Aviation of World War II
In 1943, TsAGI continued intensive experimental research to further improve the aerodynamics of the La-5FN. At the same time, the designers also improved their aircraft. As a result, already at the beginning of 1944, a new La-7 fighter was launched for testing. It was distinguished by a lightweight design (finally, metal spars appeared on La planes), enhanced armament and better aerodynamic properties. There are two ways to improve the flight data of an aircraft: by reducing the weight of the airframe and improving aerodynamics. Lavochkin also 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. Due to supplies under Lend-Lease and the establishment of production in the depths of the USSR, the situation with aluminum was facilitated. Replacing wooden structures with metal ones is a big reserve for saving weight. One replacement of wooden wing spars with duralumin ones with steel shelves reduced the weight by 100 kg. It must be said that by this time there was no longer delta-wood in the airframe design - due to the lack of resin, ordinary pine and birch gradually replaced it from the structure. Drawings of the metal wing spars and the center section were developed in the summer of 1943 in Nizhniy Tagil at the plant No. 381 under the leadership of the chief designer P.D. Grushin - later an outstanding designer of anti-aircraft missiles.
Considering a number of disasters that occurred with the La-5, on the "standard of 1944" in the rear of the canopy, an anti-hood frame was installed. The frame could save a pilot's life if the plane turned over during takeoff or landing (unfortunately, the frames did not appear on production machines, which led to the death of more than one pilot, including the famous ace A.F.Klubov from the 9th GIAP).
The characteristics of speed and rate of climb can be assessed as "standard", somewhat superior to those of the La-5FN fighter. The maximum speed at an altitude of 6,000 m was 680 km / h. Aileron and elevator control - does not require much effort and does not need further improvements. The canopy provides excellent all-round visibility from the cockpit. The maneuvering and takeoff and landing characteristics of the aircraft fully meet the requirements. However, the results came at a heavy price.
Due to the transfer of the oil cooler under the fuselage, the oil lines had to be laid directly under the pilot's feet, which is why the normal temperature in the cockpit was +40 degrees C in winter, and in summer it increased to +55 degrees. FROM. Considering that engine exhaust gases were leaking into the cockpit, and condensation was forming on the glass of the canopy, it is quite possible to compare the cabin of the "standard" La-7 with a sauna.
The main external difference between La-7 and La-5FN was the transfer of the oil cooler from under the engine hood to the lower part of the fuselage under the cockpit, and the air intakes of the carburetor and supercharger to the wing root. Part of the air entering through these intakes was taken for ventilation of the cabin. Air was supplied to the cockpit through the holes under the dashboard and in the cockpit floor between the rudder pedals, and exited through the hole in the tail segment of the cockpit canopy. However, for some time, serial aircraft with ventilation holes in the side of the fuselage in front of the cockpit canopy continued to be produced. Tests of the La-7 with an improved ventilation system were carried out from March 19 to March 23, 1945, 10 flights were performed, Colonel DG Pikulenko flew.
In addition to the excellent flight characteristics, the tests also revealed a number of shortcomings - often the hydraulics failed, there were interruptions in the operation of the motor. The last defect remained the real scourge of the La-7 until the very end of the war; it was connected with the transfer of air intakes from the engine hood to the roots of the wing planes - places more vulnerable to dust ingress during takeoff and landing, dust and soil particles led to engine failures. In frosty weather, when the La-7 was undergoing State tests, there was no dust at the airfields, so they could not identify the defect in time. An attempt to get rid of the defect was the installation of filters on the air intakes and the appearance of additional air intakes on the lower surface of the wing planes in front of the wells for cleaning the wheels of the main landing gear. State tests of the aircraft modified in this way (serial number 38102663 took place from May to the end of June 1945, the test results were considered unsatisfactory. Engine failures happened on the La-7 much more often than on the La-5FN).
Aircraft of various production series externally differed from each other in small details, such as the shape of the panels covering the joints of the wing and fuselage planes, the location of the cockpit canopy opening handle, etc. Often all sorts of minor improvements in the design of the aircraft were introduced by the mechanics of the combat units of the Air Force, the most common of which were the installation of a rear-view mirror and improved ventilation of the cockpit.
It was the most perfect fighter of the S.A. Design Bureau. Lavochkin and one of the best combat aircraft of the Second World War.
Armament Armament consists of two or three 20-mm automatic cannons, equipped with a hydromechanical synchronizer that prevents projectiles from entering the propeller blades. Most of the La-7 fighters were armed with two ShVAK guns with 200 rounds per barrel. A relatively small number of La-7s received the originally intended standard armament of three B-20 cannons with 170 rounds of ammunition per barrel. The reliability of the B-20 cannon was lower than required, which was confirmed by tests of the three-point La-7 at the Air Force Research Institute from September 10 to October 10, 1945. Of the three aircraft (serial numbers 45214414, 45214415, 45214416) that took part in the tests, none managed to achieve the required figure of 5,000 fired from one aircraft without failure of shells. On the first fighter, this figure was 3275 shells, on the second - 3222, on the third - 3155.
An attempt to solve the problems in the reliability of the B-20 cannons radically was the installation of a 23 mm NS-23 cannon on the La-7. The aircraft with the new weapon was tested from July 20 to July 31, 1945, the results were again disappointing - the weapon worked unreliably. The repeated tests of the La-7 fighter armed with NS-23 cannons, which took place from October 2 to 10, 1945, became more successful. The NS-23 cannon, along with the B-20, was put into service. It is regrettable that the B-20 was chosen for the La-7.
Several La-7s received onboard armament from three ShVAK cannons with ammunition of 130 rounds per barrel, but these aircraft turned out to be overloaded, since the mass of one ShVAK cannon in the motor version is 44.5 kg, while the mass of the B-20 cannon - 25 kg. The muzzle velocity of the projectile fired from the ShVAK cannon is 215 m / s, the rate of fire is 800 rounds / min. The ammunition kit includes armor-piercing incendiary shells weighing 180 g (capable of penetrating armor up to 20 mm thick) and incendiary fragmentation shells weighing 180 g. On two underwing nodes, it is possible to suspend bombs weighing up to 100 kg (each). The most frequently used high-explosive bombs FAB-50 and FAB-100, as well as incendiary ZAB-50 and ZAB-100; 50 and 100 - the mass of the bomb, 50 kg and 100 kg.
It should be noted that the installation of 3 ShVAK cannons on the aircraft was impossible due to their heavy weight. The weight of the ShVAK cannon in the motor version was 44.5 kg, while the B-20 was only 25 kg.
La-7 fighters at the airfield. On the left, with tail number 06, armed with three B-20 guns. From G.F. Petrov.
La-7 production continued until the end of 1945, a total of 6,158 vehicles were built. Plant NKAP # 21 in Gorky built 4610 aircraft, Moscow plant # 381-1298, plant # 99 in Ulan-Ude - 250 fighters.
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* Forcing of the engine during 10 minutes.
** On speed making 90 % from maximal.
La-7 with ASh-71
At the beginning of 1943, work began on the La-5 with an alternative power plant at the Lavochkin Design Bureau. Great hopes were associated with the new ASh-71F engine. The air-cooled double star had a power of 2200 hp. - by as much as 350 hp than ASh-82FN. The installation of a promising engine could dramatically improve the performance of the La-5.
The development of the ASh-71 began in 1940, it was a pair of two nine-cylinder radial engines M-63 and had direct fuel injection into the cylinders. In turn, the M-63 engine was an improved copy of the American Wright-Cyclone R-1820 G-5 engine. The mass of the ASh-71 engine with all the necessary units was 1556 kg.
The first copy of the ASh-71 developed a power of 2000 hp. - almost twice as much as the M-105 water-cooled engine with an in-line arrangement of cylinders that was on the Yak-1 and LaGG-3. At an altitude of 2600 m, the ASh-71 engine developed a power of 1800 hp, at an altitude of 6250 m -1670 hp. The refinement of the motor, however, took a long time - the first ASh-71, which had a more or less acceptable level of reliability, appeared at the beginning of 1942.
The first flight of the La-5 with ASh-71F was made on April 28, 1943, just a few weeks after the first flight of the La-5FN. From late April to June 1943, the aircraft was tested at the LII base in Sverdlovsk. The maximum speed near the ground was 612 km / h, at an altitude of 5500 m - 685 km / h, which was 50 and 37 km / h more than the corresponding indicators of La-5FN. In general, the characteristics demonstrated by the La-5 with the ASh-71F turned out to be lower than the calculated ones, so it was decided to organize the aircraft purge in the T-104 wind tunnel. Before purges, the camouflage coloring was washed off the aircraft.
The purges helped to find the reason for the significant discrepancies between the true and calculated characteristics - the poor quality of the external surfaces, especially the engine hoods. TsAGI engineers came to the conclusion that after correcting the shortcomings, the aircraft is capable of speeds of the order of 720 km / h.
In order to further improve flight performance, attempts were made to install more powerful engines on the La-7. Vehicles equipped with ASh-71 and ASh-83 engines were built. The La-7 ASh-71 program was quickly curtailed due to the fact that the M-71 engine was not mass-produced, and its credibility after a number of failures (in particular, with the I-185) was thoroughly undermined.
Another version of the La-7 was an aircraft equipped with an ASh-71TK engine with a power of 2027 hp. The ASh-71TK installation did not lead to the expected improvement in flight characteristics.