KING KOBRA RC54 COVERING AND FINISHING

The manufacturer's directions for applying iron-on coverings are packed with the material. Follow these closely, for different types of covering have different iron temperatures and techniques of application. Whatever kind of covering you desire to use, it will not conceal a rough framework. Sand carefully with fine sandpaper before beginning to cover.

IMPORTANT! Don't skip covering the fuselage and tail just because they are solid wood. They will be much more resistant to splitting and breaking on hard impacts if they are covered with something - Sig Silk, Silkspan, Sig Silray, Sig Koverall or plastic iron-on covering material. About the only recommended alternative to covering is to first fill the wood with Sig Finishing Resin and then paint the resin. (Fiberglass cloth is too heavy for a entire model.)
Our prototypes were covered with Sig Koverall and it's so strong and easy to use that we recommend it. Koverall is slightly heavier than silk, but not much. We covered one of our small Kobra (.19 - .35) prototypes with Koverall as an experiment and it was not noticeably different in finished weight from another that was covered with silk. On a foam wing model, the fact that Koverall is applied dry is a particular advantage. The wetting necessary for the application of silk sometimes raises the grain of the wood or a seam in the wing skins. It is more economical than silk.

Brush a coat of clear dope (Sig Supercoat, Sig Lite Coat or Sig Nitrate, depending on the final finish to be applied) on all parts of the structure that will touch the covering. When the dope is dry, sand lightly to remove any raised fuzz or grain.

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.)

Pin the Koverall in place, pulling out all of the large wrinkles. (Koverall shrinks up considerably under heat. Don't worry about such things as the packaging fold wrinkles - they will come out with the iron.)

Brush around the outside edge of the stretched Koverall with clear dope. The dope will soak through the material and adhere to the dope already dried into the framework. Glue only the outside edges down. Leave the rest of the material unattached to be heat-shrunk with the iron. Trim off the edges with a sharp, new blade. On the bottom, trim off the material flush with the wing all the way around. Go over any rough areas or places that did not stick with more dope and press the loose spots down as the dope is drying and getting stickier. Sig-Ment is a handy seam cement for this purpose also.

The top half is done in identical fashion except that the cloth should be brought down over the edges instead of being trimmed off flush. On the front, lap the material over the edge of the bottom, over-lapping about 1/8". At the back, bring the material down over the back edge of the trailing edge but do not lap it over the bottom covering.

Smaller surfaces like the ailerons and elevator were covered with one piece of Koverall. First it was pinned and glued to the leading edge, then wrapped around over the trailing edge and back up to the leading edge again.

When covering has been completed, go over the Koverall with an iron to stretch it tight. Give the entire model two or more coats of clear dope before proceeding with preparation for and application of color. Because of the tight weave, air bubbles have a tendency to be trapped between the balsa and the Koverall. To be sure this gives no problem, use dope thinned 50-50 (so as to soak through) for the first coat and work down the covering with a balsa squeegee to get out air before dope dries.

The prototype King Kobras were covered using Sig Nitrate Dope as an attacher and filler, then painted with the Sig Skybrite One Coat No-Mix Paint System. (Sig Nitrate should always be used under enamels or epoxy, not Sig Supercoat or Lite-Coat, which should only be used underneath Sig Supercoat Dope.) A brochure on the use of the Sig Skybrite system is available free. Send a self-addressed large-size stamped envelope to Sig and request it.

Painting the Cowl and Fuselage Top

The plastic parts should be sanded to remove the gloss before they are painted. Don't use coarse sandpaper, which can cut deep scratches. These scratches may open up during doping (which softens the plastic) and become more noticeable. Instead use something like 220 3-M Tri-MIte no load silicon paper to start and polish down with 360 Tri-M-Ite or 400 wet paper before color doping.

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Care should be used not to apply heavy, wet coats of dope. Put on light coats and allow them to dry thoroughly before applying a second coat. A spray gun is a good method of getting a good finish with a minimum amount of dope. Be especially careful with dope spray cans not to wet the plastic too much. Spray several light dusting coats with adequate drying time allowed.
A Cure for Fuselage Warping
You may have noticed that when a piece of balsa is doped on one side and not on the other, it will curl. The same thing can happen on the fuselage sides under the wing opening, particularly when you put on a number of coats. (The rest of the fuselage will not show this effect to any extent because it is four-sided and cannot distort.) The effect isn't noticeable until after full cure of the dope and aging, which may take several months. To prevent this from happening, give the inside of the fuselage a coat of dope every time you give the outside a coat. This has an added advantage in making the cabin area fuel proof. In addition, when the hardwood servo mounts are installed, have them a little over-long so that the cabin sides are bulged slightly outward.

Plastic may also be painted with Sig Skybrite, Sig Plastinamel, K & B Superpoxy, Hobbypoxy or Du Pont Dulux Enamel. Don't use other paints without testing first on scrap plastic. For best results, Skybrite Primer, K & B or other primer should be applied to the plastic before finishing with enamel or epoxy.

Painting the Canopy Framing

Dope is very difficult to use on the canopy plastic because of its warping action. Therefore we recommend Sig Skybrite, Sig Plastinamel or other suitable enamel or paint-for-plastic for the canopy. Epoxy can be used but it doesn't stick as well unless primer is used under it. Sanding the gloss off the canopy plastic will help adhesion on all types of paints. Mask off the edges of areas to be painted with 1/8" Stripe-Rite or similar plastic tape which will stretch around curved areas on the canopy. Mask off the rest of the unpainted areas with wider tape to protect it from scratches during handling. If some type of paint other than those mentioned here is used, test on a scrap of plastic first.
NOTE: Plan the painting so that the canopy can be glued on the fuselage as soon as the paint is dry. Don't leave the canopy lay around since it is likely to warp, either from the type of paint used or the fact that the framing is only painted on one side.
Cyanoacrylate glues may be used with caution to attach the canopy. With some brands, when a seam of glue is put around the canopy, the fumes may build up inside and cause fogging of the plastic. To avoid this, we put two holes in the cockpit floor. (In an inconspicuous place - behind the pilot's headrest.) A piece of tubing was inserted in one hole and blowing through it as the glue was applied a bit at a time, exhausted the fumes out the other hole before the canopy was harmed.

DKM-235AB Kougar Stars and Bars decal. The large stars and bars measure 7-1/4" wide, the small 4-3/8". DKM-235B Kougar Team Numbers Decal. The diameter of the circle of stars around the numbers is about 4-1/4".
DKM-235AC Kougar Black Lettering Decal. "USAF" letters are 3" high, "U.S. Airforce" is 1" high x 9-1/2" long, the buzz numbers are 13/16" high. DKM-235C Kougar Team Insignia Decal. The width of the bar on the stars and bars is 3-1/4". "U.S. Air Force" is 7/8" high x 8-1/2" long.

Color Schemes

On a non-scale model like the King Kobra, a wide range of color schemes suggest themselves. We will show here the ones used on the prototypes but in order not to increase the price for those builders who may prefer other decorations, no decals (except for the "King Kobra" name) have been provided in the kit.

The F-16 inspired color scheme on one prototype used the emblem, insignia and lettering from the DKM-235A Kougar Thunderbird Stik-Tite Pressure sensitive set (Also available individually as DKM-235AB Kougar Stars and Bars and DKM-235AC Kougar Black Lettering.)

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VISIBILITY NOTE: The F-16 scheme is a fairly simple one to execute but some fliers may prefer to have some white striping on the bottom of the wing instead of making it solid red. This makes it easier to determine airplane attitude in a bank at a distance.

These same decals could be used to work out the basic configuration of the most recent (1983) color scheme used by the Thunderbirds. This reverts to the red scalloped fin splattered with blue stars similar to one used some years ago and which appears on the prototype Kouga. The flags are from Sig Flag decal DCM-805. (This decal now has right and left handed flags instead of two left .handed, as used in the photo.


DKM STIK-TITE
Pressure Sensitive Decals

Cut out the decals with a pair of sharp scissors. Leave about 1/32" to 1/16" of clear edge around the decal. Round the corners as you are cutting. Wet the surface on which the decal will be placed with soapy water (use dishwater detergent). Place the decal on the model and squeegee the water from underneath with a balsa paddle. Allow to dry. This procedure will prevent air from being trapped underneath as is possible when the decals are applied dry.

The T-38 styled K.K. prototype used DKM-235B Kougar Team Numbers for the fin and DKM-235C Kougar Team Insignia decal for the stars-andbars, Thunderbird emblem and U.S. Air Force.

Bottom Color Schemes
NO.1 is an easy-to-do layout with all straight lines. The red top wing tip and stabilizer tip stripes are brought around the bottom, but the white and blue stripes are not. The spanwise stripes are blue. The fuselage spear is red. NO.2 shows the red-winged F-16 style King Kobra. A variation would be to leave the wing center section white with the red spear on the rear extending on to the nose. No. 3 is a more complicated version with curves. The span-wise stripes are blue, the fuselage spear is red. The red, white and blue stripes on the tips are on the top of the wing and stab only.

Patterns are shown on the plan for the curved decoration which are not on the decal sheets. Masking off these curved parts for painting is made much easier if 1/8" wide masking tape is used. This will bend around corners easier than wider tape. Strips can be cut off regular width tape with a straightedge. After the decoration is outlined, wider tape can be joined onto the 1/8" tape to block off the nearby areas not to be painted. We use paper taped on to match the rest of the model to shield for spray painting.

Another way the curved parts of the decorations can be applied is with the use of a mechanical drawing ruling pen to draw them on the model using paint in the pen instead of ink. Thin the dope slightly with blush retarder to slow the drying process and aid the flow of dope through the pen points. Clean the pen frequently with dope thinner and wipe on a cloth before reloading with fresh dope. Don't try to draw a thick line with the dope and pen but instead draw a thin line on each side of the desired pin stripe (about 1/8" wide were used on the original) and fill in between the lines using the pen free hand and opened up for a wider flow. If you have a steady hand, use a small brush. Use a French curve to outline curved parts of the decorations. The ruling pen method is also handy to touch up any rough edges of masked decoration after the tape is removed.

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A third approach makes use of the common adhesive-backed vinyl shelf paper available at hardware stores with a new blade in a modeling knife, cut the color sweep on the T-34 version, for example, out of a piece of the shelf paper and use the mask remaining for spraying or handpainting the decoration on the tail.

For models covered with plastic film, the fin flash could be cut from trim sheets. Or follow the manufacturer's directions that come with the plastic film for applying this type of decoration.

Balancing

The King Kobra design, like the Kougar, requires a farther forward balance point than commonly used on some other pattern style designs. Do not decide on the basis of your experience with other models to ignore the following recommendations and use some other balance point. Far too many modelers build a kit, install the equipment and go out to test fly without ever checking out the C.G. Don't do this!.
WHY MODELS MUST BE INDIVIDUALLY BALANCED
It is impossible to produce a kit that will automatically have the correct Center of Gravity (C.G.) position. Balsa wood varies in weight and it is easily possible for wood in the tail to be an ounce or more heavier or lighter than average. One ounce of extra weight in the tail has to be countered by about 3 ounces in the nose. Don't pile a lot of fillercoat or finish, use excess glue or make large fillets on the tail surfaces. The motor you choose, whether or not a muffler is fitted, the size and placement of your radio equipment, etc. all affect the balance. If you use an unusually heavy motor or muffler you may have to carry the battery in the radio compartment instead of the nose or even weight the tail. Don't consider 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, a Sig design should fly with only minor trim changes required.


BALANCING: Put a piece of masking tape on the bottom of the wing in the center. Mark the distances from the leading edge (the wing-fuselage joint) on it. A balancer can be made from a triangular architect's scale placed on a block high enough to get the wheels clear of the bench. Shift the model back and forth on the edge of the scale until the balance point is found. Balance with an empty fuel tank but with all the other equipment installed and the model completely finished and painted.

Our findings with 5 prototype models show that 1/2" behind the 25% point is as far back as ever will be necessary. Under no circumstances should the C.G. be moved farther back than the 33-1/3% point.

In addition to the fore and aft balancing procedure described above, the performance of manuevers is improved if the model is also in balance spanwise. For example, if one wing is heavy it may affect turning and loop tracking. Inset weight into the opposite wing tip to correct this problem.

BALANCE IS PART OF THE TRIMMING PROCESS
The balance point we arrived at for this design is a good place to start when trimming out the model for top performance. However, it should not be considered the final and irrevocable location. Individual models built from the same kit are slightly different from each other. The incidence may be changed a bit, a small or large engine selected, the total weight varies - even the skill of the pilot has bearing on just what should be the exact C.G. point. For example, when slightly nose heavy, the model is more stable and less likely to stall or snap roll from over-elevating. This also cuts down the reaction of the model to control movements which is good during test and practice flights to help prevent overcontrolling. But later, if extra sensitivity and quick reactions are desired for aerobatic performance, a position farther back may be desirable. So try different positions, but make the changes gradually, checking results and the effect of the change control responses and the performance of the model in the air at a good altitude.

Control Movements

The following control movements from neutral were used on the prototype King Kobras for test flights and are suggested as a starting point. Your own trimming and personal control reactions preferences should then be applied to determining the final measurements to be used.

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RECOMMENDED CONTROL SURFACE MOVEMENTS ELEVATOR 9/16" UP and 9/16" DOWN
RUDDER 1-5/8" RIGHT and 1-5/8" LEFT
AILERON 1/4" UP and 1/4" DOWN


FLYING

IMPORTANT: The King Kobra is not a model for low-flying time pilots. If you have little or no previous RC flying experience you cannot successfully fly a fast and responsive design like the King Kobra, particularly on test flights. It is suggested that you not attempt flying without the assistance of a modeler with experience. Contact your local model 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 all be lost in a moment of beginner's indecision. Even if you have some experience, an expert flier can help you get past the first critical test and trimming flights without damage to the model and give instruction in proper control.

NOTES ON LOOPS
A true wing will perform perfect loops. A twisted wing will loop obliquely. One wing half being heavier than the other may also affect loop tracking. A side mounted motor may make one side of the model heavier than the other. Put weight in the opposite wing tip until the model is balanced. Should your model snap roll out of the top of a loop, it may snap in the direction of any twist in the wing, but the real reason for it snapping is because of a stall. This is probably due to one or more of the following:
  • Airspeed too low.
  • C.G. too far back.
  • Pilot pulls too much elevator, a mistake aggravated by excessive elevator travel which makes the elevator more sensitive. Reduce travel of elevator and use more care in transmitter stick movement.
  • Not enough power, too high a wing loading for the available power or both.

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 model.

Takeoffs with the King Kobra from grass fields are easily made if the grass is not too long or the ground too rough. Generally a lot of elevator application is required for liftoff. Be prepared to relax control pressure partially after becoming airborne so the c1imbout will not be too steep. On surfaced or smooth dirt runways less application of elevator will be needed.

After each test flight, readjust the RC clevis links on the push rods so that the trim levers on the transmitter can be returned to a neutral position. It will take several flights before exact trim is established on all axis of flight.






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

LIMIT OF LIABILITY:
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.