Page 30-02: Fuselage pin stopper assembly

The fuselage pins are the heavy-duty steel cylinders which secure the wing spars to the fuselage in a fashion similar to that of glider wings, allowing easy and quick removal of the wings.  The fuselage pin stopper is the mechanism which keeps these pins from backing out in flight, an important task in

my estimation.  The stopper is a spring-loaded aluminum cylinder which must fit within the small steel tube welded to the main pin.  The spring is inserted, followed by the stopper, a hole within which has been tapped to allow the machine screw assembly to be threaded in, holding the whole thing together.  Problem was, the stopper was not even close to being able to fit into the said tube, the OD of the stopper being significantly larger than the ID of the tube.

I first tried fixing this by using  a pistol bore cleaning rod with a strip of ScotchBrite inserted in the slot rather than a cleaning pad.  The rod was turned in the ID of the tube with a drill.  This didn't remove anywhere near enough metal to make it fit.  I next created a poor-man's reamer by cutting the head off a 4-inch-long 5/16 bolt, then cutting a 2-inch-long lengthwise slot in the bolt

(shown in the third pic).  Into the slot I threaded a length of fine-grit 2-inch-wide sandpaper from my belt sander, wrapping enough around the bolt to make a tight fit in the ID of the tube (shown in the second pic).  I chucked the bolt in the drill.  The sandpaper looks too big in the picture because it unrolls when you're not holding it.  After lots of trial fitting and reaming it fits perfectly.  I cleaned the ID with the bore-cleaning rod (to the left in the picture) and swabs, then applied some Boelube and assembled the whole thing.

All of the other builder blogs I could find which discussed this spoke about the earlier system which required that a magnet be inserted in the stopper and it then be filled with epoxy.  The magnet was somehow used to tell the Skyview that the pins were secure.  That system apparently proved

problematic and was replaced.  Not sure how this new arrangement lets the Skyview know that everything is secure.  I suppose I'll find out in the near future.

The finished assembly is shown at left.  When the wings are installed, the machine screws allow the stoppers to be retracted and then snapped into a hole in a plate in the fuselage.  I doubt the pins would ever back out in flight even without the stoppers, but it would ruin my whole day if they did.

Service Bulletin SB 16-08-24 : Loose engine mount bracket rivets

Each one of the two upper engine mount brackets has 22 LP4-3 rivets attaching it to both the panel base and the upper firewall.  On two high-time RV-12s the aft-most six rivets on each bracket have been observed to be "smoking."  Two solid surfaces which are mechanically held in contact with each other and which are subjected to vibration can experience fretting corrosion.  Fretting corrosion

occurs when the two contacting surfaces experience relative motion, often of microscopic magnitude.  In the case of aluminum, the small-scale rubbing between mating surfaces produces fine aluminum power which quickly oxidizes, causing a smokey appearance around the rivet head.

Van's fix is to replace the offending LP4-3s with much stronger Cherry rivets.  This, of course, required drilling out the 12 LP4s in the engine mounts.

Some time back, Van's switched from the Garmin SL-40 com radio with separate intercom to the Garmin GTR-200 com radio with built in intercom.  Naturally, I had just installed the radio tray towers (the grey objects shown in the pictures) for the old radio when the announcement came out about the replacement, so those rivets had to come out as well (6 LP-4s total), so I did all the rivet removed at once.  The manufactured heads on the rivets were on the bottom of the of the panel base, so I originally started the process by awkwardly lying on my back in the fuselage drilling upward.  The drilling process in rivet removal is quite delicate, since enlargement of the #30 hole is to be avoided.  A clear view of the rivet head and a steady hand are required, both difficult to achieve in that position.  It occurred to me, somewhat belatedly, that this process would be much easier with the fuselage on its side, allowing me to sit upright to do the drilling.  Once again, I'm reminded of what a great decision it was to put off installing the tail cone as long as possible.  Without the tail cone, I have great access to the area between the aft bulkhead and the seats.  There's still lots of stuff to do there.

As much as I'd like to install the landing gear, I'm resisting that urge as well.  With the gear on, even without the tail cone, it'll seem much more like a real airplane.  I would no doubt be unable to resist the urge to sit in the cockpit and make airplane noises.  The downside, of course, is a lack of options for positioning the fuselage on its side while installing the many systems still to go in the fuselage.

Page 18-06 again: Flaperon Klöster Föken

Or, alternatively, Why I'm Re-ordering the Flaperon Skin

On several Van's designs including the RV-7 and RV-12 (unfortunately), a folded trailing edge skin is used for the control surfaces.  In general airfoil design, in order to facilitate the Kutta condition, the trailing edge should be sharp (not practical in the real world), squared off as is done with fast glass aircraft, or rounded, provided the radius of the trailing edge is less than 5% of the wing chord. I've

always considered rounded trailing edges to be an aerodynamic abomination no matter what the radius.  It offends me.  Van's did it right on the RV-9 which features a riveted trailing edge.  Coincidentally, the -9 is considered by many to be the sweetest-flying RV and it was the target for the handling on the -12.  Regardless of this complaint, having flown an RV-12 four times I can happily say that the -12 is the sweetest-flying airplane I've personally flown.  However, that doesn't mean it couldn't be better.

As discussed in the previous post, the build manual says to flatten the skins on the aft portion of the trailing edges using the hands, presumably thumbs, so that the skin is perfectly flat and parallel to the ribs.  I attempted this just prior to my annual week in Oshkosh (my 28th trip!) with limited success. Once I got to the show, I cornered an engineer from the Mothership (young guy whose name I can't remember) and asked him what I was doing wrong.  He explained to me that the way they do it at Van's is by using two blocks of wood, one on the upper and one on the lower surface, and squeezing them together with a large pair of Channel Locks.  This seemed to make sense, so upon returning to my NC home I attempted it.  The problem, and it turned

out to be a massive one, was that I misinterpreted the procedure he described to me.  I assumed that the wood blocks should be placed on the upper and lower surfaces just forward of the trailing edges, approximately where one might apply thumb pressure. Wrong.  The blocks should be placed on the trailing edge with the aft portion of the wood behind the trailing edge, hanging out in the air.  I found this out on another blog post, which re-posted the procedure from somewhere on Van's site, complete with pictures.  It turns out that this is the same procedure used to fix a "heavy" wing during flight test.  It was my mistake, but I wish Van's would publish a link to this procedure in the build manual, rather than just saying "flatten it with your hands."

Turns out I made several creases in the skin.  It wouldn't have hurt performance, and I tried to tell myself that I could build on, fly it without paint for a year or so as most people do, then build another left flaperon.  I was so unhappy with it that I drilled out several hundred rivets and removed the offending skin.  After (expletive redacted) up the left flaperon, I did the right flaperon with my thumbs (hadn't discovered the correct use of the blocks yet), and it turned out OK.  I may touch it up with the blocks later.  The new skins are on order.  They were surprisingly cheap.  

Update

It turns out that the aft flaperon skin can, indeed, be replaced while leaving the forward skin and aft ribs in place.  Upon completion of this, I discovered that the aft skins on each flaperon weren't lying flat as prescribed in the build manual.  I therefore constructed the tool shown to squeeze the trailing

edges, thereby flattening the skins.  I first practiced on one of the aft skins I had previously damaged, then proceeded to squeeze the trailing edges on both flaperons.  Success at last.

The "springs" connecting the two wood blocks are from a large binder clip.  The wood blocks have rounded edges with a large radius of curvature in order to prevent creasing the skin.

Pages 18-05 and 18-06: Flaperons

With the main part of both wings closed (hope I didn't leave any tools in there), the flaperons are the only thing left before starting the finishing kit (inventoried!).  The worst thing encountered so far is match drilling pre-punched holes in the aluminum flaperon leading-edge skin into the much harder stainless steel tube which is used as a counter weight for the flaperon.

My experience match drilling anything has not been positive, and this was by far the worst.  The #30 drill tended to "walk" in contact with the stainless, elongating the holes in the aluminum.  After this happened a couple of times I started drilling a #40 pilot hole first, then drilling the #30.  Worked much better.  I've always dreaded having to drill anything into stainless steel.













The next problem involved squeezing solid rivets such that either the manufactured head or the shop head would be seated against a curved surface.  I didn't want to machine a flat surface into the piece

since that obviously would weaken it.  The squeezer dies also wouldn't clear the flange.  The picture shows my options.  It seemed intuitively clear that the manufactured head wouldn't work at all on the curved surface.










I ended up grinding a flat surface on the cylindrical surface of the flat squeezer die (hard to see in the third pic) and putting a radius on the intersection of the two flat surfaces on the die (shown in the pic).  I also spaced the die out from the squeezer jaw with rivets.  Squeezing the shop head onto the

curvature worked fine.  The result is also shown in the third pic.  The shop head easily conformed to the curved surface.







The aft flaperon skins presented a new PITA right off the bat.  There were notes on the skin packaging warning that extreme caution should be exercised when unpacking in order to prevent damage, the reason being that these parts seem to be the most fragile I've encountered so far.  I suppose the flaperons need to be light, and therefore thin, to avoid flutter.  To make matters worse, the protective blue plastic was difficult to remove, especially on the inner surfaces.  And, for the first time in all the plastic removal I've done, a layer of sticky crap adhered to the aluminum when the

plastic was pulled off.  Somewhat belatedly, I discovered that if I apply the pulling force at right angles to the aluminum rather than at something between 135 degrees and 180 degrees as I was doing, the aforementioned sticky crap was not deposited on the aluminum.  Unfortunately, this was impossible on the inner surfaces.  Mineral spirits seem to get the deposit off with considerable effort.  What a waste of time.





Page 18-06 warns the builder to be certain that the tapered aft portion of the skins doesn't bulge out from the flaperon ribs but rather lies in a straight line against the ribs (see pic below).  Considering that this is matched-hole construction and the parts are riveted together, I don't see how the skins have any choice but to lie flat against the ribs.  Maybe I'm missing something here.  A revision in the build manual specifies a Cherry (stronger) rivet for the holes nearest the trailing edge in place of the usual LP4-3 rivets.  I suppose this is to positively

eliminate any bulging.  Unfortunately, I had to order the newly-specified rivets and am dead in the water until they arrive.

After pondering the bulging skin issue a bit more,  I think the manual is referring to the skin between the ribs even though it says "lie flat against the ribs."

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.