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Chapter 6 - Aerobatic “Wellesley”

Once the model airplane enthusiast becomes proficient in straight and level flying, his thoughts eventually turn to stunt flying. This intriguing phase of control-line flying attracts all model flyers sooner or later. Performing the various gyrations requires a quick hand and even quicker reflexes and is certainly not intended for the tyro. Dozens upon dozens of flights should be to the builder's credit before he attempts aerobatics.

As previously stated, a short tail moment arm and large elevator area are basic requirements for sensitive controls. In addition to this, the stunt craft should possess an extraordinary amount of wing area. This is necessary to reduce the wing loading and to provide surface resistance to slipping or mushing during violent maneuvers.

In view of the fact that the majority of stunts require inverted flight (flying upside down), the airfoil or wing section should be symmetrical. This means that the curvature of the upper surface must be identical to that of the lower surface, thus enabling the wing to produce the identical lifting and flight characteristics whether the model is flying upright or inverted.   The result is a relatively thick wing which incidentally aids in providing needed structural strength.

Many biplanes are suited for stunting purposes because of the large concentrated wing area. A short tail moment arm must accompany this large wing area. Notice the thick wings with symetrical airfoils for inverted flight.   This 30 inch Curtiss XPVV-8 was very successful.

Although light wing loadings are preferable, this should not be carried to extremes. If the model is too light it will, of course, be very maneuverable, but it will be easily blown off its flight path by the slightest gust of wind and will also slip toward the flyer during maneuvers which bring the craft directly overhead. This is caused by insufficient centrifugal force. Therefore, a happy medium is required for the ideal stunt control-line flyer. A wing loading of from ten to fourteen ounces per square foot appears to provide the most desired performance.

Among the many candidates for stunt scale-model use, the Vickers "Wellesley" stands out as one of the finest examples. This long range bomber, torpedo plane, or general purpose reconnaisance craft established a world's record for long-distance non-stop flying on November 5th, 1938. Powered by air-cooled Bristol "Pegasus" XXII engines, two of these airplanes flew from Ismailia, Egypt to Port Darwin, Australia, a distance of 7,158 miles.

One of the most unusual features of these aircraft is the lightweight type of fabrication. This is a diagonal basket weave called "geodetic" construction. This structural complexity had the disadvantage of preventing mass production; the "Wellesley" was therefore used only in limited quantities during World War II.

When powered with the "Pegasus" XX engine, which is the standard power plant for the service model, the maximum speed is 228 miles per hour; the range with bomb load is 2,590 miles. The landing speed was 57 miles per hour and the ceiling 35,250 feet.

Construction can begin with the fuselage. This is first carved from a balsa block and then separated along the horizontal centerline. The fuselage is then hollowed, using a gouge, as the plans illustrate. This has been described in previous Chapters Two and Three.  Sand the interior lightly.

The fuel tank is installed into the lower half of the fuselage at this time. If stunt flying is contemplated, a specially shaped stunt tank must be fitted. The most common shape is a wedge with the fuel suction line located at the apex which is located at the extreme outside of the fuselage interior. This is done in order that the centrifugal force caused by the flight circle will cause the fuel in the tank to lie in the apex of the tank whether the model is flying upright or inverted. Connect the plastic tube feed and vent lines. Make certain that the center of the tank is at the same level as the engine needle-valve body. Cement the fuselage top in place.

Cut the tail surfaces to shape, sand well, add horn, and hinge the elevator to the stabilizer. When dry, cement the stabilizer into the fuselage slot. These operations should be fairly simple since they have been fully described in former chapters.   Add the fin and offset the rudder.

The wing is made in rather simple fashion. Only one spar is required and this is joined at the correct dihedral angle by the plywood joiner. While this is drying, the ribs can be traced and cut out. Full-size patterns have been provided to ease this task.   When cut out, each rib should be sanded smooth and then slipped onto the spar. The ribs are located one inch apart. Hold in place with pins until the cement is dry. Cement the leading edges in place and follow with the trailing edge. The trailing edge has notches cut to fit the ribs. These should be ⅛" deep and 1/16" wide. Cement the solid balsa wing tip in place at this time.

Model Airplane News Photo

Many beauty models can be stunted because of their fine proportions. This should only be attempted by the experienced modeller. This Boeing F4B-4 (30" span) performed stunts beautifully for the author and yet was attractive enough to win several awards. Many dual purpose craft are available to the expert.   Remember, all experts were once beginners.

Cut the plywood landing-gear supports, as well as the bellcrank mount, from plywood. Cement securely in place between the ribs and cement also to the spar. While this is drying, the wire landing gear struts are bent to shape. Be certain to bend one right- and one left-hand strut. These struts are securely cemented and wrapped to the foundation with thread.  Do not spare the cement.

Carefully trim the leading and trailing edges with a sharp knife or razor blade until they fit the rib contour shown. Trim the balsa wood tip in the same manner. Sand well and cover the wing with "Silkspan", as described in Chapter Four. Do not water or dope until later.
Carefully saw a vertical notch into the fuselage belly up to the location of the top of the spar. Save the piece that has been removed.   Now, slip the

 wing spar up into the notch; when the alignment is satisfactory, the wing is firmly cemented in place and the piece of fuselage that was removed is now cemented back in place. Fillet the wing joint with "Plastic Balsa". Water the wing and follow this with four coats of clear dope.

Air Trails Photo

This large (44 inch span) "Consolidated PB-2a" was noteworthy for the excellent stunting it performed. Notice the large thick wing which is required for maneuvers. Although a bit heavy because of the sheet balsa covered wing, it was successful when flown on long lines (80 feet).

Cut the plywood engine mount and the cowl rings. The cowl is made by cementing laminations of ¼" sheet-balsa rings together; these vary in diameter, as the plans illustrate. Cement these to each other and to the engine mount, which in turn is well cemented to the fuselage nose. When this is thoroughly dry, it should be sanded smooth.

"Sanding Sealer" can now be brushed onto all exposed wood areas. Do not forget the sanding. Three coats will suffice. The plane is colored in accordance with the standard English camouflage. First brush two coats of sky-blue colored dope onto the lower surface of the wing and horizontal empennage. When this is thoroughly dry, it should be masked with tape and the remainder of the model should be colored with two coats of chocolate brown. This in turn should be masked as the camouflage lines require, and grass green applied over the brown in these areas. Study the plans and photographs for the exact color separation.

Cut the wheel covers from tin-can metal and spot solder these to the landing gear strut.   Paint blue.

J. Conrad  Photo

With a forty-six inch wing span and a weight of only 30 ounces, this "Bellanca Flash" models light weight allowed it to follow every movement of the control handle without hesitation. This extremely low wing loading made flying on windy days quite difficult.

Paint a round toothpick and force it into the fuselage as a radio antenna mast. The cockpit covers are "Scientific" plastic bubble canopies. These are trimmed and cemented in place at this time. Use strips of green cellulose tape for the canopy frame. Apply the rubbing compound at this time, if desired, following the directions previously described. The English bull's-eye insignia, or roundels, are generally available in decal form at most hobby counters. If these are difficult to obtain, they can be cut from 'Wondur-cal". First cut out a dot the size of the yellow circle and apply to the model. Then cut a smaller blue dot and add directly over the yellow, already in place. Repeating this operation for the white and blue will form concentric circles with a red dot in the center. The lower surface of the wing contains black numerals. These should be cut from "Wondur-cal". Black "Wondur-cal" is also used for the dummy wheel openings.

Coat the model with clear fuel proofer if fuel proof dope was not used. The wheels can now be slipped in place and brass washers soldered to the axle. Attach the lead-out control lines to the bellcrank and twist the ends as shown. Fasten two small screw-eyes to the bottom of the wing tip and pass the lines through. Screw the bellcrank to the plywood mount with a 1/16" washer between the mount and the wing. Bend the control rod to shape and slip the offset end into the horn. The other end is passed through the bellcrank and a washer soldered in place.

"The Lensman" Photo

The "Vickers Wellesley" zooms past the camera, flying inverted. Flying upside down is only one of the milder stunts capable of performance with the "Wellesley". During inverted flight, it is important to remember that controls are reversed, up is down and vice versa.   Try it.

Many bellcranks available today have two possible holes through which to insert the control rod. The selection of the correct hole governs the sensitivity of the control system. The closer the hole to the pivot point of the bellcrank, the less sensitive the system will be; therefore, the beginner should use this hole to test his plane. This can be moved later to the hole furthermost from the pivot point for extra-sensitive controls. This type of bellcrank is desired for our model. Check the operation of the control system.

The engine is now screwed to the plywood mount. If the engine you intend to use has beam mounts only, it will be necessary to make a metal mount adapter, as the plans illustrate. Engines that can be used are: Cub .074" or .099", McCoy .09", Fox .099", and quite a few foreign diesel engines.

"The Lensman" Photo

The large expanse of wing area is clearly illustrated in this photo of our stunt model. Our propeller is a wide blade plastic type. However, wood or any material wide blade propeller can be used provided it is the proper size. Cockpit covers are standard "Scientific" plastic bubble canopies.

Test flying stunt models is done as with sport or beginner craft. Several flights should be made using thirty-five-foot lengths of .008" steel flight lines. These can be lengthened to forty-five or fifty feet later on when the flyer is the true master of his craft. It must be remembered that the wind should be blowing on the flyer's back during all stunts in order to insure taut lines. The plane should be made to climb downwind and dive into the wind.

The first stunt should be an "inside loop". This can be performed only after a series of sharp and long climbs and dives have given the pilot the "feel" of his plane. Flying at a rather high altitude, execute a rather sharp dive with the wind and, at about eight feet from the ground, apply sharp "up" elevator. Pay close attention to your model during the first portion of this maneuver and be ready to step back should the lines go slack. Be certain that you hold the control handle in the full "up" position during this entire stunt. Naturally, neutralize the controls once the craft has attained its normal upright flight position.

Inverted flight consists of the first half of an inside loop and, when the model is upside down, the controls are neutralized.  It must be remembered that during inverted flight, the controls are reversed and that "up" elevator will cause the plane to dive! The plane can be righted by following the loop procedure and applying "down" elevator to cause the craft to climb up to the top of the loop, when the controls are neutralized. It cannot be overemphasized that the engine must run at its peak speed in order to provide the power required to pull the model through these maneuvers.

"The  Lensman"   Photo

This underside photo clearly illustrates the light blue bottom and black wing numerals. Also of interest is the complete control system externally installed. Notice the small screw eyes at the left wing tip that act as control line guides.

An outside loop is a bit more difficult than the two previously described maneuvers. This stunt is started with the model flying quite high, into the wind. Apply full down elevator and the craft should dive in an arc and complete a loop terminating at the starting point on the circle top.

"The Lensman" Photo

The brown and green camouflage patches on the upper surfaces are clearly defined on our "Wellesley." The light patches are brown. Engine is mounted inverted only to preserve the profile appearance. This can, however, be mounted upright. Cocard or rounded insignia are either standard decals or "Wondur-cal".

Most intricate maneuvers are merely combinations of all or several of these three basic stunts.

While on the subject of stunting and unusual flying activities, we feel that a brief description of a "glider pickup" system is in order. This is so because two of our previously described models in Chapters Four and Five are ideal candidates for this interesting stunt. The Northrop "Gamma" is a fine, steady, easy to handle craft to which the pickup hook can be readily attached, while the Waco glider is a perfect size as a companion model to the "Gamma".

This idea is identical to the system used on full-scale "pickups". A harness of string is fastened to the glider towing rig and the other end is a loop suspended between two poles, eight feet apart. It is imperative that the pilot stand in the same spot during the entire flight in order that the powered tow plane will always fly over a point between the two poles.

It is imperative that the glider towing rig be raised well above the center of gravity of the glider in order that the glider will not tend to climb and upset the flight path of the tow plane. This rig must be securely fastened to the reinforced glider fuselage. Do not try to utilize glider pickup by attaching the harness to the belly towhooks, since these are only for hand towing.

The flight is started by placing the tow model in front of the two poles and midway between them. This is to guarantee the location of the plane during flight. When the craft is airborne, an assistant can be used to advantage in signalling the pilot as to the altitude required in order to pick up the glider. Once the glider is picked up, study the flight path carefully. Should the glider tend to bank excessively, add some lead weight to the high wing tip.

Now that you have been introduced to a typical stunt scale model and the unusual tricks which can be accomplished with them, you will understand why flying model airplanes forms the leading hobby of the United States. The next chapter will endeavor to introduce the reader to speed-scale models for a taste of speeds in the neighborhood of ninety to one hundred miles an hour.

One of the most famous specially designed stunt model airplanes was "Madman" Yates' "Dragon". This is compared to the outline of our "Vickers Wellesley". It is interesting to note the amazing similarity in proportions, namely wing area, elevator area and tail moment arm. Scores of real airplanes can be adapted to stunt flying if the builder knows the required characteristics.

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