|J-3 CUB RC48 FINISHING|
It's best to mount all your radio equipment and pushrods before covering and painting, while you still have easy access inside the model. 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.
In spite of some of the things you may have heard or read, putting a radio in your 1/4-scale Cub need not be much different than for a smaller model. This section describes the control system installations that have worked best in our prototype Cubs and that we recommend. Except for the use of some "heavy-duty" parts, you'll find that the installation is pretty straight forward. As with any size model, the QUALITY of the installation more than anything else will determine how well it flys the model.
Always double check all control hookups! Locate the source of any binding, rubbing, or sticking and eliminate it.
No radio gear or servo mounting materials are supplied in this kit. Any other parts called for in the following instructions that we do not furnish are marked with an (*).
Elevator And Rudder Hookup
The elevator and rudder are each actuated by one "heavy-duty" servo. Almost every radio manufacturer produces heavy-duty servos specifically designed to handle the increased control surface weights and air loads of 1/4-scale models. Standard size servos (35 oz./in. torque or less) are not recommended for the elevator or rudder of the Cub. If in doubt about the ability of the servos you have to handle the job, consult the manufacturer of the radio gear.
The most convenient method of installing servos in the fuselage is on the plastic mounts (*) that are offered by most radio manufacturer for their equipment. These are screwed to hardwood mounting rails (*) that are epoxied across the inside of the cabin area. Mount your servos anywhere between formers F5 and F6. Further instructions on the use of servo trays are usually included with them.
A long nylon control horn is supplied for the elevator. Install it on the bottom of the left elevator with #2 x 3/4" sheet metal screws. Once installed, cut off the excess ends of the screws flush with the top of the nylon retainer plate.
Materials are supplied for building fiberglass pushrods to link the elevator and rudder servos to their control horns. Make the control surface ends of the pushrods first. Put a 90° bend in the unthreaded end of the 4-40 x 8" threaded rod. Drill a 3/32" diameter hole 2" from the end of the fiberglass pushrod tube. Slide the 4-40 rod into the tube, sticking the 90° bend through the hole.
Sand a flat spot on one side of the 3/16"x2-1/2" dowel until it can be squeezed into the tube alongside the 4-40 rod. When you get the fit right, final assemble the parts into the tubes with epoxy glue. It should not be necessary to put any bends in the 4-40 wires of either the elevator or rudder pushrod to get them to feed through the fuselage and hook up to the control horns. It's a pretty straight shot if your servos are positioned side by side as shown in a previous photo. However you may have to trim out a portion of the diagonal 5/16" sq. main frame balsa under the stab to clear the elevator pushrod wire.
Assemble the servo ends of both pushrods in the same fashion, only use 1/16" dia. x 8" music wire and solder links instead of the 4-40 size hardware. After you've got the 1/16" wires and dowels epoxied into the tubes, feed the pushrods back into the fuselage and hook up to the control surfaces. Center the 4-40 links on the threads at the tail end. Then measure and cut off the 1/16" wires at the front, to the length which will allow the solder links to reach the servo arms. Protect the servos with a rag while soldering the links onto the ends of the wires.
|Your elevator and rudder pushrods should now be complete and operating freely. Fill in around the 4-40 pushrod wires where they exit the fuselage with scrap sheet balsa, glued in flush with the
Brace the pushrods in the middle (near former F9) with 1/4" sq. scrap balsa to eliminate any possibility of in-flight vibration or bowing problems. Criss-cross pieces of 1/4" sq. stick on all four sides of each push rod. Glue them to the 5/16" sq. main frame balsa. Have the braces touching the pushrods, but not creating a bind.
Either a standard or heavy-duty servo can be used for the throttle control on a .60 to .90 glow engine. A flexible steel cable pushrod with nylon outer tubing (*, such as SIGSH559) is best for hookup of the throttle servo to the carburetor. Follow the assembly instructions on the pushrod package.
Due to the larger than normal battery drain from using heavy-duty servos, a 1000 mah receiver battery pack (*) is recommended. Wrap the battery pack in foam rubber (*, such as SIGRF240) held on with rubber bands or masking tape, to protect it from engine vibration. Secure it as far forward as possible in the nose under the fuel tank.
The receiver should also be wrapped in foam rubber and stowed as far forward as possible. Make certain that it is somehow fastened in place so it will not move around during flight. A 36" long piece of large (3/16" o.d. approx.) nylon tubing is provided for making an internal antenna mount. Glue the tube in a bottom corner of the fuselage, from the cabin area back to the tail, and slide the antenna wire into it.
The receiver on/off switch may be mounted wherever it is convenient. Some servo trays have a slot along the front for holding the switch. Then run a short length of music wire (*) from the switch to the outside of the model.
You can choose between two completely different methods for hooking up the aileron in the cub.
|Method 1- 2 Servos|
|The full-size wing plan shows this type of installation and all the necessary structural parts for it are included in this kit. In addition to a fifth servo(*), you'll need to purchase two long extension chords(*) and a "Y" harness(*) to link the aileron servos to the radio receiver in the fuselage. All radio manufacturers have these items available as stock equipment or will make them on order. It is best to keep the extension chords as short as possible - 18" should be long enough when the "Y" harness length is added to it. Excessively long chords have been known to cause radio interference under certain conditions. Consult the manufacturer of your particular radio about the need and availability of "chokes" in the extension chords to eliminate possible interference.|
Double check to see if the holes that are in the wing ribs are large enough to allow the plugs on your extension cords to pass freely through. If not, enlarge the holes until they will. By the way, it's not necessary to permanently install the extension cords in the wing panels as you may have thought. It is quite easy to feed the cords through even after the wing has been covered and painted. Simply feed a long piece of music wire(*) or dowel(*) through the holes first, then tape the end of the aileron cord to the wire and pull the wire back through.
Dry fit the two die-cut 3/32" ply Servo Mounts and your aileron servos into position between the W5 ribs in each wing panel. Bend the 4-40x8" threaded rods to the shape shown in the wing cross-section drawing on the plan. Screw the 4-40 links halfway into the threaded ends of the rods and snap the links into the nylon aileron control horns. Pin the ailerons in neutral position and get the pushrods and servos into alignment with the horns. Determine the exact angle of installation needed for the ply Mounts and whether the top of the servos will clear the 3/32" ply Hatches when they are installed later. Then epoxy the ply Servo Mounts to the W5 ribs.
When dry, realign the servos and pushrods to the aileron horns. Mount the servos onto the ply mounts using a side-mount type servo tray(*). Because of the large diameter of the 4-40 rods, it's pretty impractical to link them directly into the servo output arms. So cut off the rods near the arms and bend two small "Z" shaped spur wires out of scrap 1/16"dia. music wire(*). Bind the spur wires onto the cutoff ends of the 4-40 rods with soft copper wire(*) and solder the bindings securely.
Cut to length and epoxy in place the 1/4"x3/8" spruce Hatch supports. Use the 3/32" ply Hatch to guage the proper depth for gluing in the two Supports that go along the sides of the WS ribs. The Hatch should be flush with the capstrips when it's screwed down onto those side Supports. #2x3/8" sheet metal screws are provided for holding the Hatch in place.
Cut to shape and glue in place 3/32" sheet balsa fairings for around the aileron pushrod exits.
Method 2- 1 Servo with Bellcranks
(*no materials are supplied for this option)
One heavy-duty servo, such as recommended for the elevator and rudder, can safely operate both ailerons at the same time from the center of the wing through the use of 90° aileron bellcranks and long pushrods. The difficulty with this method is in making it operate smooth without any bending. However, it can be done if you are very careful with installation.
If you elect to try this method in your Cub write to Sig for more detailed instructions on making the installation.
Mount the 90 deg. bellcranks between the W5 ribs on the same 3/32" plywood that is supplied in this kit for the Servo Mounts in Method 1. Use the 4-40 threaded rods and links in the kit to connect the bellcranks to the aileron horns. Mount the servo in the window opening of the Center_Section and use a 1/16" diameter wire plastic-sleeved pushrod(*) to connect it to the bellcranks.
|20.||Tips On Tanks|
A 16 oz. rectangular plastic clunk tank is recommended for use with most all .60 to .90 cu. in. glow engines. Refer to the engine manufacturer's instructions for any special notes they may have on fuel tank or pump/pressure requirements for your particular engine.
The simplest, most trouble free, tank set-up to use with a fully cowled in engine is normal suction feed, without any pump or crankcase pressure. If you can run your engine on suction, assemble the fuel tank hardware as shown in the photo. There are 3 tubes installed through the rubber stopper - 1 for fuel feed, and 2 for vents. Both vent tubes should curve upwards inside the tank. The clunk line on the fuel feed tube must swing freely without hitting the back of the tank. (If your tank, as supplied, does not come with silicone tubing for the internal fuel feed line, substitute a piece of Sig Heat-Proof Silicone Tubing, SIGSH290 Large. With it installed, the tank can be left in the fuselage indefinitely since this line will not harden or deteriorate when immersed in raw fuel.)
With an inverted engine installation, the tank will be correctly located for proper fuel draw and idle characteristics if it is mounted onto the bottom of the ply Nose Joiner. Simply glue four J-Bolts (SIGSH123, not supplied) into the bottom of the NoseJoiner, and use rubber bands hooked between them to hold the tank in place, as shown.
Drill holes through the firewall large enough to pass the fuel lines through. Once the tank is installed permanently, after painting the model, seal the holes in the firewall against leakage of the exhaust oil into the fuselage with silicone rubber sealer. Run fuel tubing from both vents downward and out the bottom of the cowl at the back. Connect the fuel feed line to the carburetor. To refuel, simply pump fuel into either of the vent lines until it runs out the other. Then plug one of the vents with a short 4-40 bolt to keep the fuel from siphoning out. It's not necessary to remove the feed line from the carb to refuel.
Covering And Painting The Framework
The completed Cub framework can be covered with Sig Koverall, Sig Silk or an iron-on type of covering material (either plastic or fabric). 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 temperatures and techniques of application.
The rest of these instructions describe the use of Sig Koverall, which is a polyester based synthetic fabric ideally suited to quarter-scale models due to its low cost, workability, and toughness. Silk is applied in the same way, but it costs much more per yard. Koverall is highly recommended for the Cub - all of our prototype models were covered with it.
|Brush an unthinned coat of clear Sig Supercoat or Sig Lite-Coat 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 Koverall about 1/2" larger all around than half of the wing, with the grain running lengthwise. (The grain of woven materials run parallel to the finished bias edge.) Dip the piece of covering in water, let the excess water run off, and then lay it on the wing. Go around the edges, pulling out the wrinkles and stretching the material smooth. Brush clear dope around 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 areas or places that are not stuck down properly and apply more dope.
Use the same process to cover the top of the wing, the fuselage, and the tail surfaces. Be sure to read "Hints on Covering the Fin Fillet".
After all covering is done, allow the water to dry out of the fabric and wood. If the Koverall is slack or baggy in any places, use a hot air gun or hair dryer to shrink it tight (read Koverall package instructions).
|Next give the entire model a coat of Lite-Coat clear dope. Thin the dope until it brushes on easily and flows out smoothly. 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 results. So apply dope very lightly the first time over. The second coat will seal most of the pores of the Koverall, and from that point running through will not be a serious problem.|
You can put anywhere from 3 to 5 total coats of clear dope on the Koverall before going to color. It depends somewhat upon how heavy a coat you are putting on. Keep the dope thinned out enough to flow on smoothly. Sand well between the later coats of dope with 220 grit Tri-MIte paper. Don't bear down on the edges of the balsa structure or the fabric may be cut. Use your own judgement about when you've put on enough coats. The goal is a completely smooth and even base for the color paint. Keep in mind that weight can build up fast in finishing and restraint must be used in application. Don't try to completely fill the grain of the fabric like you would on a smaller model. The weave will not be very noticeable as long as the edges are smooth - it may even look more realistic. Sanding sealer or primer is not necessary or advisable.
Best results can usually be obtained by spraying on the color finish coats. It is also much faster than brushing would be on this large a model. Reduce the dope for spraying fifty-fifty with Sig Supercoat Thinner. Two coats of your base color should give good coverage if the surface preparation was sufficient. If any light sanding between base color coats is needed, use 360 Tri-M-Ite or 400 or finer wet paper.
When the base color has dried, mask off the edges of the color trim areas with "drafting tape" (3M Scotch brand is available at most office and art supply stores). Completely cover with paper and tape all areas that should remain base color. Brush or spray the edges of the tape with clear dope. This seals the tape, preventing leakage of the trim color underneath the tape. Spray on two coats of trim paint. When dry, carefully remove the tape.
Complete the job by spraying a coat of Lite-Coat clear dope over the entire color scheme to protect the colors from scuffing and to give the entire model a uniform gloss.
For best results, it is not a good idea to try to mix different brands of paint. Use SIG products from the start.
|22.||Sanding And Painting The Plastic Parts|
CAUTION: Do not try to cover any of the plastic parts with Monokote, Coverite, or other iron-on types of covering material. The heat can damage the plastic parts.
The cowling, dummy engine, and bungee covers are molded out of ABS plastic. We recommend that they be painted with Sig Supercoat Dope for best results. Hobbypoxy, K & B Superpoxy, and Dulux Enamel have also been proven compatible with the ABS plastic and can be used if desired. Do not use other paints, dopes, or finishes without first testing on scrap plastic to make certain that they are compatible.
In preparation for painting, the plastic parts should be sanded to remove as much of the surface gloss on them as possible. Do not use coarse sandpaper which will cut deeply into the plastic. Deep scratches will often open up wider during painting. Use 220 grit or finer 3M Tri-M-Ite Fre-Cut Finishing Paper or its equivalent.
Color paint can be put directly on the sanded plastic. Primer type coats are not necessary if a thorough sanding job was done with fine paper. Brush or spray the color paint onto the plastic parts. Do not apply heavy, wet coats which can cause an "orange peel" effect. Put on light coats and allow them to dry before applying a second coat.
Painting The Landing Gear And Wing Struts
We recommend that the completed landing gear and wing struts should be painted with epoxy type paint (such as Hobbypoxy or K & B Superpoxy) because of the large areas of metal to be covered. Dopes do not stick well to metal, but epoxy paint does and it's use here is not recommended.
Start by brushing or spraying a coat of epoxy primer on the entire part. When dry sand smooth. Make repeat applications of primer, sanding thoroughly when dry, until the surface of the wood and fiberglassed areas are smooth.
Then spray on two coats of color epoxy paint, letting it dry between coats. For best results, follow the paint manufacturer's instructions closely.
Cut out the decal you wish to apply with a sharp scissors, modeling knife, or single-edge razor blade. Trim close to the image, leaving about 1/32" to 1/16" of clear edge around the decal. Smaller designs (2 - 3 sq. in. or less) can be put on the model by "dry application", whereas larger decals go on easier using the "wet application" instructions.
|Instructions for Dry Application|
Peel the paper backing sheet completely off the decal, being careful not to let the sticky side double over and adhere to itself. Hold the decal in position just above the surface of the model while you double check to make certain it is exactly where you want it. Don't let the decal contact the surface of the model until you are sure of its location! Once it is stuck down, it can't be moved! Start the actual application by pressing just one edge of the decal into contact with the surface of the model, and then carefully work towards the opposite edge, slowly rubbing the remainder of the decal in place. Be careful not to trap air under the decal. If air is trapped under the surface, puncture the air bubble with a pin and press down.
Instructions for Wet Application
Here's a little trick that allows application of self-adhesive decals to a model without the danger of trapping air bubbles. Start by wetting the surface of the model where the decal will be placed with a generous quantity of soapy water solution (a little dish soap in water, or a commercial cleaner like Sig Blue Magic Model Airplane Cleaner, "409", or "Fantastic" brand cleaners will all work equally well). Peel the paper backing sheet completely off the decal, being careful not to let the sticky side double over and adhere to itself. Place the decal onto the wet surface of the model. The soapy water will keep the decal from actually sticking to the model until you have had time to shift it around into exact alignment. Once you have it in exact position, use a small paddle of scrap sheet balsa to squeegee the excess soapy water out from under the decal. Squeegee repeatedly to get as much of the soapy water out from under the decal as possible. Allow to dry overnight. When completely dry, wash off the soap smears with a clean wet rag.
NOTE: These decals are completely fuel proof and cannot be harmed by any common model -airplane glow fuel containing less than 20% nitromethane. Higher quantities of nitromethane may cause slight deterioration of the decal over extended periods of time.
Attaching The Tail Brace Wires
Four 2-56x10" threaded rods are provided for the Brace Wires. Cut two of them off at 8-3/4" long for the bottom brace wires. Leave the other two at 10" long for the top brace wires.
Four standard RC links (2-56 thread inside) and four solder links (unthreaded) are provided for the ends of the Tail Brace Wires. Take each link and cut off the side that has the pin in it. (A Dremel tool with an abrasive cut-off wheel works best.) Enlarge the hole in the remaining half with a #44 drill bit.
Screw one threaded link and jam nut onto the threaded end of each rod. Solder one of the unthreaded links to the other end of each.
Drill #44 holes through the stab and fin trailing edges at the brace wire attachment points drawn on the plans.
Fit the wires to the model. Bend the ends of the links as needed to make them fit flat against the model surface. Use 2-56x1/2" bolts and hex nuts to fasten the links through the stab and fin. Use #2x3/8" sheet metal screws to hold the bottom of the lower brace wires to the plywood tailwheel mount.
Adjust the threaded links and jam nuts until the wires are snug, but not pulling the tail surfaces out of shape.
Paint the tail brace wires after installation with epoxy paint.
|26.||Installing The Windshield And Side Windows|
Cut the windshield from the 1-1/12"x17" clear plastic sheet, using the pattern on the plan. Cyanoacrylate adhesives (Hot Stuff, Jet, etc.) work best for gluing the windshield in place on the fuselage. This is a tedious and sometimes frustrating job - but a little patience and thought will usually be rewarded with a good fitting installation.
First pin the windshield in place as well as possible for a trial fit. Readjust where necessary. Then go around the edges and tack glue in several places. It's best to start gluing near the middle of the nose top and at the top of F5. Then work out towards the sides and the Windshield Braces. Don't try to bend the plastic around the Braces, just glue it to the front edge. When satisfied with the fit, glue all the edges permanently. When dry, trim off the excess plastic along the Windshield Braces.
Two 5-1/2"x17" pieces of clear plastic are provided for the side windows. One piece is to cover all the window area on one side of the airplane with no seams. Lay the plastic sheets on the fuselage and mark them about 1/8" larger than the outline of the windows. Cut out and glue on the outside surface of the model.
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.
Why Models Must Be Individually Balanced
It is impossible to produce a kit that will automatically have the correct balance point. Balsa wood varies in weight and it is easily possible for the wood in the tail of a model this large to be 2 or more ounces lighter or heavier than average. One ounce of extra weight in the tail has to be countered by about 3 ounces in the nose. Don't use a lot of finish or excess glue on the tail surfaces. The motor you choose, what form of muffler is fitted, the size and placement of your radio equipment, etc. all affect the balance. Don't feel that whatever C.G. the model builds out to as "good enough". Check carefully and make whatever adjustments that are required.
With the C.G. properly located, the Cub should fly with only minor trim changes required.
Be certain to carefully range check your radio equipment and see how it operates with the engine running before attempting test flights. A lot of problems can be avoided if the 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.
A properly balanced and aligned model with a reliable engine and radio is assured of successful flights.
The Cub is not difficult to manage on the ground or in the air. However, being 1/4-scale and a taildragger, there are some differences you should be aware of between flying the Cub and flying most trainer or pattern type models. It handles more like a full size airplane than most smaller models.
When taxiing the Cub on the ground be prepared to use the elevators and ailerons in addition to the obvious rudder steering and throttle inputs. When the winds are calm, hold full up elevator while taxiing in any direction, to keep the tailwheel in firm contact with the ground for effective steering. Leave the ailerons in neutral, steer with the rudder, and control ground speed with the throttle.
|Under windy conditions, also hold up elevator when taxiing either upwind or crosswind. When going downwind, put the elevators in neutral or partly down to keep the wind from getting under the tail and flipping the Cub on its nose. Aileron deflection may also be needed while taxiing crosswind to keep the upwind wing from lifting off the ground.|
During the takeoff run, try not to overcontrol the rudder (the most common rookie tailwheel pilot's mistake) which will start the Cub 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 it 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. Actually the Cub is one of the easiest taildraggers to takeoff that you'll find.
Just keep practicing your takeoff run without lifting off until you learn to use the throttle, elevators, and rudder together.
In the air you'll find the Cub smooth, stable, and responsive. With practice it is capable of doing most basic aerobatic manuevers such as inside loops, rolls, spins, and snaps. After you've had a chance to get the model all trimmed out, practice making your turns by coordinating rudder commands in with the ailerons, as is done in a full size airplane. Proper coordination of the rudder with the ailerons will make for a more graceful turn.
Landing the Cub directly into the wind or under calm conditions is pretty much like landing any other scale model. Be careful not to let the nose get too high during banks with the power off. Either wheel landings or three-point landings can be made with the Cub. Just remember to fly the model even after it touches down (or you'll ground loop so fast it will make your head spin). Once the tailwheel gets back on the ground you'll have good steering and the model will slow down fast.
If there is any amount of crosswind, even quartering, landing the Cub (or any other taildragger) becomes a little trickier. Proper coordination of the ailerons and rudder is again needed to maintain your heading. After the model is turned onto final approach, use the rudder to hold the model on a straight heading with the runway and feed in aileron to correct any drifting to the side.
For example, with a crosswind from the left, you'll need to hold a little right rudder to correct any "crab" angle (the model will be trying to weathervane into the crosswind) and put in left aileron to keep the model from drifting to the right.
|If all these hints make it sound as if the Cub is difficult to fly, it really isn't! In many ways flying quarter-scale is easier than flying a faster, smaller model. The Cub can be safely flown by anyone who is capable of handling a multi-channel model. Once you get a few flights under your belt, you'll find rudder/aileron coordinated flying becoming second nature - and you'll be a better pilot with all types of models.|
If you have any technical questions or comments about this kit, or any other SIG product, please call us.
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