§27 R, $28 R, §29-5—7 R

 Another really productive day.  It wasn't all roses, but it was very productive and enjoyable.   Bottom line—the two wings are essentially at an equal state of assembly! 

For the record:  §27-05, -06, §27-08, -09, -10, §28-13, -18, -19, -20, §29-05, -06, -07

Section 27 was started the day before yesterday (I played hooky yesterday and went flying.  More about that below) and really is just riveting the flap mixer to the rear spar/tank.  This is where the famously expensive Cherry Max rivets are used.  These puppies can be used in lieu of driving AD470's in almost all locations, but Van's cheerfully lets you ensure you find the correct length and you must source them yourself.  Apparently there was a fire at the factory that made them and now they sell for ~$2 a pop! Ouch!   As much as I'm tempted in a few places, I'll pass for those prices.

I jumped ahead (§29) and attached the front spar to the tank and clecoed it to all of the loose ribs that would otherwise be hanging in the breeze.  This gives the assembly a significant increase in rigidity and makes me feel better about picking it up and moving it, etc.   Prepping the front spar involved riveting an extension to it using a doubler.  Those were all driven 470 rivets and, because access was easy, it was actually fun.

Front Spar clecoed in place

Section 28 involved finishing up the push rod that I had to set aside a few months ago when I spilled some loctite onto a bearing and decided I didn't want to use it.   When I went to find the replacement, I spent 5 panicky minutes searching before I realized that the smart place to have put it was in the parts bin supplied by Vans.  Yep, there it was.   The rest of that chapter was taking the previously manufactured bell cranks and figuring out which way was which and getting them installed.  Rather than last time, when I wished for a trained capuchin monkey, I discovered I could attach a push rod to a bell crank out in the open, then insert the bell crank through an access hole and into position. Much easier!

top view of the R outboard (aileron) mixer

Looking inboard, under the fuel tank top skin, 

at the inboard aileron  pushrod 

At this point, I could sort out the D-cell nose ribs and cleco them to the front, but I can only attach 11 of the 15 as I am waiting on LP4-4 rivets from Vans.  I'm also waiting on the plastic clips for attaching the wiring harness.   Essentially, the wings are at the same place and both stuck.

Steve Brown will return on Sunday to help me drive the awkward rivets for one of the nose ribs, and I'll attach what I can.  I have enough saw horses and work stands that I can actually move both wing skeletons off of the work bench.  That will give me room to start prep work on the skins so that when the errant parts arrive from Vans I can get right to work installing the skins.  That's going to be 2 or 3 days of long, tedious but FUN work!

(I played hooky yesterday because the weather was just too good to pass up.  I managed to get out to Marysville and fly the Citabria in moderate winds from about 45° off the runway.  I'm nowhere near feeling comfortable landing that plane and it was a good workout.  Surprisingly, I made 4 very good landings on the grass.  My technique wasn't really 'full stall' nor 'tailwheel'.  I was too busy not loosing control to think about classifying them.  I flew the Cirrus and did a set of engine verification procedures.  For the curious, they are called "GAMI spread determination" and "LOP mag checks."  Both went well.  Finally, I took up the RV-12 just to say I flew all 3 aircraft for which I am current.  I didn't fly the CAF PT-26 because (1) I'm not current, and (2) it has a bad mag and is grounded.)

§22R, § 24R& §26R !

 Wow!  Today was a very productive day.  It didn't start out that way.   My work/sleep schedule is truly chaotic.   I didn't feel much more tired than usual when we went to bed last night but I slept 12 solid hours and had no bouts of tossing & turning.  I woke up around 1pm, but puttered around the house and didn't even get dressed until almost 5pm.  (I might have been a touch hung over, but we won't talk about that, will we?)

In my last post, I was undecided about how to proceed.  I decided to build up the skeleton of the right wing in parallel and will then proceed with applying skins to both wings.  This way I have the open, accessible L wing to use as a reference for the R since there aren't any drawings of the R wing.  I had already purchased two portable work stands from Home Depot and Lada helped me move the L wing skeleton to those to get it out of the way and make room for the work on the R wing.

Despite not getting started until 5pm, I managed to finish 3 chapters for the Right wing!   Much of that speed was due to having already built up the mixer boxes and aileron brackets for the right wing a couple of months ago.  Today, I attached all of the main ribs to the rear spar, attached the outboard mixer box to the rear spar, and fastened the rear spar to the fuel tank.   In detail, I completed the following pages: §22-04, -05, -06,  -12, -13, -14, -15, -17, -22, -23, -24, -25, §24-05, -06, -07, -08, -09, §26-05 & -06.

Foreground: Right wing rear spar assy

Background Left wing assy

Right wing rear spar assy

I have tomorrow & the next day off.  I expect that I will be able to install the inboard mixer, finish the pushrod and install it, and then attach the main spar & D-cell nose ribs.   That will bring me to par with progress on the Left wing.  I'm waiting for parts from Van's to finish the D-cell Nose Ribs, so I might end up in a work-stoppage until those parts arrive.

§29-08, 10, 12-15, 17 Left

 Argh.  I was really hoping to finish off this section.  It's all about attaching the grommets and tie-wrap clips to the D ribs and riveting the ribs to the spar.  Surprisingly, it was the riveting of the plastic tie-wrap clips that was problematic.    5 of the 15 clips didn't hold up to the pressure exerted by pulling the pop-rivets and they ended up getting ruined.   While I could have stolen from the supply designated for the Right wing, the rivets that are called out are LP4-4's, not -3's.   I literally have thousands of -3's, but the supply of -4's is actually only half of what is needed and there aren't any surplus to borrow from.  As a result, I'll have to wait until replacements arrive from Van's before I finish out this chapter and move on to installing the wiring harness.

Ruined tie-wrap clips and LP4-4 rivets

I'm getting close to making a major decision.  Should I continue on the left wing alone, set it aside and then do the right wing, OR should I set the left wing on saw horses to use as a reference and build up the right wing skeleton, and then proceed to put skins on both of them?   I need to decide in a week or so.  Keep reading.

§21 addendum complete, Left & Right

 After 6 weeks of being stuck in the doldrums of sealing the tanks, I have resumed actual construction.  Van's issued an addendum to chapter 21 instructing me to install a bunch of nut plates on the tanks.  Since this had nothing to do with their fuel integrity, it didn't cause much headache.   One set of nut plates is around an access hole on the bottom of the skins.  That took some gentle skill because I had to mildly contort myself in order to see what I was doing and I needed to balance a 426 rivet on one die of the rivet squeezer, then thread the rivet through an upside down hole and finally squeeze it in place.  I only dropped 4 of the 48 rivets that were set that way.

Access hole being equipped with nut plates

The image above probably needs some explanation.   The bulges at the top of the image are the outboard skin of the Left fuel tank.   There's about 18" of skin both above and below the tank and we're looking at the bottom skin with its access hole.  In the foreground, you can see nut plates and set rivets.  in the background are the clecos securing nut plates that have yet to be riveted in place.   This is where I was having to balance the rivet on the squeezer and gently raise it into the open hole.  It was actually a lot of fun.

Airworthy fuel tanks, finally! §21 complete for L and R

(Mea culpa:  I wrote this 4 days ago and never hit the "Publish" button.  Doh!)

The fuel tanks are officially "done."   While I never was able to get them air tight, as some VAF members have been able to do, I have been successful in demonstrating that they would hold water and as of yesterday, that they could hold 100LL.

(recap) As you may recall, I spent nearly a month trying to get the fuel tank sensors installed correctly and without leaks.  The first few attempts were definitely learning experiences for me because it was obvious that I had done a poor job.  Each one got better (e.g., the residual leaks were smaller & slower).  I finally got the obvious leaks sealed and then proceeded to pressure testing.  There were some dumb leaks that were easily corrected, but then I really got serious about trying to make them airtight.   

I gave up on Van's idea of using a kid's balloon because there were some very thoughtful and data supported comments from VAF that it's an exceedingly poor gauge and should best be thought of as a pressure 'fuse' that will blow if you end up putting too much pressure into the tank.  Instead, I bought some clear plastic tubing, added colored water and used that as a simple manometer.   15 inH2O = ~0.5 PSI and is roughly double the pressure of a full tank of fuel, so I figured that would be a good value to use.  Unfortunately, despite everything I could think of, I could never get the tanks to hold pressure for more than 30 min.

I suspect it's the fuel caps that are leaking.  I couldn't prove it, but I just don't like their design.   I even tried sealing them with condoms, but could never find a leak nor maintain pressure.

Lada & I filled them with with water and left them to soak for a long weekend.  No leaks!    100LL is half the viscosity of water, so there might be a hole too small for water to leak through, but might pass avgas.  I drained all of the water and borrowed 29 gal* of 100LL from the Cirrus and tried it again in the Left tank.   Success!  I managed to salvage about 28 gal and put it in the Right tank.  Another success!  Neither tank had any visible moisture after 24 hr of containing 100 LL.

This officially completes section 21, as it was published on the day I received the wing kit.  More about that later!

*I have 3 jugs of 8 gal each that I use to buy premium auto gas and pump into the RV-12.  I also have a 5 gal container.  Together, they are 29 gal. The fuel tanks are 30 gals, so "close enough."  If there's a leak at the very top, it will not be operationally important because fuel won't leak up against gravity.  In addition, aircraft tanks are rarely stored in a completely full state.  I will take pains to ensure that the plane is not parked outside during rain, or will find a way to cover the fuel caps if needed.

Water tight. Not air tight, but water tight.

 I bet y'all thought I had quit and walked away.   Nope.   Thought about it a bit, but nope.

Both tanks remain stubbornly not-air-tight.  I was extremely hopeful that the through-bolt locking mechanism in the cap was the culprit.  I tried sealing the caps with rubber gloves, but there aren't any more latex rubber gloves and nitrile gloves don't have that stretch that is needed to make a perfectly smooth sealing surface.  They tend to fold and bunch up and that makes them leak way more than the cap by itself.  Condoms, on the other hand, are perfectly round in cross section and can be made to fit over the cap.  It typically took 3 or 4 condoms getting torn to lock the caps in place without damaging the condom itself, but I got good at it.

Still, the damn tanks wouldn't hold pressure.  I gave up on the balloons as pressure gauges and got some clear plastic tubing and food coloring to use as a simple manometer.   15 inH2O is about 0.5 psi and so I used that difference in water height as my pressure gauge.  Pumping up the tanks to 15 inH2O resulted in a drift down to about 1 or 2 inH2O in half an hour.  This was fairly repeatable.    Despite being repeatable, I could not find where the air was leaking using the soapy bubble water trick.  (Which is messy, by the way.  At some point, I'm going to have to haul the wing assembly out to the drive way and hose it off.)

I posted my plight on the forum and, man, did I ignite a firestorm!  Two suggestions were worth merit: one was that I had not accounted for the heat of compression and that the declining pressure was actually the heated air cooling off.  The second was to use dish soap rather than kid's bubble soap for my leak detection.   Both of these have been filed for potential future use.

Several commentators had used the logic of "it's a fuel tank, not an air tank" and simply filed their tanks with 100LL fuel and looked for the tell-tale blue stain.  Other's commented that that takes too long to see the stain, and others said balderdash and basically it turned into a debate similar to the holy war of priming vs not priming.

I like the pragmatic approach exemplified by the "it's a fuel tank."   I did a full up water test over the previous weekend.  Literally.   Lada & I filled both tanks to the brim with water and then left for a 3 day weekend.  Upon my return, there was no damp or wet spot on any of the sides or the tops.  I couldn't check the bottoms because of the weight of the water itself, but if either tank develops a leak on the bottom, I can repair those even after the wings are mounted on the plane.

Last night I drained the water and fetched 29 gal of 100LL from the airport.  I didn't have the correct hoses to configure everything (I can't use the cheap PVC tubing with 100LL, so I have to go to the hardware store for the proper fuel hose.).  I'm going to fill each tank and watch for 24 hours.  If no leak, I will declare them airworthy and get back to actual assembly.   This final step will probably take another week or so.  Stay tuned.

still leaking.

 I finally ended up using a condom to seal the fuel cap on the Left tank, but alas, the tank still leaks.  I have this weekend off work and will spend the majority of my time searching for the remaining leaks.  The good news is that the fuel sender and access plates are air tight.  The bad news is that he fuel sender and access plates are air tight...  :-(