I-185 Polikarpov. Fighter La-5 (serial number 710041), equipped with an M-71 engine.

There are two ways to raise the flight data of an aircraft: by reducing the weight of the airframe and improving aerodynamics. Weight loss threatens with loss of strength. It was this path that Yakovlev took, and this path cost the lives of hundreds of pilots. This statement is disputed, explaining the reason for the loss of strength of the wing by the use of glue that is susceptible to the influence of the fungus, however, the timely replacement of the wing with a metal one with an increase in the supply of aluminum in the last years of the war would probably solve this problem. Lavochkin managed to reduce the mass of the last series of La-5FN by about 100 kg by replacing the wooden power wing set with a metal one, while the structural strength remained at the same level.

Installation of a more powerful new more powerful air-cooled engine M-71 (ASh-71), created in the OKB A.D. Shvetsov, would dramatically improve the flight characteristics of the aircraft in the entire range of altitudes. The engine of this type was already tested in 1941 on the I-185 N.N. Polikarpov, but proved to be a very unreliable design.

Nevertheless, the I-185 with the M-71 in 1942 surpassed all Soviet fighters in their characteristics, including the La-5. The maximum speed of the I-185 at sea level was 556 km / h (for La-5 - 515 km / h), at an altitude of 6175 m - 630 km / h (La-5 - 600 km / h), flight range - 1130 km (at La-5 - 765 km / h). The I-185 was armed with three 20-mm ShVAK cannons, while the La-5 was armed with only two such cannons. The I-185 successfully passed State tests in February-July 1942, but was not transferred to serial production. Usually, the reason for not launching the I-185 in a series is called the difficulties of organizing mass production of a new type of aircraft in wartime conditions and problems with the M-71 engine. To no less extent, the fate of the I-185 was influenced by the competition between the chief designers of fighters. Polikarpov only managed to achieve the construction of four aircraft and conduct their tests in frontal conditions. The fighters operated on the Kalininsky front as part of the 728th IAP from September to December 1942. D. Kupin, A. Tomilchenko, N. Ignatiev and A. Borovykh flew on the I-185 under frontline conditions, two of them were Heroes of the Soviet Union. The I-185 operated in the Rzhev area, where the Germans were testing their new product - the Fw-190 air-cooled fighter. For the first time, the Focke-Wulfs appeared here in November 1942. The pilots who piloted the I-185 were strictly forbidden to cross the front line. It seemed that successful tests and favorable reviews from front-line pilots could turn the fate of the I-185 - in accordance with the order of the NKAP, preparations for serial production began at aircraft plant No. 81, but it went on at a slow pace. The plant was preparing to produce an improved version of the I-185, capable of reaching a speed of 560 km / h near the ground (600 km / h in emergency operation of the engine), and at an altitude of 6170 m - 680 km / h. The following fact speaks about the high-speed qualities of the Polikarpov fighter: test pilot P.M. Stefanovsky in one of the flights at the end of 1942 reached a speed of 708 km / h. At the same time, within a month (from November 20 to December 26, 1942), the M-71 engine was changed twice on the prototype, while the plane flew only 5 hours 13 minutes in a month. The point in the fate of the I-185, indisputably the best Soviet fighter at that time, was put by the disaster in which test pilot V.A. Stepanchonok.

A similar failure with the installation of the M-71, suffered in April 1943 and S.A. Lavochkin. The characteristics of the La-5 after the installation of the M-71 improved dramatically, but the unreliable operation of the engine put an end to the future of the machine.

A new version of the La-5 fighter with this engine entered flight tests on April 28, 1943. This La-5 was equipped with an already forced version of the M-71F engine with a capacity of 2200 hp. on takeoff. Compared to the La-5, the new fighter had a different hood of a larger midsection, a modified exhaust system, and a new intake manifold. The oil cooler was moved back. The dimensions were completely identical to the La-5, only the length of the aircraft, due to the changed hood, instead of 8.67 m, became 8.31 m. The weight of the La-5 with the M-71F increased due to the heavier engine and reached 3526 kg.

At the first stage of testing, which lasted until June 4, 1943, the aircraft did not show the expected data, although it significantly surpassed the La-5FN in speed. Its rate of climb was not measured. For some time, the tests continued, and then the La-5 with the M-71 was sent to TsAGI, where it was tested in a full-scale T-101 wind tunnel. It turned out that due to insufficient quality manufacturing (primarily the hood), the aerodynamic drag of the aircraft turned out to be significantly higher than expected. TsAGI aerodynamics came to the conclusion that after the appropriate improvements, the aircraft will be able to show a speed of 720 km / h. However, this promising version of La-5 still did not receive further development, since the M-71 engine was never put into production.

Thus, all that remained was to improve the aerodynamics. In order to test the effectiveness of the proposed recommendations in real flight, TsAGI modified the serial La-5FN aircraft No. 39210206. This aircraft was tested at the Flight Research Institute from December 16, 1943 to February 10, 1944. During the tests, the effectiveness of the improvements proposed by TsAGI was fully confirmed: with the same engine as the La-5FN, the new fighter showed a speed of 34 km / h more ( 684 km / h at an altitude of 6150 m). In terms of speed, the La-5 N839210206 did not differ much from the La-5 variant with a much more powerful M-71F engine.

All TsAGI recommendations were taken into account by the S.A. Lavochkin while creating a new fighter La-7.

^* Using a 10 minute afterburner.
^** At 90% of maximum speed.

Bibliography

• The history of aircraft designs in the USSR, 1938-1950. /V.B. Shavrov /
• La-7 / "War in the air" No. 70, 2001 /
• La-5 with M-71. La-5 improved / K. Kosminkov, "As" №2.3 1991 /