Wednesday, May 15, 2013

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.