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.

Page 35: She's got legs!

Installing the landing gear

The urge to install the landing gear has been almost overpowering lately, but doing that causes me to lose the ability of turn the fuselage on its side on the saw horses in order to work on the bits on the fuselage floor in relative comfort.  Since the controls are essentially done, I finally gave in.  I can't put

off trial fitting the wings any longer, so having the ability to easily roll the airplane out of the shop to provide room for the wings sealed the deal.  I'm showing the last picture first to reveal the installed gear since I'm so happy to see it.  Note that I also installed the entry steps to make it easier for me to get in, sit in the pilot's seat, grasp the stick and make airplane noises (yeah, I've done that a few times).

The Mothership emphasizes that the main gear legs must be primed with two-part epoxy and painted, I opted for SprayMax 2K rattle can primer.  It seems strange to have two-part paint in a spray can, but it works great.  The catalyst is in a separate bulb which is punctured to release it into the primer.  The can is then shaken for an appropriate length of time to mix in the catalyst and the spraying can begin.  It's expensive, but one can did both main gear legs and the nose fork.

The need for the new beefed-up nose fork has been hotly debated on the forum, but considering that I will have spent 80 large on this airplane, what's another $300 for peace of mind.  I primed and painted the fork at the same time as the main gear.  I used Rustoleum automotive rattle-can paint for the top coat.

I approached the gear installation with a bit of trepidation since I had earlier done Service Bulletin 12-11-09 (detailed in the post from 1-20-17) which involved drilling holes in the center channel which is the main structural member in the entire airplane.  The holes in all the pieces then had to line up to allow insertion of the bolts.  With a bit of

effort it all worked out.  This is fortunate since, considering the center channel can't be replaced, I would have been totally screwed if it hadn't worked.














The build manual says to hold each leg along with the seven other pieces shown in the picture in place while inserting the bolts.  Easier said than done.  I put a rope through the inboard center holes in all the pieces and looped it around the outboard end of the leg as shown in the picture.  The other bolts could then be inserted and torqued to spec.  The later version of the airframe comes with all the holes pre-drilled, which would make the assembly go together much easier.

At this point in the build, I've been pondering how many hours I've spent on this project.  Some builders faithfully record build time in a log.  I'm really glad I made the decision from the outset to not do this.  I'm glad I don't know.








The instructions at this point say to measure the toe in (or out) using blocks of wood held against the axles and a string stretched in the proximity of the wood blocks, affording a visual check of the toe.  Shims can be ordered which will adjust this.  Though not mentioned, allowance must be made for the taper of the axels.  The bigger concern for me, however, is that without the weight of the engine, wings, etc., there is considerable positive camber (clearly seen in the first pic).  As with most suspensions, even sophisticated automotive ones,

there will no doubt be a toe change associated with suspension compression and its attendant camber change.  Although it will be a much bigger PITA to do this later, my plan is to wait until all the weight is on the gear.

Is my torque wrench telling me lies?

Well, yes and no: A tale of two torque wrenches.

In addition to the approximately 12,500 rivets in the airplane, there are many hundreds of MS, NAS and AN fasteners, all of which are supposed to be torqued to spec using a torque wrench.  Over a lifetime of turning wrenches, I have managed to acquire five different torque wrenches, ranging in

size from a small beam-type, 1/8th inch drive wrench I use on bicycles to half-inch drive jobs I use on cars and trucks.  The two I have used exclusively for the airplane build are a Craftsman snap-type 3/8th-inch drive, where the desired torque value is set on the handle and a distinct snap is felt when the torque is reached, and a 3/8th-inch-drive Snap-On dial-type wrench (shown in the picture connected so as to compare torque readings).  The literature always advises that the wrenches must be calibrated in order to ensure accuracy.  I had always (erroneously) assumed that the accuracy would be "close enough" considering that all my tools are name brand and the torque specs for each size fastener are fairly broad.  Since the airplane is going to be hauling me and my braver (or more foolish) friends around in the sky, I figured the time had come to check this.

Considering how much Snap-On tools cost, I assumed (correctly) that it would be the more accurate.  I bought an electronic fish scale on Amazon and also bought a "certified" weight (accurate to +- 0.5%) to check it with.  Amazingly, the rather cheap fish scale was accurate to within 0.9%.  I used the fish scale to apply a torque to the Snap-On wrench (shown in the pic) and it seemed to be dead-nuts accurate, at least to within the error band of this rig.

The shocker came when I checked one wrench against the other: When the Snap-On read 100 inch-lbf, the Craftsman indicated 84 inch-lbf.  This is unfortunate since many of the torque values being measured are essentially impossible to read with the Snap-On.  Henceforth, I will apply a correction when using the Craftsman.

A dial-type wrench is required since the prevailing torque (the torque required to turn the fastener in the self-locking mechanism) can't be measured any other way.  Measured torque minus the prevailing torque equals the actual torque applied to the fastener.  Maybe I'm worrying needlessly considering the error which results from the varying amounts of lubrication on the threads due to handling the bolts with hands which are no doubt far from clean.  Clamping force is all that really matters, and can only be determined through measuring bolt stretch.

Page 31B-12 + 29th trip to Mecca

Page 31B-12 says to temporarily install the control sticks in order to install the push-to-talk switch in the top of each column.  A bolt and a bushing are called out for the side-to-side pivoting motion at the base of each stick.  Both sticks connect to a shaft which was previously installed (shown in the second picture).  Problem is, the bushings wouldn't fit into the tube welded to the base of the stick (near the right-angle turn in the picture) and the bolts wouldn't come close to

fitting into the bushings.  No mention of this was made in the build manual.  The OD of the bushings was fairly easy to reduce slightly using the Scotch-Brite wheel, steady rotation of the part and lots of trial-and-error fitting.

The ID of the bushing, where the actual pivoting takes place, was another story.  This is a place where the fit should be near perfect with no slop. The OD of the bolts measured about 0.3754 with a micrometer, so a 3/8th reamer (which I had) didn't work.  I could buy a 0.3755 reamer for about $75, which seemed ridiculous for a single use.  Instead, I took a 5/16th bolt, cut the head off, sawed an axial slot in it about 1 inch deep, wrapped some very fine sandpaper around the bolt (and through the slot), chucked it up in a drill and ran it carefully in and out of the hole until the bolt fit in the bushing with no play.  Lots more trial and error.

The next issue was getting the two wires through the sticks.  As shown in the pic, the wires have to make a right-angle turn and then squeeze past the aforementioned tube and bushing.  Trying to push them through didn't work.  To accomplish this, I used the ShopVac to suck a string through (the yellow string in the pic), then used the string to pull the wires through.

The sticks on the new RV-12is, shown below, have three buttons per stick (PTT, trim and autopilot disconnect) and six wires.  I asked the reps from the Mothership at the recently completed Oshkosh how they got that many wires through.  Turns out it's now OK to drill a hole in the sticks at the right-angle bend.  Now they tell me!  I'd like to have the three-button sticks, but I doubt I'll retrofit it.  I had always assumed that if the injected engine were offered, I'd get it.  Turns out it's not possible for people who have already finished the fuselage.  I'm consoling myself by thinking about the money I'm saving by sticking with carburetors.  The new firewall-forward kit costs about $5000 more with the injected engine.

Speaking of Oshkosh, I just returned from my 29th trip.  Hard to  believe.  Where did the years go?  A bucket-list item is to fly my RV to OSH.  Maybe next year.

(page 31B) A mechanical engineer doing wiring -- what could go wrong?

The wires in my hand are just for effect.  They actually came out of my antique car when I foolishly decided that the warmed-up LT1 engine I had put in it didn't have near enough horsepower.  With the

money I proceeded to spend on the followup engine I could have easily bought the firewall-forward kit for the airplane.  We live and we learn (I hope).  Money is shaping up to be a major player in how soon I can "slip the surly bonds of earth."  The avionics and engine, which is what I will have left to buy after completion of the "finish" kit, represent more than half the total cost of the airplane.

Given that the airplane will have sophisticated avionics, autopilot, etc., I've always contemplated doing the wiring with a sense of dread.  So far, the dread has been justified.  I immediately discovered that some of the holes shown in the pictures in the build manual through which the wire bundles must pass were not present in my kit, owing, I suppose, to the slow pace of my build.  During the time

lapse from when I order the sub-kit to when I actually get around to working on it, the kit has evolved.  No mention of this is made in the build manual, so step one was to drill the missing 3/4-inch holes in the instrument shelf and three fuselage bulkheads.  The left arrow in the picture shows an array of cooling holes that also aren't there, but I'll put off drilling those until I figure out what goes there.

The step drill shown worked well for these holes.  BNC connectors and two fat wire bundles go through these, so the required snap bushings will be slit, placed over the wires, and snapped into the holes later.

The cooling fans were installed at this point.  After hooking them up to 12 volts, I discovered that they blow in opposite directions relative to the fan housings, and one runs at a higher RPM than the other.

The Mothership said it's OK.  Simply flip one over to get the correct direction and the slow one will probably come up to speed after it "loosens up."  It would be so easy to replace one now rather than later, but I'll trust Van's.

The wire bundles and the three coax cables go over the rudder tube.  A wire tray will be added later. The bolts holding the rudder tubes up must be loosened in order to allow the BNC connectors to pass above the tube.  They still have to be forced through the gap.









In the picture at right, both wire bundles have been run.  Various wires are identified and pulled out of the bundles as the bundles make their way aft through the various snap bushings, with some wires going all the way back to the tail cone area, others stopping at various locations.

The build manual stresses repeatedly to run each wire individually from the instrument shelf to its final destination.  I didn't do it this way.  Instead, I laid out each bundle on the shop floor and taped the end of each shorter wire to the main bundle, then ran the whole thing through the various Adel clamps and snap bushings.  The sticks have been installed in order to run the wires for the push-to-talk switches.  Issues with the sticks will be addressed in a separate post.

Much time was wasted removing snap bushings which the build manual had me install in various bulkheads and seat ribs.  With the bushings in place, various wires with their already-installed connecters won't come close to fitting through the bushings, requiring that the bushings be removed and the wires run through the bare holes.  The slit bushings can then be placed over the wires and finally snapped into the holes.  The problem is that the already-installed bushings are difficult to reach and remove in the tight spaces.  If I were building another airplane I wouldn't install any of the bushings in the fuselage until all wires are run.  The build manual warns of this, but way too late.

Most of the builders who have gone before me agree that delaying the attachment of the tail cone is the smart thing to do (also not suggested in the build manual).  This allows easy access to the rear

bulkhead and also makes it easy to turn the fuselage on its side. Having the fuselage on its side allows me to comfortably sit while routing the wires.

One of my students dropped by and offered to help with the fine adjustments.

Service Bulletin 12-11-09 Part 2: Landing Gear Beef-up

After the RV-12 fleet started to accumulate a significant number of hours, several suffered wrinkled side skin following hard landings.  Close inspection revealed cracks propagating from the bolt holes in the  center-section channel which allow attachment of the landing gear legs.  The Mothership

developed a beef-up kit for the side skins (previously covered in a blog post) and a kit to substantially strengthen the landing gear attachment.  The kit consists of thicker aluminum and steel plates (shown in the pic at left) which go between the U-shaped bracket (U-1202) and the center section.  The T-shaped aluminum piece (T-1204V) on top of the center-section web is a drill guide with two #30 holes, which the builder was to use to match-drill through the web and the steel and aluminum plates below the web (U-1202C-B and U-1202D-B).  These #30 holes were then to be enlarged to 1/4 inch.  Happily, since I purchased my finish kit in 2016, the U-1202 parts already had the 1/4-inch holes drilled (my experience with match drilling holes has been less than enjoyable).  I only needed to drill the holes in the web.  The problem was that the holes I drilled in the web had to be perfectly aligned with the already-drilled holes in the other parts.  This wasn't an issue with the original beef-up kit since all the holes were drilled together and were automatically aligned.  Past experience using thin aluminum sheet with #30 holes as a drill guide showed that it's quite easy to "hog out" the original holes, causing the holes which are supposed to match the original to be off center.  I had visions of screwing up the center-section channel, which is the main structural member in the fuselage.  These 1/4-inch holes needed to be dead-nuts perfect.

To reduce the chance of misalignment, I ordered additional drill guides from Van's (they're cheap) so I could use stacks of three.  This allowed me to use a #30 transfer punch to accurately center punch the hole in the web and reduce the tendency for the #30 drill to walk off center during the drilling of the #30 pilot hole.  As instructed in the build manual, I used the reflection of the drill bit in the shiny drill guide to keep the #30 bit perpendicular to the web.  I then repeated the process with the 1/4-inch bit.

I won't know how well the holes align until I bolt on the gear.