Bereznyak-Isayev BI-1

Soviet research and development of rocket-powered aircraft began with Sergey Korolev's GIRD-6 project in 1932. His interest in stratospheric flight was also shared by Marshal Mikhail Tukhachevsky who supported this early work. After a long series of unmanned tests of vehicles, Korolev's RP-318-1 rocket plane flew on Feb 28, 1940. That Spring, the Zhukovsky Institute in Moscow (TsAGI) hosted a conference for aircraft chief designers on the subject of ramjet and rocket propulsion. On July 12, the Council of People's Commissioners (SNK) called for the development of high-speed stratospheric aircraft.

Early design
Aircraft designer and head of OKB-293, Viktor Fedorovich Bolkhovitinov attended the TsAGI conference along with two of his top engineers, A. Ya. Bereznyak and A. M. Isaev. The young Bereznyak had made an impression in 1938 with a high-speed airplane design that some thought could break the world speed record. Bereznyak and Isaev were excited by the idea of designing a rocket-powered aircraft, and their "patron" Bolkhovitinov approved. By the Autumn of 1940, they were able to show fellow engineer Boris Chertok a preliminary design of "Project G". The design, made up mostly from plywood and duralumin had a take-off weight of 1500 kg, and they planned to use the new 1400 kgf rocket engine under development in the Jet Propulsion Research Institute (RNII). Chertok was astounded that the aircraft could almost climb vertically.

Bereznyak, Isaev and Chertok visited RNII in March 1941, but the new rocket engine was not working yet. The engine was designed by Leonid Dushkin, who had made the engine (RD-A-150) for RP-318-1. Powered by tractor kerosene and red fuming nitric acid, it fell short of the hoped for 1400 kgf of thrust. Designated D-1-A-1100, it was expected to reach 1100 kgf. The "A" stood for "Nitric" (versus "Oxygenic"), a distinction of unusual importance and controversy among Soviet rocket scientists. Dushkin's propellant pump was causing considerable problems. It was a turbine pump driven by hot gas and steam from a small combustion chamber fed with rocket propellants mixed with water. This system was perfected a few years later in Dushkin's RD-2M engine.

The D-1-A-1100 was built from carbon steel with diffusion chrome plating. At this point in time, Russian rocket engines were built with typical aviation piston-engine manufacturing technology. Weighing 48 kg, it could be broken down into discrete forged-steel sections – a conical head with 60 centrifugal injectors, the cylindrical chamber, and the nozzle – joined with bolts and copper gaskets. It was ignited with a nichrome glow plug, later replaced with silicon-carbide. The engine was cooled regeneratively by both propellants, the chamber walls by a spiral flow of incoming fuel, and the nozzle section by the flow of oxidizer.

War-time development
On June 21, Isaev proposed a new design using compressed air instead of a pump to force propellant to the engine. The next day, Operation Barbarossa brought the Soviet Union into World War II, and the rocket-powered interceptor suddenly became important. Bereznyak and Isaev began a new more detailed design, which they finished in three weeks. On July 9, Bolkhovitinov and his project-G team met with Andrey Kostikov the head of RNII. Dushkin was not happy about the idea of bypassing his fuel pump design, but they backed the plan and cosigned a letter that was eventually shown to Joseph Stalin. After giving a report at the Kremlin, they were ordered to build the plane and were given only 35 days to do so. The official order was dated August 1, but work began in late July. The engineers were given leave to visit their families, and then literally lived at the factory until the planes were finished.

The new design was called "BI" for Blizhnii Istrebitel (close-range fighter), but the letters were also understood by everyone to stand for its inventors: Bereznyak and Isaev. The original plan to include four machine guns was replaced by a design with a pair of 20 mm ShVAK cannons. The new plane was a low-wing monoplane 6.4 meters long, with a wingspan of 6.5 meters and an estimated take-off mass of 1650 kg (including 710 kg of propellant). Working around the clock, local furniture workers were employed to build the first two prototypes (BI-1 and BI-2). The skin was 2 mm plywood with a bonded covering of fabric. The Ailerons, elevators and rudder were fabric covered, and the flaps were duralumin. In the forward section were 5 compressed air tanks and 2 kerosene tanks. In the aft were 5 compressed air tanks and three nitric acid tanks. Pressurized to 60 atm, the tanks were made from a high-strength chromium-manganese-silicon steel ("Chromansil") that was not especially resistant to corrosion. Thus, the acid tanks had to be replaced periodically. Compressed air was also used to retract and deploy the landing gear and to power the anti-aircraft cannons.

On September 1, 1941, BI-1 was completed and ready for glider tests by pilot Boris N. Kudrin. Dushkin's engine was still not ready. A few weeks later, rival aircraft designer A.S. Yakovlev took it upon himself to tow the prototype to TsAGI for windtunnel testing. This alarmed Bolkhovitinov's team, because their patron had a rocky history with Yakovlev, but Alexander Sergeevich and aircraft designer Ilya Florov studied the test results and gave them sound advice for improvements. Yaw instability was corrected by enlarging the rudder and adding two circular plates to the tail horizontal stabilizer.

Test flights in the Urals
In October, both OKB-293 and RNII were evacuated to the Urals, along with most of Moscow's war industry. Bolkhovitinov's team was stationed in Bilimbay, and Dushkin's team in Sverdlovsk, about 60 km away. A test stand was built on the shore of frozen lake Bilimbay, with a dynamometer cradle to hold the BI-1 during engine testing. A new test pilot, Grigory Yakovlevich Bakhchivandzhi, was assigned to the team. Dushkin was increasingly absorbed by other work, including RNII's own rocket plane project, the Kostikov-302. He assigned his engineer Arvid V. Pallo to oversee the installation and testing of the rocket engine.

Nitric acid presented a constant problem, corroding parts and causing skin burns and respiratory irritation. Tanks of sodium carbonate solution were kept around to neutralize acid spills. On February 20 1942, the engine exploded during a full system test. The nozzle section was blasted into the lake, and the engine head struck the back of the pilot's seat, knocking Bakhchivandzhi against the instrument panel and injuring him slightly. From a broken propellant line, pressurized nitric acid drenched Pallo. Fortunately, quick thinking mechanics dunked him head-first into a tank of soda solution. His face was yellow from the characteristic acid staining, but his glasses saved him from being blinded. To protect the pilot in the future, a 5.5 mm steel plate was added to the back of the seat.

By April 1942, BI-1 was ready for testing at nearby Koltsove airfield. A test commission was formed, with representatives from OKB-293, RNII and the airforce research lab (NII VVS). On May 2, the pilot let the plane lift off one meter under low thrust.

On May 15, at 19:02 (UTC), Bakhchivandzhi made the first real flight of BI-1, reaching an altitude of 840 meters and a maximum speed of 400 km/h. The mass of the plane had been reduced to 1300 kg (only 240 kg of nitric acid and 60 kg of kerosene loaded), and the engine was operated under a thrust of only 500 kgf. The pilot shut the rocket engine off after about one minute, when a light indicated it was overheating. Landing, the aircraft descended too rapidly because of insufficient forward speed, and the landing gear broke on touchdown. The pilot was unhurt and reported that, aside from the rough landing, the plane handled well. The flight lasted only 3 minutes and 9 seconds.

In July, Dushkin recalled Pallo to help work on the "302" rocket-plane project. Bolkovitinov asked Isaev to take over and master the technology of liquid fuel rocket engines. Isaev got permission to visit Valentin Glushko, the leading Soviet expert on rocket engines, who was then working in a special lab for political prisoners. Glushko taught Isaev the complex techniques of chamber-wall heat transfer calculation and engine design, developed by himself and Fridrikh Tsander in the early 1930s. Isaev's propellant feed system was simple, but it produced an uneven fuel pressure that diminished as compressed air was used up. Bolkovitinov and his engineers wrestled with this problem, designing pressure regulators and even a piston fuel pump driven by compressed air, but none of these improvements were realized.

Too damaged by acid to fly safely, BI-1 was retired and the second prototype BI-2 was made ready. Backchivadzhi made the second flight on Jan 10, 1943, reaching 1100 meters but with the engine still throttled back for a maximum speed of 400 km/h. The first flight had been with landing gear kept down, and some vibration has been observed. This time, the flight was made with landing gear stowed, and no vibration was observed at the cautious speed.

The third flight was made on Jan 12 (some sources say Feb 10) by a temporary test pilot, Konstantin Gruzdev, while Backchivadzhi was consulting on Kostikov's "302" project. This time the engine was opened up to full thrust of 1100 kgf and a speed of 675 km/h was achieved and a maximum altitude of 2190 meters. During the winter, the landing gear was switched from wheels to skis. On Gruzdev's flight, one ski broke off during take-off, but he was able to land safely. Backchivandzhi returned to make flights in the third test plane BI-3 on March 11, 14 and 21. He reached a maximum altitude of 4000 meters with a maximum rate of climb of 83 meters per second.

The March 21 flight was with a full load of ammunition. Most of the BI models did not contain an actual pair of anti-aircraft cannons, and some reports claim that BI-4 was used for the live ammunition tests. The guns were never fired in any flight. The BI-4 model was reportedly used as the template for the mass production of 30 to 50 BI-VS model aircraft by Andrey Moskalev's factory. Moskalev augmented the twin ShVAK guns with a load of ten thermite bombs.

On March 27, during a low-altitude test flight, Backchivandzhi pushed the aircraft's speed. After 78 seconds, the plane went into a 45-degree dive and crashed into the ground, killing the beloved pilot. The accident put a halt to flight tests, and a lengthy investigation began. Eventually, after wind tunnel testing, it was determined that the BI-1 lost control due to the effects of transonic velocity. Estimates of Backchivandzhi's final velocity range from 800 to 990 km/h, but the recording instruments were too damaged by the crash for a reliable measurement. March 27 is considered a black day in Soviet aviation history, also being the date that Yuri Gagarin died in a jet plane crash. In 1973, Backchivadzhi was posthumously awarded Hero of the Soviet Union.

Return to Moscow, Isaev's engine
In May 1943, OKB-293 returned from its evacuation and set up operation in Khimki, a suburb of Moscow. On May 18, Bolkhovitinov wrote a detailed report "On Rocket Aircraft and Further Prospects". He emphasized the need to study the dangerous regime of "shock stall", and to safely transition through transonic speed and beyond. He proposed the goal of a new rocket plane capable of 2000 km/h.

The next year, Bolkhovitinov had five more aircraft produced, BI-5 through BI-9. In the Spring of 1944, BI-6 was fitted with a pair of Igor A. Merkulov's DM-4 ramjet engines. It did not contain a rocket engine, so it was towed into the air. The pilot, Boris Kudrin, flew the BI-6 three times, but was never able to get both ramjets to start at the same time. The plane was taken to TsAGI for further tests in the T-101 wind tunnel. The DM-4 auxiliary motor was also tested on the YaK-7b fighter.

With the loss of the D-1-A-1100 engine, Isaev began designing a new engine. The RD-1 was completed and tested in October 1944. The general form of the engine was the same as Dushkin's, but with numerous improvements. Isaev fashioned the sections from 12Kh13 stainless chromium steel (13% chromium, 0.12% carbon content). The head had 85 swirling injectors arranged in a honeycomb pattern that promoted improved fuel-oxidizer mixture. It also used a more reliable electric arc starter instead of a glow plug. Isaev also improved the regenerative cooling, increasing the flow rate around the nozzle.

BI-7 was flown twice with the RD-1 engine, on January 24 and March 9 1945. Pallo reports there was an emergency with the landing gear during the January flight. In addition to the new engine, various changes were made to the plane's design: a larger rudder, smaller false keel, and different wing fillets. During the test flights, the pilot Boris Kudrin, noticed some tailfin flutter. On May 29, the pilot M.K. Baykalov tested the BI-7 in glider mode, without starting the engine, and the flutter was not detected. At this point, the plane was too corroded by nitric acid to fly again, and it was retired. To further investigate the flutter problem, BI-5 was modified in the same fashion as BI-7 (but with no engine) and tested in glider flights; however, the problem was not reproduced.

After BI-6 was sent to TsAGI, BI-9 was put into service as a replacement (marked with a "6" on its tail). Flown by Boris Kudrin and M.A. Baikalov, it was used in glider tests with extra payload weight. The fate of BI-8 is unknown.

Powered flights
The BI was flown 12 times under power, seven times with Dushkin's D-1-A-1100 engine, three times with the DM-4 ramjets, and twice with Isaev's RD-1 rocket engine.

Operators

 * Soviet Air Force
 * Soviet Air Force