RUSSIAN ROULETTE

Like the Americans the British and the French, the Russians also understood that the Germans had made great advances in the development of jet and rocket technology during the Second World War. And in spite of the fascist origin of that knowledge the Soviets were not too proud to use it. At the end of the war they had captured the unfinished prototype and wind tunnel models of the German DFS 346, the advanced experimental research plane with swept wings, a pressurized cockpit, and the HWK 109-509C rocket engine. The cigar-shaped fuselage with sleekly embedded rivets was optimized for high speeds and the T-tail had all-moving horizontal stabilizers placed high on the vertical fin to prevent shock stall and disturbances by the wings. To minimize the plane’s frontal cross section the pilot was prone on his stomach and viewed through a Plexiglas nose. The Germans had designed the DFS 346 to be air-launched from a bomber so that the maximum of 2 minutes at full-thrust would suffice to break the sound barrier at high altitude. The plane was to land on a retractable skid, saving considerable weight in comparison to a conventional undercarriage using wheels. For measuring the speed of the aircraft a long spike with a pitot tube projected ahead from the nose. Now standard equipment on any aircraft, this tube measured the relative air pressure, which is a function of the velocity of an aircraft through the air. Poking this pitot tube out in front of the plane ensured that its measurements were not affected by airflow disturbances closer to the fuselage. At least as important as capturing hardware was the recruitment of many of the German engineers who had developed this revolutionary plane, by offering them privileges such as additional food rations as well as the opportunity to continue their research (apparently Stalin had finally understood that positive motivation resulted in more progress than brute force when it came to developing complex technology).

The Soviets planned to use the DFS 346 in order to gain a head start in the Cold War competition for speed and altitude, and therefore converted the German Siebel Flugzeugwerke company, which during the war had been tasked with developing the DFS 346, into the OKB-2 design bureau under the direction of the German engineer Hans Rossing. Soon the factory and its staff were moved from the original location in Germany to Russia, where the team continued their work on the DFS 346. Aleksandr Bereznyak, one of the original designers of Russia’s wartime BI rocket interceptor, was assigned to assist (and no doubt keep an eye on) Rossing. In order to disguise the German origin of the design, the project was renamed ‘Samolyot 346’ (Aircraft 346), and the Russian form of the German engine was designated ZhRD – 109-510.

Wind tunnel tests showed that at high angles of attack and low speeds the angle of the leading edge of the 346’s wing forced some air to flow sideways out towards the

DFS 346P.

wingtips instead of parallel to the fuselage. At the wing tips the airflow could end up flowing almost completely span-wise, sharply reducing the lift and resulting in a stall on the outer part of the wing and a loss of control of the aircraft. The solution was to add two so-called wing fences, low vertical ridges running from the leading edge to the back of the wing. This solution was later incorporated in most Soviet swept wing fighters of the 1950s and 1960s.

In 1947 the first prototype was completed. Since it had no engine installed it was designated 346P (for ‘Planer’, meaning glider). This version was meant to test flight stability, practice landings, and also try out the mating to and release from the carrier aircraft. It lacked a pressurized cockpit, propellant tanks and other propulsion-related equipment. In 1948 four test flights were carried out with the 346P being dropped from under the right wing of a confiscated American B-29 bomber that had suffered damage during a raid over Japan and then gone on to make an emergency landing in Soviet territory. Interestingly, during these tests the 346P was piloted by Wolfgang Ziese, who had previously been a test pilot for the Siebel company in Germany. In Russia he had prepared for the flights using a modified DFS ‘Kranich’ (Crane) glider that had been fitted with a prone-pilot cockpit and could be towed into the air behind a Petlyakov Pe-2 bomber.

Flying the 346 into unknown areas of aerodynamics, virtually encased in the tiny aircraft in an uncomfortable prone position and having to rely upon its complicated escape system, must have taken a lot of courage. Especially since at that time some aerodynamicists predicted that at Mach 1 an aircraft would slam into a virtual wall of air and inevitably be ripped apart by violent shock waves. The successful breaking of the sound barrier in the US by the Bell X-l leaked by Aviation Week in December 1947 did tell the Soviets that faster-than-sound flight was possible, but exactly what kind of phenomena they would encounter in the 346 was still unknown; naturally, the Americans kept the X-l flight data secret.

On one flight, Ziese forgot to check that the ailerons were in their neutral position before his aircraft was released by the B-29 carrier, so the 346P immediately flipped inverted. Only after losing almost 2,000 meters (6,600 feet) of altitude did he manage

The 346P under the wing of its B-29 carrier.

to regain control of the plane. On the whole however, the 346P drops, gliding flights and landings went very well, and it was decided to proceed with the construction of a powered prototype. This 346-1 was completed in May 1949, and had a launch weight of 3,145 kg (6,935 pounds).

On 30 September 1948 the B-29 drops Ziese in the 346-1 equipped with a dummy engine from an altitude of 9.7 km (32,000 feet). He experiences some difficulties in controlling the aircraft and is obliged to land at an excessive speed (the fact that the aircraft does not have flaps for additional lift at low speeds exacerbates the problem). After the first hard touchdown the plane bounces several meters into the air, flies a further 700 or 800 meters (2,300 or 2,600 feet) across the ground, then touches down again. At that moment the ski is pushed back into the fuselage and the plane slides along the runway on its belly prior to coming to a standstill. It is slightly damaged, and the pilot is knocked unconscious but only lightly injured when his head hits the front of the cabin (apparently his seat and safety belt system were not up to the rough landing). Investigators conclude that Ziese had not fully released the skid during his approach, probably because he was fully occupied keeping the aircraft under control.

After repairs and improvements, the plane is redesignated 346-2 and glide flight testing resumes in October 1950 with Russian pilot P. Kazmin. The plane still proves tricky to fly, and on the first flight the skid once again fails to lock when lowered for landing. However, this time the landing takes place on a snow covered field and the belly-sliding does not cause any significant damage. On its second flight the 346-2 is towed by a Tu-2 bomber to an altitude of 2 km (6,600 feet) and released for a free gliding flight. This time Kazmin lands short of the runway. The aircraft is damaged and more repairs are needed. Meanwhile Ziese has recovered from his injuries and, starting on 10 May 1951, resumes flying the engineless 346-2, and starting on 6 June also the newly constructed but still unpowered 346-3 which has thinner wings better suited to transonic flight speeds. During the 346-3 flight tests the confiscated B-29 is replaced by a Soviet copy designated the Tupolev Tu-4 (reputedly copied so literally that rivets missing from the original were omitted).

Finally Ziese and the aircraft are judged to be ready for a powered flight, and on 15 August 1951 the 346-3 is driven through the air on rocket power for the first time. For around 90 seconds Ziese is the ruler of the sky. But the flight is no treat because the plane still has a tendency to roll. And due to a malfunctioning heating regulator the temperature in the cockpit rises to 40 degrees Celsius (104 degrees Fahrenheit), all but making the pilot faint. During this mission, as well as the following flight on 2 September, only the weaker cruise chamber of the engine is used in order to hold the speed below Mach 0.9 because tests in the T-106, the Soviet’s first supersonic wind tunnel have led the designers to fear that the aircraft’s control surfaces will freeze up at transonic speeds. And their fears are soon proven well-founded. On 14 September Ziese is dropped for the third low-thrust flight, ignites the smaller thrust chamber and accelerates into a climb. Shortly thereafter things go wrong at an altitude of just over 12 km (39,000 feet). Ziese reports to the ground that the aircraft is not responding to his control inputs, is rolling uncontrollably and rapidly losing altitude. Evidently the rocket thrust has pushed the plane into the transonic ‘no-go’ zone, resulting in locked control surfaces. On falling to a lower altitude Ziese manages to regain some control and ends up in a dive from which he pulls up at about 7 km (23,000 feet). When the airplane starts to roll wildly once again, Ziese realizes that he is running out of time and altitude. The controllers on the ground tell him to bail out. For the first time he triggers the explosive bolts to separate the cockpit section from the rest of the plane. The system works perfectly. The stabilizing parachute puts the cockpit into a smooth descent, enabling him to scramble out and land safely under his own parachute. The aircraft is obviously lost, along with all the flight measurements recorded and stored inside (there was no real time telemetry link with the ground, as is standard for test flights today). Nevertheless the limited data available enables investigators to figure out what probably happened. It is concluded that when it shot up into thinner air the aircraft entered the transonic flight regime and experienced shock stall at its tailplane and wings, freezing up its controls. Once the plane started to fall it accelerated out of the transonic area and exceeded Mach 1, at which moment the shock waves at the tail moved further to the rear, releasing the elevators. And when Ziese pulled out of the dive the aircraft slowed down and again entered the transonic regime, freezing up its controls once more.

It was clear that the 346 was not well suited to transonic speeds, and the aircraft shape’s aerodynamic speed limit had been achieved even without igniting the rocket engine’s more powerful main combustion chamber. The 346 project was abandoned. In any case, not much valuable data was expected to be gained from further flights because by the late 1940s Soviet jet aircraft were already flying faster than Mach 1. One ‘glass half full’ project report stated that within the speed limits imposed by the obsolete aerodynamic design all the 346-3 hardware had functioned well, including the rocket engine, the skid landing gear, and finally the escape capsule. The German engineers involved in the 346 project were repatriated to East Germany in 1953 (this was apparently standard procedure once Russian engineers felt that they had learned everything they could from their German colleagues.)

In parallel with OKB-2 and its 346 project, OKB-256 under Pavel Vladimirovich Tsybin was working on a transonic rocket plane called the Tsybin LL (with the LL standing for ‘Letayushchaya Laboratoriya’, which means Flying Laboratory). Even though this aircraft was kept very simple in terms of construction and propulsion, it was meant to approach Mach 1 and if possible surpass it. After models were tested in the TsAGI wind tunnels, two prototypes were constructed. They were made almost entirely of wood, with ailerons and flaps operated by a pneumatic system powered by compressed air (the forces on the control surfaces were expected to be very high at transonic speed, and so require more than pilot muscle power to operate). The rocket engine in the tail was a straightforward solid propellant booster called the PRD – 1500, and it could provide an average of 15,000 Newton for a duration of 10 seconds. The first prototype, LL-1, had conventional straight wings and an ejectable dolly take-off undercarriage similar to that of the Me 163. From mid-1947 pilots M. Ivanov, Amet-Khan Sultan, S. Anokhine and N. Rybko together completed a total of 30 flights with this prototype. After being towed by a Tu-2 bomber to an altitude of 5 to 7 km (16 to 23,000 feet) the pilot pushed it into a steep dive of 45 to 60 degrees in order to gain as much speed as possible prior to leveling off and igniting the rocket

Design of the Tsybin LL-1.

motor. Then a very short, horizontal high-speed powered flight was followed by a gliding return to land on a retractable skid.

During the winter of 1947-1948 the second prototype was equipped with forward – swept metal wings, the benefits of which the Russians had learned of from German wartime research, and which had also initially been planned to be incorporated in the previously described Lavochkin 162. Water tanks were installed in the fuselage so as to be able to adjust the center of gravity of the aircraft. This was designated the LL – 3. It made over 100 flights and achieved a maximum speed of 1,200 km per hour (750 miles per hour), corresponding to Mach 0.97, without any significant problems. After the LL-3 tests, the LL-1 was turned into the LL-2 by retrofitting it with swept wings, but it never flew because by then swept-winged jet fighter prototypes had already undergone extensive testing.

A more ambitious project was the Bisnovat 5 developed by aircraft manufacturer Matus Ruvimovich Bisnovat. This was intended to continue where the Samolyot 346 project had ended, providing data on transonic and low-supersonic flight speeds up

Tsybin LL-1.

to 1,200 km per hour (750 miles per hour) at an altitude of 12 km (39,000 feet), which was Mach 1.1. Bisnovat had prior experience of rocket planes because he had been responsible for the production of the Kostikov 302 prototypes by OKB-55 during the war and later had been involved in a number of missile projects. Similar to the DFS 346-based Samolyot 346, the Bisnovat 5 was an all-metal monoplane that had wings swept back at 45 degrees and augmented by fences, and a pressurized cockpit. It was also to be dropped from a carrier aircraft, in this case from under the right wing of a Petlyakov Pe-8, and then land using a simple ski undercarriage. The main ski under the fuselage was set at an angle to enable the aircraft to land with its nose slightly up to ensure sufficient low-speed lift for a soft impact. UnUke the uncomfortable prone-pilot position and complicated escape capsule of the 346, the pilot had a conventional ejection seat and sat upright, although slightly reclined in order to reduce the plane’s cross section. A single Dushkin-Glushko RD-2M-3VF dual-chamber rocket engine was installed in the tail and fed nitric acid and kerosene propellants by a turbopump powered by hydrogen peroxide. This engine was similar to those of the Florov 4303, Kostikov 302P, the Polikarpov Malyutka and the MiG 1-207 but the combined thrust chambers provided a maximum thrust of 16,500 instead of 15,000 Newton at sea level.

Models were tested in the TsAGI T-104 wind tunnel at up to Mach 1.45 and then one-third-scale models that were powered by small liquid propellant rocket engines were launched from carrier aircraft. After these tests had validated the aerodynamics of the new design, the first flight prototype was constructed and prepared for gliding flights. The first flight of this ‘5-1’ aircraft on 14 July 1948 almost ended in disaster when it hit the Pe-8 carrier shortly after being released. But test pilot A. K. Pakhomov managed to keep the 5-1 under control and made an emergency landing in a rough field. This incident severely damaged the prototype but it was repaired,

Bisnovat 5-2.

and the pylon under the wing of the Pe-8 was revised to carry the Bisnovat 5 with its nose pointing slightly downward to reduce the risk of the aircraft flying up and hitting the carrier after the drop. The next glide flight showed that the aircraft had poor roll and yaw stability. This problem had not yet been resolved when the third flight was made on 5 September 1948 and caused the plane to land tilted to one side, hit the ground with a wingtip and topple over. The plane was almost broken in two and beyond repair, but Pakhomov was okay.

The ‘5-2’ prototype was modified based on the lessons learned during the gliding tests with the 5-1. The vertical tail was swept back further aft to improve directional stability, and the simple metal wingtip bows were replaced by shock-absorbing skids better suited to dampening the impact of touchdown. The test campaign was resumed on 26 January 1949 with pilot Georgi Shiyanov taking the 5-2 on its first glide flight. Again the mission ended in a hard landing with severe damage to the aircraft, this time because the pilot had difficulty in finding the proper approach to the rather short runway and therefore came down beyond it. The 5-2 was repaired and further improvements made. The main ski, which had previously been set at an angle in the vertical direction for improved lift prior to landing, was now put horizontal and thus parallel to the fuselage to improve the pilot’s view of the runway. This meant that the small ski on the tail could be removed and replaced with a ventral keel fin to further improve flight stability. No major problems occurred during the next flight but roll and yaw stability were still insufficient. This led the engineers to install downwards angled fins at the wingtips like those of the Florov 4302. The next six ghde flights showed that the stabihty had improved, and that the plane was controllable at least up to the highest speed of Mach 0.77 that was attained in a dive.

But before the powered flight test campaign could commence, the authorities had shifted their interest to further developing supersonic jet aircraft. On 26 December 1948 test pilot I. E. Fedorov had opened the throttle on his swept-wing Lavochkin La-176 (derived from the La-168 jet fighter), pushed the plane into a shallow dive and attained Mach 1.0, marking the Soviet Union’s entry into the world of supersonic flight (just over a year after Chuck Yeager made his historic flight in the X-l). Hence the authorities did not see much use for a Mach 1 rocket aircraft.

There was never a Russian equivalent to the American Douglas D-558-2 and Bell X-l series of experimental rocket planes, and no subsequent evolution into a vehicle Uke the X-15. The Samolyot 346 flew until September 1951 but never managed to exceed Mach 1 and (as noted above) this project was also terminated after the loss of the 346-3 aircraft.

Nevertheless Soviets engineers continued to develop many supersonic aircraft that were as good as anything in the West, and during the Cold War proved themselves to be masters of aerodynamic theory and design. It is however clear that Soviet spies in the US aviation industry and NACA provided data that was of great assistance to the Russian designers, and at least partly made up for their lack of a supersonic research aircraft program.