The Yak-15 (NATO codename: Light Feather)[1] was the first Soviet jet fighter developed by the Soviet Union after the war. The Yak-15 and Sweden's Saab-21R, equipped with reverse-engineered Jumo 004 jet engines, are the only jet fighters in the world that have been modified from piston engines and successfully mass-produced. Almost all of the 280 fighters produced in 1947 were used to train experienced piston fighter pilots to adapt to the flight operations of jet aircraft.
At the end of World War II, Germany, the United States and the United Kingdom all developed and equipped jet fighters. Compared with the above-mentioned countries that have completed research and development, design and finalization, and mass production and service, the Soviet Union lags significantly behind in the field of jet aircraft. After analyzing and evaluating the captured German equipment, it was found that the Soviet Air Force had lagged behind in technical equipment. The Soviet government decided to make up for the time to catch up and asked the major design bureaus to design a new jet fighter in a short period of time. On 9 April 1945, the Council of People's Commissars issued instructions to the Jacques Design Bureau for the design of a new fighter, which included a single seat and the equipping of the captured Junkers Jumo 004. To save time, Jacrev decided to directly modify the latest variant of the most maturely designed Yak-3 fighter, the Yak-3PD. To accommodate the jet engine, the nose was redesigned. Jet engines are mounted below and below the fuselage so that the tail flames are discharged from below the middle of the fuselage. In order to protect the fuselage from the high heat tail flame, a steel heat shield was installed underneath it. The sunken nose air intakes and engines make the aircraft's configuration similar to a single-engine pod. Except for the nose part, the all-metal fuselage has hardly been changed. The redesign of the nose allows the Yak-15 to add one NS-23 cannon to two compared to the Yak-3PD. Thanks to the pod-like design, additional fuel tanks were added to the fuselage above the engine and around the engine. In terms of wings, there were no aerodynamic changes except the removal of the oil cooler and the oil-cooled air intakes, and the bending of the front wing girder in an inverted U-shape to make room for the injection engine. In the rear wing, the vertical stabilizer has been slightly enlarged, and the horizontal stabilizer has not been modified. The entire landing gear, except for the addition of steel plate suspension to the tail wheel, has been largely unchanged. Carrying 1,300 pounds of fuel, the new design for the Jumo 004 engine was tentatively named the Yak-3 Jumo.
In October 1945, the Jacques-3 Jumo began to run on a slide test. In the test, it was found that the additional heat shield was too short, which eroded the duralumin skin of some fuselages, and the engine tail flame also melted the rubber tires of the tail wheels. At the end of December of the same year, a new metal tailwheel was installed, the heat shield was modified, and a second prototype with an enlarged vertical stabilizer was shipped, and the first prototype was also revised at the same time. After several run-and-run tests, it was transferred to the Central Aerodynamics Institute for a comprehensive wind tunnel test. Wind tunnel testing was completed in February 1946, and on the 26th of the same month, the People's Committee gave specific indicators of the aircraft's performance, requiring a maximum sea level speed of 480 miles (770 kilometers) and an altitude of 16,400 feet (5,000 meters) and an altitude of 530 miles (850 kilometers). At the same time, it is required to climb to 16,400 feet (5,000 meters) within four and a half minutes, a practical ceiling of 49,210 feet (15,000 meters), and a cruising range of 310 miles (500 kilometers). Two prototypes are ready for the September 1 acceptance test flight.
Competition from within the USSR
At the same time, the Mikoyan Design Bureau also designed and developed the MiG-9 fighter according to the instructions. According to aviation historians Bill Goston and Yeffy Gordon, representatives of the two design bureaus flipped a coin at a flight test meeting on April 24, 1946, to decide which design bureau aircraft would be the first Soviet jet to fly first. The MiG-9 won the opportunity, and the reluctant Pilot of the Yak-3 Jumo circled the field a week before landing. [7] On June 22 of the same year, the flight tests of the Jacques Design Bureau were completed. However, based on the success of the first flight, the Council of Ministers issued a new directive on April 29, three days after the first flight, requiring major design bureaus to adopt domestically produced RD-10 engines in the acceptance test flight of the new fighter. In view of the test results of the RD-10 engine, the flight indicators have also been adjusted: the maximum sea level speed has been lowered to 430 mph (700 km/h) and the utility ceiling has been lowered to 45,930 ft (14,000 m). The acceptance date is not changed.
Since the RD-10 was the product of the reverse engineering Jumo 004, it was not difficult to retrofit two aircraft ready for acceptance with domestic engines, one of which also participated in the Tusserno Air Show in August 1946 (the predecessor of the present-day Moscow Air Show). On the second day of the air show, Stalin met with Mikoyan and Jacrev and asked the design bureau in charge of the two men to build 15 new fighter jets each for the military parade on The anniversary of the October Revolution on November 7 of the same year, and the acceptance date could be postponed until the end of the parade. Jaclev soon took aim at the Tiberis XIII factory, which was still producing the Yak-3 and the design bureau had only 15 new fighters in demand, and the switching between production lines was relatively easy and less costly. Although the avionics were incomplete and there was no armor or armament, all 15 aircraft were built by the deadline, and a fuel tank was temporarily installed in the space where the weapons were originally equipped for emergency. Although the air show was cancelled due to the harsh weather on the day of the military parade, the internal pair of the Design Bureau favored the unarmored and lightweight show aircraft. After the two show aircraft had perfected their electronic equipment, removed the temporary fuel tanks and installed a single cannon, they were assigned to participate in the acceptance test in order to better test results, and were given the official designation Jacques-15.
Officially put into production
The test site of the Yak-15, painted in magenta and armed with a single NS-23 cannon, marked the official start of a five-month acceptance test that ended in April 1947. Tests revealed problems: the thickness of the wings inherited from the Yak-3's aerodynamic structure affected the aircraft's top speed; the rear three-point landing gear layout caused the engine tail flame to ground and damage the runway; the overheating and oil leakage of the fuel tank around the engine filled the cockpit with fuel vapor and smoke; and the range that was not up to standard. Although problematic and difficult to improve, test results show that the Yak-15 is extremely easy to maneuver and very easy to fly, especially for pilots accustomed to piston fighters. This is one of the reasons why the Soviet Air Force was happy to accept the Yak-15 as a pilot-turned-trainer aircraft. [9]
Another reason is that in December 1946, when the acceptance test began, Jaclev had already used contacts and lobbied the Council of Ministers to put the Yak-15 into mass production. Initial planning was for the production of the first 50 single-seat fighters and two-seat trainers, all equipped with single-door NS-23s, from January to April 1947. But the Design Bureau was so overwhelmed with acceptance that the first full production of single-seat fighters was produced. All production aircraft participated in the May Day air show in Moscow in 1947. By the end of 1947, in addition to the prototypes, a total of 280 Yak-15s had left the factory. Some of them were assigned to Soviet aviation regiments in Poland, Romania, Hungary and the Kanto Oblast, all of which were converted as pilot-turned trainers. A small amount arrived in China as aid after the start of the Korean War and was also used for pilot transformation. Good performance also made the Yak-15 popular among some air show teams. [