Horizontal Stabilizer Installed – What Worked – What Didn’t

The Rotax 912 engine needs to come out of the box very soon … prior to installing the engine, the carburetors and intake manifold need removing in order to install the FF-1207 fiberglass cooling shroud. I would prefer doing that work on a work bench but the second workbench has the horizontal stabilator sitting on it. So prior to digging into the engine, wanted to get a couple of tasks completed. First, I plan to paint the FF-1207 fiberglass cooling shroud prior to installing it. However, the fiberglass was really rough and porous, so a mixture of epoxy resin was thinned with Acetone and slathered onto the cooling shroud to soak into all the nooks and crannies … this will create a much smoother surface for the paint and hopefully better visual appeal. After the shroud was coated with the thinned resin, it was placed into the hot box to cure. Now it has dried and is looking for the most part, very smooth … so thinning the epoxy with Acetone worked great for getting rid of all the roughness.

After a mixture of epoxy resin was thinned with Acetone, it was slathered onto the FF-1207 cooling shroud to fill in all the roughness of the glass weave.

Second, and more importantly, I need a workbench freed up so the engine can be placed on a sturdy surface while working on it, as opposed to working on the floor … and that meant installing the horizontal stabilator to free up the workbench it is sitting on.  The plan: Tilt the tail cone down to meet with the level of the horizontal stabilator, roll the workbench into position and bolt it up. I told Bernie about my plan to make a wooden block with a V notch so the front tire would not roll and then place wood underneath it to lift the wheel and drop the tail cone so I could keep the stabilator on the workbench and only need one helper. Bernie came up with the great suggestion of using a cement block he had and letting the wheel sit in one of the holes. This worked great to meet my low workbench … in fact, had to also add one piece of 3/8" plywood under the block to get it perfect.

The nose wheel placed in the hole of a cement block to lower the tail cone worked perfectly. Thanks for the idea Bernie.

Tail cone lowered to meet with the level of the horizontal stabilator sitting on the workbench.

So far so good … next the long counterweight arm was slid into the sockets on stabilator and bolted in place. This makes the stabilator want to roll from all the weight and from this point on things became a challenge and an exercise of patience. The workbench was rolled forward until it almost touched the tail cone and the stabilator was slid forward and aligned with the bearings as best as possible.

Now for what did not work. I was hoping there would be enough access to install the bolts and washers from up above. This is where the wheels fell off and that proved to be pure folly because there is not much room to work yet alone see while bent over the top of the horizontal stabilator. At one point I climbed up onto the workbench and although the view was better it was truly difficult to even get the bolt started yet alone worrying about the washers. Finally got a bolt through the bearing on the left side without any washers just to hold positioning.

Getting back on track, it was determined the task would be far easier to complete if done from below, so with a bolt holding positioning on the left side I commandeered Mike’s creeper from the hangar next door (thanks Mike T.) and accessed the situation from bellow. Seemingly there was more room when Mike K. rotated the stabilator a little and held it so I was able to easily get a bolt fed through the inboard washer. To hold the washers, a wooden pop sickle stick was filed to have a curve on the end that matched the washer, then masking tape was used to adhere the washer onto the stick. From below the view was better and could see to easily get to the bolt in the hole, then using the pop sickle stick, placed the washer in position and slid the bolt through the washer and ultimately into the bearing when Mike K. gently moved the assembly around. I had not glued the outboard washers as suggested in the plans but found that using the stick to hold the washers the outboard washers were easily slipped into position … however a thin strip of metal was needed to push on the edge of the washers to position them correctly so the bolt would capture them.

Having the bolt and washers for the right side bearing in place, it was determined that repositioning the workbench only underneath the left side of the stabilator would give me more room to work on the bolt and washers for that side. Mike moved the stabilator until a neutral point was found that allowed me to remove the bolt that was temporarily slid through the bearing to hold position. The pop sickle stick trick was employed again and with a little patience the bolt and washers were in place. For those builders interested in the washers used … the inboard washers ended up being AN960-416 and the outboard washers were AN960-416L.

A proud moment - the horizontal stabilator is finally installed. Could not have done it without Mike K.’s help. Thanks Mike!

To finish off the horizontal stabilator instillation the anti-servo tabs were installed. The hinges need to have 3/4" of the end bent to 90 degrees … this is so the hinge pins can be safety wired onto the stabilator.

Using a seeming tool to bend the end of the anti-servo tab hinge pins to 90 degrees.

Installed the left anti-servo tab first and while installing the right side, discovered the hinge pin needs to be installed from the bottom. The hinge pin for the first anti-servo tab installed can be inserted from the top or bottom … however, which ever anti-servo tab is installed last the hinge pin needs to be inserted from the bottom. Ask me how I know.

Installing the hinge pin for the left anti-servo tab.

Installing the hinge pin for the right anti-servo tab - tghis needed to be done from below by deflecting the anti servo tab up to get clearance.

Completed tail feathers for DOG Aviation RV-12.

The Eagle Grows Two More Feathers!

Late yesterday evening the AN470AD4-4.5 rivets I have been waiting for to complete the anti-servo tabs arrived. It appears as though DOG Aviation must be located near the end of the UPS route because deliveries rarely arrive prior to 5 PM. With rivets in hand this morning work began on riveting the hinges for the left and right anti-servo tab spars.

                                 The 4.5 rivets are the perfect length as one can see by looking at the rivet gauge.

To accommodate using solid rivets on the hinge, the assembly order was changed slightly. The bottom skin was not riveted to the internal ribs until after the hinge was riveted to the lower skin/spar assembly using a longeron yoke on the pneumatic squeezer.

                             Using the pneumatic squeezer to rivet the hinge to the anti-servo tab’s skin and spar.
                            The solid rivets look great! To bad they won’t be seen.

Once the hinges were riveted to both the left and right anti-servo tabs, the lower skin of each anti-servo tab was then riveted to the ribs using the flush rivets I’ve been using on all the external skins in place of the LP4-3 dome rivets.

                    Riveting the lower anti-servo tab skin to the ribs with flush rivets using the pneumatic rivet puller.

Once both left and right anti-servo tab skins were riveted to the ribs, the upper skin to spar joint was riveted with LP4-3 rivets finalizing the rivets on the anti-servo tabs.

                       To prevent the skin from lifting away from the spar at the outer edge of the spar during riveting,
                               a Cleco clamp is used to hold the skin tight to the spar when setting the first rivet.

                Using the pneumatic rivet puller to pop the last row of rivets that will finalize the anti-servo tabs.

                                                                Two more finished RV-12 tail feathers!

Drilling the AST Hinges - The First Oops

Before it got really hot outside decided to get an early morning start on the project. The next items to work on were the two hinges that will attach the left and right anti-servo tabs to the stabilator. The hinges were cut to size yesterday and needed to be drilled. Van’s provides a drilling template which is placed between the piano hinge eyelets … the template has holes in it for drilling evenly spaced holes.

                                                The drilling template installed on the hinge ready for drilling.

If one looks at the template above closely you can see there are two rows of holes …only one of which gets drilled … the bottom row. I was going to place tape over the upper holes NOT to be drilled, but first wanted to show the entire template in the photo. Needless to say, after taking the photo I forgot to install the DO NOT DRILL HERE tape and in my early morning grogginess and lack of enough coffee to be fully awake, I began happily drilling away. My happiness soon turned into sorrow when I realized I never taped off the holes that are NOT to be drilled. Oh well, a new hinge is on the way.

                                                         Drilling the anti-servo tab hinges using a template.

                                      You can see the two oops holes if you look at the upper hinge in the photo.

Oops … drilled more holes than I want to admit. After the fact, blue tape was placed over the holes not to be drilled.

                                The three finished hinge pieces – the fourth is in the mail. That is a lot of drilling.

Not to be deterred, work progressed to deburring the edges of all the components that make up the anti-servo tabs with the 1” Scotch-brite wheel.

                                               Deburring an anti-servo tab spar with the 1” Scotch-brite wheel.

After all the parts were deburred all the ribs and the two anti-servo skins were dimpled for accepting flush rivets.

                                                            Dimpling one of the anti-servo tab skins.

                                                                Dimpling the ribs of the anti-servo tabs.

Preparing AST Hinges

With temperatures hovering just under 100 degrees with a fair amount of humidity and it being a Holiday, not much RV-12 production was accomplished at DOG Aviation today. That said, the plans were perused to get an idea of upcoming tasks and a little time was spent researching where solid rivets can be installed in the place of the LP-4 blind (pop) rivets. There was only one part that was actually worked on today and that was the hinges for mounting the anti-servo tabs.

The anti-servo tab hinges are made from two aluminum piano hinges which come in the kit as a 36” long hinge. The hinge wire is pulled out of both hinges and then all 4 pieces are cut down to 32 1/2" long.

                                                               Marking the cut line on the hinge pieces.

                                                                    Cutting the hinges on the band saw.

After the pieces were cut to the proper length, they were filed smooth and a slight radius put on the edges. The next step will be to use a drill guide supplied by Van’s to drill holes into the hinge material. The drill guide ensures the holes to be drilled are at the proper locations so they will match up with the pre-drilled holes in the anti-servo tab skin they get riveted onto during final assembly.

Jumping Ahead To The Anti-Servo Tabs

In an effort to have more parts to prime, decided it best to jump ahead in the plans and begin working on the anti-servo tabs. Because Van’s designed the RV-12 to use a stabilator (which means the horizontal stabilizer and elevator are one unit or essentially a flying tail), the anti-servo tabs are used for trim control or another way of saying it … pitch adjustment. There is a left and right servo tab and they will be attached to the stabilator (which is not assembled yet) .

The anti-servo skins come with metal tabs at each end that are cut off per the plans. (I’m guessing the tabs were used to hold the position of the material during CNC machining). After using a pair of tin snips to cut the tabs off, a file is used to remove any excess material until the edge is smooth.

The remnants of the tabs that were cut off will be filed down to make a smooth edge.

The ribs used in both the left and right anti-servo tabs are all the same. Because some ribs are faced inboard and others outboard, the holes nearest the trailing edge (thinnest) need to be matched drilled. The reason for this step is because Van’s offset the holes at the narrow end of the skins so the rivets there won’t interfere with one another. To make the ribs universal, Van’s has two small pilot holes drilled at the narrow end of the ribs on both sides. This allows the ribs to be installed either facing inboard or outboard in either the left or right servo tab … once installed, the appropriate pilot hole gets drilled out.

 The offset in the rivet holes at the narrow end of the skin can be seen along with the two pilot holes in the rib.

If the above photo is enlarged, one can clearly see the two pilot holes at the narrow end of the ribs along with the offset of the holes drilled into the skin.

                                                  Match drilling the trailing edge holes on the anti-servo tabs.

The two control horns were the next items that required a little TLC. After separating the left and right control horns from each other, the five rivet holes in each that will attach them to the anti-servo tab needed  to be countersunk.

                                 Fortunately the countersink cage was still set correctly from the last time
                                 it was used so countersinking all the holes was quick and easy.

                                       Countersunk control horns … looking closely, you can see how a rivet
                                      sets flush in the front center hole of the control horn on the right .