Around the end of 1936 a “4B” motor was installed in an He 112 fuselage, but there were still distressing explosions and failures, usually caused by delayed ignition. Modifications were imperative. A sort of pilot light, or small flame, became the new igniter. To fit a rocket to a manned aircraft meant that the thrust had to be throttlable and the controls simple. The aim was to provide the pilot with a single lever that controlled engine thrust by controlling the release of the nitrogen gas that forced the propellants out of the tanks. But the Ordnance group did not have high confidence in this system. When the Luftwaffe test pilot assigned to fly the rocket-equipped He 112, Captain Erich Warsitz, first came to Kummersdorf, he stood beside the aircraft and watched as von Braun started the engine from the cockpit. The noise was ear-splitting. Later that night von Braun told him in a Berlin bar that he had witnessed the first time ignition had been done from inside the aircraft. Usually the engine was controlled from a concrete bunker many meters away. But von Braun and one of Heinkel’s designers had feared that Warsitz would never get in the cockpit if he observed the engine test that way!39
Eventually the He 112 was flight-ready. On June 3, 1937, Warsitz attempted to ignite the rocket engine in the air for the first time after taking off under normal power. The experiment was carried out at an out-of-the-way airfield at Neuhardenberg, north of Berlin, because Peenemünde-West was unfinished. Warsitz started the ignition flame and then attempted to turn it off. Since it would not go out, he ignited the engine at half-power to prevent overheating. The acceleration was mild, and after ten seconds he stopped it again. The official report states:
After a short gliding flight, the pilot noticed a strong acrid odor of burning rubber and paint and clearly perceptible hot gases flowed under the pilot’s seat. The pilot looked to the rear and noticed a strong flickering in the tail area. The airplane at this time was still at an altitude of about a hundred meters. Because the pilot had to fear that the mobility of the control surfaces would be compromised by the fire in the tail section, and because the nitrogen for fire extinguishing was completely exhausted, he decided on an immediate landing. Sufficient altitude to extend the landing gear was no longer available. The aircraft landed with fully extended flaps on its belly and skidded about 45m along the ground.
Damage was significant. An unanticipated region of low aerodynamic pressure around the tail had caused alcohol fumes to be sucked back into the fuselage, where they were ignited by heating or the ignition flame.40
The aircraft was repaired and flown at least a few more times over the summer by Warsitz. But the safety of the system was doubtful, so a redesign was in order. Ordnance, Heinkel, and the Air Ministry decided to use turbopumps instead of gas pressurization as the means of forcing the propellants into the combustion chamber and to employ an electric glowplug instead of an ignition flame. The development of turbopumps had begun as far back as mid-1935 because of the anticipated need for them in large rocket engines. Employing them in an aircraft had been discussed in early 1937, either for the He 112 or the pure rocket aircraft project, “P 1033,” which received the official Air Ministry designation Heinkel He 176 in December 1937. From the fall of that year, Ordnance engine development for the Luftwaffe followed two parallel tracks: similar but not identical turbopump-driven motors and tankage systems for the He 112 and 176. Innumerable design problems, however, caused both aircraft to lag farther and farther behind schedule. The He 112 equipped with an Army alcohol/liquid-oxygen engine was not to fly again until the autumn of 1939. The tiny He 176 never flew with such an engine at all.41
Through 1938 and the first half of 1939, interservice relations between individuals in the rocket plane program continued to be cordial. A new project was even added. In August 1938 the Air Ministry asked the Army to design an alcohol/liquid-oxygen takeoff-assist system for heavily loaded aircraft. Two teardrop-shaped pods of 1,000-kg thrust each would be strapped under the wings of an airplane and then jettisoned and parachuted to the ground after use.42
But the Luftwaffe strove, from 1936 on, to acquire independence from the Army in the rocket field, and the alliance declined after 1937. From late 1935 on, the Air Ministry became more and more deeply involved in Hellmuth Walter’s hydrogen peroxide rocket development in the port city of Kiel. In March 1936 Walter, who had recently set up an engineering company with the assistance of the Navy, notified Ordnance that he no longer needed consultation in rocketry because he had received Air Ministry contracts for takeoff-assist rockets and engines for “aerial torpedoes” and aircraft. Parallel to the cooperative program with the Army, the air force had Heinkel build He 112 and He 176 versions with the less efficient but more practical hydrogen peroxide rocket. Other aircraft were experimentally fitted with Walter motors as early as January 1937.43
For military use in the field, peroxide had a number of advantages over liquid oxygen, which had a tendency to freeze valves and boil away. Hydrogen peroxide (H2O2) in high concentrations (80 percent or more) was not easy to deal with either, because of its tendency to explode, but Walter was able to develop a system for handling it. He could also offer two different versions of his rocket, “hot” and “cold.” In the “cold” version, the inherently unstable peroxide was run over a catalyst and decomposed into superheated steam and oxygen; in the “hot” version catalyzed peroxide was burned with a hydrocarbon fuel, producing more thrust. Because of their adaptability, Walter’s rockets had useful applications in a number of Luftwaffe projects, despite their relatively poor efficiency compared with Ordnance’s engines. As time went on, the air service committed itself more and more to this technology. Around the turn of 1938–39, it initiated the Me 163 rocket aircraft project at Messerschmitt by combining Walter motors with the radical tailless, delta-wing glider designs of Alexander Lippisch. The main line of takeoff-assist systems came to be designed by the Kiel company as well. Apparently the Air Ministry had asked Ordnance to design a liquid-oxygen/alcohol version in 1938 only because of fears that hydrogen peroxide would be in short supply.44
If the Luftwaffe’s cooperation with Walter suggests a gradual evolution away from dependence on the Army rocket program, the strange story of Eugen Sänger indicates that at least some people in the Technical Office wanted to lay the groundwork for independence even at the height of the alliance. Sänger (1905–64) was an Austrian spaceflight enthusiast and engineer who had pursued rocket research at the Technical University in Vienna beginning around 1929. He put in a proposal to the Germans in 1934 after its rejection by the Austrian military. Although the Ordnance rocket group was aware of his useful publications, it was not keenly interested, but it did ask for an investigation of his political views by the SA, which no longer posed a threat to the Army after the bloody purge of mid-1934. (Ordnance was unaware that Sänger had briefly been a member of the Austrian Nazi Party and SS in 1933.) Because the SA never responded, and because Sänger was not a German citizen and his work apparently was no more advanced than von Braun’s, Ordnance did not take up his proposal. Zanssen suggested that the Air Ministry might be more interested, because the Austrian had made theoretical investigations into rocket aircraft. But in October 1935, after the founding of the alliance with the Luftwaffe, von Braun recommended that the Air Ministry not hire Sänger since his efforts would be duplicative. A 1937 document suggests that the aristocratic young engineer may well have perceived the Austrian as a rival.45