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Tail wheel, and tail feathers:
I've decided to concentrate my next efforts on the tail section of the
airplane. I feel that the most complex parts will be in the tail, simply
because of the limited space I have to work in. I figure before gluing in
any formers, or sub flooring, that I should first figure out how
everything will fit, and function.
The first thing I've done so far is to cut out the tail wheel doors from
the fiberglass fuse. But before I attach the doors, or attach the tail
wheel, I still want to test fit the stab, rudder, pushrods, etc to see if
anything will interfere.
Note: I will be jumping from one section to the other as I proceed
through the tail section.
Since the fin is part of the fiberglass fuse, I only need to build up the
rudder. The rudder is basically built like the elevators. A built up,
sheeted surface and like the elevators, I had to draw out the scale
hinge lines, then build them into the leading edge.
Before I completely build the rudder, I've test fit the stab, rudder post,
and tail wheel to see where my push rods are all going to go. I want to have
hidden elevator, and hidden rudder linkages to give it a more scale
appearance, so my next steps will be to figure out how that will all
function.
After looking at numerous ways to do the rudder linkage, I came up with
the following: I decided to make a rudder rib out of some circuit board,
sandwiched between balsa, then drilled and tapped to accept ball links.
I then took the rib, and glued it into the rudder structure along with the
other ribs. I reinforced the area around the rib with some balsa to give
it a little more strength and rigidity. I then took the rudder post and
cut slits that will allow the ball link/pull pull wire to pass through, to
the eventual servo. I also added a hinge in between the two ball links to
add a little more scale realism, and further rigidity in that location.
After looking at the scale P-47, I noticed some sort of slit that is in
the same location to where my linkage is. I believe that is where the
scale linkage for the rudder control is, so it should work out well.
I also noticed that the rudder line is not completely straight, in that as
you reach the point where the rudder hinge line, intersects with the stab,
the hinge line moves further into the rudder.
I compensated for this, and cut the rudder post, in the same location.
This should hopefully give my P-47 a more scale outline. There are other
curves and features that I've noticed in the rudder, but will do them at a
later stage when I have more of less figured out how the rest of the tail
section will fall together.
Now that I have somewhat figured out the tail section, I want to switch my
efforts to the tail wheel, and tail wheel door assembly. I want to first
install the tail wheel, before I glue in the tail feathers. This way I
will have as much room as possible to wok in. In the picture above you can
see the Robart tail wheel assembly and former. That whole assembly will
eventually be glued into the fuse, once I've calculated how the doors will
function and operate.
I had already cut the doors out in earlier steps to make more room to
maneuver in. Now I wanted to better fit the doors, for their
eventual installation. I used some 1/64 ply to create a door stop that was
glued into the fuse. This way the doors would have something to rest on. I
also didn't like the way the doors lined up, so I added a small lip of
West System Epoxy, mixed with fairing filler to fill the edge of the door.
This filler when dry, sands quite easily.
Since I wasn't sure of the geometry required to make the tail wheel doors
function properly. I decided to just temporarily tack glue things in
place, to see how they work. I temporarily glued some offset door hinges,
using some thin CA. Then I also temporarily glued in a piece of hardwood
that I could hold the cylinder in place with. I drilled a few holes along
the hardwood, and tried different arms on the door, to see which
combination worked the best. The cylinders I'm using have a 3/4" throw and
are made by Ultra Precision
Valves. Eventually after a little fooling around, I got the doors to
work rather nicely.
Since I am waiting on a few parts to finish off the tail wheel assembly, I
decided to switch back to the stab, and finish off the linkages.
Originally I wanted to have hidden linkages in the stab, but the more I
looked at it, and thought about it, the more I convinced myself that
having positive direct linkages in the stabs was the way to go. At least
for me, in that I would feel more comfortable about it, and since the
linkages will be underneath the stab, the likelihood of people noticing
them will be very slim.
JR makes some very small relatively powerful servos that work well in my
situation. They have a servo called a JR3421, which is roughly 1/2" thick
X 1" X1.25" yet has 65oz of Torque at 4.8 volts. Plenty of power for each
stab half, and will fit nicely in my stabs.
I decided to make servo bays at the trailing edge of the stab. I cut the
stab skin with an exacto, then made a hatch cover out of some 1/8 light
ply. Once I had cut out the skin, I needed to make some ribs that will
support the edges of the already cut skin.
It may be hard to see, but where I made the cuts, I had to use a little
scrap balsa to make some supports that will finish off the rest of the
servo bay. Once I had a nice bay, I
then used some hardwood tri stock to make a ledge that will eventually be
used to support the plywood plate.
My next step is to finish off the plate. Again I used some hardwood to
make mounts that will hold the servo in place. I then cut a slit in the
plate to allow the servo arm to move freely. I also drilled some
holes that will be used to hold the plate in place.
Now that the plates were complete, I placed them back in their positions
to see how they fit. I purposely recessed the hatches by about 1/16th
in the bay.
The reasoning for recessing the hatches, is because I wanted to add a
piece of balsa on top. I do this because plywood is very flat, and hard to
shape, yet balsa will shape quite easily. So once I glue the balsa on, I
can put them back in the stab, and finish sanding the hatches to perfectly
match the contour of the stabs. I then glassed the hatches to give them
some hardness..
I finally received some hardware, I had been waiting on, and finished off
the linkages for the stabs. I used Nelson Hobby, RCL linkages, that
utilize a 6-40 screw as a horn. They worked out rather nicely, and are
very positive.
Since I'm waiting on some products to come in the mail, I have to put
finishing off the stabs till my supplies come in. I have a specific order
of how I would like things to go, and not having certain items, sort of
puts a curve in that schedule. So I've decided to jump around and do some
other small jobs while I wait.
Since I'm using a pull pull system for the rudder, and a pull pull system
for the tail wheel, I had to make some sort of servo tray for those
servos. I decided to make a tray that has two levels. This way, the wires
will not interfere with each other. I made the tray out of light ply, then
reinforced the edges with some carbon fiber tube to give the tray some
rigidity. The tray will sit right behind the wing saddle, and directly in
line with both the tail wheel, and rudder linkage.
Well after checking my mail every night, I finally received a delivery,
and can now finish off the tail wheel assembly. I had been waiting on some
BVM off set hinges, and now they had finally arrived. Since I had already
calculated how the tail wheel doors would operate, I just basically had to
copy them, and make a more permanent installation. As I had the proper
geometry from my trial fit, I made some light ply blocks, to hold the
cylinders. I then glued them into the fuse at the right angles so they
would actuate the doors. In the process, I also routed the air tubing for
later on. Since I still want to be able to take the doors off and on for
finishing, I used some BVM flush mounted panel screws to hold the doors
on. This way I can remove them later on if needed. I also added a little
scale detail to the inner parts of the doors. I just figured it would be
easier now.
Construction Page 1
Construction Page 2
Construction Page 3
Construction Page 4
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