Not too long ago I had my first formal inspection of tail and wings components. In Canada an inspector
needs to examine both sides of virtually all rivets and surfaces. What this means to the builder is that
very few components can be completely closed up prior to the inspection. In the case of the RV7A tail
and wings, the only pieces I could install all the rivets on were the flaps. It has been a long time coming
to finish those last few rivets off in a lot of pieces. As a result, the leading edges of the rudder and
elevators were not completed until now. I was determined to come up with a method that would
require no hand tweaking and yet result in a reasonable outcome.
What follows is a method that worked for me, it is in reality only slightly different than the supplied
instructions, but for me made a significant difference. My goal was to come up with a method that would
work on each leading edge section of the rudder and elevators. What I was looking for was no creases
next to the forward spars of each and a flat seam. I also didn't want excessive forces on the rolled
pieces in order to install the rivets or have to use hand tweaking which can lead to some ripples in the
skin if not done just right.
- Inside surfaces were taped to protect from scratches (ok ok, this is optional), Gorilla brand duct
tape sticks very well, you can see the first piece of tape installed sticky side up on what is the top
skin of the outboard section on one of the elevators. - A length of 3/4" water pipe (about 1" in outside diameter is taped to the leading edge as per the
instructions, the top skin is rolled first. - This is where my method changes a bit, roll the edge while maintaining downward force so that piece
being rolled does not lift off the bench at the spar, but ONLY roll it about 30 to 40 degrees up. - A slightly smaller water pipe is used next (1/2" water pipe, which is about 3/4" outside diameter).
This pipe is partially wrapped in masking tape (again, optional to help prevent scratches). It is
clamped to the bench such that it just touches the spar the entire length of the section being rolled.
I used a piece of 3/4" plywood with a 3/4" hole cut in it, then cut in half to make it easy to clamp
the round pipe at the edge of the bench.
- Using a block of wood, piece of angle, or anything that won't slip easily but is quite stiff,
slowing and in small increments, bend the edge the remaining amount, 5 to 10 degrees past vertical. - The finished bend of the top surface with the the water pipe still installed.
- The result after removing the water pipe is seen here.
- Flip the control surface over and apply the duct tape to the outboard bottom skin section.
- Using the larger pipe, the edge is rolled again to only 30 to 40 degrees up.
- The large pipe is then removed leaving the partial bend near the forward edge.
- Clamp the smaller pipe just against the spar close to the edge of the bench.
- Bend the bottom skin edge up in the same method as before as much as possible limited by
hitting the previously bent upper skin. It will end up about 20 to 30 degrees short of where
it needs to be when done.
- I then used a plastic sheet (actually a thin flexible cutting board from the aviation
aisle of the dollar store), to help get the bottom skin under the top skin. - The final bending of the bottom skin is then done using a piece of angle wrapped in
duct tape so it doesn't slip (or scratch) the skins. - The bent skins sit very close to their final position even without clecos or rivets.
- The end result after the pulled rivets were installed.
Some hints:
- Go slow when bending, do a small amount of bend at a time while applying
constant pressure along the entire segment. - Do one segment at a time starting at the top of the rudder or outboard edges
of the elevators, it is way too difficult to get a good result when doing the whole
length at once in my opinion. - Make sure the smaller pipe is well clamped so you can use your hip to really
lean into the work when doing the longer segments. - Use something that is almost as long or even slightly longer, then the segment
you are bending as the hand-held bending break. If you use something shorter, you
will stretch the skin in the wrong direction resulting in ripples along the edge. Yes,
you really have to lean into it on the longer segments, hence the previous comment. - I used 1/4" diameter holes in the large pipe (8 around the diameter should be
enough, 4 makes it more difficult to hold the pipe down to the bench while doing
the bending). The holes were also offset left to right on opposite sides around the
diameter so that the 1/4" diameter screw driver shats wouldn't poke through the
pipe and damage the skins.
(i.e. the leading edge and the spar) which are not parallel, is to better approximate
an ideal curve given the fact the rolled segments vary in both height and length from
one end to the other of each control surface.
This is not meant to be new how-to, it is simply the way I got the job done, I'm
sure there are many ways to get a good result.
While there are still a few tasks remaining on the tail and wings, I'm deferring them
until later and with the above tasks out of the way, and with the closing up of most
other pieces, I'm officially moving on to the fuselage!
