Tuesday, March 17, 2015

Lavochkin La-5F

The La-5F from 303-rd Division 1-st Air Army at 1944.

Service tests of the La-5 revealed a many defects. In combat it was inferior to the Messerschmitt Bf109, but it had great development potential. This was appreciated by Semyon Lavochkin, who constantly thought about his new creation. Aerodynamic improvements, engine updating, better cockpit view, control enhancement and weight reduction were the main aims of the work carried out during late 1942 and early 1943. A government decree issued on 9th December 1942 authorised development work on the fighter.

To increase maximum level speeds, extensive research using four series-produced aircraft was made jointly by the Tsentral'nyi Aerogidrodynamichesky Institut (TsAGI Central Aerodynamic and Hydrodynamic Institute), the LII and the Tsentral'nyi Institut Aviatsionnogo Motorostoeniya (TsIAM - Central Institute of Aviation Motors ).

The principal modifications resulting from this work were:
• the engine cowling joints were sealed;
• the shape of the oil cooler ducts was improved;
• a new inlet pipe was fitted;
• the area of the exhaust pipe cross-section was increased;
• the tailwheel doors were stiffened.

The test results showed that speeds equal to those of the LaGG-3 M-82 prototype, which the series-built aircraft had failed to match, could be attained. Together with engine designer and builder Arkady Shvetsov, Lavochkin's workers sought to eliminate the M82' s main deficiencies, namely spark plug failures after five to ten hours' use, unsatisfactory oil pump capacity and a tendency for the 44 exhaust pipes to burn through. As a result of the measures taken, engine service life increased from 100 to 150 hours, and the operating time at augmented power was not limited, allowing pilots to build up supercharger pressure without fear of the consequences. Thus the M-82F engine was created, and from January 1943 its series-production and installation in the Lavochkin fighter (consequently designated La-5F - Forsirovanny, enhanced, or literally 'boosted') began.

Work on the installation of an M-82FNV, augmented by direct fuel injection into the cylinder heads, in place of the carburettor-equipped M-82 and M-82F, proved promising. Development tests of the La-5FNV showed that speed increased to 340.5mph (548km/h) at sea level and 384.6mph (619km/h) at 18,400ft (5,600m) at normal power rating, and the engine later went into series-production as the M-82FN. This boost allowed an increase in take-off power of 1,700 to 1,850hp (1,268 to 1,380kW), and in normal power from 1,300hp (969.8kW) at 17,700ft (5,400m) to 1,460hp (1,089kW) at 15,250ft (4,650m) without ram-air.

To improve the pilot's view, from the ninth batch (November 1942) the fighter was given a lower dorsal rear fuselage fairing and a teardrop canopy with armoured glass; in spite of pilots' wishes the windshield was not armoured. This work was similar to that carried out on the Yak-1.

At about the same time, in November 1942, the control column to control surface and aileron gain was changed in accordance with the chief designer's instructions. The shape of the trim tabs was repeatedly altered, the control surfaces were reduced in in area, and flap area was increased. These alterations gave a more favourable combination of controllability and manoeuvrability.

In attacking the problem of reducing the fighter's excessive weight, the designers did not leave a single component unaltered. The wing centre section, the canopy, the landing gear and the powerplant were revised and lightened without detriment to structural strength. The attachment fitting of the landing gear shock struts was welded directly to the front spar, and the shock strut stroke was increased to soften shock absorption. Changes in the structure of the main spars made it possible to reduce the total weight of the wing. The fuel system was altered to use three fuel tanks instead of five, reducing fuel capacity from 118.5 to 102 gallons (539 to 464 litres) and eliminating the wingtip tanks which hampered manoeuvrability.

The first aircraft incorporating all of these changes was sent to the NIl WS and LII, where it was tested during December 1942 and January 1943. The results of the tests pf a full-scale aircraft in the TsAGI wind tunnel were also taken into account.

In accordance with the development process at Plant No.21, the prototype was designated Type 39 (the previous La-S had been designated Type 37). Its weight was reduced to 7,054lb (3,200kg), the dorsal fairing was lower, the cockpit gave a better rearward view and fuel tankage was reduced. One of the synchronised cannon was replaced by a large calibre synchronised machine gun.

The test results were outstanding. The aircraft reached 321.8mph (518km/h) at sea level at normal power rating, and 345.4mph (556km/h) with augmented power (a speed not previously attained by Soviet fighters), 361.6mph (582km/h) at 11 ,800ft (3,600m) and 372.8mph (600km/h) at 20,500ft (6,300m). Manoeuvrability was good; a banked turn was performed in 18 to 19 seconds, and the aircraft climbed 3,200ft (1,000m) within a combat turn at normal power rating. During the tests the M-82F was augmented at the second supercharger speed for the first time, and this increased the maximum speed to 380 mph (612km/h) at 19,000ft (5,800m). Tests could not be completed owing to failure of the transmission system for the supercharger's second speed. Additionally, pilot A Kubyshkin found the structural strength of the lightened La-5 inadequate during diving tests.

The new La-5 resembled the first series built aircraft only superficially. Tests carried out by Plant No.21 in January and February 1943 confirmed that the speed increment was 18.6mph (30km/h), and that all the other performance figures had improved. Even range was not greatly diminished, because the saving of 3301b (150kg) in weight gave the fighter greater endurance despite its reduced fuel tankage. The La-5F began to be widely used on all fronts during the Soviet winter counter offensive of 1942 and 1943.

The 215th Fighter Air Division commanded by Lieutenant General G Kravchenko, twice declared a Hero of the Soviet Union, gained complete familiarity with the La-5 before running the Leningrad blockade. From 6th January to 26th February 1943 the 215th flew 1,761 missions, during which it shot down 103 enemy aircraft, the 2nd Guards Fighter Air Corps under Col E Kondrat giving a particularly good account of itself. However, 26 pilots were lost, Division Commander G Kravchenko and Major Kuznetsov, Commander of the 233rd Fighter Air Corps, being among the officers killed.

The fate of First Lt P Grazhdaninov was unusual. After arriving at the 169th Fighter Air Corps with other ferry pilots he remained there. An outstanding fighter pilot, he completely mastered the La-S but did not survive long, being killed in battle on 5th March 1943, by which time he had scored 13 victories.

The 4th Guards Fighter Air Corps of the Baltic Fleet was converting from the Polikarpov 1-16 to the La-5 in April 1943. Although the pilots and their commander, Major V Golubev, considered the La-5 a modern aircraft not inferior to the Bfl09F and Fw190A in speed, they became aware of its disadvantages: a tendency to turn sharply to the right during take-off, difficult to taxy on soft ground and a propensity for the engine to overheat during ground running.

These and other defects were observed at the other fronts as well. When large numbers of La-5s began to enter service in early 1943, the failure rate was three times as great as those of other fighters. Urgent measures were required to improve reliability. Specifically, Viktor Rastorguev and Alexey Grinchik conducted inverted spinning tests in early 1943, and as a result recommended piloting techniques for the La-5 were passed to operational units. Previously, pilots in these units had abandoned their aircraft if they entered an inverted spin.

Some comment is required regarding the La-5's survivability. The use of self-sealing fuel tanks and an inert gas system in two areas, and, of course, the use of a highly-survivable air-cooled engine, placed the aircraft in a good light compared with LaGG-3s and Yaks. However, only in early 1943 were radical improvements achieved. The adoption of central fuel tanks of greater capacity, relieving the wings their hazardous fuel load, and the drastic shortening of the fuel and oil lines resulted in a reduction in combat losses, especially during ground-attack sorties.

In the spring of 1943 the La-5 was not inferior to its opponents with regard to combined flying qualities. At that time Plant No.21 was sending 350 to 400 La-5s to the lines monthly, and Plant No.99 in Ulan-Ude and Plant No.381 in Moscow also started assembling the type. This allowed certain reserves to be accumulated by the summer. On 1st July the forces in the field had 978 La-5s and La-5Fs, more than a quarter of all the fighters available. Only 85 needed repair; the rest were combat-ready on the eve of the great battle of the Kursk Bulge. Among those keeping watch in La-5 cockpits was Ivan Kozhedub of the 240th Fighter Air Corps, unknown at the time but destined to become the greatest Soviet ace. By early June 1943 about 200 aircraft powered by M82FNs had been assembled; they were delivered unfinished to service units.

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