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.
