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« 346 »

Rocket airplane

OKB-2

In the late 1940s, the OKB-2 team that H. Ryossing headed was engaged in preparations for testing the Siebel-346 experimental rocket airplane (after 1948 this machine is called "346" in documentation).

The flights were prepared very painstakingly. Because the pilot had to fly the aircraft while in the prone position, the Flight Research Institute conducted preliminary experiments to study piloting techniques with this layout. For this, the German series-produced Kranich glider converted so the pilot was lying prone was used. As test pilot M.L. Gallay, who had flown this machine remembered, the horizontal position wTas rather uncomfortable for handling the aircraft. Nevertheless, the scheme was retained since a conventional canopy extending above the fuselage would mean the aircraft had to be completely rebuilt and drag would increase.

The jettisonable cockpit and ejection system also were tested at the Flight Research Institute. The cockpit with a dummy occupant was suspended from the fuselage of a B-25 bomber and jettisoned in flight. The tests went well.

During the latter half of 1948. the "346-P" glider version of the aircraft was completed. It was of a simplified construction, without a pressurized cockpit, engine, and fuel tanks. Ballast was used to compensate for the weight of the equipment. The glider was used to develop the procedure for separating from the launch aircraft, to test stability and handling of the machine with different CG positions, and to accumulate experience in flying in a prone position and skid landings.

OKB-1 employee pilot-engineer Wolfgang Ziese, who had 20 years of flying experience, tested the "346-P". He had graduated from the flying school attached to the Hannover Aviation Institute.

In 1948-1949 four flights was made in the "346-P". The glider was suspended beneath a B-29 launch aircraft that lifted it to the desired altitude. The glider then separated and the test pilot glided to earth. Separation of the mother aircraft and glider took place at a speed of 300-350 km/h. The flight weight of the glider varied from 1880-2180 kg. The tests went well, with the exception of one case when the pilot did not check the position of the ailerons before separation from a launch aircraft. The "346-P" winged over and the pilot just managed to level it off.

In the spring of 1949. a flying "346-1" prototype was handed over for testing. It conformed to the design in full but had a mockup instead of a real engine. Its weight without fuel was 3125 kg.

During the entire summer of 1949. preparations for tests of the "346-1" continued at Teplyy Stan Airfield. The first flight was made on 30 September 1949. The aircraft was suspended from the wing of a B-29 and lifted to an altitude of 9700 m. After separating from the carrier flown by A. A. Yefimov and N. A. Zamyatin, Ziese began his gliding descent. It soon became clear that the machine was hard to handle.23 But the pilot managed to control the aircraft. At an altitude of 2500-3000 m, Ziese extended the skid and began to land. But he made a mistake in approach planning and the plane's speed was significantly higher than estimated. During the landing the skid collapsed and the aircraft began sliding on its fuselage along the runway. His safety harness proved unreliable and Ziese was thrown forward, banged his head on the canopy frame, and lost consciousness. He was only slightly injured and, after a short stay at the hospital, resumed his flying activity.

A special commission set up to investigate the matter concluded that the cause of the accident was that the skid had not extended fully and, as a result, it was not locked.

The damaged aircraft was repaired and its control system changed. While Ziese was recovering, pilot P. I. Kaz'min continued testing the "346-1". During the first flight, the skid again did not lock but, in this case, the landing was made on snow and everything turned out happily. Some time later, Kaz'min flew for the second time when the aircraft was lifted to 2000 m. Again the landing failed because the pilot landed short and again repairs were needed.

Despite these landing difficulties, the conclusion was drawn that the handling qualities of the aircraft were, in general, satisfactory and it was possible to begin the main portion of the testing program, i.e. flying with the rocket engine running. For this, the second "346-3" flying prototype with a real liquid-propelled jet engine was prepared.25

The assembly of "346-3" was finished in May 1950. It differed from the first prototype in its different tail planes with thinner airfoils and higher sweep. As a result, the allowable speed for the "346-3" increased to 0.9 M.

This time, the flight tests had to be conducted at another airfield because, as already stated, Air Forces representatives were against the presence of Germans at the military airfield in Tephy Stan. Construction of a new plant airfield had begun 100 kilometers southeast of Moscow (near Lukhovitsy). The construction, manufacture of test equipment and aircraft, and its shipment to the new place took several months.

In early 1951, Ziese, now recovered from his injury, began training flights on "346-P" and, on 6 April, he performed a sortie in "346-3" without activating the engine.

Finally, everything was ready at the airfield near Lukhovitsy for the basic tests. On 15 August 1951, Ziese flew "346" for the first time with engine running. Maximum speed was limited and, therefore, only one chamber was used, providing a thrust of 1570 kg. The power plant was ignited at 7000 m, 1 minute and 40 seconds after separation from the mother aircraft. The rocket motor burned for a minute and a half, then a gliding flight and landing were made.

Handling of the aircraft was very difficult because, in flight with the engine running, the machine began losing its lateral stability and the entire time Ziese had to operate the ailerons to level the wings. The situation was exacerbated by the fact that the heat regulator did not work properly, the temperature in the cockpit rose to 40?C, and, in his words, Ziese had nearly fainted.26

After ventilation valves were installed in the cockpit, the next flight on 2 September went quite well. But. during the third flight with the engine running, an accident happened and the aircraft crashed. This happened on 14 September. Ziese had separated from the launch aircraft at 9300 m. Then the pilot ignited the engine and began climbing. After 2 minutes of engine operation, his speed exceeded 900 m/h and Ziese reported over the radio that the aircraft was out of control and falling. He was ordered to abandon the aircraft. The recovery system activated perfectly. At an altitude of 6500 m, the cockpit separated and the stabilizing parachute opened. At 3000 m, the ejection system ejected the pilot from the cockpit, and he descended to the earth by parachute.

But Ziese did not live long. On 28 August 195 3, the 46-year old pilot died of cancer and was buried in a cemetery in Podberez'ye. Later, his remains were taken back to his homeland.

Experts who investigated the accident did not have a single opinion as to its cause. One version was that the aircraft went into a spin due to pilot error, while others thought that Ziese accidentally exceeded the speed constraint and lost control of the machine because loads were redistributed on the wing and tail unit.

After the accident, work on Aircraft " 346 " ceased. The following conclusion was drawn in the flight test report:

Despite the Aircraft "346" accident, one should consider that the aim of tests, taking into account the speed limitations, were attained and the tests performed showed:

1. Good trouble-free operation of the liquid-propelled jet engine, both during ground testing and in the air, on Aircraft '346'. Reliable ignition of the hypergolic engine at altitude.

2. Perfect operation of the pilot recovery system successfully solved on Aircraft '346' through separation of the pressurized cockpit from the fuselage, with subsequent pilot ejection at low speeds. It was tested at the time of the accident and during preliminary testing.

3. Possibility of handling the aircraft in prone position, which allows larger loads on the pilot's body in comparison with conventional positioning.

4. Capability of landing an aircraft with skids on an unprepared dirt strip at speeds of up to 33Okm/h.

5. High rate of climb at all flight altitudes and intensive acceleration of aircraft with rocket motors.

6. Satisfactory operation of all equipment.

Despite the positive results it is not advisable to earn' out further tests of the remaining 346-1 prototype for the following reasons:

1. Further flights of Aircraft 346" cannot yield significant results.

2. The remaining first Aircraft 346' prototype has a high speed constraint (up to 0.8 M) compared to the one lost in the accident (0.9 M).

3. It is not expedient to improve the aerodynamic qualities of the remaining prototype with the aim to remove the speed constraint because the equipment is old, was stored out in the open for a long time, and it does not guarantee safety during further flight testing.2"

Since the aircraft was developing a speed exceeding 900 km/h while using only half the engine thrust, one could presume that, with two combustion chambers burning, the jet could well exceed the speed of sound. But its imperfect aerodynamic configuration would not allow such tests to be performed.

In the 1950s, sufficiently improved laboratory methods of studying supersonic aerodynamics appeared. As a result there was no longer any need for experimental rocket aircraft, the flights of which, as experience showed, were dangerous.

Development of Aircraft "346" was the most expensive Experimental Plant No. 1 program. From April 1946 until September 1951, some 55 million rubles were spent on it.

Using Aircraft "346" as the foundation, supersonic tailless fighter interceptor "486" with a slim delta wing was designed at OKB-2 in 1949 with participation of former Heinkel engineer S. Giinter. It was supposed to use a multichamber rocker motor, take off from a trolley, and land on a skid.

In order to carry out preliminary tests and measure flying characteristics at speeds up to 500 km/h, a wooden "466" glider duplicating the "486" layout was built at the plant in 1950 and its wind tunnel tests began at TsAGI.

However, by that time, it became clear that the use of rocket motors on aircraft was not advisable since flight duration was very short. Therefore, in June 1951, having spent 10.7 million rubles on "486" development, the Ministry of the Aviation Industry- decided to stop financing the project. OKB-2 was soon closed down and its employees were distributed along the plant's other sections.

D.A. Sobolev, D.B. Khazanov

References

  • "The German Imprint on the History of Russian Aviation " /D.A. Sobolev, D.B. Khazanov/

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