Editing Yakovlev Yak-1 (section)

==Design and development==
Before the war, [[Yakovlev]] was best known for building light sports aircraft. His [[Yakovlev Yak-4|Yak-4]] light [[bomber]] impressed the Soviet government enough to order the [[OKB]] to design a new fighter with a [[Klimov M-106]] V-12 liquid-cooled [[Reciprocating engine|engine]]. Formal specifications, which were released on 29 July 1939, called for two prototypes – '''I-26-1''' with a top speed of {{convert|620|km/h|mph|abbr=on}} at {{convert|6000|m|ft|abbr=on}}, combat range of {{convert|600|km|mi|abbr=on}}, a climb to {{convert|10000|m|ft|abbr=on}}) of under 11 minutes, armed with 2 × {{convert|7.62|mm|in|abbr=on}} [[ShKAS]] [[machine gun]]s and 1 × {{convert|12.7|mm|in|abbr=on}} [[Berezin BS]] heavy machine gun. '''I-26-2''' had a [[Turbocharger|turbocharged]] M-106 engine with a top speed of {{convert|650|km/h|mph|abbr=on}} at {{convert|10000|m|ft|abbr=on}} and armament of 2 × {{convert|7.62|mm|in|abbr=on}} ShKAS machine guns. The design took full advantage of Yakovlev OKB's experience with sports aircraft and promised agility as well as high top speed. Since the M-106 was delayed, the design was changed to incorporate the [[Klimov M-105]]P V-12 engine, with a {{convert|20|mm|in|3|abbr=on}} [[ShVAK]] cannon in the "vee" of the engine block, in a {{lang|ru|motornaya pushka}} mount.

I-26-I first flew on 13 January 1940 and suffered from oil overheating which was never completely resolved, resulting in 15 emergency landings during early testing. On 27 April 1940, I-26-1 crashed, killing its test pilot [[Yu.I. Piontkovskiy]]. The investigation of the crash found that the pilot had performed two consecutive barrel rolls at low altitude, which was in violation of the test flight plan. It was believed that during the first roll, the [[Landing gear|main landing gear]] became unlocked, causing it to crash through the wing during the second roll. It has been speculated that Piontkovskiy's deviation from the flight plan was caused by frustration that his aircraft was being used for engine testing while I-26-2, built with the lessons of I-26-1 in mind, was already performing [[aerobatics]].

Technical problems with sub-assemblies provided by different suppliers raised the I-26-2's weight {{convert|400|kg|lb|abbr=on}} above projected figures, which restricted the airframe to only 4.4 G, while oil overheating continued to occur. The many defects caused I-26-2 to fail government testing in 1940. Fortunately for Yakovlev, its competitors, I-200 (future [[Mikoyan-Gurevich MiG-3]]) and I-301 (future [[LaGG-3]]), also failed testing. Requested improvements were incorporated into I-26-3, which was delivered for testing on 13 October 1940. Although it passed on 9 December 1940, the aircraft was still very much unfinished, its engine problems still unresolved.

Troublesome and slow testing and development concerned Soviet officials, since I-26 was ordered into production under the name "Yak-1" on 19 February 1940, a mere month after I-26-1 made its maiden flight. The gamble was intended to reduce the time between the prototype and the beginning of production of service aircraft; the I-200 and I-301 were also ordered into production. The Yak-1 was slower than the I-200 and less heavily armed than the I-301, it enjoyed the advantage of having been started earlier, which gave it a consistent lead in testing and development over its competitors. Due to [[Operation Barbarossa]] the Axis invasion of the Soviet Union on 22 June 1941, development of promising designs, like the [[Polikarpov I-185]], proved unfeasible. Yakovlev might have been [[Joseph Stalin]]'s favorite, which may have been in the Yak-1's favor.

Simultaneous manufacturing and testing of a design that required as many improvements as I-26 caused much disruption of production. Almost 8,000 changes were made to the blueprints by 1941, with an additional 7,000 implemented the following year and 5,000 more in 1942.{{clarify|date=September 2016|7000 ''and'' 5000 changes in 1942?}} Production was further slowed by shortages of engines, [[propeller (aircraft)|propellers]], [[radiator (engine cooling)|radiators]], wheels and cannons. Shortages of quality materials resulted in [[plywood]] being shed from the wings of several aircraft. Factory No.292, the main manufacturer of Yak-1s was bombed on 23 June 1941 and burned to the ground; production resumed amid the ruins on 29 June. Due to loose tolerances, each aircraft was unique, with workers performing the final assembly having to mate dissimilar components. The left and right main landing gear could be of different lengths and different angles relative to the aircraft, which required adjusting their attachments to ensure an even stance for the aircraft and parts were often not interchangeable. Production of the Yak-1 ended in July 1944, with somewhere around 8,700 built.