Tuesday, March 17, 2015

Lavochkin La-5FN

A delay in the testing of the La-5 Type 39 did not stop Semyon Lavochkin's work. During March 1943 the bureau completed the second prototype Type 39, a duplicate powered by the already tested M-82FN engine. Unlike other La-5s it had metal main spars, like those of the Yak-9. Like the series aircraft, however, it was armed with two synchronised ShVAK cannon, and its finish and aerodynamics were even more improved. Pilot A Nikashin managed to attain a speed of 369.7mph (595 km/h) at sea level at augmented power, and 402.6mph (648km/h) at 20,000ft (6,300m). The time to 16,400ft (5,000m) was 4.7 minutes at normal power rating. Reduction of the aircraft's weight to 6,9841b (3, 168kg) enabled it to perform a banked turn at low altitude in 18.5 seconds. Just after these flights the Government issued a decree ordering the aircraft into series-production, and requiring that the performance of the second prototype be matched in the production machines.

This was the last occasion that Semyon Lavochkin and A Nikashin worked together. A skilled pilot and gifted engineer, Nikashin devoted much effort to improving the LaGG and La fighters, and his outstanding role in testing the 1-301 and starting its series-production must be acknowledged. In June 1943 he was killed while testing the Gu-1 fighter designed by Mikhail Gudkov.

Unfortunately, not all of the innovations could be incorporated in series aircraft in the spring of 1943. They had a wing, centre section and other components similar to those of series-built La-5s and a flying weight of 7,2861b (3,305kg).

Performance proved to be rather worse than that of the prototype Type 39. Speed fell to 329.3mph (530km/h) at sea level and 379mph (610km/h) at 19,000ft (5,800m), and time to 16,400ft (5,000m) was about five minutes (a figure typical of all subsequent La-5FNs). Tearing of the fabric covering from the surface prevented tests with augmented power. During the trials, manufacturing defects were noticed.

This did not impede the service tests of the La-5FN. The first series-produced aircraft became operational with one of the best Soviet Air Force regiments of the time, the 32nd Guards Air Corps, commanded by Hero of the Soviet Union Colonel V Davidkov. During the battle of Kursk the regiment's pilots flew 25 combat missions on La-5FNs, bringing down 33 enemy aircraft (including 21 Fw 190As) for the loss of six, four being shot down and two crashing during forced-landings. Soviet aces greatly appreciated the new fighter. Hero of the Soviet Union Captain V Garanin noted:
'Combats were fought at altitudes up to [13,000ft] 4,000m with obvious advantages over the Fw190 and Bfl09, both in speed and in horizontal and vertical manoeuvring. The La-5FN with an open canopy [as Soviet pilots used to fly it] overtakes hostile fighters, albeit slowly, gets on their tails during banked turns, and in a vertical air combat always turns to get above the enemy'.

Shortcomings were also reported. Gun aiming was made more difficult by the presence 50 of the top air intake cowling, which could obscure the target, and by the high position of the sight, which precluded the possibility of flying with the canopy closed. It was claimed that the cockpit was very hot and that exhaust gases entered it, and also that radio communication was inadequate. When assessing the results of the service tests it should be borne in mind that they took place when the opposing forces were very strong. The Soviet pilots faced the Fw190A-4s of the Luftwaffe's Jagdgeschwader 51, assigned to Luftflotte 6, and it is worth comparing the two fighters.

The intention of Focke-Wulf chief designer Kurt Tank to provide the Fw 190 with powerful ordnance and adequate armour led to a considerable growth in payload and, consequently, to an increase in the total flying weight. The Fw190A was at least half a ton heavier than the La-5FN. At the same time, in an effort to ensure maximum speed, Tank opted for a rather high wing loading, which degraded take-off and landing characteristics and manoeuvrability. Of no small importance was the fact that, with similar dimensions, cubic capacity, speed and boost, the power of the M-82FN engine was much greater than that of the BMW 80 ID-2 at altitudes up to 14,700ft (4,500m). It was at low and medium altitudes that the German fighters were most inferior in speed. Even with the MW 50 methanol-water injection system used on the Fw 190A-4 and the La-5FN being flown with its canopy open, the latter had a 9.3 to 15.5mph (15 to 25km/h) higher speed up to 10,000ft (3,000m) and could get on the enemy's tail after the first combat turn.

Kurt Tank's creation had advantages as well. Its all-metal structure had much higher survivability, and vital components were heavily armoured; the pilot's view, both in flight and on the ground, was better; a single master control operated from the central control column greatly facilitated piloting; and its armament was about three times as powerful. On the whole, however, the comparison was not in the Fw 190's favour.

German experts considered the La-5FN the most dangerous threat on the Eastern Front in the summer and autumn of 1943. When one forced-landed on enemy territory, it was repaired by the Luftwaffe and tested extensively. The resulting report was clearly intended to reassure German pilots, as the Soviet fighter was described as 'rather primitive' and 'not completely equipped', and as having 'unreliable equipment, a rudimentary sight and a very troublesome hydraulic system'.

In spite of its merits, the La-5FN was not put into quantity production immediately because M-82FN engines were not available in the numbers required. Production in sufficient quantities and delivery to Gorkii began only in the autumn of 1943, while the other plants continued building La-5Fs.

In November 1943 La-5FN No.39210495 was thoroughly tested at the air force NII by pilot A Kubyshkin and leading engineer V Alexeenko. It was stated that the improved aerodynamic elevator balance made the aircraft nicer to fly, but attention was mainly directed at performance. At a weight of 7,3231b (3,322kg) the La-5FN developed a speed of 336.7mph (542km/h) at sea level (356mph 573km/ h with augmented power), 377mph (607km/h) at 10,500ft (3,250m) and 385mph (620km/h) at 20,000ft (6,150m), maintaining excellent manoeuvrability in both the horizontal and vertical planes.

Aware of the La-5FN's high performance, German pilots refused to engage with them at medium altitudes, trying either to draw them higher or attack them during a final dive.

Soviet airmen gained a tactical advantage from the close external similarity of the La5FN to its slower and less powerful predecessor, the La-5F, because Luftwaffe pilots could not tell them apart.
It is acknowledged that the La-5FNs played an important part in establishing Soviet air superiority and around 1,500 were built up to late 1943.

Lavochkin La-5 with Shvetsov M-71
Work on the installation of the more powerful M-71 engine in the La-5 is interesting. Compared with the series-produced aircraft, the air intake was relocated to the lower portion of the engine cowling, and dual and triple exhaust pipes were fitted in place of the exhaust collector ring. The oil cooler was moved rearwards to position the centre of gravity further aft, and improvements were introduced into the fuselage structure, landing gear and engine mounting. The M-71 delivered 2,200hp (1,641 kW) at sea level, compared with 1,850 hp (1 ,380kW) of the M-82FN at take-off. It was also shorter, reducing the aircraft's overall length by 7.8in (200mm).

The La-5 M-71 was flight tested by G Mischenko from late April to early June 1943. Having made 20 flights he observed:
'Compared with the series-built La-5, the La-5 with the M-71 is less stable longitudinally, which gives it better control sensitivity, easy and pleasant handling, and improved manoeuvrability; landing is simple to perform'.

The aircraft was extensively tested and developed by the LII in the autumn of 1943, the evaluations of stability and controllability being especially exhaustive. On the whole, the comments were favourable, and the aircraft's performance was also pleasing. At a weight of 7,7731b (3,526kg), which had increased because of the heavier engine, it reached 380mph (612km/h) at sea level and 425.6mph (685km/h) at 18,000ft (5,500m).

The main reasons why the La-5 M-71 was not put into production were the unavailability of M-71 engines in sufficient numbers and a reluctance to upset the already organised process of La-5 production.

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