Sig's famous EASY HINGES have been included with your kit to hinge all of the control surfaces. Each ultra-thin hinge is actually a three-part laminate - a tough plastic inner core sandwiched by an absorbant wicking material. They have been chemically treated to slow down the reaction of thin CA (which is normally instant), to allow the glue time to soakall the way to the ends of the hinge and into the wood surrounding it. Once the glue has dried, the hinge cannot be pulled from the structure without tearing wood out with it! We recommend that all surfaces be covered before hinging.


Using a No. 11 X-Acto blade (or similar), cut slots approximately 1/2" in depth and slightly wider than the hinges. Cut four slots in the stabilizer and four slots in the elevators at the locations shown on the plans.


After all of the slots have been cut, insert EASY HINGES halfway into the stabilizer slots. DO NOT GLUE THE HINGES YET! Next, carefully slide the elevators onto the hinges. You'll find it easiest to slide the elevators onto the hinges at an angle, one at a time, instead of trying to push it straight onto all of the hinges at once. Don't be concerned if the hinges aren't perfectly straight or centered in the slots - they don't have a centerline.


  1. To set the hinge gap, deflect the elevators to the maximum amount needed. For best control response, the gap should be as small as possible but big enough to allow full movement of the control surface.
  2. EASY HINGES were designed to use THIN CA (any brand) for maximum glue penetration. Place three or four large drops of thin CA directly onto the hinges in the gap. The glue will wick into the slot as it penetrates both the wood and the hinge. Continue this process, gluing the same side of all of the hinges, then turn the stabilizer over and repeat the gluing process on the other side of each hinge.


After the glue has cured (3 to 5 minutes) the joint should be flexed to full deflection in each direction a couple of dozen times to reduce the stiffness. Don't worry about shortening the life of the hinges, as they are almost indestructible.


The rudder is hinged in the same manner as above, but it is easier to install AFTER the fin has been glued to the fuselage. Cut slots for three hinges now (3 slots in the rudder, two in the fin, and one in the back of the fuselage).

NOTE: The fuselage slot may be difficult to cut, but don't be tempted to omit it. The bottom hinge is vital to the integrity of the rudder because it absorbs loads from both the servo and the tailwheel (if used). Jab the knife straight into the joint at the rear of the fuselage, pull it straight out, reposition it slightly, and repeat the procedure until you have a slot that's long enough for the hinge.


The ailerons are hinged exactly like the tail surfaces, but the torque rods must be glued as well. Start by cutting the slots in the wing and the ailerons (four per aileron) and install EASY HINGES halfway into the ailerons.


  1. Slide a small piece of wax paper between the torque rods and the wing. Working with one aileron at a time, apply Kwik-Set epoxy to the slot and hole in the aileron leading edge and slide it onto the torque rod, working the EASY HINGES into the wing slots at the same time. Try not to get any epoxy on the brass tubing! Before the glue sets, be sure to deflect the aileron back and forth to set the proper hinge gap.
  2. Once the epoxy has dried, remove the wax paper and apply thin CA to the hinges as you did earlier.



  1. Temporarily position the stabilizer on the stab support at the back of the fuselage. Again refer to the General Alignment Diagram on page 20 of "The Basics of Radio Control". When satisfied with the alignment, draw cut lines on the bottom of the stabilizer at the fuselage sides. Remove the stabilizer and cut away the covering on the bottom where it will be glued to the fuselage using a sharp knife.
  2. Glue the stabilizer to the fuselage using Kwik-Set epoxy. Recheck its alignment and adjust before the glue dries.


  1. Cut away a 3/16" wide strip of material from the center of the stabilizer where the fin is to be glued. Epoxy the fin to the top of the stabilizer, using a triangle to check its alignment as it dries. Make certain that the back edge of the fin is lined-up with the back edge of the fuselage sides.
  2. Hinge the rudder to the fin and fuselage using three EASY HINGES.


(OPTIONAL) Although the fin attachment method in the previous step has proven to be more than adequate on our test models, some modelers may want some extra strength in that area, particularly if they fly on a rough field where models have a tendency to flip over on their back. Then again, there are some of us who tend to flip our models over even on smooth fields! The optional fin braces shown in the photo aren't exactly pretty, but they do add a tremendous amount of strength to the area and are recommended for any MId-Star 40 pilot who is more concerned with day-to-day hardknocks flying than with looks.

The fin braces can be cut from the 1/2" triangle stock provided in the kit and shaped as shown in the picture. Cover the outside face of the braces, and cut away the covering material on the fin and stabilizer before gluing the braces in place on each side of the fin.


Now is a good time to apply the decals. Use the plans and photos of the finished model for proper positioning. Cut out the decals with scissors, leaving about 1/32" to 1/16" of clear at all edges and rounding the corners. as you cut. Wet the surface on which the decal will be placed with soapy water (use a couple of drops of dishwashing detergent in a small bowl of water). Place the decal on the model and squeegee the water from underneath with a balsa paddle. This procedure allows time for repositioning and prevents air from being trapped under the decal. Allow several hours to dry.


Install 2-3/4" main wheels on the aluminum landing gear using the hardware as shown on the plans. A drop of CA on the inner nut will help keep the assembly from vibrating loose. Once the wheels have been attached, the landing gear assembly can be bolted to the fuselage using four 4-40 x 1/2" mounting bolts.
NOTE: If you are building the optional taildragger version of the MID-STAR 40, skip step 84 and proceed to step 85. If you are building the standard tricycle gear version, perform step 84, skip step 85, and proceed with step 86.


  1. Bolt the nose gear bearing to the front of F-1. Install a 2-1/2" dia. wheel on the nose gear strut using two 5/32" wheel collars (not included, SIGSH587), then assemble the strut and steering arm to the nose wheel bearing. When putting the nose gear together, you can adjust the length of the wire strut a little if necessary to get the model to sit at the proper ground attitude (see page 21 of "The Basics Of Radio Control"). The MID-STAR 40 should sit on its tricycle gear so that the top edge of the Lite-Ply fuselage side (behind the wing) is perfectly level in relation to the ground. The adjustment is made by loosening the set screw in the steering arm and sliding the wire strut further in or out of the nose gear bearing. To prevent the steering arm from twisting on the strut, grind or file a small flat spot on the wire strut where the set screw makes contact.
  2. Install the nose gear pushrod using the guidelines in "The Basics Of Radio Control" (page 9). To prevent unwanted flexing, the outer nylon tubing should be glued firmly to F-1, F-2, and a scrap balsa standoff at the end closest to the servo. The flexible cable is attached to the servo with a solder clevis, and to the steering arm with the pushrod connector which was installed earlier.


Install a 3/4" dia. tailwheel on the tailwheel wire using two 1/16" wheel collars (not included SIGSH584). A cleaner, but more difficult installation would be to solder small flat washers to the wire on both sides of the tailwheel. Solder the inner washer first, then slide the tailwheel in place followed by a temporary spacer made from thin cardboard. Solder the remaining waher, then remove the spacer when cool. Whether you use wheel collars or washers, trim off any excess tailwheel wire.


NOTE: The remaining section of these instructions concerning engine and fuel tank installation, radio installation, pre-flight checkout, and flying provide information that is specific to the MID-STAR 40. For a more in-depth look at any of these subjects, please refer to "The Basics Of Radio Control" booklet also included with this kit. In particular, it is strongly recommended that you go through the "Pre-Flight Checklist" in Chapter 7 carefully before attempting to fly.

Engine And Fuel Tank Installation

Engine installation on the MID-STAR 40 is simply a matter of bolting the engine mounts that were prepared in step 28 to F-1, then bolting your engine to the mounts. Install the throttle pushrod using the guidelines in "The Basics Of Radio Control" (pages 8 - 9). Like the nosewheel pushrod, the outer nylon tubing of the throttle pushrod should be glued to F-1, F-2, and a scrap balsa standoff.

An 8 ounce fuel tank is recommended for the MID-STAR 40, although most tanks from 6 oz. to 10 oz. will work. Sullivan 8 to 10 oz. Slant type or RST type tanks will fit easily. A Du-Bro 10 oz. will not. Most engines will require the tank to mounted as high as possible in the fuselage. Use foam rubber under the fuel tank as necessary to position it properly.

Radio Installation

Screw the nylon control horns onto the rudder and elevator as shown on the plans, then re-install the inner nylon pushrods that you prepared in step 56. Snap an R/C link on the rudder horn, then cut off the excess nylon tubing, leaving a 1/8" gap between the end of the tubing and the R/C link. Cut a 2-56 x 10" threaded rod to an overall length of 3-1/2", measuring from the threaded end. Install the threaded rod in the nylon tubing, smooth end first, so that approximately 1/2" of the threaded portion remains exposed. (The metal rod will help prevent the nylon tubing from buckling under flight loads.) Thread the R/C link onto the end of the pushrod until the rudder is neutral, then repeat the procedure for the elevator .

The aileron servo can be mounted to two 3/8" sq. x 1-1/2" basswood rails, as can be seen on the W-1 cross-section drawing on the plans. The nylon aileron connectors can be moved up or down the torque rods to adjust the amount of aileron throw. Tape the servo wire to the wing to keep it from getting tangled with the aileron servo, as well as the servos in the fuselage.

A typical radio installation is shown in the photo above. The receiver and battery on this model are wrapped in foam rubber and positioned just forward of the servos. A scrap balsa stick keeps them from moving around during flight. If you use a lightweight engine, you may need to install the battery under the fuel tank to achieve proper balance.

Notice that the aileron connector wire and the charging jack are left accessable, but are tucked away enough so that they can't interfere with the servo arms and linkages. The antenna has been routed away from all other wiring and out the fuselage side (opposite from the engine exhaust) and up to the top of the fin.

Pre-Flight Checkout

IMPORTANT: For first flights, make certain that the model balances somewhere in the range shown on the plans. If it balances further back, add weight to the nose as necessary. Trying to fly with the balance point too far aft is much more dangerous than the slight increase in wing loading caused by adding lead to the nose. Always balance the model with an empty fuel tank.


Be certain to range check your radio equipment according to the manufacturer's instructions before attempting test flights. A lot of problems can also be avoided if your engine has been well broken-in and the idle adjustments perfected on a test stand or in another airplane before installation in the new model.

Before flying, you should adjust all of your push rod linkages so that the control surfaces are in their neutral position when the transmitter sticks and trim levers are centered. When you get to the field, don't be surprised if the elvator and rudder are suddenly misaligned. Temperature and humidity changes can cause the nylon push rod tubes to expand or contract slightly. Use the trim levers on the transmitter to reneutralize the control surfaces, and do the final trimming in the air.

The control surface movements listed are recommended for the first flight of your MID-STAR 40. These movements will provide the model with a fair degree of aerobatic capability if it's balanced correctly. Test flights may indicate a need for slightly more or less movement, depending on individual model performance and personal preference.
For test flying, the following are suggested:
ELEVATOR 1/2" UP and 1/2" DOWN
AILERON 3/8" UP and 5/16" DOWN

WARNING - DANGER Important: Read These Warnings:

Do not fly control line or towline models within 300 feet of electric power lines, instant death from electrocution can result from coming close to them. Direct contact is not necessary.
A model airplane motor gets very hot and can cause serious bums. Do not touch the motor during or after operation. Keep clear of the propeller, it can cut off a finger or put out an eye. Make sure the propeller is securely fastened in place and is not cracked. Model airplane fuel is flammable and poisonous. Take the same precautions while transporting and using it that you would with a can of gasoline or a bottle of poison.
Remember that it is possible to lose control of a model airplane. Do not fly in locations where the model may hit people or damage property if loss of control occurs. Check your model and equipment regularly to insure it is in safe operating condition.


The MID-STAR 40 is a fun aircraft to fly, but it is not a basic trainer. If you have no previous R/C flying experience, we suggest that you not attempt to fly this model without the assistance of an experienced pilot. Contact your local club or ask your hobby dealer for the names of good fliers in your area and a suitable location for flying.

When you are ready for takeoff, point it into the wind and apply throttle. You'll probably need a touch of right rudder to keep it going straight because engine torque will try to make it drift to the left. When you reach flying speed, pull back slightly on the elevator stick for a gentle liftoff.

If you are using a relatively large engine, don't expect the takeoff roll to last very long! With its big wing, the MID-STAR 40 likes to jump into the air and get down to business!

During the first part of the flight, concentrate on trimming the model to fly straight and level. Novices should spend time flying around smoothly and getting used to the "feel" of their new airplane. Experienced modelers will find the model capable of almost any trick "in the book". Experiment With different control throws and balance points until the model flies exactly the way you want. Make any changes, especially to the balance point, gradually.

We recommend that you shift the balance point no more than 1/8" at a time. In general, moving the balance point forward will make the model more stable, slowing down snap rolls and spins. Moving the balance point back increases its sensitivity to control inputs; but if carried too far, the model can become completely unstable and uncontrollable. The balance range shown on the plans is a "safe" area to use for test flights. Don't exceed the rearward limit unless you are a very experienced pilot


When landing be ready to go around if it looks like you're going to overshoot the runway. It will take a few flights to get a feel for the correct approach and landing speed. Remember to keep your control inputs smooth and gentle to avoid overcontrolling.

When you are certain the model will make it to the runway (even if the engine quits), bring the throttle to full idle and concentrate on keeping the wings level during final approach. Slow the model down during the entire approach by slowly feeding in up elevator. Just before the model touches, flare the landing by carefully feeding in more up elevator. Hold the model just inches off the ground until your elevator stick is pulled all the way back. The MID-STAR 40 should settle in for a perfect nose-high landing with a short rollout.

The canopy gives the MID-STAR 40 its stylish look. Just don't forget to take it with you to the flying field! The small screw and washer that hold the canopy in place should be kept in the wing at all times, so that they don't get misplaced.


If you have any technical questions or comments about this kit, or any other SIG product, please call us.

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SIG MFG. CO., INC............Montezuma, Iowa 50171-0520

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