Replacement Stall Warning Micro-Switch

In spite of surviving the end of the Mayan calendar, Christmas hustle & bustle, and the first winter storm of the season requiring the use of DOG Aviation’s emergency snow removal equipment, RV-12 construction at DOG Aviation is about to resume. The project has been in somewhat of a holding pattern waiting for a micro-switch, some wire and tools. Now the micro-switch is here but still waiting on the shielded wire for the strobe light wiring which was ordered a week ago and will be needed real soon.

About that the replacement micro-switch for the stall warning assembly ... behind the scenes, DOG Aviation’s research department is constantly looking into modifications that improve on the already excellent RV-12 design. One such modification pioneered by Joe (the RV-12 builder in Michigan who came up with the AOA modification) is to replace the stall warning micro-switch with one having a slightly longer arm … this makes fine tuning the stall speed warning alarm much easier. I ordered a new switch from Mouser which requires much less force to operate, it is Cherry part number E22-50KL. The replacement Cherry switch is the exact same switch electrically as the original, it differs physically in that the roller arm is moved forward to give a better mechanical advantage.

Is this modification really necessary? Truthfully, … nope. That said, to me it makes good sense because once the wing is assembled, adjustment access through the small inspection port is well, at best, challenging so at $4 and change for a micro-switch, why not go for it if it makes fine tuning the stall warning easier?

I ran two mounting screws through the two micro-switches in the photo bellow to keep the switches in alignment so it is easier to see the subtle difference between the original Cherry switch shipped in the parts from Van’s and the replacement Cherry switch purchased from Mouser.

            The original micro-switch from Van’s is on the bottom and the replacement micro-switch purchased from
            Mouser is on the top. One can easily see the slightly longer arm on the replacement micro-switch.

Merry Christmas From DOG Aviation!

Twas the night before Christmas, when all through the shop not a rivet was stirring, not even a pop; Well you get the idea … Merry Christmas from DOG Aviation!!

Earlier in the day, in an effort to move forward with the project no mater how small the task, a small amount of time was spent machine countersinking the VA-195A mounting plate for the stall warning indicator’s micro-switch. The mounting plate has two holes that accept #4 screws used to mount the micro-switch for the stall warning indicator system. These two holes are drilled out to #30, then machine countersunk using the 100 degree #30 countersink bit until the #4 screws set flush into the VA-195A mounting plate.

                               Machine countersinking the two holes on the VA-195A mounting plate which
                               will accept the #4 mounting screws for securing the stall warning micro-switch.

The VA-195A has another hole that receives a #8 screw which also requires machine countersinking … this hole is drilled out using a #19 drill and machine countersunk using a #20 countersunk bit. This #8 screw will be both a mount and pivot point for a vane that has a downward bend where it protrudes through a small slot in the wing’s leading edge and into the airflow.

The theory behind this assembly is simple … under normal flight conditions, because the vane is bent downward, the wind will push down on the vane preventing the vane from rising and tripping the micro-switch. However, when the angle of the wing becomes higher (as when approaching a stall) the airflow will get under the vane, lifting it, thus tripping the micro-swich causing alarms to sound in the cockpit.

                              Finished VA-195A mounting plate, machine countersunk and ready for assembly.

Left Wing Wiring and AOA Plumbing

One option that was purchased along with the wing kit was a lighting kit which consists of navigation lights, strobe lights and position lights all in one unit for each wing, along with a landing light for the right wing, all manufactured by Aeroleds.

The parts do not look like they will be a piece of cake to install … but the instructions appear to be concise enough to allow for a hopefully smooth install. Van’s includes 18 gauge wires for wiring the navigation light power, strobe light power and strobe sync lines to the Aeroleds lights. One discrepancy I noticed immediately on a schematic in one of the Aeroleds boxes is the use of shielded wire. I know I’ve read about builders mentioning they can hear a little noise in their headsets when the strobes are on. Installing the strobe wiring using shielded wires as opposed to running unshielded wire may really help keep strobe noise out of the electrical system.  A call to Aeroleds confirmed my thoughts and they have 3 conductor shielded cable available so will probably place an order for that today.

Before any wiring begins in earnest inside the left wing, I want to have all the components together to see if there is plenty of room in the grommets that will be placed in the ribs for wire runs …. May have to go to the next size up because of the shielded wires and plumbing I plan on installing.

Pluming in a RV-12 wing you may be asking? Yes, for the AOA indicator of course!! (Similar to a reserve lift indicator). One of the features built into the Dynon SkyView which Van’s elected not to utilize because of the RV-12’s removable wings, is an AOA (angle of attack) display.  A builder in Michigan (Joe) did the research and pioneered a working method where a small piece of tubing is connected to a port strategically placed at a 30 degree point under the leading edge of the wing. When the RV-12 approaches a stall, the tube’s air pressure changes and the SkyView analyzes that pressure change and displays a bar scale with increments in green, yellow, and red (falling out of the sky).  Quite a few builders on the forums have modified their RV12’s to take advantage of this very useful display function (which adds another element of safety) and all have been very very pleased with the results.  Since the RV-12 is being built as E-AB and not E-LSA, I will install the AOA plumbing now.

                              Just a hand full of small inexpensive parts are needed to install the AOA hardware.

The parts consist of: … Center in the photo - 1/16” ID Tygon tubing ( I chose tubing rated at Shore 64 because it is firmer than totally soft but still considered soft), below the tubing is a threaded 1/8” NTP male adapter which will screw into the ADHARS for the SkyView and allows the small Tygon tubing to be attached.  Upper right - a female Luer Lock, Lower left - a male Luer Lock. Luer Lock connectors are a ¼ turn release connector and will be placed at the root of the wing for easy disconnect during wing removal.  On the left side of the photo there are Luer caps: Top – female caps, Bottom – male caps. The caps are for protecting the tubing from contamination when the wings are removed and are really not necessary … I noticed them while placing the parts order and they seem like a good idea so picked them up as well. The 1/8” NTP adapter was the only item available as a single unit all the Luer connectors were in bags of 10 but they are very cheep. All total think the parts were around $20 from McMaster-Carr. (Not including the Locktite 243 which is for installing the stall warning micro switch).

At a strategic location under the leading edge of the wig, in the bay with the inspection plate, the tubing is connected to a drilled hole for a port which can be a rivet similar to the static port rivets (mandrel driven out) or a sports ball inflating needle as the original author of the modification used. Builders have had great success with either method. One good thing about using a ball filling needle is where the threads protrude the wing skin, a cap can be screwed onto the threads (where an air hose would normally go) to protect the tubing from insects and dirt. while the plane is on the ground.

Mental Pause

Those following the Blog will notice there have been a few days of non activity since the wing skeleton was completed. This is due in part to waiting for materials needed to move forward, coupled with a bit of a mental pause on my part.

After finishing the left wing skeleton, the next steps in the plans regarding instillation of components for the stall warning indicator were quickly perused to see what would be involved. My eye caught two items which placed the brakes on the build… the first was Locktite 243 thread sealant which the DOG Aviation procurement department desperately tried locating locally, to no avail I might add, so an online order was placed.

The second item was a reference to machine countersinking two screw holes in a mounting plate for #4 screws. A moment of total mental pause!!!  Countersink for #4 screws?? … The procurement department never ordered a countersink bit for #4 screws!! Build time was now diverted to research time to find a vendor for #4 countersink bits plus another side issue I’ll mention later. (Cleaveland Aircraft Parts does carry them).

The moment of clarity … Yes, I would have needed to wait for the Locktite 243 anyway but after SLOWLY rereading the instructions, the first step is to final drill the mounting plate screw holes to #30 …. DUH!! Don’t need a special countersink bit for #4 screws, I can use the countersink bit with the #30 tip I already have. Issue solved.

RV-12 Left Wing Skeleton Completed!

Taking advantage of an unseasonably warm day, decided to remove the right wing spar from the crate and use the airbrush to prime the factory mounted rib clips as was done on the left spar. That was followed by changing the oil in the snow blower so it will be ready for action if the snow slated for the end of this week becomes substantial. Once all side the chores were completed, work resumed on completing the left wing skeleton beginning with riveting the remaining two nose ribs.

                                                 Using the close quarter pop riveter to attach a W-1208-R rib at the
                                                 third rib clip in from the root of the wing using LP4-3 pop rivets.

As mentioned previously, the second and third ribs from the innermost rib require riveting using LP4-3 pop rivets where the web of the ribs attach to the rib clips … this is because the adjacent rib clips interfere with the body of the pneumatic squeezer preventing proper access.

                          Finished third rib in from the root of the wing ... AN470AD4-4 rivets attach the aft
                          flange onto the left spar and LP4-3 pop rivets attach the rib’s web to the rib clips.

                                        Using the rivet gun and bucking bar to rivet the aft flange of the lone
                                        W-1208-L nose rib onto the left spar using AN470AD4-4 rivets.

Because of the extra support needed for the wing walk area, the rib spacing is closer near the root of the wing. Unfortunately, this closeness prevented the pneumatic squeezer from having good access and almost prevents the pop riveter from having access. My standard pop riveting tool did not come close to fitting between the ribs. Fortunately, the close quarter pop riveter worked, but just barely and not without flexing the neighboring rib so the riveter’s handles could be opened enough to allow the riveter to get a second grip on the rivets … the rivets never pop during the first squeeze and require the riveter getting a second grip before they pop. It was really a chore getting Clecos in and out so needless to say, it was a fight to set the pop rivets in this area of the wing.

                                                       All ribs now riveted onto the RV-12’s left wing spar.

Better view of all the ribs riveted onto the left spar ... note the closer spacing of the nose ribs for the wing walk area.

The left wing’s stub spar assembly is the last component to complete the left wing’s skeleton. The stub spar assembly is riveted onto the nose of the inner most six ribs.

                      Attaching the stub spar assembly onto the W-1208 nose ribs with Clecos in preparation for riveting.

Access for the pneumatic squeezer was good enough to allow riveting the stub spar assembly onto the W-1208 nose ribs using solid rivets. AN470AD4-4.5 rivets were used to rivet the stub spar assembly onto the nose ribs …. in those areas where there was a doubler plate, AN470AD4-6 rivets were used. This was another one of those cases where the 4-6 rivets were slightly to long and the 4-5 rivet was much to short.

                                Using the pneumatic squeezer to set the last rivet attaching the stub spar assembly
                                onto the W-1208 nose ribs and thus completing the left wing skeleton.

                      With the stub spar assembly now fully riveted, the RV-12’s left wing skeleton is completed.

Final tally … out of the 151 rivets holding the nose ribs onto the left spar and stub spar assembly, only 12 ended up being LP4-3 pop rivets due to clearance issues with the pneumatic squeezer.

Left Wing Skeleton Almost Completed

Progress … was able to get a few good hours in and now have all the nose ribs riveted except for two. While pounding the nose rib aft flange rivets into submission with the rivet gun and watching the nice anodizing on the rivets get pummeled, a thought came to mind. Interestingly, decided to try using some Boelube on the rivet set and it works rather well!

Top three rivets were pounded with the rivet gun as usual and the bottom rivet was pounded with Boelube on the rivet set.


Above is a photo showing the top three rivets set without Boelube on the rivet set and the bottom rivet was pounded with Boelube on the rivet set … big difference, so the rest of the pounded rivets are now receiving a small drop of Boelube on the rivet set prior to being pounded with the rivet gun.

                                                   Riveting the forth rib from the inboard end of the left spar.

SPEED BUMP – Up until this point all the ribs have been able to be riveted with solid rivets. Unfortunately, the second and third ribs from the inboard end of the spar will need to receive some LP4-3 pop rivets. The four rivets securing the aft flanges of these nose ribs onto the left wing spar can still be solid rivets, but the six rivets attaching the web of these two nose ribs to the rib clips will need to be LP4-3 pop rivets. There is a clearance issue because the body of the pneumatic rivet squeezer is hitting on the rib clips where the extra rib is for the wing walk area. The interference prevents the squeezer from being able to get squarely (or even close) on the rivet head. At least the four rivets that secure the nose rib's aft flange onto the spar can be pounded, so I don’t feel quite as bad about it.

                                        One can clearly see the body of the pneumatic squeezer hits the rib clips
                                        preventing the squeezer from obtaining proper alignment with the rivet.

Luckily the pneumatic squeezer just barely fit on the rivets securing the inner most inboard rib to the rib clip. Was able to use four solid rivets on the rib but had to use LP4-3 pop rivets on the upper and lower holes because the large spar rivets prevented the squeezer from gaining access to the rivets at those two locations.

                                     The inner most inboard rib with four solid rivets and two LP4-3 pop rivets.

I thought briefly about possibly pounding rivets where the squeezer could not fit but after testing with some scrap metal, decided it would not be a good idea. Pounding 1/8” rivets with an offset rivet set into thin .020 metal results in dented material. I tried several techniques and did not find a way that worked for me to pound a 1/8” rivet correctly AND have no metal deformation.  Not saying it can’t be done, but it is beyond my current skill set.

Riveting The First W-1208-R Nose Rib With An Aft Flange

Once determining the aft flanges of the W-1208-R ribs can be riveted using solid rivets, the rivet gauge was used to determine which size solid rivet would be an acceptable choice … 4-6 rivets were a little short and a 4-7 rivet is ever so slightly long so I went with the rivet closest to the perfect fit, which was the AN470AD4-7 rivet.

Due to the second funeral this week for a family member, only worked in the shop a little while this morning … really only enough time to completely rivet one of the W-1208-R nose ribs with and aft flange and take a photo of the riveting. Bucking bar access was acceptable … so in addition to using solid rivets to secure the nose rib to the rib clips, the aft flange of the nose rib received four AN470AD4-7 solid rivets in the place of LP4-3 pop rivets. The aft flange rivets required the use of the rivet gun and bucking bar because the pneumatic squeezer could not reach the rivets.

                                       Using a rivet gun and bucking bar to set AN470AD4-7 rivets attaching
                                       the aft flange of the W-1208-R nose ribs onto the left wing spar.

Assembly Of Left Wing Nose Ribs Continues

The five outboard W-1208-Rnose ribs which have had the aft flanges removed are now riveted onto the left wing's spar. Access was great so they were easily and quickly (relatively speaking) riveted onto the rib clips previously attached to the left spar.

                The five outboard W-1208-R nose ribs with the aft flanges removed riveted onto the spar assembly.
               The sixth rib is one of three uncut W-1208-R ribs clecoed in place ready to be riveted next.

The next three ribs to be installed are the only three W-1208-R nose ribs which were uncut. These ribs receive more rivets the usual six on the web of the rib by way of an additional four rivets on the rear flange of the rib.

While removing the rear flanges of the W-1208 ribs I wondered why some aft flanges were left intact.  It all makes sense now after really looking at how things go together. In a nut shell, the spar keeps getting thicker and thicker towards the root of the wing because of layer after layer of doubler plates added for strengthening. Because of this, the rib clips only have two large rivets attaching the clips to the spar which, all things considered, is not much support. Therefore, all the nose ribs in the area where there are doubler plates  have their rear flanges riveted directly onto the spar. The photos below illustrate the need for the aft flanges on those nose ribs.

                             The gap behind the rib clip and spar can be easily seen here as well as the four holes
                             on the spar where the aft flanges of the W-1208-R nose ribs will be riveted.

                                        In this photo of the root of the spar one can easily see the gap behind the
                                        rib clips is considerable because of the many layers of doublers on the spar.

Photo of one of the W-1208-R nose ribs clecoed to a rib clip with the aft flange ready for riveting onto the left spar.

It was a 20 degree morning, so I only spent a couple of hours in the shop and did not begin riveting any of the ribs with the aft flanges. But will try to make progress tomorrow by first seeing how difficult it will be to buck the rivets attaching the aft flanges of the W-1208-R ribs to the spar. A quick check before quitting for the day revealed using solid rivets to rivet the aft flanges onto the spar appears doable at first glance … however the rivets will need to be bucked.