Yak-1 M ('Moskit') fighter prototype. The Yak-3's predecessor was the Yak-1 M fighter, the prototype of which was also dubbed 'Moskit' (Mosquito). The wings of the new fighter were structurally similar to those of the Yak-9, featuring metal spars, metal and wooden ribs and plywood skinning. However, wing area was reduced by 2.3 sq m (24.7 sq ft) in comparison with the preceding Yaks and made up 14.85 sq m (159.7 sq ft).
The fighter's wing span was reduced to 9.2 m (30 ft 2.2 in). A production break coinciding with the fuselage axis was introduced; this afforded the possibility of replacing the port or starboard wing panels in field conditions in case of damage. The control system, the fuselage and the undercarriage were all borrowed from the production Yak-1. As distinct from the latter, the fuel system comprised three tanks: two main tanks in the wing outer panels and one service tank in the wing centre section. As for the armament, equipment and armour protection, the Yak-1 M had much in common with the Yak-1 in the version featuring improvements in visibility, armour protection and armament.
The engine's cooling system featured a more efficient radiator buried more deeply in the fuselage. Two circular-shape oil coolers working in parallel were placed in the wing centre section under the cockpit floor. This made it possible to eliminate excrescences on the lower panel of the engine cowling and make it smooth, thus considerably improving its outward contours.
The Yak-1 M had an all-up weight of 2,665 kg (5,876 lb), ie, some 245 kg (540 lb) less than that of a production Yak-1 manufactured in 1943. The wing loading rose marginally from 169 to 179 kg/sq m (34.70 to 36.75 lb/sq ft) while the power loading was noticeably reduced - from 2.40 to 2.19 kg/hp (5.30 to 4.83 lb/hp). The weight reduction was achieved mainly by reducing the wing area and substituting duralumin alloy spars for wooden ones; all this produced a weight saving of 150 kg (331 lb).
The prototype was completed in mid-February 1943. Throughout the spring months the aircraft was subjected to development work conducted under the direction of leading engineer M. Grigor'yev who had taken an active part in the design and construction of the Yak-1 M. Pavel Ya. Fedrovi, chief test pilot of the Yakovlev OKB, made an uneventful first flight at the end of February 1943, after which the machine entered the factory tests phase.
Testing of the aircraft at Nil WS lasted throughout June 1943 (with A. Proshakov as project test pilot and A. Stepanets as leading engineer, both being the most experienced specialists of the Institute as regards Yakovlev's machines); the tests revealed the new fighter had excellent performance.
But the OKB held the opinion that the fighter's improvement potential had not yet been exhausted. At A. S. Yakovlev's insistence additional tests were conducted to determine the changes in the basic performance characteristics after the boost pressure of the M-105PF engine had been increased from 1,050 to 1,100 mm Hg.
Initially V. Ya. Klimov, Chief Designer of the engine, gave his consent to increasing the boost pressure only at the first supercharger speed. Additional tests showed that augmenting the engine's power by increasing the boost pressure produced a 6 to 7 km/h (3.7 to 4.35 mph) gain in maximum speed at low altitude, reducing the time to 5,000 m (16,400 ft) by 0.1 minutes and affording an extra 50 m (164 ft) in altitude gain during a combat turn. It also led to a marginal improvement of field performance and entailed virtually no change in the engine's water and oil temperature.
Later theoretical calculations showed the possibility of boosting the engine also at medium altitude. The boost pressure was also increased at the supercharger's second speed. While the M-105PF engine developed (without regard to the dynamic pressure) 1,180 hp at 2,700 m (8.856 ft), after boosting its output rose to 1,244 hp at 2,100 m (6,888 ft). With the boost pressure increased to 1,100 mm Hg the engine was designated M-105PF-2, and from the spring of 1944 onwards it bore the designation VK-105PF-2.
As regards performance, the Yak-1 M was on a par with the best fighters of the final stage of the Second World War. Thus, in terms of maximum speed it surpassed production Yak-9s throughout the altitude range by at least 25 to 35 km/h (15.5 to 21.7 mph); it outperformed the Fw 190A-4 at altitudes up to 8,300 m (27,224 ft) and the Bf 109G-2 up 5,700 m (18,696 ft), judging by the results of tests at Nil WS. The Yak-1 M enjoyed the greatest advantage at low altitude, whereas at high altitudes the German fighters were faster owing to the better high-altitude performance of the Daimler-Benz DB 605 and BMW 801 engines. For example, at the altitude of 7,000 m (22,960 ft) the Bf 109G-2 surpassed the Soviet fighter in speed by nearly 50 km/h.
With regard to the rate of climb up to 5,000 m (16,400), the Yak-1 M was unrivalled among the contemporary fighters of the world. All known versions of the Bf 109, which was justly considered to be one of the best in performing upward vertical manoeuvres, were somewhat inferior to the Soviet fighter. The reduction of the wing area was accompanied by a reduction of the Yak-1 M's all-up weight; as a result, it did not entail a deterioration of its field performance, spinning and diving characteristics. The handling of the prototype fighter, like that of the Yak-1, Yak-7 and Yak-9, was within the capabilities of wartime pilots possessing an average and even below-average skill level.
The test report noted: 'As regards the effectiveness and harmonious action of controls (from the point of view of stick forces from control surfaces) the Yak-1 M, along with the Spitfire Mk VB (it was tested at NII VVS in June 1943 - Author), is exemplary for all fighter aircraft, both indigenous and foreign.'
A few shortcoming of the prototype, typical for the Yaks (such as overheating of oil during climb at the optimum climb rate, poor functioning of the breather, oil leakage from various sealed joints, inadequate range of radio communication between airborne aircraft and with the ground etc.) could not spoil the favourable overall impression produced by the machine.
Yak-1 M 'Dooblyor' (second prototype). While the first prototype Yak-1 M was undergoing State trials, construction of the second prototype Yak-1 M (dubbed 'dooblyor'', in accordance with the practice of the time) was nearing completion under the direction of engineer M. Grigor'yev. It turned out to be still more refined and well-thought out in every respect.
Thus, the fuel tank bays were separated from the cockpit by sealed bulkheads; the fabric skinning of the fuselage was replaced by plywood skinning; the cockpit hood was provided with an emergency jettisoning system; some other improvements were introduced as well. The fighter was fitted with a new VISh-105SV-01 propeller which featured a lightened hub and blades with airfoil sections at the roots.
There were also changes in the armament. Instead of the ShVAK cannon the designers installed a prototype ShA-20M lightened cannon designed by Boris Shpital'nyy and reinstated the second UBS-12.7 heavy machine-gun after the pattern of the Yak-7B. At the same time the avionics suite was expanded. A feature that was bound to attract attention was the radio which could be remotely controlled by a push-button at the throttle lever. This was a novelty in the Soviet aircraft construction. The Yak-1M 'Doobfyor' dispensed with the aerial mast, making use of a single-wire aerial.
As a result, the all-up weight remained virtually the same at 2,660 kg (5,865 lb). Construction of the aircraft was completed on 9th September 1943. At the beginning of October, after brief manufacturer's flight tests, the second Yak-1 M was handed over to Nil WS for State trials which were successfully conducted by pilot A. Proshakov and engineer G. Sedov within ten days.
The tests showed an improvement of performance: the 'Dooblyor' attained a speed of 570 km/h (354 mph) at sea level and 651 km/h (405 mph) at 4,300 m (14,104 ft); it gained 1,280 m (4,198 ft) of altitude in a combat turn and could perform a full-circle banking turn at low altitude within a mere 16 to 17 seconds. In addition, it was noted that the installation of more effective radiators, changes made to the ducting and the greater maximum opening of the radiator shutter had substantially improved the engine's temperature conditions. For the first time on an aircraft of the Yakovlev fighter family the possibility was ensured of performing prolonged horizontal flight at maximum speed and of gaining altitude in the maximum rate of climb mode with the engine at nominal revs (2,700 rpm).
Thanks to the thorough electric bonding and shielding of the basic metal elements of the structure, the range of reception of radio messages from the ground in the cockpit rose to 90 km (56 miles), and pilots could confidently maintain communication between themselves at a distance of 20 km (12.4 miles), which represented very good characteristics for the radio equipment of Soviet fighters at that time.
It is difficult to single out another Soviet aircraft that had received as many laudatory comments from test pilots, both those of the OKB and the military ones. For example, A. Koobyshkin considered it to be the best among the known fighters of World War Two in overall performance. Test pilot V. Khomi-akov who had flown the prototype fighter wrote in his report: 'The cockpit is comfortable. Forward visibility has been improved. The instruments and control levers are well placed and their arrangement almost fully conforms to the standard cockpit. Taxying is easy. (...) When airborne, the aircraft is stable and simple in handling. The machine has an excellent rate of climb and manoeuvrability, both in the vertical and in the horizontal plane. Performance has been considerably improved in comparison with its predecessor, the (first prototype] Yak-1M.'
Bearing in mind these and other comments, the Government decision was not long in coming. Already in October 1943 the Yak-1M 'Dooblyor' was launched into production under the designation Yak-3, supplanting the 'straight' Yak-1. The designation Yak-3 had already been assigned to one of Yakovlev's fighters - that was the name intended for the production version of the I-30, but production of this fighter did not get under way in 1941 or at any later time. The destiny of the new machine proved to be much happier.
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* Forcing of the engine during 10 minutes.
** On speed making 90 % from maximal.
- "Yakovlev`s Piston-Engined Fighters" /Yefim Gordon and Dmitriy Khazanov/
- "Stories of the aircraft designer" /Alexander Yakovlev/
- "The Soviet planes" /Alexander Yakovlev/