Aviation of Word War II
High-altitude La-5TK. Modifications of the La-5.
Air battles of the great war, mainly took place at low and medium altitudes, where attack aircraft and dive bombers worked. The production of the high-altitude MiG-3 was curtailed, but the need for a vehicle of this class remained, and on November 12, 1942, the NKAP issued order No. 835ss on high-altitude modifications of the Yak-9 with VK-105PD, as well as La-5 with the M-82A and the TK-turbocharger. 3. OKB-21 received 20 days for the preliminary design ...
Due to a number of circumstances, including the refinement of the turbocharger itself, La-5 with TK-3 (La-5TK) first took to the air only on April 17, 1943. Already in the first flights, a speed of 660 km/h at 8000 m was obtained and ceiling 12,200 m, the compressor was working fine, but the motor was overheating. In terms of flight data and characteristics, the La-5 M-82F with the TK-3 was superior to the Yak-9PD, but inferior to the Mikoyan I-231 fighter with the AM-39 engine.
However, the results obtained did not meet the new requirements, according to which it was necessary to bring the ceiling to 13,000 m. Then the VMG of the aircraft was redesigned, installing the M-82FN with two TK-3s. This version also passed the main test program, which was conducted by the test pilot of the LII Yuganov and the factory pilot Samsuyev. The modified La-5TK flew from July 9 to September 17, when the engine was removed, as chips were found in the cylinders.
After replacing the engine and installing an enlarged oil cooler, flights resumed on October 7. Another pilot of the LII Shiyanov joined the work. By November 26, 33 flights were performed, including 18 with an climb of more than 9 km. The aircraft flew very confidently at 12,500 m, but the steady flight at a higher altitude was prevented by overheating of the oil and cylinder heads. Struggling with overheating of the engine, CIAM proposed either to increase the degree of enrichment of the mixture (in this case, the part of the gasoline that was not burnt would take heat and carry it away through the exhaust), or switch to gas-alcohol fuel, or supply water to the cylinders. This was soon done, but flights showed that the problem remained.
By the end of September 1943, a project was prepared for the La-5TK "backup" designed for a combat altitude of 13,500 m. The aircraft had many differences: an increased wingspan and stabilizer, an M-82FN engine with two TK-3s of a new series, air cooler in the boost line. The cockpit was designed for a sealed ventilation type, and the pilot received a new oxygen mask designed for an altitude of 14 km. The NKAP proposed to make an experimental series of La-5TK, submitting the first 2 aircraft for testing by October 30, and the last 4 by December 30, 1944. For this Lavochkin asked 100 skilled workers, the assistance of CIAM, plant number 289 and design bureau for pressurized cabins A.Ya ... Shcherbakov, as well as engine plants No. 19 and No. 300. All this was provided, and in addition, Myasishchev Design Bureau specialists, who had extensive experience gained while working on the pressurized cabins of the "102" bomber, were sent to Plant 21.
The La-5TK "backup" was built in January 1944, but the engine turned out to be defective - the flights had not yet begun, but chips were found in it. While the new high-altitude M-82FN arrived from the factory, the weather deteriorated. Only in March, they made 2 flights to test stability and controllability, without rising above 3000 m.Shiyanov began the main test program on March 17. The new power plant turned out to be worse than the old one. The temperature of the cylinder heads reached 240-260 ° C when climbing above 2 km, the pressure in the fuel system dropped sharply by 5 km, and the fuel tanks began to smoke so that there was nothing to breathe in the cabin. There were many other troubles going on. After modifications, with great difficulty, it was possible to climb 12,750 m. By order No. 208s of March 22, 1944, the NKAP allocated part of plant No. 381 to an independent plant No. 81, which became a branch of OKB-21. There, work was carried out on many experienced La-5s, including the flight-development tests of the La-5TK.
In the meantime, intelligence reported that, in addition to the Ju 86P high-altitude reconnaissance aircraft flying over Moscow at an altitude of 12-13 km, the enemy is already testing bombers and fighters with an altitude of 15-17 km and is developing aircraft capable of flying for a long time at 18-20 km. Work on high-altitude fighters was taken over by a member of the State Defense Committee G.M. Malenkov. In the People's Commissariat, Alekseev, the head of the 7th headquarters, was responsible for this topic. Since mid-May, he reported on the progress of testing the high-altitude versions of La-5 and Yak-9, as well as the I-222 aircraft designed by Mikoyan every day, but things did not move. Moreover, refusals have become more frequent. On May 27, the flight of La-5TK had to be interrupted at an altitude of 10,500 m. butter began to beat from the prompter. On June 11, oil flowed at an altitude of 11000 m, and two days later - at 9500 m. Flights were interrupted for improvements. But even after them, on July 4, it was possible to reach only 7800 m, while the loss of oil in 33 minutes was 15 kg.
The factory tests of the La-5TK "backup" had to be completed by July 15th. But July passed, then August, and it was not possible to achieve reliable engine operation at altitude, and the TK-3 itself did not cause any complaints. The need for a special high-altitude motor became obvious.
At the end of September, we finalized the oil system, but overdid it - by 10,000 m the oil temperature dropped below the limit. On October 5, Anokhin flew to measure fuel consumption and determine the most advantageous water injection mode at an altitude of 3500 m. In flight, the torch of the right turbocharger began. The pilot saved the car, but the starboard side of the La-5TK was burned. This was the end of the program. At that time, Ju 86Ps had already ceased to appear over Moscow.
Further work on air defense fighters was carried out with the expectation of jet thrust. On May 22, 1944, the GKO Resolution No. 5946ss was issued, and on May 30 - the order of the NKAP No. 371 it, in which, among other works, OKB-21 was instructed to create a modification of the La-5FN with an M-82FN or M-83 engine and a single-chamber liquid-propellant rocket engine RD -1 designs by Glushko. Experienced La-5RD No. 1 should have been transferred for testing in September 1944, No. 2 - in October, and No. 3 - in January 1945. With the liquid-propellant engine switched on, it was necessary to reach a speed of 780 km/h, and gain an altitude of 5 km in 3 minutes ...
Experienced La-5RD built plant number 81 using Gorky serial units. Factory # 16 sent its first RD-1 only on October 16, although at the beginning of July it was supposed to deliver 5 "firing" liquid-propellant rocket engines. The first plane was taken to the airfield on October 21, but the drive of the LPRE pumping unit did not provide the required pressure. The dvigatelists eliminated the problem by November 18, but further work on the La-5RD was stopped, since on October 21, the construction of a similar La-7R-1 was completed, and plant number 81 concentrated its limited forces on it.
They tried to improve the altitude and speed characteristics of the La-5 in other ways. In April-May 1943, the experimental La-5FN Nos. 0871 and 1618 were tested with the new E-67 driven centrifugal supercharger developed by TsIAM. The characteristics of the monitoring station were improved by increasing the revolutions, and the gear shifting with the change in height became automatic. However, the development of the E-67 lasted for more than 2 years; it was not implemented on the serial La-5.
On Stalin's personal instructions, the installation of imported engines on domestic aircraft was worked out. The American engines Wright R-2600 Duplex Cyclone (takeoff power 1700 hp) and Pratt-Whitney R-2800 Twin Wasp (takeoff power 2000 hp) were tried on La-5. Calculations showed that with the first, all flight data of the La-5 decreased, and with the second, the speed at the ground increased by 5 km/h, and at 6000 m - by 35 km/h. Taking into account the slight improvement in characteristics and the complexity of the alteration, they did not build the aircraft, but proposed to make a modification with the domestic M-71 similar in power and dimensions to the R-2800. As a result, the M-71F with a takeoff power of 2200 hp was installed on the serial La-5FN No. 0204 at the plant No. 21. At the same time, due to the peculiarities of the engine, the air intake of the monitoring station was moved under the hood, and the oil cooler - under the cab. On April 28, 1943, La-5 M-71F (aircraft "E") made its first flight, and on June 4, its factory tests were completed. They showed that the plane develops a speed of only 685 km/h instead of the specified 720 km/h, but it has a decent rate of climb - it reached 5 km in 4.4 minutes. The car was transferred to TsAGI to improve aerodynamics, and then it "flew" only in a wind tunnel. Serially, this option was not built, but the experience gained was used to create La-5 M-82FN No. 0206, which became the prototype of one of the best fighters of the Second World La-7. The La-5 variant with the new ASh-83 engine, which made its first flight in March 1944, also did not go into production.
On October 26, 1943, the GKO decree No. 4431 cc was issued, which obliged the Lavochkin Design Bureau to make, on the basis of the serial La-5FN, a modification of the La-5D with metal wing spars and enlarged tanks. The reason for this work was not only the need to accompany the bombers further and further beyond the front line, but also the instability of serial AK-82BP carburetors and NB-ZU direct injection pumps, which led to excessive fuel consumption. But work on the wing with metal spars was delayed due to the lack of qualified designers and workers in pilot production. Tests of the experienced La-5D began only on April 1, 1944, when all forces were thrown into fine-tuning the La-7.
At the Air Force Flight Research Institute and the Air Force Research Institute, the methods of long-range piloting were worked out, but they were too complicated for the average pilot. In 1944, they focused on ensuring the high-speed range due to the constancy of the enrichment of the mixture and the selection of methods for controlling the motor. As a result, it was possible to bring the range of combatant La-5FN at 90% of the maximum speed to 900 km.
By April 1944, work was completed on the La-5B fighter-bomber project. Like the Yak-9L, the bombs on this aircraft were going to be placed in the inner-fuselage compartment, however, given the shortcomings of the Yakovlev car, it was designed not for the FAB-100, but for 40 small anti-tank PTAB-2.5-1.5. But the customer considered the Il-10 attack aircraft more promising, and the La-5B did not appear.