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Chapter 5 - “Northrop Ga Ma” Sport Flyer

Scale models are ideally suited for sport flying. On the premise that the vast majority of model-plane enthusiasts fly for pure enjoyment, it is little wonder that sport models are by far the most popular. The average modeller is interested in an attractive model which does not require exceptional skill to operate. A craft that is sluggish to control, as in training models, is hot desirable.

In order to obtain a fairly responsive control-line model airplane, the tail moment arm (distance between wing and horizontal tail surface) must be of moderate length and the elevator (movable portion of the horizontal tail) of moderate area. If the moment arm is exceptionally short or the elevator surface is very large, an extremely sensitive performer will result. This type of craft will respond immediately to every wrist movement and is therefore ideal only for stunt flying; it is very tiring to operate merely for "Sunday" flying. The majority of full-scale aircraft fulfill the required sport-model proportions.

Another requirement for a sport flyer is moderate wing area. Here again, excessive wing area will cause an extremely light wing loading (weight of model divided into the total wing area) which in turn produces extremely sensitive performance. On the other hand, a craft with a small wing will be too fast and, when the engine stops, requires care in landing because of its rapid rate of descent. Here again, moderation must be applied to the average airplane for sport flying.

"The  Lensman"   Photo

A clear view of the wing and tail decal markings are shown in this photo of our Northrop "Gama" 2-E. Black decal strip on wing simulates wing walk space on full size plane. Note rudder offset to pull plane away from flyer in order to maintain tension on the flight lines.

When the average enthusiast visits his favorite flying field, he disdains to have to take care lest he break struts or other rigging on his model. A scale-model selection that does not possess these external structures and protuberances affords more carefree flying and can resist rougher handling without damage. This does not mean that all sport craft should be strutless, only that it is preferable from the maintenance standpoint. There are many exceptions to this rule, however, one example being the author who enjoys flying both the complexly rigged models and the plain monoplanes.

Many scale models fulfilling these requirements have been built so attractively that they have won numerous beauty contests, thereby destroying any illusion the reader may have formed that sport models are drab, lifeless, and unattractive. The author merely wishes to point out the fact that sport models are perfect for the builder who does not care to or does not have the time to treat his model with extreme care on the flying field. The relationship between sport models and potential beauty winners is very close; in many cases the main difference lies only in the quality of the workmanship.

"The  Lensman"   Photo

Of special interest in this view of our modelarethe control line guides on the left (port) wing tip. These are made from music wire and firmly attached to the tip. The enormous wing fillet is easily made from sheet balsa and "Plastic Balsa." Entire model is colored silver with black trim.

Despite the sport-model specifications described above, many advanced modellers are not content with straight and level flight with an occasional loop. These experts crave high speeds and intricate maneuvers and build craft similar to those described in Chapters Six and Seven. These planes in that case become sport models. This would indicate that it is most difficult positively to define all sport craft.

In the author's opinion, one of the handsomest and easiest to fly models that he has ever built is the subject for our sport model presentation. This is the third model of this design built by the writer; all were a pleasure to fly. All exhibited moderate speed and fair response to controls.

The late Captain Frank Hawks, famous speed flyer and record holder of pre-war years, flew this attack plane and two-place fighter-bomber from Buenos Aires to Los Angeles, a distance of 8090 miles, in 39 hours and 52 minutes. Nine inter-city speed records were broken during this flight! The strange part of this story is the fact that the plane was not specially fitted for racing and that the flight was planned only 24 hours before the start.

Northrop Aircraft Photo

Clearly visible in this "Gama 2-E" airplane photograph are the bomb racks located between the landing gear which could hold over a thousand pounds of bombs. This craft also was fitted with three machine guns. Many records were smashed by this plane and her sister ships flown by Lincoln Ellsworth, Frank Hawks, Howard Hughes and many others.

It all began during May of 1935 when Captain Hawks and Gage Irving, an associate, were in Buenos Aires demonstrating the plane, a Northrop Gamma 2-E, to the Argentine Navy. When Hawks received a cablegram from the Northrop factory ordering him home within four days, everyone said it could not be done because it would take two days to prepare the plane for the long flight home. Hawks insisted he could do it, and did. The famous flier skillfully piloted the airplane the entire distance and caught cat naps during refueling and servicing stops. Mr. Irving supervised these operations while Hawks rested.

One of the most exciting incidents of this flight occurred while at 18,000 ft. altitude flying through a tropical storm. The engine coughed and stopped while over the Pacific Ocean! After much ingenious manipulation of engine controls and stretching the glide as long as possible, the engine finally backfired and started running at less than 6,000 ft. above the water!

The attack plane Hawks flew on this record-breaking flight is the "grand daddy" of many World War II and present-day attack planes and dive bombers. The pre-war Army A-17 and A-17A, as well as the wartime SBD "Dauntless" and A-25, plus the present-day "Skyraider", were all evolved from this basic design. The U. S. Army also obtained airplanes similar to the 2-E and designated them the A-13 and A-16. England, China, and many of our South American neighbors purchased these craft. This plane is very similar to planes flown by Lincoln Ellsworth, Jacqueline Cochran, and Jack Frye and is almost a twin to Captain Frank Hawks's famous "Sky Chief".

"The Lensman" Photo

It will be noted that the control lead out wires emerging from the fuselage do not extend through the lead out guides on our Northrop Model. The reader can, however, extend these through the guides if he so desires.

Notice, also, the extensive amount of lettering on the cowl.   This is done with pen and India ink.

A$ before, the plans must be enlarged to full size before construction can be started. In order to assist the reader we have presented all bulkheads and wing ribs full size. This will aid measurably in the enlarging process. This control-line model is larger than the craft described in Chapter Two and therefore requires engines of greater power. Any engine of from .19 to .35 cubic inch displacement can be used. Some power plants that fall in this category are: K & B .19" or .29", Forster .29", Ohlsson or Fox .19", .23", or .29", O.K. Cub .19", Veco .29", and McCoy .19" and .29", as well as several others. These are all "glo-plug" engines and do not require an electric ignition system,

Trace the horizontal fuselage keel onto sheet balsa and cut to shape with a single-edge razor blade or coping saw. Treat the bulkheads in the same manner. These should be securely cemented to each side of the keel, top and bottom. Cut the engine mounts from hard wood, similar to birch, and very firmly cement into the slots in the keel. The distance between the above-mentioned slots is governed by the engine to be used and this should be determined beforehand. Bend the landing gear to shape from wire and sew to the plywood bulkhead, using a needle and strong thread. Sew through the small holes several times and, when finished, smear with plenty of cement.

Numerous commercial tanks, either rectangular or cylindrical, will fit this craft. Install this item now. Make certain that filling and vent extensions (plastic tube), as well as feed line, are fitted.

Cut the elevator and stabilizer to shape and sand to a streamline cross section. Cement the elevator halves to the dowel spar and then install any commercial control horn. We used a "Scientific" horn. Hinge the elevators to the stabilizer in the manner described in Chapters One and Two. There are, however, several commercial hinges specifically intended for this purpose. One of these is the "Pylon" brand nylon hinge. Cement the stabilizer to the top of the horizontal keel after the hinges are complete.

"Veco", "Scientific", "Pylon", and many other concerns market bellcranks. The wire lead-out lines should be securely attached and the ends twisted into loops, as was done with our "Aeronca" in Chapter Two. Bolt (screws will not hold on a model of this size) the bellcrank to the mount and firmly cement this bellcrank mount to the fuselage frame. Bend the wire control rod and slip the ends into the horn and bellcrank.   Check the controls to insure their proper operation.

Sport and beauty models often fall into both categories. This "Spitfire" model has often been considered as a beauty model by fellow modellers because of its fine finish and detail. Yet the author places it among his finer sport models in view of its lack of outstanding detail which is required to capture beauty events.

Solder a metal washer to each end of the control rod to prevent it from disengaging from the horn or bellcrank.

It will be noted that the fuselage and wing center section are constructed as one unit with the plywood bulkhead acting as spar and wing joiner. Cover the center section with sheet balsa after the required ribs have been cemented in place onto the plywood. This covering should first be roughly cut to size and then cemented to the spar. When this is dry, apply cement to all of the rib portions behind the spar and pin the covering to them until the cement is dry. Repeat the process on the forward portion. It will be noted that no leading or trailing edge is required, but that the lower covering must be bevelled to fit the upper covering, which is applied last.

The fuselage is covered with strips of balsa running from nose to tail much in the same manner as on a small wooden boat. This method is called "planking". This procedure is much simpler than it at first appears. Cement the first strip along the fuselage top, being certain to attach it well to all bulkheads. Repeat this for the bottom and each side. Hold in place onto the bulkheads, using straight pins, until the cement has dried. Now, cement a strip to each side of the four strips already in place. Continue in this fashion until the entire fuselage is covered. It will be found necessary to bevel the edges and taper the shape of the last several strips in order to fit the remaining opening.

The large wing fillet is made from sheet balsa. First cut the bottom piece which extends aft of the trailing edge and cement this in place. The grain should run spanwise. Trace the main fillet pattern onto sheet balsa and fit in place, curving gently to fair into the fuselage and wing.   Trim to suit your individual model because no two models are identical, even when built from the same plan. When this fits well, it should be cemented to the wing, fuselage, and bottom fillet. Final touches can be made to the wing fillet and the small cracks in the fuselage planking by filling in with "Plastic Balsa", made by Aero-Gloss Products. This fillet compound dries to a consistency of real balsa wood and can be cut and sanded when dry. When all the cracks, etc. have been filled and are thoroughly dry, the entire fuselage assembly should be well sanded until very smooth.

"Mayberne"   Photo

This sleek model of Frank Hawk's "Sky Chief" was the author's favorite sport flyer. In view of the fact that it is a sister to the "Gama 2-E", the author elected to present the latter as the ideal sport model. Good looks, excellent proportions and lack of struts place these craft high among sport candidates.

Air Trails Photo

This replica of James Doolittle's Lockheed "Orion" is the veteran of hundreds of flights without a mishap. Note the clean simple lines and moderate proportions that result in carefree flying.

Air Trails  Photo

Easily passing as a beauty winner, this North American "Mustang" is well suited for sport flying because of its ideal proportions. Here again, a model fulfills both categories depending upon the amount of detail the builder cares to install.

Model Airplane News  Photo

Sport and stunt models are often closely related. Although this Pfalz D-12 model was built for sport use, it contained sufficient wing area for stunting. The only factor that prevents this craft from being a fine stunt model was the tail moment arm which was a bit too long.

The two wing panels are constructed at this time. Taper the balsa spar as specified and cement the wing ribs to it. Note that the root rib is tilted to provide dihedral. While this is drying, cement balsa sheets together to form the correct width for the wing covering.   Notice the seams on the plan. Cement the ribs and spar assembly to the lower covering and hold with pins until dry. Bevel this covering and add the upper cover, starting at the spar and working toward the leading and trailing edge. Cut out and add the solid balsa wing tip. Be sure to make one right- and one left-hand wing and make certain the spar stub is allowed to protrude so that it can be slipped into the opening in the wing center section rib. The wing panels are attached to the center section by smearing plenty of cement onto the spar stub and rib sides. Now join the two panels to the center section, being certain that the spar stub makes contact with the plywood bulkhead-center-section spar. This contact is a great source of strength. Sandpaper the entire structure thoroughly.

Air Trails Photo

Despite the unusually long tail moment on this 18" span World War I "Fokker E-l" replica it was not suited for the tyro because of the relatively small wing area which created higher speeds. This craft was, however, an excellent sport craft with superb handling qualities. The thread rigging was not too cumbersome.

Now that the major components have been assembled, the cowl, vertical tail, and wheel pants are fitted. Cut the fin and rudder from sheet balsa, sand streamline, and cement the fin to the fuselage. The rudder is cemented to the fin at the angle shown in the top view on the plans. This offset is important to keep the flight lines taut. Fit the wheels on the axles and solder a washer to the wire axle to retain them.

The pants are made in such a manner as not to touch the landing gear at all to enable the landing gear to flex without injuring the pant.  Laminate ¼" sheet balsa as shown and then carve and sand to shape. Cement well to the underside of each wing and fillet with several coats of cement. Bend the wire tail-wheel strut and flight-line guide and cement in place.

If a lathe is available, it should by all means be employed to turn the cowl from hard balsa. It is advisable to take your block of balsa and a full size pattern of the cowl to a local wood turning shop in order to save time and effort. The cost should be about one dollar and fifty cents. As an alternative, the cowl can be carved in the same manner as a fuselage. When this is completely sanded, a hole must be cut for the needle valve and a notch provided at the cowl rear to allow for the engine cylinder. These items will vary in accordance with the engine used. The cowl is cemented in place only after the plane has been completed and the engine installed.

At this time, the cockpit opening can be carefully cut out; this is optional, however. The model is now ready for painting; after a thorough sanding with finishing paper, several coats of Sanding Sealer should be applied as described in previous chapters. The quality of the finish depends on the number of coats and fine sandings as well as on the model builder's patience and ability. When the model is smooth, the silver dope is brushed on; three coats will suffice. After a brisk rubbing with compound, the celluloid-sheet cockpit canopy is added and "Wondur-cal" frame applied. Black "Wondur-cal" is used for the license numbers.

Fuel proof the entire ship, if fuel proof dope was not used, and install the engine, using steel nuts and bolts, not screws. Cement the cowl in place, using fuel-proof cement. If the craft balances well, we are ready to fly.

Control lines should be at least .010" stainless steel wire, either solid or braided. The author recommends a "Jim Walker U-Reely Control Handle and Reel". This ingenious instrument is a control handle and reel combination that can vary the length of the lines, even during flight.   The prototype model "Northrop Gamma" 2-E" was flown on fifty-foot lines. Thirty-foot lines can be used for the first few test flights. Take good care of the flight lines to prevent them from kinking and thereby weakening. Flying is the same as described in Chapter Two. When much experience has been accumulated with straight and level flight, a loop or two can be attempted. This procedure will be described in Chapter Six.

It is self-evident, in this sport model comparison, that the North American "Mustang" compares favorably with the "Scientific" Little Devil. The latter is one of the leading specially designed sport models in the country and yet possesses virtually the identical design proportions as the "Mustang". The "Mustang", of course, has a bulkier fuselage but this does not affect the handling qualities. There are countless other full size airplanes that can be used as sport type models.

Any model larger than 30" wing span and powered by an engine of .23 cubic-inch displacement or larger can be fitted with a hook for glider pickups. Our "Northrop Gama" was fitted as is shown. The .032" wire spring forces the 1/16" wire hook downward at all times. Note the stop which holds the hook at the proper angle. When the model is on the ground the weight of the craft forces the hook backward and upward. However, once airborne the hook occupies the down position throughout the flight.

There are many biplanes that qualify for sport use and this Waco "N" Tricycle is among the finest. The construction alone of this particular model keeps it out of the beginner class. Wing is built up and tissue covered while the fuselage is sheet balsa. This structure creates a light model which, in turn, would be more sensitive than a solid structure and, therefore, not suited for the rank novice.

The troop glider described in the preceding chapter can be fitted with a harness for use in glider pickup stunts. Should this operation be anticipated, it is then advisable to incorporate this apparatus into the craft during and not after construction.   This unusual stunt is described in Chapter Six.

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