It's easiest to mount all your radio equipment(*) and pushrods in the Astro-Hog before covering and painting. Once the initial installation has been made and all the bugs are worked out, you can take the radio system back out while the painting is being done.
Always double check all control hookups! Locate the source of any bending, rubbing, or sticking & eliminate it.

Mounting Servos(*) in the Fuselage

The most convenient method of installing the elevator, rudder, and throttle servos in the fuselage is on plastic trays(*) that are offered by most radio manufacturers for the equipment. These plastic trays are screwed to hardwood mounting rails(*) that are epoxied across the inside of the fuselage. We recommend that the hardwood rails be made of at least 3/8"sq. or 3/8"x1/2" basswood, pine, spruce, or practically any other hardwood you have on hand. Do not make the rails out of balsa! Further instructions on the use of servo trays are usually supplied with them.

In the Astro-Hog the fore and aft location of the servos is not critical for balancing purposes. In all of our prototype models, the servos were centered directly under the former F3. Trim away the bottom of F3 flush with the lit-ply cockpit floor so the servos can be mounted high enough in the fuselage. (If your servos are not overly large, you can probably glue the hardwood servo rails against the bottoms of the 1/4"sq. fuselage corner stringers like we did, see photo.) Glue scraps of balsa sheet to the fuselage sides around the ends of the servo rails so that they can never come loose in flight.

The photos, drawings and text in these instructtions describe the servo and pushrod arrangement that worked out best in our prototype Astro-Hog models. The fuselage servos were mounted side-by-side with the rudder servo on the left, the throttle servo on the right and the elevator servo in the middle. The nose gear and rudder pushrods and control horns were on the left side of the model, while the elevator and throttle pushrods were on the right side.
If your radio equipment has servo reversing capability (either in the Tx or via different rotation servos), you will probably find that this arrangement will work well for you too. If you don't have servo reversing you might have to make a slightly different arrangement, changing servo locations or running a pushrod off the opposite side of the servo. Determine which arrangement works best for your particular equipment.

Receiver and Battery Pack(*)

Wrap the receiver and the battery pack separately in foam rubber(*), such as SIGRF240, held on with rubber bands or tape(*), to protect them from engine vibration. The best location in the fuselage for the receiver and battery can't be determined until your model is completely finished. Shifting these components fore or aft slightly can be used to help get the model balanced properly. Final balancing and positioning will depend to a large extent on the engine used. For example: We found that with a light 2-stroke .60 in our Astro-Hog, the receiver and battery both needed to be put under the fuel tank. With a heavier 4-stroke engine in our second Asto-Hog, the receiver and battery were both mounted behind former F2, right in front of the servos. Or it's possible that you might have to put the battery under the tank and the receiver back behind F2. After determining the best locations, glue temporary pieces of scrap balsa across between the fuselage sides to hold the receiver and battery in place so they will not move around in flight.


The receiver on/off switch can be conveniently mounted in the ply cockpit floor, where it can be easily reached from the outside. You may also find it handy to mount your radio charging jack in the cockpit floor.

OPTIONAL: A Williams Brothers 2-5/8" scale, standard style pilot was used in our prototype models, as shown.


Elevator and Rudder Hookup

Two nylon control horns are supplied for the elevator and rudder. Install the control horns on the control surfaces with #2x3/8" metal screws. Mount one horn on the left side of the rudder, and the other horn on the bottom of the right elevator.

Materials are provided for making 5/16" sq. balsa pushrods to link the elevator and rudder servos to their control horns. Both pushrods are constructed in eactly the same manner.

Make the control surface ends of the pushrods first. Cut and bend a 2-56x10" threaded rod to match the pattern below. Drill a 1/16" dia. hole 2" from one end of the 5/16" sq. balsa pushrod stick. Push the 90 deg. end of the wire rod into the hole, wrap the wire to the stick with thread(*), and coat the winding with glue. Let dry.

Carefully try to determine the spot on the fuselage where the pushrod will exit and line up with the control horn and servo. Cut a 1/8"x1-1/2" slot at this spot. Feed the pushrod through the fuselage, sticking the threaded rod through the slot. Screw a self threading nylon RC link onto the end of the pushrod and hook it up to the control horn.

Hold the control surface in neutral position and cut off the servo end of the balsa pushrod stick about 2" short of reaching the servo's output arm. Unhook the RC link from the control horn and take the pushrod back out of the fuselage. Cut the piece of 1/16"x12" straight music wire that is furnished into two 6" long pieces. Put a 90 deg. bend into one end of the 6" wire and then bind that wire with thread to the servo end of the pushrod stick in the same manner you did the other end. Coat with glue and let dry.

Feed the pushrod back into the fuselage and hook it back up to the control horn. Make sure the nylon link is centered halfway on the threads at the tail end so that you will have equal adjustment range either way. Then hold the control surface in neutral position and install your choice of servo connector(* See below).

Complete both the elevator and rudder pushrods and make sure both operate smoothly. If necessary, recut the exit slots in the fuselage sides so that they don't interfere with the pushrod's movement. Fill in the miscut portion of the slot with scrap balsa and sand smooth.

You also may elect to install optional plastic pushrod exit guides(*), like those that appear in the photos of our first prototype model.


A wide variety of servo connectors are available from the Sig Catalog for attaching the servo end of each pushrod to its servo output arm. No servo connectors are supplied with this kit because modelers usually develop a personal preference for one type over another and often already have them on hand. You will need a total of 6 servo connectors for the Astro-Hog - 1 each for the elevator, rudder, throttle, and nose gear; and 2 for the ailerons. Here are photos of a few types.
Sig Solder Clevises (SIGSH527) are dependable and very easy to install. They can be soldered onto the end of any of the pushrods in the Astro-Hog, either plain 1/16" wire or tinned flexible-cable. Notice in the radio installation photos that the solder clevises were used on all of the pushrods in our prototype Astro-Hogs. If you are unsure what type of servo connector to use, try solder clevises.
Du-Bro 1/16" Ball Links (#190) get the pushrod action up above the servo control arm to avoid any chance of interfering with the arm's center post. It is good for cable or wire pushrods. A fine adjustment of the pushrod length can be made by screwing the end in and out.
A Sig pushrod connector (SIGSH736) is especially handy for cable end attachment. One is supplied in the kit for holding up the firewall end of the nose gear steering pushrod to the nylon steering arm. They can also be used for the servo end of any of the Astro-Hog pushrods, either wire or cable.
Sig Nylon Pushrod Keepers (SIGSH184) can be used on a 1/16" wire pushrod after the end of the wire has been bent 90 deg. and inserted into the servo arm. Not recommended for cable pushrods.
You won't need any connector for the 1/16" wire pushrods if you can put a "Z" bend in the end of the wire. It's a little tricky to make a good clean "Z" bend, so practice with some scrap wire before trying it on your good pushrod. Not suitable for cable pushrods.

Throttle Hookup

Materials are provided for making a flexible cable pushrod to link the throttle servo to the engine's carburetor control arm. The pushrod consists of a 1/16" dia. steel cable sliding inside a round nylon outer tube. The pushrod is semi-flexible, which means it can be bent in gradual flowing curves if necessary to make its ends line up with the servo and carburetor control arms (it's hardly ever a straight line shot between these two places in the model).

Construct the pushrod by first cutting the 32" long piece of nylon outer tubing provided in half. Slide one of the 16" long pieces through the hole in the firewall that was drilled for it during step 5i. Direct the tubing back around the fuel tank towards the throttle servo arm. Keep any curves in the tube as smooth and gradual as possible. Do not glue the tube in yet!

Sweat solder the treaded coupler provided onto one end of the 1/16" steel cable (see "Preparing Cable Pushrods" below). When cool, screw a nylon RC link halfway into the threaded coupler. Then feed the other end of the cable into the nylon tube from the front and push it all the way back into the fuselage until the RC link can be snapped onto the engine's throttle arm. Check the movement of the throttle by working the servo end of the cable by hand. It should be smooth and free! Epoxy the outer tube into the hole in the firewall after you've determined how much of it needs to stick out the front to support the cable.


Moving the servo end of the pushrod, cut a support block(*) from scrap balsa and glue it in place against the fuselage side about 2" ahead of the servo's output arm, and at the same height as the arm. Shape the block so that the nylon tube can be glued to it and will aim the pushrod cable directly at the servo arm. When satisfied, epoxy the nylon outer tube to the support block.

Cut the nylon tube and the cable to the final length needed to accommodate your choice of servo connector(*) and install it into the end of the cable.

To keep ends of cable from unraveling during handling, tin the end with solder. Use a non-corrosive paste flux (shown here is Kester, available at hardware stores) and rosin core solder. Use a very hot iron to heat the cable and then flow the solder completely through the strands.

When cool, grind or file the end smooth. Taper it down slightly so that it will go int the pushrod fittings and nylon outer tube easily..

After the proper length is arrived at, sweat solder the area to be cut so that it will not unravel while being cut. Cut through the tinned area with a good pair of side-cutting pliers, a cut-off wheel on a motor tool or a file.

Nose Gear Steering Hookup

A 16" length of nylon outer tubing and 16" of steel cable should be left over from the throttle pushrod installation. Use these pieces to make a pushrod to link the nose gear steering arm to the rudder servo. Install it in the same manner as you did the throttle pushrod.

At the firewall end, use the supplied pushrod connector (as shown in the section 5 diagram) to fasten the pushrod cable to the steering arm. Install the connector in the middle hole of the steering arm before bolting the nose gear assembly onto the firewall. Then feed the cable into the hole in the connector and tighten down the clamp screw. Notice that when the nose gear is in neutral position, the steering arm is angled slightly forward. That way when the servo pulls it back for a left turn, the arm will clear the face of the firewall. You'll have to arrive at the proper amount of forward angle for the steering arrm by trial and error.

At the servo end of the steering pushrod, shape and install a scrap balsa block to support the end of the nylon outer tube and aim the cable at the servo arm. Install your choice of servo connector(*) onto the end of the cable. In the photo under "Mounting Servos in the Fuselage", you'll see that we elected to use a threaded coupler and metal RC link at the servo end for easy adjustments.

Aileron Hookup

Cut two pieces of hardwood to serve as mounting rails(*) for the aileron servo. Glue them into the pocket in the center of the wing. When dry, mount your aileron servo to the hardwood rails. The exact dimensions and location for the rails must be taylored to fit the size of your particular servo. Plan your installation so that the servo is mounted as low in the wing pocket as possible.

The aileron pushrods are made from two 2-56x10" threaded rods. Screw a nylon RC link onto the threaded end of each rod. Next screw the self-threading nylon aileron connectors that are provided halfway down the aileron torque rods that are sticking out of the wing. Snap the RC links into the aileron connectors and line up the pushrods with the servo arms. Then cut off the pushrod wires to accommodate your choice of servo connectors(*) and install them.



A 12oz plastic clunk-type tank is recommended for use with most .60 size 2-stroke engines. If you are using a .60 4-stroke or a .45 - .50 2-stroke, then you might want to use an 8 or 10oz tank. Refer to the engine manufacturers instructions for any special notes that they may have on fuel tank requirements for your particular engine.

The shape of the fuel tank can be either round or rectangular. Either shape will fit equally well inside the Astro-Hog. We feel that for most typical engine installations a standard style tank with the cap hole at the front, is the easiest to install. However, for a 4-stroke engine which has the carburetor on the back, you might find that a slant or shelf-style tank will work better. They have the tank cap hole recessed back away from the firewall.

The simplest, most trouble free fuel tank setup is with normal suction feed. Assemble the fuel tank hardware as shown in the photo. There are 2 tubes installed through the rubber stopper - 1 for fuel feed and 1 for overflow vent. The vent tube should curve upwards inside the tank.

The clunk line on the feedtube must swing freely without hitting the back of the tank. If your tank, as supplied, does not come with silicon tubing for the internal clunk line, substitute a piece of Sig Heat-Proof-Silicon Tubing, SIGSH290 Large (*). With it installed, the tank can be left in the fuselage indefinitely - this line will not harden or deteriorate when immersed in raw fuel.

After the model is covered and painted, you can mount the fuel tank permanently. For best fuel feed with an upright engine, the tank should be mounted as high as possible in the fuselage. Make scrap balsa supports for the bottom and back of the tank to hold it in place. Glue the supports to the fuselage sides. Seal around the hole in the firewall where the fuel line comes through with silicone rubber sealer (*) to prevent exhaust oil from leaking inside the fuselage. Should the need ever arise to remove the tank for servicing, simply break away the balsa supports and silicone.

Use Sig Heat-Proof-Silicon Fuel Tubing to connect the tank's feed tube to the engine's carburetor. Use another length of silicone fuel tubing to extend the tank vent out the bottom of the cowl. To fill the tank with fuel, disconnect the fuel feed line from the carburetor and pump the fuel in there until it runs out the vent line.

Optional Muffler Pressure Feed

If the engine you are using is equipped with a muffler that has a pressure tap in it, make use of it for a more reliable fuel feed. The hookup for pressure feed is shown in the picture. The internal arrangement of the tubes in the tank is the same as shown for normal suction feed. To fill the tank, remove the fuel line from the carburetor and pump the fuel in there. When the tank is full, it will overflow through the muffler pressure line. Stop pumping when you see the fuel reach the muffler pressure line. Should some fuel happen to get in the muffler, drain it out before starting the engine.


Main Gear

Grind, file, or sand any burrs off the ends of the preformed 5/32" main gear wires. Insert the wires into the grooved landing gear blocks built into the bottom of the wing. It may be necessary to clean out the landing gear block hole and groove a little to let the wires slip in and out easily. The wires are designed to be removable. Four nylon landing gear straps and eight #2x3/8" metal screws are supplied for holding the main gear wires in the groved blocks. Use two straps per wire. Mark and drill 1/16" dia. pilot holes in the grooved blocks for the screws.
Do not glue the wires into the blocks!
3" diameter wheels(*) are recommended for the main gear. Retain the wheels on the axles with 5/32" i.d. wheel collars(*).


Nose Gear

A drawing of the nose gear assembly is included in section 5. 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. The Astro-Hog should sit on its trike gear perfectly level or just slightly nose up in relation to the ground for best takeoff and landing characteristics. 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.
A 2-3/4" diameter wheel(*) is recommended for the nose gear. Retain the wheel on the axle with 5/32" i.d. wheel collars(*).

Optional Taildragger Landing Gear

All of the patterns necessary to convert your Astro-Hog from the standard trike gear arrangement back to the original taildragger configuration are shown on plan sheet 2. No extra materials are furnished for making the conversion, however many of the parts that are in the kit are common to both types of landing gear.

Extra Parts Needed(*): Note that the trike main gear wires supplied in the kit are different from the taildragger mains shown on the plan and will not work. You can either bend your own taildragger main gear wires and tailwheel wire to match the patterns on the plan, or write to Sig about purchasing a pre-bent set direct from the factory. Ask for the Astro-Hog Taildragger Wire Set SIGRPCK255. The set includes 1 pair of main gear wires, 1 tailwheel wire, and 1 nylon tailwheel bracket. You will also need two 3-1/2" dia. wheels for the main gear and one 1-1/4" dia. wheel for the tail, plus the appropriate wheel collars. All other parts you need (grooved landing gear blocks, nylon retaining straps, scrap plywood etc.) are already in the kit for the trike gear version and can be used in the conversion.

The following is an exact listing of the differences in the construction sequence required for building the taildragger version.
  1. Step 1c - Same except, open up notches in front of the spar slots instead of the notches behind.
  2. Steps 5f, 5g, and 5h - Omit
  3. Step 7i - Omit
  4. Step 13 "Nose Gear Steering Hookup" - Omit
  5. Step 15 "Main Gear" - All the same except main wheel size for taildragger is 3-1/2" dia.
  6. Step 15 "Nose Gear" - Omit

Tailwheel Assembly- Using the pattern on the plan, Cut a 3/32" plywood mount out of scrap from the die-cut plywood sheet that F1A and F1B came in. Notch the bottom rear of the fuselage and epoxy the ply mount in place. Let dry.

Insert the tailwheel wire into the nylon bracket. Bend the top section of the wire parallel with the bottom of the rudder. Insert the wire into the bottom of the rudder and screw the nylon bracket in place on the fuselage with #2x3/8" metal screws. Reinforce the bottom of the rudder with fiberglass cloth and epoxy glue.

A 1" or 1-1/4" dia. tailwheel(*) is recommended. Retain it on the axle with 1/16" i.d. wheel collars(*).


Remove the landing gear, radio, engine, and fuel tank before painting.

All of our prototype Astro-Hogs were covered with Sig Koverall fabric and painted with either Sig Supercoat Dope or Sig Skybrite Paint - see Sig Catalog. An iron-on covering material (either plastic or treated fabric) that doesn't require painting could also be used. Whatever type of covering you desire to use, it will not conceal a rough framework. Be sure all surfaces are smooth before proceeding.

The manufacturer's directions for applying iron-on coverings are packed with the material. Follow these closely, for different types of material have different iron-on temperatures and techniques of application.

The rest of these instructions describe the use of Sig Koverall. Koverall is a polyester-base, heat shrinkable, synthetic fabric much like the covering that is used on classic full-scale airplanes. It is relatively low cost and super strong. The Koverall should be adhered to the balsa model framework with Sig Nitrate Clear Dope (Do not substitute butyrate clear dope if you want to use Skybrite Paint for the final color finish).


Start by brushing an unthinned coat of clear dope over all parts of the framework that will contact the covering. When dry, resand with fine sandpaper to remove any fuzz or raised grain. Brush on a second coat and sand again.

The bottom of the wing is a good place to start covering. Cut a piece of material about 1/2" larger all around than half of the wing, with the grain running lengthwise. (The grain of woven materials runs parallel to the finished bias edge). Lay the Koverall on the wing, pulling the wrinkles and stretching it smooth. Brush clear dope around all the edges. This will soak through the fabric and adhere it to the dope already dried into the framework. Let dry before trimming off the excess material with a sharp razor blade. Check for any rough edges or places that are not stuck down properly and apply more dope. Let dry.

After both sides of the wing are covered, use a hot air gun, hair dryer, or household iron to shrink the Koverall tight (read the Koverall package instructions).

Repeat the process until the entire model is covered. Then give the whole airplane a coat of clear dope. Thin the dope until it brushes on easily and flows out smooth. Brush the dope on sparingly over the open framework areas. If too much is applied, the excess dope may rub off the brush, run completely through the covering and puddle against the covering surface on the other side. When these puddles dry, the large amounts of dope solids in them cause more shrinkage than in the rest of the covering and a scarred area may result. So apply dope lightly the first time over. The second coat of clear dope will seal most of the pores of the Koverall and from there on ruinning through will not be a problem. Sand the model lightly with fine sandpaper after the second coat is dry. Then give it a third coat of clear dope and when dry, sand again.

The model is now ready to be finished with either Sig Supercoat Dope or Sig Skybrite Paint. Further instructions on the application of these two finishes is included with them. Do not try to mix different brands of paint. Use Sig products from the start and follow the instructions that come with them carefully for best results.


Cut the windshield from the 3-3/8"x8-1/2" clear plastic sheet provided, using the pattern on the plan.
Pin the windshield in place on the fuselage for a trial fit.
When satisfied with the positioning, glue it to the model with Sigment solvent-base model cement or cyanoacrylate "super" glue.

Cover the glue seam when dry with a strip of plastic trim tape (* such as Sig Superstripe) for a neat finished appearance.


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 adjustment perfected on a test block or in another airplane before installation in the new model.


Various brands of servos can give different amounts of control surface travel. By moving your pushrod linkages into a different hole of the control horn and/or into different hole of the servo arm, you can change the total amount of control surface travel you'll get when the Tx stick is moved to full throw position. Adjust your pushrod linkages to produce the amounts of movement listed below. Measurements are made at the trailing edge of the control surface.


For test flying, the following are suggested:
ELEVATOR 3/4" UP and 3/4" DOWN
AILERON 3/8" UP and 3/8" DOWN

The control measurements listed above should give full aerobatic capability if your Astro-Hog is properly balanced. Test flights may indicate a need for slightly more or less movement, depending on individual model performance and personal preference.

Before flying, you should also adjust all your pushrod linkages so the control surfaces are in neutral position when the Tx sticks and trim levers are centered in neutral. After the first flight, readjust the linkages if necessary so that the trim levers can be returned to neutral position. It may take several flights before exact trim is established on all the flight controls.

Balance your model at the point indicated on the plan. If it balances further back, add weight to the nose as necessary. Trying to fly with the C.G. too far back is much more dangerous than the slight increase in wing loading caused by adding lead to the nose. Balance with an empty fuel tank.

It is impossible to produce a kit that will automatically have the correct balance point. Balsa wood varies in weight and so do model engines. The form of muffler you use, the size and placement of your radio equipment and the amount of finish you apply can also affect the balance. Don't feel that whatever C.G. the model builds out to is "good enough". Check carefully and make whatever adjustments that are required. With the C.G. properly located, the Astro-Hog should fly with only minor trim changes required.


The Astro-Hog is not difficult manage on the ground or in the air. However, it is not a basic trainer. If you have no previous RC experience we suggest that you not attempt to fly your Astro-Hog without the assistance of an experienced pilot. Contact your local club or ask your hobby dealer for the names of good fliers in your vicinity and a suitable location for flying. Many hours of work are involved in the construction of a model and it can be lost in a moment of beginner's indecision. A skilled flier can help you get past the first critical test and trimming flights without damage to the model. To a pilot who has learned the basic skills, the Astro-Hog will be a very easy airplane to fly.

Line the Astro-Hog up in the middle of the runway for takeoff. If you haven't had much experience, it's best to stand directly behind the model so that you can easily see any changes in heading that will need to be corrected during the takeoff run. Leave the elevator in neutral. As you advance the throttle smoothly to full open, the Astro-Hog will try to drift to the left from torque. Feed in right-rudder as needed to keep the model going straight. When you have reached flying speed, pull back slightly on the elevator stick for a gentle liftoff.

During the takeoff run, try not to overcontrol the nosegear steering (the most common rookie pilot's mistake) which will start the Astro-Hog swerving from one side of the runway to the other. If you find yourself in that situation, pull the throttle back to full low and get the model stopped. Taxi back for a fresh start. Never try to hurry the model off the ground by pulling full up elevator just because the model isn't going straight! The damage from a premature snap roll on takeoff would be much more severe than anything that could happen on the ground. Just keep practicing your takeoff runs without lifting off until you learn to use the throttle, elevators, and rudder together.


In the air, you will find the Astro-Hog smooth, stable and responsive. It will perform all the basic aerobatic maneuvers with ease. After you've had a chance to get the model trimmed out, you might want to experiment with slight changes in control surface travel until the model reacts just the way you want it to. Increasing the surface travel will make the model react much quicker, but it can also make the model "touchy" in level flight if you go too far. Shifting the balance point slightly (1/2" maximum) forward or backward can also change the model's flight characteristics.

Having the balance point forward will make the model more stable and less likely to do snap and spin maneuvers.
Having the balance point further back will make the model react faster and more extremely to control inputs, to the point of making it hard to control if carried too far.

If these ideas make it seem that the Astro-Hog is difficult to fly, it really isn't. These are basic laws of airplane design that apply to all models, not just the Astro-Hog. Experimenting with different balance points should only be attempted by experienced pilots. You'll most likely find that your Astro-Hog will fly very well with the balance point shown on the plans. That's where all our prototype model's balance.

The Astr-Hog can be safely flown by anyone who is capable of handling a multi-channel RC model. In fact, you will probably come to agree with hundreds of modelers before you - that the Astro-Hog is a very special design.

It's a real pleasure to fly!

© Copyright SIG Mfg. Co.,.Inc.
SIG MFG. CO., INC............Montezuma, Iowa 50171-0520

In use of our products, Sig Mfg. Co.'s only obligation shall be to replace such quantity of the product proven to be defective. User shall determine the suitability of the product for his or her intended use and shall assume all risk and liability in connection therewith.