Use a 35 mm long servo horn and install the linkage with a ball link, so that you can move
the linkage around 3-dimensionally. This is needed to attach it to the elevator. You need to
practice a little to remove and attach the elevator linkage, you can do it without removing
the rudder, it just requires a little try and error and then practice. The 35 mm long servo
horn is a little longer than what’s required for the final deflection of the elevator but with a
good modern HV servo with 25-35 kg torque you can a
ff
ord to reduce the servo throws to
60% without losing more than the essential torque. You do need the longer arm to make it
easier to remove and attach the linkage. We do NOT recommend to use on the elevator
anything else but the included 3mm ball link mounted between the two phenolic horns.
The rudder is attached to 2 hinge posts with a 2mm steel pin, and if you use the clevises
included in the hardware, it is very fast and easy to remove the rudder if need be.
4) Engine Choices, if any
We o
ff
er the service to pre-cut and pre-install the mounting formers for either a
retractable turbine mount or a retractable EDF. Unfortunately both units mount very
di
ff
erently and require also a di
ff
erent shape of cutout, so we cannot provide a universal
prefabrication here. The extra service has to be extra ordered, after you have decided
which type of propulsion you would like to install. However, it is not too complicated to
cut the opening yourself and install the formers. There is no glass work needed and no
additional reinforcement to be done. The fuselage has all the strengthening for the large
opening already in its layup. Cutting templates for both style openings are included in the
kit, as well as all the pre-cut formers to choose from. And for the turbine version we o
ff
er
a conformal fuel tank with 2 l volume, this set also includes a small header tank.
-
cut the openings with a thin diamond disk in a dremel tool. The EDF hatch stays one
piece, the turbine hatch must be split in the middle into a right and left door. The
turbine doors get hinged to the fuselage with either o
ff
set hinges or steel pin hinges,
similar to a jet gear door. They are spring loaded in the rear. The engine opens the
doors when it slides through, and two small carbon tabs on the side of the mechanics
will create a support where the spring loaded doors rest against while the engine is
extended. The EDF hatch gets glued on top of the outer duct frame in alignment with
the fuselage contour, while the EDF is retracted.
-
The EDF mounts to a former in the rear of the opening. The turbine mechanics mount
to a former in front of the opening. The included former could be reinforced with a
horizontal board approx 30 mm wide, glued from the front against this former in the
wing saddle area, to create more sti
ff
ness if a heavy and very powerful turbine is used.
-
The fuel tank mounts in front of this former, above the wing joiner. 1-2 wooden sticks or
small carbon tubes across the fuselage below the tank will support and hold it
su
ffi
ciently. The header tank should be mounted on th bottom of the fuselage, in front
of the retract former.
5) General Setting
The CG of the Kobuz is at 110-115 mm behind the leading edge at root. That is approx.
10-15 mm behind the front edge of the wing joiner to start with. It can be moved 5 mm
further back gradually after a few flights, as you feel comfortable.
