§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. 

§21-06 Fuel Tank Inspection & Wash

Well, I got all prepped and studied up for doing section 20.  I got the tanks out of their containers & unwrapped them and was pleasantly surprised that section 20 was completed by the factory.  One more down w/o any effort!

Section 21 is all about prepping the tanks and sealing them up.  I inspected the insides with a video scope and found them to be spotless.  There were no 'hanging chads' of sealant, any debris to be found, and all of the specified internal passages were open. 

The book says to fill each tank with 3 or so gal of 100LL and throughly rinse the insides, including turning the tanks upside down.  I looked at the 4 big open inspection plates and decided that it would be a good idea to put the plates on, otherwise we (Lada & I) were going to just pour all that avgas all over the garage.  There are two fuel pickups (6D) and two vent lines (4D), but the kit only included 1 each of the end caps, so fuel did make a bit of a mess.  Lada took the brunt of  the spill but didn't complain because she has a curious appreciation for the smell of oil & gas and stuff.

I did try to stem the mess by hand threading the fuel vent lines into their ports.  The L tank was straightforward, but the right side wouldn't thread.  I gently applied some torque w/ a wrench and promptly sheared the first couple of threads inside the coupling in the bottom of the tank.   I did some research and verified that it's a 1/8" NPT which is readily available at Harbor Freight.  I'll pick up a tap in a couple of days and will very gently chase the threads and try again.

Left Flap completed, §36-24 thru -26

Well, yesterday I said that I had estimated it would take 3 hr to complete the Left Flap.  I must be getting better at this (or at least lucky) since it took 2:50 to finish the job.   Lada helped during the pro seal application and fitting the trailing edge.  It's much easier with 4 hands instead of just 2.  I propped the skin up with some rags under the skin and against some ribs.  I only used about 1/2 of the jar of proseal and made essentially no mess.  Then both of us flexed the trailing edge around the back and it was done.  I spent the rest of the afternoon pulling the rivets, putting the ailerons & flaps into moving blankets and then cleaning the garage.  All in all, a very satisfying afternoon.

 completed Left Flap

both ailerons & both flaps

All wrapped up!

about 1500 pop-rivet mandrels

Right Flap completed §36-25, 26

I got off to a late start today because I worked a night shift last night and then had a 4 hour morning course to renew that pesky ATLS certificate.   I slept until 5:00pm before heading out to the shop.

I left off yesterday with the right flap fully skinned but not yet riveted, so all I had to do this afternoon was  pull rivets and finish the FL-15500-002 Right Flap. 

FL-15500-002

Close up of the vortex generators on the upper surface

Once that was done, I got to work on the left side.  The lower/training skin was peeled & deburred.   I hadn't deburred the vortex generators on the leading/lower skin so that got done, too.   I've fully clecoed the leading edges of the skins, but will stop here.  Tomorrow, I will rivet the leading edge & generators together.  That will provide excellent alignment for the one-and-done fitting of the trailing edge once the B2 sealer is placed on the rear lip.   It should take about 3 hours (so I'll budget 6) to finish before I go back to work tomorrow night.

§36-05 through -20 (Left), §36-21 thru -23 (both)

 It's been a very productive couple of days.   I built up the substructure of the Left flap, installed it into the forward/lower skin and verified that the upper/rear skin fit on both flaps.  I fully riveted the forward/lower skins on both of them.  

close up of typical cleco and rivets prior to pulling

overview of same state of construction

Dale came over and helped me bend the upper/rear skins.  The general portion of the KAI recommends using two boards that are hinged together to make a tool to bend the sheet metal into the final shape.   It didn't work worth a damn.  Bending the trailing edge all of the way to touch the other side did nothing; it simply sprang back to its original shape.   Following the advice of a VAF post, I ended up putting the flap skin on the floor, laying the board over it and literally walking on it back and forth and even springing up & down for good measure.   This produced about 75 % of the desired decrease in radius of curvature.   It was enough that it was not difficult to cleco together,  In fact, it was much easier than the leading edges of the ailerons, so I suspect that I'm in the correct ballpark.  I will enlist the opinions of other RV builders regarding the final shape of the trailing edges.

Last night I tackled the dreaded fuel sealant step and actually didn't make too much of a mess.  I had already riveted the forward/lower skin.  I scuffed the area that would get the fuel sealant.  I slide the upper/rear skin under the forward skin and fully clecoed it in place.  The natural spring in the sheet metal kept the rear edge away from the lip that got the sealant.   I smeared the sealant in place in about 12 minutes (out of a 30 min working time) and had a pretty easy time of clecoing the upper skin down onto the sealant.  I flipped it over, and clecoed/riveted the underside.  I was about half way through finishing all of the riveting (boring, but very satisfying) before having to close shop and go to work.

I'm expecting that I'll finish up both of them with another solid day in the shop.

RV-12 myth busted

 A few months ago I read a comment that you could tell your non-flying partner that in the event of pilot incapacitation, they could close the throttle and trim the plane full-up in order to achieve a controllable, low speed (and hopefully survivable) forced landing.

I had my doubts since the RV-12 has a very powerful stabilator and I can't recall ever getting close to full-up or full-down.  I took her up and tried it out.  Yep, it's not a good idea to put in full up trim. Even without power (prop wash over the stabilator), the plane was nearly in a trim stall with only 75 % trim.  I didn't push it any further and went home to continue building.