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In 1944, interest in the creation of high-altitude interceptor fighters increased again. If in 1943 the reason for this was the flights of high-altitude German reconnaissance aircraft over our territory, now we had to take into account the appearance of American and British high-speed high-altitude bombers with pressurized cabins. Such as the B-29 or the Spitfire XIV high-altitude fighters.
In July 1944, in a letter to A.S. Yakovlev, 44, with reference to the order of the NKAP dated June 5, 1944, Sukhoi was asked to develop and submit a draft design of a high-altitude fighter within a month.
The aircraft's practical ceiling was supposed to be 15,000 meters, the working height of loitering - 14,000 meters with a vertical speed reserve at this height of 4 m/s. Loitering time is not less than 1.5 hours. The maximum speed at an altitude of 12000-14000 meters should be 670 km/h. Armament cannon 20 mm caliber with 120 rounds of ammunition. It was necessary to provide for the installation of a second cannon on the plane with the same ammunition. When designing, first of all, it was necessary to pay attention to ensuring the requirements for the ceiling and loitering time.
The result was the Su-7 (the first with this name), an experienced Fighter-Interceptor, which is essentially a modification of the single-seat Su-6 attack aircraft, but without an armored box. Power plant - combined: engine - ASh-82FN with two turbochargers TAK-3 and rocket accelerator RD-1-X3 V.P. Glushko. The rocket engine thrust was 300 kgf with a fuel consumption (kerosene and nitric acid) of 1.6 kg/s. The taxiway was installed in the extreme tail section of the fuselage, the fuel was installed behind the cockpit. The flight weight was 4360 kg. Armament: three 20 mm cannons (370 rounds).
The aircraft was produced in 1944 and passed factory tests, during which the power supply system and the regulation of the rocket engine were tested. It was first flown by test pilot Komarov in January 1945. The maximum speed at the ground was 480 km / h, at an altitude of 7500 m - 590 km/h without a liquid propellant engine and 680 km/h with a liquid propellant engine and at an altitude of 12,000 m - 510 and 705 km/h, respectively, the ceiling is practical - 12,750 m of continuous operation of the rocket engine was about 4 minutes, the length of the takeoff run with it was about 300 m. Flight tests were inhibited by strong torching of the exhaust pipes, leading to burning of the paint on the sides of the fuselage. All attempts to eliminate this phenomenon were unsuccessful, and in the end, the turbochargers were disconnected from the exhaust system. The second stage of testing began on February 18, 1945, and lasted until mid-December. The tests revealed the unreliability of the RD-1 engines and the unsafe operation of them. In December 1945, by the decision of the 18th GU NKAP, work on the aircraft was stopped.
The experience of using VRD and LPRE accelerators in combination with piston engines on combat aircraft has revealed their complete futility for mass use in aviation. The most realistic one, meeting the requirements of further growth of altitudes and flight speeds, was the turbojet engine (TRD).
Construction the aircraft was mixed. The wing, center section and tail are metal, the fuselage is wooden. Rudders and ailerons are covered with linen. The wing is two-spar, with a working skin. Fuselage - monocoque, birch veneer sheathing. There is an additional gas tank and two TK-3 behind the cockpit. The rear bottom is made of armor steel 12 mm thick. Pressurized cabin of compressor-ventilation type. The AV-9-118 screw is four-bladed, 3.2 meters in diameter.
In the response of the Air Force Research Institute to the preliminary design, it was noted that the flight data did not fully meet the requirements, the project was developed unsatisfactorily and not in full. The designers were asked to reduce the wing area, increase the ammunition for cannons to 300 rounds, and for machine guns up to 350 rounds.
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