Removing The U-1220 Main Gear Legs For Priming

Savvy RV-12 builders following the Blog may have noticed the gear legs on the DOG Aviation RV-12 were not primed … even though the gear legs are just about the only component on the RV-12 that Van’s assembly instructions make a special note in bold print informing the builder to MAKE SURE the gear legs are primed with a high quality primer, preferably epoxy primer. During the late fall massive primer session for the finishing kit parts, the gear legs were overlooked because they were at the bottom of a crate with cardboard over them …. out of sight, out of mind. This oversight was not noticed until it was time to install the gear legs so the decision was made to continue moving forward and deal with it later …. and later would be now. Because the gear legs are showing signs of the beginnings of corrosion, as can be seen in the photo below, felt it would be best to make it right during the condition inspection.

The beginnings of surface corrosion can be seen because of the lack primer on the gear leg. Priming the U-1220 gear legs is called for in the plans … Van’s recommends an epoxy primer as a first choice. The corrosion developing on both gear legs looked pretty much the same as this right main gear leg.


Removing the main gear legs involves removing the wheel and axle/brake assembly. Decided to take a short cut and not remove the brake lines from the calipers. This was accomplished by removing the wheel nut after removing the two bolts that secure the outboard brake pad … this allows the wheel/rotor assembly to be removed from the axle leaving the caliper and inboard brake shoe attached to the axle assembly. After the wheel was removed from the axle, a thick paint stir stick (the thick type used to mix 5 gallon pails of paint) was quickly used as a substitute rotor and the outboard brake pad was bolted back on finger tight. The reason for placing the thick paint stick between the brake pads is to prevent the brake piston in the caliper from popping out of the caliper and creating a huge mess of brake fluid everywhere. Felt this would be a good idea because the brake assembly will be off the gear legs for a few days, so didn’t want any unexpected surprises similar to what a friend experienced with his airplane’s caliper piston popping out overnight and draining all the brake fluid onto the floor of his hangar.

My finger is pointing to the paint stick placed between the two brake pads to prevent the piston from popping out of the caliper during the extended time the brake assembly will be off the aircraft.


After removing the axle assemblies from the gear legs, each gear leg was easily unbolted from the center channel and removed. The gear leg removal was a piece of cake … (but the same could not be said when it came time for reassembly). The corrosion on the gear legs was cleaned up by soaking the gear legs in Alumiprep 33 which is basically phosphoric acid with cleaners formulated to clean aluminum. Long time readers of the DOG Aviation Blog may recall Alumiprep 33 was also used when preparing all the wing ribs for primer. Because the surface of the gear legs are not perfectly smooth, a brass wire brush was used to help clean down into the pores of the metal.

In addition to being a product to clean and prepare aluminum for priming, Alumiprep 33 is also a great product for helping to remove surface corrosion on aluminum.


After using Alumiprep 33, it is necessary to give the parts a good rinse with water. Although not called for, I used distilled water for the rinse water. Unfortunately, after using Alumiprep 33 and rinsing the parts off really well ... as soon as the parts are dry, they need to be primed immediately. This made for a long work session by the time all the spray gun cleanup was completed.

Both U-1220 main gear legs freshly primed with Akzo epoxy primer and ready to reinstall.

Reinstalling the gear legs was a total fight … not fun … in fact, it was a pain in the neck both literally and figuratively. The difficulty stems from lack of access. When the gear legs are first installed on the RV-12 access is good because, in addition to the access hole in the belly skin, the F-1275G cover plate is not installed yet. Without the cover plate in position, the gear hardware is easily accessed with both hands. However, after the main gear legs are installed, the left and right F-1275G cover plates are riveted onto the fuselage leaving only a tiny slot for the gear legs to pass through.

Photo of the F-1275G cover plate … this plate is not riveted in place until after the gear legs are installed. As one can see from the photo, when the F-1275G cover plate is riveted in place, it eliminates all access for a second hand to reach the gear leg mounting hardware. This is one area where I feel using nutplates to secure the F-1275G cover plate would have been a great idea …. but in reality, once the main gear legs are installed, there is no need to remove them on a regular basis. That said, having the F-1275G cover plate secured with screws would sure make checking the bolt torque much simpler.


The lack of access created a huge problem dealing with the U-1202 outer attach bracket and associated bolts … this is because only one hand barely fits into the inspection hole on the belly of the airplane making it seemingly impossible to hold the bracket (which is about 6" or so further in from the access hole) and install a bolt at the same time all with one hand. After fighting and fighting with the hardware inside the center channel for a very very long time and exhausting my entire dictionary of choice cuss words, Bernie came up with a brilliant idea that was simple and truly worked quite well … once we learned the “how to”, quick progress was made. Bernie suggested sliding a wooden dowel rod or brass rod into the gap between the gear leg and fuselage skin to hold the bracket in place so the mounting bolt could be inserted. This worked out great! As an example, I could roughly position the U-1202 attach bracket and Bernie inserted the rod to hold the bracket in position so I could let go of the bracket and free my hand  for inserting a bolt into the bracket and subsequently up into the center channel. This method also came in handy when torqueing the bolts on the attach bracket … I could not see the bolt when my hand was in the access hole, so I would hold the socket end of the torque wrench so I could feel it slip onto the bolt then Bernie reached in with the rod and pushed up on the torque wrench to keep it in position on the head of the bolt while I repositioned my hands to the handle to begin torqueing the bolt.

Bernie’s idea of inserting either a brass rod or dowel rod through the gap adjacent to the gear leg and pressing up on the U-1202 bracket or the torque wrench to free my hand for a few moments worked great.


With both main gear legs now reinstalled, bolted and torqued down ... the axle, caliper and brake assemblies were reinstalled on the gear legs. Decided to switch the wheel bearing grease to a full synthetic grease so the wheel bearings were washed in mineral spirits (akin to Stoddard fluid) and blown out with compressed air. This was repeated three or four times until the bearings were spotless. I would caution fellow builders not to let the bearings spin when blowing them off with compressed air …. it is always a temptation, but it is truly not good for the bearings. After hand packing the bearings with fresh full synthetic grease, the wheels were placed back on the axles.


The following was mentioned previously in the Blog the first time the wheels were installed ... but bears repeating. The wheel assemblies used on the RV-12 are manufactured by Matco. The wheel bearings supplied by Matco for the wheel assemblies used on the RV-12 ARE NOT the typical automotive wheel bearing so the procedure for tightening the axle nut is different. On a car, the axle nut is tightened until there is a slight drag placed on the wheel bearings then the axle nut is backed off a little and locked in place with a cotter pin. This method will not work for the Matco wheels used on the RV-12 because the bearings used by Matco have a built in grease seal. The procedure for tightening the axle nut on the Matco wheel is to tighten the axle nut while slowly rotating the wheel … all the while looking at the grease seals. The grease seals will spin with the wheel until such time as there is sufficient pressure applied to the bearings by the axle nut that the pressure prevents the grease seals from spinning when the wheel is rotated. This is UNLIKE a car wheel because the axle nut IS NOT backed off from this point. In fact, if the cotter pin won’t drop into one of the holes in the axle, the axle nut is TIGHTENED a little further until it does. The result is not a free spinning wheel, but one that has a little bit of drag … this is fine, because the bearings are designed this way.

RV-12 Nose Gear Fork Upgrade/Modification

Now that the DOG Aviation RV-12 is out of service for the annual condition inspection felt it would be a good time to change the nose wheel fork to the new WD-1230-1 RV-12 gear fork Van’s Aircraft has changed over to. The reason behind this change stems from a few RV-12 builders experiencing cracking of the nose forks adjacent to the welds and in a couple of cases, a complete collapse of the nose fork. It is felt that extensive flying from sod fields was a major contributing factor to the stress cracks forming.


To Van’s credit, the nose fork was redesigned and made from much thicker materials and the nose wheel mounting hardware was also changed in such a fashion to allow for full torqueing of the wheel axle without pressing on the bearings. (With the old assembly, the wheel nut was tightened until the wheel bearing was compressed creating a drag on the wheel then the nut was backed off 1/4 turn… the new hardware allows the axle nut to be tightened to full torque specs for the hardware without compressing the bearing to the point of placing a drag on the wheel).


Because the DOG Aviation RV-12 will be flown almost exclusively from paved runways, I was not going to change the nose wheel fork to the new model. What tipped the scale in favor of making the switch now was discovering wheel pants (still sitting on the shelves) installed on the old nose wheel fork can be reinstalled on the new nose wheel fork assembly … but it requires drilling six new  mounting holes. So, should I switch to the new nose fork at a later date after installing the wheel pants on the old style fork, it means there will be six vacated holes that will need to be filled, sanded and of course the wheel pants will need repainting. After hearing that, decided to just switch over to the new wheel fork now and that way there won’t be any issues when attaching the wheel pants when I get around to it. So the new nose fork was ordered along with the hardware changes necessary to install the wheel fork and wheel pants.

Photo of all the parts that come with the new wheel fork assembly and the additional hardware for the wheel pant attachment. The bag contains wave washers, new wheel spacers, longer bolts for the tow bar mounting point and a longer axle bolt with lock nut.


The above parts were separated where necessary, edges smoothed then the parts were prepared for primer then sprayed. One major difference that is quickly apparent is how much thicker the material is on the new nose fork which is very evident when looking at how the wheel pants will mount. As can be seen in the photo below, the old nose wheel fork was bent forming a flange that the wheel pants attach onto with nutplates … because the new wheel fork material is so much thicker, aluminum brackets need to be riveted onto the new nose wheel fork using long AN470AD4-9 rivets so there is a mounting surface for the wheel pants. One tip here, if priming, try not to get any primer inside the bushing the axle passes through or the two bushings that are on either side of the wheel because it will need to be removed to allow the axle bolt to pass through the tight fitting bushings … ask me how I know?


Frequent readers of the DOG Aviation Blog know I embrace modifications that make sense to me … so prior to installing the new nose fork, decided to add a grease fitting so the two bushings inside the nose fork can be kept well lubricated. The modification was quite easy ... just drilled a hole in the front of the new nose fork and tapped it for a standard grease fitting thread.

As one can see in this photo, the new WD-1230-1 nose wheel fork for the RV-12 on the left is much beefier than the old nose wheel fork on the right which was thin enough to bend creating a mounting flange for the wheel pants. The new wheel fork is too thick to bend like that, so there are rivet holes along the upper edge what will allow for mounting a bracket onto the side of the wheel fork for later use to mount the wheel pants. Also of note, one can see the grease fitting modification that was added to the nose fork.


Decided to begin the condition inspection by placing the RV-12 on a sawhorse so the new nose wheel fork could be installed. The new nose wheel fork comes with longer AN5 bolts for the toe bar attachment points (all the old washers are reused). Because I plan on installing the wheel pants in the near future, also riveted the mounting brackets in place. With the nose fork now ready to install, the swap was easy … but I did run into a small confusing hiccup by not looking at the new drawings. At first, I incorrectly “assumed” that the two Belleville washers and flat washer that were under the castle nut of the old nose wheel fork would be reused … but the hole in the gear leg for the cotter pin was not visible. I quickly figured out if the flat washer was removed, the hole for the cotter pin would be visible … when all else fails read the instructions. After referring to the new drawing, sure enough, it was discovered the large flat washer is not used with the new nose wheel fork … the castle nut now rides directly on the Belleville washers.


Prior to installing the cotter pin, one thing that needs to be checked is the preload tension … which should be between 18-20 pounds. A piece of wire was placed through the holes for the axle bolt and attached to a digital fish scale. The fish scale is pulled on until the fork swings and the castle nut is progressively tightened to compress the Belleville washers until the nose wheel fork swings at the desired 18-20 pound pull. The assembly ended up around just slightly over 20 foot pounds because that is where the existing hole for the cotter pin aligned with a slot in the castle nut.

The flat washer in my fingers is not used with the new WD-1230-1 RV-12 nose gear fork assembly.. only the two Belleville washers and the castle nut are reused to mount the nose gear fork onto the nose gear leg. The mounting brackets for the wheel pants can be seen here riveted onto the nose fork with AN470AD4-9 rivets.

Completed instillation of the new WD-1230-1 nose gear fork with grease fitting modification on the DOG Aviation RV-12.


With the nose wheel fork upgrades now complete, decided to direct my attention to the main gear legs which were overlooked during the priming session for the finish kit parts. More about that in the next posting.

Cockpit Interior Completed - Almost

Finished up installing the RV-12’s interior and discovered two minor issues. The piece of carpeting that covers the center tunnel in the area under the instrument panel has a recess cut into the forward edge of the carpet for the wiring bundle … unfortunately, that recess is not big enough because of the much thicker brake lines, the additional tube for the static line going to the backup instruments and the ADS-B coax cable. As such, the carpet can’t be placed as forward as necessary so the edges that should be close and parallel to the firewall are not. Because of the alignment issue I did not attach the Velcro strips for that piece yet. Will need to take the carpet piece to a tailor at some point in the near future and have the recess made both a little wider and deeper.


The other issue involves the interior trim piece that covers the air vents. This piece has a cutout for the air vent but it is completely covered with a fine mesh material. Installing the trim piece will require cutting a slit in the mesh for the lever that controls the position of the vent. This, in and of itself, is not a big deal but the mesh is fine so I feel it will really significantly cut down the airflow. So at this point, I left the piece off until I make a decision … leaning towards removing the mesh all together. Guess I could fly the plane without the piece in place and see just how much air the vent produces then install the panel and compare the airflow with the mesh in place and go from there.

Seats and interior carpet in place in the cockpit area.

Photo of the interior carpet under the instrument panel. These pieces are just loosely set in place because the center tunnel piece needs to be tweaked as mentioned above. I didn’t realize it at the time, but the issue with the wiring bundle can’t be seen in this photo. One of the previously mentioned air vent can be seen to the right of the right control stick.


One of the few remaining tasks that needed to be accomplished was adjusting the takeoff trim position that is displayed on the EMS. I was searching for the words “trim” calibration or some such thing and couldn’t find it listed on the EMS calibration page. That sent me on a tangent referring to the SkyView documentation with no joy   … well it IS there …. it is listed as “elevator” and not trim. The calibration wizard can be accessed by going to SETUP MENU > HARDWARE CALIBRATION > EMS CALIBRATION> ELEVATOR. Calibration is easy …. the SkyView has the user run the trim motor full down and full up then has the user place the trim in the takeoff position to complete the calibration. Based on what other builders have suggested, I set the trim takeoff position to 1 7/8". This is done by moving the control stick full aft and measuring the distance from the aft edge of the anti-servo tab to the aft edge of the stabilator. This should be a safe initial starting point and can always be readjusted later if desired.

Photo posted on the VAF forums by John a builder in Texas that shows a good starting point for setting the position of the trim tab for takeoff.


While the SkyView was still powered up, decided to pre-set some frequencies into the Garmin GTR200 radio following the Garmin User manual. Also decided to adjust the blaring stall warning sound down from a mind-numbing screech to a level louder than any of the other audio signals, but not blaring. The Garmin radio has two audio inputs … AUX 1 is for the stall warning tone and AUX 2 is for annunciations coming from the Dynon SkyView.


To reduce the stall warning sound level, the adjustment was made at the Garmin radio using the volume adjustments for the AUX 1 input. There is also an adjustment potentiometer on the AV-50000 module as well, but I did not play with it.


I discovered a little background noise in the headsets coming from the Skyview …feel it is originating from the SkyView because the sound is in sync with the clock seconds. It was getting late evening so decided to leave this for the next work session … will try turning down the EFIS potentiometers on the AV-50000A module a bit to see if it helps since the radio has tons of gain available for the audio input. This may be a sound that is being transferred from wires running adjacent to the music inputs. I still have the music inputs muted so will need to do a little experimenting to find out what the deal is.

Inspection Panels & Interior Installed

Frequent readers may have been wondering when the first flight of the DOG Aviation RV-12 will occur ….. soon, very soon.


As mentioned in the previous post, it was necessary to remove the wings to install the F-1228 cover. Two Sundays ago after the MAPS museum’s pancake breakfast, Bernie and Mike K. gave me a hand removing the wings so the F-1228 seat floor cover could be installed down over the flap handle. Now that we have done it a couple of times, the process was a snap … it took far longer to get all the screws in the cover plate than it did to remove and replace the wings.


While I had the flap handle disassembled, I used the opportunity to remove ½" from the VA-114 spring inside the flap handle. This makes the button far easier to push and reduces the likelihood of pinching fingers or thumb on the button. This was done in accordance with Van’s Notification 15-10-01.


Then the monsoons hit …. it rained every day last week, so I didn’t get much done. I figured there was no urgency, so why spend time in a cold damp hangar listening to the defining sound of rain hitting the metal roof if it is not necessary? However, the time was not entirely wasted in that custom made checklists were printed out and laminated.


This week during the last few work sessions all the covers for the center tunnel and baggage bulkhead have been installed along with most of the interior pieces. I did run into a small issue installing the F-1230 tunnel cover. This is the cover that readers may recall needed to have the slot for the wiring harness cut out a little larger (this was done months ago during a trial fitting). Then installing the cover I had troubles getting it to seat correctly … it would not slide down low enough around the bundle of wires and brake lines. One of the brake lines was interfering with the cover. Further investigation revealed the stiffness of Bowden cable for the parking brake was the root of the problem … in that, it was preventing the brake line from moving downward. The cable for the parking brake had been routed behind the brake lines going to the parking brake and prevented the brake lines from moving. The solution was to reroute the Bowden cable on top of the brake lines in the valley between the two lines. This solved the issue and actually made for a better instillation but sucked up most of an afternoon in the process. Unfortunately, I did not take any photos.

Installing the F-1227 seat ramp cover, and the remaining baggage floor covers and the modified F-1207F baggage bulkhead went smoothly, but took a toll on my knees and legs because of the position necessary to lean over the cross brace to gain access to the screws in the baggage area.


At this point, I was planning on balancing the audio, but got sidetracked and decided to install most of the interior carpet and side panel kits. Mainly because I did not want my shoes to scrape up the paint when pushing on the rudder pedals. At first I was only going to install the one piece of carpet but decided to just go for it and install them all in the cockpit area. All went smooth for the most part, but it took much longer to install the Velcro strips than I thought it would. But the end results look nice.

Working on installing the carpet over the seat pans.

I discovered there is a long piece of Velcro that needs to be installed underneath the spars. Not going to happen now … so I just have it laying there stuck to the carpet for the time being because I am not removing the wings just to install a strip of Velcro. Will make a note of it so the next time the wings come off, I can install the Velcro.


Note to fellow builders that have purchased the carpet kit. While you have the wings off to install the cover plate that goes over the flap handle do yourself a favor and install the carpet for the seat pans at this time.


The side panels are installed by placing a bunch of Velcro strips on the inside of the fuselage skin and setting the panels in place. The panels are a very snug fit and shaped perfectly … nice job Abby!

Installing one of the side panels on the right side of the DOG Aviation RV-12.

Did not have enough time to finish installing the arm rests, so will finish that up first thing during the next work session. I have a carpet kit for the baggage area as well but will hold off on installing that until my knees recuperate a bit.