Tuesday, December 18, 2018

Completing Service Bulletin 18-02-03

In addition to Service Bulletin 18-02-02 for the stabilator (recently completed), Van’s also released Service Bulletin 18-02-03 the very next day calling for an inspection of the anti-servo tabs that mount onto the stabilator. Service Bulletin 18-02-03 addresses potential cracking on the forward edge of anti-servo skins adjacent to the HS-1220-R & L control horns and between the spar and the control horn. This is another service bulletin that was introduced due to a very small number of RV-12’s developing cracks adjacent to the HS-1220 control horns. Fortunately, the DOG Aviation RV-12 did not have any cracks on the anti-servo tab skins … but decided to complete Service Bulletin 18-02-03 anyway, so there won’t be the need to mess with it later after the airplane is painted should a crack develop.
My finger is pointing to the area on the anti-servo tab skin that needs to be inspected for cracks.

Depending on the results of an inspection of the anti-servo tabs, Service Bulletin 18-02-03 will take the builder/owner on one of three paths:

1. - No cracks are discovered (that's good) fly on and reinspect during the next annual condition inspection.

2. - No cracks are discovered ... however, the builder/owner decides to go ahead and perform the steps in Service Bulletin 18-02-03 and just replace the inboard ribs to prevent cracks from forming.

3. - Cracks are found - This will involve not only replacing the inboard ribs on the anti-servo tabs and but also installing doublers to cover the cracks and strengthen the weak area.

Builders/ owners take note …. the DOG Aviation RV-12 was constructed using flush rivets, so you will see dimpled holes and flush rivets on the anti-servo tab’s skins and ribs in most of the photos in this post. Those of you using the photos found here as a general reference, please disregard the skin and rib dimples and the use of flush rivets attaching the skins to the ribs … your anti-servo tab’s will not be dimpled so you will be using the standard Van’s LP4-3 pop rivets that come with the service bulletin to secure the skins to the new ribs.

Performing the work on the service bulletin (via either path 2 or 3) involves removal of the HS-1222 inboard rib on each anti-servo tab (the rib that the HS-1220 control horns are riveted onto) and replacement with a new HS-1230 rib included with the service bulletin parts.  In addition to the two new HS-1230 ribs, Service Bulletin 18-02-03 also contains additional parts used to reinforce the anti-servo tabs if cracks are discovered … those parts are HS-1226A & HS-1226B (upper and lower doublers which come as one piece and require separating) and the HS-1228 spacer.

Parts included with Service Bulletin 18-02-03 consist of two HS-1230 ribs, HS-1226A upper doubler (on the left with the slot), HS-1226B lower doubler and the HS-1228 spacer.

Because the DOG Aviation RV-12 had no cracking on either anti-servo tab, the doublers will not be used …. however, the drawing and photo below shows where the parts will end up being installed if cracks are discovered.
Figure 7 from Service Bulletin 18-02-03 showing the placement of parts if cracks are discovered on the anti-servo tab skins.
This is how the parts will be installed should cracking be discovered on the anti-servo tab’s skins. The spacer bar will be installed between the anti-servo tab and the HS-1226B lower doubler.

So what does replacing the inboard ribs of each anti-servo tab accomplish? It makes the assembly much stronger and will greatly reduce skin flexing adjacent to where the control horn attaches to the anti-servo tab’s inboard ribs. By looking at the close-up below, one can clearly see that the original HS-1222 inboard rib ends just forward of the control horn leaving an open gap between it and the spar that allows the thin skin to flex between the HS-1222 rib and the spar. The HS-1230 replacement rib now goes all the way forward and has tabs which will be riveted to the anti-servo tab’s spar … which can be seen in the photo below on the far right in the photo below.
Side view close-up of the inboard portion of the left anti-servo tab. As one can clearly see, the HS-1222 rib that the control horn is riveted onto ends just forward of control horn leaving a large gap between it and the anti-servo tab’s spar on the far right.
The replacement HS-1230 rib sitting adjacent to the inboard side of the anti-servo tab … one can see it is longer and will extend further forward to the anti-servo tab’s spar. Also noteworthy, there are now two additional flanges on the HS-1230 rib that will be riveted onto the anti-servo tab’s spar. The new flange my finger is pointing towards to will be riveted to the anti-servo tab’s spar at the rivet location my other finger is pointing towards. Extending the rib forward to tie into the spar should eliminate the skin flexing.

Following the steps in the service bulletin, if no cracking is found, the builder/owner is instructed to skip to Step 4 which is the removal of eight rivets holding the HS-1222 inboard rib in place and two spar rivets. Step 5 instructs the builder/owner to drill out the rivets holding the HS-1220 control horn onto the HS-1222 rib.

I would strongly suggest reversing the order of Steps 4 & 5 because the offset of the HS-1220 control horn makes it very difficult to safely pound out the mandrels of the rivets adjacent to the control horn prior to drilling. For me it was much easier to carefully remove the rivets securing the HS-1220 control horns to the HS-1222 inboard rib first. Once the control horn was removed pounding out the mandrels in the rivets adjacent to the control horn was a piece of cake.

To remove the rivets from the HS-1220 control horns the center of each rivet was marked and then center punched followed by very carefully drilling a tiny lead hole. This was followed by using a #40 drill bit with tape on it to denote the depth I wanted to drill which was just shy of getting all the way through the rivet head. After drilling most of the way through the head a nail set was used to carefully pop the head of the rivet away from the HS-1220 control horn. The HS-1220 control will be reused and riveted onto the new HS-1230 rib … so once the HS-1220 control horns are removed, mark them and set them aside.
After a tiny lead hole was drilled into the center of each rivet, a #40 drill bit was covered with masking tape to denote the depth to drill … which was not quite all the way through the head of the rivet.
My finger is pointing to the right anti-servo tab’s HS-1220-R control horn removed from the anti-servo tab assembly. After removing both control horns from the anti-servo tabs mark them and set the control horns aside … they will be reused.

With the control horns removed, pounding out the rivet mandrels is now an easy task. After the mandrels were removed from the pop rivets, the rivets were removed using a #30 drill bit with a metal collar on it that only allowed the drill bit to go down just deep enough to almost go completely through the head of the rivets … but not quite. Then a nail set was used to remove the head of the rivets. After all the rivets are removed from the HS-1222 ribs, the ribs are removed … and discarded.
Carefully pounding out the mandrel from one of the rivets that would have been very difficult to access if the control horn were not removed first.
The original HS-1222 rib on the right will be replaced with the new HS-1230 rib on the left.
Here one can see a close up of the old HS-1222 rib on the right and the design of the new HS-1230 rib on the left. The new HS-1230 rib is longer and also has two flanges that will be riveted onto the anti-servo tab’s spar.

After removing the old HS-1222 ribs, the new HS-1230 ribs are inserted in each anti-servo tab and secured with Clecos. There are four rivet holes that need to be match drilled. Two holes on the aft end of the HS-1230 ribs (one on each side of the anti-servo tab). The remaining two holes will be drilled through the anti-servo tab’s spar into the flanges on the new HS-1230 ribs.
Using a #30 drill bit to match drill the anti-servo tab’s spar to the flange on the new HS-1230 rib.

After the four holes have been drilled, the HS-1230 rib is removed from the anti-servo tab and the freshly drilled holes were deburred. Preparations for the final assembly begin by securing the HS-1220 control horns onto the new HS-1230 ribs with Clecos … then riveting each HS-1220 control horn onto the new HS-1230 ribs using five AN426AD3-3.5 rivets.
The right HS-1220 control horn secured on the new HS-1230 rib with Clecos and ready for riveting.
Riveting a HS-1220 control horn onto one of the new HS-1230 ribs using AD426AD3-3.5 rivets.
Both HS-1220-L&R control horns riveted onto the new HS-1230 ribs and ready for final riveting onto the anti-servo tabs. Here again, disregard the dimples in the ribs ... they are unique to the DOG Aviation RV-12.

Final assembly is straight forward … insert each HS-1230 rib/ HS-1220 control horn assembly under the anti-servo tab’s skins and secure with Clecos. Eight rivets are used to rivet the skins to the ribs and two more rivets are used to rivet the spar to the flanges on the new HS-1230 ribs. The offset on the HS-1220 control horn does create a small access issue for the two rivets adjacent to it. The easiest way to get around the issue is to place a slight bend on the rivet’s mandrel with a pair of pliers and then use a small piece of AEX wedge slid over the rivet. Doing this will place the hand rivet puller at a small enough of an angle to clear the HS-1220 control horn and still allow the rivet to be kept square to the skin while the rivet is set. Long time readers of the DOG Aviation Blog have seen this method used before when setting rivets in tight spots.
Riveting the anti-servo tab’s skin to the new HS-1230 rib and HS-1220 control horn assembly using a pneumatic rivet puller. The pneumatic rivet puller can be used on all the rivets except the two adjacent to the HS-1220 control horn.
In this photo, one can see the PRG-26A close quarters hand rivet puller is outfitted with an AEX wedge between the rivet and the nose of the rivet puller. The use of a piece of AEX wedge as shown in this photo is a great way to access tight spots. The mandrel of the rivet is bent a little with pliers and the AEX wedge allows the rivet puller to be placed at a slight angle while pulling the rivet.
Completed Service Bulletin 18-02-03 (rib replacement only) … both anti-servo tabs now have the new HS-1230 ribs installed and are now ready to be placed back in service.

In the grand scheme of things, Service Bulletin 18-02-03 is not very time consuming and quite easy to accomplish. The only task that one really needs to perform as careful as possible is drilling out the HS-1220 control horn rivets … because one does not want the rivet holes to become elongated. As mentioned above, carefully mark and center punch the rivets, then drill a tiny lead hole #60 or smaller to minimize drill bit drift when drilling with the #40 drill bit.

Friday, December 7, 2018

Doing Service Bulletin 18-02-02 Part 3 of 3

Apologize for the long delay between posting Part 2 and Part 3. The weather made a drastic change with many days of rain followed by a quick temperature plunge and snow. Not being too keen on working in a cold damp hanger or dealing with the loud noise levels from rain hitting the all metal roof, I decided to wait out the rains and unseasonably cold daytime temps and wait for a day with more favorable temps to finish up … which took far longer than anticipated.

The two previous posts Part 1 & Part 2 covered the steps necessary to perform the needed modifications to the WD-1207 & WD-1208 stabilator horns and preparing the stabilator for the new hinge bracket assemblies and new HS-01231C hinge gussets. Here in Part 3, the steps used to complete the instillation of the new bearing bracket assemblies and  new hinge gussets to complete Service bulletin 18-02-02 will be covered.

As mentioned in Part 2, the decision was made to use all solid rivets for the three rivets that attach the HS-01231C stabilator hinge gussets onto the flanges of the inboard hinge bracket assembly. This involved a little more extra work than I anticipated but everything worked out quite well.

Assembly of the bearing brackets begins by bolting the outboard hinge bracelet assemblies to the stabilator. This is a final instillation so all new AN3-4A bolts were used because the bolts are being screwed into nutplates and every insertion wears the threads down a little. These bolts will likely never be removed again so figured bolts are cheap just may as well replace them with new hardware.

Because of my desire to install all AN470AD3-3.5 rivets in the flanges of the inboard bearing bracket, it becomes the sticky wicket during reassembly … in that, the inboard bearing bracket assemblies pose a problem for riveting because the bolts for the HS-1210 stabilator stops need to be removed along with the bolts for the bearing bracket mounting bolt for to allow access for the rivet squeezer’s yoke. (Note to fellow builders/owners … if not installing the aft AD470AD3-3. 5 rivets and using the LP4-3 rivet called out in the service bulletin, there will be no need to remove the bearing bracket mounting bolts during riveting). Guessing this is why Van’s instructs the builder/owner to use a pop rivet at this location. To save wear and tear on the nutplates, I decided to cheat a little and used short AN525-10R7 screws to temporarily hold the inboard bearing brackets for riveting).

As can be seen in the photo below, the inboard bracket assembly was mounted with the temporary use of AN525-10R7 washer head screws in lieu of the regular bolts. The HS-01231C hinge gusset was secured onto the stabilator with #30 Clecos and the inboard line of AN470AD3-3.5 rivets were set in place to assure positioning. A Cleco clamp was used to hold the HS-01231C hinge gusset firmly down on the flange of the inboard bearing bracket. Note the bearing stop bolt is in position and a standard nut was temporarily used to snug up the assembly to assure proper positioning during riveting.
The HS-01231C hinge gusset is secured to the stabilator with Clecos ready for final riveting. Note the AN525-10R7 washer head screw used temporarily to keep the inboard hinge bracket positioned during riveting. Also note the bolt for the hinge stop is also in position and temporarily snugged down with a standard #10 nut (not in view).

To accomplish the actual riveting, the pneumatic rivet squeezer was outfitted with the “no hole yoke”. I found during bench testing it offered more surface area than the standard yoke with a flat rivet set. There is not a lot of excess room to reach the aft most rivet so felt the “no hole” yoke was the best choice since there is one in the tool box. I also discovered the aft most rivet needed to be accessed from the front and not the side in order for the squeezer to be properly squared to the rivet head during riveting. The first step in the riveting process was to rivet the forward most AN470AD3-3.5 rivet as can be seen below.
Using the pneumatic rivet squeezer outfitted with a “no hole” yoke to set the forward most AN470AD3-3.5 rivet that attaches the HS-01231C hinge gusset to the flanges of the inboard bearing bracket assembly.

At this point, to gain access to the remaining two AN470AD3-3.5 rivets that need to be set, it is necessary to remove the bolt for the HS-1210 hinge stop and the bolt for the inboard hinge … which is why I used the short AN525 screw. (Actually, I had given this quite a bit of thought while waiting for the weather to improve and thought the much smaller head of the AN525 screw would allow access for riveting … not so, because the clearances are very tight. Even using the AN525washer head screws there was not enough clearance for the yoke of the rivet squeezer to access the rivet properly). With the hardware out of the way, the next rivet squeezed was the aft most AN470AD3-3.5 rivet.
Using the pneumatic rivet squeezer outfitted with a “no hole” yoke to set the aft most AN470AD3-3.5 rivet that attaches the HS-01231C hinge gusset to the flange of the inboard bearing bracket assembly. Also note the center rivet was left sitting in the hole to assure positioning just in case the HS-01231C hinge gusset tried moving a little … it didn’t.

The last AN470AD3-3.5 rivet set on the inboard flange was the center rivet. After setting the three AN470AD3-3.5 rivets on the inboard flange of the bearing bracket assembly, a new AN3-4A bolt was screwed into the bearing bracket assembly and torqued to specifications (20-25 inch pounds plus the running torque of the nutplate). At this point, the remaining #30 holes in the HS-01231C hinge gusset received pop rivets. Because flush rivets were used on the skins of the stabilator during the construction of the DOG Aviation RV-12, those rivet holes common to the stabilator skins received flush rivets and the remaining holes received the standard van’s LP4-3 low dome pop rivet. Most builders/owners can ignore the last comment because your RV-12’s used the LP4-3 rivets exclusively on the stabilator skins. When riveting of the HS-01231C hinge gusset is completed, the bolt that secures the HS-1210 hinge stop was final installed using a new AN365-1032 lock nut.

Gee this was just so much fun … let’s repeat the process again three more times for the remaining three HS-01231C hinge gussets that need to be installed.
Setting one of the five flush rivets in the HS-01231C hinge gusset. Note: These flush rivets are unique to the DOG Aviation RV-12 … most all other builders/owners will be using the standard Van’s LP4-3 rivets to secure the HS-01231C hinge gusset to the stabilator assembly.
Completed riveting of the two HS-01231C hinge gussets onto the top side of the stabilator … time to flip the stabilator over and begin riveting the other side.

After all four HS-01231C hinge gussets are riveted in place, the last remaining chore before the stabilator can be bolted back onto the RV-12’s tail cone is installing the WD-1207 & WD-1208 control horns onto the stabilator. Assembly is straight forward, in that, each control horn is first bolted in place and then the HS-1232 stabilator horn doubler is riveted to the HS-1211 spar cap. Once bolted, the position of the control horns won’t change … so prior to bolting the WD-1207 & WD-1208 control horns all the LP4-3 rivets were placed in the HS-01232 stabilator horn doubler but not set. With all the LP4-3 rivets sitting in place on the HS-01232 stabilator horn doubler, four new AN3-4 bolts were installed to secure each control horn to the stabilator spar box. This is followed by setting all the rivets securing each HS-01232 stabilator horn doubler to the HS-1211 spar cap which completes the service bulletin.
Using a torque wrench to final torque of the AN3-4A bolt that attaches the WD-1208 stabilator horn to the stabilator spar box. Note all the LP4-3 rivets are sitting in the HS-01232 stabilator horn doubler prior to tightening the four bolts that secure the stabilator horn to the spar box.
Using a hand rivet puller to rivet the HS-1232 stabilator horn doubler /WD-1208 stabilator horn assembly to the stabilator spar cap.
Completed riveting of the HS-1232 stabilator horn doubler /WD-1208 stabilator horn assembly to the stabilator’s spar cap.

If the instructions in the service bulletin are followed correctly, you will find yourself with four leftover AN960-10L washers. This is because the original plans called for an AN960-10 washer to be placed under the heads of each of the four bolts that secure the four HS-1210 hinge stops and an AN960-10L washer under each of the four AN365-1032 nuts. Following the service bulletin, during reassembly the AN960-10 washers that were under the head of the bolt are moved to under the nut and the thin washers are NOT reinstalled.  I’m guessing due to the extra thickness of the two thin HS-01231B brackets installed during the service bulletin Van’s decided it was cheaper to eliminate the thin washers as opposed to requiring longer bolts.
The two bolts the arrows are pointing to will not be reassembled with washers under the head of the bolts. (The same applies to the other hinge bracket assembly not in view). Instead, the AN960-10 washers that used to be under the bolt heads are moved to under the AN365-1032 nuts. The thin AN960-10L washers (which used to be under the AN365-1032 nuts) sitting on the table are NOT reinstalled.
Completed Service Bulletin 18-02-02 on the stabilator assembly ready for reattachment no the RV-12’s tail cone. After completing the entire service bulletin decided it may be a good idea to place a dollop of torque seal on the heads of all the bolts and nuts.

Bolting the stabilator back on the RV-12’s tail cone was NOT a piece of cake it requires lots of patience. It was hard to do the first time during the initial build … but with the addition of the box around the hinge bracket, it increases the level of difficulty. In full disclosure, I did not crazy glue the washers in place first … because others have reported they tend to fall off anyway, so I figured why bother and used a thin metal ruler with masking tape to hold the washers during insertion between the bearing bracket and bearing. What helped out the most after fighting with it for quite some time and ultimately ended up being a workable solution was to forget about the washers at first and just get the stabilator aligned enough so the bolts to go through the bearings. Then once both bolts are inserted, pull back one bolt and insert the necessary washers as the bolt is being reinserted … then do the same to the other side.

Unfortunately, I will likely need to remove the stabilator again in the spring for painting. My plan is to use the two old AN4-12A bolts and grind down the threaded area on the bolts to form a slight taper so the bolts will help self-align the parts as the tapered bolts are being inserted. Will likely also remove a little material (not much) from the shank of the bolt so it will be easier to slide then in and out of the bearing brackets and bearings. Once these bolts are used to “pin” the stabilator in place … then they can then be removed one at a time so the actual threaded AN4-12A bolt and appropriate washers can be inserted.

As mentioned in Part 1, the upper and lower stabilator cables were removed from the stabilator horns without loosening the adjusting barrels. So to aid in reinstalling the stabilator cables, I made a tool out of a piece of scrap aluminum and cut out a slot with a rounded bottom. A hole was drilled near the end of the piece of scrap metal so a used bolt and nut could be attached to make it easier to pull on the tool. Just place the tool over the cable and pull back so the bolts can be reinserted.
A scrap piece of bent aluminum with a slot cut in it with a rounded bottom will hold the stabilator cable while it is being pulled taunt so the cables can be reinstalled on the stabilator’s horns.
The homemade cable pulling tool in place on the upper stabilator cable for a proof of concept test. All was well but the tool was tweaked a little to remove sharp edges and allow it to capture the cable just a little further aft.

In summary, Service Bulletin 18-02-02 requires a lot of time to install … it is NOT a 2 hour job. If one wants to take the extra time, it is possible to not drill into the HS-1211 spar cap when match drilling the WD-1207 & WD-1208 stabilator horns to the HS-01232 stabilator horn doublers. It is also possible to use all AN470AD3-3.5 rivets on the inboard line of rivets securing the HS-01231C hinge gussets to the inboard hinge brackets for a more uniform look. Oh, I have not installed the upper & lower tail cone fairings yet, but be aware they will require a small amount of trimming to make room for the HS-01231C hinge gussets … so fellow builders/owners make it a point to check that after completing Service Bulletin 18-02-02.