Yakovlev Yak-3

Yakovlev Yak-3

Yakovlev Yak-3 is considered one of the best World War 2 fighters, invariably praised by those who flew it in combat for its remarkable performance.

The Germans also treated it with respect, which is perhaps best illustrated by Generalleutnant Walter Schwabedissen’s remark: The Yak-3 was a tough nut to crack for our pilots. It outperformed our machines in speed, maneuverability and rate of climb.
The emergence of Yak-3 was a compromise between the need to improve the Yak-1’s characteristics and the limitations of Soviet aircraft industry and its outdated technologies. The basic design concept took those shortcomings into account, which allowed a rapid launch of mass production of this inexpensive fighter. This in turn would provide frontline units with timely deliveries of new equipment to recoup combat losses.
The key to Yak-3’s success was not the use of a new powerplant (in those days hard to come by in the USSR), but rather squeezing every bit of performance out of the M-105PF engine, which resulted in a five percent increase in power output. In combination with some serious weight shedding, the Yak-3 had a significantly better performance than the Yak-1. At altitudes up to 5,000 m (which is where most of the air combat over Eastern Front took place), Yak-3 outperformed both the Bf-109 and Fw-190 in rate of climb and maneuverability. Unlike the Yak-1, the new fighter could also stay with the enemy in a dive.

Yak3   zdj1

Its advantages notwithstanding, the Yak-3 also had some serious drawbacks, which affected its modernization potential and limited the scope of combat application of the machine. Its main weakness was a rather modest fuel capacity, which limited the fighter’s range making it unsuitable for long-range combat patrols (with twenty percent fuel reserves, the Yak-3’s endurance was just about 45 minutes). Also, because of its “short legs”, the fighter had to be based fairly close to the frontline. Although the Yak-3’s armament did provide enough punch to combat enemy fighters, it was insufficient against bombers. There were more problems to overcome if the machine were ever to be equipped with a more powerful engine, once such became available. It quickly became obvious that such a modification would never be possible due to short landing gear struts and lack of space for installation of more efficient water and oil radiators that a new powerplant would require.

Yak3   zdj2

Origins of the design
The history of the Yak-3 design (not to be confused with the experimental I-30 aircraft built in 1941 and armed with three cannons – the first design to have received the designation) dates back to the fall of 1942 and the emergence of the Yak-1M Moskit (Mosquito) – a light-weight version of the Yak-1, powered by the M-106P engine (the M-105PF and M-107A engines were also considered as powerplants for the new design).
In its early iteration the Moskit project was based on the Yak-1 airframe and retained its characteristic hump behind the cockpit, but fairly soon the design underwent radical changes. The new fighter was originally designed around a stock Yak-1b fuselage, which was modified to accommodate a BS gun and a new coolant radiator ducting. Mated to the fuselage was the Yak-9 wooden wing with its duralumin main spar and four load-bearing ribs, which featured reduced wingspan and wing area (9.2 m and 14.7 m2, respectively). Since the new design was much lighter, the resultant wing loading was the same as in the Yak-9 carrying identical armament. Elimination of aileron counterbalance provided additional 10 kg in weight saving. In addition, the Yak-1M wing was split along the aircraft’s longitudinal axis, which facilitated removal of damaged panels and made their ground transport a lot easier.
The overall design of the landing gear was the same as on the Yak-1, but its shock absorbers featured a greater stroke, so some of the components were adopted from Yak-7. Retractable tailwheel and tailplane were unmodified Yak-1 units. There were some minor modifications to flight control mechanisms, which included lowering the rudder pedals by 50 mm and relocating the elevator control cables. Armament was limited to a single MP-20 cannon firing through the propeller hub (120 rounds of ammunition) and a fully synchronized BS machine gun (200 rounds) mounted on the portside above the engine. The BS gun was equipped with a simple iron ring sight. According to design calculations, the aircraft’s all up weight should not have exceeded 2,650 kg and its supercharged M-105PF engine was expected to propel the fighter to 630 – 640 km/h.

 Yak3   zdj3


The Yak-1M project was launched following a GKO requirement issued on December 9, 1942, but instead of the M-106P engine the designers planned to use the M-106sk powerplant equipped with a two-stage supercharger, hoping that the aircraft would be able to achieve a top speed of 670 km/h at 5,500 m. Unfortunately, the M-106sk program ran into some serious delays, which meant the designers had to settle for the M-106-1sk engine with a single stage supercharger. In the fall of 1942 that engine was installed on the Yak-9 (a double of the Yak-7DI fighter powered by the M-105PF engine), but the powerplant’s numerous shortcomings were quickly exposed during factory trials launched in November 1942. In the end, the attempts to iron out the kinks of the M-106 engine were abandoned and the 300 units that had already been manufactured were probably scrapped. Things looked just as bleak in the case of the M-107 engine, which was notoriously unreliable and prone to malfunctions. As a result, the Yak-1M design team had no choice but to use the tried and tested M-105PF engine in their new fighter.
 Yak3   zdj4


Although Yakovlev didn’t have high hopes for improvement of the engine’s performance, he nonetheless did ask V.Y. Klimov how much the boost pressure could be tweaked to increase power output. Klimov suggested that the boost pressure in the first stage operation could be increased to 1,100 mm Hg, but no changes to the boost pressure were possible in the second stage, which had to remain at 1,050 mm Hg. Such modification didn’t produce much in terms of power increase, but was, nonetheless, a small step towards delivering the ultimate Yak-3 design. Accidentally, Yakovlev’s inquiry into the potential improvement of Klimov’s powerplant resulted in the development of M-105PF2 (VK-105PF2) engine, which contributed to an increase in performance of LaGG-3 fighters and Pe-2 bombers equipped with those powerplants.
The Yak-1M made its first flight on February 28, 1943 with P.Y. Fedrovi at the controls and M.A. Grigoryev acting as the lead engineer. The aircraft was powered by a standard M-105PF engine (still without the additional boost) driving a VISh-61P propeller. Following the uneventful maiden flight a series of factory trials began, which lasted for three months (fairly long, considering wartime conditions). One of the reasons the factory trials went on for so long was a serious engine failure that took place on March 22, 1943. It wasn’t until June 7 that the machine was finally handed over to NII VVS for state trials. During the flight test program the aircraft was flown by A.G. Proshakov. Assigned as the project’s lead engineer was A.T. Stepanets. (FOTO 10, 11)
During the trials that lasted until July 22, 1942 (or, according to some sources, until August 1942) the aircraft reached a top speed of 545 km/h at sea level and 632 km/h at 4,450 m. At cruise power setting the demonstrated range was 845 km, while a full turn at 1,000 m took some 15 – 17 seconds. Compared to a stock Yak-1 manufactured at Saratov plant (s/n 2985) an empty Yak-1M was 282 kg lighter. The new aircraft carried 35 kg less fuel than its predecessor and its maximum take-off weight was 245 kg less than Yak-1’s. Since both the Yak-1 and Yak-1M were powered by engines delivering identical power outputs, the latter’s top speeds at sea level and at altitude were higher – by 35 and 62 km/h, respectively.
After Klimov’s green-lighted the use of higher boost pressure in his engine, the NII engineers modified the powerplant to deliver 1,100 mm Hg in the supercharger’s first stage (stage selector lever in the cockpit was mechanically restricted to first stage only). Further testing proved that increased boost pressure did produce higher power output, but at a cost of less efficient coolant and oil cooling caused by inadequate radiators capacity. After some modifications to the cooling system had been introduced, the aircraft was handed over to TsAGI for wind tunnel testing (the facility had recently re-opened after the threat of German air raids had subsided). The wind tunnel test results were used in the development of the second prototype, dubbed Yak-1M Dooblyor (Double), which was powered by a supercharged M-105PF engine driving a 3 m VISh-105SV-01 propeller. That particular propeller, developed in September 1943, featured a lighter hub than a standard VISh-105SV model and modified blade tips profile. During flight test program the propeller performed well and no faults or malfunctions were recorded.
Yak3   zdj5

In order to improve the Dooblyor’s performance the engine featured individual exhaust stacks, rather than exhaust manifolds, which utilized thrust produced by ejection of exhaust gasses to obtain a slight increase in speed. Propeller control and throttle levers were placed in such a way that desired power settings could be obtained with a single move of the pilot’s hand. Another weight saving measure was the removal of a ground start receptacle from the propeller’s spinner, which also improved the aircraft’s aerodynamics.
Dooblyor’s wings featured four fully protected fuel tanks (only two were installed in the first prototype), which were separated from the cockpit by a pair of sealed bulkheads. This arrangement required installation of two additional metal ribs in the wing’s structure. The wing tanks were equipped with mechanical fuel meters, unlike the service tank in the wing’s center box, which featured an electric fuel gauge. Although the center box tank’s fuel capacity was reduced from 30 kg to 10 kg, the aircraft could carry a total of 275 kg of fuel, i.e. 5 kg more than the first prototype. The fuel system featured inert gas installation (utilizing cooled exhaust gases), which neutralized fuel fumes in the tanks.

Yak3   zdj6

Introduction of a new water radiator required installation of redesigned frame four of the fuselage. Other structural modifications included simplification of the engine mount and redesigning the BS gun platform to accept a second machine gun. Fuselage fabric skin was replaced with 2 mm plywood panels and cockpit canopy received jettison mechanism copied from the British Spitfire design. The framed windshield was replaced with a single Perspex unit, which resulted in a more streamlined shape. A PBP-1a reflector gunsight was installed in place of the rudimentary iron ring sight. The ShVAK cannon was replaced by a lighter ShA-20M weapon, which at that time had yet to pass state acceptance trials. At the same time the ammunition capacity was reduced from 120 to 110 rounds. A second, fully synchronized UB gun was also installed and supplied with 150 rounds of ammunition (The Yak-1M carried 200 rounds for a single gun).
Dooblyor’s armored protection also underwent modifications. The 8.5 mm armor plate behind the pilot’s seat was shortened to cover only the back of the seat and its sides were bent forward to improve pilot’s overall protection. The headrest, made of reinforced glass mounted in a heavy steel frame, was attached to the armor plate behind the seat. This arrangement eliminated tensions causing micro cracks in the glass and loss of transparency. An armrest was installed on the cockpit’s port side measuring 3.5 – 4 mm in thickness, 500 mm in length and 100 mm in height. The pilot’s head was not protected from the front or from above and the armored protection was only effective against 6 – 8 mm caliber bullets.
Replacement of two type “05” oil coolers with a single OP-555 unit required modifications of the ducting and engine lubrication system. The OP-492 water radiator was removed and replaced with an OP-554 device. Modifications of radiator ducting were carried out based on the advice provided by TsAGI engineers. Another improvement was the installation of an ART-41 automatic engine temperature control unit with an associated indicator in the cockpit. This modification allowed the removal of radiator shutter control lever from the cockpit.

Yak3   zdj7

 

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Versions armed with a 37 mm gun