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.