Once I made the 20 wing rear ribs, I moved on with the rudder construction.
This is a good idea considering that the rudder is made of a few parts,
and that there is a wide variety in those parts. For instance; there
are rounded parts (tip rib and nose ribs), straight formed parts (RR1,
RR2, RR3, RR4), bent parts (spar and spar doublers), formed skins and thick
metal (1/8" sheet rudder horn and extrusions for bearings). Additionally,
the rudder is tapered, bringing another level of complexity to the job.
to do it my myself may be questionable, as I had to
remanufacture most of the parts several times before getting good quality
components. But I was fortunate to have support from my advisor who gave
me advice and inspected my parts. Without such support, I would
strongly recommend attending the Zenair or Flypass workshop.
||Making the form block
When building from scratch, we have to make the parts ourselves.
Some can be formed using a bending brake while others must be formed with
a hammer... For those parts, a form block must be made.
Once a template is drawn (I used MS-Word for that---no CAD software
available for me and I am really bad of drawing manually), I transferred
it to a piece of hard wood (here, I am using oak). The piece must
then be cut. There is a 10 degree angle on the side flanges to compensate
for springback when we form aluminum.
To be precise, the blank is filed down to the line instead of directly
cut (the cut is about 1/16" larger than required. A 1/8" radius is
also filed to avoid cracks in aluminum.
On my project, I was very fortunate to have most form blocs already made.
Fernand Levesque, a previous builder, graciously lent me his blocs.
Only a couple have been made by me.
||Hammering down the flange
Once I have a block, I can make a rib blank. A 19mm line is drawn
around the bloc on a piece of aluminum (on a flat table, of course).
Then, with a desired 4mm line at the tip of the rib, I join the 19mm line
with the 4 mm line where the tangent makes it a nice cut.
The blank must then be filed and smooth (I used 220 and 320 grit aluminum-oxide sand paper) before it is installed in the vise.
the picture, we see the backing piece which is cut more rapidly than the
forming block itself. The rib blank is positioned between the forming
bloc and that backing piece.
I used a plastic dead bolt hammer and a soldering bar to form the rib
flange. For the final touch on the tip of the rib, I also used a
small round head hammer.
||Taking it out of the mold
It is far from being a nice rib when we take it out... in fact, a bit
more work is required to make it straight (now, it is more like a banana).
Using flutting pliers, we can create flutes at strategic locations to straighten
the part. Once this was accomplished, I looked at the angle at the
tip (the desired angle is 15 degrees for this part). I had to adjust.
||Finally! An airplane part is made...
I must admit... I did not start with the easy stuff (Only one among
these parts part is required). I did it four times. The difficulty is
in forming the tip. The curve is quite pronounced and I initially
had difficulty in shrinking the metal and avoiding any damage.
damaging the part, make sure the flange at the tip is no more than 4mm.
Also, make sure you are not tired when forming (we all make mistakes!).
Finally, take slow! Hammering too fast or too hard will create
waves or even cracks that cannot be removed.
It is a good idea to have an expert look at your part before you put
it on the airplane. One of the difficulties for me was to determine
"what is good quality". What is a scratch? What is a nick?
What the correct radius? Etc. etc...
So.. early in the morning, about at the same time birds wake up, I had
this gentleman inspect my rib. Fernand Levesque also looked
at it later, before assembling.
||That was one of many...
A similar process should be followed for the other parts. Those
on this picture are a bit simpler because there are no curves in the part.
Therefore, there are no flutes (except for RR1 which bent a bit while forming).
||Making the spar
The spar is made of 0.025" 6061-T6 aluminum. It was bent with my
8 foot bending brake. The first time I made it, I forgot to account
for bend allowance. This resulted in a fat spar about 3mm woo wide.
This is why we see a spar blank beside the formed spar on the left.
||Making the spar, part deux
Once the spar is formed, we must make the spar doublers. The complexity
here is that the angle of the spar is not the same at the bottom and at
the top (this applies to the previous step as well). The flanges bend 5.5 degrees inside, at the bottom and 3.5 degrees at the top of
the spar (4.2 degrees at the top of the doublers).
||Making the spar , part trois
This is the fun part... after the components are primed, I assembled
them with clecoes and riveted them together with A4 rivets.
Priming involves a few activities: sanding with Scotch-Brite (3M), cleaning
with a lacquer thinner and applying a primer. The one I utilized
is a Zinc Chromate replacement from Canadian Tire (a local hardware store).
||A sense of accomplishment!
The feeling of completing an assembly is great! I look forward
to see what feeling I will get once I complete the rudder.
||Making the rear skin
On this picture, I am marking the rivet pitch. This was done after
I traced the contour of the ribs inside the skin. The next step is
to pre-drill the skin at the marked rivet pitch.
Not shown is the forming process for the rear skin. I started
by bending the skin to about 110 degrees on my bending brake. To
complete the bend, I positioned the skin on the floor with a radiused 1/4"
radiused masonite sheet inside. My wife was standing on the masonite
sheet to hold it in place while I was pushing on the top skin with a 2"X4".
Finally, I jumped on the 2"X4" in a precise pattern :) to complete
||Pre-drilling the other side
The holes are copied on the other side by drilling through the pre-drilled
holes directly into the table. The skin is also clecoed to the table
with smaller clecoes during that process (#040 drill bit is utilized).
||Getting disappointed real fast :(
Once the skin was pre-drilled, I drilled and clecoed it to the skeleton.
Following my adviser's advise, I decided to cut the skin only once it was assembled. This
was to make sure the cut is precise according with
the final measurements of the rudder. I started with a rough cut
of the bottom of the rudder... yikes! Being too tired for the task,
I cut too far inside the rudder and so had to look at different alternatives
to repair this mistake.
For a more detailed picture of my mistake, click here.
Some of you may have noticed that the 1"X2" block is not on the correct side. I did not assembled the rudder like this... I
had turned the rudder
over for inspection before taking the picture.
||After a sleepless night
While it was possible to repair the cut and have a safe rudder, I decided
that I did not want to have such an apparent default on my aircraft...
at least, not yet. After all, making new parts to reach the same point
would take me only five hours.
I then decided to make new middle ribs (RR2, RR3 and RR4) since it would
be difficult to duplicate the exact same location for the holes on the
skin. RR1 was not drilled yet so the problem does not exist for it.
It is not a problem either for the tip rib as it is easy to duplicate hole
location for that rib.
I took the opportunity to make a new form bloc out of a 2"X6" for RR2.
The form bloc that I initially utilized was 535mm long while the plans
call for a 515mm RR2 rib length.
||Finally! We can proceed with the next step
This is my rudder along with the old rear skin and ribs. To cut
the skin to proper size, I made a rough cut about 1-2 inch from the spar
and bottom rib. I then used a pen to mark the cut line and I cut
about 1/8" inside that mark.
||Will that nose rib stay in place?
It was quite difficult to keep this rib immobile while positioning
the nose skin. Finally, I got this idea of fixing it with a square
and some pieces of duck tape.
||And the result is...
A completed rudder (minus the horn, attachments and tail light).
||The lower rudder hinge
I made this part twice... the first time, I ended up with an incurred edge distance on
the central hole. The second time, I used an easy technique to make the
part... I started with a 27 degree bend (made on a hydraulic press at a
friend's place). Then I cut the part to size and drilled the
holes. Finally, I unbent the two control cable attachment points to 13
degrees as specified in the plans.