perjantai 3. huhtikuuta 2015
The Lavochkin La-7 (Russian: Лавочкин Ла-7) was a piston-engined Soviet fighter developed during World War II by the Lavochkin Design Bureau (OKB). It was a development and refinement of the Lavochkin La-5, and the last in a family of aircraft that had begun with the LaGG-1 in 1938. Its first flight was in early 1944 and it entered service with the Soviet Air Forces later in the year.
A small batch of La-7s was given to the Czechoslovak Air Force the following year, but it was otherwise not exported. Armed with two or three 20 mm (0.79 in) cannon, it had a top speed of 661 kilometers per hour (411 mph). The La-7 was felt by its pilots to be at least the equal of any German piston-engined fighter and even shot down a Messerschmitt Me 262 jet fighter. It was phased out in 1947 by the Soviet Air Force, but served until 1950 with the Czechoslovak Air Force.
By 1943, the La-5 had become a mainstay of the Soviet Air Forces, yet both its head designer, Semyon Lavochkin, as well as the engineers at the Central Aerohydrodynamics Institute (Russian: TsAGI), felt that it could be improved upon. TsAGI refined earlier studies of aerodynamic improvements to the La-5 airframe in mid-1943 and modified La-5FN c/n[Note 1] 39210206 to evaluate the changes. These included complete sealing of the engine cowling, rearrangement of the wing center section to accommodate the oil cooler and the relocation of the engine air intake from the top of the cowling to the bottom to improve the pilot's view.
The aircraft was evaluated between December 1943 and February 1944 and proved to have exceptional performance. Using the same engine as the standard La-5FN c/n 39210206 had a top speed of 684 kilometers per hour (425 mph) at a height of 6,150 meters (20,180 ft), some 64 kilometers per hour (40 mph) faster than the production La-5FN. It took 5.2 minutes to climb to 5,000 meters (16,404 ft). It was faster at low to medium altitudes than the La-5 that used the more powerful prototype Shvetsov M-71 engine.
Length: 8.6 m (28 ft 3 in)
Wingspan: 9.8 m (32 ft 2 in)
Height: 2.54 m (8 ft 4 in)
Wing area: 17.59 m2 (189.3 sq ft)
Gross weight: 3,315 kg (7,308 lb)
Powerplant: 1 × Shvetsov ASh-82FN 14-cylinder, two-row, air-cooled radial, 1,230 kW (1,650 hp)
Propellers: 3-bladed VISh-105V-4
Maximum speed: 661 km/h (411 mph; 357 kn) @ 6,000 meters (19,685 ft)
Range: 665 km (413 mi; 359 nmi) (1944 model)
Service ceiling: 10,450 m (34,285 ft)
Rate of climb: 15.72 m/s (3,095 ft/min)
Time to altitude: 5.3 minutes to 5,000 meters (16,404 ft)
Armament: 2 × 20 mm ShVAK, 200 rds per gun or 3 × 20 mm Berezin B-20 cannons with 100 rds per gun
Bombs: 200 kg (440 lb) of bombs
Lavochkin had been monitoring TsAGI 's improvements and began construction in January 1944 of an improved version of the La-5 that incorporated them as well as lighter, but stronger, metal wing spars to save weight. The La-5, as well as its predecessors, had been built mostly of wood to conserve strategic materials such as aircraft alloys. With Soviet strategists now confident that supplies of these alloys were unlikely to become a problem, Lavochkin was now able to replace some wooden parts with alloy components. In addition Lavochkin made a number of other changes that differed from c/n 39210206.
The engine air intake was moved from the bottom of the engine cowling to the wing roots, the wing/fuselage fillets were streamlined, each engine cylinder was provided with its own exhaust pipe, the engine cowling covers were reduced in number, a rollbar was added to the cockpit, longer shock struts were fitted for the main landing gear while that for the tail wheel was shortened, an improved PB-1B(V) gunsight was installed, and a new VISh-105V-4 propeller was fitted. Three prototype 20 mm (0.79 in) Berezin B-20 autocannon armed the 1944 standard-setter (Russian: etalon), as the modified aircraft was designated.
The etalon only made nine test-flights in February and March 1944 before testing had to be suspended after two engine failures, but quickly proved itself to be the near-equal of c/n 39210206. It was 180 kilograms (400 lb) lighter than the earlier aircraft, which allowed the etalon to outclimb the other aircraft (4.45 minutes against 5.2 minutes climb to 5,000 meters). However it was 33 kilometres per hour (20.5 mph) slower at sea-level, but only 4 kilometers per hour (2.5 mph) slower at 6,000 meters (19,685 ft). The flight-tests validated Lavochkin's modifications and it was ordered into production under the designation of La-7, although the B-20 cannon were not yet ready for production and the production La-7 retained the two 20-mm ShVAK cannon armament of the La-5.
Five La-7s were built in March by Factory (Russian: Zavod) Nr. 381 in Moscow and three of these were accepted by the Air Force that same month. The Moscow factory was the fastest to complete transition over to La-7 production and the last La-5FN was built there in May 1944. Zavod Nr. 21 in Gorky was considerably slower to make the change as it did not exhaust its stock of wooden La-5 wings until October. The quality of the early production aircraft was significantly less than the etalon due to issues with the engine, incomplete sealing of the cowling and fuselage, and defective propellers.
One such aircraft was tested, after these problems had been fixed, by the Flight Research Institute (Russian: Lyotno-Issledovatel'skiy Institut) and proved to be only 6 kilometers per hour (3.7 mph) slower than the etalon at altitude. Aircraft from both factories were evaluated in September by the Air Force Scientific Test Institute (Russian: NII VVS) and the problems persisted as the aircraft could only reach 658 kilometers per hour (409 mph) at a height of 5,900 meters (19,357 ft) and had a time to altitude of 5.1 minutes to 5,000 meters.
Combat trials began in mid-September 1944 and were generally very positive. However four aircraft were lost to engine failures and the engines suffered from numerous lesser problems, despite its satisfactory service in the La-5FN. One cause was the lower position of the engine air intakes in the wing roots of the La-7 which caused the engine to ingest sand and dust. One batch of flawed wings was built and caused six accidents, four of them fatal, in October which caused the fighter to be grounded until the cause was determined to be a defect in the wing spar.
Production of the first aircraft fitted with three B-20 cannon began in January 1945 when 74 were delivered. These aircraft were 65 kilograms (143 lb) heavier than those aircraft with the two ShVAK guns, but the level speed was slightly improved over the original aircraft. However, the time to climb to 5000 meters increased by two-tenths of a second over the older model. More than 2000 aircraft were delivered before the war's end, most by Zavod Nr. 21. A total of 5753 aircraft had been built by Zavod Nr. 21, Nr. 381, and Nr. 99 in Ulan-Ude, when production ended in early 1946.