Right Tank Deburring Part 1

This is a quick build update as there isn’t much of an update.  I disassembled the right tank and then removed the plastic from the parts so I could start the arduous process of deburring, edge finishing and dimpling.  I logged a little over an hour tonight, and that was mostly deburring all the holes.  I did one piece at a time, deburred the holes then deburred and finished all the edges of that part before setting it on the shelf as completed.  I got through MOST of the parts, except for a half dozen ribs or so, and then called it for the night.  I did a little shop cleaning afterwards, but I am not counting the time spent cleaning the shop 🙂

Here’s the parts after disassembly and ready for deburring:

This is to be continued in the next build session!  Thats all for tonight.  Super simple.

Hours worked: 1.25

Right Tank Resistive Float Sender and Vent Line

More progress made on the fuel tanks tonight! I picked up with the right tank, and I wanted to get the vent line trimmed and finished.  I had left it a little long so I could trim it down to size once I bought a tubing cutter.  Well, I remembered to stop by Ace Hardware today on my way home from flying a PA-11 Cub and bought a decent little tubing cutter.  I spent a good deal of time playing with the cutter as well as my Parker flare tool that came in my tool kit, learning on scrap bits of tubing until I felt confident at making the cuts and flares on the actual parts.  Here’s the carnage from my little learning session.

Eventually, I got brave and made the cut on my vent line for the right tank.  I measured roughly where I’d need to cut the tubing to line up with the bulkhead fitting, and then made my cut.  I can still push the excess tubing out to the outboard side, and just trim there if I haven’t made a precise measurement, so no real worry.  I am pretty happy with the way my first official “production’ flare and fitting went!


I have about an inch of extra I will need to trim on the outboard side, where the vent attaches to the clip on the filler neck, but thats an easy one since theres no fitting thats go on it.  I marked where I think it should be and trimmed it with the cutter.

Then I put all the ribs back on the tank, and did my first official test fit.  I only went finger tight on the fittings just to see if the alignment and flares were good, and I am pretty stoked about how nice it looks in the tank!

The next thing I wanted to tackle was fitting the resistive float style senders.  Since I don’t have flop tube in the right tank, I can use the traditional method of installing the sender as outlined in the Vans plans.  So I pulled the sender from the shelf, making sure I had the proper one, as there are two different senders and they are specific to each wing.  After double checking against the plans, I grabbed the F-385C sender. This is what comes in the box.

Notice the float arm is straight.  We need to bend it per the plans with a 3″ arm, then a 90′ degree bend with another 3″ section.  Like this:

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Heres the kicker! The plans don’t tell you that you need to bend another 90 degree turn that slots into the sender body to hold the arm! I would not have caught that but I was reading the instructions that came with the sender and noticed that we need a 0.6″ bend to slot in the body.  So, I measured things up, and made the bends.  This is how it came out.  Notice the little bend at the end of the float arm!  I did have to trim the excess off with a hacksaw and then ground the end down nice and smooth.


Once I had the arm bent into shape, I clecoed the sending unit onto the tank access plate, and then inserted the arm to make sure it cleared everything.  I did have to bend it a little this way and that to get the float to work like I wanted but eventually after some gently bending I managed to get the float to rest just above the tank bottom, with it traveling all the way to the top almost touching the top skin.  Then I hooked up a Vans fuel level gauge I bought from another builder so I could make sure it worked OK.

Here’s a video of it working.  Forgive me, I shot this with my iPhone while I was trying to hold it and work the fuel sender as well.

After I tested the fuel sender, I called it a night.  Tammy had dinner cooking and it was making the whole house smell AMAZING, even down in the shop.  I was getting to hungry to push on any further for the night! But, this essentially finished up the actual fitting portion of the tanks.  I do still need to install the float sender in the left tank, but due to its flop tube, I will need to put the float sender on the baffle, and I may wait until I have some prosealing done before doing that work.

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Google Photos Link: https://photos.app.goo.gl/Zb3cMxNkRWSwhdjJ6

Hours Worked: 2.0

Right Tank Vent Line and Capacitive Senders

After a short break, I came back down to do some more work on the airplane. Tonight, I was able to get the right tank vent line and the right tank capacitive senders assembled and ready.  This time I cleco’d all the ribs and skin for the right tank in the stand so I could get some work done on it.  Once I had it all assembled, I grabed the 1/4″ soft aluminum tubing and began unrolling and straightening it to form my tank vent line.

Then fed the line through the holes in the tanks ribs until it was at the very end of the outboard outside rib.  I left about a foot extra on the inboard side, because I need to bend it a little to go to the fitting on the inboard outside rib, which I still need to drill the hole for.  Thats next up. So grabbed the inboard outside rib, and marked where I wanted to drill the hole for the vent line fitting.  We’re not given any specific spots, just a rough location where we should put it.  I made sure I had enough clearance to work around for the BNC connector for the capacitive senders, marked the hole and drilled a pilot hole with a #40 drill bit, then enlarged it to the proper size for the AN833-4D bulkhead fitting using my step drill bit. Once I had that done, I started bending the vent line so that it would meet up with the fitting nice and straight.  This took some trial and error and many times putting the rib on and off to get it just right. I also installed the modified / notched SB437-r bushings in the ribs.

But, after a bit of fiddling and work, I am very happy with the results.  I honestly like this better than my left tank, and I will probably go back and re-bend my left tanks vent line so it looks as nice as this one 🙂

Now that I had the vent line made up, I pulled it from the tank and put it in a safe place and continued on working.  I figured I could probably knock out the capacitive sender plates for this tank tonight too, especially since I had the tank already assembled.  So, just like the left tank, I inserted the plates to double check the orientation, marked it, and then removed the ribs so I could back drill them.   And just like the left tank I done earlier tonight, I measured the distance from the back of the rib (4.5″) and then used a 5/32″ center punch as a spacer to get the clearance on the top and bottom of the plates just right.  Then I clamped them down, and back drilled using a #20 bit into the ribs with the pre-punched T-813 sender plate as my guide.  I did this for both the ribs / plates in the right tank, as there are two plates. Recalling that we need to remove the plates, and then enlarge the holes in the RIBS ONLY to a 1/4″ hole as well.

Once I had both the inboard and outboard inner ribs and plates drilled.  I deburred all the edges and holes in the plates as well as the new holes in the ribs and then dimpled the proper side of the sender plates to accept the AN426AD3-3.5 rivets for the nutplates.  Once I had them dimpled, I clecoed on the nutplates and then squeezed the rivets, double checking that I had the nutplates on the correct side, as its VERY easy to get these wrong.

Recalling that the outboard most sender plate needs to be notched a bit to clear the stiffeners since it is mounted on the opposite side of the flanges.  I clecoed on the stiffeners, and then did a rough assembly of the T-813 sender plate and its plastic washers and spacers, to get an idea of where to notch. I marked on the plates where I needed to notch them, used some snips to cut the required pieces off  the one plate out so that it cleared nicely around the stiffeners per the plans.  Once I was happy with the fit, I took the plate over to the bench grinder to deburr the newly cut edges nice and smooth.





Once I hand the edges trimmed and deburred, I clecoed on the nutplate for this outboard sender plate and squeezed the rivets to hold the nuteplates on, and did another test fit using the hardware to make sure it fit nice and perfect.


That pretty much completes the fabricating and fitting of the sender plates for both tanks.  I can’t really install them until I am close to sealing the tanks, so they will go in the parts stack for their respective tanks until I get ready to seal things up.  I went ahead and finsihed assembling the right tank in the stand, including cleco’ing on the access plate, and fuel pickup tube.  I will be installing the resistive senders in the next build session, so I wanted to get the tank ready for that step.


Thats all for tonight.  I am happy with the amount of work I got done tonight, and I’m in a good starting point for the next build session.  It’s getting close to sealing the tanks. I just need to finish up these last little bits of fitting, then I need to deburr and dimple and do final skin preperations for the parts before riveting.  The tanks do not get any primer, so we can skip that step at least!

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Google Photos Link: https://photos.app.goo.gl/zn7mZSEkp6px4gPs5

Hours Worked: 2.75

Left Tank Capacitive Sender

Getting to do some neat work on the fuel tanks now!  I started on the capacitive sender plates that I am planning on putting in the tanks.  These will be my primary means of fuel level indications, with the float style senders being a backup.  Yeap, I am installing both capacitive and float style senders, since they are both lightweight and easy to do with the tanks being assembled.  I read over the instructions several times, and looked over the plans and drawings to get an idea of how these go in.  They are pretty dead simple:  Two aluminum plates mounted on the ribs, and electrically isolated from the fuel tank with insulators “dip” into the fuel thats in the tank and measure its resistance / capacitance to get an idea of how much fuel is in the tanks.  The tank skins and ribs are the other side of the circuit, with the fuel being the conductor between the sender plates and the tank skin/ribs.  Dead simple system with no moving parts to wear out.  The only downside is that its calibrated to the fuel type, in my case 100LL.  If I ever decide to run a different fuel blend (mogas, 100LL, or whatever) I’d need to re-do the calibration which involved fueling to a known quantity and running the calibration program of the fuel sensor units.

The work starts off by fitting the pre-punched T-813 sender plates into the outboard most inner rib and measuring its clearance distance. We need it to be 4.5″ inches from the bottom of the rib, and it needs 5/32″ clearance between the rib flanges.  So, I measured it out, and used a 5/32″ center punch to get the measurements correct and clamped the plate down.

Once I had it clamped into place, the plans tell us to use a #20 drill and then back drill into the ribs for the screw holes using the T-813 plates as a guide.  Then it has us remove the plates, and then enlarge the holes in the ribs ONLY to 1/4″.  After that, we do the same exact process on the inboard most inner rib.  Once the holes were drilled, I deburred all the holes in the ribs, as well as the sender plates. The next step has us rivet the nutplates onto the sender plates, double checking the orientation is on the correct side of the sender plate.  After a study of the drawings, I riveted on the nutplates with my squeezer. Take note, the plans has us use AN426AD3-3.5 rivets, so I had to dimple one side of the sender plate to accept the head of the rivet.  I did this to both ribs / senders of the left tank.

Next up was to drill the hole in the inboard external rib for the BNC connector that goes to the sender plates.  Following the drawings, I positioned my marks roughly where the plans has us, and then double checked that my flop tube would not hit the wiring or the inside bits of the BNC connector, then drilled a #40 pilot hole, and opened the hole to the right size for the BNC using my step drill bit.  I went ahead and did this to the right tanks inboard rib as well, while I had the drill bit chucked up.


The other hole you see in the pictures is where the fuel tank vent line goes, trust me its not a stray hole 🙂  I did a rough assembly of the parts to make sure everything was looking good in the tanks.  I notched the bottom of the sender plates as per the plans, but after I did the assembly, I don’t think i really needed to.


You can see how the plastic washers act as spacers and isolators for the sender plates.  There is also a plastic tube that I will cut to 15/32″ to that the screw goes into to fully insulate the screw from touching the ribs. Finally the plans has us cut some of the 18AWG wiring to 15″ lengths, strip one end and solder it into the BNC connector.  Once we install the BNC for good, we’ll be slathering this thing in plenty of proseal to not only seal it up, but also protect the soldered connection as a sort of strain relief too.  So, I took the wire up stairs in my office where my soldering station is, cut them to length and soldered them into the BNC’s.  I went ahead and did both the left and right tank BNC’s since I had the iron fired up. Here’s how they came out:


Thats it for this build session.  Going to grab some dinner, and then I’ll probably come back down and start doing this work on the right fuel tank.  It should go alot quicker now that I know what I am doing.

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Google Photos Link: https://photos.app.goo.gl/fAy5jGWGLnEELWcV7

Hours Worked: 1.75

Left Tank Vent Line

Super short session tonight.  I came back in town from being on the road, and wanted to get something done on the build to keep the progress going.  I left off with the left tank clecoed back together so I can start working on the last bits and hardware,  and this session I decided to get the vent line cut and ready to go.  I pulled out the stock of 1/4″ soft aluminum tubing which came with the wings.  Vans sends 19 feet of it most of which goes for the pitot system, but I am going with a different system for pitot and AOA, so I will have PLENTY of extra to play with.  I uncurled enough tubing to give me about a foot extra of vent line for the left tank. Then straightened it out and feed it through the holes in the ribs.  I removed the inboard rib since I need to drill a hole for the fitting.

Next up was to locate and drill the hole for the elbow fitting.  This is the plans for the fitting, and the rough location of where to drill the hole for it.

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So, I made a mark in the rough location of where it shows in the plans, and then drilled a #30 pilot hole.  Then opened the hole up to the proper size for the AN833-4D bulkhead elbow with a stepped drill bit.


Since I am going to install capacitive senders in my tanks, I needed to notch out the bushings that the vent tube slides into in order to make room for the wiring.  I used my chainsaw sharpening file to notch out the lips in the SB437-4 bushing.  To make sure, I fitted the bushings on the vent line and inserted the wiring checking there was enough clearance.

I need 5 of these for the ribs in each tank, so I went ahead and notched out 10 of them, which is enough for both tanks.  Then, I snapped five of the bushings into the ribs for the left tank after I had deburred the holes for them.  After that, I threaded the aluminum tubing into the ribs, through the bushings so that I could get it lined up and cut to length and flared.  I need to pick up a tubing cutter before I cut to final size. My tool kit came with a nice Parker flaring tool but not a cutter. heh.  So, I’ll order a tubing cutter this week and get it ones its way.  Heres where I ended up tonight:

Thats where I leave it for the night.  I’ll get a tubing cutter on the way, but I can start working on the capacitive senders while its being shipped.  I left my tubing a little long to give me some room for margin, and I also have some scrap tubing to practice cutting and flaring on before moving on to my “production” parts.

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Google Photos Link: https://photos.app.goo.gl/zYoputXmk6761L2H6

Hours Worked: 0.75

Anti-hangup Brackets and Fixing the Trap Door and Anti-rotation Bracket

I told myself this was going to be a quick sesison,  just finish up the anti-hangup brackets and we’re done for the night…….it didn’t happen that way :-0 I actually ended up doing a LOT of work, 3.5 hours worth, but I am glad I got it all done.  At this point, I am ready for the fuel vent tube, and the capacitive senders.  I started this one off by making the anti-hangup brackets that keep the flop tube from getting stuck on the nutplates for the access panel.  Van’s wants us to make a simple one by riveting a piece of .020″ alclad onto the back of the reinforcement plate, but that would block any easy access into the tank if you ever needed it.  So, a bunch of clever builders came up with ways of making anti-hangup brackets that attach to the access plate, and come out with the access plate so as to give you full access through the hole when the cover is off.  Thats how I am doing mine.  It takes a little more time to do it now, but its worth it if you ever need into your tanks. I went through a few different iterations, and several pieces of scrap became smaller pieces of scrap in the process, like below:

But, eventually I came out with something like this below.  I used .025″ alclad, cut to about 3/4″ wide and long enough to fit from the top of the tank to the bottom with a little bit of clearance.  Then I made some Z-brackets out of the same alclad and bent them so they could be riveted on to the access plate, and give enough room that you could work the bracket into the fuel tank while it was attached to the access plate.  Here is my rough layup.  I am using packing tape to hold things together as I trimmed, and adjusted everything.  It worked pretty good as it was easy to move around and held things nicely.

Here’s what it looks like when the cover is in the tank, and the flop tube is resting against the anti-hangup bracket. You can see how well it holds the flop tube away from the platenuts and anything else that it could snag on.

Here’s a quick video of the layout process:

Once I had it where I wanted it, I left everything taped up and then drilled the holes for the Z-brackets into the access plate.  After cleco’ing those into place, I then drilled the holes to attached the anti-hangup bracket onto the Z-brackets.  I am going to use flush rivets for these to keep a nice smooth surface for the flop tube to ride against, so I will deburr and dimple these as well.

I decided to use flush rivets here to hold the ant-hangup bracket assembly to the access plate, so that I could easily get my long nose flush squeezer yoke in there to squeeze these rivets.  These rivets will also get prosealed since they are penetrating the tank.

I did go ahead and deburr all the edges and new holes on the assembly, as well as dimpling the Z-brackets and anti-hangup piece.  I then machine countersunk the access plate to accept the dimples from the Z-brackets.  I went ahead and riveted the anti-hangup to the Z-brackets since its safe to do so at this time. And this is how it came out!

Here’s a video after everything was completed, and showing why and how I did it this way.

One thing I noticed was that my anti-rotation bracket on the flop tube didn’t allow me to easily remove the flop tube if I ever needed to change it.  It actually held the fittings from turning, which meant I’d need to drill the bracket out if I ever decided to change the flop tube.  Now was the time to fix it, while it was easy and no loss.  So, I trashed the old bracket, and made a new one, placing it a little further down from the fittings that screw onto the 90′ elbow.   It was a simple thing to make, using some angle aluminum just like the first one.   I marked out some lines for my edge distance, and them trimmed out a section to fit around the red portion of the flop tube.  Then drilled two holes to attach it to the rib.


Here’s how it works.  The red nut is where the flop tube rotates freely on its fitting.  We don’t want the fittings to turn when we tighten them down, nor do we want the flop tube rotating anything when its flopping around during acro.  The blue fitting is where we put a wrench on to tighten the flop tube down onto the blue 90′ elbow fitting.  with this setup, I can use a wrench, loosen the blue nut, and pull the flop tube up and out of the anti-rotation bracket, for easy removal if I ever need.   I like this setup WAY better.

After completing that part, I decided I wanted to remake my little trap door that holds the fuel in the inboard bay during acrobatic flight.  I wasn’t really happy about my trimming job on it, so I figured I may as well go ahead and re-do it while it was easy to do.  So, I drilled out the three rivets on the old little door, and cut a new piece from 0.25″ alclad per the plans dimentions of 1.75″x1.75″.  Then, since I already had the tank and ribs clecoed together in the stand, I thought it’d be best to go ahead and test fit my trap door with the skin and make it perfect.  The old trap door is the one on the bottom of the photo below.  I wasn’t happy with my trimming job.  The new one is the one in the top of the photo.


It fits WAY better now.  Sometimes its best to re-do your mistakes while its easy, even if they are not really a bad mistake in the first place.  My original, janky trimmed door probably would have given great service, but it bothered me everytime I looked at it. HAH!  I am much happier with this new version.  It sits really close to the skin so it will seal up great when I am doing acro.


I went ahead and riveted the top hinge to the rib, since I was 100% happy with the door.  I can simply pull the hinge pin out and remove the trap door and put it on the shelf until I am ready to close up the tanks.  The only other thing I done tonight was install all of the ribs into the fuel tank and cleco them in nice and tight.  I need to cut the vent line and install the capacitive sender plates, and I want the tanks assmebled to do that work.

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Google Photos Link: https://photos.app.goo.gl/2mXa67zZcnzU8E6eA

Hours Worked: 3.5

Right Tank Access Plate and Anti-Hangup Brackets

Picking up from my last session, I decided to go ahead and finish the right tank access plate.  I had already cut the access hole in the rib when I was working on the left tank in the last session, so I really just needed to do a little to finish this up.  I also started out on the anti-hangup brackets too. Since the right tank will be getting a normal pickup tube, I can place the fuel level sender in the stock location and use the T-708 tank access plate that is pre-punched for both the pickup, and the fuel level sender.  So, It’s just a matter of aligning it with the tank access hole, and clamping it in place.

I made sure to attach the fuel pickup, its fittings and anti-rotation bracket to the access plate so I could make sure i had everything in the proper orientation as well as in the proper locations so that the fuel pickup sat as low as possible.

You can see in the photo below, I have the pickup as low as it can go to pickup the most amount of fuel in the tanks.  I am using the pre-built fuel pickup from Van’s because its cheap, well made and simply fits into place with zero effort.  It’s a no brainer!

Once I had the access plate in place, I used it as a template to back drill the screw holes into the rib.  This was just the same procedure as my last session.  I’d drill a hole, and then stick a cleco in to make sure nothing moved, and everything was tight and aligned.

Once I had the rib back drilled, I removed the access plate, and then clecoed on the T-407 reinforcement plate, as I needed to use it as a template to back drill into the rib for the platenut attach holes.  So,  I cleco’d it on, and then drilled the #40 holes into the rib using the plate as a guide.

Once I had all the holes drilled, it was time to deburr everything and then dimple the holes in the rib, and machine countersink the holes in the reinforcement plate.  For details on this see my previous post on the left tank…same process here.  Then, I re-assembled the reinforcement plate onto the rib, clecoing it on with its platenuts, so I could rivet them.

The squeezer made quick work of these guys, and after a few minutes, it came out looking great!

Since this work didn’t take long, I decided to go ahead and start working on on the anti-hangup brackets in the left tank for its flop tube.  We need these little brackets fabricated so that the flop tube won’t get hung up on anything in the tanks as its flopping around.  They are simple to make, and the plans calls for them to be made like this:

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So, I re-assembled the left fuel tank, using the 3 most inboard ribs to hold the shape so I could get these made correctly.  You can really see why we need those brackets here! There is potential for the tube to get hung on the nutplates, and between the rib and stiffener on the outboard side.

I went digging in my scrap bucket again for some .025″ alclad to make some brackets, measured out a ~1/2″ wide piece and started forming it to make the ant-hangup brackets. I ended up going through three iterations before getting this right, as the alclad would crack when I’d go to bend it to the shape needed.


These are my first two iterations, headed back to the scrap bucket!

I wound up using some clamps to hold it in place on the stiffener while I made the bends and checked everything.  Then I drilled a #40 hole in the piece mounted onto the rib where I’ll rivet it in place during final assembly.  I did the same on the bracket through the stiffener, which will get riveted during final assembly.

And that was all I had the energy to do tonight.  Tammy was making a nice smelling dinner (Taco Soup!), and I couldn’t resist anymore.  I went upstairs and ate dinner with the family.  I’ve got some plans for the anti-hangup bracket on the access plate, but it’ll take some fabricating so thats a good start for the next session.

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Google Photos Link: https://photos.app.goo.gl/hhhbfBJ4Sez1Utez9

Hours Worked: 2.75

Fuel Tank Access Plates

I had to pick up a tool to help with cutting the access plate holes for the fuel tanks.  Vans recommends using a fly cutter to cut the access holes, and I thought I had one.  Turns out, the fly cutter I had was for cutting holes in drywall, and would not work on metal.  So I swung by Ace Hardware and picked out one of these for about $22 bucks:

It’s designed with a carbide tip thats suitable for soft metals.  And its fully adjustable.  It’s well worth the price.  So, to get things ready, I spent some time aligning the T-408 reinforcement ring and T-411 access plate per the instructions and making sure I had all the right clearances and measurements.  Then I traced out a line of where I wanted to cut the hole in the rib, to give me a reference to use for the fly cutter.  After chucking the cutter in my drill press, I used a piece of scrap plywood as a backer for the rib and to give the fly cutter something to cut into, instead of my drill press 🙂

Then I adjusted the fly cutter to line up with the blue cut line, making sure to slowly turn the chuck by hand to make sure I had the rib centered up on the cutter.  This took me longer than it should have, and I am sure there is a better way of finding and marking the center of a hole, but this worked.

Then I set my drill press on its slowest speed of about 240 RPM.  You don’t want to use a fly cutter at high rpms!  Once I was ready to go, I slowly and gently pressed down on the fly cutter and let it do its work.  It makes a HELL of a racket, so just go slow and gentle with the quill pressure and it will make a nice neat cut.


I went ahead and cut the access hole for the left wing tank as well, since I already had the cutter chucked and adjusted.  I did it the same was as the right, and it came out great as well. Next up, we need to back drill the screw holes for the T-411 / T-708 access plates.  I decided to start on the left wing tank, since I need to finish up the flop tube anti-hangup brackets, (more on that in a few posts).  Since I am using a flop tube in the left tank, I wont be mounting the fuel level sender on the access plate as per the plans.  So, I am going to use a T-411 access plate on the left wing, which is a standard plate that does not have pre-punched holes for the level senders, or fuel pickup tubes.   So, I got the part from stock, and lined it up on the rib making sure the flat part of the plate faced the little bump on the rib as per the instructions.

Once it was lined up, I clamped it down tight and then used the pre-punched screw holes in the T-411 plate to back drill into the rib, clecoing the new holes as I went.

Once I had them all drilled, I removed the T-411 access plate, and then clecoed on the T-407 reinforcement ring using the new holes in the rib for alignment.  We need to drill the #40 holes use for the nutplates.  Straightforward this part.

I used the larger, black colored clecos to hold the T-407 in place so I could back drill the #40 holes using the T-407 as a guide. Eventually I wound up with the rib fully drilled. The next thing to do was deburr all these new holes, and of course deburring the sharp edges of the newly cut access hole with some scotchbrite.  I also ran the T-407 and T-411 on the bench grinder to get those edges nice and smooth as well.  Next I dimpled ONLY the #40 holes that are used to hold the nutplates in, making sure to get the dimple going in the right direction.  We have to machine countersink the T-406 to accept these dimples due to its thickness.


The instructions tell us we can go ahead and rivet on the nutplates without sealant because there is a cork gasket that will be used on the outside of the access hole that seals this section.  So, I clecoed on all the nutplates and started squeezing them with my squeezer.

And here is where I made two mistakes for the night, and had to drill out some rivets.  The first mistake was I squeezed a rivet, without making sure it was actually going through the hole in the nutplate!  Such a boneheaded move. HAH.

Shortly after that, I smushed a rivet over because I didn;t have the squeezer set squared up and centered.  Thankfully, I have gotten pretty decent at drilling out rivets by now, so I simple drilled these mistakes out, and cleaned up the holes and fixed those mistakes pretty well! The blue lines are where the bad rivets were at 😉

That finished up the left wing tank access holes.  After making those two mistakes, I figured it would be best for me to call it a night to prevent more from being tired.  This is a good stopping point, and I’ll pick up on the right tank access plate next time.  Then I’ll move on to building the flop tube anti-hangup brackets.

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Google Photos Link: https://photos.app.goo.gl/HsMA36nfyKSgNr3U8

Hours Worked: 2.25


Installing the Flop Tube

After a quick break and bite to eat, I went back down to do some more work.  I decided to go ahead and get the flop tube installed for now, and do the capacitive senders in the next session.  I’m only doing a flop tube in one tank: The left tank, so I’ll be sure to placard the fuel selector as “Acro on Left Tank Only” just for the cool factor of it.  The real reason is that there is a good bit of extra work to get the flop tube installed, and you have to move the float fuel level senders out from the access panel to one of the inner fuel bays, making it damn near impossible to service it if needed.  Thats one reason I am also installing capacitive fuel sender plates in my tanks, they’ll give me a backup fuel level source, and they are pretty easy to install during assembly and they need zero maintenance.  So, I’ll install both capacitive and float senders in my tanks.  The right tank will have the standard Vans fuel pickup, and it’ll be standard assembly as well.

The session starts of with trying to find a good location on the tank attach angle brackets to drill the 9/16″ hole for the flop tube bulkhead fitting.  I tried to center mine up as much as possible, while also trying to keep the flop tube as low as possible, but it was a compromise.  Here is where I decided:

I made a circle using the inside of the blue bulkhead nut as my guide to find a spot.  Then I drilled a pilot hole using a #30 bit.  This hole went all the way through the T-405 tank attach angles, the T-703-R rib, and the T-410 reinforcement plate.  Then, I chucked up my step drill bit in the drill press and drilled the holes out to the proper 9/16″ size.


I put some masking tape on my flop tube to keep trash and debris out of it, and also to protect the little rubber o-ring bumper during the assembly process.  I wasn’t very happy with the way the anti-rotation brackets from Vans worked out, as I didn’t have enough room to fit one of them. The plans don’t call for an anti-rotation bracket on the flop tube, but does have us safety wire that fitting.  That safety wire will only keep the fitting from rotating, it wont stop the actual bulkhead from rotating as the flop tube…flops. So, I decided to fabricate my own bracket.  They are simple enough to make, and I had plenty of stock angle to work from.  This actually took me longer than I had thought it would to make, and I went through several iterations before I had one I was happy with.  Thank goodness I had plenty of angle stock to work with!

I angled my flop tube and its associated anti-rotation bracket slightly downward so that the fuel pickup would rest as low as possible in the fuel tanks.  It will still flop around perfectly fine and pick up fuel in the inverted and knife-edge flight attitudes.  Here is the anti-rotation bracket clamped down and getting drilled into place.

And below is what I eventually ended up with.  The rounded section goes against the rounded shoulder of the bulkhead fitting with a few 16ths clearance, while the squared end is roughly 11/16″ which is just slightly bigger than the flats on the fitting.  This way, when I tighten the flop tube up on its fittings, I can rotate the flats to line up with the bracket, which will serve double duty:  Keeping the flop tube from rotating around the where the bulkhead goes, as well as keeping the fitting from rotating counterclockwise and loosening itself off the threads. I actually notched the bottom of the bracket so that the points of the fitting would sit nicely down in it, giving me good clearance.  I am actually pretty proud of this little bracket!  It’s really simple, but took quite a bit of learning and work to create.  I will be much better at making them if I ever decide to build another RV 🙂

I wish I had snapped some more photos of the actual process of making this silly thing, but I kind of got into the “zone” and forgot to take some until it was nearly done.  The little black marking on the upper left of the bracket is where I needed to trim the corner ever so slightly to make room for a rivet that is in a nearby hole.  I did indeed make that trim and then tested it for fitment.  Next up was to fabricate the trap door that holds the fuel into the inboard fuel bay so it doesn’t drain outboard when you are inverted or doing knife edge flight.  The plans tell us to make this out of some 0.020″ alclad thats 1.75″ x 1.75″ and a piece of piano hinge. We have this to go by in the plans as well:

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Which is pretty easy to go by.  So, I went digging in my scrap bucket for some 0.020″ alclad, marked up a little piece and snipped it out with my snips. I did the same for the piano hinge, luckily I had a piece almost the right size in my scrap bucket.

Then I measured for edge distance, and marked a reference line, broke out my rivet fan spacer and marked up three rivets holes, then drilled them.


Once I had the trap door drilled, I trimmed my piano hinge and fitted it where it would work best, trimmed it to the right size and bent the little tang to serve as a stop to keep the flap from flopping all the way up. I also decided to cut a little spacer of 0.020″  to go behind the top hinge to help the trap door sit totally flush against the rib.  If i hadn’t done this, the top of the hinge would have been sitting right against the rib. while the bottom of the hinge would have been angled slightly because of the flap riveted to it.

Then I dimpled the flap and the hinge so I could use flush rivets to help keep the flap sitting nice and flush against the rib.

Finally, I riveted the flap onto it’s section of hinge using my squeezer and some AN426AD3-3.5 rivets and clecoed it onto the rib with the spacer behind the top portion of the hinge.  You can see how it works now.  The spacer is the same thickness as the flapper on the trap door.  This keeps the hinge pieces at the same height, and lets the trap door flapper swing very freely, and sit totally flush against the rib.

I also trimmed around the flapper a little towards the bottom, to keep the flap from getting hung up on any stray proseal that may happen to get down there when its time to seal it up. I want this little door to be able to swing totally freely, and then close completely when needed.

I decided to block off the hole in the inner rib.  Some builders do this, and some don’t.  For me, I want that inner fuel bay to be sealed off so I can do sustained inverted or knife edge flying.  If I left this hole unblocked, that would allow fuel to drain back to the outboard side of the tanks, away from the flop tube in some flight attitudes.  In addition, it looks like the flop tube may actually get caught in the hole in some situations.  So, closing it up is pretty simple:  a 4.5″ square of 0.020″ alcald and a few rivets.  I measured and cut some of my scrap alclad, and marked up the rivet holes with edge distance in mind.  Then I drilled the holes in the plate.

Once the holes were drilled and deburred, I went ahead and dimpled the blocking plate as well as the ribs so I could use flush rivets on the inner side of the fuel bay, giving even more less things the flop tube could catch on.   I used some AN426AD3-3.5 rivets to attach this blocker plate to the rib, making a nice flush surface for the flop tube to rub against, while at the same time, blocking any fuel from leaving my inner fuel bay when flying knife edge, with the left wing low, and the trap door flapper closed.

I’m really pleased with how this came out. I spent a good 4 hours or more just fabricating and fitting these parts.  I still need to fab and install the anti-hangup straps that go in the tank to keep the flop tube from hanging on certain bits.  But, I was out of steam for the day, and figured that would be a good “Part Two” for my next session.


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Google Photos Link: https://photos.app.goo.gl/iTp5eMERkYinN43e7

Hours Worked: 4.25

Drilling the Tank Angle Attach Brackets

Short session to start today.  I wanted to get the tank attach angles drilled, and after doing some reading last night, this actually seems straightforward.  Vans gives us a rough idea of where to drill the rivets for the angle attach bracket in the plans with this drawing:

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We just need to be cautious of edge distance, so I used my square and made a few lines to give me plenty of edge distance, and then drilled the brackets with a drill press to get the holes nice and straight since these are chunky bits of metal.

Then I deburred these holes, and placed the bracket into the rib and lined it up and nice and square so that I could use the bracket as a template to back drill the holes in the rib.  I used some clamps to help hold it in place.  Notice that I left off the reinforcement plate that goes on the back side of the T-703-R/L rib. I did that on purpose so it would be easier to line up.

With the bracket lined up and clamped, I simple back drilled into the tank rib using the bracket as my template.  Once I had the rib drilled, I removed the bracket and then placed the T-410 reinforcement plate on the inside of the tank rib, and lined it up.  Once it was lined up where I wanted it, I clamped it down and used the newly drilled holes in the T-703-R/L tank ribs to back drill into the T-410.

Now that all three parts were drilled, I clecoed everything together to make sure it all fit, and then double checked alignment.  It looked pretty good, so the last thing to do was to deburr all thees new holes and then move on to the outboard rib.

The outboard ribs were much simpler to do, since we don’t have the T-405 angle attach bracket to worry with.  We simple just need to align the T-410 reinforecment plate on the leading edge of the rib, on the inside of the tank, and then choose 3 to 4 rivet holes and drill.  Again, vans doesn’t give much guidance here, so I simply measured for edge distance, gave myself another 1/16″ for a buffer and then tried to space the rivets out in a decent pattern, then drilled the holes through both parts while they were clamped.

Once the outboard side was drilled, I removed everything and deburred the holes.  I think I did the left tank first, but after I had one tank done, it was time to move on and do the opposite side in the exact same manner.  Like always, the second time goes much faster, and I didn’t take any photos of it, since its the same as the other side.  Time for a quick break for a bite to eat, and then I’ll do another session tonight.  Probably either the capacitve senders, or the flop tube.  These are the fun parts of the build!

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Google Photos Link: https://photos.app.goo.gl/WkDGgx4wffPUXRXM7

Hours Worked: 2.0