Left Flaperon Skins Ready For Riveting

The A-1202A & B aft flaperon skins posed a unique challenge. Dimpling the top and bottom aft most rivet holes in the very narrow “V” of the skins required some creative thought because the dimple dies with the holes in them for a nail to be used with a hand rivet puller would not work. The nail could not be placed in the rivet hole because of its length interfering with the narrowness at the bottom of the “V”. Not wanting to relax the bend in the metal to gain access, another method was developed which proved to be a little time consuming, but ultimately worked well.

A #6 screw, nut and washers were used in conjunction with the dimple dies that have the holes in them to form the dimples. However, it first required a considerable amount of filing to custom fit the #6 screw to the dies. The tops of the threads on the screw required gentle filing with a diamond file … but just enough so the screw could barely slip into the dimple dies, this took a little time to get it right.

The filed #6 screw, nut and washers in place and ready to form a dimple.

                           Creating dimples in the hard to reach holes - pulling the dimple dies together

                           by tightening a filed #6 screw with a screwdriver while holding a wrench on the nut.

 Using the hand rivet puller to create dimples by pulling on a nail placed through the dimple dies.

Pealing off the protective film from along the rivet lines on one of the flaperon’s aft skin.

Smoothing the sharp edge on an aft flaperon skin with a file.

Aft flaperon skins Clecoed onto left flaperon skeleton and ready for riveting.

RV-12 Left Flaperon Skeleton Completed

Assembly of the left flaperon has progressed slowly mostly due to only having the opportunity to work in small snippets as of late. Then of course there is the DOG Aviation approach of making the simple complicated and time consuming … such as dimpling, priming, using solid rivets on skeleton components wherever possible, melting the plastic film away from rivet lines using a soldering iron, not to mention  smoothing the edges of parts that will never be seen.

With two exceptions, all the components that attach to the flaperon spar were attached using solid rivets in place of LP4-3 pop rivets. The assembly order of the components was also changed to facilitate the use of the pneumatic squeezer. Riveting the actuator bracket requires care because the rivets are VERY close to the actuator’s web. Suggest placing the factory head of the AN470AD4-6 rivets on the spar and forming the shop head on the actuator using a SMALL diameter rivet set … if a large rivet set is used, it will gouge into the actuator’s web because the clearance is very tight.

Riveting the flaperon’s actuator bracket onto the left flaperon spar with the pneumatic squeezer.

Riveting the inboard A-1205 aft rib onto the actuator/spar assembly with AN470AD4-6 rivets.

Riveting the inboard nose rib onto the left flaperon spar with AN470AD4-4 rivets.

The two pivot brackets were riveted onto the left flaperon spar using AN470AD4-4.5 rivets.

Counterbalance nose rib riveted onto left flaperon spar with AN470AD4-4 rivets.

 

The two locations that have a nose rib and aft rib sharing the same rivet holes in the flaperon spar proved problematic for the pneumatic squeezer … the far outboard rib location and at a point approximately one third in from the inboard edge of the flaperon. It was easy to set a solid rivet in the center hole of the outboard pair of ribs … however, the upper and lower holes proved problematic because the body of the squeezer was hitting the aft rib and not able to get directly square on the rivets so LP4-3 pop rivets were used.

 

To allow for a solid rivet to be set in the ribs at the point a third of a way in from the inboard portion of the flaperon, the aft A-1205 rib was flipped around so the direction of the web on the aft rib matched the direction of the A-1210R nose rib’s web. This allowed the pneumatic squeezer access to set a solid rivet in center rivet hole. Flipping the A-1205 rib poses no assembly problems because the rivet holes in the aft ribs are totally symmetrical.

One of the two locations where a solid rivet was set in the center rivet hole where a nose rib and aft rib share the same holes in the left flaperon spar … upper and lower holes have LP4-3 pop rivets.

 

                            Completed flaperon skeleton assembly with the exception of the counterbalance

                            which will be installed after the aft skins in the foreground are riveted in place.

Dimpling Of The Left Flaperon's Ribs

Once the match drilling the flaperon’s stainless steel counterbalance pipe and the   A-1204 & A-1210 nose ribs was completed, the components were disassembled for deburring and the nose ribs were dimpled for flush rivets using the dimple dies with the hole for a nail.

                                          Dimpling the flaperon’s nose ribs for flush rivets using the 120 degree
                                          dimple dies with holes for a nail to be pulled with a hand rivet puller.

The big burrs were removed from the stainless steel counterbalance pipe using a metal broom handle with an open end placed inside the stainless steel pipe to help scrape off all the burrs on the inside of the pipe … this was followed up by using a hand deburring tool.

Scraping burrs off the inside of the stainless steel pipe using the edge of an old metal broom handle.

Using a hand deburring tool to remove any left over burrs in the counterbalance.

Prior to riveting ribs onto the flaperon spars, there was a substantial amount of dimpling which needed to be finished up. The A-1205 aft ribs required dimpling and were dimpled using the “no hole” yoke on the pneumatic squeezer and the small female die with a hole in it stuck onto the yoke with tape. This method was used for dimpling all the holes except the very last top and bottom hole at the narrow aft end of the rib. These holes required using the C-clamp method to squeeze the dimple dies together to form the dimples.

Using a pneumatic squeezer to dimple the “easy” holes on the flaperon’s A-1205 aft ribs.

                     Setup for creating dimples in the tight spots on the A-1205 ribs using the C-clamp method. The head

                     of the nail goes from the outside through the male die and into the female die to hold alignment.

C-clamp in position and about to create a dimple in one of the tight aft holes on the A-1205 rib.

Flaperon Components Readied For Assembly

Having the left flaperon’s spar sitting on the bench along with the drawings, quite a bit of time was spent reviewing the assembly instructions and what, if any, impact would be created by dimpling the underlying components. Also under scrutiny, was accessibility for the pneumatic squeezer and the feasibility of attaching components to the flaperon’s spar using solid rivets.

The flaperon uses a stainless steel pipe as a counterbalance which is a familiar concept … Pete’s RV-9A ailerons incorporated the same method. The pipe is placed onto two nose ribs which have seats for the stainless steel pipe to rest on.  The assembly is temporarily covered with the A-1202C-L nose skin and there is a row of holes on the skin which will be used to match drill into the stainless steel pipe. Only two holes are drilled into the pipe at this time … they are the holes on the very inboard and outboard edge of the A-1201C-L skin.

A lesson learned on Pete’s airplane when drilling the round stainless pipe is that drill bits tended to walk big-time … plus the stainless pipe dulls drill bits rapidly so they need to be changed often or they will walk. The walking issue can be mostly eliminated by taking a couple interim steps ... first center punch the hole, then use a tiny drill bit to make a small crater in the stainless pipe at the center punch location. Follow this by drilling with a SHARP & LUBRICATED #40 drill bit all the way through the pipe. Once a #40 hole is in the pipe, the #30 drill bit will go through the pipe like butter.

Flaperon’s stainless steel counterballance pipe seated on outboard nose ribs and ready for drilling.

Match drilling the stainless steel flaperon counterbalance to the edge holes in the A-1201C outboard nose skin.

After a hole is drilled at each end of the stainless pipe, the A-1201C nose skin is removed so the holes in the stainless pipe can be deburred. The pipe is then rotated and the two freshly drilled holes will align with existing holes in the pipe’s “seat” on the nose ribs. At this point, if following Van’s plans, the pipe is to be riveted in place onto the nose ribs, then the nose skin goes back on and the whole row of holes on the A-1201C skin are match drilled into the stainless pipe.

Here is where DOG Aviation deviates temporarily from Van’s assembly instructions. Because access for riveting the flaperon’s internal ribs using the pneumatic squeezer has been deemed acceptable, the stainless pipe will be left off until all the ribs are riveted with solid rivets. There is just enough clearance to rivet the stainless pipe onto the nose ribs afterwards, using the close quarter hand rivet puller.  Why the change? That stainless pipe adds so much mass to the flimsy structure, that having the pipe riveted in place then repeatedly flip flopping the spar for rivet squeezer access would be a recipe for disaster. Trust me … when the counterbalance pipe is in place, the RV-12 builder will want to make certain the spar/pipe assembly is ALWAYS clamped to a bench. Mine almost slid off once while reviewing the assembly procedures and another builder on the forums had his fall off his workbench kinking the spar which subsequently required replacement.

There is one small problem to overcome … the stainless pipe also still needs to be match drilled to the row of holes on the nose skin. The pipe requires being in its permanent position as if it were riveted in place … so it was temporally secured into position with hardware so the A-1201C nose skin could be placed over the assembly for match drilling into the stainless pipe.

The stainless pipe temporally secured in its permanent position on the nose ribs with a screw and nut.

Once the stainless pipe was secured in position using a small nut and screw, the   A-1201C nose skin was placed back over the pipe/nose rib assembly so the holes in the nose skin could be used to match drill into the stainless pipe using the procedure described above.

Placing a center punch mark in the stainless pipe at the center point of the hole in the outboard nose skin.

                            Using a very small drill bit to make a tiny crater in the stainless pipe at the center punch

                             location … no need to drill all the way into the pipe all that is needed is a small crater.

                                            Using the small crater to help hold the position of the #40 drill bit,

                                            the hole is carefully drilled all the way into the stainless pipe.

The #30 drill bit will now go through the stainless pipe like butter without drifting.

Completed match drilling of #30 holes into the stainless steel counterbalance pipe.

While the outboard nose skin is still in place, both the nose ribs also require match drilling to the holes in the nose skin. The inboard nose skin was also set in place at this time and it’s nose ribs were match drilled as well.

Completed match drilling of left flaperon's inboard and outboard nose skins to nose ribs.

For a brief moment, countersinking the stainless steel pipe for flush rivets was pondered. Fortunately, some semblance of sanity returned and that idea was determined to be folly because when the flaperons are installed onto the wings, the nose of the flaperon is hidden from view underneath the overlap where the wing’s top skins extend aft of the rear spar.