention priming until the very end of this section, where it appears they are talking about priming the entire tiedown assembly (with attached spacers).  I figured these bits of aluminum are both very thick, and will be away from moisture, so I didn’t prime them before riveting them together.  I will, however, prime the entire assembly before I mount it permanently, just to be safe. That will only leave the two surfaces of aluminum that are riveted together (facing each other) not primed.  I think it will be alright.

Riveting these together is your standard procedure for nutplates.  Cleco one side, rivet the other and repeat across all the other nutplates.  I used a squeezer because why not?  They turned out great!

Completing both of these tiedown assemblies to this point was about 4 hours or more of work, so I called it a night.  I’ll drill the hole for the stall warner tomorrow, and may even go ahead and prime these.  I am going to go with a Dynon panel, so I will need to order the servo mounting kit because in one wing, the servo attaches to the aileron bellcrank, which then bolts to this tiedown bracket. I’ll get that on its way this week, and a few other odds and ends as well. Here’s all the photos from tonight:

Google Photos Link: https://goo.gl/photos/sPF5MJKnv1kmqRoZ6

Hours Worked: 4.25

Countersinking Nutplate Screw Holes

I was able to wrap up all of the fuel tank attachment nutplates and the inspection cover nutplates tonight.  In the last session, I installed all of the nutplates, and tonight I finished them up by machine countersinking all the screw holes to accept the dimples in their mating metal.  The work started out by first setting up my microstop countersink with a #30 pilot in the #8 nutplate screw holes.  Van’s has a pretty good tip on getting this depth correct:  Cut the head off a #8 screw and use it as a guide.  Once the screw head sits flush with the surface, go a few “clicks” deeper with your microstop so there will be enough depth for the dimpled metal.  Here is my homemade “gauge”:

It worked really well.  A lot of builders go out and do some weird things using dial calipers, and other extremes, but the main spar has a lot of metal and so long as you go just slightly deeper than the screw head, it’ll be perfect.  Here’s a good shot showing how it looks with my “gauge”

You can just barely see the fresh aluminum around the head of the screw. To give it a really good test, I used some scrap sheet aluminum the same thickness as the tank, drilled and dimpled a #8 screw hole in it and made sure it would nest into the countersunk hole flush.  It did, so I locked my microstop down at that setting and countersunk all the other fuel tank attach screw holes on both spars.

The next bit of work was to countersink the screw holes for the inspection cover nutplates.  Theres three inspection covers on each of the underside of the wings, and the forward 4 holes are all attached to the main spar with #6 screws and nutplates. I did these pretty much the same way as the #8’s above.  I cut the head off a #6 screw and used it for my gauge, then set my microstop a few clicks deeper and countersunk a test hole.  Then I grabbed one of the inspection covers, drilled it to size, dimpled it and laid it across the spar to make sure it seated flush against the spar.  I had to tweak the counterisnk a few more clicks deeper, but finally ended up with a nice flush fit, and then locked it down to do the remainder of the holes in both spars. Heres how the inspection cover looked against the spar:

Finally, the last thing to do was to prime these new countersunk holes.  The spar ships anodized, and drilling the countersinks leaves the metal in those spots open to corrosion. Vans recommend that we prime these spots to prevent corrosion.  So, I mixed up 10 mL of AKZO (5 mL of each of the two parts) and let it sit the required 30 minutes for induction.  In hindsight, 10 mL was a bit too much, I probably would have been just fine by mixing about 5 mL total.

Yep, thats a high tech paint applicator and mixing cup…courtesy of Q-tip and Gerber baby food. I used about 5 Q-tips to apply the primer after it had inducted, and the worked well enough.  I got a little messy with the application on purpose, as I wanted to fay the primer out from the holes to ensure there was no edges that moisture could penetrate.

I made sure to get decent coverage on all the countersunk holes, and then called it a night.  I’ll let this stuff cure until tomorrow and then start another session.  It looks like I’ll be building the tie-down brackets!  Here’s all the photos from tonight:

Google Photos Link: https://goo.gl/photos/4s2RkHuLaTHUK2Wt7

Hours Worked: 4.25

Attaching the Main Spar Nutplates

Nut Plates….tons of nutplates.  I worked a good 3 hours tonight on nothing else but riveting the nutplates to the top and bottom of the main spars.  I think there is something like 150-ish total of these little things that need to go on.  I need to get these guys riveted on so that I can use the nutplate hole as a guide for the pilot on my countersink.  Then I’ll be able to countersink the last of the holes for the tank skin dimples and attaching screws.   I did have a helper tonight though:

The work started off by clecoing the K1100-08 nutplates to the main spars, taking careful note of which pre-drilled holes the go into.  There are a few other pre-drilled nutplate holes for a K1000-06 nutplate to attach the inspection cover, but we will get them after these fuel tank attachment nutplates.  This is a pretty straightfoward process of just lining up the holes of the nutplate and inserting a cleco into one side to hold it.  Once I had them all cleco’d into place, I came back and dropped in a AN426AD3-4 rivet in the other hole.


I did this one spar at a time so I could keep up with which part goes where on these spendy main spars. Once I had one side of nutplates all clecoed, I followed it up by squeezing the rivet with my squeezer.  This is quick work, but patience was used just because I didn’t want to mess the spar up.  Once I had the first rivet set, I went back, removed the cleco and set the second rivet spot checking the all rivets with a rivet gauge.  Once I was happy with one side, I flipped the spar over and did the same on the opposite side (top/bottom). Then I repeated this same procedure exactly on the other main spar.  The rivets look really great when set:




After I had done all the tank attach nutplates, i moved on to the inspection plate attachment nutplates which are located on the bottom of the main spar flange, at 4 stations.  These guys use K1000-06, which are slightly smaller for a #6 screw (the tank attach nutplates are for a #8 screw), so I saved these for last so as not to confuse them with the wrong nutplate. The procedure was exactly the same as for the tank attachments, even down to using the same size rivets, and I completed it for both main spars.

Once I was happy with those few little nutplates, I decided to go ahead and attach the last 4 for the main spars (well until we do the fuel tanks down the road).  These are for the center section attachments points and they are facing in a different direction so as to allow the doubler plate to fit flat against the reinforcement bars of the center section.  I read the plans very carefully to make sure I had them in the right orientation.  Attaching these is the same process as all the others, except that they use an AN426AD3-6 rivet, a bit longer to go all the way through the thick doublers on the main spar.  I also had to swap out the yoke on my squeezer to the 4″ so I could reach them without any problems.  They turned out great:


Heres a neat shot of all the nutplates fully attached to both main spars, and even a selfie to prove that I am the guy actually doing the work 🙂

That wrapped up the session for tonight.  That was a solid packed 3-ish hours of nutplate attachin’ work.  It feels good to be back to building after the 8 week hiatus waiting on the wings to get here.  Heres the photos from tonights work:

Google Photos Link:  https://goo.gl/photos/GhzP7Qx9gVTzQsoW6

Hours Worked: 3

Riveting the Left Elevator Stiffeners

More Stiffeners!! Tonight I think I should be done with stiffeners at least for a little while (wing kit maybe?).  I worked to rivet the last remaining stiffeners on the left elevator, and then moved on to attaching the E-615PP trim support plate.  First, I started off by working on dimpling and countersinking the E-615PP support plate to get it ready to rivet on the nut plates.  I found my #6 dimple die and I have decided to use NAS1097 3-3.5 rivets to hold the nut plates on.  I used my deburring bit and machine countersunk the E-615PP by hand.  This took a little time, but it guarantees a very nice finish.  I test fit each rivet in the holes to make sure they were nice and flush.

Then I dimpled the screw hole with a #6 dimple die to fit the dimple in the trim cover plate and its screw.  Once I had all the holes countersunk and dimpled, I began back riveting the nut plates onto the plate.  I decided to back rivet because this leaves a very nicely finished rivet and doesn’t take any extra work. I am really happy with how the nut plates turned out:

With the E-615PP completed, I moved on to the last of the stiffeners!  There isn’t much to talk about here, since I have done this several times in the past, and the process is the same.  I back rivet the stiffeners onto the skins and make sure everything is flush and straight.  The only difference is that this time, we are also going to back rivet the E-615PP support plate to the skin as well.  It serves as both a stiffener for the inboard end, as well as a doubler for the electric trim servo and its mounting plate.  I took my time, and everything came out looking really nicely.

This was about 2 hours of work, but I decided to take a break and then start working on my bending brake for the trailing edge of the elevators, and maybe bend one up.  Thats all for this session, here are all the photos from the build:

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Google Photos Link: https://goo.gl/photos/JTmj5mFvK3qrvBbr8

Hours Worked: 2

Riveting the Elevator Stiffeners

Stiffeners.  I swear this plane has more stiffeners in it than skin. Since I am holding off on bonding the trailing edge of the rudder for a few more days, I decided to move on to the elevators and start riveting the stiffeners on.  This will help get me to the point of bending their trailing edge and bonding the trailing edge stiffeners, which is what I am waiting on for the rudder.  This way I can mix up one batch of ProSeal and do them at the same time.  I already have my skins and stiffeners primed and ready, I just need to deburr and dimple them before riveting.

Thats where tonights work started.  I deburred the stiffener holes in the both the E-701 left and right skins.  Then I fired up the DRDT-2 dimpler and dimpled both skins, as well as all the stiffeners for both sides.  This went pretty quickly, since they were all AN4263-3.5 rivets. The dimples always turn out nice:

Next up was to back rivet all of the stiffeners to the skins, so i started on the right being that its the easiest.  Back riveting is one of my favorite ways to rivet, and I’d gamble probably most of the other builders out there as well! The rivets set so nice and perfect, and its pretty easy to do so long as you keep an eye on where your back rivet plate is.  I picked up a longer 16″ plate to have more room to work and its been awesome.  Here’s some quick shots of the end result on the right skin.

After I had the right skin all completed, I put it on the shelf and started on the left.  The left is slightly more complicated because it has the elevator trim system, so we have a few more pieces to work with.  I started out by marking where the E-615PP support plate went on the inside of the skin, and then deburred and dimple those holes on the skin and the plate.  This plate will get some nut plates around the inside opening, so I need to dimple the nut plate mounting holes and screw hole.  Here’s where I had a head-scratcher.  I have in my dimple die collection a 5/32 and a #6 dimple die….The plans call for a #6 screw to be used with the nut plate, so that means I need to use a #6 dimple die, but I cannot figure out which is the 5/32 and which is the #6!!! The markings are no longer on the side of my dies and they are VERY close in size.  I also took some time fitting the plate and pondering if I should dimple the AN4263-3.5 holes that the plans calls for, or if I should use some NAS1097 rivets and countersink them.  If I dimple, I will have to fiddle with dimple the nutplate ears, and that gets messy.  I am thinking about using some NAS1097, AKA “oops rivets”, instead.  They have a smaller countersink on the head, but since these are just holding the nut plate in place there isn’t much load on them.  Using NAS1097’s will let me machine countersink the plate and get a very close fitting rivet set and not have to worry about the nut plate ears.  I figured I would just call it a night here, and put some thought to this overnight and ask some folks on the Vans Airforce forums.  Maybe they can help me sort out which is a 5/32 and which is a #6 die as well! 🙂  Here’s the work I did get done one the E-615PP:

In the next session, I will back rivet on the stiffeners to the left skin, and figure out this E-615PP support plate conundrum, and probably make up the trailing edge bending jig.  Here’s the photos from tonights work:

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And heres the Google Photos link: https://goo.gl/photos/ZMa9huaebXyCxRGS7

Hours Worked: 3.25