Michael Neufeld - The Rocket and the Reich

A second critical innovation was finding a method to determine whether the A-5 and A-4 would be stable as they passed through the speed of sound. No wind tunnel before the late 1940s could successfully produce velocities between Mach 0.85 and 1.2, and theory regarding this “transonic” region was in an equally primitive state. An unreliable Mach 0.95 test run (at Aachen?) suggested to Hermann that the A-5’s center of pressure would move far in front of its center of gravity, making the rocket unstable—it would tumble out of control. To gain some data on the problem, the head of the aerodynamics group proposed in July 1938 that an iron model could be dropped from an airplane at an altitude of 7,000 meters (about 23,000 feet). It would pass through the speed of sound at 1,000 meters while being carefully photographed from the ground and observed from the air. 32

Those tests were started no later than the autumn of 1939, using a Luftwaffe He 111 bomber from Peenemünde-West. A new recruit to the guidance group, Dr. Walter Haeussermann, witnessed one of the drops at the end of 1939 from a second plane piloted by Wernher von Braun. After the release from the He 111, von Braun dove his airplane after the model to observe its behavior and to radio to recovery crews where it hit the water. In the end, the drop tests laid aside concerns about serious transonic instability problems for the A-5/A-4 design but were not exacting enough to show that no problem existed. In fact, repeated launches of the A-5 from 1939 to 1942 demonstrated that the rocket was marginally unstable in the transonic region. Its nose would wobble in a circular motion of a few degrees radius, creating enough drag to prevent it from ever passing through Mach 1. Thus, when the first A-4 launches were attempted in 1942, the aerodynamics group, along with everyone else, had to cross their fingers and hope that, in the quick transition through the sound barrier, the control system would prevent any dangerous movement of the missile. 33

It is thus clear that the Peenemünde wind tunnel was not essential to the fundamental shape of the A-4, but assembling a highly competent aerodynamics staff was. Even so, the systematic work that began in the tunnel in 1940, along with the subsonic experiments of Dr. Max Schirmer at Zeppelin, was highly important for the refinement of the rocket’s design and the elimination of uncertainties in many areas. When the rocket group began working on the A-3 and the A-5, virtually nothing was known about the heating caused by friction with the air. For the A-4 the problem was especially urgent because of much higher velocities and the need to survive reentry into the earth’s atmosphere after passing the 80-kilometer (50-mile) peak of the trajectory. Peenemünde aerodynamicists undertook fundamental heat-transfer research in their tunnels using simple shapes and rocket models equipped with temperature sensors. Their data helped verify theoretical calculations and provided guidance to the designers as to the steels that would have to be used. Elaborate pressure measurements were also taken on the surface of wind tunnel models cut in half lengthwise, allowing many more sensors to be installed. That procedure helped verify the predicted loads on the vehicle—information crucial to the structural designers. Another area where Peenemünde broke new ground was in assessing the impact of engine exhaust jets on the aerodynamic characteristics of missiles. Using compressed air jets in the tails of models, the group found that drag increased in the subsonic range but decreased in the supersonic. Without that kind of information, launching the A-4 would have been very much a shot in the dark. 34

As compared with propulsion and, especially, with guidance and control, the contributions of university research after the start of the war were less important, in part because virtually all aerodynamicists were already working for the Air Ministry. But academic contractors to Peenemünde made a couple of valuable theoretical innovations, and they built or refined measurement technology for the tunnels. Corporate research, in the form of Schirmer’s work at Zeppelin, was of more significance, although still modest. The end of the airship era, resulting from the Hindenburg accident and Hitler’s and Göring’s dislike for those fragile vehicles, must have created an opening for the rocket program in the company’s aerodynamic facility. 35

Among the most important contributions of Zeppelin—in conjunction with supersonic work at Peenemünde—was new research into winged missiles. In June 1939 a member of Riedel’s design bureau, Kurt Patt, proposed that the high energy of an A-4-type missile as it approached impact be employed instead to generate aerodynamic lift. Through the use of wings, the A-4’s range could thereby be doubled to 550 kilometers. That idea—later called the A-9—was taken up enthusiastically by von Braun’s group because it seemed a relatively cheap way to extract extra range from a missile powered by the 25-ton engine. Patt’s design, essentially a fuselage-less flying wing, was too radical, but affixing aircraft-type wings to an A-4 appeared to be a feasible alternative. That idea would require basic research into the configuration of a supersonic airplane that could ascend as a missile and descend as a glider. By 1941 a workable design emerged: a simple sweptback wing. More radical airfoil shapes were also tried, but producing a compromise that worked at all velocities proved to be anything but simple. A-9 research continued into 1942 before it was halted altogether by higher-priority projects. In the last months of the war it was revived and given the designation A-4b. 36

A prominent feature of the glider missile project, as in the case of the A-5/A-4, was the repetitive, systematic wind-tunnel work required to evaluate different designs at different Mach numbers and different angles of attack (the angle of the missile’s nose to the direction of airflow). Doing comprehensive pressure measurements on a half-model, to take an extreme example, entailed more than 100,000 gauge readings recorded by hand by twenty people for two weeks in two shifts. As the war went on at Peenemünde, the inherent character of aerodynamic research, combined with intense political pressure to finish the A-4, made the work process increasingly stressful, routinized, and factory-like. A second 40-by-40-centimeter test section was built so that one would be available while changes were being made on the other. The aerodynamics group went to multishift operation nearly around the clock. In addition to all the missile work, extensive research was also done for Army Ordnance on artillery shells, including the fin-stabilized “Peenemünde Arrow Projectiles” designed in-house. 37

This mass production of research reinforces a basic point about the revolutionary breakthroughs in key technologies that Peenemünde achieved between 1936 and 1941. In aerodynamics as in propulsion, brilliant ideas and excellent management were not by themselves sufficient. Only the existence of a massive and well-funded organization allowed the rocket group to create working technology in a short period of time. The case of guidance and control—the most difficult challenge in the whole A-4 project—illustrates this point even more clearly.

Unlike the other two key technologies, the transformation of research in guidance and control did not begin around the turn of the year 1936–37. Until just before the disturbing failures of the A-3s in December 1937, Ordnance remained dependent on Kreiselgeräte as its sole contractor in this area. Those failures then greatly accelerated a twofold shift in philosophy: toward competitive development by a number of firms in the gyroscope and autopilot sector, and toward a buildup of in-house expertise at Peenemünde. Although those two processes overlapped, it was not until 1939 that Wernher von Braun began in earnest to put together a large guidance laboratory. He did so because he was increasingly dissatisfied with the corporations. The extreme and specialized demands of ballistic missile guidance, combined with Ordnance’s pressure to produce results quickly, strained the research and development capability of contractors already overburdened with Luftwaffe and Navy work. Rather than accept delays, von Braun used his rapidly expanding budget to construct a new laboratory at the center.