Time was spent in the shop Thursday not so much for doing RV-12 assembly, but taking care of lose ends and solving a troubling dimple dilemma that required resolution prior to wing tip closeout taking place.
One lose end was the fit of the landing light
mounting ribs. I believe in a previous post, it was mentioned that the wing skin
tended to pull in a little when securing the landing light ribs to the wing
using Clecos … this was because there was a small gap between the landing light mounting ribs and the wing skin. It was not too bad, but bothered me for I would prefer
not having the airfoil being distorted at all, if it can be helped. The issue was resolved more to my liking by playing with
both landing light ribs until a uniform gap was obtained. Then shims were made
out of 2024-T3 aluminum .050” thick to close the gap between the ribs and the
skins. Once the shims were drilled and dimpled, they were primed and are now
ready to install. The rivet holes in the W-1203L outboard skin for mounting the
landing light ribs were then dimpled. The landing light components are now ready
for the landing light to finally be permanently mounted.
The next task was dimpling the most challanging component of the build ... the wing tip ribs. The effort to dimple for flush rivets
on the RV-12's outer skins has thus far been, for the most part, a piece of cake … time consuming to be sure, but not difficult. However, the wing tip ribs posed a huge challenge and required an unconventional solution. Yes, there have been a few
tight spots requiring creativity such as the C-Clamp method. Last Fall when I was
fighting to stay ahead of the cold temperatures and priming the components
for both wings, I could tell just by looking at the W-1204E & W-1204F forward and aft
wing tip ribs that they were going to be … challenging. Because time was tight, I elected
to forge ahead and primed the parts figuring a solution to the problem could be
worked out eventually. I’m happy to report to other RV-12 builders willing to
take on the challenge of dimpling their RV-12 project, that even the wing’s tip
ribs can be successfully dimpled without the need to deform the metal to gain
Over the last couple of months, the DOG Aviation
think tank had been using the few working brain cells remaining to analyze
different scenarios that could possibly be used to complete the dimpling of the
two outer wing tip ribs. The tip ribs are the termination point for the wing's upper and lower tip skins. Each
of the tip ribs are shaped differently and as such, required a different
approach for successful dimpling. The method of using a nail, with
the special dimple dies that have holes drilled in them for a hand rivet puller
would not work ... just not enough clearance for a long nail to
be placed into the rivet hole. Yes, I
could have used the C-clamp method I came up with (and successfully used
previously), but there were lots of holes to do and I really only want to use
that method when there is no better options … because the dies tend to rotate
as the clamp is tightened, which is not good on the primer or metal. So for me,
that approach is a last resort method.
Thinking outside the box – dimpling of the W-1204E
& F ribs. Because a lot of thought went into to the problem, the creative dimpling solutions
utilized for each rib worked almost flawlessly. One side of the W-1204E-L rib could be done with the pneumatic squeezer as usual, but the angle of the other side prevented access. For dimpling the one side where conventional
squeezing would not work, a “no hole” yoke (a type of yoke with no hole that acts as
the rivet set and compresses the rivet directly) in the pneumatic squeezer. The
“no hole” yoke has a thin nose which fortunately barely fit into the area being dimpled along
with a female dimple die.
Tape was used “stick” the female die onto the no
hole yoke on the pneumatic squeezer.
The yoke pulled in on the female dimple die from
behind as the pneumatic squeezer ram outfitted with the male dimple die pushed
into the metal being dimpled from the front. The point of the male die holds
alignment because it slips into the female die when the dies are squeezed
together as the dimple is formed. Plus, the tape once compressed from the first
squeeze held the female die in place and it never fell off during the dimpling
of the remaining holes.
The W-1204F-L tip rib was the huge challenge because it
has a very narrow channel so there is little space to work with. To give the
readers an idea of the clearance, it is tight for a finger and if a pop rivet
were placed in the upper and lower holes they will touch one another. Here
again, the C-clamp method could have been utilized, but the dies tend to twist
as the C-clamp is tightened and will remove primer … plus, there are lots and
lots of holes so a better way was required. Because the upper and lower holes
are aligned, it presented a unique opportunity which played a large role in the
Thinking way way way way outside the box
resulted in the crown jewel of the project to date … as far as creative tool usage
goes. (I’m still patting myself on the back for coming up with this idea.) Taking the adage from one of the recent
AT&T TV ads where “more is better” the DOG Aviation think tank applied that
to dimpling the W-1204F-L wing tip rib by using TWO female dies back to back INSIDE
the rib’s channel and placing a “carefully crafted” nail through the dies to
hold centering. A standard yoke was used WITHOUT a rivet set so the alignment nail
went up into the yoke's hole as the male dimple die penetrated the metal being
dimpled. The head of the nail was first ground down to allow it to pass into
the hole where rivet sets would normally be attached to the yoke … yet enough of the nail head was left so it would not pass
through the holes in the rib and would also keep a washer in place. The length of the
nail proved to be some what critical … it had to be long enough to keep the
parts together yet allow the yoke to be positioned in place. Once the yoke's hole was positioned over the nail, a finger nail was used to push the nail alignement pin up
into the hole in the yoke clearing the way for the male dimple die on the
pneumatic squeezer to slide into one of the female dies inside the rib's channel.
This initial setup worked well for setting
dimples in the W-1204F aft wing tip rib, but needed refinement … the tape made
it difficult to remove the dies after the dimples on both sides were set.
Because the rib was actually squeezed from the
outer sides, a washer was placed on the nail for the yoke to push against, thus preventing
marring the outside surface of the rib as the male dimple die attached to the pneumatic squeezer's ram compressed
the opposite side of the rib into the female die. The two female dies inside the channel of the W-1204F-L wing tip rib
were almost a perfect fit … but still a little loose, so one washer was used to
take up the additional space so the rib would not deform while the dimples were
The beauty of this idea was, once the first hole was dimpled,
the nail was removed and then slid in from the other side so the opposite side
could then be dimpled without the need to reposition the dies. Brillant! This idea worked great because both
the female dies were positioned facing towards the outside. It was a joyous moment at DOG
Aviation when it actually worked as envisioned!
The components used to set the dimples in both
sides of the W-1204F-L wing tip rib.
The first two side to side dimples were made with the two
female dies stuck together with tape as depicted in picture two photos
previous. At the time, this seemed like a good idea for easy install/removal of
the dies. However, once both female dies contained dimples, pulling the dies out together proved to be
problematic without flexing the metal.
So a slight procedural modification was made which worked out perfectly.
Basically, the washer taking up the gap was moved in-between the two female
dies so after each side of the rib was dimpled, the washer was removed allowing
the dies to be easily removed one at a time. This method worked great!!!!! …
And did not mar the Akzo primer, so that method was proudly used with much glee for all
the remaining dimples.
The final setup used to set all but the first
two dimples in the W-1204F aft wing tip rib. Two female dies placed back to
back inside the W-1204F-L wing tip rib with a washer placed between them for
spacing and easy die removal!
Setting dimples into the W-1204F-L aft wing tip
rib with the pneumatic squeezer using the previously described setup.
Think it is finally time to actually begin
closing out the wing tip!