A MINITURE FLYING STINSON 0-49

A Detailed Model of a U. S. Military Plane Especially Suitable for Flying Scale Contests

By EARL STAHL

NEWEST type observation plane for the United States Army Air Corps is the Stinson 0‑49 now being produced in quantity by Stinson Division of Vultee Aircraft Inc. Former observation planes of larger sizes and greater speeds here to fore purchased by the Army are not able to use the small fields usually found in the occupied areas; for that reason fast, large ships are not adaptable to work with infantry divisions. The Stinson O‑49, designed not only to cooperate with the infantry but also to adjust artillery fire, is a short range, highly maneuverable plane featuring short landings and quick takeoffs.

Contrary to the recent trend to low-wing designs for military aircraft, this plane is a high‑wing job of conventional construction. Pilot and observer are seated in tandem in a rather large cabin which features exceptional visibility Two‑way radio is installed and the ship is said to be unarmed. Automatic‑type slots span the wing's entire leading edge and huge flaps extend inboard to the fuselage from the ailerons. The power plant is a nine cylinder, air‑cooled Lycoming of 280 horsepower.

Due to military regulations, official performance figures have not been divulged; however, one should obtain a rather accurate estimate of performance by comparing the 0‑49 with the Feiseler "Storch," a similar type plane used by the German Army. With a 200 horsepower engine the "Storch" has a top speed of 120 miles per hour: it takes off as readily as an autogiro and climbs at a very steep angle. Landing speed is 20 m.p.h. after a gliding approach that appears to be nearly vertical. The excellent aerodynamic design and additional power of the Stinson should make a speed of 130 m.p.h. possible with the landing speed probably not exceeding 30 m.p.h.

 

Model builders will recognize the Stinson 0‑49 as an excellent subject for a flying scale contest model. In appearance it is attractive yet not difficult to build. Best of all, the aerodynamic proportions are near perfect; our test model was built to scale and it was unnecessary to even increase the wing's dihedral or enlarge the proportions of the tail surfaces to obtain long, stable flights. The relatively long fuselage permits use of a powerful motor of considerable length, thus increasing the length of power flights. To make possible use of a propeller of sufficient size the landing gear is shown in the extended or flight position. In addition to its excellent flight qualities, the Stinson offers a wealth of detail to be reproduced in the radial motor, cabin windows, etc., for those who seek maximum "scale" points in flying scale contests.

Fuselage

The fuselage underframe is constructed first; it is shown lightly shaded on the plan. Work directly over the plan and make two side frames; longerons and uprights are 3/32” square balsa. While the curvature of the lower longerons is not excessive, it is advisable to steam them to shape so they will not have a tendency to draw the upper longerons out of alignment when removed from their jig. When dry, the side frames are joined by 3/32" square cross‑pieces. Check frequently to assure proper alignment of the entire structure.

With exception of the cabin formers, the fuselage formers are cut from soft grade 1/16" sheet balsa. It will be noticed that some of the formers lack notches for the stringers, and where this is the case the stringers are attached directly to the sides, as shown. Cement formers to their respective positions and then add the 1/16" square stringers. The stringers that extend along the sides are cemented directly to the underframe.

Because of the cabin's unusual shape, special care must be exercised to insure accuracy and strength. Full size cabin formers are shown and they are made from hard grade 1/16" sheet. Assemble the parts of formers C‑1 and C‑4 directly over the plan ‑ they must be exact. Looking at the side view of the fuselage, it will be noticed that C‑1 is attached at an angle to the top longeron. Cut a cardboard pattern to exact angle, to aid in accurately attaching the front member to place. Cement C‑1 and C‑4 to place and then cut two ribs to shape indicated on the side view; assemble them to the notches in the formers. If you have reproduced the structure with greatest care, the ribs will have the correct incidence 2‑1/2 degrees positive. Attach the other formers and the 3/32" square pieces that form the cabin. Thoroughly recement all joints.

To effectively represent the metal nose of the real ship, the front from section No. 1 to No. 2 is covered with soft 1/32" sheet. Two 1/8" sheet balsa discs are cemented to the front of section No. 1 and then shaped as indicated. The engine cowling is made in a similar manner. A frame consisting of two circular bulkheads and four 1/16" square spacers is assembled as indicated by the broken lines; this structure is covered with 1/32" sheet. The rounded nose section is made from laminations of 1/8" sheet, the centers of these discs being removed to the extent indicated by broken lines. Details of the nose plug are indicated. The removable section is made to fit accurately to the crank case which is cemented within the cowl front. Finish the nose and cowl by sanding to finished shape but do not cement the cowl to the nose until later.

Landing Gear

Before constructing the landing gear full size sketches of the various wire parts are made; these parts are bent from .034 music wire. With needle and thread sew the top member of the front unit to the fuselage longerons and cross‑member. Since the nose is covered with sheet balsa, long nose pliers will probably prove helpful for working the needle about the wire and through the formers. The other two wire units can be temporarily held to place until the parts are accurately fitted and the whole structure properly aligned. Neatly but firmly solder the struts together. Securely bind the rear struts to the lower fuselage stringer, then reinforce the area with 1/16" sheet, as shown. The center strut is not attached to the fuselage, it being left free to twist and spring and thus absorb shock. The balsa and rubber tubing fairings are not attached to the landing gear until later.

Wheels are made from laminated balsa discs or they may be purchased. Bearings should be cemented to the sides so they will revolve smoothly and accurately.

Wing

Because of limited space a full size wing plan could not be reproduced, so a full scale layout should be made on a large sheet of paper and work done directly over it. Taper and sand the trailing edges before pinning them into position over the plan. Ribs are cut from light grade 1/20" or 1/16" sheet; sixteen regular and two tip ribs are required. Pin ribs to position and then attach the leading edges and spars. Assemble tip pieces, which are cut from 1/8" sheet, and cement them to place. Once the leading edges and tips are trimmed and sanded to shape the wing frames are completed.

Tail Surfaces

Construction of the tail surfaces is quite simple. Both rudder and stabilizer are made similarly, the plans being nearly self‑explanatory. Make the stabilizer in one piece. The streamline rib shape is made by gluing 1/16" square strips of a soft variety to both sides of the underframe and later cutting them to shape. This manner of construction is strong yet light. Carefully trim and sand the parts so a smooth covering job can be made.

Propeller

Carve the propeller from a very hard balsa block 8" x 1‑1/2" x 1"; lay out the blank as shown. Always cut the back face of the blades first. The hardness of the wood will determine the thickness of the blades, its shape can be seen on the photos. Thoroughly sand the propeller and then apply several coats of clear dope with light sanding between each coat to produce a nice smooth finish. Equip the prop with some kind of free‑wheel device so the glide will be improved.

The propeller shaft is bent from .040 music wire. Place several washers between the prop and nose plug and bend a loop on the front of the shaft into which a mechanical winder can be hooked.

Covering and Assembly

Before starting to cover your Stinson the entire frame should be lightly but thoroughly sanded to remove all roughness. The several flat windows between sections C‑1 and C‑4 are covered with cellophane at this time --other windows are celluloid and not added till later. Being an Army plane, standard blue and yellow colors are used. Use banana oil for adhesive and cover the fuselage with blue tissue; to prevent wrinkles numerous small pieces of tissue should be used. The sheet‑balsa‑covered nose and cowl are tissue covered, too. Wings and tail surfaces are covered with yellow tissue; grain runs spanwise. Tips, etc., require separate pieces. The parts are lightly sprayed with water to tighten the tissue but are not doped until the ship has been assembled.

To assemble your 0‑49 follow this procedure: Finish the cabin windows first. Use the very lightest celluloid available -- film negatives boiled in water to remove the emulsion are excellent. Start at the back and make accurate paper patterns of each section, cut the celluloid to shape and cement to place, being careful to avoid cement smears. Pattern for the front windshield is given but it may need slight altering to exactly fit your model. Thin strips of tissue doped to the windows, as pictured, will improve its appearance.

Finish the landing gear by cutting the balsa covers from 1/8" x 1/2" soft balsa; these members are streamline in cross section. Cut 1/16" deep grooves in the struts to hide the wires and cement the wires fast; do not, however, attach the tops of the struts to the fuselage. Cover the struts with several layers of colored tissue. Split the rubber tubing, slip on the rear struts and then recement. Wheels are colored and held to place by washers soldered to the axles. It will be necessary to temporarily cut the tail post to admit the stabilizer, which is attached by cement at the angle shown. The rudder is off set 1/16" so the model will glide in right circles. The wings are fitted to the fuselage with tips elevated 1‑1/2" ‑‑ scale dihedral. The "vee" wing struts are shown half size on the plans; they are 3/32" x 3/16" balsa cut streamline. Struts join the wings at the "X". If the builder wishes to add engine details within the cowling it is best done before the unit is cemented to the nose. Now that the model is assembled, a coat of clear dope is applied to all the covered surfaces.

Minor details are usually the features that make the model really attractive. The 0‑49, an Army ship, of course should have the regular wing stars and rudder stripes. These can be made from colored tissue as can the "U. S. ARMY" on the wing's under‑surface. Control surface outlines, flaps and slots, etc., are represented by thin strips of black tissue. As noted before, engine details within the cowling will go a long way in adding to the ship's attractiveness. Naturally the propeller and other exposed wood parts are color doped.

About ten strands of 1/8" brown rubber are required to power this model. Measure the strands to the correct length and attach them to the prop shaft loop. Drop the rubber into the fuselage and slip the bamboo pin into place to attach the rubber in the rear. Your model of the Stinson 0‑49 is now ready for its first flights.

Flying

Select a calm day and a grassy field for the test flights. However, before taking the ship to the flying field, it should be made to balance by adding weight to the nose or tail, until it rests on an even keel when held at the center of the wing's chord. Test glide the plane and readjust the weight, as necessary, to obtain a nice smooth glide. Once the glide is satisfactory, try short power flights and if any corrections are required, make them by offsetting the thrust line. A sliver of wood at the top of the nose plug tilting the thrust line down at a slight angle will probably "iron out" a stall, while right or left thrust will adjust the circle during the power flight. While under power, circles should be large and to the left; in the glide it should turn to the right. A little effort and caution will reward you with a fine plane which is truly attractive yet a remarkable flyer.

Happy Landings!