SIG SIGRC106 User guide
Sig Mfg. Co., Inc...401
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7 South Front Street...PO Box 520....Montezuma, IA 50171
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0520
Assembly of the FOUR
manual first to get familiar with the various parts and the assembly sequences.
Congratulations on your purchase of the SIG FOUR-STAR 20EP. For many years the SIG Four-Star series of low-wing sport
airplanes have proven to be among the most popular and versatile at the flying field. Originally designed for 2-stroke glow
engines, Four-Stars have also excelled with 4-stroke, gasoline, and now electric motors. The secret to their popularity is their
light flying weight and low wing loading, combined with excellent aerobatic performance. The maneuverability and smooth
handling of the Four-Star will make it the sport model you'll want to take to the flying field every time.
The FOUR-STAR 20EP is the first Four-Star kit designed primarily for electric power (although the structure is configured to
easily accommodate a glow engine if you wish to go that way). This use of a modern electric power system in the legendary
Four-Star has produced a marvelous little R/C ship that is a pure joy to fly. It's small enough to carry around in your vehicle
completely assembled and ready to fly almost anywhere, anytime!
-STAR 20EP is quick and easy, following the detailed instructions in this manual. All parts are CAD-
drawn and the majority are laser-cut, so that everything fits the way it should! We strongly suggest that you read through the
.
Additional Items Needed
worked well for us in our prototype models. You should select equivalent items.
area. The lighter the final weight is, the better this airplane will fly! The radio equipment you install will have a great effect
The following items are not supplied in this kit but are needed to complete the airplane. Because of the wide variety of brands
available and the influence of local preferences, the final choice of these items is left to you. In most cases, we will list what
BRUSHLESS OUTRUNNER ELECTRIC MOTOR
200-300 watts with a kv specification suitable for turning a 9x6E propeller. Motor should also include prop adapter
hardware and a radial-style motor mount.
ELECTRONIC SPEED CONTROL (ESC)
Matched to your motor - typically 35 amp.
* We use and recommend the Maxx Products Co. Combo 19A
(www.maxxprod.com), which is a packaged motor system that includes
their Himax 3510-1100 Brushless Outrunner Motor, a Castle Creations
Thunderbird 36 amp ESC, a radial motor mount, an APC 9x6E
propeller, a prop adapter, and mounting screws.
Himax 3510-1100 Motor specs:
Diameter 35.2mm (1.39")
Length 32.2mm (1.27")
Shaft Diameter 4.0mm
Weight 89g (3.1 oz.) motor only
Max. Power 250W
Any other brand of outrunner motor and speed control of equivalent
size and specifications would also work.
Kv=1100 Rm=.055 lo=1.2
3S1P LITHIUM-POLYMER BATTERY PACK
1800-2400 mAh
BATTERY CHARGER
For maximum performance from your battery pack, you MUST use a proper battery charger! Make sure your charger is
designed for the type of cells in your battery pack. Using the wrong battery charger can be very dangerous! We
recommend that you use a quality peak detection lithium-polymer battery charger with cell balancing.
SPINNER (if desired)
2" to 2-1/4" diameter spinner is optional. You could also use an "acorn" style prop nut alone. Your choice.
2-1/4" dia. MAIN WHEELS
4-CHANNEL RADIO CONTROL SYSTEM with 4 SERVOS
"Standard" size radio gear is not recommended for an airplane as small as the Four-Star 20EP. The Four-Star gets its
great flight performance from many factors, but two of the most important factors are its light weight and generous wing
on the flight performance of your airplane. Maximum performance can only be achieved with light weight components.
RECEIVER a small or micro size receiver should be used in this model. In our flight tests we have used the Hitec
Electron 6 (weight: 19 grams) and the FMA M5 (weight: 11 grams). Both are dual conversion receivers.
SERVOS standard size servos, the ones that come with most sport radio systems, are too big and too heavy for the
Four-Star 20EP. You will need smaller servos. In our prototypes airplanes, we used Hitec HS-81 Micro Servos, which
have a torque rating of 36 oz/in and weigh .58 oz each. Any other brand of servo that is in the same size and torque
range will also work just fine.
SERVO CHORDS You will need one Y-Harness chord to connect the two aileron servos together inside the wing.
Every radio manufacturer has Y-Harness chords available for their radio systems. If they have an option for a short YHarness or a long Y-Harness, you can probably use the short one due to the small size of the airplane. In addition,
you will also need a short standard Servo Extension Chord to plug into the receiver and connect to the aileron YHarness.
COVERING MATERIAL
Any brand of quality iron-on plastic covering material is suitable for the Four-Star 20EP. If the manufacturer has a
"lite" version, use it to save a little weight. The color choice is entirely up to you. It will take approximately 1 to 1-1/2
rolls of covering material to cover the Four-Star 20EP, depending upon how many colors you elect to use.
.
GLUES
Pins, Paper Towels,
different size wood dowels are also handy to have around.
mount and a plastic 4 oz. fuel tank. You will also need to buy a 5th servo for the
Any references to right or left, refer to your right or left as if you were seated in the cockpit of the airplane.
the model's covering. Use a soft pencil instead of a pen.
Choice depends a lot on you personal preference. We used Thin, Medium, and
Thick SIG CA; CA Accelerator; Fine point CA applicator tips; and SIG Epoxy
Glue (5-minute and 30-minute).
BASIC MODELING TOOLS
Screwdrivers, Pliers (regular, needle nose, flat nose), Wire Cutters, Scissors,
Ruler, Pencil, Metal Straight Edge, Triangle, Flat Building Board, Hobby Knife
with #11 Blades, Single-Edge Razor Blades, Wax Paper, T& Rubbing Alcohol (for cleaning off excess epoxy glue).
POWER DRILL with Assorted DRILL BITS
SOLDERING IRON and SOLDER
COVERING IRON and TRIM SEAL TOOL
LIGHT WEIGHT WOOD FILLER
SANDPAPER BLOCKS and SANDPAPER
Use 80-100 grit to rough sand and shape parts; 220-300 grit for finish sanding.
A good general purpose sanding block can be made by wrapping a full 9"x11"
sheet of sandpaper around a piece of hardwood or plywood. Use screws or
thumbtacks along one edge to hold the overlapped ends of the sandpaper in
place. In addition to that block, make a small sandpaper "file" by gluing a strip
of 80 grit sandpaper onto a scrap plywood stick. Sandpaper glued or taped to
Glow Power Option
The Four-Star 20 can be powered with a 2 or 4-stroke glow engine instead of an
electric motor, if you prefer. We recommend glow engines in the .15 to .20 cu.in.
range. No major structural modifications are necessary to accommodate a glow
engine.
The checklist of changes if using a glow engine is short:
1. Leave the 3 small circles near the bottom of the F-1A and F-1B plywood
formers in place. Do not punch them out. Work some glue into the cut lines to
keep them permanently in place. The purpose of those 3 holes was to cool the
electric motor battery. Obviously not needed in a glow version. In fact, they
need to be sealed up so that glow fuel exhaust residue does not enter the nose
of the airplane.
2. Do not install the plywood BT (Battery Tray) in the nose. You will need that
clear space in the nose for a fuel tank.
3. In addition to the glow engine, you will need to purchase a suitable engine
throttle, and a suitable throttle pushrod.
Notes Before Beginning Construction
To build good flying models, you need a good straight building board. Crooked models don't fly well! The building board can be
a table, a workbench, a reject hollow wood door from the lumber yard, or anything else that is pefectly flat and untwisted. Cover
the top surface of the building board with a piece of celotex-type wall board or dense foam board, into which pins can be easily
pushed.
When building directly on top of the full-size plans, cover the plan with wax paper to prevent gluing the parts to the plan.
Don't use a ball point pen for making marks on the model during construction. If not sanded off, the ink marks will show through
.
All of the other parts can be identified by the "KIT INVENTORY LIST" that follows. Sort the different sizes of sticks and sheets
into individual piles to avoid confusion during building.
3/32"x3"x13" Fuselage
Threaded Couplers; for
The laser cut balsa and plywood parts can be identified using the "KEY TO LASER CUT PARTS". Mark the identification
numbers on the corresponding parts before removing them from the laser cut sheets. Leave all the laser cut parts in the sheets
until needed in construction. Then remove the pieces from the sheets carefully. Use a sharp #11 hobby knife to cut through any
"tabs" that are holding the parts in the sheets. Lightly sand off any remainder of the tabs, flush with the actual edge of the part.
COMPLETE KIT PARTS LIST
Laser Cut Balsa Wood Parts
2 1/16"x3"x36" Sheet No.1: wing ribs W-2,
W-3, W-4, W-4A
2 3/32"x4"x36" Sheet No.5: Fuselage Sides 1 3/16"x3"x36" Sheet No.6: tail parts Tail
1 3/32"x3"x36" Sheet No.2: Fuselage Top 1 3/32"x3"x36" Sheet
Parts; S-1, S-2, S-3, S-4, S-5, S-6, S-7, S-8,
S-9, E-1, E-2, E-3, E-4, E-5, E-6, E-7, R-1,
R-2, R-3, R-4, R-5, R-6, R-7, R-8, F-1, F-2,
F-3, F-4, F-5, F-6, F-7
No.3: fuselage parts
FBT-2, FD-1
1 3/16"x3"x36" Sheet
No.7: W-1A,
Ailerons, Wingtips
1 3/32"x3"x36" Sheet
No.4: W-1 wing ribs,
Spar Webs
Laser Cut Plywood Parts
1 1/8"x6"x24" Sheet No.8: APG, F-1A, F-1B,
F-2, F-2B, F-3, F-4, F-4T, F-5, F-5T, F-6, F6T, FBT-1, BT, DB, FHR, HT-1, HT-2, LG-1,
LG-2, P-1, P-2, SM-1 (4), T-1, T-2, TWM,
WBP
2 1/4" Motor Spacers
Balsa Wood Sticks
3 3/32"x3/16"x36" Stringers 1 1/16"x1/4"x18" Capstrips 8 1/8"x1/8"x24" Sub
Spars
4 1/4"x1/4"x24" Leading & Trailing Edges
4 1/8"x3/8"x36" Main
Spars, Main Spar
Doublers, Servo Bay
Balsa Wood Sheets
2 1/16"x1-1/4"x24" Trailing Edge Top Sheet 2 1/16"x1-1/2"x24" Trailing Edge Bottom
Sheet
2 1/16"x2"x24" Wing
Center Section
Sheeting
1
Top Sheeting
Hardwood
2 1/4"x1/4"x2-9/16" Servo Mount Rails 1 1/4" dia.x1-1/2" Birch Dowel
Music Wire
1 1/16"x4-3/8" formed Tailwheel Wire 1 1/16"x4-1/4" formed Elevator Joiner 2 1/32"x24" Elevator
& Rudder Pushrods
Plastic Parts
1 Molded Plastic Canopy 1 Molded Plastic Cowling
Hardware
2 2-56x10" Threaded Rods; for aileron
pushrods
2 Left Nylon Control Horns; for rud(1), right
ail(1)
8 #2x1/2” Sheet Metal Screws; for control
horns
2 4-40x3/8" Bolts; for main landing gear 2 6-32x1-1/2" Bolts; for axles 2 6-32 Lock Nuts; for
14 Hinges; for ail(6), ele(4), rud(3), tailwheel
(1)
1 1/16" id Wheel Collar & Set Screw; for
tailwheel
1 3/4" dia. Tailwheel 4 Nylon RC Links; for
rud(1), ail(2), ele(1)
1 Nylon Landing Gear Clip 1 Nylon Tailwheel
Bracket
1 2-56x3/8" Bolt; for tailwheel 1 2-56 Hex Nut; for
tailwheel
axles
1 10-32x1" Nylon Wing Bolt 1 10-32 Blind Nut; for
wing hold down
1 Hex Key Wrench
2 Right Nylon Control
Horns; for ele(1), left
ail(1)
8 #2x3/8" Sheet Metal
Screws; for cowling,
hatch, tailwheel
bracket
2 4-40 Blind Nuts; for
main landing gear
4 6-32 Hex Nuts; for
axles
2
elevator & rudder
pushrods
Misc
1 formed Aluminum Landing Gear 2 .130 odx19 Nylon Pushrod Tubes 1 Decal Sheet
SIGDKM106A
1 Decal Sheet
SIGDKM106B
.
.
WING PANEL CONSTRUCTION
start with the LEFT WING PANEL. To get started, tape or pin the wing plan to your building board. Cover the plan with a layer of
waxed paper to keep glue from sticking to the plan.
Add rib W
Add the W
it should be tipped very slightly with the top edge towards the wingtip to account for the wing's dihedral angle. The correct
We will build the wing in separate right and left wing panels, and then join the panels together after they are assembled. Let's
1a. Cut four 1/8"x3/8"x36" balsa sticks down to 24" long for the Main Spars. Cut the
four pieces of leftover stick to 9" long. These will be the Spar Doublers. Glue one
Spar Doubler to one end of each Main Spar. Let dry.
b. Pin one of the main spar assemblies in place on the plan. Align the center end of
the spar assembly (the end with the doubler on it) exactly with the line on the
plan that indicates the center of the wing. Let the excess spar length extend past
the wing tip.
2a. Remove all the balsa wing ribs from laser-cut sheets no. 1, 4, and 7. Make sure
you have correctly marked the ribs with their part numbers according to the KEY
TO LASER-CUT PARTS diagrams. You should have: (2) W-1 ribs, (2) W-1A, (2)
W-2, (2) W-3, (12) W-4, (2) W-4A, and (2) Wingtips.
b. Glue W-1A to the front of each W-1 rib, being very careful to get the edges
exactly aligned. Be sure to make a right and left W-1 rib assembly.
3a. Carefully remove one of the Spar Webs from laser cut sheet no. 4. Hold the Spar
Web against the plan and familiarize yourself with it's exact orientation. Note that
the open rib notches should be along the top of the Spar Web when it's installed
in the wing, not on the bottom.
b. Slide ribs W-2, W-3, and W-4 into their
notches in the Spar Web. Pin this
assembly in place on top of the Main
Spar. Pin down only the Spar Web at
this time, not the ribs - the ribs must
remain loose until the trailing edge
pieces are added in a few minutes.
c.
d.
angle is pre-cut into the end of the Spar Web. Just make sure you pin W-1 firmly against the end angle of the Spar Web that will insure that you are within tolerance for the dihedral angle later.
-4A.
-1/W-1A rib assembly, pinning it in place on the end of the Spar Web. Note that W-1 will not sit perfectly vertical
.
4A ribs, as shown on the plan. Glue the capstrips in place flush
with the bottom of the ribs.
Note: Do not install any 1/16" balsa sheeting to the bottom of the center section at this time.
is tight).
d. Drill pilot holes for your servo mounting screws and then mount the servo. When done, remove the servo and set aside.
4a. Slip the 1/16"x1-1/2"x24" Balsa Trailing Edge Bottom Sheet in place under the
back ends of the wing ribs. Slide it forward against the notches in the bottom of
the ribs. Now pin the ends of all the wing ribs to the Trailing Edge Bottom Sheet
and firmly to the plan.
b. Pin the 1/14"x1/4"x24" Balsa Trailing Edge in place on top of the Trailing Edge
Bottom Sheeting and up against the ends of the wing ribs.
5.
Check one more time that all the wing parts are properly aligned and pinned
together and pinned down to the building board. Then glue all the joints with Thin
CA adhesive. Let dry.
6.
Fit one of the Main Spar assemblies (from step 1a.) in place in the notches in top
of all the ribs. Glue securely and let dry.
7.
Glue the 1/16"x1-1/4"x24" Balsa Trailing Edge Top Sheet in place.
8a. Cut a piece of 1/8"x3/8" balsa stick to fit between ribs W-4 and W-4A, where
shown on the plan at the rear of the aileron servo bay. Glue it in flush with the
bottom of the ribs.
b. Cut two pieces of 1/16"x1/4" balsa stick for the Capstrips that go along the sides
of the W-4 and W-
9.
Glue the 1/4"x1/4"x24" Balsa Leading Edge in place.
10. Glue two 1/8"x1/8"x24" Balsa Sub Spars in place in the top rib notches.
11a. 1/16"x2"x24" balsa is provided for sheeting the center section of the wing. Start
by cutting the stock into seven 3-1/4" long pieces.
b. Glue one of the 3-1/4" long pieces in place up against the trailing edge top sheet.
Trim the width of another 3-1/4" long piece of sheeting stock to fit between the
first piece and the back of the top main spar. Glue in place.
c. Trim more pieces of the sheeting stock to fit between the top Sub Spars, as
shown. Glue in place and let dry.
12a. When all the glue joints are dry, take out all the pins and remove the wing panel
from the building board.
b. Glue two 1/8"x1/8"x24" Balsa Sub Spars in place in the bottom rib notches.
13a. Now is a good time to fit your aileron servo in the wing. Remove two SM-1 pieces from the laser-cut plywood sheet. Be
sure to sand off any excess part of the "tabs" that held the parts in the big sheet (the fit of SM-1 between the W-4 wing ribs
b. Glue the front SM-1 part in place.
c. Measure the length of your servo case
to determine exactly where the rear SM1 part should be located. Then glue it in
place.
.
14.
Cut a 1/2" dia. hole in the top sheeting just behind the main spar. This is for the aileron servo chord to exit the wing panel.
Use a large sanding block to sand any excess spar ends or sheeting flush with the
last W
-
4 tip rib.
b. Glue the 3/16" balsa Wingtip in place on the end of the wing panel. Make sure to match up the edges perfectly with rib W
-
4.
end of the 1/4" balsa leading edge where the dowel will be installed later.
The LEFT WING PANEL is now basically done. Repeat steps 1 through 17 to build a RIGHT WING PANEL.
Joining The Wing Panels
panels perfectly. Use pins or clamps to hold the wing panels tight together until the
20. Install 1/16" balsa center section sheeting to the bottom of the wing panels, just as you did in step 11 for the top of the wing.
Trim and sand down the top surface of the 1/4" sq. balsa trailing edge to blend with the shape of the wing.
15. Use a large sanding block to sand any excess spar ends and sheeting flush with the W-1 rib. Use a sanding block large
enough to sand the entire part at the same time. Work slowly to insure that the end rib remains flat and straight.
16a.
17. Wrap a small piece of 80 or 100 grit sandpaper around the 1/4" hardwood dowel provided. Use this to sand a groove in the
18.
Note the dashed lines that are cut into
the W-1 end ribs to indicate the location
for the laser-cut plywood DB Dihedral
Brace. Use a sharp #11 hobby knife to
cut through the rib between the dashes
to create an opening for the Dihedral
Brace. Do the same for both the W-1
end ribs of BOTH wing panels.
19a. Trial fit both wing panels together with the Dihedral Brace installed. Make sure the
panels come together tightly with no gaps. Then take the wings back apart.
b. Glue the DB Dihedral Brace halfway into one of the wing panels. Epoxy glue is
recommended.
c. Coat the end rib and the Dihedral Brace with glue and then slide the other wing
panel in place. Push the panels together tight! Match up the edges of the wing
glue dries.
21. Sand the wing to final shape. Round the 1/4" sq. balsa leading edge as shown in the cross-section drawings on the plan.
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