Design Philosophy

When developing the Four-Star 40, two design considerations were at the top of the list in importance:
  • Impeccable Flight Performance - Like all Sig kits, it had to have smooth, reliable flight performance with no surprises. It had to fly through maneuvers, not just be pulled through by brute force of the engine. Gentle slow speed and stall characteristics were equally important.
  • Easy Construction - Most modelers want to get in the air quickly, and who can blame them? Low parts count and minimal sanding/shaping were deemed necessary to help reduce building time and effort. It also had to be easy to cover with iron-on coverings with little painting required.
The following paragraphs are meant to give you a bit of insight on the aircraft's design by discussing individual parts and the thought process behind them. Several prototypes have been built and flown to test the ideas and we believe the final design presented in this kit represents the finest blend of building and flying characteristics from those tests.

Fuselage Construction - Lite-Ply fuselage construction has become very popular in the last few years and with good reason. It's fast, strong, and lightweight (with proper attention to lightening holes, etc.). The plywood fuselage doubler sets the thrust line, reinforces the wing saddle, and provides locations for the tank floor and wing hold-down blocks. A shapeless box doesn't look good, so three stringers and a slightly curved top deck were added to give it some shape without adding much work. A plastic cowl would have looked nice, but would have added complexity and weight, as well as required painting, so simple "cheeks" were used instead.

Canopy - A nicely rounded canopy adds even more shape to the airplane, and it's already made for you! It doesn't require painting because the frame is highlighted with striping tape. Setting the canopy relatively far back on the fuselage gives the model an aerobatic/fighterish look.

Landing Gear - Aluminum landing gear is durable and easy to install. Mounting it on the fuselage instead of the wing simplifies wing construction and lowers the parts count. The tailwheel is a bit unique in that it's attached directly to the rudder without the usual plastic tailwheel bearing. We've tested this installation quite extensively without any problems. The amazing strength of EASY HINGES and cyanoacrylate adhesive make this simple, effective tailwheel installation possible.

Tail Surfaces - What could be easier than totally pre-cut tail surfaces that come out of the box ready to sand? There's a small weight penalty over built-up surfaces, but the time saved during construction is worth it.

Wing Construction - No leading edge sheeting saves considerable building time. The strength of the wing is derived primarily from the spruce main spars and shear webbing. The leading edge uses a large radius for superior slow speed handling and stall resistance. The flat wingtips are actually very efficient and don't require carving and sanding like rounded tips made from balsa blocks.

Airfoil - The airfoil is nearly symmetrical for great aerobatic performance, but is flat aft of the bottom main spar so it can be built flat on the table.

Ailerons - Like the tail surfaces, the ailerons are pre-cut from sheet balsa. The taper gives the illusion of a tapered wing, but it is also good from the standpoint of flutter resistance. Many designs taper just the outer few inches of each aileron at the tip, because that's where flutter usually first develops. On this design, the taper simply extends the full length of the aileron. The aileron torque rods have been specially bent to provide a small amount of differential movement which improves the roll characteristics.

There are many different glues available today for model construction that it can be confusing to even the experienced modeler. To simplify matters, most glues can be classified as one of four basic types:
  1. Fast cyanoacrylate adhesives (abbreviated in this book as "CA") such as SIG CA, Hot Stuff, Jet, etc ...
  2. Easy-to-use water-based glues such as SIG-BOND (yellow) and SIG SUPER-WELD (white).
  3. Super strong (heavier) two-part epoxy glues such as SIG KWIK-SET (5-min cure) and SIG EPOXY (3-hour cure).
  4. Traditional solvent-based model cements such as SIG-MENT.


Each of these types has different characteristics and advantages. Often times, the choice of which type to use is strictly a matter of personal preference based on your experience with a previous model. However, because of the vast use of Lite-Ply and hardwoods in the FOUR-STAR 120, we have found that the CA glues seem to work the best for general construction. In fact, the construction sequence of the fuselage is designed with the use of CA glue in mind. Other glues could be used, but CA is recommended as our first choice because of its ability to penetrate an already assembled joint. In other words, the fuse parts can first be assembled dry (without glue), the alignment checked and adjusted, and then the glue can be applied to the joints. You should also have on hand some epoxy (both 5-minute and slow dry) and SIG-BOND because these glues are called out in several of the steps in these instructions.
SIG CA, like most brands of cyanoacrylates, comes in three viscosities thin, medium, and thick. Odorless CA's are also available from several manufacturers. Odorless CA is generally more expensive, but is ideal for people who can't tolerate the fumes of normal CA. An accelerator spray and debonder are also available and are described below.
  • Sig CA Thin - Watery in consistency, thin CA should only be used when the two parts to be joined are in perfect contact with zero gap. Capillary action pulls this glue deep into the wood resulting in a very strong bond and it dries in just a few seconds. Thin CA can be used to tack assemblies together, but these joints should be glued again later with medium or thick CA. Thin CA is also necessary for installing EASY HINGES.
  • Sig CA Medium - Our medium thickness CA is excellent for almost any step during construction, and is particularly recommended for gluing the plywood fuselage parts. The extra thickness allows the glue to fill small gaps, but it dries a little slower than thin CA. If you want only one type of CA, use medium thickness.
  • Sig CA Slow - This thickest formula is good for filling large gaps and building up strong fillets at joints requiring extra strength. It also dries slow enough to allow you to apply it to one part and position it on another before it dries. (With the thin and medium CA's, the parts must be in contact and positioned correctly before glue application.) This feature is useful when laminating large sheeted areas like a fuselage side and a fuselage doubler.
  • Sig Kwik-Shot Accelerator - Spraying accelerator on CA (any thickness) will cure it almost instantly. Although CA is fast, it's sometimes nice to speed it up even more.
  • Debonder - This can be used to separate parts, but you'll probably use it for unsticking your fingers more than anything else!
CAUTION: Some people have experienced allergic reactions when exposed to epoxy or cyanoacrylate glues. This is very rare. However, it is always important that such glues, and also paints, thinners and solvents, be used with adequate ventilation to carry fumes away.

Engines Propellers, and Mufflers

There is a tremendous variety of engines available in the size range specified for the FOUR-STAR 40. Both 2-stroke and 4-stroke engines work equally well in this model, so choose your favorite type, keeping in mind the type of performance that you wish the model to have. If you want maximum aerobatic capability and vertical performance, use an engine towards the upper end of the recommended size range. If this is your first low-wing model, engine sizes from the bottom of the range may suit you better. Engines at the bottom of the range will still pull the FOUR-STAR 40 through most aerobatic maneuvers.

Use only those propellers recommended in the instructions supplied with your engine. If you use a very high-power engine in your model (such as a schneurle-ported 2-stroke .40), it's recommended that you opt for a propeller with a relatively large diameter and low-pitch. This will give you loads of pulling power during maneuvers without a lot of excess speed.

There is no one type of muffler that is best suited to the FOUR-STAR 40. It all depends on the particular engine that you have selected. If you have a 2-stroke engine, use the muffler that was supplied with it or one of the many aftermarket mufflers that are available. Most 4-stroke engines don't require a muffler because of their low noise production.

.30 - .402-Stroke
- 40 - .504-Stroke

Radio Requirements

A four-channel radio system is required for the FOUR-STAR 40 to operate the ailerons, elevator, rudder, and throttle. The fuselage is spacious enough that any common brand of radio equipment with standard size servos and battery pack can be used. Be certain that your radio system's frequency is approved for use in RIC model aircraft.


You'll Need a Good Sanding Block

An assortment of different size sanding blocks are indispensable tools for model construction. A good general purpose block can be made by wrapping a 9"x11" sheet of sandpaper around a piece of hardwood or plywood. Use three screws along one edge to hold the overlapped ends of the sandpaper. Put 80-grit paper on the block during general construction. Switch to 220-grit paper for final finish sanding just before covering.

In addition to the large block, there are places where a smaller one is handy. Also, a sandpaper "file" can be made by gluing sandpaper to a flat spruce stick or around a hardwood dowel for working in tight places.

About The Building Sequence

The quickest and most efficient way to complete a model is to work on several pieces at the same time. While the glue is drying on one section, you can start on or proceed with another part. Keep in mind that the number, sequence used in these instructions was chosen as the best way to explain the building of each major component and is not intended to be followed in exact one-two-three fashion. Start on the wing at No.1 and after doing as many steps as is convenient, flip over to "FUSELAGE CONSTRUCTION" and do a step or two there, then back to "WING CONSTRUCTION" and so forth. You will arrive at points where you can go no farther until another component is available. Plan ahead! Read the book completely and study the full size plans before beginning construction.

Refer to "The Basics of Radio Control"

In addition to the instruction booklet you are reading now, the booklet "The Basics of Radio Control" has been included with this kit as a reference for installing the engine, fuel tank, and radio in the FOUR-STAR 40. It also contains very important information on preparing the model for flight. Modelers of all experience levels are encouraged to read this book and follow its guidelines for success.

Laser-Cut Balsa Sheets
33/32"x3"x9" W-I Wing Ribs 43/32"x3"x18" W-2 Wing Ribs I3/32"x4"x18" Fuselage Top Deck, BP
Sheet Balsa
21/16"x1-1/4"x30" Top Trailing Edge Sheeting 21/16"x1-1/2"x30" Bottom Trailing Edge Sheeting 21/16"x3"x30" Wing Center Sheeting, Top and Bottom 183/32"x3"x1-3/16" Shear Webs (3 bundles of 6)
Stick Balsa
63/16"x3/16"x30" Front Spars, Rear Spars 33/16"x1/4"x18" Fuselage Stringers 21/4"x1/4"x30" Trailing Edges 25/16"x5/16"x30" Leading Edges
11/2"x24" triangle- Braces for F-I, Wing Hold-Down Blocks, and Fin
Special Shaped Balsa
13/16"x3"x9" Pre-Cut Rudder 13/16"x5"x6" Pre-Cut Fin 2 1/4"x1-5/8"x27-3/4" Pre-Cut Ailerons 21/4"x2"x9" Pre-Cut Elevators
11/4"x5"x18" Pre-Cut Stabilizer
Laser-Cut Poplar Plywood (Lite-Ply)
21/8"x6"x48" Fuselage Side, Fuselage Doubler 11/8"x4"x36" HR, Cockpit Floor, FBR 11/8"x4"x24" F-2 thru F-6, APG, Stab Support, F-3S, F-4S, and IP 11/8"x4"x24" FBF, Tank Floor, ASCG, Dual Tool, and Wing Tips
Laser-Cut Birch Plywood
13/32"x5-1/4"x9" Firewall, Dihedral Brace


Sawn Birch Plywood
21/16"x3/4"x1-5/8" Wing Hold Down Plates 11/4"x1-1/2"x3" Landing Gear Mount
I1/4" dia.x2" BIRCH; Wing Hold Down Dowel 2 1/4"x1/4"x2" BASSWOOD; Grooved Torque Rod Blocks 21/4"x3/4"x1" BASSWOOD; Wing Hold Down Blocks 43/16"x3/8"x30" SPRUCE; Main Wing Spars
Formed Wire Parts
11/16" dia. Tailwheel Wire 13/32" dia. Elevator Joiner 14-40x5" Threaded Rod- L.H. Aileron Torque Rod (with 1/8"o.d. x1-1/2" Brass Bearing) 1I4-40x5" Threaded Rod- R.H. Aileron Torque Rod (with 1/8"o.d. x1-1/2" Brass Bearing)
Formed Plastic
1.03 Clear Plastic; Canopy
Miscellaneous Parts
2Glass Filled Engine Mounts 1.090 Aluminum Landing Gear 11" x 24" Fiberglass Tape (for wing center and tailwheel wire) 16-3/4"x20" Decal
1I10"x27" Decal 138"x50" Full-Size Plan 116 page Photo-Illustrated Instruction Booklet 1"The Basics of Radio Control" Booklet
4#2x1/2" Sheet Metal Screws (for control horns) 36-32x1/2" Mounting Bolts (for landing gear) 46-32x3/4" Mounting Bolts (for engine mounts) 28-32x1-3/8" Mounting Bolts (for wheel axles)
76-32 Blind Nuts (4/engine mounts, 3/1anding gears) 48-32 Hex Nuts (2 per axle) 21/4-20x -1/2" Nylon Wing Bolts 24-40 Nylon Aileron Connectors
52-56 R/C Links (2/ailerons, I/elevator, l/rudder, I/throttle) 1Small Nylon Control Horn (for rudder) 1Medium Nylon Control Horn (for elevator 2.190"o.d.x24" Nylon Outer Tubing (pushrods for elevator and rudder)
1.130"o.d.x30" Nylon Inner Tubing (for throttle pushrod) 11/16"x15" Steel Cable (for throttle pushrod) 1Solder Link (for throttle push rod) 12-56 Threaded Coupler (for throttle pushrod)
42-56x10" Threaded Rods (2/ailerons, l/elevator, l/rudder) 15Easy Hinges

Notes Before Beginning Construction

Any references to right or left refers to your right or left as if you were seated in the cockpit.

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 "door core" from the lumber yard, or whatever - as long as it is perfectly flat and untwisted. Cover the top surface of the building board with a piece of celotex-type wall board or foam board, into which pins can be easily pushed Don't hesitate to use plenty of pins during assembly to hold drying parts in their correct position.

When pinning and gluing parts directly over the full-size plans, cover the plan with wax paper to prevent gluing the parts to the plans. Don't use a ball point pen for making marks on the model during construction. If not sanded off, these ink marks will show through the model's final finish. Use a pencil instead of a pen.

Leave all laser-cut parts in the sheets until needed in construction. Then remove the pieces from the sheets carefully. If difficulty is encountered, do not force the part from the sheet - use a modeling knife to cut it free.

The laser-cut balsa and plywood parts can be identified using the plans and the "KEY TO LASER-CUT PARTS" below. Mark the identification numbers on the corresponding parts before removing them from the laser-cut sheets. All of the other parts can be identified by the "COMPLETE KIT PARTS LIST" above. Sort the different sizes of sticks and sheets into individual piles to avoid confusion during building.

SPECIAL NOTE: Any future references to die-cut parts will actually be refering to laser-cut parts.



Building The Wing Panels

Before beginning wing construction, carefully splice together the Left Wing Panel plans so that the "X" and "Y" indicators meet. Use a straightedge to double check the alignment of the plans before taping them at the seam. Tape or pin the plans to your building board and protect them with a layer of waxed paper. Build each wing half separately.
  1. Pin the 3/16"x3/8"x30" spruce main wing spar in place on the plan. Be careful not to place pins where they will interfere with wing ribs which will be added later.
  2. Pin the 1/16"x1-1/2"x30" balsa bottom trailing edge sheeting in place.
  3. Use about three wing ribs to accurately position the 3/16"sq. x30" balsa rear spar, then pin the spar in place.
  1. Glue eight W-2 wing ribs to the spars and trailing edge sheeting.
  2. Place scraps of 1/16" balsa near the main spar to accurately space the W-1 wing ribs up from the building board. (The spacing is required for the center sheeting to be added later.)
  3. Use the dihedral guage side of the die-cut Dual Tool to set the root W-1 rib at the proper dihedral angle before gluing it in place. Add the two remaining W-1 ribs.
  1. Glue the 1/4"sq.x30" balsa trailing edge to the top of the L.E. sheeting and the ends of the wing ribs.
  2. Remove the pins in the bottom L.E. sheeting and re-pin the back of the wing through the trailing edge stick that you just installed.
  3. Add the 1/16"x1-1/4"x30" top trailing edge sheeting. For this step it is recommended that you use Sig-Bond (aliphatic resin) along the back edge of the sheeting that glues to the trailing edge. That will make the joint easier to sand when you reach Step 11. Use thin CA to tack the front edge of the sheeting to the wing ribs.



Install a pre-cut 3/32"x3"x1-3/16" balsa shear web in each rib bay except the one between the two most inboard W-1 ribs (where the dihedral brace will be installed later). Notice that the wood grain is vertical for maximum strength. Trial fit each web before gluing, sanding the ends as necessary to make them fit snugly between the ribs on either side. The bottom of the shear webs should be centered on the bottom main wing spar; the top of the shear webs should be centered on the notch for the top main wing spar.

NOTE: The shear web to be installed between the second and third W-1 wing ribs will need to be shortened significantly to fit.


  1. Trial fit the 3/16"x3/8"x30" spruce top main wing spar. If any of the shear webs are too tall, they should be trimmed to allow the spar to sit all the way down in the rib notches. When satisfied with the fit, glue the spar in place. Check the inboard W-1 rib again with the Dual Tool to be sure it is still at the correct angle.
  2. Glue the 5/16"sq.x30" balsa leading edge to the front of the ribs.
  3. Glue the 3/16"sq.x30" balsa top forward spar in the rib notches.
NOTE: Remove any pins from tbe structure that are located under the area where the top center sheeting will be installed (in the next step). Otherwise, you may find it difficulf to remove your wing from the board later!


Pieces for the top center sheeting should be cut from the 1/16"x3"x30" balsa provided in the kit. Again, Sig-Bond is recommended for the front and rear edges of the sheeting to make it easier to sand the joints smooth. Also use Sig-Bond on the center W-1 rib. The sheeting can be glued to the ribs on each end using CA.


When the glue has dried, unpin the wing half from the board and install the 3/16"sq.x30" balsa bottom forward spar.

IMPORTANT: If you have been using thin or medium CA glue during construction, now is the time to go back over every joint using medium or thick CA. Don't be stingy here - the integrity of your wing depends upon strong glue joints. Glue each side of each joint. Make certain the shear webs are bonded to the spars AND the wing ribs on each side. Double check the L.E. stick and the T.E. sheeting for complete bonding to the ribs.


Install the bottom center sheeting except in the area between the bottom forward spar and the bottom main wing spar. Cut pieces for the sheeting from the 1/16"x3" balsa that you used earlier.


Cut oft and sand the spars, L.E., T.E., and sheeting at both ends of the wing flush with the end ribs.


Sand the leading edge to a round crosssection as shown in the diagram below.
NOTE: The L.E. notches in the ribs were intentionally made slightly oversize so the ribs could be sanded down to the leading edge.


11. Carefully carve the top of the trailing edge to match the slope of the top T.E. sheeting using an X-Acto #26 whittling blade. Wrap the top of the blade with masking tape (to protect the sheeting), leaving about 1/2" exposed at the base. Use the masked portion to guide the blade at the corred angle. Final sand the T.E. so that the back edge of the wing is about 1/4" thick (same as the ailerons).


Glue the die-cut Lite-Ply wingtip to the outboard end of the wing panel.
(Don't be tempted to omit the wingtip to save weight. The plywood is necessary to keep the covering material from "sucking in" the end rib.)

If you prefer rounded wingtips over the square ones, simply add a balsa block to the wingtip (instead of the Lite-Ply part), then carve and- shape as desired.


  1. Sand the top center sheeting smooth. (The bottom center sheeting is sanded in step 21.)
  2. Position the die-cut Lite-Ply Aileron Servo Cutout Guide (ASCG) on the inboard W-1 wing rib. The top of the ASCG should be flush with the top of the center sheeting, and the notches on the ASCG should fit around the main wing spars. Trace around the ASCG with a sharp pencil.
  3. Remove the guide, then measure and mark the cutout area on the top center sheeting using the dimension shown in the photo. Using a modeling knife, carefully cut out the outlined area. This step accomplishes two things. First, it clears an area for the aileron servo, and second, it provides an open area between the main wing spars for the dihedral brace.


Repeat steps 1 through 13 to build the opposite wing half.

Joining The Wing Panels


  1. Trial fit the two wing halves with the dihedral brace installed between the main wing spars. Be certain that the dihedral brace is not preventing the panels from making solid contact with each other at the center. If necessary, trim or sand the dihedral brace for a snug fit.
  2. Glue the dihedral brace into ONE of the wing.panels. Make certain that it is positioned accurately between the main wing spars.
  3. Use slow CA or epoxy (either 5-minute or slow-dry) to join the two wing panels. Apply glue to the end ribs and the exposed edges of the dihedral brace, then carefully slide the other wing panel into place.
    Before the glue dries, make certain that the L.E. and T.E. of each panel are aligned. The dihedral angle of 20 per wing panel will be automatically built-in by the dihedral brace. If you want to check the angle, place the wing on a table so that one side sits flat, and the other side is raised. The distance from the table to the bottom of the wingtip should be 2", but a variation of up to 1/4" either way is acceptable. The most important thing is to have a solid joint at the wing center with no gaps.


  1. When dry, double check through the servo opening on top and the center sheeting opening on the bottom that the dihedral brace is glued solidly to the main wing spars and the W-1 wing ribs.
  2. Glue the die-cut balsa piece BP into the aft end of the servo opening. When dry, trim BP flush with the top center sheeting.


  1. The aileron torque rods have been pre-bent so that the threaded portion leans forward slightly inside the fuselage (see the W-1 wing rib crosssection on the plans). That small angle will provide your Four-Star 40 with a bit of differential movement (more up than down) in the ailerons, which makes for smoother rolling characteristics. Prepare the torque rods for installation by roughening the brass bearings with sandpaper, then wiping them·clean.
  2. Locate the 1/4"sq.x2" basswood grooved torque rod blocks and cut a notch in each of them as shown in the photo.
  3. Glue the torque rods into the blocks being very careful not to get any glue in the brass bearings. The outer end of the bearings should be even with the outer end of the blocks.


  1. Glue the torque rod/block assemblies in place on the wing T.E., again being very careful not to get any glue in the bearings.
  2. Notch the balsa trailing edge just forward of the notches in the torque rod blocks to allow full movement of the torque rods.
  3. Sand the top of the basswood blocks to match the slope of the trailing edge sheeting. A small sanding block is handy for this step.


The 1/16"x3/4"x1-5/8" plywood wing hold-down plates can be sanded to a more pleasing shape as shown in the photo. Glue them in place on the bottom of the wing, even with the back of the torque rod blocks.

NOTE: Complete the steps in "Mounting The Wing To The Fuselage" before proceeding.

Finishing The Wing


Finish off the bottom center sheeting, again using 1/16" balsa.


If you haven't done so already, give the wing a final sanding. Sand just enough to take off any prominent high spots or bumps. Excessive sanding may distort the airfoil shape.


The 1" wide fiberglass tape can be applied to the wing center joint (top and bottom) using one of the two methods listed.


  1. Coat the wing center joint with slow-drying epoxy glue.
  2. Lay the tape on top of the glue.
  3. Holding one end of the tape so it won't slip, "squeegee" the glue through the tape with a small paddle of scrap balsa. Scrape over the tape several times with the paddle to smooth the tape and remove any excess glue.
  4. When dry, sand lightly to remove any rough spots. Try not to sand into the fiberglass tape itself.
METHOD 2: (Shown in the photo)
  1. Cut the tape to length, then lightly spray one side with a spray adhesive (such as 3M "77").
  2. Position the tape on the wing center joint.
  3. Soak the tape with thin CA. The spray adhesive simply holds the tape in place - it won't affect the strength of the CA. A second coat of CA will help fill in the weave of the fiberglass, resulting in a smoother surface. Rub the second coat with your finger (protected with plastic wrap - keep it moving!) to smooth out the glue. Use a fan to keep the CA fumes away from your face.
  4. When dry, sand lightly to remove any rough spots. Try not to sand into the fiberglass tape itself.



Sand the trailing edge of the aileron round and bevel the front using a sanding block. A pencil line drawn down the center will keep the bevel symmetrical.


Position the aileron on the back of the wing, leaving a 1/32" gap between the inboard end of the aileron and the outboard end of the torque rod block. Mark the location for the torque rod installation. Slot and drill the aileron leading edge to receive the torque rod wire.


Trial fit the aileron to the torque rod. Once it fits, temporarily tape the aileron in place and sand the outboard end flush with the wingtip.