Dornier Do-335 Pfeil

Anyone familiar with German weaponry of the Second World War knows how much research has been done in tracking down every proposed German aircraft prototype. These prototypes have been fleshed out in illustrations and in projected operational data by interested researchers. These illustrations fill numerous books and magazines as well as several Internet web-sites dedicated to the idea of what might have been if the Third Reich had lasted another year (see Luftwaffe ‘46 site). Because of the intensity of this work and the number of years that it has been in progress, it is truly gratifying to stumble upon something new and unreported at this late date.

The concept of this aircraft came from Dr. Zippermayr’s work on another project, the L-40 aerial torpedo. Dr. Zippermayr’s solution to the problem of the L-40 aerial torpedo led directly to a subsequent project, the ‘Pfeil” aircraft.

The standard German aerial torpedo was released at about 50 meters (slightly over 150 feet) from the ocean’s surface by an aircraft in horizontal flight at an airspeed of about 300 km/hr or about 180 mph. To release higher and faster would cause the torpedo to impact the water at too great a speed, damaging the torpedo’s steering mechanisms. The Germans suffered substantial losses to their attacking aircraft using these weapons and tactics. The low altitude and low speed simply left the attacking aircraft vulnerable.

What was needed was a new torpedo with a new attack methodology. The Germans needed a torpedo that could be fired from a distance at a high altitude, and at jet-plane speeds. They wanted the new torpedo to be launched at 1.5 kilometers from the target, at any height, at any angle and at speeds up to 700 km/hr (435 mph).

Dr. Zippermayr reworked the internal components of the new aerial torpedo with these goals in mind. But what was most interesting was his aerodynamic solutions for the new torpedo. This solution was a new gliding surface that automatically balanced the torpedo in flight. This gliding surface was a new wing with a special shape. It was attached to the top edge of the torpedo and its wings were “V” shaped as seen from the front or rear. This wing design automatically confirmed stability on the flying craft since its center of gravity was directly below what we call its point of suspension, the mid-point between the V-wing surfaces. Test were performed in which the torpedo was dropped from an aircraft flying at speeds up to 720 km/hr and from heights of over 1,000 meters. The Arado 234 was envisioned as using this weapon. The work was carried out from January 1944 until the end of the war.

The success of the L-40 torpedo design had obvious implications for high-speed aircraft. Besides Dr. Zippermayr, Messerschmitt, Augsburg, was already present at Lofer (Austria) for work on the Enzian rocket.

Dr. Wurster and none other than Dr. Lippisch worked on this project. Given all the aviation genius, it is no surprise that the Aerodynamische Institut der Technischen Hochschule, Hanover, was put to work conducting wind tunnel and other tests of the torpedo design. They passed the opinion that the structure was sound and suitable, and could be applied successfully to aircraft. Their findings were published in their technical research manuals (Berichte des General-Luftzeugmeisters). Orders were given to Dr. Zippermayr to incorporate the torpedo principles in developing a jet-propelled aircraft capable of extremely high speed.

The first aircraft was to be a high-speed fighter. But, at the same time, experiments were to be conducted to determine the value of the new design in the construction of gigantic, high-speed airliners. These plans were to have been successful as far as they were able to progress before Germany’s defeat.

The first step was to build a model glider, complete with instruments to register flying and diving qualities of the aircraft. This model would be released from a tow line at high altitude. The results of these experiments were then used in the construction of the first full-scale glider model. It was during the construction of this full-scale model, about three-fourths complete, that the war ended and construction stopped. At least for a time, the model was stored at the Hagen carpenter shop in Lofer (Austria).

After flight tests of the full-scale model was completed, work was to begin on the jet-propelled prototype. The Army report states: “Dr. Porsche, located at Schuttgut near Zell-am-See had already been assigned the task of supplying the jet units (Porsche 109-005?).”  Yes, this is the very same Dr. Porsche whose cars we all know and love.

The Zippermayr wing design had two advantages over contemporary wing design. The first was tremendous speed. Even as the Army wrote up their findings, in July of 1945, two years before the sound barrier would be officially broken, there was already discussion in the report of this wing design going supersonic. The reason these wings were credited with “speed” is that they offered considerably less resistance, drag, to the atmosphere than wings in current usage. In other words, this type of wing was more efficient at high speed.

The second advantage bestowed by this wing design is stability. The stability was especially apparent on the transverse axis, which made the aircraft easy to control. The torpedo prototype flew without any automatic steering device and, even at speeds of 80 to 200 meters per second, was perfectly stable. At an incidence angle of 52 degrees the torpedo showed no tendency to stall nor were there any irregularities in the flight direction. It was also claimed that the wing loading was much less than for conventional wing types.