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Chapter 1 - “Bell X-1” Whip Controller

Today's fastest growing model airplane activity is control-line flying. This type of model performs at the end of two lines ranging in length from twenty to one hundred and fifty feet, depending on the size of the model and the skill of the flyer. These lines not only keep the model flying in a circle around the "pilot", who turns facing the craft at all times, but also control the elevators which cause the model to climb and dive, loop, and perform a wide variety of aerobatics. The model operator holds a "C" shape handle in his hand. One line is attached to each leg of the "C", while the other ends of the lines are fastened to the arms of a bell-crank which is firmly attached to the model with a screw or bolt and is allowed to pivot around this fastening. A third arm of the bellcrank is connected to the control rod and, through this, the elevators are moved when the lines are pulled.

Three major factors have contributed to the increasing popularity of control-line flying; these are:

1. In view of the fact that the model cannot bank or veer to the left or right because of the control lines and is controlled in its altitude through the movable elevators, it has been found that this type of craft does not require the same meticulous adjustments and exacting design as its pilot-less free-flight brothers. This class of models can also be built heavier and much smaller than uncontrolled craft. This produces more carefree flying and building.

2. The confining flight circle allows control-line models to be flown on the local baseball diamond, corner lot, school yard, or even on a dead-end street, whereas free-flight models require large tracts of open land for successful operation.

These wide open areas are hard to find in the average community. The author flies his small controlled models in front of his home, while the nearest free-flight area is over five miles away.

3. Probably the most important reason for this enormous following is the fact that the flyer exercises control over the craft and thus achieves the thrill of piloting his creation through the air at speeds of from 25 to 175 miles per hour! With more experience he can perform almost any maneuver of a full-scale airplane.

Factor number one indicates that special design is not required; therefore, exact scale models can be built and flown successfully in control-line fashion, without any alteration in outline shape, whether they be high wing or low, biplanes or triplanes. The fact that these craft can be heavily built allows more detail to be added, such as complete cockpits, bombs, etc., as well as more applications of paint (dope) for a more attractive appearance. This, coupled with factor number three, which allows for complete realism during these maneuvers, causes control-line flying to become the ideal medium for scale-replica aircraft.

Skilled flying of control-line models can be learned quite easily and inexpensively through "whip" controlled models developed by Neville E. Walker. Generally, these craft are "profile" types. This means that they possess solid flat fuselages (body) approximately &" thick. Wings are cut from solid sheet balsa, as are the tail surfaces (empennage).

Whip-control models do not contain engines. The "whip" is used for the motive power. Obtain a bamboo pole (a fishing rod is ideal) about six feet long and attach wire loops as the plans illustrate. These should be wrapped to the pole with thread and cemented. Pass the control lines through the loops and we are ready to fly as soon as we have constructed our model. More about flying later.

An airplane which will go down in the pages of aeronautical history as a true record-smasher has been selected to be reproduced as our "whip" controller. The Bell X-l research plane, of which three were built, is the first man-carrying airplane to fly faster than sound.

Early in December of 1944, while the aircraft industry was still concentrating on the production of airplanes with which to end the war, the Army Air Forces discussed with the Bell Aircraft Corporation the possibility of designing a man-carrying supersonic research airplane.

A decision was jointly reached that this airplane should adhere insofar as possible to a conventional arrangement in order to prove whether or not such an arrangement is practicable at transonic speeds. Similarly, it was decided that relatively conventional methods of construction to standard tolerances which could be duplicated in production aircraft would be employed. The experimental supersonic X-l airplane was the result.

Consideration was given to air launching and the use of skids for landing. Wartime .considerations of possible tactical development of the aircraft, however, dictated that it be able to take off under its own power; a tricycle landing gear was therefore used.

The X-l is of conventional configuration, having a wing area of 130 square feet, and a wing loading at the beginning of its flight of 100 lbs. per square foot. It is 31 feet long and has a span of 28 feet. The pilot is enclosed in a sealed cabin. Behind him and within the fuselage are tanks carrying liquid oxygen and alcohol feeding for 4.2 minutes a 6,000 pound rocket motor mounted in the tail. At launching, it weighs 13,034 pounds, burns up over 8,000 pounds of fuel, and lands weighing 4,818 pounds at about 110 m.p.h.

Bell Aircraft  Photo

This interesting photo of the Boeing B-29 "Mother Plane" carrying the Bell X-l aloft demonstrates the unusual method of launching this craft. The small research plane is released high in the sky thereby allowing all the fuel to be used for high speed flight rather than be wasted for climbing.

Bell Aircraft Photo

The full size Bell X-l in flight presents a most interesting picture and many miscellaneous external details can be found in this photo. Note the rocket blast from the four engines in the tail which drive the craft faster than sound.

The four rockets may be run separately or in combination as selected by the pilot. The motors are started by a small igniter located in the forward end of the cylinder, which fires a stream of fuel and gaseous oxygen by means of a spark plug. When the chamber pressure reaches a value of approximately 50 psi, the propellant valves open to admit the fuel and liquid oxygen. No provision has been made to throttle the individual rockets; hence the pilot has at his command only 25%, 50%, 75% and 100% of full thrust.

The pilot's windshield does not protrude as in normal practice but conforms to the fuselage's ogive nose shape; as a result, visibility during landing is marginal. It is of double thickness plexiglas to prevent fogging; the air space intervening between the two panels is dehydrated. The pilot's exhalation is likewise dehydrated through a cannister attached to his oxygen mask. It was desired to avoid the use of plate glass in the windshield due to the difficulties in producing double curvature safety glass. The increased potential flight speeds which have been gained by air launching, however, has made it mandatory that a new windshield capable of withstanding elevated temperatures be installed. As a result, plate glass is now being substituted for plexiglas in the windshield.

The pilot enters through a rectangular door on the right side of the fuselage located in such fashion that in case of bail-out he is fore d to go downward, thereby increasing his chances of missing the tail. His cabin pressure is sealed with him just prior to launching and no replenishment is necessary for a flight of this airplane's short duration. Internal cabin pressure is maintained at 3 psi above atmosphere, which is sufficient to maintain pilot safety irrespective of altitude. The cabin is tested to leak at a rate no greater than 1 psi per hour at 3 psi internal pressure.  We find this is actually quite conservative, since replenishment from the pilot's exhaled breath through his oxygen mask is actually quite appreciable.

A standard B-29 was supplied by the Air Forces to carry the X-l into the air. Its bomb doors were removed and the X-l was suspended from a standard Air Forces D-4 bomb shackle. An enclosed ladder was installed between the B-29 and X-l in such a manner that the X-l pilot or flight personnel could go back and forth between the two airplanes while in the air.

For loading purposes the X-l is lowered into a pit, the B-29 rolled over the pit, and the X-l pulled up and partially into the B-29 by means of a hoist located in the "mother" airplane.

In October, 1947, Captain Charles E. Yeager, U.S.A.F., piloting the X-l, became the first man to fly at supersonic speeds in straight and level or climbing flight. Since then, the Air Force has announced, repeated flights in the X-l have attained supersonic speed. Among pilots achieving such rates of speed in this research vehicle have been Captains Lundquist and Fitz-Gerald, both of the Air Force, and Howard Lilly and Herbert Hoover of the National Advisory Committee for Aeronautics.

Speaking before the Air Force Association in New York in September of 1948, Secretary W. Stuart Symington of the Air Force said that the X-l had flown "hundreds of miles" faster than the speed of sound. This is the closest to a specific statement of performance yet made.

It may be well to suggest that the plans and photographs be studied with care and this chapter read and reread until every construction step is known and understood. Only in this manner can a successful model be constructed.

The entire model is cut from ¼" thick sheet balsa wood. This wood is universally used for model airplane construction because of its high strength-weight ratio. Plans on the accompanying pages have been presented one-half actual model size. These must be enlarged by redrawing and doubling all dimensions. Photostating is a quicker but more expensive method of obtaining full-size plans.

Begin construction by tracing the fuselage (body), wing, and empennage (tail surfaces) onto the sheet balsa. Cut these out, using a sharp single-edge razor blade or coping saw. It will be noted that the fin and rudder are built integral with the fuselage. Also, in view of the fact that balsa wood generally is available in two- and three-inch widths, it will be necessary to butt joint the sheets together to form the correct widths. Note the seams on the plan. Securely cement the lead weight into the fuselage nose as the plans illustrate.

Carefully carve the wing to shape to agree with the section. These sections are called the "airfoils". We recommend a very sharp knife for this operation, an X-Acto No. 26 blade. Sandpaper all parts well, using 1/0 sandpaper followed by 3/0.

With the wing carved to shape, we are ready to install the bellcrank mount to the underside of this component. A small hardwood "nose button" has been used for many years on small light craft for the bellcrank mount. These "nose buttons" are sold at hobby shops as bearings for rubber-powered craft. Should these "buttons" not be available, cut a piece of hardwood to a size of ½" x ½" x ¼". Now, cut out a ½" x ½" opening ¼" deep in the underside of the wing and cement the block into the hole.

Cut two ¾" lengths of plastic sipping straw (available at any 5-and-10-cent store) and cement in place as the plans illustrate, on the underside of the wing.

Cut the slots in the fuselage (body) to receive the wing and horizontal tail. Slide the wing into its slot and apply plenty of cement. This cement is available at any hobby shop and is a very fast drying glue of cellulose composition. It is available in tubes or jars. Tubes are preferable. Check the wing alignment.

"The Lensman" Photo

All markings are made with draftsman's ruling pen and India ink. Stars are decals. Of special interest in this photo of the Bell X-l model is the wide slot in the rudder in order to make room for elevator movement.   Cabin is white gummed paper.

While this wing joint is drying, we can proceed to hinge the elevator to the stabilizer. The former item is the movable portion and the latter is the fixed portion of the horizontal tail. Attach the control horn to the elevator at this time. Many commercial horns can fit this model. We used a "Scientific" horn. Cloth hinges are almost universally used on control models. These are usually of ⅜" x ¾" size and cut from cloth of handkerchief weight. Some of the larger models (larger than 40" wing span) use crinoline cloth for hinges. It will be noted that one-half of the cloth is cemented to the bottom of the elevator and the top of the stabilizer; the next piece is attached to the top of the elevator and the bottom of the stabilizer. Alternate in this fashion until the two components are joined. Slip the stabilizer into the fuselage slot and cement well.

Painting this craft is as simple as its basic construction. In view of the fact that balsa wood is very porous and absorbs paint like a blotter, most experienced builders elect to fill these pores before applying the paint. Many liquids are available for this sealing operation. These solutions dry to a rather soft finish that powders when sandpapered, which eases the task of smoothing the surface. It is the builder's option to use wood filler on this model. The author used it and recommends Testor's "Sanding Sealer." Two coats should suffice. Sand well with 3/0 sandpaper after each coat has dried.

Bell  Aircraft  Photo

The tricycle landing gear, used only for landing, is clearly shown in this photo of the full scale Bell X-l as it is being towed back to the base after landing. Many additional details can be added to your model if desired, such as wheel doors and markings. These are optional, of course.

The full-scale plane as well as our model is colored all bright orange. This color was chosen on the real X-l because of the excellent visibility required to distinguish this experimental speedster in the air. It also helps the novice follow his model as he flies it. Brush on two coats of colored dope, available at your hobby shop, using a soft brush.

Insignia of most nations are available at your hobby shop in decal form and in a wide variety of sizes. These decals are easy to apply. They consist of a colored cellulose film attached to a paper backing by means of glycerine. When dipped into warm water for about ten seconds, the glycerine dissolves and the decal can be slid into place on the model. Pat dry with a soft cloth and the result will surpass any attempt to duplicate the insignia by painting. The cockpit windows were cut from white label gummed paper and pasted in place.

The fine lines representing control surfaces on the wing (ailerons) and other fine markings are made by drawing onto the finished model with a draftsman's ruling pen and India ink. These pens can often be purchased in a stationery or school-supply store for as little as fifty cents. The ink is readily available.   A ruler or straight edge should be used to guide the pen. Be sure to clean the pen after using it. Study the photographs for marking information.

"The Lensman"   Photo

All the equipment required to fly our Bell X-l whip model is shown in this photo. The fishing pole can be either the bamboo type or meteal as illustrated. A metal or plywood control handle with two  twenty-five foot lengths of heavy carpet thread is also required.

The addition of the control system will complete the model. Carefully measure and bend the wire control rod using flat-nose pliers. Care should be taken when bending music wire because of its extreme hardness which causes such brittleness that the wire will not stand continuous bending. Slip the offset end into the hole in the horn and the 90° bend into the bellcrank arm. The bellcrank should then be screwed into its foundation with a 1/16" thick washer inserted between the bellcrank and the mount. Test the controls.

The landing gear is optional. The full-scale plane was designed to land either on the wheels or its belly skid. Although our model does not carry wheels, these are easily bolted to the fuselage via the sheet metal struts. Note that the two nuts on either side of the sheet metal are tightened towards each other, thereby locking the bolt in place. Make certain the wheel can be turned freely.

"The Lensman"   Photo

So simple is the operation of whip models that even young enthusiasts can have many hours of wholesome, inexpensive enjoyment in building and flying them. In this photo the author's daughter launches the Bell X-l for an assistant, who holds the "whip" in his right hand and control handle in his left.   Note how he leads the model to maintain flying speed.

Select a flying site that will accommodate twenty-five-foot-long flight lines. This means that a clearing of more than 50 feet is required. Cut two lengths of heavy carpet thread, available in any 5-and-10-cent store. These lines should be 25 feet long. Securely tie one end of each line to the control handle and pass through the loops on the pole. The remaining ends are fastened to the bellcrank by first passing them through the plastic straws previously cemented on the wing top. These straws are used to keep the model from banking excessively.

It is imperative that the craft balance exactly as shown. This can be achieved by adding additional lead weight to the nose or tail to remedy any unbalanced condition.

Normally, it is advisable to use an assistant to launch the model. With the flyer in the center of the circle and, with lines taut and free from twists, the assistant can throw the craft forward while the flyer "leads" with the pole. The author is right-handed and holds the handle in his left hand while holding the pole in the right. Our model is flown counterclockwise. It seems that right-handed flyers exercise more delicate control with their left hand and vise versa. Once the model is airborne, hold the controls neutral and observe the behavior of the craft. Twisting the wrist up or down will control the altitude of the model.

Should the line become slack, turn faster and dive the model slightly to tighten the lines. Never allow the lines to slacken, for loss of control and a crash will result. After several successful flights, stunts can be attempted. Stunt procedure for all control line craft can be found in Chapter Six.

Unassisted takeoff can be accomplished with a little practice. Merely place the model on the ground, facing down wind; quickly lead the "whip" and the model will leave the ground immediately. Hold controls in neutral for all takeoffs.

Repeated flying with this replica of a famous pioneering airplane will prepare you for your first engine-powered control-line scale-model airplane.

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