Completing Service Bulletin SB-00023 WD-1221 Engine Mount Standoff Inspection/Replacement

Service Bulletin SB-00023 involves inspection/replacement of the RV-12’s WD-1221 upper engine mount standoff. There have been a few RV-12 aircraft that have developed cracks near weldments on the WD-1221 upper engine mount standoff discovered during inspections. Van’s took quick action and redesigned the WD-1221 using tubing double the thickness thereby “theoretically” making the areas where the cracking occurs much more robust.

Service Bulletin SB-00023 requires inspections of the WD-1221 upper engine mount standoff be conducted every 100 hours and ongoing log book entries be made unless a crack is found … which, if discovered, requires a mandatory replacement using the new WD-01221-1 upper engine mount standoff. Figured while I still had access to the engine hoist I borrowed from Tom (a fellow RV builder at the airport putting the finishing touches on his RV-10 for his first flight), may just as well go ahead and replace the WD-1221 standoff (even though mine is not cracked) and just be done with it.

All and all, with the exception of dealing with the two sets of double Adel clamps that attach onto the WD-1221 upper engine mount standoff, the process of changing out the standoff was not all that difficult. Fortunately, no fuel, oil lines or wiring needed to be removed (all those items were installed following Van’s suggested path). It was tight but there was enough room to shoehorn the old mount out and install the new mount without jumping through a lot of hoops.

Design and outward visual appearance of the two upper engine mount standoffs seem identical ….however, the new standoff appears to have a tiny hole on the endcap. The new part number for the redesigned WD-1221 upper engine mount standoff is now WD-01221-1. The following  photo shows the new WD-01221-1 standoff and the next two photos show the existing WD-1221 standoff and Adel clamp placement.

As one can see from this photo of the new WD-01221-1 upper engine mount standoff it visually looks identical to the original, which can be viewed in the two Adel clamp photos bellow.

Photo of the pair of Adel clamps used to secure the main firewall forward wiring harness to the WD-1221 upper engine mount standoff. Reattaching these Adel clamps after the upper engine mount has been changed out will be a challenge. Fortunately, there are tricks that help ease the pain … but it still presents a challenge because there is not a lot of room for good access.

This photo is of the second pair of Adel clamps attached to the WD-1221 standoff … these clamps are used to secure the throttle and choke cables to the WD-1221 upper engine standoff.

Unfortunately, accessing the bolts that secure the WD-1221 upper engine mount standoff to the firewall requires removing the F-1240 upper forward fuselage skin. Once the F-1240 upper forward fuselage skin is removed, closing the canopy will allow great access to the WD-1221 standoff’s mounting bolt heads … as such, this can be done as a one person operation. There was one unexpected complication involving removal of the two mounting bolts that created a little extra work. The bolts could not be completely removed because they contacted the F-00055 com supports.  Solving this issue required placing a sawhorse under the tail cone and jacking the engine until the tail cone contacts the sawhorse … then jacking just a little more causing the isolation mounts to separate from the WD-1221 standoff so the isolation mounts could be removed to garner the enough room to slide the WD-1221 standoff forward far enough to clear the bolts protruding the firewall. Guess I could have bent the lower ear on the com supports … but really did not want to do that.

This photo shows how the F-00055 com supports prevent the mounting bolts from being completely removed.

This photo shows when the bolt was pulled aft to the point of touching the com support, there was still quite a bit of the bolt extending beyond the firewall.

With the WD-1221 upper engine mount standoff rotated upward, it can easily be fished out towards the left side of the aircraft.

The new WD-01221-1 upper  engine mount standoff is slid in from the pilot's side of the aircraft following the same path used to remove the old mount,  then it is rotated down and slid aft over the protruding bolts. Next the isolation mounts are reinstalled. Also of note: Rotax recommends replacing the rubber isolation mounts as part of their 5 year rubber replacement protocol …  so all of the engine’s isolation mounts have been replaced (forgot to mention that in the last posting). After all the bolts are inserted, the castle nuts are torqued to 160 in lbs … after torqueing to 160 in lbs, if a castellation is not yet aligned with the hole in the bolt, the castle nut is tightened more until a cotter pin can slide into the hole in the mounting bolt. The upper limit for the torque is 190 in lbs. so there should be enough margin to allow a castellation to align with the hole in the mounting bolt without over torqueing.

The new WD-01221-1 upper engine mount standoff installed and ready for the two pairs of double Adel clamps to be attached.

The new WD-01221-1 upper engine mount standoff completely installed … the new mount looks identical to the old WD-1221 standoff with the exception of the tiny hole in the endcap.

The last item left to do is reinstalling the two pairs of double Adel clamps … this is a challenge. Adel clamps are very springy and want to spring open so even if there is plenty of room to get your fingers on them, they are a challenge. That difficulty is upped dramatically when reinstalling the two pairs of Adel clamps onto the new WD-01221-1 upper engine mount standoff. There just is not much room for fingers and tools …. especially when reinstalling the two Adel clamps that support the firewall forward main wiring harness. Even using the tricks I know, reinstalling these Adel clamps was an exercise of patience.

Best photo I could get showing both double sets of Adel clamps attached to the new WD-01221-1 upper engine mount standoff.

Builder tip: The easiest way I have found to install double Adel clamps is to use Adel clamp pliers in conjunction with safety wire. First squeeze each Adel clamp separately and wrap a thin safety wire around the clamp to keep the clamp from fully opening when the pliers are removed. Then align the two clamps together and place the Adel pliers over the two clamps, tighten the pliers, then slide the alignment awl through the bolt holes in the clamps. When the holes are aligned, quickly remove the awl and insert the bolt. Here is where it gets a little dicey …. usually, the bolt is not long enough to allow a nut to be installed because the thickness of the Adel pliers takes up a lot of room. So what usually works well is to press down on the head of the bolt, then slide out the pliers and reposition pliers on top of the bolt head and tighten the pliers again. This should leave enough threads beyond the pliers to get a nut threaded onto the bolt. Once the nut has caught a few threads, remove Adel pliers and thread the nut on the bolt a little more. Next remove the safety wire, final position the Adel clamps, then tighten the mounting bolt. Below is a photo sequence of the steps involved.

Adel clamp pliers and the awl that comes with the pliers.

Using Adel clamp pliers to squeeze the clamp’s ears together so thin safety wire can be wrapped around the clamp. Leave the ends of the wire long so the wire can be unwrapped by easily by hand.

Example of how the awl that comes with the Adel clamp pliers is inserted through the holes of both Adel clamps to align the holes so a bolt can pass through the clamps.

As can be seen here, typically an AN3-3 bolt is not long enough to allow a nut to be threaded onto the bolt because of the thickness of the pliers.

Once the AN3-3 bolt is inserted through the pliers and Adel clamps,  forcefully press down on the bolt head then remove the pliers. Quickly reposition the Adel pliers to capture the head of the bolt …. this allows the threads of the bolt to extend beyond the pliers just enough to thread on a nut.

This photo shows how repositioning the Adel clamp pliers to press on the head of the bolt will allow enough threads extend beyond the pliers to allow a nut to be threaded onto the AN3-3 bolt.

As one can see, clamping the bolt head with the Adel clamp pliers allows a nut to be threaded onto an AN3-3 bolt. Now remove the safety wire, final position the Adel clamps and finish tightening the nut and bolt.

As mentioned previously, completing Service Bulletin SB-00023 was not that difficult … but dealing with the two sets of double Adel clamps located in tight quarters is actually the most challenging aspect of replacing the WD-1221 upper engine mount standoff with the new WD-01221-1 standoff.

Completing Service Bulletin SB 19-08-26 Rev 2

Service Bulletin SB 19-08-26 Rev 2 involves replacement of the RV-12’s WD-1201 nose wheel gear leg. There have been a few RV-12 aircraft that have developed cracks in the nose wheel gear leg’s tubing which were not visible during inspections until the nose wheel gear leg became seriously compromised.  My understanding is that the cracking begins at an internal structure not visible to the eye during inspections. Van’s has redesigned the WD-1201 nose wheel gear leg and “theoretically” made the area where the cracking began much more robust …. The new part number for the redesigned nose gear leg is now WD-1201-1-RTR.

The new parts required to complete the service bulletin can be ordered from Van’s using part number SB-19-08-26 for the RV-12 or SB-19-0826iS for the RV-12iS. The DOG Aviation RV-12 required part number SB-19-08-26. As can be seen in the photo below, the kit contains the new WD-1201-1-RTR nose wheel gear leg, two drill bushings, an Adel clamp (used to support the lower radiator hose) along with a screw and nut for mounting the Adel clamp.

Contents of the service bulletin kit part number SB-19-08-26 …. The new WD-1201-1-RTR gear leg, two drill bushings and an Adel clamp with mounting hardware used to secure the radiator’s lower coolant hose.

A closer look at bag 981 containing the drill bushings and bag 982 containing the Adel clamp and mounting hardware that comes when ordering part number SB-19-08-26.

Also of note: In addition to needing the drill bushings used to drill mounting holes into the new gear leg, it is also necessary to procure LONG 18" drill bits sized 1/8", 1/4" and 3/8". The 18" long drill bits can be procured locally or ordered from Van’s using part numbers TOOL-00040, 41 and 42 respectfully.

Before the fun begins, there will be a need to procure an engine hoist. A big thanks to Tom a fellow RV builder at the airport who was kind enough to loan me his engine hoist (Tom is building a RV -10 just about ready for a maiden voyage).  Hoisting the Rotax 912ULS engine is accomplished by placing straps around the intake manifolds and using the straps to hoist the engine up. Prior to hoisting the engine much, remove the thirteen AN3-4 bolts from the nose gear’s fuselage mounting plate. At this point, Van’s suggests placing a padded sawhorse under the tail cone. This is because it is necessary to hoist the engine until the tail cone contacts the sawhorse, then hoist a little more to allow the isolation dampers to separate from the nose gear’s firewall mounting plate. While hoisting the engine, there will be a point where most of the weight is off the mounting bolts … when that happens, remove the bolts and slide the WD-1201 gear leg assembly down off the firewall.

Using an engine hoist to lift the engine via a strap passed under the intake manifolds so the WD-1201 nose wheel gear leg could be removed. Thank you Tom for loaning me the engine hoist.

After removing the old nose wheel gear leg assembly, the nose wheel fork & tire assembly is removed and moved to the new WD-1201-1-RTR nose wheel gear leg. (Do not perform the nose wheel break-out force adjustment at this time because the gear leg will be removed again after drilling). The new gear leg and wheel assembly is placed in position and four AN3-4 bolts are used to temporarily attach the gear leg to the bottom of the fuselage. Next blocks of wood ¾” to 1” thick are placed between the engine mount and the gear leg’s firewall mounting plate and the hoist is lowered to place weight on the nose wheel which, in turn, pushes the firewall mounting plate tight against the firewall. Continue lowering the hoist so the engine mounts are now pressing on the blocks of wood …. Thus forcing the gear leg assembly even tighter to the firewall and ready for drilling. The wood basically simulates the thickness of the isolation mounts.

The 3/4" blocks of wood can be seen here sandwiched between the nose gear’s firewall mounting plate and the lower engine mounting point. The engine weight pressure on the wood helps keep the gear leg’s mounting plate pressed tight to the firewall for the drilling process.

Because the new WD-1201-1-RTR gear leg comes with the firewall mounting plate undrilled ... it is necessary to match drill the new gear leg to the existing bolt holes in the firewall. This is where the drill bushings come into play. The existing mounting bolt holes in the firewall are 3/8" so it is necessary to begin by drilling a much smaller 1/8" lead hole. The small drill bushing is inserted into the existing mounting bolt hole and the long 1/8" drill bit is inserted through the center of the drill bushing so the lead hole will be drilled perfectly in the center of the existing 3/8" hole. Sounds simple right? Actually, it is  … once one figures out how to keep the drill bushing from falling out of the bolt hole in the firewall. One option that works quite well is to slide a sleeve over the 1/8" and 1/4"drill bits so the sleeve can be pushed into the aft side of the drill bushing … thus keeping the drill bushing firmly seated in the 3/8" bolt hole during the drilling process.

This photo shows the three long 18" drill bits used to drill into the WD-1201-1-RTR nose wheel gear leg mount. Note the 1/8" drill bit has a piece of brake line slipped over it and the 1/4" drill bit has a piece of vinyl tubing slipped over it. The brake line and vinyl tube allows the person drilling to push on the back of the drill bushing thus keeping it firmly seated during the drilling process.

A couple of drilling tips:

First tip:  I like drilling with Boelube because it is drawn to heat. I figured it would be hard to use liquid Boelube so I used solid Boelube instead. If one looks closely at the photo above, you can see strategically placed painters tape on the 1/8" and 1/4" drills … the tape is used as a marker so the drill bits don’t completely penetrate the bushings as can be seen above ... this allows the tip of the bushing to be packed with solid Boelube. The sleeve can then be held at the tape location without the drill bit pushing the Boelube out when seating the drill guide into the existing 3/8" bolt hole in the firewall. After drilling a while, the drill bit/ bushing was removed and repacked with more Boelube.

Second tip: Drilling the hardened steel of the landing gear mounting plate requires slow speed. Suggest not using a high speed air drill. This is one place where a high torque battery operated hand drill set to slow speed is your friend. (Thanks Bernie for loaning me your drill). Work on one hole at a time so that a bolt can be inserted through the gear leg mounting plate to assure nothing will move while drilling the second hole.

Unfortunately, I forgot to get a couple of photos of the drilling in progress, but it required a firm forward force. In order for me to see where I was drilling, it required sitting in the left seat while drilling the right hole … and vice versa. After both holes are drilled into the WD-1201-1-RTR nose wheel gear leg, the engine is hoisted once again so the gear leg can be removed for deburring. After deburring the WD-1201-1-RTR nose wheel gear leg, it is placed back in position and bolted in place using the thirteen AN3-4 bolts. Then the engine is moved up or down as necessary to allow the bolts to pass through the WD-1201-1-RTR nose wheel gear leg’s firewall mounting plate and through the engine’s isolation mounts. The torque range for the mounting bolts is between 160 -190 in lbs. (13.3 – 15.8 ft lbs.).  However, only initially tighten to 160 in lbs. and if a castellation lines up with the hole in the bolt your done … if not, continue tightening until the next castellation lines up with the hole in the bolt and install the cotter pins.

The new WD-1201-1-RTR nose wheel gear leg mounted to the firewall.

All that is left to do to complete the gear leg replacement job is adjusting the nose wheel breakout force to between 18-20 lbs. … then drill the nose gear leg for the cotter pin using a #30 drill bit. For determining the breakout force I use a Rapala digital fish scale and run a wire through the bolt holes in the nose wheel fork so the fish scale can be pulled on the centerline of the wheel. After the breakout force is established, the last step is to drill new holes into the gear leg for the cotter pin that locks the castle nut in place. Below is a photo showing the Rapala fish scale being used on the old style nose wheel fork (which has been changed out long ago for the stronger newer one).

Setting the nose wheel breakout force using a Rapala fish scale. The nose wheel fork’s castle nut is tightened against the Belleville washers until the breakout force is between 18 – 20 lbs. … I ended up a tad over 19 lbs. Note: This is a photo showing the old nose wheel fork but the measurement method using the Rapala fish scale is the same … a wire passed through the fork’s axle holes and pulling the fish scale to determine the breakout force, then tightening the castle nut to create more friction until the breakout occurs within the acceptable 18-20 lb range.

Service Bulletin SB 19-08-26 Rev 2 completed on the Dog Aviation RV-12. The bird is now sitting on the new WD-1201-1-RTR nose wheel gear leg.

All and all, replacement of the WD-1201 nose wheel assembly was not as difficult as I had envisioned … although drilling the bolt holes while sitting inside the cockpit was a little uncomfortable.

Completing Safety Directive SD-00001 Replacement Of Trim Servo Motor

A potential safety issue has been identified with RV-12’s that have the Ray Allen ES MSTS-T3-7A-2 trim servo motor installed. The issue involves the threaded portion of the trim servo motor shaft just forward of the AN315-3R lock nut that secures the AN665-21R clevis. The shaft is bending and, in some very rare cases, snapped altogether. The service directive requires mandatory replacement of the ES MSTS-T3-7A-2 trim servo motor with an upgraded Ray Allen ES MSTS-B6-7T-165 trim motor if the shaft is determined to be bent … or after 1000 hours of flight time.

Drawing from Safety Directive SD-00001 showing the location of the fatigue area.

The replacement Ray Allen trim servo motor has a part number of ES MSTS-B6-7T-165 and MUST to be installed with a bushing (Van’s part number BUSH-BS.188X.313X.222) that slips over the short threaded area of the shaft preventing the shaft from bending. Van’s also suggests when replacing the trim servo motor to also replace the F-1287A servo mounting tray with the newer F-1287A-1 mounting tray. The new F-1287A-1 mounting tray supports the DB9 connector Van’s has switched to … replacing the micro-Molex connector (problematic for some builders not having the proper crimping tool for the tiny pins) used on legacy RV-12’s.   When switching to the new F-1287A-1 mounting tray, you will also need to order an additional AN315-3R nut and Bag 2670 from Van’s which contains the male and female electrical pins, bodies for the new DB9 electrical connectors along with the necessary mounting hardware, plastic bushings and some rivets.

Drawing from Safety Directive SD-00001 showing the new ES MSTS-B6-7T-165 trim motor, bushing BUSH-BS.188X.313X.222 and AN665-21R clevis.

The decision was made that it would be better to take the approach of being proactive rather than reactive so decided to change out the trim motor …. Especially because, to Ray Allen’s credit, the company is offering RV-12 owners a substantial rebate if exchanging the old trim motor for a new one.

The DOG Aviation RV-12’s trim servo motor did not have a bent shaft. However, decided to make the exchange anyway and not need worry about the trim servo motor shaft bending issue anymore. Plus, I liked the idea of switching over to the new F-1287A-1 mounting tray which supports a DB9 connector to replace the micro-Molex connector.

New F-1287A-1 mounting tray which needs to have the doublers cut away and riveted onto the servo tray. Also, my finger is pointing to the new mounting flange for the DB9 connector.

After separating and smoothing the edges of the servo tray parts, they were primed with SEM primer and top coated with white paint for extra protection. Van’s calls for LP4-3 rivets to assemble the doublers onto the servo tray, but I used solid AN470AD4 rivets instead for the assembly. Next the plastic bushings are installed and filed down so they just clear the servo tray. (This is the same process as used on the original servo tray … in fact, I probably could have gotten by using the plastic bushings from the old servo tray).

Below is a photo of the new Ray Allen trim servo motor on the right and the old trim servo motor on the left. The three most notable differences on the new motor are … the round brass portion of the actuator that the new brass bushing will seat against, only four mounting holes as opposed to the six on the older unit and if one looks closely, the four corners of the case are scalloped a little.

Original Ray Allen ES MSTS-T3-7A-2 trim servo motor on the left and the replacement Ray Allen ES MSTS-B6-7T-165 trim servo motor on the right.

On the original trim motor instillation, Van’s covers the trim motor’s mounting flanges with doublers … but they are not called for on the new trim motor. I like the idea of the doublers because the trim motor’s mounting flanges appear to be just a tough plastic. Unfortunately, because of the scallops on the case of the new trim motor the old doublers can’t be used. I tried to file the correct profile in one of old doublers and was not happy with the results … because of the center hole in the old doublers, it leaves a very thin doubler in the area of the center hole.  Although not called for, I decided it would not hurt to just make a pair of doublers as can be seen in the photo bellow.

After trimming the old doubler (top of the photo) to fit the new trim servo motor, one can see how thin the metal is around the center hole (which is not on the new Ray Allen trim servo motor). So a new doubler (bottom of photo) was fabricated to mount the new trim servo motor in the F-1287A-1 mounting tray.

The new Ray Allen ES MSTS-B6-7T-165 servo trim motor installed in the F-1287A-1 mounting tray with my handmade doublers added for good measure.

For the final assembly, the forward threaded shaft temporarily receives two AN315-3R nuts which are tightened together or "double nutted", as they say. The nuts are temporarily used so a wrench can be used to hold the shaft from twisting and torqueing the internals of the trim motor when the AN665-21R clevis is tightened against the bushing. Prior to final assembly Van’s wants the clevis to be 15° from vertical when dry fitting the parts together using only fingertip pressure.

Two AN315-3R nuts are used to double nut the servo motor’s shaft so a wrench can keep the servo motor’s shaft from twisting and possibly damaging the servo when the bushing and AN665-21R clevis are tightened together.

The bushing in the above photo is slightly longer than necessary. To insure a proper fit, Van’s recommends using a drill press with some sandpaper to remove a little material at a time from the bushing so the bushing’s edges remain square. This is one place you don’t want to do any hand filing because Van’s wants the bushing to be a tightly mated fit between the trim motor and the clevis. Material is removed from the bushing until the slot in the AN665-21R clevis is approximately 15° degrees BEFORE vertical when the clevis is hand tight to the bushing. Note: Go slow! … only remove a few thousands at a time because it doesn’t take removing much material to make quite a difference in the positioning of the clevis ( I almost over did it on the second cycle to the drill press where I removed quite a bit more material than I did the during the first cycle). When a finger tight dry fit 15° shy of vertical is achieved, the bushing is ready for final assembly. Permanent red Loctite thread locker is applied to the aft threaded portion of the trim servo motor shaft and while holding a wrench on the double nuts to prevent the shaft from twisting, the clevis is threaded on further beyond the 15 degree point where it should become snug as the clevis reaches its proper vertical orientation.

Completed trim servo assembly ready for electrical connections and final instillation. Note, the two AN315-3R nuts are not yet removed from the forward threaded portion of the Ray Allen servo motor. The two nuts need to be removed at this point prior to installing the assembly back on the RV-12.

As previously mentioned, the new F-1287A-1 servo tray is designed for use with a DB9 connector. Female pins are attached to the wires coming from the trim servo motor and male pins are attached to the wires exiting the tail cone. There is a small change in the colors of the two power wires going to the new trim servo motor (the three trim position wires remain the same colors). The old trim servo motor power wires are both white … the new trim servo motor uses a white and a gray wire. Before permanently installing the wires into the DB9 connector bodies, I thought it best to use a 9v battery to make sure the new motor moves in the same direction as the old motor did … doing this insured the two white wires (servo trim motor power) exiting the tail cone will be connected to the new trim servo motor so motor movement is the same as the old trim motor. After the correct motor movement was established, the trim motor power wires exiting the tail cone were marked. Next, the pins were inserted into the DB9 housings. Van’s suggests sealing all the wires with silicone RTV so that was done prior to final assembly.

After the silicone RTV cured, the DB9 connectors were installed onto the F-1287A-1 trim servo tray. While trial fitting the connectors together, I noticed the DB9 connector was not fully seated. Upon a little investigating it was determined that because the male DB9 connector from the tail cone rests on top of the F-1287A-1 servo tray which has approximately a .060" or so of thickness, the standard sized threaded barrels are a tad too long … so I removed .060" from each threaded barrel and now have a fully seated DB9 connectors (If one chooses not to do this, it is not a big deal. However, I wanted my connectors fully seated and it was easy to accomplish just by removing a little material from both threaded barrels).

The DB9 connector #4 mounting hardware is NOT a piece of cake to install. Access is limited and the use of the tiny #4 MS21042 all metal hex stop nuts makes instillation a real hassle. The hex stop nuts are slightly egg shaped so they really grip the pan head screws … the problem is they grip just a little too tight when trying to install in such close quarters using a 5/32" wrench and only being able to tighten one flat at a time. I finally resorted to placing the head of the screw in a vice and running the metal stop nuts on and off a couple of times using CorrosionX as a lubricant to reduce the bite. The other issue I ran into was my long thin Philips screwdriver was 70 miles south at the southern outpost, so I needed to cobble together another way of accessing the #4 Philips screw heads from above the stabilator while using the 5/32" wrench from underneath the stabilator. Standard Philips screwdrivers are too short to accomplish this task when working by yourself. Below is a photo showing a drawing of how the DB9 connector is to be mounted onto the F-1287A-1 servo tray and the Rube Goldberg use of tools to fashion a way to get on the heads of the #4 Philips mounting screws from above.

Lacking immediate access to my very long thin Philips screwdriver, a Rube Goldberg assembly of various tools from the tool box was used to devise a way to hold the #4 Philips screws from above the stabilator. The photo also shows the drawing for mounting the DB9 connector.

Completed instillation of the new Ray Allen ES MSTS-B6-7T-165 trim servo motor, F-1287A-1 servo tray with the DB9 connector in place. Per Van’s instructions, silicone RTV is applied to the wires to seal the connector.

With the exception of dealing with the #4 mounting hardware for the DB9 electrical connectors, swapping out the RV-12’s trim servo motor went smooth and is not a daunting task. However, one does want to be careful when using the drill press to remove material from the bushing. Go slow and only remove a little material at a time to creep up on that 15° sweet spot.

Beefing Up The F-1254 Roll Bar Support Frames

Entering and exiting the RV-12 is not hard or extremely awkward for the pilot or passenger but there are places one naturally wants to place their hand for support such as on the F-1254 roll bar support frame. In some instances, applying body weight to the F-1254 support frame has caused deformation of the support frame or an outright kinking and bending of the metal.

The F-1254 roll bar support frame is the angled piece in the photo that also has a slot for capturing the canopy’s C-1206 guide plate. As can be seen in this photo, there is a large unsupported area adjacent to the seat which is right where there is a natural tendency to place a hand for support when entering or exiting the RV-12.

Builders have come up with various clever methods of stiffening the F-1254 support frame but when Van’s changed the RV-12’s fuselage design to support the Rotax 912iS engine, they also designed a stiffener that can also be used on a legacy RV-12 fuselage, which the DOG Aviation RV-12 has.

I’ve known about this weak spot ever since the initial flight and have instructed passengers not to place their hands on the weak area while entering or exiting the cockpit. I had already purchased a piece of angle aluminum that I was going to rivet onto the underside of the F-1254 roll bar support frame … but when I discovered there was a Van’s solution consisting of adding a stiffener of sorts, I ordered the new part. The Van’s part number is 12-01254A which comes as two stiffeners that when separated become a left and right part.

The F-1254A-L stiffener clamped in place on the pilot's side of the RV-12 and ready for drilling.

Instillation is not complicated. Van’s suggests breaking the edge on the upper portion of the F-1254A stiffener that will be riveted onto the F-1254 roll bar support which is what I did. The bottom edge that will be riveted onto the F-1234 canopy deck does not need to be broken, but it won’t hurt to do so. One needs to take a little care prior to drilling to align the stiffener then clamp and drill away.

Drilling the F-1254A-L stiffener onto the F-1254 roll bar support.

Completed instillation of the F-1254A-L stiffener riveted onto the F-1254 roll bar support and the F-1234 canopy deck.

The F-1254A L&R stiffeners were installed quite a long time ago on the DOG Aviation RV-12. While reviewing camera photos for an upcoming project, it was discovered the instillation process and photos were never posted on the Blog.

I would suggest all legacy RV-12 owners who have not taken it upon themselves to reinforce the F-1254 roll bar support frame with some sort of stiffener consider this easy to install solution from Van’s. It promotes piece of mind knowing one does not need to closely watch where passengers place their hands as they get in and out of the bird.

Installing FOBO Tire Pressure Monitors

RV-12 owners (and probably owners of most Van’s aircraft) know once wheel pants are installed, it becomes a real pain to check tire pressures. The wheel pants cover the majority of the tires, leaving absolutely no access to the air valves … thus requiring the removal of the wheel pants just to check tire pressures. Sure, some have drilled holes in the wheel pants for access … but then trying to perfectly align the air valve stem with the hole is a pain … plus, it makes it very difficult to use the protective valve stem caps ... so the caps are typically left off which allows crud to get into the valve stem. Hindsight being 20/20, I should have taken a little more time with the wheel pants and installed a hinged access door with a Camlock fastener or two.


One way to get around removing the wheel pants just to check tire pressures, is by installing remote tire pressure monitors … akin to the tire pressure monitors used in most modern cars. I have read positive things about remote tire pressure monitors on the forums so decided to give them a go. FOBO makes just such a product that transmits via Bluetooth to their free App … FOBO’s free App supports both Android and Apple products. FOBO manufactures tire pressor monitors for cars, bikes, motorcycles and trikes. I purchased a trike kit from a company in California called SlingMods which sells the latest sensor 2 version.

The FOBO trike tire pressure monitor kit with the latest version 2 sensors purchased from SlingMods.

The FOBO monitoring system for trikes includes three sensors which screw onto the tire’s valve stem. Included are three lock nuts that can (if desired) be screwed onto the valve stem and cinched up to the back of the sensors to lock them in place … a convenient special molded wrench is supplied for tightening the lock nut up against the backside of the sensors. Also included in the kit are three backup batteries (standard CR1632 coin/button batteries) and three short valve stems for use with tubeless tires.

As can be seen in this photo, the FOBO sensors are actually quite small, about the size of a penny.

The FOBO sensors themselves are quite small (as can be seen in the above photo) and only weigh 7.6 grams … probably not  enough weight to worry about rebalancing the wheel, but I'll be sure to be on the lookout for take off or landing vibrations. The life span of the replaceable CR1632 battery is 1 year. Battery replacement is easy … the top screws off the sensor and the old battery is slid out of a holder and new battery slid in, piece of cake. The sensors support both Bluetooth versions 4 & 5, which is how they report to the free FOBO App. The free FOBO App supports Apple’s iOS 9.3 operating system and Android version 5.0 or later. I installed the FOBO App on my smart phone (which is running Android version 10) without running into any issues. The FOBO App is full featured allowing the user to select wheel configurations, set pressure high and low alarm points, altitude compensation, etc. and share the settings with another device or user. As a deterrent for theft, the FOBO App registers the sensors with FOBO … so if the sensors are stolen, they will not work on another vehicle.


First time setup is easy, after the desired wheel configuration is selected, the App will tell you when to install each sensor so it can be paired with the FOBO App and registered online with FOBO. This part of the process takes a few moments as the App scans, pairs, then registers the sensor. After the sensors are paired, they immediately begin updating the FOBO App with each tire’s pressure reading,  current temperature and sensor battery status. As previously mentioned above, entering the settings page will allow editing the settings for optimum tire pressure and to set high and low pressure alarm points.

Photo of a FOBO tire pressure monitoring sensor installed on one of the main gear’s wheels.

There is plenty of clearance to install the sensors on the main landing gear’s wheel … however, I did discover a clearance issue when installing the FOBO sensor on the nose wheel. The DOG Aviation RV-12 has the new thicker and much stronger WD-01230-1 nose wheel fork installed. The new nose wheel fork also requires a new mounting bracket for the nose wheel pant. The new mounting method involves riveting a mounting bracket directly onto the nose wheel fork. The clearance issue I discovered involved the shop heads of the two aftmost rivets used to attach the U-00006E-L-1 mounting bracket onto the wheel fork. The FOBO sensor cleared the nose wheel fork just fine, but made contact with the two aforementioned rivets. ( This should not be an issue for RV-12 owners who have not installed the new style nose wheel fork because the rivets that caused me grief are not present on the old style nose wheel fork). I used a file to remove a little material from the shop heads of the offending rivets so a little clearance could be obtained.

After filing down the shop heads of the two rivets a little, the sensor cleared the rivets as can be seen here if looking closely …  but just barely. Clicking on this photo should bring it up to full size making it easier to see.


Not feeling comfortable with so little clearance, I decided to add a 1/16" shim (washer) between the nose wheel fork and the U-01210B-1 axle spacer, essentially moving the wheel 1/16" to the right … so fabricated a 1" washer from .062" aluminum scrap. I remembered when first installing the nose wheel on the new WD-01230-1 fork, the fork pulled in a little as the axle bolt was tightened. So I felt pretty confident there would be room for the 1/16" washer to slip in between the U-01210B-1 spacer and the WD-01230-1 wheel fork without much of a fight. Sure enough, as the axle bolt was loosened, a gap appeared between the U-01210B-1 spacer and the WD-01230-1 wheel fork … so I inserted my newly minted washer in the gap and reinstalled the axle bolt. After tightening the axle bolt, there is now acceptable clearance between the FOBO sensor and the rivets. I can now flex the valve stem and clear the rivets …whereas before, any flexing of the valve stem would create interference between the FOBO sensor and the rivets.

Looking very closely, one can see loosening the axle bolt created about a 1/16" gap between the U-01210B-1 spacer and the WD-01230-1 wheel fork … just what I needed, the spacing washer was inserted into that gap.

1"x 1/16" washer fabricated to offset the nose wheel 1/16" to the right.

Photo of the nose wheel assembly with the washer in place. Now the wheel assembly is offset 1/16" to the right creating clearance between the FOBO sensor and the rivets that secure the U-00006E-L-1 mounting bracket.


The FOBO sensors appear to be working nicely and sensitive enough to track pressure differences caused by temperature changes …. in that, reported tire pressures are slightly higher during a hot afternoon compared to the cooler mornings. The FOBO App works great and if selected in the setup menu, can also sound an alarm on the device you are using should any tire pressure go beyond the user assigned normal operating range. Below is a photo showing what the FOBO App display looks like after a front wheel trike configuration was selected, sensors installed and pressure limits configured. If a tire’s pressure is out of range, the FOBO App will display a red background for the offending tire.

Photo of the FOBO App on my smart phone after installing the sensors and configuring desired parameters in the setup menu.


Thus far, I’m very pleased with the FOBO sensors … they appear to be accurate and the FOBO App is easy to install and configure. Time will tell if the sensor battery lasts to the one year point … hopefully it will so it can be routinely changed during the yearly condition inspection. At this point the FOBO sensor system appears to be a good option for those pilots who don’t want to remove the wheel pants just to make a tire pressure check. Moving forward, I’ll be sure to update this post if any issues develop with the FOBO sensors. Oh, at the time of this writing, the FOBO sensors cost around $49 per wheel.

Return from the future: 

The clearance that was created between the FOBO tire pressure sensor and the nose wheel fork proved to be not enough. As previously mentioned above, I had to press quite hard on the sensor to deflect the tire’s valve stem enough to contact the nose wheel fork assembly. After completing some high speed taxi testing and checking it appeared all was well.

Not so! Apparently, the centrifugal force created by the 5” nose wheel instantly ramping up from 0 to 25 or 30 MPH must be very significant. After shooting a couple of touch and go landings, I returned to the hangar and inspected the sensor and found, much to my amazement, there was evidence of contact with the nose wheel fork assembly … so the nose wheel sensor  was removed from the nose wheel.

Guess I will have to check the nose wheel pressure the old way from now on. At least the sensors are working well on the main gear and the main gear wheel fairings are much more time consuming to remove.