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!)
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.
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.
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.
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.
first construction problem surfaced when it came to installing the
The solution was to sand down
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.
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 .
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
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.
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
"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.
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.
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.
a picture of the first time I mounted the prop and spinner and ran
was taken just before the maiden flight, just in case it didn't
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.......
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.
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
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.
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
When a few days of good weather did come I took advantage of them and got five flights in two days.