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If you plan to use the rubber-band
wing-mounting system, join the wing as I outlined last month. The
installed aileron linkage usually gets in the way when aligning the wing
halves during the joining process, requiring the entire installation to
be removed before joining the wing. Therefore, do the linkage
installation after joining the wings to save work.
After the wing is
joined, reinstall the aileron servos. On which side to position the
servo arm seems to depend on the radio system used. Although it is
possible to mount the arms on either side and then adjust the
transmitter to suit, it is an easier programming job if the arms are on
a particular side.
Many JR radio systems are easiest to flaperon-program
if the servo arms are positioned toward the wingtips. Some Futaba radio
systems seem to prefer mounting the arms toward wing center. I don't
know about the other popular systems, but before positioning the aileron
control horns, hook up your servos and "imagineer" which side is easiest
to program using your radio.
Once the servo arms are mounted, position a
control horn perpendicular to the aileron's span (constant-chord wings)
and in line with the servo output arm hole. Make sure the control-horn
holes are precisely over the hinge centerline. Use two threaded rods
with a Du-Bro solder coupler. Make sure to flux the rods and have the
ailerons and servos centered before cutting the rods to length. Assemble
and solder in place.
Do not use Z bends; they eventually enlarge the
output arm hole. A quick pass with a small file trims the solder and
usually makes it shiny if the joint was soldered properly.
Rubber bands
are okay, but they are a mess to handle and detract from an aircraft's
appearance. The unfinished wood dowels used on many ARFs don't seem to
blend in well. Bolt-on wings have a performance advantage and look
better.
With rubber bands, each flying session can have different trim
settings based on the wing's positioning. Even marking the wing center
doesn't always work since the wing can drift from this setting
throughout the course of several flights because of handling, accidental
hangar bumps, and other factors.
The trim settings for a bolt-on wing
remain constant from one flight session to the next. This makes learning
easier for the new pilot because the day's first flight is usually in
proper aileron trim.
Installing bolt-on wings in most of today's
high-wing ARF trainers can be a problem. The usual twin rear bolts with
a front dowel hold-down system is difficult to position properly when
the fuselage is already made and covered; many of these aircraft have
little or no fuselage area above the wing to hold the dowel in position.
Instead, try the old pattern system using three bolts. A front bolt
holds down the front of the wing while the traditional twin bolts secure
the wing's rear.
If you want to try this method, the work begins before
joining the wing halves. You will need two 1/4-20 2-inch and one 1/4-20
3-inch nylon bolts with washers and a 6-inch length of
1/4-inch-inside-diameter fiberglass arrow shaft. I use leftover pieces
of Dave Brown fiberglass pushrods, but any arrow shaft will work as long
as it is the right size. You will also need a 12-inch-long maple "block"
that is at least 3/4-inch square.
Position the 3-inch long, 1/4-20 nylon
bolt along each wing half and draw its outline on both. Using scrap 1/4
balsa that is long enough to reach roughly 1/2 inch behind the rearmost
bolt mark, trace the wing's center airfoil. Cut out the airfoil shape
the thickness of the wing's sheeting—approximately (metric sheeting,
remember) 1/16-3/32 inch. The wing sheeting can be measured around the
original aileron opening.
Use carpenter's glue to adhere the 1/4
"thickeners" inside each wing center rib. Carefully cut a slot along the
bolt outlines. The depth should be slightly more than half the arrow
shaft's outside diameter. Do this in each wing half.
Join the wing, but
do not install the arrow shaft yet. Put the nearly completed wing aside
for now. It is easier to install the fuselage's servo tray if the rear
maple blocks are not in the way.
Move the fuselage onto the workbench.
Most ARF trainers have the servo tray glued to two formers and the
fuselage sides. The Hobbistar 60 is no exception, but the formers are
1/8 or thinner plywood, and the tray never seems to fit the fuselage's
width at every point.
The servo tray takes a beating from flight loads,
hard landings (it is usually mounted near the main gear), and stress
from a bouncing nose wheel. If the tray comes loose in flight, it can be
difficult to make a smooth and graceful landing; elevator control can be
lost, and the rudder and elevator trim settings go haywire.
Before
installing the servo tray, reinforce the servo screw areas. The Hobbistar 60 already has this modification, but most ARFs do not.
Reinforce the mounting area with small pieces of 1/4 x 1/8 spruce stock.
Be sure to glue the spruce pieces under the tray and out of the way of
any servo.
Mount the servos. It is a good idea to place card stock between the
servo sides and the wood tray to ensure that the servo never "vibrates"
against the tray. Remove the card stock when the servo is mounted.
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