Composite-ARF SPARK Instruction Manual page 20

Composite-ARF SPARK
The main retract units should be secured to the
integral plywood mounts using the M3 x 12mm
allen bolts and T-nuts supplied, in the usual way.
You can trim the bottom wing skin a little more
around the retract openings, if necessary, to get
them into position. Use a straight edge to make
sure that both units are exactly in line with each
other, and also centred on the cutouts in the
wing skin that are already made for the wheels
(which can be enlarged a little as needed).
Fit the retracts as outboard as possible, to give
the maximum leg length - and therefore the
biggest rotation angle before the stabiliser tips
touch the runway. For the same reason, only
leave a minimum of 10 - 13mm space between
the retracted wheels in the centre of the wing.
Drill Ø 3mm through one of the mounting holes
in the retract unit, and insert one of the M3 x 12
allen bolts to hold it in position. Then drill the
other 3 holes, also inserting a bolt to keep the
correct alignment after each hole is drilled.
Remove the retract unit and open up all the
holes to Ø 4.5mm for the M3 T-nuts. Using a M3
bolt and a large washer, pull the spikes of each
T-nut into the top surface of the mounting rails
just a little, with a drop of 30 minute epoxy on
each. Re-install the retracts and tighten all four
bolts, which will make sure that the T-nuts are
perfectly aligned when the glue has cured.
Fit the Ø 4mm wire legs to the retracts, with the
coils oriented as shown in the photo here. Only
file a very small flat spot on the legs for the set
screw to sit against. Make a small semi-circular
cutout behind each leg to accommodate the coil
when the legs are retracted.
If you chose to install plastic wheels, then you
need to bend the legs to form the axles in the
usual way, solder a Ø 4mm washer to the leg on
the inside of the wheel, and secure the outside
with a Ø 4mm wheel collar, or similar. Note that
the wheels are fitted on the outside of the legs,
and are completely hidden in the central section
of the wing when retracted.
If you have the optional Behotec aluminum wheels and brakes, then proceed as follows:
Clean the wire legs well with green Scotchbrite or fine sandpaper in the approx. position that the
axles will be fitted, and degrease both parts using Acetone or equivalent. Fit the bolt-on axles to
the legs loosely, and slide the brake units onto these, followed by the short Ø 6mm aluminum
tube spacer included, and then the wheels and finally the 'E-clip' that retains the wheels onto the
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(above) The Spring-Air 301 'Firewall' retract
set fits the Spark perfectly and is available as
an option directly from Composite-ARF.
(below) The optional Behotec 'slim' wheel &
brake set also includes 3 bolt-on axles and a
compact combined retract/brake valve that is
designed for air-in/spring-out systems. Wheels
are 60mm Ø and double ball-raced.
(above) Maintain at least 10mm of wing skin
between the 2 main wheel wells. Balsa scraps
used to retain tubes are seen here.
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