Lavochkin La-5FN

After designing the LaGG-3, the designers split on how to increase is performance. Improved production and experimental variants of this aircraft with water-cooled engines did not provide a satisfactory solution. Then a radical solution came with the suggested installation of the M-82 14-cylinder radial air-cooling engine, which was lighter and much more powerful than engines of M-105 family. What was also ideal was that M-82 production was well set and huge stocks of this engine were available. Created to power single-engine bombers of the Su-2 class, it just waited for another airframe to be fitted to. V.P.Gorbunov and M.I.Goudkov came up with their solutions, slightly different by the degree of modifications to the LaGG-3. But their conversions (LaG-5 and Gu-82) had only limited success.

S.A.Lavochkin also managed to modify the LaGG-3 to accept this engine, despite the lack of official support. Lavochkin's Factory N°153 (Novosibirsk) was taken over by A.S.Yakovlev (the Yak-1 was in production there in parallel with the LaGG-3). He was left with only a nucleus of his team in Tbilisi. He was so out of official favor that the factory director refused to cooperate with this potential saboteur and enemy of the people. So the La-5 prototype was assembled and kept out in the 'open' and was ready at the very end of 1941. After factory trials the La-5 was evaluated by the military in May 1942 and approved for pre-production.

Ten pre-production aircraft were found to be 40 to 50km/h slower than the prototype. A specially assigned group of TsAGI aerodynamic experts traced the problem to gaps in the engine cowling and it was quickly cured. Vibration problems caused by the lack of propeller blade balance were also fixed. But when two aircraft were lost in fatal accidents due to wing failure, the test flights were halted. Only after exhaustive searching and ground tests did Lavochkin find the cause. Factory workers had been enlarging the holes for the wing attachment bolts to make them easier to assemble - but this weakened the wing and caused its failure. After the positive conclusion of its trials the La-5 was rushed into production and front line service. The first regiments were manned by factory pilots and arrived at Stalingrad in September1942. As many as 1129 were assembled during 1942

This aircraft used the same delta-wood technology as the LaGG-3 and shared a lot of its components. The La-5 also had a retractable tail wheel (it was fixed on the LaGG-3). Early batches even had a 2-layer nose section, one (inner) inherited from the LaGG-3 and another (outer) just an aerodynamic transition from the large diameter M-82 cowling to the slim LaGG-3 fuselage. Without production interruptions, numerous changes were made. Delta-wood relied on imported epoxy, and was gradually replaced by thicker (but less dense) pine parts - and later by metal ones. From 1943 on the fuselage behind the cockpit was lowered, providing a better view for the pilot.

The flow of cooling air was provided by a pair of large adjustable louvers on each side of fuselage. This solution proved to be no less efficient than commonly used 'all-round' cooling gills, but more technological and reliable. It became a common feature for the entire line of Lavochkin's piston engined fighters. On the La-5 these louvers had an articulated fairing (covering the large diameter joint exhausts). This was deleted in later aircraft of this type. Other 'marks' of production of the La-5 were a step-shaped nose intake - pushed up in later models with supercharged engines.

In 1943 more powerful engines were fitted. Experiments with the M-71 were officially discouraged. The boosted M-82F was installed on some batches of production aircraft. Those differed by a Cyrillic 'F' painted on the engine cowling. All M-82F powered aircraft had a cut-down upper fuselage. Those aircraft are often referred to as the La-5F. But this is not an official designation and a number of 'Lavochkins' with an all-around canopy had an original M-82 engine.

Like all Soviet aircraft, the La-5 offered little in the way of cockpit sophistication and pilot comforts. In the Summer time cockpit ventilation was insufficient, and pilots complained about excessive heat coming from the engine. But as a fighting aircraft, it was exceptional. The La-5 inherited the 2-level neutral gas protection of the fuel tanks that was used on the LaGG-3. With less vulnerable radial engines the La-5 was a very hard-to-kill aircraft. And the Pilot was protected by a 10mm armor seat back.

Built in a few different variants, the La-5 is often poorly represented by Western sources. Designations used are often wrong or misused, like the Lag-5. Some sources mix the La-5 with La-5FN and even with La-7.

During the offensive stage of the Battle for Stalingrad the new Lavochkin aircraft made its debut. In the Summer of 1943 the La-5FN was delivered in substantial numbers making a massive show during the Kursk Bend battle. While the La-5 was equal to most of the German front line fighters at low to medium altitudes, it still had a comparatively poor climb rate. With the new 'Lavochkin' arrival this gap was filled.

Externally the La-5FN differed from the late production La-5 by the more articulated air intake on the top of the engine cowling, providing more room (and more air) demanded by new ASh-82FN supercharged engine with direct fuel injection. Farings on the cooling/exhaust side louvers were removed. Slightly larger new VISh-105V (3m diameter) propellers were installed.

But the 'hidden' changes were even more substantial. A more powerful engine with better altitude performance was supplemented by airframe improvements. These included new suction operated leading edge slats and radically improved and balanced controls (following the TsAGI expertise). As a result the La-5FN and later aircraft of this line became the most lightly controlled fighters of their time. In addition, large ailerons provided it with excellent roll characteristics. Improvements in the wing structure allowed the use of larger fuel tanks, but this opportunity was realized only on a few aircraft. Commonly, the fuel tank's volume is the same or smaller than on the La-5.

The La-5 pilot's complaints about excessive cockpit heat were taken into account and the La-5FN provided sufficient comfort. Spartan cockpit instrumentation was sufficient for a daylight prop fighter.

In an effort to improve the high altitude performance of the La-5FN a small number of La-5FN-TK were built. These fighters were equipped with turbochargers designed by Treskin. Quite commonly, marginal high altitude advantages were outweighed by performance losses at low and medium altitudes - where 'Lavochkins' were mostly used. However, a high altitude fighter on Eastern front was not a pressing priority, and this project was abandoned.