Great Planes GPMA0158 User Manual

INSTRUCTION MANUAL

WARRANTY

Great Planes Model Manufacturing Co guarantees this kit to be free from defects in both material and
workmanship at the date of purchase This warranty does not cover any component parts damaged by use or
modification In no case shall Great Planes' liability exceed the original cost of the purchased kit. Further, Great
Planes reserves the right to change or modify this warranty without notice

In that Great Planes has no control over the final assembly or material used for final assembly, no liability shall be
assumed nor accepted for any damage resulting from the use by the user of the final user-assembled product By the
act of using the user-assembled product, the user accepts all resulting liability

If the buyers are not prepared to accept the liability associated with the use of this product, they are
advised to return this kit immediately in new and unused condition to the place of purchase.

PO Box 788 Urbana, IL61801 [phone]

CUB2P02 05/95 V 1 Entire Contents © Copynght 1995

PRECAUTIONS..............................................................3

INTRODUCTION................................................................3

Engine selection........................................................3

Other items required .................................................3

Suggested supplies and tools...................................4

Common abbreviations............................................4

Types of wood...........................................................4

The what and how of adhesives ...............................4

Die-cut patterns.........................................................6

Metric conversions....................................................7

GET READY TO BUILD.................................................7

BUILD THE TAIL SURFACES

.......................................7

Build the rudder.........................................................7

Build the fin ...............................................................8

Build the stabilizer.....................................................8

Build the elevator ......................................................9

Join the elevators......................................................9

BUILD THE WING

........................................................10

Assemble the wing tip .............................................11

Build the wing panel ................................................11

Install the wing tip

...................................................12

Finish installing the spars........................................13

Sheet the top leading edge .....................................14

Sheet the bottom leading edge ...............................15

Joining the wing panels...........................................15

Sheet the center of the wing ...................................17

Wing completion .....................................................17

BUILD THE FUSELAGE ..............................................19

Build the fuselage sides..........................................19

Join the fuselage sides ...........................................20

Install the firewall ....................................................22

Install the engine ....................................................23

Sheet the nose & fuselage......................................24

Install pushrod tubes...............................................25

Install the stabilizer base.........................................25

Sheet the fuselage bottom ......................................26

Mount the wing on the fuselage..............................27

Mount the stab and fin ............................................28

Install the fuselage stringers ...................................28

Install the tail fairing ................................................30

Install the control horns...........................................30

Install the tail gear...................................................31

Install the main landing gear...................................31

Build and install the wing struts...............................32

Install the cowl

........................................................33

Scale details............................................................34

FINISHING........................................................................35

Final sanding...........................................................35

Balance the airplane laterally..................................35

Cover the structure with

MonoKote®

film

................35

Painting...................................................................36

Fuelproofing............................................................36

FINAL ASSEMBLY.......................................................36

Install the control surfaces ......................................37

Install the wheels ....................................................38

Install the windows..................................................39

Install the landing gear fairing .................................39

Radio installation.....................................................39

Balance your

model

................................................40

Finish

radio installation

...........................................41

Control surface throws ............................................42

Install the pilot.........................................................42

Preflight...................................................................43

Balance the propeller..............................................43

AMA Safety Code....................................................44

FLYING........................................................................44

Takeoff.....................................................................45

Flying ......................................................................45

Landing...................................................................45

Your Great Planes Piper J-3 Cub 20 is not a toy, but
rather a sophisticated, working model that functions very
much like an actual airplane.

Because of its realistic performance, the Cub 20, if not
assembled and operated correctly, could possibly cause
injury to yourself or spectators and damage property.

To make your R/C modeling experience totally
enjoyable, we recommend that you get experienced,
knowledgeable help with assembly and during your
first flights. You'll learn faster and avoid risking your model

before you're truly ready to solo. Your local hobby shop has
information about flying clubs in your area whose
membership includes qualified instructors.

You can also contact the national Academy of Model
Aeronautics (AMA), which has more than 2,300 chartered
clubs across the country. Through any one of them,
instructor training programs and insured newcomer training
are available.

Contact the AMA at the address or toll-free phone
number below.

Academy of Model Aeronautics
5151 East Memorial Drive
Muncie, IN 47302-9252

Toll Free [phone]

Fax# [phone]

2

Thank you for purchasing the Great Planes Piper J-3

Cub 20 for your next project We are sure that you will find

a great deal of modeling satisfaction while building and
flying this 1930's classic

You will find the J-3 Cub easy to build and fly, very
predictable and fairly acrobatic, yet it has no bad habits
Traditional Great Planes interlocking construction makes it
simple to build a great looking and straight airplane that is
sturdy enough to take along every time you go to the
flying field

If you have chosen this kit as your first R/C model, it is
important that you find an experienced modeler to help you
throughout the building and flying of this plane He should
thoroughly check the plane over before flying it and help
you with the first flights The J-3 Cub lacks the self-recovery
characteristics of a good basic trainer such as the Great
Planes PT Series airplanes On the other hand, if you have
already learned the basics of R/C flying and you are able to
safely handle a "trainer" airplane, the J-3 Cub is an
excellent choice to sharpen your skills and learn the art of
flying a taildragger So, dust off your work bench, put a new
blade in your hobby knife, load some fresh sandpaper and
let's build a 'J-3 Cub'

Please inspect all parts carefully before starting to
build! If any parts are missing, broken or defective, or if

you have any questions about building or flying this
model, please call us at [phone] and we'll be
glad to help. If you are calling for replacement parts,
please look up the part numbers and the kit
identification number (stamped on the end of the
carton) and have them ready when calling.

6 You must fly the model only with the help of a
competent, experienced R/C pilot if you are not already

an experienced and knowledgeable R/C pilot at this time

Note: We, as the kit manufacturer, can provide you with
a top quality kit and great instructions, but ultimately the
quality and flyability of your finished model depends on
how you build it, therefore, we cannot in any way
guarantee the performance of your completed model,
and no representations are expressed or implied as to
the performance or safety of your completed model

Remember: Take your time and follow directions to end
up with a well-built model that is straight and true.

There are several engines that will work well in the Cub 20

For a relaxed flying experience, an 0 S 15FP is a good

choice For a more spirited model an 0 S 20- 25FP or

26 Surpass (4-stroke) will work very well Your choice of
2-stroke or 4-stroke engine will determine the location of
the throttle pushrod exit, so you must acquire the engine
early in the building process, and plan ahead.

Note Items in parentheses (GPMQ4130) are suggested
part numbers recognized by distributors and hobby shops
and are listed for your convenience GPM is the Great
Planes brand, HCA is the Hobbico® brand and TOP is the
Top Flite® brand

1 You must assemble the plane according to the plans and
instructions Do not alter or modify the model, as doing so
may result in an unsafe or unflyable model In a few cases
the plans and instructions may differ slightly from the
photos In those instances you should assume the written
instructions are correct

2 You must take time to build straight, true and strong.
3 You must use a proper R/C radio that is in first class

condition, the correct sized engine and correct
components (fuel tank, wheels, etc ) throughout your
building process

4. You must properly install all R/C and other components
so that the model operates properly on the ground and in
the

air.

5. You must test the operation of the model before the first
and each successive flight to insure that all equipment is
operating, and you must make certain that the model has
remained structurally sound Be sure to check the nylon
clevises often and replace if they show signs of wear

D 4 Channel radio with 4 servos
D Engine 15-25 2-stroke

20- 26 4-stroke

D Propeller (A Top Flite Power Point® is recommended,

see the engine instructions for size)
D 6oz Fuel Tank - (GPMQ4102)
D 12" Medium Fuel Tubing - (GPMQ4131)
D (2) 2-1/2" Main Wheels - (GPMQ4223)
D (1) 1" Tail Wheel - (GPMQ4241)
D (4) 5/32" Wheel Collars - (GPMQ4306)
D (2) 3/32" Wheel Collars - (GPMQ4302)
D (2) Rolls MonoKote® Cub Yellow

Covering - (TOPQ0220)
D 1/2" Latex Foam Rubber Padding - (HCAQ1050)
D Cub Yellow LustreKote® - (TOPR7220)
D 1/16" Black Striping Tape - (GPMQ1460)
D Fueling Valve - (optional GPMQ4150)

D Switch and Charge Jack Mount - (GPMM1000)
D Screw-Lock Pushrod Connectors - (GPMQ3870)
D Flexible Cable Pushrod for Throttle - (GPMQ3700)
D 2" Pilot Figure - (optional - Williams Bros #184)

3

We recommend Great Planes Pro™ CA and Epoxy

D 2 oz Thin CA Adhesive - (GPMR6003)
D 2 oz Medium CA+ Adhesive - (GPMR6009)
D 1 oz. Thick CA- Adhesive - (GPMR6014)
D 6-Minute Epoxy - (GPMR6045)

D 30-Minute Epoxy - (GPMR6047)

D Pacer Formula 560 Canopy Glue

D Hand or Electric Drill
D Sealing Iron - (TOPR2100)
D Heat Gun - (TOPR2000)
D Hobby Saw - (X-acto® Razor Saw)
D Hobby Knife with #11 Blades
D Razor Plane - (Master Airscrew®)
D Screw Drivers - (Phillips and Slot tip)
D Flat File
D T-Pins Medium - (HCAR5150)
D String
D Straightedge with Scale
D Masking Tape - (required for construction)
D Sandpaper- (coarse, medium, fine grit)*
D T-Bar Sanding Block - (or similar)
D Lightweight Balsa Filler- (HCAR3401)
D #10-24 Tap and Tap Wrench
D IsopropyI Rubbing Alcohol - (70%)
D Dremel® Moto-Tool® or Similar - (optional)
D Kyosho® Curved Scissors (optional) - (KYOR1010)

*0n our workbench, we have four 11" T-Bar sanders,
equipped with #50, #80, #150 and #220-gnt sandpaper
This setup is all that is required for almost any sanding
task Custom sanding blocks can be made from balsa
for sanding hard to reach spots We also keep some
#320-grit wet-or-dry sandpaper handy for finish sanding
before covering.

T-Bar sanding tools are made from lightweight extruded

aluminum and can be found at most hobby shops A

2" x 11" strip of sandpaper is attached to the T-Bar by

gluing it on with rubber cement. Apply the rubber
cement to both the bottom of the T-Bar and the back of
the sandpaper When both surfaces are dry, press the
sandpaper firmly onto the T-Bar Spray adhesive can be
used for this purpose but it's harder to remove the
sandpaper when you need to replace it Wooden
sanding blocks can be made from straight 11" lengths
of 1" x 2" scrap lumber Start on one side, then wrap a
sheet of sandpaper completely around the wood,
ending on the same side as the one you started on.
Push 3 or 4 thumbtacks into this side, then trim off the

excess material.

Elev = Elevator
LE = Leading Edge (front)
Ply = Plywood

TE = Trailing Edge (rear)

Fuse = Fuselage
LG = Landing Gear
Stab = Stabilizer
" = Inches

Balsa Basswood Plywood

Cyanoacrylate: or CA glue has changed the way models

are built more than any other advance in modeling
technology In the good ol' days, model cement like
Ambroid, Duco, Comet and Sigment were the glues of
choice They all had a strong odor that could cause
dizziness, dried slowly (compared to CA) and became
brittle with age CA, on the other hand, is stronger, works
almost instantly and is bottled in three different viscosities
(thicknesses) CA is used for most glue joints, except where
epoxy is specified CA does emit rather strong fumes (some
say it's like tear gas) as it cures, so rule number one is to
work in a well ventilated area. All CA glues work best if the

joints are smooth and fit well.

Thin CA is also known simply as CA This
is the adhesive that has revolutionized
model building because it allows you to
assemble the parts first, then apply the
adhesive The thin formulation flows or
"wicks" into the joints and sets almost
instantly, eliminating the need to use pins to
hold things together while the glue dries.
You will often use thin CA for the initial
bond, but then follow with medium or thick
CA for extra strength, especially when
gluing plywood or hardwood.

CA+ is also known as medium or gap
filling CA CA+ is used for surface gluing,

filling small gaps between poorly matched
parts and for general purpose applications.
It cures slower than thin CA, allowing you to
apply a bead to two or three parts before
assembly Curing time without accelerator is
20 - 30 seconds.

4

CA- or thick CA is used when extra positioning

time is needed CA- is a great gap filler and is
also used in conjunction with accelerator to
make fillets when a little extra strength is
required Curing time is about 1-2 minutes.

Accelerator is a liquid chemical that comes in a
spray bottle for use in speeding up the cure time
of all CA types It should be misted on, not
sprayed heavily on the joint Accelerator may
cause exposed CA to bubble and sometimes
change color If accelerator is sprayed on heavily
it may weaken the glue joint, so use it sparingly

A WORD ABOUT CA SAFETY
After applying CA, don't stand directly over the work, to
avoid the puff of vapors All CA glues will bond skin
almost immediately If this should happen, CA Debonder
(available from your hobby dealer) or acetone fingernail
polish remover will dissolve the CA if allowed to soak into
the bond for a few minutes Don't use vigorous means to
separate a skin bond Never, never point the CA
applicator tip toward your face' Be especially careful
when opening a clogged tip In case of eye contact, flush
thoroughly with water and then seek medical attention,

but don't panic. Please, keep CA (and all other
modeling chemicals) out of the reach of children!

6-Minute epoxy is used for simple,

small gluing operations where
elaborate alignment is not required.
Working time (before it's too gooey to
use) is about 5 minutes, handling
time 15 minutes, and it's fully cured
in about 1 hour

30-minute epoxy is used for extra
strength (because it can penetrate
longer) and where several parts must
be aligned and checked before it
cures Working time is about 25
minutes, handling time 2 hours, and
it's fully cured in 8 hours.

Epoxy:

Great Planes has two Epoxy formulations available for the

modeler Both offer exceptional strength and convenient
working times Use epoxy when the joint requires exceptional
strength, such as when installing the firewall, when joining
the wing panels and when installing wing hold-down blocks
As with most epoxies, you mix equal parts of resin and
hardener, stir well, then apply a thin film to each part Parts
should be clamped, pinned, taped or weighted in place until
fully cured Before the epoxy cures, clean off any excess with
a paper towel A word of caution about mixing epoxy — don't
use extra hardener in the hopes of making the mixture
harder or work faster Just about all epoxies work best with
exactly a 50/50 mix When you increase the amount of
hardener you run the risk of causing the cured epoxy to
become either brittle or rubbery — neither being as strong as
a properly mixed batch.

Inch Scale

Great Planes Pro Wood Glue is an aliphatic resin glue
that works well on all types of wood It is non-toxic, virtually
odorless, and dries clear Some people are sensitive to CA
and epoxy fumes, so this is a good alternative for general
modeling use Its only drawback is that it is slow to cure,
requiring the parts to be securely clamped, pinned, or taped
while the glue dries

Metric Scale

5

6

Inches x 25.4 = mm (conversion factor)

1 /64" = .4mm 3/4" = 19.0mm
1/32" = .8mm 1" = 25.4mm
1/16"= 1.6mm 2" = 50.8mm
3/32" = 2.4mm 3" = 76.2mm
1/8" = 3.2mm 6" = 152.4mm

5/32" = 4.0mm 12" = 304.8mm
3/16" = 4.8mm 18" = 457.2mm
1/4"= 6.4mm 21"= 533.4mm
3/8" = 9.5mm 24" = 609.6mm
1/2" = 12.7mm 30" = 762.0mm
5/8" = 15.9mm 36" = 914.4mm

D 1. Unroll the plan sheets. Reroll the plans inside out to
make them lie flat.

D 2. Remove all parts from the box. As you do, determine
the name of each part by comparing it with the plans and
the parts list included in this kit. Using a felt tip pen or ball
point pen, write the part name or size on each piece to
avoid confusion later. Use the die-cut patterns shown on
page 6 to identify the die-cut parts and mark them before
removing them from the sheet. Save all scraps. If any of the
die-cut parts are difficult to punch out, do not force them!
Instead, cut around the parts with a hobby knife.
After punching out the die-cut parts, use your T-Bar or
sanding block to lightly sand the edges to remove any
die-cutting irregularities.

Tape the plan to a flat building surface, then cover the fin
and rudder section with waxed paper. Refer to the plan to
identify the parts and their locations.

D 1. Place the die-cut 3/16" balsa rudder parts R2, R3, R4
and R5 over the plan in their locations. Check their fit and
sand the mating edges as needed. Use a T-bar or other flat
sanding block to make any necessary adjustments. Pin the
parts to the building board after proper alignment and fitting
has been done. Do not glue the parts together at this time.

D 2. Select the straightest piece from the four
3/16" x 5/8" x 18" balsa sticks. Set this piece aside for use
later on the stabilizer trailing edge.

D 3. As you identify and mark the parts, separate them into
groups, such as fuse (fuselage), wing, fin and stab
(stabilizer) and hardware.

IMPORTANT: For a model that flies well with no
unexpected tendencies, all good modelers understand that

each assembly, especially the wing, must be built on a flat
surface. Also, a relatively soft, flat building board that you
can stick "T" pins into is required. This is for pinning down

individual parts during construction. A suitable building

board is a sheet of "Celotex" used in home construction.
This material may be found at hardware or home

improvement stores. If the building board is not flat, it must
be clamped to your flat building table. Now we're ready
to begin!

Okay, you've got your work space ready, your tools are
at hand and you know how to choose and use the right
glue for the job. Let's get started!

D 3. Cut the rudder LE from another 3/16" x 5/8" x 18"
balsa stick. Fit the LE into the notch in R3 and against the
edge of R5. Cut the horizontal frame section from the
3/16" x 5/8" x 18" left over from the rudder leading edge,
and fit it in position. Pin the LE and horizontal frame section
in place and glue all the parts together with thin CA. Wipe

off any excess glue from the surface before it cures.

NOTE: Leave all the parts pinned to the building board.

7

D 4. Cut the ribs from the 3/16" x 3/16" x 24" balsa stick.
Position the ribs in the rudder frame and glue them in place
with thin CA.

D 5. Remove the rudder from the building board and

inspect all the glue joints. Add thick CA to any open joints.

D 1. Pin the die-cut 3/16" balsa fin leading edge R1 in
place on the plan.

D 3. Cut the three ribs from the 3/16" x 3/16" x 24" balsa
stick to fit between the forward and aft frames. Position two
ribs above the lower frame for additional bracing and the
third rib at the location shown on the plan. Glue the ribs to
the frame with thin CA.

D 4. Remove the fin from the building board and inspect all
the glue joints. Apply thick CA where necessary.

D 2. Cut the fin top, fin base and the inner and outer fin
TE from the remaining 3/16" x 5/8" x 18" balsa sticks.
Check the fit and sand their mating edges as needed. Pin
the parts in place, then glue them together with thin CA.
NOTE: Leave all the parts pinned to the building board.

D 1. Work over waxed paper covered plans. Place the
die-cut S1, S2, S3 and S4 balsa parts over the plan to

check their fit. Sand their mating edges as needed and pin

the parts in place.

D 2. Cut the Stabilizer TE from the 3/16" X 5/8" X 18"
balsa stick you set aside earlier. Fit the TE between the S4
parts on the plans. Glue all the parts together with thin CA.

NOTE: Leave the parts pinned to the building board.

8

D 3. Refer to the plan, then cut six ribs from the
3/16" x 3/16" x 24" balsa stick. Position the ribs in the
stabilizer frame and glue in place with thin CA.

D 4. Remove the stabilizer from the building board and
inspect all of the glue joints. Apply thick CA to any
open joints.

D 1. Carefully sand all the tail surfaces flat with 150-grit
sandpaper and a large sanding block or T-bar. Remove as

little material as possible and don't get carried
away - inspect your work as you proceed. It's easy to
sand a low spot into the ribs or trailing edge, so be
careful to avoid doing this.

D 2. Draw centerlines around the outside edges of the fin,
rudder, stabilizer and elevator to assist in sanding and
hinge installation.

D 3. Position the rudder over the plan and align the bent
wire tail gear over the bottom end of the rudder as shown.
Mark the tail gear "arm" location on the centerline of the
rudder LE. Drill a 7/64" hole, 3/4" deep at this spot (the hole

is drilled slightly oversize to create a hard epoxy "sleeve"
around the wire). Cut a groove from the tail gear hole to
the bottom of the rudder that will allow the nylon tail gear

bearing to fit flush with the LE of the rudder. Do not glue
the tail gear in at this time.

D D 1. Position the S5, S6 and S7 from the die-cut 3/16"
balsa parts over the plan and check the fit of the mating
edges and sand them as needed. Cut the elevator LE from
a 3/16" x 5/8" x 24" balsa stick. Pin the parts in place over

the plans and glue them together with thin CA.

D D 2. Refer to the plan, then cut three elevator ribs from

the 3/16" x 3/16" x 24" balsa stick. Position and glue the

ribs in the elevator frame with thin CA.

D D 3. Remove the elevator from the building board and
inspect all the glue joints. Apply thick CA to any open joints.

D 4. Repeat this process to build the other elevator.

9

D 4 Trial fit but do not glue the tail gear wire in the rudder.
Make adjustments if necessary.

D 5 Temporarily pin the elevators on the plan Lay the
3/32" elevator joiner wire in place on the elevators and
mark its outline using a soft leaded pencil NOTE: Mark the
elevator joiner wire outline very lightly so that it can be
sanded off easily

D 6 Accurately drill a 1/16" diameter pilot hole

approximately 3/4" deep and perpendicular (90°) to the LE,
at each location Then drill the final hole with a 7/64" drill bit
to a depth of 7/8" (The hole is drilled slightly oversize to
allow for positioning, and to allow room to create a hard
epoxy "sleeve" around the wire).

D 7 Use your sharpened 1/8" diameter brass tube to cut a
groove in the leading edge of both elevators to accept the
elevator joiner wire Slightly round the inside corner where
the groove meets the hole to allow for the bend in the
elevator joiner wire.

D 10 Sand the leading edges of the stabilizer and fin and
the trailing edges of the elevator and rudder to a rounded
shape, as shown in the cross-section on the plan.

We have found that it's much simpler to do all hinging
after the model is covered.

D 1 Build one wing "half" or panel at a time You may want
to cut out each wing panel from the plan sheet to place on
your building board Tape the plan to your flat building
board and cover it with waxed paper Begin with the right
wing panel.

TWO WARPED SPARS INSTALLED

THIS WAY WILL RESULT IN A

STRAIGHT WING

TWO WARPED SPARS INSTALLED

THIS WAY WILL RESULT IN A

WARPED WING

D 8. Test fit (do not glue yet) the joiner wire into both

elevators Position the elevators against a straightedge to
check for straightness of the LE with the joiner wire
installed If the leading edges don't match up with the

straightedge, you may slightly enlarge the holes drilled in
the elevator leading edges Make sure both elevators are
flat on the work surface If both elevators do not lie flat, you
can make slight adjustments by twisting the joiner wire.

D 9. Carve or sand the bevel on the leading edges of the

elevator and rudder A razor plane allows you to rough-in

the bevel before finishing with a sanding block Refer to the

plan for the correct angle

D 2. Locate all four 1/4" x 5/16" x 27" balsa spars and
examine them carefully for possible imperfections Look for
knots, soft spots, diagonal grain and any other
imperfections If possible, position each spar so the
imperfections are on the outer half of the wing panel
(toward the tip), where they will be least affected by high
stress If the spars are warped slightly try to "balance them
out" by installing the warped spars in opposite directions
(see sketch above).

D 3. The shaped and notched wing leading edges (LE)

and trailing edges (TE) are fastened together by thin strips
of balsa Separate them by cutting with a hobby knife, as
shown in the sketch above

10

D 4. Carefully remove all the die-cut 1/16" balsa R1
through R6 wing ribs from the die-cut sheets. Sand the
edges slightly to remove any die-cutting irregularities.

D D 1. Place the die-cut 3/16" balsa wing tip parts T1,T2
and T3 over the plan and check all joints for proper fit.
Make adjustments if necessary. Pin the parts over the plan
and glue them together with thin CA.

D D 2. Without gluing, place ribs R2 through R5 on the
spars in their locations as shown on the plans.

D D 2. Remove the wing tip from the building board and
inspect all glue joints. Apply thick CA to any open joints.

D D 3. Place the wing tip on your work surface and lightly
sand both sides smooth with 80-grit sandpaper. Set the
wing tip aside for now.

D Repeat steps 1 -3 for the other tip.

D D 1. Do not use any glue until step five. For now,

we're just making preparations and familiarizing

ourselves with the layout. Place one of the 1/4" x 5/16" x

27" balsa lower main spars and one of the 1/8" x 3/16" x
27" balsa lower forward spars on the wing plan. Pin only

the main spar down with crossed T-pins as shown in the

sketch. We recommend crossed T-pins at every rib bay (the
space between the ribs). The lower forward spar is for
alignment at this point and will be glued to the ribs later.
NOTE: Align the end of the spars with the outboard edge of

the wing rib R5. Leave the spars' "overhang" at the root

(inboard end) of the wing. We'll trim it off later before joining

the wing halves,

D D 3. Match the notches in the shaped balsa LE and TE
with the plan. Add the LE and TE to the ribs making sure
each rib is fitted into its respective notch. Center the LE
vertically so there is an equal amount of space above and

below each rib.

D D 4. Pin the TE to the building board. Place a piece of
scrap 1/16" balsa sheet under ribs R2 and R3 at the TE to

center them in the TE. Check that ribs, R4 and R5 are

against the building board.

D D 5. Use a small building square or draftsman's triangle

to make sure each rib is vertical to the main spar. Glue the

ribs to the main spar with thin CA.

D D 6. Adjust the LE up or down until all the ribs are

centered in the notches in the LE. Note that the LE is
angled down slightly as shown in the cross section on the
plan. Apply thin CA to each joint between the ribs and
the

LE

and

TE.

11

D D 7. Install the 1/4" x 5/16" x 27" upper main spar in
the wing ribs. Check that the top of the main spar is flush
with the top of the ribs. Make sure the end of the upper
main spar is flush with the outboard edge of rib R5. Glue
the main spar to the ribs with thin CA.

D D 8. Install the 1/8" x 3/16" x 27" upper forward balsa

spar in the wing ribs with one end of the spar flush with the
outboard edge of rib R5. Glue the forward balsa spar to

the ribs with thin CA.

D D 3. So that the wing tip can fit properly between the
LE and rib R5, sand the front of the wing tip to match the
angle of the LE. Trim the TE flush with R5 so you can fit the
tip properly in place.

D D 4. Insert the front of the wing tip into the slot in rib
R5. The aft end of the wing tip is attached to the TE of

the wing and the side of rib R5, while lying flush on the

building board.

D D 1. Locate the die-cut 1/8" plywood wing tip brace, the

die-cut 1/16" balsa wing tip rib R6, and your previously

assembled wing tip. Notice the plywood wing tip brace has
a small "die-cut bump" at the tip. This is to allow you to
finish the piece to a perfect point where the die-cutter may

have difficulty in this area. Take a minute to sand off the

bump so the profile continues along the intended outline.

D D 2. Fit the 1/8" plywood wing tip brace into rib R5. The

top "arm" on the wing tip brace should be flush with the top

of the upper main spar and the slot for rib R6 should be
over the rib location on the plans.

D D 5. Insert rib R6 in the slot in the plywood wing

tip brace.

D D 6. Check the fit of all the wing tip parts and sand any
mating edges as needed. Glue the wing tip parts together
and to the wing panel with thin CA.

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D D 1. Carefully remove the wing from the building board.
Turn the wing upside down. Press the balsa lower forward

spar into the notches in the ribs. Note that the front edge of
the notches in ribs R4 and R5 is 1/16" below the aft edge of
the notch. The lower forward spar should be flush with the
front edge of the notch and flush with the edge of ribs R2
and R3. Glue in place with thin CA.

D D 2. Carefully remove the wing from the building board
and turn it right side up. Align the spars and ribs with the
plans and pin it back on the building board. Test fit the
die-cut 1/8" ply forward and aft strut mounting plates to

the wing at the locations shown on the plans. Glue them to
the wing with thin CA. Then use thick CA to form a

reinforcing fillet at the glue joint.

D D 4. Glue eight 1/16" x 2-3/8" x 1-3/16" balsa vertical

grain shear webs to the rear of the balsa main spars
starting between ribs R3 and R4 and ending between the
last two R4 ribs. Shear webs will be installed between ribs
R2 and R3 after the wing halves are joined. The shear

webs are provided slightly thinner than the wing so they

may be positioned without protruding above or below the
top and bottom spars. It is not necessary to glue the shear
webs to the ribs - but, it is important to glue the shear

webs securely to the spars.
Note: At this point the wing should still be pinned to the

work surface. Of course, we cannot add shear webs if the
crossed T-pins are in position so remove the T-pins as you
go. Then replace the T-pins through the sheer webs in
order to keep the wing flat on your building board - or, use
weights on top of the wing instead of the T-pins to hold the
wing flat as you glue the shear webs in position. You only
need to replace T-pins at every other rib bay.

D D 5. Locate the 1/8" die-cut plywood dihedral gauge

(DG). Hold the gauge next to the main spar with the corner

of the gauge at the wing centerline on the plan. Mark both
sides of the main spars using the (DG) as shown in
the photo.

D D 3. Test fit the die-cut 1/8" ply strut mounting plate
brace over the aft strut mounting plate. Make sure the
brace contacts the wing ribs and the strut mounting plate.
Glue the brace with thin CA, followed by a fillet of thick CA
on all three pieces.

D D 6. Connect both lines by drawing a line across the top

of each spar.
D D 7. Follow the same procedure for the forward spars

and TE.

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D D 1. Use a T-bar or flat sanding block with 150-grit
sandpaper to lightly sand the top edges of the ribs to
smoothly blend the ribs to the main spar and remove
any bumps.

D D 2. Butt one of the 1/16" x 1-1/2" x 30" balsa wing LE
sheets against the leading edge. For the strongest glue

joint, sand or cut a bevel at the front edge of the sheet to

match the angle between the leading edge and the ribs.

D D 6. To provide a gluing surface for the sheeting, carve
a slight bevel on the wing tip where the sheet will meet
the

tip.

D D 7. Position the leading edge sheeting against the rear
edge of the LE and covering rib R2. Using thin CA, glue the
front edge of the sheet to the LE. Slightly wet the entire
sheet to bend it to the spar. Apply a bead of thick CA to the
forward spar. Working quickly, bend the sheeting to the
spar holding it down with something flat like a T-bar sander
or flat block of wood until the CA cures. Do not glue the
sheet to the LE past rib R5.

D D 3. Mark the sheet so that its aft edge is 1/16" ahead of
the aft edge of the top forward balsa spar. The exposed
spar will provide a "step" for the cap strips to glue to later.

D D 4. Before attempting to bend the sheet so it may
reach the outer wing tip, the sheet must be thoroughly
wetted from R5 outward. Use a spray bottle or a sponge

to liberally apply water to the tip area of the sheet outboard
of rib R5. Carefully "work" the sheet with your fingers by
bending and twisting it in the direction required to meet the
wing tip. Replace the sheet on the wing and test bending
the sheet into position. Don't force the sheet - add more

water if necessary.

D D 5. Starting at rib R5 the aft edge of the sheeting will

have to be trimmed to keep it parallel with the front spar
(notice that the sheeting bends backward as it is curved to
meet the tip). Trim and test fit the sheet until it conforms to
the desired straight line.

D D 8. Lift the wing off the building board. Wick thin CA
between the ribs and the sheet from the inside of the wing.
Add a fillet of medium or thick CA along the inside of
the

LE.

D D 9. Wet the sheet one more time in the tip area - the

water may have evaporated from the balsa. Test bend the

sheet to the tip. Apply thick CA where the sheet will contact

the outer tip. Add thin CA to the joint between the sheet

and rib R6. Fill the small seam between the LE and the

front of the sheet between ribs R5 and R6 with a scrap

piece of balsa.

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D D 9. Trim off some of the excess sheet past the wing tip

to allow the bottom sheet to make contact with the wing tip.

D D 1. Turn the wing over and install another

1/16" x 1-1/2" x 30" balsa wing LE sheet almost the same
way you installed the top except cut the sheet so it goes to
the aft edge of the forward spar. This time apply thick CA to
the ribs before you add the sheet.

time. It's easier to remove material than it is to add it.

Now that the right wing panel is completed, dust off your

building board and build the left wing panel.

D 1. Locate the die-cut 1/8" birch plywood dihedral brace
(A) and the die-cut 1/8" birch plywood dihedral brace (B).
Measure and draw a vertical centerline on both dihedral
braces. Glue the two dihedral braces together with

30-minute epoxy, lining up the centerlines. Clamp the

braces together and remove any excess epoxy with a
paper towel moistened with rubbing alcohol. While the
epoxy is curing, move onto the next step.

D D 2. Notice on the plan that the LE does not begin to
curve back until outboard of rib R5. Refer to the plan for
the correct shape. A razor plane works well to cleanly

remove material until you get close enough to use
sandpaper. Be careful with the razor plane - take a little
off at a time. Then use 150-grit sandpaper to rough sand
the wing tip to shape.

D D 3. Use a razor saw to cut both forward spars,
both main spars, and the TE on the lines previously drawn.
(See steps 5-7 on page 13).

D D 4. Sand the end of the spars and the trailing edge up

to the lines. Remove only a small amount of material at a

D 2. Without using glue, temporarily join the wing halves
using the die-cut 1/16" birch ply forward and aft spar
joiners and the die-cut 1/8" LE joiner. Also test fit the
die-cut 3/32" balsa sub ribs 1A in front of the forward spar
joiner. You may trim the ends of the forward and aft spar
joiners, but the LE joiner determines the width of the center
section and this should not be changed. With one of the
wing panels lying flat on your work table, prop up rib R5 of
the other panel 15/16" to account for the dihedral. Check
the fit of the spars, joiners and TE. At this time test fit the
1/4" x 1-3/4" wing dowel to check that it is perpendicular to
the leading edge joiner when fully seated into the forward
spar joiner. If you have to make adjustments here, do not
modify the LE joiner but adjust the position of the wing
dowel hole in the front spar joiner instead. Make sure you
have not built any "sweep" into the wing by making the
spars or TE too long or too short. Be sure to maintain the
correct spacing between ribs R2 per the plan so the wing

will fit on the fuselage.

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