Angle of attack probe -- thank you Joe Gores

Before closing up the skin on the left wing, it made sense to plan for and lay out everything needed to use the built-in feature of the Dynon Skyview which allows a display of angle of attack.  All that is needed is a pressure signal from a port on the leading edge positioned at a specific angle to horizontal.  All the hardware and positioning information is given in the thread shown below on Vansairforce.net.  This thread should be read in its entirety.

AOA link here

As suggested, I mail-ordered the parts from McMaster-Carr for the princely sum of about $15 for all the fittings, tubing, etc.  The hardware can't actually be installed prior to receiving the airworthiness certificate from the FAA, of course.  (Voice from the future: Van's came out with their own version of this with the hole in a slightly different place.  The slightly different placement is accommodated in the calibration.  Works the same.)

For the port itself, an LP3-6 rivet with the mandrel punched out works great.  A short piece of the same 1/8th inch ID tubing used for the static ports fits nicely over shop head, sealed and held in place by a glob of instrument-safe RTV. A 1/16th inch ID tube is coupled to the 1/8th ID tube and run to the wing root for later attachment to the Skyview. A mockup of these parts is shown in picture two.  The way it will be installed in the leading edge is shown in picture one.

The method that Joe Gores came up with and detailed in the link above can be used to locate the angular position of the port without actually having to measure any angles.  I'm sure that the calibration procedure can accommodate some angular position error in port location.  The early users of this method employed a common needle valve used for inflating basketballs (or deflating footballs if you're from New England) for the port.  By all reports, the hollow rivet works as well and is indistinguishable from the other few thousand rivets in the wing.

Some have suggested that the 1/16th ID tubing will fit into the existing grommets installed in the ribs for the wing-tip light wires (seen in the picture).  I couldn't make this work, even if I removed the string that we all ran according to plans to make is possible to run wires after completion.  There's a convenient route for the tubing against the spars, shown in the pic.  After closing the wing, everything can be reached with the inspection plate removed (the inspection hole can be seen at the lower right of pic one).

Both wings are now complete and are stored in the wing stand.  Work is proceeding on the flaperons.

(page 40-08) Fiberglass fairings for wingtip position/strobe lights

The fairings as they arrive with the lighting kit from Van's must first be trimmed to some nearly invisible lines scribed into the fiberglass.  The approximate nature of these lines was immediately obvious to me when I compared the left and right fairings, the most obvious difference being the aft

ends which match up with the hand-holds in the closeout.  I didn't notice this difference until I had already finished the trimming, but I suppose it won't matter considering that once installed it's impossible to see both fairings at once.  I puzzled over the proper fore-and-aft positioning, finally settling on sliding it aft until the aft end of the fairing butts up against the existing rivet in that area.  This required re-trimming the curve where it matched the hand hold.

Speaking of existing rivets, three LP4-3 rivets per wing must be drilled out when installing the fairings.  It would have been nice if the build manual had pointed out that if the lighting kit was going to be installed, these rivets should be omitted during construction of the wing closeouts.  Not a big deal, I suppose, since the offending shop heads and other debris that comes with drilling out rivets can be removed through the large holes in the closeouts specified for the wires.  While making these large holes, I opined in an earlier post that it seemed that a 3/4-inch hole with suitable grommet should have sufficed, although it did occur to me that having a hole big enough to reach into the wingtip may prove beneficial.  Little did I realize just how beneficial.  After completely riveting the right closeout, I discovered to my horror that a pair of fluting pliers had been left in the wing.  With

visions of drilling out 20 or 30 rivets dancing in my head, I instead enlisted the aid of the Spousal Unit (my favorite IronMan triathlete and wife, Karen) who was able to reach through both the wiring hole and a rather small lightening hole in a rib to retrieve the pliers.

The trial fit looked pretty good, with the flat, vertical face of the fairing upon which the light mounts seeming to be oriented properly relative to the wing, so I drilled the holes corresponding to horizontal clecos in the picture.  The fairing has dimples showing the remaining hole locations, except for three holes which must be match drilled into existing holes in the wing closeout (the three whose rivets had to be drilled out previously -- the two nearest the hand hold and the forward-most one in the closeout).

A band of flox-epoxy mixture is added to the upper flange of the fairing (the wing is upside-down in the picture) and is clecoed in place before the epoxy cures.  A release agent such as car wax is liberally smeared on the surface where the epoxy-flox will touch, allowing removal of the fairing.

This theoretically ensures a tight fit of the upper flange of the fairing against the wing tip.  For my first attempt at this I used too little flox-epoxy to fill the voids and had to repeat the process.  A glob of children's modeling clay is used to keep the flox-epoxy out of the area where one of the three nuts securing the mount for the light goes, visible in the picture at left.  I could have used a smaller glob.

Holes for the light mounting bracket are drilled at three dimpled locations.  At first, I doubted the dimple locations because it caused the centerline of the bracket to not be aligned with the centerline of the teardrop-shaped flat surface.  After holding the light up to the fairing, I decided that they are correctly located.

The holes in the fairing along the flange where the flox-epoxy is added get machine counter sunk for flush-mount rivets.  The flox-epoxy gives enough meat to do this.  If the fairing shown doesn't seem to match the picture from the build manual, it's because the manual shows the left wing and I built the right wing first.

The wiring requires crimping Molex connectors on all the appropriate wires and inserting them into the connector housings.  At this point in the build, I'm pretty confident with the crimp tool (of course you absolutely must use a crimper made for Molex).  I learned from watching how-to videos on EweTube (they're still a bunch of sheep) that for the #18 wire we're using, a superior crimp can be had if the tabs on the Molex connector which grab  the wire insulation are shortened about 1/32nd inch.  The tabs which get bent over and plunged into the conductor are OK as is.

 The final step involved sealing the whole thing with Flame Master (aka Pro-Seal) and riveting it to the wing tip.  Update: When I ordered the goop formerly known as Pro-Seal from the Mothership, the package which showed up says 3M Aerospace Adhesive AC 240-B 1/2.  Same stuff, I suppose.

I tried to fill the gaps between the fairing and the
aluminum by smearing the Pro-Seal, but the appearance is not satisfactory.  I'll use some sort of filler before paint.

(page 17-06) Wingtip close out

I had dreaded starting on the wingtip close out, because with all those tabs to be bent to all those different angles, I figured there would be lots of trial-and-error fitting.  A wooden tool was required to be built, which greatly facilitated the physical bending of the tabs, but the amount of the bend was

left up to the eyeball.  As can be seen in the picture, the amount each tab needs to be bent is specified to one degree.  At first I took this to be more Oregonian humor, but decided it's the perfect angle that the CAD model spit out, and the builder is to come as close as he or she can to this ideal.  Fortunately, close is good enough.  The tabs can easily be bent with the fingers to fine tune everything during installation.






I sketched the angles in five degree increments on a piece of cardboard cut from a white paper plate  (shown on the second pic) and eye-balled it as best as I could.  Worked great.  The only two tabs to

require a bit of fiddling were the forward-most two (left in the first pic), with one being a bit greater than 90 degrees.  I straightened and re-bent those two a couple of times, finally lining the holes up with the ice pick enough to insert clecos.









Overall, this was nowhere near as bad as I expected.  The cleo insertion was fairly typical, requiring the usual tools (ice pick, 1/8th inch punch

used as a reamer and, on a couple of holes, the hand held #30 drill bit mounted in an old chuck).  Now, the only thing left on the right wing is the strobe light fairings and electrical connectors.  The fiberglass fairing has to be bonded and riveted to the aluminum.  Doesn't look like fun. Then I get to do it all again on the left wing.

Service Bulletin 14-11-03: Wing Skin Doubler

One of the Mothership's higher time RV-12s used as a demonstrator was found to have a few "smoking" rivets on the lower inboard wing skin.  This condition arises when a rivet loosens and allows fretting corrosion (very small scale relative motion between mating surfaces due to vibration) and subsequent oxidation of the resulting aluminum dust which is produced.  The loosening was no

doubt a result of the high stress in the skin at this location.  Putting on my engineer's cap for a moment, I'd say this location has the highest skin stress of the entire airplane.

The fix involved installing a rather robust (0.04 inch thickness rather than 0.03 inches for the wing skin) doubler plate with four different rivet types, eight of which are 5/16th inch rather than the usual 1/8th inch diameter rivets.  I was thinking "Wow, it's great that I received the kit for this service bulletin before I installed the wing skins.  Now I won't have to drill out 20 rivets per side like many builders are having to do because their skins are already on!"  Then I proceeded to install all the rivets in the right wing skin, then had to drill out the aforementioned 20 rivets.  This required the invention of several new, stronger swear words since I have essentially worn out all of the customary ones during previous mistakes in this project.  I won't (I hope) make the same mistake with the left wing.  I'm astonished at the strength and complexity of this fix (four different rivet types!), considering that the fix isn't mandatory.

The plans call for final drilling the holes for the 5/16th rivets with a #22 bit, which I did using a bit from my new #1-through-#60 bit set, obtained from Amazon rather than Spruce or one of the other "name brand" aircraft suppliers.  The rivets would not fit into the holes.  Upon measuring the bit diameter I discovered that the #22 bit was considerably smaller than spec, and that the #21 bit in the set had a smaller diameter than a proper #22.  You get what you pay for!  I had checked the bits with a go/no-go gauge, but that didn't catch it.

At last, a valid reason for making no progress on the RV-12

All of my other lame excuses pale compared with this one.  On September 27th, while riding my bicycle in the rain (first act of stupidity for that day), I fell while crossing a railroad track and broke my femur into three pieces.  The railroad track runs at about a 45 degree angle to the road, simply requiring that I slow down and steer the bike so that I'm crossing the rails at a 90 degree angle.  Cycling 101, right?

Instead, as is my usual habit (second act of stupidity), I attempted to bunny hop over the track and fell as if smacked down by the hand of god (I said smacked, not shmacked -- even if I do spend part of the year in Boulder). This resulted in a new titanium rod in my leg, extending from my knee to my hip.  The titanium structure below the knee is a result of a car wreck in 2005, and extends from ankle to knee.  In all future bike crashes, I'll try to fall on that side since it would be difficult to break it again with all the titanium in there.  I suggested to the Spousal Unit (my beautiful Ironman wife, Karen) that when she has me cremated she should retrieve all the titanium and put it on the mantle over the fireplace.  She didn't see the humor in that.

The good news is that after going from a walker to two crutches to one crutch, I'm now able to stand long enough to actually make progress on the airplane.  I still can't stand for long periods, but it's a start.

I ordered the finishing kit (a deceptive name since when it's finished I'm nowhere near finished with the airplane). The kit arrives in one month, which means the wings have to be finished and on the wing stand before the finishing kit arrives.  The right wing requires only that I finish the wing tip, then I have to repeat the entire skinning process for the left wing (except for the landing light, thankfully -- anyone who installs a landing light in both wings is a glutton for punishment).  Looking ahead, it seems that money will be the limiting factor in the completion of the project.  When I look at what I've built, it seems that I'm way more than half way done.  From a cost standpoint, however, I'm not.  The engine kit and avionics kit are horrendously expensive.

(Page 40-xx and 17-yy) Wing miscellaneous

After enduring the pain of installing the landing light I can say with some certainty that no one ever did this installation after the wing was built.  The build manual for the lighting kit is written for a person adding the kit to a completed airplane.  No way. 

Even without the wingtip installed, allowing access to the back of the light, starting the bolts into the sides of the light was difficult.  It was with trepidation that I applied 12 volts to the power wire for the light, my big fear being, of course, that the light would not illuminate.  This would require removal of the light, which I sincerely hope to never do.  It worked!

Cosmetically, the landing light is, by far, the worst thing I've done.  The primer on the upper surface of the wing is a result of scratches I inflicted on the aluminum during the numerous trial fittings.  The lens fits the opening poorly, though it's not immediately obvious to the casual observer.  Close inspection reveals a slight gap between the Plexiglas and the aluminum at some points.  The problem arises from drilling using the paper template which appears in the build manual.  If I ever build another -12, I'll devise another way.  I blindly followed the manual, which is usually a good procedure.  A little more thought before drilling would have helped.

Wing Stand

Even though I haven't finished the right wing (much less the left), I figured it would be a nice break to so some carpentry and build the wing stand.  I built the standard EAA wing stand, complete with

castors. 

Even though I evicted the car which used to share the garage with the airplane, I'm back to having a space problem, with a wing on each work table and the fuselage between them.  There's nowhere to put the stand once a wing is on it.

Update:  Turns out that the length of the carpet strips was too great, allowing the wings skins to come very close to the plywood gussets.  A lot of wood had to be removed from the gussets to make everything clear.  I also should have centered the carpet strips on the center of the horizontal 2X4s and probably should have made the strips wider.  Additionally, I should have bought higher quality castors with larger diameter wheels.  When pushing the stand around in the shop, the wheels frequently (usually) won't self-align, causing me to have to align them manually, an unnecessary PITA.  We live and learn.

(Pages 17-02 through 17-04) Gimme some (wing) skin, part deux

I cleco, therefore I am -- a new philosophy called Existential RVism

After the exercise in frustration that involved cutting the hole for and installing the landing light, skinning the right wing (I did that one first rather than the left as shown in the manual so I could see just how bad the landing light looks) was a walk in the park.  As was the case when I skinned the stabilator and rudder, I was surprised when all the rib holes lined up with the holes in the skin,

considering how much straightening and fluting had to be done to the ribs.  I was always able to pull the holes into alignment with an ice pick and awl, allowing clecos to be inserted.  The key seemed to be starting at the leading edge and going hole by hole with the alignment tools.  As I've always done, I primed the mating surfaces before joining. 

The pneumatic rivet squeezer has always been my favorite tool, and I made ample use of it (my first one wore out after the first few thousand rivets, found a great but cheap one on the aviation aisle at Harbor Freight).  I also bought from Aircraft Spruce their new design for cleco pliers which has the handles rotated up ninety degrees from the jaws.  This works much better on the horizontal wing surfaces, keeping the wrist in a natural position.

The bottom and top skins went on surprisingly easily (with the exception of the landing light), it's just quite tedious when you consider the process: align the holes, insert the clecos, remove the clecos, insert the rivets (about 70% of which require running a 1/8th-inch punch through the holes for final alignment/reaming), pull the rivets, repeat a few thousand times.

If you've ever been in my office, you'll probably notice a resemblance between my office and my shop in the first picture.  I use the same organization scheme in both.