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Chapter 3 - “Heinkel 162” Free-Flying Rocket

One of the problems which confronted the scale-model airplane builder until recently was the preponderance of jet-and rocket-powered airplanes in these modern times. American Telasco, Ltd. has solved this problem for the scale enthusiast by providing him with an inexpensive series of rocket engines with which to power replicas of these modern craft. These engines can power ultra-light control-line models, but are more suited for free-flying craft. "Jetex" engines, as they are called, are available in three sizes. Solid-fuel cylinders are burned in the metal combustion chamber and the resultant gases from this ignition rush out of a restriction in the rear of the chamber, causing a forward thrust. These are true miniature rocket engines.

In addition to being light, the successful "Jetex" engine-powered models must have the engine located in such a manner that the heat radiated by the engine will be dissipated before it can harm the airframe. For this reason, most builders locate their "Jetex" engine outside of the fuselage to enable the airstream to carry off the heat. In view of the fact that most full-scale jets of today contain their engines within the fuselage, the model enthusiast must insulate these replicas against engine heat and also cut access hatches in order to refuel the engine; these present two annoying but not insurmountable problems. There are, however, some full-scale craft which mount the engine on the exterior. These craft are ideal subjects for "Jetex" engine replicas.

One full-scale craft which meets the above requirement is the last jet-propelled airplane produced for the German Air Force during World War II. Designed and built by Ernst Heinkel, the 162 was primarily intended as an interceptor to combat the waves of American and English bombers which hammered Europe during the closing days of the war. Considered a rather small and light fighter, the Heinkel 162 was developed as an easy-to-fly and expendable airplane. Top speed was in the neighborhood of 500 miles per hour and armament consisted of two 30-millimeter cannon (approximately 1¼ inches). The craft was nicknamed "Volks-jaeger" or "Peoples' Hunter" because of the fact that the Germans had hoped to use "raw", basically trained pilots in almost suicidal attempts to hunt down Allied bombers. Only a handful of Heinkel 162 fighters saw action.

In order that our free-flying model would perform well, we enlarged the wing and tail slightly; however, the original scale outline is also shown for the reader's information. Free-flight craft fly more readily with large wing areas. Good design also demands that the horizontal tail area should be from 25 to 35 per cent, of the wing area for stable flight. It will be noted that our wing and tail surfaces are cut from 1/32" sheet balsa and are curved to form an airfoil contour. This was done to take advantage of the fact that considerably more lift is generated by the upper surface of any airfoil than by the lower. The bottom of our wing was left uncovered in order to save weight. The increase in weight would cancel the gain in lift if the lower surface were covered. Of secondary importance is the increase in strength obtained by curving the wing.

"Jetex" engines are available in the "50", "150" and "350' sizes. The Heinkel 162 plans illustrated on these pages are full size for the "50", which is the smallest jet engine available. If the plans were doubled in size, the "150" would fit perfectly. Lightness cannot be overemphasized; therefore, keep your model's weight down to one-half ounce.

"The  Lensman"   Photo

This underside view of our rocket powered plane displays the ribs attached to the sheet covering to create the airfoil curvature. Note the fuselage seam that separates the sheet balsa tail cone and hollowed balsa block nose piece. Bottom of plane is not painted to simulate light color of camouflage on full scale craft.

Select very soft balsa for the fuselage forward section. Treat the fuselage as described in Chapter Two by tracing the top and side views, sawing, and then carving to a circular cross section, Notice the annular notch to meet the sheet balsa tail cone. Now that the fuselage is sanded smooth with 3/0 sandpaper, it should be carefully split in half along the horizontal center line. Using the utmost care, with a gouge hollow each half as close to the outer wall as is possible. Remember, lightness counts. Cement the two halves together and set aside to dry. Using the pattern on the plan, cut the tail cone and gently attempt to bend it around the notch on the fuselage forward section. Do not force this operation. If the sheet balsa does not bend readily, either steam it by holding the wood over a kettle or pot of boiling water or dip it into some hot water and bend to shape while wet. When dry, apply cement around the notch and along the cone seam. Hold in place with ½" long straight pins until the cement has dried.   Sand lightly with 3/0 sandpaper.

Trace and cut the wing outline from sheet balsa and sand lightly- Cut the ribs to shape and cement together to form a 1/16" thickness. These are then cemented and pinned to the sheet covering in the location shown to form the airfoil camber. The camber is the curvature of either the upper or lower airfoil surface. Notice that rib No. 1 is cemented at an angle to enable the two wing halves to be joined to form the correct amount of dihedral. In order to prevent free-flying models from banking or rolling, the wing tips must be higher than the wing junction with the fuselage. This is called dihedral. Join the two wing halves at this time by cementing the ribs No. 1 of each wing to each other. Hold to the correct angle with pins and set aside to dry. Add the wing tip end plates when dry.

The empennage is constructed in much the same manner as the wing.

The top of the fuselage should be flattened slightly to fit the wing and tail surfaces. Cement these components in place, making certain that the correct incidence angle noted on the side view of the plan is followed.

Since the landing gear on the model would have no function, we elected to omit this item from the prototype replica. However, this is illustrated for those who desire to install it. We advise against it because of the added weight. The full scale Heinkel 162 carried a retractable landing gear, and our model therefore appears most realistic in flight. Belly landings are very common with this class of model.

"The Lensman" Photo

Of particular interest in this photo of our model is the engine enclosure. This is made from two plastic bubble canopies. The upper section must be removable in order to enable the engine to be refueled and is held in place with small patches of cellophane tape. The cockpit cover is also a standard bubble.

The engine housing or cowl can be carved from very soft balsa wood if desired. The author recommends the use of two plastic bubble canopies. These are available at most hobby shops and are normally used as cockpit covers on modern replicas. The use of canopies for the cowl saves both weight and work. Carefully trim the front, back and bottoms of the bubble canopies until a neat fit is accomplished. Cement the lower half in place atop the wing. Cut a small ⅜" x ¾" piece of asbestos sheet and install this between the "Jetex" engine mount and the lower canopy or cowl half. Gently screw the mount to the fuselage through the wing and cowl. The above-mentioned asbestos, mount, and screws are all supplied with the engine. It is imperative that the engine be located no closer than ⅛" from the cowl; 3/16" is preferable. The upper portion of the cowl is held in place with four small pieces of transparent scotch tape, about ⅛" x ¼", because it must be removed after each flight in order to charge the engine with new fuel.   Should the upper cowling prove a nuisance, the model can be flown successfully without it.

As has been stressed before, light weight is important in this model, therefore all painting should be light. The full-size Heinkel was colored dark green on all upper surfaces; the entire underside was light gray. The under surfaces of the prototype model were left unpainted, while the top was colored with dope thinned with 50 per cent, dope thinner (lacquer thinner). One light coat is sufficient. It might be wise to weigh the craft before painting to see if the model can afford the added weight. The bubble canopy is a "Scientific" product and should be added at this time.

This must be trimmed to fit the model as illustrated. The crosses can be cut from "Wondur-cal" (previously described), commercial decals, or can be drawn on gummed labels, cut out, and pasted in place.

Before the model is taken out to fly, it should balance correctly; the addition of strips of solder to the nose or tail will accomplish this. The author's model required slight weight in the nose.

Do not attempt powered flight until the model has been thoroughly pre-flight tested. Select a grassy site for the first test glide. Hold the model, with the thumb and index finger, just behind the balance point and gently release the model with a sweeping motion, into the wind, aiming at a spot on the ground about thirty feet away. Closely observe the behavior of the model and note any tendency to dive or stall. The glide should be smooth and without hesitation. Repeat this procedure as often as necessary in order to achieve a smooth, flat glide with a slight turn in- either direction.

Warping one rudder gently while exhaling on it will produce a turn. Should the model dive in the glide, the trailing edge of the horizontal tail should be warped upward in the same manner. A stall is remedied by warping this trailing edge downward. These adjustments should be made a little at a time, trying several test glides after each adjustment. When the glides are satisfactory, we are read; for powered flight.

"The  Lensman"   Photo

Our Heinkel "Volksjaeger" is very simple to construct. Note the wing tip plates which actually improve wing efficiency by preventing the airstream from spilling over the wing tip thus destroying lift. Cross insignia can be either decals or gummed paper. Model must be lightly constructed for efficient flying.

When the rocket engine has been charged in accordance with the manufacturer's instructions, ignite the fuse with a cigarette, punk or, as a last resort, a match. Wait until a slight hissing sound is emitted from the engine and then immediately launch the craft in the same manner as in the test glides previously described. However, the model should now be directed at a slight skyward instead of a ground-ward angle.

The first powered flights should be observed to detect any erratic tendency. If the plane stalls during the powered portion of the flight but glides well, this may be remedied by inserting an additional sliver of asbestos between the rear of the engine mount and the model in order to produce what is called "down thrust". Should the model refuse to climb but glides well, add the above-mentioned sliver at the front end of th*e engine to direct it upward. Your replica should climb in forty-foot-diameter spirals and glide in about the same path, but the glide should be shallow.

The mention of "rocket engine" may instill a fear in the reader and cause him to regard these engines as dangerous. It is true that the engine becomes hot; however, the exhaust is of quite a lower temperature about 1½" away from the nozzle. There is no record of any accidents with these engines and the author considers them quite safe.

Air Trails Photo

Another successful "Jetex" powered model by the author was the "Opel Rocket Plane." Rocket engines can power models from 12" to 36" wing spans. These can vary in construction from simple sheet balsa to more complex tissue covered structures. Engines are inexpensive and simple to operate.

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