§23

Section 23 is a very short, straight foward chapter that builds the Outboard Mixer Boxes.  It's literally just installing 1 nut plate and riveting 4 pieces together with 16 of the easy-peasy pull rivets.   It took me about 2 hrs to do both L and R sides.

I decided to do them both because I do have a lot of trouble with mentally mirroring the drawings.  I built up the Left in its entirety, then set up the parts for the R and used the physical structure as my mirror source.

I learned a little bit about rivets.  The kit calls out for a very specific rivet, NAS1097AD3-3.5 rather than the much more common AN426AD3-3.5.  In fact, the entire wing kit has just four of the NAS rivets.  They are to be used in shear loads only, as they have a very small head and won't resist much axial loading.    They are typically used in very thin material.   What's odd is that Van's almost always called out the AN426's for similar applications and the material in question was actually pretty thick, 0.050", so I have no idea why they went to the trouble of stocking these specifically.  Oh, well.

L & R Outboard Mixer Boxes

Leaks identified

While working on the R spar, Marc came over to help figure out the tank issues.  He's also an engineer and I wanted a fresh pair of eyes on the problem.  He agreed that there should be no leaks based on my procedure and his visual inspection.  Back to testing: we split up the tasks of one person pumping and the other spraying bubble soap, but never saw any bubbles.   We finally took the compressor and blew air into the tank.  We could feel a breeze on our fingers on the inboard edge (with all of the connections) but couldn't make any bubbles appear nor feel our way to the leak.

Rather than using expensive, toxic, smelly and flammable avgas I decided to do an old fashioned test.  We filled the tank with water from the hose.  Viola!  The Proseal around the fuel sender leaks like a sieve!  Water streamed from the entire circumference.  Mystery solved.

This also validated my gut feeling that it was a systemic issue.   Recall that I used left over Proseal that had been in the freezer.   While working with it, it was appropriately sticky and gummy and I thought it was OK, but apparently it was by then too viscous to actually flow when I tightened down the fuel sender plates.

I'll order some more Proseal (or B2 sealant as it is now known) and re-do the senders when it arrives.  I'm feeling much more optimistic that we'll get something that is water tight next time.

§ 22-4 thu -17 Left, -18 thru -21 R

Got lots of building done this weekend.   The rear spar is the topic of construction for the next 4 or 5 chapters.  § 22 is pretty straightforward, if somewhat long.  I was really hoping to be able to complete the entire L rear spar on Saturday, but ran into a minor glitch.    

If you notice the title, I suddenly switched from building the L rear spar onto building the R rear spar.  Curious, no?    Page 18 calls out starting with W-15016B-002.   That's odd.  a -002 part implies that you've probably come across the corresponding -001 already.  I proceeded until I came to the conclusion that I had indeed built the corresponding assembly (outboard aileron attach point) for the other side.

No problem, I thought to myself.  I went to the parts shelf but for the life of me, I couldn't find the expected -001 part.  My inventory sheet shows I had it in my hand at one point, but neither myself nor my wife could find it in the shop.

I'll order another one this weekend and will eventually get to finishing the L rear spar, but during the meantime, there's other stuff to be done so I'm not stuck.

most of the L rear spar

Quick update

Just a quick update so you know I'm still here.

I've laid out the parts for the next section and feel pretty good that it will come together quickly in the next day or so.   

I finally received the last few back ordered parts from Van's.  My wing kit is now officially complete.  

There is much gnashing of teeth on VAF regarding some misaligned holes on a few wing spars.   Those spars are apparently ~$3K each!   I dug mine out and clecoed together the areas of question and the holes are well aligned, so I don't have to deal with getting Van's to replace them.   

Marc is a partner in the Cirrus and we're going to go flying tonight.  Tomorrow, he's going to swing by the house and I'll enlist him in helping me find the source of the leaks in the tanks.

Setback -- The Fuel Tanks Leak. A lot.

Well, I finally had an opportunity to work on the fuel tanks again.  I lost a day or so because I never read the manual on the little bicycle tire pump and I was putting it on incorrectly.  I thought it was defective and went to the aviation division of Walmart to find a pump with a different kind of connector.  There weren't any.  There was, however, one brand that thoughtfully provided an instruction card and I learned I had been trying to attach the pump while it was in the locked position.  Duh.

I got home, correctly attached the pump and tried to pressurize the left tank.  The balloon barely quivered with each stroke.   Damn.

Armed with my granddaughter's bubble soap, I put the tank on stands out on the driveway and liberally soaped up all of the seams, the access panels, the fuel sender, the supply lines, vent lines and balloon neck.   Nada.  I can't generate any bubbles at all.   I'm pretty bummed.   I washed off the soap and put the tank back on a solid table.   I rigged up the right tank and got equally nowhere, but I didn't bother to soap it up.

I've learned not to do anything when I get into a spot like this.  By doing nothing, I can't make it worse.  The fact that both tanks are completely incapable of holding any pressure at all implies that I'm missing something fundamental that will probably be obvious in retrospect once I find out what it is.

Tonight, I'm going to think about options.  I'll write to Van's and ask how they pressure tested the tanks without them being sealed and see if that sparks any intuition.  I'll look into acquiring a 4' x 6' x 1' plastic tub and might try to immerse the tanks under water and look for bubbles that way. (That's going to be 240 lb of buoyant force to deal with, so I'll need some brawn to help!)   I'll check w/ some RV builders at DLZ and invite them to come help me troubleshoot.   Something.

Tomorrow is a day off and I don't want to throw it away by doing nothing at all, so I'll start on the next section of constructing the aft spar and ribs.  As long as I don't attach anything to the tanks, I am maintaining their current state and not impairing my ability to troubleshoot later.

§21-11R, -13. Sealed access plates R tank, installed fuel drains

As expected, it wasn't difficult to apply B2 sealant to the access plates on the top of the right tank.  Overall, it took about an hour and about 3/4's of the jar of sealant.

As expected, it was much more difficult than it should have been to install the fuel drains.   The instructions on page 13 are deceptively simple -- Install (1) into (2), where (1) and (2) refer to the fuel drain and fuel tank, respectively.  It doesn't mention using anything to create a seal, but I know that those types of threads (NPT) aren't actually fluid tight and must have a sealant of some sort.   Basically, it boiled down to using B2, as is used everywhere else, or Loctite 565 which is called out in a different chapter but never mentioned in the actual instructions.  I posted a query on VAF and was told RTFM (section 5) where it generically calls out Loctite 565, so that's what I went with.

As mentioned a few posts ago, I had tried a simple trial fit by installing (finger tight only) those components, and somehow managed to strip threads.  I wasn't really sure if they were stripped inside the tank (horrible) or just on the $30 part (not too bad).   

I researched the drain and found that it was a 1/8" NPT.  I couldn't find any technical description of the threads for the part from Van's.  It appears that all 1/8" NPTs are 27 pitch but that was only because that was the only pitch number I ever encountered and it was rare to find it at all.  I bought a set of cheap taps & dies at Harbor Freight that included the desired NPT.  I've tapped internal threads before, but never cut or chased external threads.

Some scrap Al from the RV12 was used to make a test hole with the tap and I was able to thread the fuel drains into that.  This confirmed that they were indeed 1/8 NPT 27.  I debated chasing the external threads on the drains, but wasn't sure which side of the die was the starting side.  Since NPTs are tapered, doing it backwards would probably destroy the part, so I deferred.  In retrospect, I think running the drains through the test hole actually chased them a little anyway.

The tap was used to very gently chase the tank.  I only used finger pressure and no tools.  The drains got gooped up with 565 and I tried to install them.   Nope, the threads wouldn't engage.  I finally got them to engage and tighten by pushing up on the drain with my thumb to and apply a fair amount of axial load while gingerly rotating them with a closed 1/2" wrench.  Finally, success.  It only took an hour to install two bolts.

Right Fuel Drain

§21-07 thru -10, -11 L, -12. Installation of fuel senders, access ports, fuel caps

Two days ago I got a lot done and pretty much finished sealing up the Left tank.  I ran out of time, energy and sweat and didn't seal the access plates on the Right tank, but that is now one of those "just get 'er done" things since I've gone through the process and know what / how to do. 

To explain; we left off with both tanks inspected and rinsed w/ 100LL avgas.  There was no debris and we found nothing in the rinse process.  The tanks had a few days to dry before I got to work on Monday.  The plans call for bending the float attach arms for the two fuel senders and give some engineering drawings to show how to do it.  I did both of them backwards.  Luckily, it turns out that that configuration is perfectly acceptable.  The only variation is that the float arms are 'pointing' in the direction opposite of the drawing, but this is on an axis that is parallel to the actual pivoting, so it makes no difference.  (sin 0° = sin 180°).

The R fuel float was very stiff and would actually stay in whatever position I put it. This is not going to give an accurate fuel level measurement since the goal is for the float to fall by gravity and float by buoyancy in the fuel.   I actually didn't realize this until after I had applied the pro seal (or "B2", as Van's now calls it) and was in the middle of trying not to make a thorough mess.  I was able to gently apply a little bend in the mechanism such that it no longer was binding and free falls properly.

Right Fuel Sender, Internal View

I got both fuel senders sealed in place with the left over B2 sealant from the second flap.   It definitely was harder to work with and was getting stringy towards the end, so I'm pretty sure that it only had a few minutes of shelf life with which to work, but it was still spreadable enough that I'm comfortable that I have good seals on the fuel senders.   We'll find out soon.

Right Fuel Sender, External View

The inspection ports on the Left tank weren't too bad, but I was surprised that I used up most of a jar of B2.  I have one left in the freezer to do the Right tank later today.

As mentioned last time, I stripped the threads from the L fuel drain.  I have the 1/8' NPT tap from Harbor Freight and will address that later today, too.  With that done, the R tank will be curing for 24-48 hours and I'll start pressure testing the Left.

Stay tuned.