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The La-5FN in World War II
One of the marvels of this series of aircraft is the accomplishment of engineers, working with (by Western standards) inferior materials and poorly trained and skilled work forces, to produce one of the most effective medium altitude fighters to see combat in WWII (The Lavochkins). The design origins of the Lavochkin series of GPW fighters upto the La 7 are all borne of the origins of the LaGG series of fighter preceding them.
"Even if only one small grove of trees is left in Russia" said Gorbunov, "even then we shall still be able to build fighters."
The world was equipping its self for war and all majors powers were designing and building new aircraft for it. The key material of choice was duralumin (duraluminium). This light but strong aluminium alloy was, by 1939, well proven in the structural members of airframe design for fighter and bomber applications. Many aircraft also used other aluminium alloys for outer frame skins.
Aluminium was scarce in Russia and any aircraft dependant on it wholly would find its production capacity also dependant on its supply and hence restricting output at the very time that it should be increased.
Vladimir Gorbunov (Peoples Commissariat of the Aircraft Industry) put forward in 1939 the concept of an all wooden airframe (and skin) combat fighter arguing the ability to greatly increase the out put of combat fighters over that caused by the lack of aluminium.
The main contributer to this design study was one Semyon Lavochkin latterly aided by Mikhail Gudkov. The key component originally envisioned was the use of a phenol-impregnated wood as developed by German engineers for wooden propellor design. However co-incidentally Leonty Ryzhkov (Chief engineer Kuntsovo propeller / ski factory) had developed a process based on the use of impregnation using birch tar. Such impregnation made the wood heavier, much stronger and fire resistant. The design, forwarded in spring 1939, used this process for all primary load bearing structures such as wing spar caps and fuselage longerons.
The design was approved in May 1939 and 2 prototypes were ordered in June. Without a production facility Lavochkin, Gorbunov and Gudkov were transferred to GAZ No.301 ( a former furniture factory) which had just undergone the cancellation of a programme(whilst still preparing for) to manufacture French Caudron aircraft under license.
Progress was slow, manufacturing facilities were not suited and personnel were not experienced for modern aircraft development. Although the bureau had 93 workers in December 1939, it was still disorganised. Further the three key designers constantly disagreed and eventually it was decided that one should be appointed to take responsibility. Semyon Lavochkin was chosen.
Other problems had yet to be solved. The adhesive chosen was still in its development stage. It contained phenolic acid and so caused serious irritation to workers skin. After handling instructions had been drawn up, it, however, also proved to be a particularly strong adhesive compensating for machining inaccuracies and filling clearances between joints upto 3mm in width.
The final design was approved by the NII VVS (scientific and research institute of the air forces of the USSR) in January 1940. The prototype fighter (designated I-301) was completed in March 1940, some 12 months after the project had started.
"The I-301 was a single seat, low wing monoplane. Its fuselage was a wooden semi monocoque structure, skinned with birch veneer and plywood, like the wings. Phenol-impregnated modified wood was mainly used for the wing spars and local re-enforcement of the structure. The 2 spar wing comprised a centre section attached to the fuselage and two detachable outer panels. Three self sealing fuel tanks were located between the spars and the centre section and the panels. Rivetted metal split flaps and ailerons with metal frame work and fabric covering (like the elevators and rudder) were arranged in the wing trailing edge. The tailplane included two panels attached to the fuselage."
Aerodynamic properties of the aircraft were considered excellent from the point of view of surface drag. The birch ply was filled and sanded to a very smooth finish and subsequently lacquered to give a finish much better than that found when using rivetted panels. This finish was later found to be retained even through repair throughout the life of the craft. Where as aluminium panels became upset and distorted by repair.
Flight tests proceeded in March and continued through to August when the prototype was damaged. Many defects had been found and some corrected others left to be resolved in series production aircraft. Some were to stay with the type through out its series to the La7 some were corrected as will be recorded here. Among the main faults with the I-301 were...
the cockpit was hot the visibility out through the cockpit was poor stick forces required were high longitudinal stability was inadequate undercarriage required modification LaGG-3
As the 2nd prototype was being wheeled out on the 2nd of October the government issued an edict that all new fighters should have a range of 621 miles. This meant a larger fuel system than that currently installed. The design team duly decided that the future serial production machines would have an additional (4th & 5th ) fuel tank would be mounted in each of the detachable outer wing panels. This could not be incorporated into the 2nd prototype which had a gravity drained tank mounted behind the pilot for trial purposes. On the 29th of October the aircraft met is range trials and was ordered into full production. As the I-301 was considered to be renamed the LaGG-1 it was never produced as the longer range LaGG-3 (with 5 fuel tanks) was made the production variant from the out set.
The LaGG-3 was the most prolific Russian combat fighter under production during 1941.But it was not a popular aircraft and competed poorly (both in terms of pilot and political acclaim) in comparison with Yakovlevs Yak 1 and Yak 7 aircraft, both of which used the same engine variant as the LaGG-3. Whilst showing good combat abilities against ground targets and enemy bombers it was not the equal of the German Bf 109E and was out classed by the latest Bf109F. Although more robust and with higher survivability under fire than the Yaks the LaGG-3 was considered too heavy and despite some modification to armament and stripping out all non essential equipment was branded by many pilots as the Lakirovannii Garantirovannii Grob ( varnished guaranteed coffin). This was further made worse by continued defects appearing in front line aircraft due to poor production disciplines.
Design modifications were undertaken extremely reluctantly by Lavochkin as he had (supposedly) 4 plants ( Gorkii, Taganrog, Novosibirsk and Leningrad)dependant upon designs emanating from the main Gorkii plant and field modifications were costly and unpopular as they removed aircraft from service when undertaken.
Novosibirsk was planned to be a large LaGG-3 production centre but after a visit from Yakovlev in October 1941 his report condemned the production planning as inadequate, with the slightest delay causing the workshop to fill with incomplete airframes and the delivery schedule being totally disrupted. Many have since disputed the accuracy of Yakovlevs reports re the above but the out come of these plus other films he submitted to Stalin showing filthy production facilities in comparison with immaculate Yakovlev production lines caused Stalin (in January 1942) to switch the Novosibirsk plant over to the Yakovlev bureau for the production of Yak-1's.(this never occurred and later the plant was used for production of Yak 7 in both A & B variants) Having achieved this Yakevlov then turned his attention to Lavochkins Gorkii production line then the largest of Russia aircraft production facilities.
At Gorkii extensive efforts were now being made to improve the LaGG-3's performance and combat capabilities. Refinements were added to increase speed but not validated by the NII VVS. Later trials carried out by the NII VVS were conducted in "less than sympathetic" conditions with the aircraft fully laden with rocket projectiles, the canopy removed and radiators shutters left fully open continuously. Their report further condemned the plane as now having a high noise level, high control column forces and poor range.
Production at Gorkii went ahead at maximum out put during the early months of 1942 to provide aircraft to the front line at a rate of between 200 and 270 planes per month throughout this critical period whilst other production facilities were being moved to the East. Shortages of material forced the successful development of wooden fuel tanks made of birch using a tar adhesive. Shortages also forced the development of wooden propellor blades which, while functional, reduced the top speed by a further 14.9mph. A complete production batch was sent to the front lines regardless in order to maintain production rates.
In April 1942 it was decided that Gorkii would cease production of LaGG aircraft and with the Taganrog production in the process of being switched to Tbilisi in Georgia and the Leningrad plant also under evacuation (to inner Russia where it would switch to the production of MiG-3 aircraft) Lavochkin was to be left with the fledgling Tblisi production facility short of experienced production staff as his only manufacturing plant whilst much of his design team remained at the Gorkii plant.
Desperate to improve performance Lavochkin had undergone the development of the air craft with respect to new more powerful engine plants to replace the 1,000 hp Klimov M-105 used to date. His development teams followed two routes. Firstly the main thrust of work was to upgrade to the 1,400 hp Klimov M-107 whilst in parallel and as a precaution a LaGG-3 had been prepared with a Shvetsov M-82 radial engine. Lavochkin had no faith in the ability of this powerful radial engine to bring favourable results.
By this time all the other leading Soviet designers had attempted the fitting of the Shvetsov radial onto their existing designs with only limited success. Indeed a promising development of installing the engine on a LaGG -3 fuselage had already been undertaken by Gudkov who had installed the power plant bodily from a Sukhoi Su-2 in 1941. However although reportedly flying well in September 1941 his prototype was lost between moves to and from Novosibirsk and Gudkov moved to other development work.
Arkady Shvetsov (chief designer engine plant No.19)was concerned with the lack of demand for his engine of which he had hundreds in store; only in demand for use on short range Su-2 bombers. Lavochkins affairs were also looking decidedly bad as production of LaGG aircraft was about to be totally with drawn. After a meeting, with Lavochkin, Shvetsov sent his best design team to Gorkii to form a task force with some of Lavochkins designers with a view to optimising the coupling of engine and fuselage. Given that the LaGG was about to be removed from production it was decided that the whole project would be abandoned if a complete redesign of the aircraft was required. Hence the decision was made to remove some air frames from production and modify them to receive the M-82 engine.
Several problems remained to be solved not the least was the design of a method of mounting armament and the problem of the great width of the engine in terms of drag and its additional weight (250kgs more) and its affects on the aircraft centre of gravity and overall performance.
Key areas were addressed
A skirt was designed to fit over and be bonded to the mid section load-bearing fuselage of the production aircraft to allow for the engines greater width. A new design of engine mount was produced. Two ShVak 20 mm synchronised cannon were fitted over the engine. The engine was "close cowled" with cooling being controlled by variable cooling flaps on the fuselage sides. The first fighter was rolled off the assembly line for initial trials in February 1942 and first evaluations revealed a number of problems regarding engine cooling but also showed an increase in straight line speed by 10%! An outstanding achievement given that all bureaus were developing their aircrafts with only a few mph gained for considerable effort. Lavochkin continued to refine the prototype over the next month despite obvious reluctance on behalf of administrators at Gorkii who were planning to increase production of the Yak 7B at that plant to take its full capacity.
News of Lavochkins new development was reported to Stalin by the Peoples Commissariat of Aircraft Industry and by fortunate co-incidence a positive report by pilot engineer Nikashin had separately been given to the State Defence Committee who also reported to Stalin. A joint commission was urgently formed and visited Gorkii on the 21st April 1942 where by pilots of the NII VVS carried out test flights. The report was "promising" and future tests carried out over May were to "change the fate of Lavochkin aircraft considerably".
Performance of the then specified LaGG-3 M-82 was higher than all other aircraft in service in the VVS. It showed good climb rates to 5,000 metres (16,400ft) and in the all important combat turn whilst climbing to gain an altitude of 1,100 metres it out performed all aircraft (including enemy) currently used at the front. Problems of overheating (or in some conditions over cooling), high stick forces (particularly when rolling from one banked turn to another), and a slow turning circle still prevailed. The advantages were to prevail however and after giving a brief "businesslike" description of the aircraft to Stalin , Lavochkin was ordered back to Gorkii to prepare for series production.
Work started on the then designated LaG-5 in early June 1942 with the immediate conversion of 10 LaGG -3 airframes to the new engine. This "dreadful haste" produced many errors compounded by the lack of drawings which were being made up from produced parts rather than the other way round. Even so between the 20th and the 30th of June Gorkii workers produced 37 LaG-5's with a further 145 produced in August along side 148 LaGG-3's still with the Klimov engine.
These series production aircraft were inferior in performance to the prototype craft and yet were proving very popular with units operating them at the front. In particular the high survivability and protection afforded by the large radial engine. In September 1942 it was redesignated the La-5.
The La-5 underwent continual development in terms of reducing weight and drag. Pilots had to be persuaded to fly with the canopy closed and tail wheel raised to improve performance further. By the end of 1942 1,129 La-5's had been produced and the mark had proven itself in combat over Stalingrad.
The engines maximum continuous power was 1540hp at 2050metres using its 7:1 compression ratio via a 2 speed supercharger. It was rated to use 94 octane fuel.
The wing was modified to take automatic slats on the leading wing edges requiring the repositioning of the pitot tube. A trim tab was added to the inner edge of each aileron and the wing fuel filler ports were combined to a single filler point per wing. Landing lights were eliminated.
Other than the above changes, the wing and fuselage was virtually identical to the original LaGG-3 design. The two spar wing used NACA 23016 profiles at the wing root and NACA23010 at its tip. The all metal flaps could be deflected 50 degrees for landing and 10 to 15 degrees during combat to improve the fighters turning radius.
The 5 fuel tanks were retained, manufactured from a alu- magnesium alloy and covered in layers of resin impregnated fabric to a thickness of 8mm. In the event of bullet damage the resin fabric acted as a self sealing agent within 10-15 seconds of coming into contact with fuel. The fuel tanks were also filled with cooled inert exhaust gases to inhibit the risk of fire....the only Soviet fighters to use such a system at that time.
Whilst initial production batches used the windscreen and canopy from the LaGG-3 these were later modified to take a windscreen of flatter design with 2 additional cross frames to accommodate a 55mm armour plate glass mounted behind it. The canopy rear frame was also strengthened.
The gunsight was the rudimentary PBP-1A lens type reflector with 2 rings . One for 200kmh and one for 300kmh. The sight was unable to give a fine degree of deflection and required the firing of bursts before through and after the target to ensure hits.(Unfortunately this vibrated to such an extent when the 2 ShVAK cannons were fired as to render it useless)
Cockpit was spartan by Western standards. Instrumentation included a basic compass, speed indicator, rate of climb indicator, engine rev counter, temperature gauges for oil and engine, and a clock. Radio equipment was very basic some aircraft fitted with receiver only.
The pilot was initially protected by a 10mm sheet of steel behind his seat but this was later reduced to 8.5mm to save weight and his seat position had to be raised to provide a better view out of the canopy around the radial engine."
The air craft was extremely unsophisticated by Western standards. Yet this basic fact was to stand it (and its future variants) in good stead with ground crews and pilots, who were forced to operate under difficult "make do" conditions across the Russian / German front line. Conditions which resulted in much lower levels of serviceability in other more sophisticated types (as seen with lend lease Spitfires used by Russian units during that and later periods.)
Shvetsov had not remained idle however. The Ash-82A was very sensitive to cylinder head temperature for safe running and optimum performance best conditions were achieved between 200 and 220 degrees Celsius whereby if pilots allowed temperatures to exceed this the resultant overheating often caused loss of cylinder head or indeed complete disintegration of the cylinder its self. It also suffered a short spark plug life substandard oil pump capacity and a tendency for exhaust pipes to burn through. This led to the joint development of the Ash-82F, Ash-82FN & Ash-82FNV engines. The Ash-82F first appearing on La-5 planes in December 1942. The new engine produced improved performance above 1500metres (4921 ft) but was still aspirated by a conventional carburetor.
Semyon Lavochkin likewise saw tremendous development potential in the La-5 (which he considered a hastily put together stop gap). After putting forward improvements re aerodynamic efficiency, better cockpit view, control enhancement and weight reduction, government decree was issued on the 9th December 1942 authorising further development work. This work was carried out by the TsAGI (Central Aerodynamic and Hydrodynamic Institute).Its principle modifications were
Engine cowling joints sealed Shape of the oil cooler ducts modified new inlet pipe was fitted Area of exhaust pipe cross section was increased Further development work on the fuselage had already taken place (November 1942)on late La-5 air frames to give the pilot a 360 degree range of vision by lowering the rear dorsal fuselage and adding a tear drop canopy with armoured glass. The La-5 had also been under continuous review with respect to trim tab design, control and flap surface area (to achieve the optimum control column to control surface gain) and every component had been revisited with a view to reduce the overall weight whilst retaining structural integrity( again eliminating the wing tanks which had hampered manoeuverability). The first aircraft incorporating these changes were tested during late December 1942 and January 1943.
The tests were outstanding and continued through January and into February whilst serial production commenced in parallel. The type now designated the La-5F was delivered to the fronts from April 1943 and by June 1943 the combined fleet of La-5 and La-5F fighters stood at more than a quarter of the Russian fighters available. Plant no 21 (Gorkii) was now sending 350 to 400 of the latest plane to the front monthly and two other plants were starting to assemble the type. Finally the Russians had a fighter whose combined abilities were at least equal to those of the enemy. Whilst special training had to be given to recover from an inverted spin the aircraft otherwise enjoyed excellent handling characteristics and much improved survivability during ground attacks.
Other minor modifications included the more advanced (but similarly ineffective) PBP-1B gun sight. Small inlets placed just below the windscreen to improve cockpit ventilation and revisions in aerial mast design and strength.
Modifications to lighten and improve the wing design continued with the replacement of some "delta"wood components with conventional pine and the main spars were modified to use fir. The wing ribs were change to fir strips and plywood. Later La-5F wing spars were made of steel angle and duralumin brackets. Production of the La-5F had ceased by the end of 1943 in favour of the La-5FN.
Semyon Lavochkin had in fact conducted 2 development projects in parallel during the development of the La-5F. The 2nd made use of Shvetsov's ASh-82 FN engine which incorporated direct fuel injection boosting its take off power further to 1850 hp which was apparently sustainable as augmented power for a period of minutes during flight.
Work continued on the La-5FN throughout the La-5F trials of January and February 1943 and the first prototype La-5FN was ready for testing on the 26th March 1943.
The key advances were around the use and mounting of the engine. A large super charger air intake had been added to the top of the engine cowling to provide air for the deep breathing Ash-82FN engine. The exhaust stack was modified to provide independent exhausts for each cylinder to be routed to the revised exhaust flap. Thus cutting down exhaust pipe degradation and allowing better control over cylinder head temperatures. Cowling was slightly modified to give a lower drag characteristic.
Venting of the rear engine compartment and cannon compartment was improved. The prototype had a metal main wing spar but this was not incorporated until late 1943 production runs. A duraluminum plate was added below the cockpit above the wing roots. In the cockpit thicker armoured glass (front and rear) was included in later models, the radio was improved and opening of the canopy made easier.
Tests performed during April of 1943 showed it to be a significant improvement over the La-5F, specifically in terms of climb and speed. The La-5FN was immediately ordered into serial production and the first batch was sent to the Kursk front in June 1943.
Whilst still suffering many of the cockpit discomforts of the earlier La-5 series it quickly proved its self in action. It out performed the Bf109G2 in speed and vertical manoeuvring and equalled the then new Bf109G6 in both aspects of performance. It could not however equal the top speed of the FW190A3-4 but was able to both out climb and out turn it in the much quoted combat turn manoeuver.
However through out 1943 and 1944 the La-5 FN benefited from a continued weight saving program as certain wooden parts were replaced with light alloy parts. The fuel tanks were later changed to a 3 tank set ( when the metal sparred wings were adopted) but this did not add to the aircrafts range which had been reduced by the heavier breathing engine. Combat mission flight duration at full power was now only 40 minutes, however this could be extended to 2 hours and 32 minutes when at reduced engine revs .
Continued development of the control surfaces and trim reduced control stick forces to a point where these "provided a considerable improvement in handling and manoeuverability".
During 1943 a total of 5048 La-5F and La-5FN aircraft were built across 4 aircraft factories. 4619 being built at GAZ-21 Nizhny-Novgorod (Gorkii). Production of the La-5FN continued until November1944 during which time a further 3826 were produced in parallel with the then latest mark the La-7.