While I was putting my Decathlon together I took lots of photographs, some just to record the build, and others to show to people when I was unsure how to deal with a particular bit (normally when something didn't quite fit!)
The
first problem that became apparent was that I hadn't realised that
the batteries I have bought were so long ! The picture shows that
even with a battery pushed right up to the firewall, it reached back
over the servo tray. Various options were considered, such as
building a sloping tray to raise the rear up clear of the servos.
I
have already bought two batteries so that I wouldn't have to wait for
a recharge between flights, so I wanted to be able to easily change
the battery without having to take the wings off. Plus, I didn't
particularly like the idea of charging Lipos with them mounted inside
the fuselarge Luckily the batteries' width will allow then to fit in
the space normally occupied by the i/c motor's silencer.
By
cutting a hole in the back of this space the battery can be slid in
from the front, and will sit a bit further forward and thus not
interfere with the servo tray. Also the battery is positioned
slightly lower and thus sits under the servo tray.
Alister
built a tray to for the battery to slide into inside the cockpit. A
slight enlargement of the hole in the front of the cowl allows the
battery to be easily inserted and removed.
The
first construction problem surfaced when it came to installing the
fin.
The solution was to sand down
the front
edge of the fin until it was a good fit and allowed the fin to fit
correctly into the slot in the fuselage Note the sheet of paper
to protect the fuselage covering from the sand paper.
And
then when I came to try and fit the wings for the first time I
discovered they wouldn't seat properly. The picture shows the
gap between the top edge of the fuselage and the bottom surface of
the wing .
And
as you can see the same problem on the other side of the fuselage
It appeared that the trailing edge was not directly being held "up",
but that the leading edge was being held "down" by the
position of the dowels that locate into the holes shown in the
next picture.
As
you can see, rather than try and move the dowels on the wings, I
decided to reshape the holes. In the picture the holes have
been enlarged slightly on their upper edges, and small pieces of
balsa have been glued into them. The one on the right has
already been worked away to allow the dowel to enter and be held in
the correct position. When both had been done the wing nearly
sat correctly on the saddle, but a small amount of material needed to
be removed from the saddle to make it match the profile of the bottom
of the wing. Also the wing rocked slightly across the diagonal,
so the material was removed from the leading edge on one side and the
trailing edge on the other side. I was concerned that these
modifications may have altered the angle of incidence of the
wing.
Another builder had repositioned the dowels in the wings, and in
doing so had decreased the angle to such an extent that the model
would hardly fly, but since my modifications could have only
slightly increased the angle I wasn't too concerned.
Now
that the wings were in place I mounted the aileron servos and control
horns. I mounted the horns where the instructions suggested,
but when I came to test the servos I realised that placing the
linkage into the outermost hole in the servo arm gave too
much control surface throw. I could have just
used
"low rates" on the transmitter to overcome this, but using
the innermost hole but one gave throws very close to the figures in
the manual. However I was unhappy with the clevis coming off
the horn at an angle.
So
I built a jig to put a couple of bends into the control rods.
Of course on the first attempt I put the bends in the wrong way and
had to go and buy two new rods and start again.
When
it came to mounting the motor, we decided to try and use the existing
i/c motor mounting holes in the firewall even though they were at an
odd angle and were spaced too wide. A cardboard "mock up"
proved the principle but we realised it would be hard to get a
screwdriver onto the bolts into the firewall.
So
for the final version we did it slightly differently. The
picture is misleading as it looks like the motor has some left thrust
but it is an optical illusion. You can also see the platform in
the silencer space that supports the front of the battery.
The
balsa tray in the cockpit was made the right size to hold the battery
in place, but I added two further retaining methods.
First I mounted a simple sliding "finger" on the firewall
that stops the battery sliding forward. Secondly when we
installed the platform we put slots in to allow a strap to be
threaded over the battery and pulled tight.
When
it came to mounting the cowl I wanted to put the screws into the edge
of the firewall rather than just into the thin covering at the back
edge of the cowl. In order to mark where I needed to drill
holes in the cowl I put a 12V "brake light" bulb
inside and used the shadow of the front edge of the firewall to
position the holes.
Here's
a picture of the first time I mounted the prop and spinner and ran
the motor!
This
was taken just before the maiden flight, just in case it didn't
survive !
The range check proved problematical but some
repositioning of servo leads, receiver and antenna seemed to sort out
the interference that caused the motor speed to "hunt" at
greater than half throttle. However the first flight showed the
problem still persisted. A change of ESC (From CC to
Hacker) and moving the receiver/servo battery away from ESC and
putting ferrite rings on several of the leads cured the problems.
A range check before the next flight was "all clear"
so.......
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After
getting the trims sorted out during the flight, I took this
picture.
During the flight I had let another club member fly it for a while,
and he commented that a bit of "right thrust" would help
the handling.
It
was quite easy to add a bit of right thrust by putting a couple of
washers under the left hand side of the motor mount. Because
the "X" mount is at an angle this also added a little bit
of down thrust as well but this doesn't seem to have caused any
problems.
Then
disaster struck ! A practice dead stick landing didn't
quite go to plan, and the undercarriage was neatly ripped out of the
bottom of the fuselage :( The only other damage was to the wing
spars on one side which were slightly bent. The
undercarriage was reattached with some epoxy resin and the small
amount of damage to the side of the fuselage above the undercarriage
was covered with some "hacker" stickers.
The
damage was all repaired within a week or so of the accident, but then
the model sat for several weeks over Christmas until the weather was
good enough to fly again. I realised the weight of the model
resting on the soft foam wheels was putting "flats" on the
wheels, so it now rests on supports with the wheel clear of the
ground.
When a few days of good weather did come I took advantage
of them and got five flights in two days.
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