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.

(Page 12A-01) Stabilator tip fairings

The stabilator on the RV-12 as built to plans has squared-off tips, giving it, in the opinion of most builders it seems, an unfinished look.  I always sort of liked the look, but very much disliked the tooling holes (12 or so can be seen in the pic below) in the end ribs as well as the many holes in the wing tips where the tabs are bent and riveted and other holes in various places on the fuselage.  I'm convinced that all these holes were left

there in order to dirty up the aerodynamics to keep the speed below the LSA limit of 120 knots.  My plan all along has been to embark on an extensive aerodynamic clean up as soon as the FAA hands me the airworthiness certificate.  The stabilator also was limited to exactly an eight foot span to keep it legal for trailering on the highway.  Tips put it over the limit.

A couple of after-market companies make and sell rounded tip fairings and I've seen quite a few RV-12s with them installed (legal only after the airworthiness certificate has been awarded), but I couldn't decide if I liked them, other than the fact that they close all the offending holes.

Then, fairly recently, the Mothership got in the game and offered an officially-blessed kit.  What actually pushed me over the edge was doing the recent service bulletin 18-02-02 (covered in the previous post).  Complying with this SB involved drilling out a lot of rivets (punching their steel mandrils into the interior of the spar box) and drilling a lot of new holes in the spar box.  All this

resulted in quite a bit of debris in the spar box where it couldn't be reached.  It occurred to me that removing the end ribs as required to install the new tips might allow me to shake out a lot of the debris.  It still had to exit the few holes in the sides of the spar box, then make it through the lightening holes in all the ribs.  I could hear all the crap rattling around in there and I couldn't stand the thought of flying that way.  Tips it would be!

Installation of the tip kit involved drilling out 94 rivets to remove the existing end ribs (remember, I have achieved world-class status as a rivet remover), then replacing the end ribs with new ones reversed so that the flanges are out rather than in.  With the end ribs out, the shaking commenced in the driveway outside the shop.  I may have resembled a sign-spinner on a street corner in LA.  Along with a small amount of metal, I started seeing bits of shredded fabric, and I knew immediately

what that meant: mice had built a nest (shown in the pic above) in the spar box.  Visions of metal severely corroded by mouse urine danced through my head.  Inspection with a super-bright flashlight showed the nest to be not far from one of the few holes in the spar and I was able to hook most of it with a bent coat hanger and extract it (shown in the picture above).  A sudden epiphany lead me to tape a flexible piece of PEX tubing to the Shop Vac hose.  With this rig (pic at left) I was able to suck out not only the remaining bits of the mouse nest but all the metal debris which started all this.

At this point I inspected the entire interior of the stabilator with a bore scope to look for mouse urine corrosion.  Happily, the only spots I found were on the end ribs which were removed and replaced with the new ones in the kit.  A few small corrosion spots were found on the interior skin adjacent to the end ribs.  These were sanded and primed.

I keep live-capture traps set all the time in the shop (yeah, I'm that tender hearted), and had trapped and relocated a couple of mice a year or so ago.  Nothing since.  They had to be the culprits.

The new end ribs have to be straightened by fluting the flanges, just like all the other ribs in the

airplane.  The kit instructions say to modify the fiberglass flanges which slide underneath the rib flanges, making appropriate notches to clear parts of the spar, shop heads on rivets, and the humps produced by the fluting.  Lots of trial fitting here.

The instructions say to trim the fiberglass flanges to 15/32nd of an inch, which really means something less than 1/2 inch.  If this isn't done, the flange won't slide all the way in.  I used a Dremel tool with a sanding drum to "scallop" the fiberglass flange to

clear the fluting humps.  Files were used to make the rest of the notches.  I was not completely pleased with the cosmetics of the finished product, but I keep telling myself that perfection is the enemy of flying your airplane.

Service Bulletin SB 18-02-02: Cracks in the stabilator spar box

A high-time RV-12 was discovered to have a crack in the front spar box in the vicinity of where the stabilator horn is connected.  I don't know how the hell anyone discovered this crack considering that

dye penetrant was used to make it visible.  After dye penetrant was applied, the part was sanded to bare metal and application of a bright light revealed the crack.  Amazing!  I'm trying to imagine what prompted them to suspect that a crack was there. Anyway, the Mothership came up with a fix consisting of doubler plates which go between the horn bracket and the top and bottom of the box spar, doubler plates which go between the stabilator hinge brackets and the front of the box spar, and gussets which connect the hinge brackets to the stabilator skin and the spar, top and bottom.




The result of all this is an upgrade which is massively stronger than the original part.  I don't mean simply 50% stronger. I mean massively stronger.  The original stabilator hinge brackets simply bolted to the spar web, and the stabilator horns bolted to the spar box flange.  The new system rivets doubler plates to the stabilator horns, which then get bolted and riveted to the spar, top and bottom.

New, two-piece hinge brackets are riveted together and then bolted and riveted to the spar.  New doubler plates go between the hinge brackets and the spar.  Gussets tie the new hinge brackets to the stabilator skins and the spar, top and bottom.  The six #40 holes seen in the top of the spar (also on the bottom) are left open.






In the finished product (below), the original hinge brackets (green pieces on the table) are shown for comparison.

Quite a few rivets had to be drilled out, with their mandrels punched into the center of the box spar.  When I'm moving the stabilator around, I can hear them rattling around in there.  This tipped the scales in favor of installing the new fiberglass tips on the stabilator (what's another $130 at this point?).  Installation of the tips requires drilling out all the rivets in the end ribs and reversing them.  When they're out I can dump out all the debris.  Ordered the kit today.

Service Bulletin SB 18-03-06: Cracks in the anti-servo tab skin.

On three high-time RV-12s (hours > 900) cracks were discovered in the skin of the anti-servo tab where the control horn attaches to the inboard-most rib.  All of the internal ribs in the AST have angled tabs at their leading edges which attach the rib to the spar and the skin.  The inboard end ribs,

to which the control horn attaches, did not have these tabs.  Makes sense, right?  The one rib which transmits all the load from the pitch input from the stick didn't, in the original design, connect to the spar in the leading edge of the anti-servo tab.  This original is shown in the picture.






The fix for the poor blokes with already-flying airplanes involved stop drilling any cracks, adding various doublers and replacing the end ribs.  For those of us with airplanes still under construction, all that was required was end-rib replacement.

One of the few benefits to working as slowly as I have is having an easier time with service bulletins.  The fix involved drilling out a total (both ASTs) of 10 solid rivets and 16 pulled rivets, match drilling some holes (my 273rd favorite thing), countersinking holes for the solid rivets, and re-installing everything.  I have become an absolute expert at drilling out rivets.

I appreciate the concept of service bulletins.  As the fleet ages, problem areas appear and a re-design of various parts ensures safety.  As I implement the changes, however, I feel that I'm simply treading water, re-doing something I've already done and making no progress toward that first flight.  The worst of these was the landing gear beef-up, but it's clearly a more solid airplane now.  I guess I'm just tired of building and ready to fly.  Building this airplane has been one of the most interesting things I've ever done, but I'm really ready to "slip the surly bonds of earth" (thanks again, John Magee, for the poem that has inspired me for most of life).  My new goal is to fly the airplane to my home in Colorado next summer.  I'm still on the waiting list for a hangar at KLMO, and have been called several times as one became available there, only to turn it down.  My big fear is that nothing will be available there when I'm ready to go.  That airport is 1.5 miles from my home, so no other airport makes sense.  I will, of course, have to have a hangar here in NC at KVUJ (three miles from my NC home) for the flight test period.  I think it's a fundamental law of nature that RVs can't live outside in the elements as so many store-bought airplanes do.

(page 30-02) Trial-fitting the wings (or dumb-assery on display)

So with the gear mounted and the fuselage easy to move out of the shop (and back in quickly if it started raining) I decided the time had come to trial fit the wings.  I was somewhat apprehensive after having read other blogs with descriptions of this, but there was no reason to wait.  Moving the wings around is a two-person job, so I enlisted the help of two of my former star students (thanks Sam and

Kristin!).  The procedure involved moving a wing from the wing rack onto some blankets near the fuselage, then with one person holding the wing-tip handle and another person handling the spar and attempt was made to slide the spar in all the way.  Notice I said attempt.

The first problem involved interference between the spar and the skin surrounding the slot previously cut into the skin.  In retrospect the slot should have been at least 1/16th inch larger in both directions, probably a bit more.  There's no downside to making the slot larger.  It's completely hidden by the wing root.  The Vixen file made enlarging the slot fairly easy.

The second problem involved rivet heads in the spar interfering with the fuselage skin.  Easy fix with a Dremel tool.  The spars still wouldn't slide in all the way.  At this point we had tried both wings with similar frustrating results, leading me to try wiggling the wing a bit too vigorously.  The result

was a broken electrical connector at the wing root.  The connectors had been installed in the wing roots and in the fuselage at a much earlier date and it didn't occur to me that I could have made a mistake at that point.  One of the locating "pegs" on the male (they're actually kind of hermaphroditic) plug broke off.

Turns out I had installed the connectors upside down in the wing roots.  The locator pegs would slide into their receptacles and move in a half-inch or so, but the part making the electrical connection wouldn't mate.  This was discovered, of course, after I broke the peg.

A new connector was ordered from the Mothership for only a few dollars, but that wasn't the problem.  The problem was extracting the pins crimped onto the wires from the connectors.  The really maddening thing was that I had extracted these pins months (years?) ago after inadvertently putting them into the wrong holes in the connector.  This time, I couldn't figure out how to get them out.  I have acquired a collection of pin-extraction tools, but nothing worked.  I ended up having to cut/break the connector apart (it was being replaced anyway) to get the pins out.

The really bad part is this:  I still don't have the wings fitted.

The new connectors are installed and a new wing-fitting session is imminent.

Although I swore I'd never teach summer school again, classes start tomorrow.  I need the money to continue pursuing this madness called "building your own airplane."  $40k down and $40k to go.  Hope the Spousal Unit (my beautiful and brainy wife who is now known as Dr. KTH to her students) doesn't read this blog.