RBC kits JIMMY Instruction Manual

Building Instructions JIMMY
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JIMMY
BUILDING INSTRUCTIONS
Build the JIMMY, a radio controlled model aeroplane especially designed
for the first time builder or flyer.
The JIMMY is a model plane which is easy to be built by a first time builder, and can be
flown by a novice pilot. The design is based on a number of pre-cut parts in balsa wood or
poplar plywood.
To build the plane, you will need some tools and glue. Here is a summary:
1. A sharp hobby knife, such as a small sized, break-off blades type.
2. A sanding block, a wooden block with a piece of sanding paper stuck to it with double
sided sticky tape. Use grit size 150. Make a second block with 100 or 120 grit to trim
the edges of the plywood parts. This will wear it off a bit faster, so you can keep the
150 grit block fresh for the balsa parts.
3. Dressmaker’s pins to keep the parts in place during drying of the glue. Use only glass
headed pins, the ones with plastic heads tend to lose their head when a bit of force is
applied, ending up with an unpleasant hole in your finger. Special modelling pins are
also available. To assemble plywood parts it is best to use short pin board pins, which
have a stout grip.
4. Clothespins/pegs for the same purpose. You can use ordinary clothespins, but they
tend to leave traces on the soft balsa. Purpose made little clamps are better, look at
the pictures to get the idea.
5. Glue. PVA glue is the most suitable, since it will give you some time to adjust the parts
to their proper position, and surplus glue can easily be removed with a piece of wood,
or just use your fingers. PVA glue will clean off the skin without problems before it sets.
6. Building board, MDF, minimum thickness 12 mm when you can support it on a flat
surface, but thicker when standing on its own. Make sure it is flat and not warped.
The parts will be supplied while still fixed in the balsa or ply sheet material from which they
are cut, and your first task is to release them by cutting the bridges with a sharp knife.
Sand off the remainder carefully, beware of changing the shape of the part by too much
sanding.
Dry-fit each part before applying glue to ensure a proper fit, and adjust where necessary.
Please note: In the following instructions right hand and left hand are referred to as seen in
the flying direction, i.e. looking from the rear to the front."

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Start with building the fuselage.
Pick the side panels up and lay
them on a plastic sheet to
prevent them from sticking to
your work surface. Glue the
balsa side panels to the ply
parts using the zigzags to align
them. Check the picture below
for their orientation.
Lay down the bottom panel. Note
that the front is not square, but at
an angle to the right. This will
offset the propellor thrust
direction to the right, which is
necessary to compensate for the
air flow twist caused by the anti-
clockwise rotation (as seen from
the front) of the propellor. So
check that the right hand edge of
the bottom panel is shorter than
the left hand edge.

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Glue the servo mounting plate to the
rear former, check the squareness
again (the rear former differs slightly
from the picture).
The stabiliser support (balsa) and tail
skid support (ply) parts are glued to
the right hand side panel.
Glue the main former to the bottom
panel, make sure it sits square to
the bottom.

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Glue the assemblies as prepared in the previous steps to the right hand side panel.
Before the glue sets, glue the left hand side panel in place, and ballast the complete
assembly with a weight of your choice. The bottom picture shows the tail end glued
together, don’t do this as yet, as this will be explained in detail in the next steps!
An old iron as shown in this
picture of another model
under construction is perfect.

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Mark the center of the two formers with a vertical pencil line, and……
line them up by sighting the two pencil lines and glue the side panels together ensuring
their symmetry by aligning the stabiliser support slot with those lines:

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"
Complete the nose. The side panels first, the
shortest one on the right. Apply glue to the
teeth and on the side of the bottom panel.
Slide the teeth into those on the fuselage
sides and swing the sides inwards to close
the joint with the bottom panel. Clamping may
be a bit difficult, so use pins or tape to fix the
joints.
Glue the captive parts for the landing
gear leg ends to the sides. Orient the
parts such that the slot corresponds
with the opening in the bottom panel.
Clamping will be a bit difficult, fix the
parts with pins or sand a bit of balsa
scrap to size and push it between the
parts. Keep the slot and the bottom
opening free from glue, any excess
should be removed with a matchstick or
similar to enable sliding in the L/G legs
from below.
Use the mounting cross included with
your motor to establish the correct
position of the self tapping mounting
screws. Center the cross over the
hole in the middle of the firewall, mark
the mounting holes and pre-drill the
holes with an appropriate size drill.
Screw the cross in place temporarily,
do not over tighten the screws.
Unscrew it again. When available,
harden the screw holes with thin
cyano glue, alternatively glue some
scrap plywood pieces on the back
side to provide more ”flesh” for the
screw thread. Dry-fit the firewall.
Slightly bevel the recessed surfaces
of the side and bottom panels to
provide a nice fit of the gluing
surfaces, but do not overdo it to avoid
altering the side and down thrust
angles of the motor/propellor. Glue
the firewall in position.

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"
Glue the front part of the nose top in
place, and sand it to shape after the
glue has set. Sand the rear part to size
but do not glue it to the fuselage. This
part serves as battery and motor
controller access hatch, and should be
kept removable.
Dry-fit the control cable support in the rear end of
the fuselage. Slide the outer control cables
through the holes in the rear former and the rear
support. The rear end of the cables should just
protrude from the fuselage, the elevator cable
through the opening at the rear of the fuselage,
and the rudder cable through the top, accounting
for the 1.5 mm top planking of the fuselage still to
be fitted. The front end should protrude some
10-15 mm through the holes in the rear former.
Check the drawing for the exact routing of the
cables, and glue everything in place. It is
important to run the rudder cable in such a way
that the steel inner cable only needs a minimum
of bending on its way to the rudder control horn.
Glue the top and bottom planking of
the fuselage, with the grain direction
across. Fix with dress pins. Start at
the front with a slightly oversized
piece, and continue to the rear by
holding the balsa sheet against the
previous piece, mark the size with a
pencil, cut slightly oversized again,
and glue in place. Maintain 2-3 mm
oversize, and sand flush with the
fuselage sides later.

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Prepare the 3 mm balsa tail surfaces, but wait
with glueing those to the fuselage until after
the iron-on covering has been applied. Glue
the two pieces of the tail fin together, sand
smooth and round the front and top edges.
The rear edge shall remain squared since this
is where the rudder hinges.
Finally, add a strip 3 mm balsa to
the inside of the fuselage sides at
the wing rest, and bevel these to the
dihedral angle of the wing to give it
a larger supporting surface. This
does not add any strength or rigidity,
but it avoids indenting the wing
bottom surface.
Glue two 50x8x2 mm pine pieces to the fuselage bottom,
on either side of the removable landing gear. To adjust
their position, temporarily slide the L/G legs into their
mounting holes with the wires against each other, apply
glue to the pine parts, position them close to the L/G wires
and slide these against the wires while the glue is still wet.
Remove the legs carefully without moving the pine parts
and remove any excess glue.
Glue the 3 mm ply tail skid directly to its ply support after
making a slot in the balsa planking that covers it (no
picture, see drawing).
Sand the stabiliser smooth and round all edges except the rear edge, the elevator hinges
here.
Bevel the front edges of the rudder and elevator parts at an angle of approx 40 degrees
to allow deflection to either side (no picture, see drawing).

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Wing
The wing will be built on top of the drawing, so start by getting a building board made out
of a piece of mdf or
chipboard of sufficient size
for one half wing. Stick the
drawing to the building board
with tape, and cover the
drawing with transparent
plastic sheet to prevent
glueing the parts to the
drawing. As an alternative,
you can cover the drawing
with tape where parts will be
glued together and touch the
drawing, i.e. all ribs to the
lower spar and to the trailing
edge. The leading edge will
stay clear of the drawing, so
no need to protect the drawing there.
Fix the 6x6 mm lower spar to the building board with pins. Accurately cut a piece of 1.5
mm balsa to size for the planking of the root part and glue it to the lower spar. Fix this
planking to the building board with pins. The trailing edge consists of a lower and an
upper part made from 1.5 mm balsa sheet. Cut the lower part to size, and glue it to the
rear edge of the planking and fix the rest of it with pins. Ensure that the lower trailing
edge sits flat on the drawing board and exactly matches the spanwise lines on the
drawing (a little oversize on the ends is ok).
Glue the 9 outer ribs (2 mm balsa) to
the lower spar and the trailing edge
in the positions indicated on the
drawing. Ensure that the ribs stand
square to the building board and that
the bottom edge of each rib rests on
it.

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Check the fit of the upper spar in the
ribs. The fit should be tight, but not
overly so. Adjust the cut-outs in the
ribs where necessary. Glue the upper
spar in position.
Now for a slightly tricky bit: the root ribs
are in two parts each, a front and a rear
part. They are glued in a sequence
combined with the wing dihedral brace:
front parts first, then the brace, and lastly
the rear part. An extra complication is that
the first root rib has to be angled so that it
matches its counterpart on the other wing
half. Start with the front part of rib #1.
Glue it at the required angle using the 3
mm ply template provided, checking
alignment with the drawing by looking
from above. Slip a piece of 1.5 mm scrap
balsa underneath to allow for the planking
thickness. Check the front cut-out
alignment by sighting and comparing it
with the other ribs, or hold the leading
edge against it. Told you it was tricky…
Glue the two other root rib front parts
in place, square and upright. Test the
front cut-out alignment.

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Glue the ply dihedral brace to the rear
of the spars and to the bottom
planking. The dihedral brace dictates
the way the two wing halves fit
together, so ensure that the underside
is parallel to the building board. The
kink in the brace should exactly match
the position of the slanted front rib
part. If necessary, sand a little off the
end of the brace to achieve this. Be
sure to clamp the brace to the spars
until the glue has set.
Glue the rear parts of the 3 mm balsa
root ribs onto the bottom planking and
against the dihedral brace. The first rib
is again angled at the same angle as
the front part (check with the template),
and at right angles to the spars.
Glue the 8x8 mm leading edge in
the cut-outs of the ribs, and
temporarily fix it with pins as shown
in the picture.

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Use a plane to shave the bottom
trailing edge to an angle, such that
the top trailing edge fits flat in the
rib cut-outs and on the bottom
trailing edge. Ensure the top butts
against the front of the cut-outs.
Glue the top in place and use pins
and clamps to keep it in place while
the glue sets:
Cut and sand the last 2 planking
sections to size, and glue/pin in
place. Sand the excess planking and
spars off, flush with the slanted first
rib. The other wing half should fit
against this.

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2.50
Cut the 1.5 mm balsa webbing pieces
to size. These are the rectangular
pieces which are glued between the
ribs to the rear of the spars, with the
grain vertical!
Shape the leading edge to the
correct cross section. The easiest
way is to mark the balsa strip with
two pencil lines 2.5 mm offset from
the front edge, and start shaving it
vertically up to these lines. After that
shave and sand to its final shape:
Sand the spars, leading and trailing
edges flush with the outer rib. Glue
the 5 mm balsa end ribs on and
sand the edges to match the last rib.
Round off the outer edges.

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The second half wing is constructed
the same way as the first, except that
the dihedral brace, the rear part of
the root ribs, the top planking, and
the top trailing edge are all left to be
completed until after the two halves
are glued together.
Support the completed half wing at
the tip with a 120 mm high stack of
books, blocks, etc., and rest the root
on the building board. Offer up the
second half, and fettle the joint until
you have an exact fit. Glue the two
halves together. Be sure to clamp the
dihedral brace to the spars until the
glue has set.
Glue the rear root rib parts in place.
Glue the top trailing edge and the
1.5 mm top planking in place.
To avoid any damage caused by the
rubber bands that hold the wing
down it is best to add two rounded
pine strips at the trailing edge of the
wing. Try the wing to fuselage fit first,
and adjust the position of the pine
strips such that they are just in front
of the rear former of the fuselage, as
the V-form of the wing makes it sink
slightly into the fuselage aperture.

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Finishing
Wing and fuselage are now ready to get their final finish. Sand everything smooth, and
round the corners of the fuselage. Do not overdo it, avoid reducing the glue areas too
much. The simplest way to finish all surfaces and open structures is to use iron-on
covering film. It is important to apply the covering at a low temperature setting of your
iron to reduce initial shrinking, and only when everything is attached properly raise the
temperature to tighten the covering and remove any wrinkles. This is especially important
with open structures, i.e. the wing, which should be covered at low setting on top and
bottom first, and only then raise the setting to tighten it evenly. Be careful not to introduce
warping of the wing, but when you do you can iron those out by ”counter-warping” the
wing by weighting one half down on the board and carefully rotate the other tip by hand,
reheat the covering and let it cool before you release it.
It will be difficult to describe the details of iron-on covering in a few words, best is to let
an experienced modeller show you how it’s done, or refer to the instructions of the iron-
on film supplier, e.g. Solarfilm, Oracover and others.
As mentioned before, the tail surfaces
are best covered before final assembly.
Leave the area to be glued to the
fuselage free from covering.
Mark the position of the rudder horns,
cut a slot and glue the horns to the
control surfaces. Check the drawing for
the exact positioning of the horns.
Attach the elevator to the stabiliser with
sticky tape. Stick the tape to the top of
the stabiliser, leaving one half past the
edge to stick to the elevator. To ensure
a minimum hinge gap and a maximum
deflection angle, hold the elevator in a
downward attitude against the rear
edge of the stabiliser and push down
the tape onto the elevator.
Attach the rudder in the same way, pay
attention to the bevel on the front edge
of the rudder.

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Propulsion and controls
Propellor, r.p.m. and battery voltage can be applied in different combinations to achieve
appropriate propulsion. The following combination works well on the prototype:
Battery: 3s lipo type, 1000mAh, which stands for 3 cells in series (= nominal voltage
11.1V) with a capacity of 1000 milliAmpere/hour
Motor: outrunner 100W type, 1100KV (1100KV = 1100 r.p.m. per Volt)
Propellor: 7 x 4 ( = 7 inch diameter, 4 inch pitch)
What remains is to choose a motor controller a.k.a. ESC (= Electronic Speed Controller).
Although current draw of the combination as described above will be around 10A
maximum, it makes sense to choose an ESC suitable for a maximum continuous current
of 20-25A. A BEC (= Battery Elimination Circuit) supplies power to the receiver and
servos) is integral with most ESCs, if not it will have to be added separately.
The rudder and elevator pushrods are
connected to the servo arms with
cylindrical connectors into which the
pushrod is clamped with a setscrew.
Drill the hole in the arm which is
approx. 10 mm from the servo center to
the correct diameter (usually 1 or 2
mm) to receive the connector, which
should be free to rotate with a minimum
of play. Mount the connectors on the
arms and mount the servos in the
dedicated openings.
Cut the two pushrods from a length of 0.8 mm dia.
pianowire. Bend the ends in two steps as shown in
the picture, leaving approx. 2 mm straight where it
rotates in the control horn. Slide the pushrods into
the control cables in the fuselage from behind,
pass them through the servo connectors and twist
the bent end into the hole of the control horn, see
the pictures on the previous page.
Make sure the servo is in its neutral position with
the arm at 90 degrees, and fasten the setscrews of
the connectors

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Solder 2 mm dia. gold connectors to the
motor and ESC, and insulate with heat-
shrink tubing. Push the motor wires
through the opening in the firewall and
connect them to the ESC. Mount the
motor (without propellor!) to the firewall
with two screws, temporarily connect the
battery and check that the motor runs
counter-clockwise. If not, take the motor
off again, pull the connectors clear, swap
two of them and push them in again.
Mount the motor permanently with all
screws. Do not mount the propellor as
yet, see the ”Control Adjustments” chapter.
Use velcro to mount the battery onto
the battery carrier plate. This will allow
to mount the battery in various
positions to adjust the balancing point
(a.k.a. the Center of Gravity or CG) of
the plane.
The battery carrier plate remains
removable to simplify removing the
battery for charging, but the notches
in both sides lock into the bottom of
the opening in the main former to
keep it in place. The battery has to
be immobilised further with a piece
of foam of sufficient stiffness stuffed
into the opening of the main former.

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The ESC remains loosely pushed in
place above the battery and under
the nose top cover. It will have to be
pulled back partly to allow the battery
to be removed for charging. Space is
limited, but it should be just enough
to close the hatch.
Connect the servos and the ESC to
the receiver, find a place for it and
immobilise it with a piece of foam,
and route and fix the antenna(e) as
per the manufacturers instructions.
Final assembly
Open the holes for the wing holders in the fuselage by cutting the covering away with a
sharp hobby knife, and insert the 4 mm dia. beech dowels. These will hold the elastic
bands that in turn will hold the wing in place.
If you have not already done so (see page 8), bend the landing gear legs from 2 mm
pianowire, and slide these into the holes in the fuselage. Fix the gear with the two ply
straps screwed down into the pine strips alongside the gear. Mount the wheels and fix
them with a wheel collar on both sides, clamped onto the wire. Alternatively, small, tight
fitting sections of control cable can be used, the outer ones glued on with a dab of
superglue.
The battery hatch has to be opened for each charge so add the 1.2 mm ply lip to the
forward edge in such a way that it slides under the permanent nose cover, see the
drawing. The hatch can be held in place with an extra small rubber band attached to the
wing dowels.
This finalises the build of the JIMMY, but before you can go flying something else needs
to be done, namely adjusting the……..
Center of Gravity or Balance Point
For the stability of flight it is important the the plane is balanced properly. The balance
point shall be at the position as indicated on the drawing, which can be adjusted by
sliding the battery backward and forward. Temporarily mount the propellor and -adapter,
insert the battery upside down so the velcro does not ”bite”, balance the assembled
plane on your fingertips by resting the wing on them, slightly forward of the wing spars,
close to the fuselage. When the battery is at the correct position, the plane’s bottom will
hang in a horizontal attitude. Turn the battery over and fix it in this exact position. Further
adjustments can be made after flight testing by an experienced model pilot, or following
instructions to be found on the internet (search for ”CG dive testing”). Remove the
propellor.

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Control Adjustments
Charge your battery. Be aware that Lithium Polymer (Lipo) type batteries need a
dedicated type of charger, set to the correct charging current and voltage
depending on the cell count and capacity. Check the manufacturers instructions,
ignoring these instructions may have serious consequences!
Do not mount the propellor as yet. Loosen the set screws on the pushrod connectors.
Switch on your transmitter. Connect the battery to the ESC. The built-in BEC will supply
power to the receiver and the servos. Bind your receiver to the transmitter per the
manufacturers instructions of your RC set. Check that the servo arms are in their neutral
position, i.e. at right angles to the pushrods. If this is not the case, adjust the electronic
trims of your transmitter (a.k.a. ”Sub Trims”). For large adjustments, you will have to
remove the arm by undoing the mounting screw and reposition it on the splines of the
servo drive end. Manually position the control surfaces until they are inline with the fin/
stabiliser surfaces and fasten the set screws in the pushrod connectors.
Check the ESC instructions how to adjust your ESC to the throttle settings of your
transmitter. Finally, mount the propellor on the motor shaft with an appropriate adaptor.
Materials to be purchased separately:
Transmitter and receiver, 3 channels minimum
Motor 100W 1100KV with mounting cross
ESC 20-25A
Battery 1000mAh, 20C or higher discharge current
Propellor 7”x4”
Propellor/motor adapter
Electrical connectors motor/ESC (3x pair) 2mm dia.
Electrical connectors ESC/battery (2x pair, depending on battery standard)
Servos (2x) 5g
Pushrod connectors (2x)
Wheels light/foam type (2x) 40-50mm
Iron-on film 2m x 60cm
Rubber bands (4x + spares)
Velcro 100mm

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