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Chapter 13 - Radio Controlled Piper Cub

One of the most fascinating aspects of model airplane construction and operation is radio control. The ability to maneuver your craft at will and literally put yourself in the "driver's seat" has caused the radio controlled phase or models to become one of the fastest growing hobby-sports in recent years. Radio control projects can range in complexity from elementary single channel affairs which control the rudder and, at times, also the engine; up to vastly complex multi-channel systems which not only control the rudder and engine speed but include the elevators, retracting landing gears, and ailerons.

In the not too distant past radio control equipment was priced out of reach for the average model airplane enthusiast. With the many current advancements being made in the design and manufacture of electronic equipment the price of transmitters, receivers, and escapements has now fallen within the financial ability of the average model builder. The market is literally flooded with foreign and domestic euipment of diverse designs which will fit any application and any pocketbook.

Our "Cub" is shown posed by the "Aristo-Craft" transmitter and ready for action. The amazing realism of this model on the ground in no way compares with the model as it soars   overhead.

The apparatus described in this chapter is an easily understood, single channel, and commercially available, companion transmitter and receiver and these are typical of the elementary equipment to be found at any hobby shop. It is important to select simple, light weight, but reliable equipment for use in radio controlled or "R.C models.

As previously mentioned; the basic purpose of the radio equipment is the operation of the rudder. The action of the rudder not only controls the direction of the flight but, when properly used, can control the general altitude of the craft. An escapement is used to actuate the rudder. A long rubber band loop within the fuselage powers the escapement and this must be wound prior to each flight. When the transmitter spring switch is depressed the signal is received by the radio receiver in the fuselage and this relays the impulse to the escapement which permits the twisted rubber band to turn the rudder and the model turns in that direction. The model will continue to circle in this direction until the switch is released at which time the rudder returns to the neutral position and the craft resumes straight flight. A double depression of the transmitter will cause the rudder to swing in the opposite direction and again returns to neutral when the button is released.

The direction of rotation of the vast majority of model engines throughout the world causes the airplane to tend to veer and roll toward the left. This is called torque. Continuous application of left rudder will, therefore, cause the model to bank and turn toward this direction quite sharply and execute a spiral which will make the airplane lose altitude. The craft can be made to climb by flying it into the wind with the rudder in the neutral position. A right turn usually helps the craft maintain a constant altitude. As you can see, the rudder can be used to control altitude and this is done with the vast majority of radio control model airplanes in existence today.

No license is required to operate radio control equipment. All that is required is that the operator register his set with the F.C.C. A registration blank is supplied with each transmitter.

The plans included in this chapter illustrate commercially available radio equipment which the author has used on numerous occasions with outstanding success. The Aristo-Craft "Rangemaster" Transmiter and TRR transistorized receiver are matched pieces of equipment designed for each other and their simplicity makes them ideally suited for the novice in the radio control field. A companion to the above equipment is the Aristo-Craft Compound Escapement which actuates the rudder via a push rod and control horn. Any similar equipment can, of course be used for this project.

Radio control model aircraft are essentially free flight models, however, the construction is usually considerably heavier. Extra sturdiness is required because of the additional equipment that the craft must carry. It is preferable to fly radio controlled planes which are heavier than free flight models because the additional weight reduces the amount of drifting due to wind conditions and permits more exacting control over the descent of the craft. The rate of climb will also be reduced and wind penetration will be improved. The latter is important when the plane is in a position downwind of the operator and an attempt is made to bring it back. Invariably all aircraft attempt to gain altitude on the long upwind run and a heavy model will eliminate the necessity of performing altitude losing maneuvers during this condition. There is, of course, a limit to the weight of any model plane and if the plans shown here are followed, an ideal condition will result.

High wing aircraft are overwhelmingly superior to low wing or biplane free flight configurations. Only the advanced model builder should forsake the former for the sometimes more glamorous latter. We have selected the world famous "Piper Cub" lightplane as our candidate for an easy to construct and operate radio controlled model airplane. It is questionable whether there is any person in the civilized portions of this earth who has not heard of the "Cub" airplane. This plane was one of the first economical personal airplanes to be produced. In addition, its ease of handling made the "Piper Cub" the ideal craft for student flyers and it is said that more people have learned to fly in "Cubs" than in any other airplane.

The structure of the Piper Cub model is clearly visible in this photograph because the silk covering has not yet been painted. Slight variation will be noticed between this picture and the plans in this chapter. The reader should be guided by the plans because they include several refinements which were the result of experience with the prototype model.
 
The specific model we have selected is the "Cub Special" which is a two place aircraft with the seats arranged in tandem fashion. It is powered with a 65 horsepower, air cooled, four cylinder engine and the 16½ gallon wing fuel tank affords a range of 300 miles without refueling. Top speed is 100 miles per hour and the fuel consumption is about twenty miles to only one gallon of gasoline!

The structural design of the subject model follows the method of construction used on the vast majority of free flight and radio controlled model planes. It is very similar to that described in Chapter Four for the Troop Carrying Glider except that the fuselage sides are built up from strips of balsa wood instead of being cut from a flat sheet of balsa and the wing employs two heavy spars in lieu of the many light spars used for the glider. The wing span is 65 inches and the wing area is 560 square inches. Any engine from .14 to .23 cubic inch displacement can be used such as: Fox; O.K. Club; K & B; McCoy; or Cox.

Enlarging the plans is the first step prior to undertaking construction. This can be accomplished by using the graphic scale which appears on the plan. It is not necessary to draw every single detail full size. Only the wing planform, fuselage side view and tail planform are neded for actual construction. Photostating may be used, however the price is unquestionably prohibitive for the maojrity of model enthusiasts.

The basic structure of the fuselage is of rectangular cross section. Auxiliary formers and stringers are added to this to attain the final cross section. Lay the fuselage side view full size plan directly upon your work bench or a flat board. Be certain that the surface is perfectly flat and warp free. Now, place a sheet of kitchen type waxed paper over the plan in order to prevent the cement from sticking to the drawing. Select very hard balsa strips for the longerons. These are placed directly on the waxed paper over their proper location as shown on your full size drawing which is under the waxed paper. The balsa strips are pinned in placed by driving straight pins directly through the balsa and into the work bench or board. Cut away any excess length of balsa with a single edge razor blade. The pins can be pressed in place with the fingers or with a small hammer. After the longerons are pinned in place the uprights and diagonal braces are cut to exact length from medium hardness balsa strips and pinned to the work table between the two longerons. Pin the sheet balsa gussets in place as shown after they have been cut to shape. Carefully apply cement liberally over each joint made by the longerons, and uprights, and diagonals. After the cement is dry the pins are removed and the "side frame" can be lifted from the plan. Repeat this procedure for the other "side frame" which should be identical to the first in every respect. All joints should be recemented on both sides of each "side frame" after they have been removed from the table.

With the two side frames completed we can now add the top cross braces. Cut the top cross braces to length as the top view of your plan indicates. Join the fuselage sides at the rear holding them together, while the cement dries, with small "C" clamps or straight pins. Insert the first set of top cross braces, top and bottom, starting from the rear. Hold these in place with pins and apply plenty of cement. Proceed to insert the remainder of

 the cross braces, top and bottom, starting from the rear. Hold these in place with pins and apply plenty of cement. Proceed to insert the remainder of the cross braces cementing each as it is installed working from rear to front. When you arrive at the nose you are finished.

Two single channel compact receivers are shown here. The photograph above is the "Aristo-Craft Rangemaster TRR Tone Receiver" which is transistorized. The "Aristo-Craft Range-master TRR Carrier Wave Receiver is shown at the bottom of the page and the tubes can be seen protruding through the plastic case. "Tone" equipment is slightly more expensive than "Carrier Wave" units but are preferred for their ease of operation and dependability. The weight of these units is only two ounces each!

The three plywood bulkheads are now traced and cut to shape with a coping or jig saw. Cement these in place as the plans indicate using plenty of cement. Repeat this procedure for the landing gear foundation which rests against the bottom of bulkheads "C" and "D". In order to make this possible it is most important that these plywood bulkheads do not extend all the way down to the fuselage bottom. A ⅛" space must be left for the landing gear foundation. Recement the bulkheads and foundation joints several times.

Cut the engine mounts to proper length and slip the two pieces through the rectangular openings in the bulkheads. When the mounts are properly located apply several coats of cement to this installation.

Install a commercial fuel tank in the location shown. This should be well braced with balsa and cement. Straps cut from sheet brass can be used to hold the tank firmly against the bulkhead with small wood screws. Add the fuel tank filling, vent, and engine supply plastic tubing extensions at this time and be sure they extend beyond the outer limits of the fuselage covering. The engine fuel supply tube should be passed through the hole in the forward bulkhead at this time and it must be long enough to reach the engine with ease. Seal the open tubing ends with tape to keep out foreign matter. Remove the tape when model is complete.

Cut the fuselage side and top formers to shape and cement in place to the uprights and cross braces. When the cement is dry the stringers are cemented into the former notches and to bulkhead "B". The window framing piece is cut to shape and cemented between the upper side stringer and the longeron.

That portion of the fuselage between bulkheads "B" and "D" should be reinforced with X" thick balsa sheet of fairly soft hardness. This stock should be cut carefully in sizes that will fit snugly between the stringers and bulkhead "B". In effect the result is a task of inlaying the pieces in place. Set aside to dry.

An indication of the large size of our radio controlled Piper Cub is illustrated by this photograph. Carolanne Musciano holds Dad's model prior to a fun packed day of flying. Notice the engine cowl which is carved from a block of balsa wood and beautifully encloses the powerplant.

The engine cowl is carved to shape in the same manner as the fuselage for the "Aeronca Sedan" in Chapter Two. This should be carefully hollowed to a 3/16" wall thickness after the exterior has been completed. Cement the cowl to bulkhead "B" in temporary fashion using only a few drops of cement here and there.

When all is dry the inlaying can be carefully trimmed to the shape of the fuselage using an X-acto No. 26 blade. The entire fuselage framework is sanded smooth using fine sandpaper wrapped around a block of wood. This component can be set aside and our attention is now directed to the tail surfaces.

All rib pieces, leading and trailing edges, and tips for the tail surfaces should be cut to shape. Assembly is the same as described for the "Troop Carrying Glider in Chapter Four. Sandpaper smooth when the structure has been well cemented. Note that the rudder is hinged to the fin and this is accomplished in the same manner as was described for the elevators in Chapter One.

The ideal covering material for radio control models is silk. Heavyweight silk-span is often used however silk is recommended for our "Cub". This is available at any hobby shop. Cover the horizontal and vertical tail surfaces at this time using cement as the adhesive. It may be of interest to the reader to learn that many expert model builders wet the silk before they apply it to the framework. In this manner the cloth can be stretched tightly in place for a perfect covering job. After the piece is cut to size it should be wet thoroughly and squeezed as a ball in the hand. Do not wring or twist. Apply four coats of clear fuel proof dope to the silk after it is applied and dry from the water.

The tail is cemented to the fuselage at this time. Install a commercial radio control horn to the rudder in the manner shown; such as the "Bonner".

Mount the rudder escapement, with screws, to a sheet of plywood which is as wide as the fuselage. Now, cement the plywood to the forward side of the fuselage uprights as shown. While this is drying the control push rod can be assembled. This consists of a length of ¼" square hard balsa with a piece of 1/16" diameter music wire at each end. The wire is bound to the wood with thread and well cemented several times. The wire is bent to resemble an "L" and one end is slipped in the hole in the escapement bellcrank while the other end is slipped in the hole in the rudder horn. Be certain that the push rod is of the correct length in order that the rudder is neutral when the escapement is in the neutral position. Solder washers to the push rod ends to keep it from slipping off the horn and escapement.

The escapement drive rubber band is installed next. Cut a plug for the bottom of the fuselage rear that fits between the longerons and cross braces very snugly. The face of the plug should be 1/16" plywood while the core can be ¼ balsa sheet. Bend a hook as shown and slip it through a hole in the plug. Cement well. Use a loop of ¼ flat brown rubber, which can be purchased at any hobby shop, for the escapement drive. The loop should be made about ten inches longer than the distance between the rear hook and the escapement hook. Tie the two ends together securely and locate the knot at the aft end. The rubber is wound by using an ordinary hand drill which uses a hook in the chuck in lieu of a drill bit. This hook can be easily bent from a headless nail or coat hanger with a pair of pliers.

Celluloid or other clear plastic sheet is used for the windshield and side windows. Cut the various pieces slightly over size and hold each in place while the correct outlines are drawn on the plastic with china marking pencil or fountain pen. Cement in place and hold in the correct position with straight pins until dry. Windshield material can be in the neighborhood of .015 inch thickness.

Silk is recommended for the fuselage covering and is applied at this time. Cut the silk with a pair of scissors to at least one inch larger than the side view and top view. Cover the fuselage in four pieces; top, bottom and two sides. It is suggested that the silk be wet before it is applied as described previously. Apply the cement, "Ambroid" is recommended, to the longerons and only the structure which borders the area to be covered. Do not apply .cement for covering to the structure within the area to be covered. Apply the covering quickly by rubbing with the fingers to smooth out the surface and cause the adhesive to penetrate the covering. When this initial attachment is dry proceed by working forward and then aft always applying not more than six or eight inches of adhesive at one time because of the rapid drying rate of the adhesive. Repeat this procedure for the four sides. The wetting will shrink the covering to a drum-like tightness. If, after the covering dries, it is not tight and still contains wrinkles, several more water applications should tighten the silk. When thoroughly dry apply three coats of clear dope. This will create additional tautness of the covering and make it airtight and comparatively water resistent.

Do not cover the fuselage in way of the wing location. Cut ¼ dowel into four lengths that are l½" longer than the fuselage is wide at the cabin area. Insert these through the fuselage gussets at the points shown on the plans,

 The purpose of the dowels is to hold the wings and landing gear in place. Rubber bands are looped over the ¾" protrusion of the upper dowels and passed over the wing to hold it in place while other rubber bands are looped over the lower dowel protrusions and are passed under the landing gear struts to hold the landing gear in place.

The simplicity of the wiring required for the single channel equipment is clearly illustrated in this diagram for the "Aristo-Craft TRR Receiver." All connections must be soldered and colored wire is recommended as is shown on the drawing in order to facilitate ease of installation and "trouble shooting". Wiring should not be stretched between the pieces of equipment. It is advisable ot allow plenty of slack to prevent taut lines which can cause trouble. Switch and jacks are available at any radio supply store or model shop.

The "Aristo-Craft Rangemaster 2AP Tone Transmitter" is of the type recommended for simplicity and reliability of operation. This is a single channel transmitter measuring only 3" x 5" x 8" and is supplied with a telescoping antennae. Like the majority of United States equipment this unit operates on a frequency of 27.25 me. which does not require a license to operate. A similar and less expensive unit is also available; this is the "Aristo-Craft Rangemaster 1AP Carrier Wave Transmitter." This is less expensive than the "tone" equipment but either price is within the reach of the serious model builder. It is important that the transmitter and receiver be matched in order to prevent any complications. Wave length and type of transmission must be the same in both units.
 
Wing construction is similar to that described in Chapter Four except that the entire upper surface between the leading edge and auxiliary spar is covered with 1/16 sheet balsa. After the outer wing panel structures are complete the center section must be constructed. Notice that the spars are omitted and have been substituted with "wing joiners" which are cut from plywood. The entire center section is covered with 1/16" sheet balsa to complete this structure. During the wing panel construction it will be noted that the spar notches in wing ribs No. 2 were oversize. This was done to accommodate the "wing joiners" when the three wing assemblies are joined. Cement the outer panels to the center section at this time and be certain that plenty of the adhesive is spread on the face of the "wing joiner" that comes in contact with the spar. Note the dihedral angle shown on the plans.

When the wing is thoroughly dry it should be well sandpapered and then covered in the manner previously described. Apply three coats of fuel proof clear dope to the silk.

Bend the landing gear wire struts to shape following the dimensions on the plans and bind the struts together with fine copper wire. Solder this joint securely. Fill in the space between the struts with sheet balsa and bind this with several layers of scrap silk and cement. Attach the wheels.

A very gentle sandpapering of the entire model is in order with fine garnet finishing paper. Brush on three more coats of clear dope and then paint the craft any color combination that you choose. A trip to the local private airport will be very helpful in choosing a color by viewing the vast array of combinations used on "Cubs" and other craft. The standard factory finish for the "Cub Special" was yellow and blue as the photograph shows. Apply at least three coats of colored dope to the model. Remove the cowl and apply several coats of dope to the cowl interior and the engine mounts and bulkhead. Drill holes in the mounts and bolt the engine in place. Make certain that holes are cut in the cowl for engine cooling, needle valve operation and exhaust port. The cowl is held in place with rubber bands and hooks.

The radio receiver and batteries are installed at this time through the open fuselage top. This equipment governs the correct balance of the model and therefore can be rearranged to balance the airplane properly. Light weight aluminum battery holders made by "Acme" are recommended and these are screwed to the interior bulkheads. The radio receiver is strapped against the bulkhead with rubber bands which are looped around screw hooks which have been attached to the plywood. A foam rubber pad at least ¾" thick must be inserted between the receiver and the bulkhead in order to absorb the engine vibrations. Mount the equipment in the locations shown and then install the wing and landing gear. Check the balance of the completed model and, if necessary, rearrange the battery and receiver locations to remedy any unbalanced condition. Once the items have been permanently located the wiring can be connected. All radio equipment manufacturers supply an easy to read diagram illustrating the recommended method of connecting the equipment. A typical diagram is included in this chapter.

Expert radio control model builder, Ronald Weiss, poses with his bright red Fokker D-VIII radio controlled replica. Notice the radio transmitter in the foreground. Models with high wing positions are the ideal subjects for radio and free flight application due to their exceptional stability. The clear, unobstructed flying field in the background illustrates the ideal site for free flight or radio control flying.
 
Solder all connections well and use rosin core solder. Mount the switch, earphone jack and test meter jack through the fuselage side in order that they are accessible without removing the wing. Do not forget the aerial wire which is stretched between the fuselage and fin.

The model must be very carefully tested before powered flight is attempted. Once the model balances correctly it should be hand glided over tall soft grass. This is first accomplished by running into the wind holding the model by the fuselage at shoulder height, just behind the balance point and releasing it gently now and then to check its reactions. If all appears well it can be launched with a gentle and smooth push, aiming at a spot on the ground about forty feet away. Carefully observe the glide. These tests should be repeated many times until the glide is steady and flat, if the model zooms up and stalls; add a sliver of hard wood between the wing trailing edge and the wing mount. If the model tends to dive add the sliver under the leading edge of the wing. Modify the thickness of the sliver as required by test glides. The engine should be pointing downward about two degrees (downthrust) and to the right about one degree (right-thrust to counteract torque) before powered flight is attempted.

Above is the rear view of an "Aristo-Craft Quadrol Escapement". This is the same as the "Aristo-Craft Selective Compound Escapement", which is recommended for this project, except that it consists of both elevator and rudder on a single channel. Note the hook for the long rubber loop and the gear stops which hold the mechanism in position until the signal is received. Below is the front view of the "Aristo-Craft Selective Compound Escapement" showing the actuating arm to which the rudder push rod is attached. This escapement is simple to operate and is recommended for the novice.

This beautiful painting prepared by famous aviation artist Jo Kotula, for Piper, clearly illustrates the color pattern of the Piper Cub Cruiser when it leaves the factory. The wing and horizontal tail surfaces as well as the upper portion of the fuselage and vertical tail surfaces are medium blue. License numbers should appear on the top of the right wing panel and the bottom of the left wing panel. These can be cut from black "Wondur Cal."

The author launches his radio controlled replica of the Fokker D-VIII for a pleasure packed flight. Hand launching is recommended unless the flyer is very experienced and a very smooth surface is available for take offs from the ground. Models should be launched with a smooth but positive forward motion just above shoulder height. Always allow the model to climb into the wind and gain altitude before attempting to control the craft.

First flights should be conducted on a very calm day. Check the radio equipment thoroughly, even with the engine running. Once the engine is running smoothly the model can be hand launched into the wind, in the same manner as was used for test glides, with the rudder neutral.

Do not try to control the model immediately. Allow it to climb to a safe altitude of at least fifty feet. When the engine finally stops try to maneuver the model so it will land while heading into the wind.

If the plane did not climb at all remove a slight amount of the down thrust; and if it tended to climb too sharply almost to the stalling point add a bit of downthrust. If the model controls appear too sensitive move the control rod to a hole in the horn further away from the rudder. Reverse the procedure if the model does not respond sufficiently to commands.

In order to insure the proper operation of your radio equipment it is imperative that the voltage, amperage and resistance be measured periodically. The simplest method to accomplish this operation is through the use of a multiple test meter. One of the most economical and yet reliable test meters is shown here. This is the "Aristo - Craft Multi-Tester" which measures Volts, Amperes and Ohms with accuracy. No radio control enthusiast should neglect this instrument. Complete operating instructions always accompany the equipment.

The first few flights should not be longer than two minutes. Control this by measuring the amount of fuel that is put in the tank. Run the engine on the ground and time the engine run in order to determine the correct amount of fuel required.

It maye be of interest to the reader to know that this craft can be flown as a free flight sport model without radio equipment. The engine should be smaller for a free flight versions than for the radio operated craft. Any engine from .099 to .199 cubic inch displacement can be used for the free flight version. It is imperative that the duration of the engine run for the free flight version be controlled in a precise manner in order to insure against losing the model in the air with an out-of-sight flight. The engine run can be timed within seconds through the use of a fuel cut off timer such as "Aristo-Craft" or "Elmic". This device is placed in the fuel supply line to the engine and stops the flow of fuel after a desired interval of time which stops the engine. This causes the craft to glide down to a landing. An engine run of 20 to 30 seconds is recommended. The following engines can be used for the free flight sport version of this "Piper Cub": Fox .09; 15; or 19; K & B .15 or .19; O. K. Cub .14, or .19; McCoy .19; and many others that your hobby dealer will be glad to recommend.

Whether it be radio controlled or free flight your "Cub" will provide many enjoyable hours of flying pleasure and the amazing realistic appearance of the model in the air will deceive many spectators into believing that it is a full size plane from a nearby airport.

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