Page 12-05: Tail cone fiberglass fairing -- third on the list of least-fun parts of the build

First the good news: It can be done well without removing the stabilator.  The previous section in the build manual had the builder (me) install the stabilator, a royal PITA to be sure.  I'd been itching to install all the tail feathers anyway, so after double-checking that I could get the airplane through the garage door with everything on (except the wings), I did it without reading the next section (yeah, I know, read ahead).

The vertical stab was easy even though it required a crow's foot on the torque wrench for a couple of bolts.  Gotta be at a 90 degree angle to the wrench (as shown) to read correctly.  Otherwise, some cipherin' is involved (to quote Jethro Bodine).







Bolting the stabilator on required that everything be at the correct height for the bolt holes to align, easier said than done.  It can't simply be held in the right position, even if I'd had a helper, because it's too ungainly with no easy hand holds.  I built a U-shaped structure from 2x4s and other wood scraps to support it and finally wrestled it into position.  I guess having two helpers would make it work.

  

Part of the problem with the stabilator attachment is getting the washers into position while inserting the bolts.  This was made much easier with a product called Washer Wrenches.  If I'd had these things for the entire build I'd probably have more hair left on my head.









With the vertical stab, stabilator, anti-servo tab and trim motor installed I turned to page 12-05 only to discover that it was assumed that the stabilator was back off the airplane.  In fact, as per the procedure laid out in the build manual, the stabilator has to be installed and removed several times to carry out all the trial fitting and trimming required for a good fit.

This is all necessitated by the build manual calling for the slot for the anti-servo tab actuator rod to be delayed until near the end of the section, making it impossible to remove the fairing with the trim motor in place.  I decided to cut the slot early, which allowed the whole thing to happen with the stabilator in place.  In fact, I plan to fly the airplane having installed the stabilator only once.

I cut the slot, taped a 3/4 inch piece of wood in place to provide the needed rigidity, and ended up with a good fit.

According to the build manual, drilling for the nut plates which hold the fiberglass fairing to the aluminum tail cone is to be done from the inside out using a long, flexible drill bit.  I couldn't make this work, even with my Tight-Fit Drill Kit, shown below, which has bailed me out of tight situations on numerous occasions.  As small as the head on this thing is, it still couldn't put the bit at right angles to the surface.

Instead, I made a drill template consisting of a curved piece of aluminum (below) representing the curve and thickness of the actual tail cone.  With this I attached the nut plates and drilled from the inside out through the nut plate rivet holes, the tail cone stand-in and the template.  With this template I drilled from the outside in through the tail cone.  Worked perfectly.  Even if I'd had the stabilator off, I couldn't have done it inside-out.

The whole thing required a lot of trial fitting and trimming/sanding.  I used a Dremel tool with a cutoff wheel or sanding drum for most of it.




I started out using a cartridge-style mask but discovered that I was ingesting a lot of fiberglass dust, probably because my facial hair prevented a good seal.  I finally resorted to my red-neck respirator (below) which involves a long hose with a mouth piece from a snorkel: breath in through the mouth and out through the nose.  It's the only thing that works well.

The tabs which connect the two pieces of the fairing together (below) are first match-drilled through the fiberglass while positioned on the outside, then switched to the inside for riveting.  Setting solid rivets in fiberglass made me a bit nervous but it turned out OK.








The bad part of this section is all the sanding of fiberglass and endless trial fitting.  When I over-sanded a seam, I filled the gap using a product called Bondic (cheap at Lowe's) which was developed

for filling teeth.  It's some sort of hard plastic which cures using a UV light (included) in a matter of seconds and can be sanded immediately.  There must be many other uses for this stuff.











A part unrelated to the tail cone fairing showed up today: four little plastic plugs which fit into the open ends of the boarding steps, lowering the drag a bit.  I have no comment about these parts.😬

Page 37: Fuel tank -- There's gotta be a better way

The tank is made up of four large pieces of aluminum sheet which comprise the walls, plus lots of other bits and pieces -- structural stuff which goes on the outside and various baffles which go inside. All of this has to be riveted together with different rivet types plus a few machine screws.

There are a couple of hundred rivets providing a couple of hundred sites for potential fuel leaks.

The piece shown at left (one marked scrap that I screwed up and the replacement) has seven different kinds of rivets or machine screws, some counter sunk, some not.  It's a beefy piece supporting two of the three bolts which actually attach the tank to the airplane.  The bolts are frangible (hollow) designed to shear in a crash or super-hard landing so the tank won't distort and spill fuel in the cockpit (something which could ruin your whole day).  All the rivets in this piece, along with all the rest, pierce the inside of the tank (leak possibilities).

Here's the bad thing about all these rivets: Each one has to be washed in naphtha and coated with ProSeal before being set.  ProSeal has a working life of two hours from the time it's mixed with the

catalyst until it hardens and can't be used.  This means that the process has to be carefully choreographed, with the appropriate rivets laid out, washed, and ready to be set.  As shown, I washed the rivets using a strainer belonging to the Spousal Unit (who is more than ready for the airplane to be finished).

A major mistake I made was ordering the ProSeal in the small (2 oz?) tubes which contain the sealant, the catalyst, and a built-in plunger to mix the two, thinking I'd break the process into multiple events, wasting less sealant.  Wrong.  A much better plan is to buy a quart and do the whole thing within the shelf-life window (90 days).  Turns out, one of the 2-oz batches I got was bad, causing indescribable anguish (more below).





Over three riveting sessions I installed all the aforementioned pieces along with the fuel-sender plate (actually two circular plates), which doubles as an access panel should a need arise to get back into the tank after it's sealed, a horrifying prospect which came true twice.

The assembly is to be leak tested after allowing the ProSeal to set up for several days by attaching a ballon to the tank, pressurizing the tank until the balloon inflates, then spraying soapy water all over the tank and looking for bubbles.  The balloon limits the pressure to something which won't cause the sealant to fail, supposedly less than one psi.  Being a curious sort, I decided to measure the pressure required to inflate a balloon by constructing a manometer. Turns out that every balloon I inflated needed about 1/3 psi (8 inches of water).  It took more to initially inflate it, but once stretched, 1/3 pis did it.  The Mothership says pressurize to one psi, but as long as I have a big enough delta P to blow bubbles, I think I'm good.  And blow bubbles I did.

With bated breath I pressurized the tank and proceeded to squirt the soapy water all over it.  Leaks appeared in six places.  After the misery of building the tank, it was as if someone had stepped on my soul. As Tom Cruise's sidekick said in Risky Business, sometimes you just have to say WTF?  I had

followed instructions, had done each procedure carefully, and this!  WTF!  At this point I had no choice but to open the tank, which involves inserting a putty knife between the access cover and the tank, removing the cover, then re-sealing all the offending sites from the inside.  The group wisdom of the Van's Air Force forums (and the Mothership) said don't be tempted to try it from the outside!

Turns out, contrary to what other blogs said, opening the tank was easy.  This should have been my first clue that the batch of ProSeal was bad, but it didn't occur to me yet.  I opened the tank, applied more ProSeal to the offending areas, and repeated the balloon test.  More leaks (picturing now a razor blade making lengthwise cuts of the arteries in my wrists).  I resigned myself to once again opening the tank and proceeded to do so.

This time it's almost impossible to do, far harder than the first time.  Bad sealant the first time!  I know I was within the shelf life, but it was bad.  I now bought a quart of ProSeal from the Mothership

and a digital scale from the aviation aisle at Harbor Freight, and did it all again.  Incredibly, there was another leak in the center of one of the rivets that was supposed to be "solid."  Rivet failure!  No way would I open the tank a third time.  I applied a suction to the tank, filled a cut-off syringe with ProSeal (needle removed, of course), and applied as much pressure as I could to the center of the rivet from the outside.  Success!

My rig for pressurizing the tank is shown at left: a 12-volt emergency pump for cars.


After letting the ProSeal cure for a couple of weeks, I put seven gallons (limiting the weight to about 50 pounds) of ethanol-free gas in the tank.  Over the course of a few days I turned the tank so that five of the six sides were down (didn't put it on its top), letting it sit this way for a day or so, and observed no leaks.  Of course, in the airplane the tank will be flexing somewhat, but I can't simulate that.

Boats don't have this problem.  The tank should be made of nylon or plastic or anything but riveted aluminum.  Horror stories about leaking tanks are plentiful on the forums, even the factory-made ones.  This now resides at the top of my Worst Jobs of the Build list, above the landing light and the tail cone fiberglass fairing.


Off Topic

This past summer I made my 31st pilgrimage to Mecca. Hard to believe I've been to Oshkosh that many times.  Can't wait for next year!  While there, I spoke with an insurance broker who told me that due to my age (hard to believe I'm 55....Oh, wait....) I should be insured and flying before another birthday happens.  Gotta be in the air before next September.  I'm on a waiting list for a hangar in Colorado and NC.

Painting the interior (while trying to build the gas tank)

For various reasons, I decided to go ahead and build the gas tank, something I expected to be an odious task and it didn't disappoint.  The building of the tank involves choreographing the rivet installations (eight different kinds I think), each of which must be cleaned with naphtha and smeared with the Devil's Own Glue called Proseal (it actually has a new name but everyone still calls it Proseal), which has a two-hour pot life.  Reading ahead in the build manual, I saw that one part of the tank build required centering the filler neck in a hole in the turtle deck.  Well, it turns out that I had

delayed installing the turtle deck to give plenty of room to do some critical drilling in the flaperon actuation linkage when that got installed.  I therefore needed to proceed with the installation of the flaperon linkage, the first instruction of which read "Install the wings."  In a post back in May (the subtitle of which is "dumb-assery on display") I detailed my attempts to persuade the wing spars to fully insert into the fuselage (didn't happen).  I now had no choice but to complete the wing installation.  The gas tank and the wing fit will be described in a future posts.

For some reason people who build RVs like to paint the interiors gray.  I'm no exception, although the dark gray I had envisioned couldn't be found in flat or matte finish.  Custom colors can be had in a rattle can but the cost is prohibitive.  I had primed the inside surfaces of all panels forward of the rear bulkhead using NAPA 7220 which is light

gray.  I finally settled for Krylon Colormax Matte Deep Gray as a top coat for everything but the roll structure (shown above).  The roll bar is still in primer, but it's hard to see the difference in the pic.  I definitely wanted a darker color for the roll structure, so once again I settled (like settling for a girl friend when you're sure you could do better but you're tired of looking) for Rust-oleum Universal Metallic Flat Soft Iron.  I found both of these on the aviation aisle at Lowe's.  In reference to the aforementioned settling, I put all that permanently behind me when, after looking for love in several wrong places, I committed holy matrimony with Dr. KTH (as her students call her) in 2009.

After painting everything but the roll structure, I masked as shown in the pic and painted the roll bar and the longitudinal member running aft from the roll bar which is not visible in this view.
All in all, I'm happy with the results.  Adding the turtle deck made everything look much better (last two pics).  We're on spring break, so I'm off the rest of the week and should be able to complete the tank.  I resisted the urge to spend the week in Colorado.  My webcams at my house there show a lot of snow, so I made a good decision.

Looking at my blog, I noticed that I haven't posted since attending the Oshkosh show for the 30th time last July.  The highlight of the show, I suppose, was watching the Van's crew and thousands of volunteers build the One Week Wonder, a complete, flyable RV-12iS built in one week.  Made me feel kinda bad considering I've been working on mine since 2011.