The La-7 fighter was truly the pinnacle of the development of Lavochkin's aircraft during the Great Patriotic War. It surpassed its main enemy, the German FW-190A, in speed, rate of climb and maneuverability, and had quite powerful weapons. Of course, the car also had weak points, caused primarily by the peculiarities of production during the war years. In the initial period of operation, the unreliable operation of the power plant caused problems. The mixed design of the airframe of the aircraft with the predominant use of wooden materials led to the fact that the resource of the La-7 was determined at three years, which was critically small for operation in peacetime. However, during the war, the La-7 was perhaps the best Soviet fighter.
Despite the fact that "La Seventh" appeared in 1944, the story about it should start from the pre-war years. It should be noted that Soviet fighters during the Second World War were a unique phenomenon. In those days, not a single country in the world, except the USSR, created its own fighter aircraft, and indeed military aviation based on wood as the main structural material. In the West, timber-framed combat aircraft were no longer built in the early thirties, and soon linen siding was finally a thing of the past. In our country, almost all fighters created immediately before the war (at least serial ones) had either a mixed or an all-wood design.
It is known that, with equal strength, a duralumin structure is 40% lighter than a wooden one, not to mention such advantages as durability, incombustibility and resistance to weathering. Nevertheless, on the eve of the war, other tendencies prevailed in the USSR. The first place was given to the availability and cheapness of raw materials, simplicity and manufacturability of the design, in short - the possibility of large-scale construction of aircraft at minimal cost and minimal need for qualified workers.
On the basis of this, many argue that our aviation was developing according to the principle of "maybe more in number, at a cheaper price", and this could not but affect its combat capabilities and, ultimately, at the level of losses.
Meanwhile, the war confirmed the correctness of the chosen concept. When, in a few months of the German "blitzkrieg", the production of duralumin in the USSR fell by 80%, the focus on wooden aircraft construction came in handy. Of course, the country's leadership hardly foresaw such a scenario, but history provides many examples when a more than dubious decision suddenly turns out to be the only correct one.
Of the pre-war "triad" of new machines - MiG-1, Yak-1 and LaGG-3 - the latter is the most unusual for its time. Its solid wood construction is unprecedented in the world of fighter aircraft. Comparison with the famous English "wooden miracle" ("Mosquito") is hardly appropriate. Firstly, in "Mosquito" everything is subordinated to one single idea - speed. Its creators did not even think about the possibility of conducting air battles. And although the aircraft subsequently turned into a heavy night fighter, it had to solve completely different tasks than the Lavochkin on the Eastern Front. Secondly, exotic ultra-light balsa and phenol-formaldehyde resins were widely used in the Mosquito design. The creators of LaGG dealt with heavier, but common in our forests, pine and birch.
The widespread belief that LaGG was built from delta timber is not true. This material (wood impregnated with VIAM B-3 plasticizer, which increased its strength) was present only in the spar shelves, ribs and some nodes in the nose of the fuselage. And on La-5, they completely abandoned it, so as not to depend on foreign supplies of chemical components that were not produced in the USSR.
Working with deliberately unprofitable materials, the designers of the Lavochkin Design Bureau managed to create the LaGG-3 fighter, which is generally at the level of modern requirements. Its maximum speed, armament and combat survivability did not cause any particular complaints; But the incurable diseases of the overweight machine - inertia, poor maneuverability, poor climb rate - left the pilot of our fighter with little chance of winning a battle with the Messers. No wonder front-line pilots called LaGG-3 "iron".
Heart transplant - replacing the VK-105 water-cooled engine with the M-82 radial engine breathed new life into the aircraft. The new engine was 250 kg heavier than its predecessor, however, due to the abandonment of fluid cooling systems (radiator, pipelines, pumps, etc.), it was possible to keep the takeoff weight of the car at the same level. But the power of the power plant increased from 1050 to 1330 hp. Flight performance has improved accordingly. In March 1942, the plane, designated LaGG-3 M-82, successfully passed factory tests at the airfield of the Gorky plant number 21 - the head enterprise for the production of LaGGs.
The data for the new machine were so promising, and the need for it was so strong that, in parallel with the treatment of its "childhood diseases" and even before the state tests, preparations began for mass production. In October 1942, the fighter, named La-5, went to the troops.
Meanwhile, although the new fighter was superior to its predecessor in almost all parameters (except for horizontal maneuverability), it was never able to achieve the indicators of the Me-109G and FW-190, which appeared at about the same time on the Eastern Front. In addition, the aircraft was characterized by a suffocating heat in the cockpit caused by poor thermal insulation of the engine and lack of ventilation, not very reliable operation of the engine and weapons. And although, as the serial production was deployed, these shortcomings were gradually getting rid of, the La-5 did not bring our aviation a qualitative superiority over the enemy. Therefore, in the fall of 1942, the Lavochkin Design Bureau began work on the further modernization of the fighter.
Engineers began to reduce the weight of the car while increasing engine power. In December, they conducted state tests and put into the series La-5F with the M-82F engine (forced). The mass of the aircraft decreased due to the abandonment of cantilever gas tanks (such aircraft were called "three-tank", in contrast to the earlier "five-tank") and, a number of other, smaller tweaks. The thickness of the armor plate has been reduced by 1.5 mm, the landing headlight has been removed, etc. The fuel supply dropped by 60 liters. Accordingly, the flight range was reduced, but it was considered insignificant, the main thing was to catch up with the Messerschmitt. And so far it has not been possible to catch up.
On the prototype, which was tested in April 1943, in order to facilitate, even one of the two ShVAK cannons was replaced with a UB machine gun. However, they did not dare to "put on stream" the fighter with weakened armament.
The next step was La-5F, lighter, with improved visibility. On it, the rear-side gargrot was lowered and the glazing area of the rear part of the lantern was increased. Instead of an armored headrest, a 66-mm bulletproof glass appeared.
Finally, in May 1943, state tests of the La-5 with the M-82FN engine took place (in the spring of 1944 it was renamed ASh-82FN - forced with direct injection). The takeoff power of the engine increased to 1850 hp, the maximum power - up to 1630 hp.at the first and 1500 - at the second border of altitude. In addition, on the La-5FN, the thermal insulation of the cab was improved, the efforts on the controls were reduced and the landing gear was lightened. The external distinguishing feature of the new modification is the long engine intake manifold on top of the hood.
La-5FN first appeared at the front in the summer of 1943, during the battles on the Kursk Bulge. In Soviet times, it was indicated that this version of the La-5 achieved complete qualitative superiority over the German fighters of that period. As evidence, data from comparative flight tests with captured aircraft were cited. But at first glance, quite convincing figures require serious critical analysis.
First of all, the brand-new, carefully adjusted La-5FN was compared to aircraft worn out in battles, or even survivors of forced landings. Our mechanics did not possess the peculiarities of setting the parameters of German power plants. Serial La-5FN, due to the lower production culture than on the prototypes, had correspondingly lower flight performance. By the way, when the Germans tested the captured La-5, they received data that were strikingly different for the worse from the test results of this fighter at the Air Force Research Institute. If we compare the results of tests of German machines, obtained under comparable conditions, with the tactical and technical characteristics of the La-5FN, it turns out that in a number of parameters we again had to act as a catch-up.
The situation was further complicated by the fact that the ASh-82FN engine had exhausted its forcing reserves. Attempts to further increase power were unsuccessful, and there was nowhere to take any other power plant for the La-5. There were only two ways left: another weight reduction and a scrupulous "licking" of aerodynamics.
Back in April 1943, a full-scale instance of the La-5 was tested in the T-104 wind tunnel of TsAGI in order to determine the factors affecting the decrease in drag. As a result, recommendations appeared on the introduction of a number of improvements into the series, which together provide an increase in speed by 30-35 km / h. The greatest effect was given by the internal sealing of the aircraft - 24 km / h - and the complete closure of the landing gear -6 km / h. In addition, it was noted that transferring the oil cooler from under the hood to the fuselage, where the cross-sectional area is much smaller, halves its drag and increases air flow through the radiator by 35%.
Later, it was found a positive effect on the aerodynamics of the machine by transferring the air intake of the power plant, from the roof of the hood to the root of the center section. So, literally drop by drop, additional kilometers of speed were gained.
When it comes to weight loss, this was also not an easy task. There was practically nothing left on the plane that could be painlessly removed. And to lighten the structure by reducing the strength and endurance (as did A. S. Yakovlev) S. A. Lavochkin did not. But there was another huge reserve - the replacement of wooden structural elements with metal ones.
In 1943, an all-metal wing spar was developed for the La-5, consisting of steel T-flanges connected by duralumin walls. The weight gain was 100 kg. This alone shows how much wood is inferior in weight efficiency to "winged metal".
At the end of 1943, La-5 No. 206 appeared with partially improved aerodynamics. And at the very beginning of 1944, the construction of a new modification, originally designated as "La-5 - the standard of 1944", was completed. On it, in addition to the installation of metal spars, all TsAGI recommendations for aerodynamic refinement of the machine were taken into account. First of all, external and internal sealing of the propeller group and the airframe was introduced, additional flaps were installed that completely cover the landing gear. The oil cooler was moved under the fuselage, and the suction pipes of the supercharger were placed in the nose of the center section. We changed the shape of the wing fairings, reduced the number of bonnet covers and reduced the size of the movable side flaps.
In addition, to reduce the effort on the handle, the aerodynamic compensation of the elevator was increased. Instead of the previous control handle with a grip for both hands, a shortened P-1 "Messerschmitt" handle, such as under the right hand, was installed. The engine was equipped with individual cylinder exhaust pipes and a new variable pitch propeller VISH 105V-4 was installed. The landing gear struts were extended by 80 mm, and an anti-hood frame was installed in the rear of the canopy.
Armament became much more powerful. Instead of a pair of SP-20 cannons (a synchronous version of the ShVAK cannon), three new UB-20 Berezin cannons were installed. On February 2, 1944, this aircraft, which was destined to become the best Soviet fighter of the Second World War, took off. Factory test results have been very encouraging. The maximum speed at the ground was 597 km / h, against 546 km / h for the La-5FN and 560 km / h for the FW-190A-5.
On February 16, the car was handed over to state tests, which were not without troubles. On February 20, due to an engine accident in flight (broken connecting rod), test pilot Kubyshkin barely landed the plane. The tests continued on March 8th. And on March 22, when most of the program had already been worked out, due to a gross assembly defect in the taxiing, one of the fuselage frames collapsed. And this time the pilot's skill helped to avoid a serious accident.
But, despite all the difficulties, on March 27, the test cycle was successfully completed. By this time, the design bureau received the task of the State Defense Committee to bring the maximum speed of the La-5FN to 685 km / h. The new fighter was supposed to be the answer of Lavochkin's designers to this task.
In the test report, Major Kubyshkin pointed out that the “standard” had significantly increased speed characteristics compared to the standard La-5FN. At an altitude of 6,000 m, the fighter accelerated to 680 km / h - the best result of all Soviet fighters of that period.
But aerodynamic perfection came at a high price. When the engine was running at high revs, the temperature in the cab reached 40 degrees (in February) and there was a strong smell of exhaust gases and burnt rubber. Thus, the "birth defect" of the early La-5s - poor thermal insulation - again declared itself.
The situation was aggravated by the fact that with the installation of an oil cooler under the fuselage, pipelines with hot oil began to pass directly under the pilot's feet, and the external sealing of the hood forced exhaust gases through the smallest cracks into the cockpit. It is clear that in such conditions, ordinary flight, not to mention air combat, turns into torture. In addition, the tester noted that moisture condensation accumulates in the cab (another result of the lack of ventilation), the loads on the pedals are excessively large, and a quick emergency exit from the car is not provided.
But despite this, the conclusion of the report read: “According to its flight data, the aircraft is one of the best fighters. It is necessary to speed up the serial construction with the simultaneous elimination of the above defects. This was followed by specific recommendations: to improve the thermal insulation and ventilation of the cockpit, to facilitate emergency exit from the aircraft, to reduce pedal forces, to improve the cooling of the cylinder heads and to facilitate the control of the propeller group, for which to make a combined control of the propeller pitch and gas, install an automatic blower speed changeover and an automatic valve control hood.
Such automation was installed on the Focke Wulf 190 fighter, due to which a complex change in the operating parameters of the power plant was carried out with one movement of the throttle. The pilots of the "Lavochkin" had to do up to eight consecutive movements for this, which is practically impossible in the fleeting conditions of air combat.
Unfortunately, when the new fighter was launched into the series, only one of these recommendations was fully implemented: a mechanism for automatic change of the propeller pitch was installed (it is not clear why this was not done earlier, because "VISH-automata" were known back in the thirties). Attempts to normalize the temperature inside the cockpit by attaching heat-insulating covers to the oil tank and oil pipelines gave almost nothing, and the severe heat, which reached 55 degrees in the summer months, continued to complicate the already difficult work of the pilots.
Only later, on some production vehicles, a ventilation cap appeared over the frontal armored glass. Then the ventilation air intakes were placed in the leading edge of the center section. The external air boost prevented hot gases from the engine from entering the cab, and the microclimate improved markedly. As for the automatic adjustment of the motor modes, devices of this kind for the ASh-82FN appeared after the war.
Meanwhile, with all its shortcomings, the aircraft at altitudes up to 6000 m surpassed in flight characteristics almost all types of both domestic and German piston fighters.
In the first days of May, the "standard of 1944" under the new name La-7 was put into mass production. It is noteworthy that in July the last LaGG-3 rolled off the assembly line of the Tbilisi plant No. 31. The production of La-5FN (already with metal spars) continued, gradually decreasing until November 1944.
