24k b/w I-26 (first prototype) from 'Notes of an aircraft designer'
by A.Yakovlev;
T he Spanish Civil War experience proved the necessity to boost speed of domestic fighters from
500km/h of the I-16 family to at least 600km/h at the combat altitude.
In 1939 Soviet industry already produced the 1050hp liquid-cooling
M-105 powerplant, capable to provide necessary speed. Even more powerful engines
(like the 1350hp M-106) were under development.
A.S.Yakovlev visited the Great Britain in
1936, where he had seen the Supermarine Spitfire at first hand, and later in Germany
he examined Bf-109R and He-100. Designer's experience with light speedy aircraft turned to be in agreement with general European light
fighter concept, and he combined it with maneuverability, simplicity in construction from readily available materials, multiplied by
superior Yakovlev's weight culture.
For his high-speed fighter A.S.Yakovlev used construction that proved successful
on his light trainer/sport airplanes like UT-1: fuselage strength was provided by wielded
soft steel tubes frame, while the skin was supported by light wooden ribs and stringers. Nose section covered with duralumin, while
tail section - with fabric. Wing of wooden construction with plywood skin, covered with fabric. Tail surfaces and all controls -
duralumin frame covered with fabric.
Aircraft was armed with 20mm ShVAK cannon with 120 rounds, firing through the
propeller shaft and pair of synchronized 7.62mm ShKAS machineguns (750 rounds per
gun) installed above the engine. The M-105P (Pushechnyj, cannon ready) engine was
not ready at the moment, and the first prototype was flown without the cannon, with 'conventional'
M-105 engine.
First flight was performed by Yu.I.Piontkovskij on January 13, 1940. Without
further delay pilot pushed prototype 550m, circled airfield twice (with landing gear down) and landed. Performance
was exceptionally good for an aircraft that early in its development, with maximum achieved speed 586km/h. On 27 April the
first prototype was lost in fatal accident, killing long time Yakovlev's test pilot Yu.I.Piontkovskij. The cause was a manufacturing
defect and pilot's hurry to push prototype to its limits.
Despite the accident, I-26 was approved for mass production in the mid-1940, even
prior to completion of the State Acceptance Trials. Sixty four were ready in 1940.
I-26 was first seen on public on October Day fly-past over the Red Square.
State acceptance trials started on 10 June 1940. Pilots were impressed by the
aircraft's aerobatic and spinning characteristics, but complained of insufficient climb rate and horizontal speed.
Trials continued until November 1940. Normal for radical new design problems were
cured already during production and early service period. Those included strengthening of aluminum fuel pipes (or employment of
the flexible ones) to cure gasoline leaks, installation of additional under-nose oil radiator. Retractable tailwheel of the
prototypes was replaced by the fixed one. Below is list of I-26 prototypes features:
I-26 I (1st version) Fully-covering 3-part u/c doors. Retractable tailwheel. Oil cooler intake under the fuselage. No
armament installed, but all provisions made. No armored glas, just 8mm plate protecting head and back of the pilot.
I-26 II Enlarged, different shape vertical tail and rudder. Shortened water cooler duct. Non-retractable tailwheel
250x95mm. Main wheel door of different shape.
I-26 III Different shape of oil cooler. Adjustable oil cooler flap at the outlet. Non-retractable tailwheel. Air intake at
the base of port wing.
In December 1940 production version(s) of the I-26 was assigned a designation
Yak-1.
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