W-1202-L Skin Inspection Hole & AOA Port

Due to an extremely late afternoon start in the shop decided it best not to rivet the W-1202-L skin and chose to work on the inspection port and the air port for the angle of attack plumbing. The inspection hole required a little attention so figured may as well finish it up now instead of waiting until later as in the plans.

Started with drawing the positioning line for the AOA port. Joe the Michigan builder who did the math for the AOA port location gives measurements based on the leading edge rivets. Since his airplane used LP4-3 rivets, I temporally placed LP4-3 rivets into the rivet holes and then made a line tangent to the rivet heads per his instructions. The AOA port may be drilled anywhere on this line. I’m choosing to locate the hole for the port about an inch or so from the rib outboard of the stall warning micro-switch … there will be no interference with the operation of the stall warning micro-switch and it is also far enough away from the access port that making inspections or adjustments to the stall warning indicator should not pose a problem.

A line was drawn tangent to the aft edge of the two leading edge rivets. Anywhere on this line is where the AOA port can be located. For those interested in the math behind this location, it's approximately 30 degrees off the chord and 60 degrees off vertical. As a stall is approached, the port becomes more aligned with the air stream and thus the pressure in the tubing will increase. This pressure increase is analyzed by the Dynon Skyview and displayed on the screen as a bar graph.

                                                     Joe’s 30 degree AOA hole location verified by a protractor.

                                                                   Drawing the pilot hole line for the AOA port.

At this point I’m torn as to which method I want to use to connect the AOA plumbing to the W-1202-L skin. Builders have used rivets with the mandrels removed as ports and others have used a sport ball inflating needle with the threads protruding the wing skin and Tygon tubing slipped over the needle (the original method pioneered by Joe a builder in Michigan). Both methods are reported to work great and both have advantages and disadvantages. Of course, a rivet looks great and is virtually unnoticeable … however the small hole could easily become clogged with dirt, paint or wax and there is really no good way to “protect” the port when the plane is on the ground, plus it is harder to connect the Tygon onto the rivet because an "adapter" tube will be needed. On the other hand, the inflation needle requires a ¼” hole, needs to be set in epoxy to keep it in place and the threads do  stick out of the skin …. however, a valve cap can be screwed onto the threads to protect the port from dirt, wax, paint, ect. when the airplane is not in use. For purely cosmetic reasons, I’m leaning towards just using a flush rivet with the mandrel removed and if there is ever any issue with the port clogging, I can always drill out the 1/8” rivet hole to ¼” and install the inflation needle. An example of the inflation needle method used by Joe is in the concept photo below. The right needle’s threads protrude through the wing skin and the tubing would be run 15 foot or so to the left needle which is screwed into the AHARS for the Dynon Skyview in the fuselage.

                                                        Joe's example of the inflation needle method for AOA.

While pondering which AOA method to use, went to work on the inspection access hole in the W-1202-L skin. The ten inspection plate screw holes require being dimpled for #6 screws and the rivet holes for mounting the ten nutplates also require dimpling along with the nutplates themselves. I suggest builders dimple the #6 holes first, then use a small diameter female dimple die to dimple the nutplate rivet holes for flush rivets. If the nutplate rivet holes in the skin are dimpled first, the large head of the #6 dies will likely be up against the rivet hole’s dimple and possibly distort it.  The rivet holes in the K-1100-06 nut plates require dimpling as well.

                                            Dimpling the ten screw holes in the inspection hole for #6 screws.

                                                                   Dimpling a nutplate for flush rivets.

             Using the pneumatic squeezer to rivet nutplates onto the W-1202-L wing skin's inspection hole.

                                                 Finished inspection access hole in W-1202-L bottom wing skin.

                                                   AOA hole location is on the bottom left and circled in red.

Bottom Center Wing Skin Positioned For Riveting

Today the W-1202-L bottom center skin was positioned onto the left wing skeleton and prepared for riveting by removing the blue protective film along the rivet lines with a solder iron.

                         Jan helping position the W-1202-L bottom center skin in place on the left wing skeleton.

            Using a soldering iron to melt lines adjacent to the rivet holes so the blue protective can be pealed away.

Once the blue film was pealed away from the rivet lines, the skin was Clecoed in place. Before riveting the skin in place, there are yet a couple of items that need to be addressed. This skin has an inspection hole for accessing the stall warning indicator assembly and the yet to be drilled port for the angle of attack indicator plumbing (which needs to be installed as well). The access port receives a few nutplates which secure the cover plate and the holes  for the cover plate screws require dimpling because the screws are flat head with tapered sides. Figuring on doing this now so if something goes awry, it won’t be necessary to remove a slew of rivets to replace the skin.

Clecoing the W-1202-L skin in place readying it for riveting. It is actually starting to look like an airplane wing now.

The Little Dimples That Weren’t

Friday while Clecoing the W-1203-L skin in place for riveting, noticed the holes on the outer most nose rib appeared to be slightly off … I could see a little of the edge of each of the rib’s rivet holes when looking down through the W-1203 wing skin. All the other holes on the skin aligned perfectly with the ribs underneath except for the holes on just this one rib.  Even though the alignment was not perfect, a Cleco would still go through the holes. Unfortunately, this was the last rib Clecoed and it was getting late, so figured I would sort it out Saturday.

Saturday afternoon I removed all the Cleco’s securing that rib in the hopes I could get it repositioned … no luck. A tinge of doubt crossed my mind … do I move on or remove all the Clecos on the entire skin to reposition it slightly? Wait! … This is a Van’s kit, remember the adage “if it does not fit right you are probably doing something wrong” . Yep, I was.

Decided to just bite the bullet and remove ALL the Clecoes to reposition the skin and inspect the rib. In doing so, discovered all the rivet holes on that side of the nose rib weren’t dimpled. DUH! Amazingly, being the outside rib, I must have walked past it at least a hundred times in the past month and never noticed. A check of ALL the remaining ribs revealed no anomalies. Being totally disgusted with myself, Clecoed the now perfectly fitting skin back onto the left wing skeleton and decided to call it a day. To protect the guilty, no photos were taken.

Today was a cold one … morning temps in the teens which warranted warming up the DOG Aviation production facility with the dual burner heater my friend Mike loaned me. It did a great job of quickly taking the cold chill out of the shop.

                          Mike’s dual burner propane heater pointed towards the W-1203-L skin about to be riveted.

Much the same as the W-1201-L skin, the W-1203-L skin has areas that are not to be riveted at this time. Both sides of this skin are overlapped by other skins, so both sides are not riveted, nor are the leading edge rivets and the holes for the flaperon bracket assembly. Riveting began at the forward end of the nose ribs and continued aft to the rear spar. Everything aligned perfectly (now that all the ribs were properly dimpled) and the riveting went fairly quickly.

                               Setting the first flush rivet into the W-1203-L skin with the pneumatic rivet puller.

                                          Nose ribs all riveted and now setting the first rivet into the main spar.

On the home stretch … just a few more rivets need to be set into the rear spar and the W-1203-L skin is done.

                                                          The completed W-1203-L skin.

By the time the W-1203-L skin was riveted in place the temperature in the shop was around 50 degrees so decided it was warm enough to spray a little primer onto the W-1203-L skin where the overlap joints will be. Prepared the edges of the skin with Scotch-brite and Acetone, masked the area and spayed a light coat of the PTI zinc chromate primer onto the skin where it will be overlapped.

W-1201-L Skin Riveted Onto Left Wing Skeleton

Unlike the snow flurries falling all day outside which resulted in no significant accumulation, inside the DOG Aviation shop there was a significant accumulation of completed RV-12 left wing rivets.

The W-1201-L wing skin riveting began by working from the left wing's leading edge back to the rear spar and using flush rivets in the place of the standard LP4-3 rivets. Two locations do not get riveted at this time … the row of holes on the outboard edge of the W-1201-L skin because the center skin will overlap this row and the inboard leading edge rivet holes in the region where the extra ribs are for the wing walk area because a wing walk doubler skin will overlap at this location.

W-1202-L skin Clecoed onto the left wing skeleton and ready for riveting with the trusty pneumatic rivet puller.

                             Setting the first leading edge rivet in the W-1201-L skin with the pneumatic rivet puller.

                              First row of completed leading edge rivets on the W-1201-L skin ... lots more to go.

Because it was a cold day outside and I was planning on spending an extended period of time in the shop, though it would be prudent to fire up one of the heaters my friends loaned me. The temperatures were in the upper 20’s so did not use the two burner unit and settled on the smaller single burner unit. Placing a box fan (with most of the air intake blocked with cardboard) behind the heater helped prevent the heat from just going straight up and allowed it to circulate better in the shop.

Dave, a fellow RV-12 builder at Schmetterling Aviation, calls his propane heater with a built in fan his “cone of comfort”.  I won’t go so far as to say my heating system creates a cone of comfort …  it creates more or less a “region of bearability”.

Single burner propane heater with a box fan running on low behind it creates a “region of bearability” in the shop.

Riveting the W-1201-L skin progressed smoothly and there were no hitches. All the holes aligned perfectly … a testament to the precision Van’s accomplishes in producing the CNC components for the RV-12.

                                            Riveting of W-1201-L skin to forward nose ribs almost completed.

                                                             Setting the last row of rivets into the aft spar.

                                 Finished W-1201-L skin – the flush rivets look awesome if  I must say so myself!

                                      One skin down and two more to go before all the ribs are covered by a skin.

Once the W-1201-L skin was riveted in place, the W-1203-L bottom outboard skin is next in line for riveting onto the left wing skeleton. This is the skin that was cut to accommodate the landing light. After the W-1203-L skin was set in place, a soldering iron was used to remove the blue protective film along the rivet lines. Once the blue film was removed from the rivet lines, the skin was then Clecoed into position for riveting.

                                         Clecoing the W-1203-L outboard bottom skin into position for riveting.

                                  W-1203-L outboard bottom skin Clecoed into position and ready for riveting.

Left Wing Lower Inboard Skin Prepped For Riveting

The covering of the RV-12’s left wing skeleton begins by turning the spar/skeleton assembly upside down and positioning the W-1201-L lower inboard skin onto the wing skeleton. After the skin was gingerly set into position, the blue protective film along the rivet lines needed to be removed with a soldering iron prior to riveting.

                                       Jan helping to set the W-1201-L lower inboard wing skin into position.

                                              Using a soldering to melt peal lines into the blue protective film.
                                              This makes removing the blue film from the rivet lines a snap.

After the rivet lines were cleared of blue film, the skin is secured onto the wing skeleton with lots and lots of Clecos. My hands were starting to get cold so did not totally finish securing the skin onto the skeleton so there will be a little more Cleco work before riveting begins.

                                          Using Clecos to Secure the W-1201-L lower inboard skin onto the left
                                          wing skeleton. The Clecos will hold the skin in place during riveting.

Preparing Landing Light Ribs & Lens Backing Strips

The afternoon was spent preparing the landing light mounting ribs for both wings along with the lens backing strips. The landing light ribs require a doubler plate to give them some rigidity in the area where the light mounts. AN426AD3-4 flush rivets are used secure the doubler plates onto the landing light ribs. The doubler plates were machine countersunk prior to priming, so they were ready to rivet onto the landing light ribs.

                              Using the pneumatic squeezer to secure one of the doubler plates onto a landing light rib.

                         Front and back views of the landing light ribs after the doubler plates were riveted in place.

The plans would have the builder drill mounting holes into the Plexiglass lens along with trimming the lens at this point. However, from everything I’ve read, it should not be attempted if the Plexiglass is below 70 degrees. Guess I will need to wait until spring thaw to finish that aspect of the landing light install.

While the pneumatic squeezer was in use, decided to finish up the preparations for the lens backing strips used to secure each landing light’s lens onto the W1203L&R wing skins. The backing strips receive K1000-06 nut plates which require dimpling because the rivets used for mounting the nutplates are flush rivets. The reason for this is the backing strip compresses the Plexiglass lens onto the wing skin to keep it secure, therefore the backing strips need to be smooth so they won’t crack the lens. The backing strip rivet holes were dimpled prior to priming as were the nutplates … so once again it was easy to just rivet the previously prepared components together.

                                             Using a pneumatic squeezer to rivet a K1000-06 nutplate onto one
                                             of the lens backing strips with AN426AD3-3.5 rivets.

                                Completed lens backing strips for both landing lights … ready for final assembly.

The rivet holes in the W1203L skin for mounting landing light ribs have not been drilled yet. I wanted to see if it was possible to insure a really perfect fit for the landing light ribs between the top and bottom of the W1203L wing skin … so I experimented a little. I temporally mounted the landing light onto the landing light ribs and tried to position the assembly perfectly behind the leading edge. That idea turned out to be pure folly because it was almost impossible to hold the light assembly in position just to look at it, yet alone drill. Even if I had another pair of hands, I don’t think my small 90degree drill would have been usable in the cramped quarters. Guess I will have to use the template with blind faith and hope for the best.