Jakovlev Jak-15 [kód NATO: Feather]

Yakovlev Yak-15

The first Soviet jet-powered fighter aircraft was an interim solution. Designer Evgeny Adler, belonging to Yakovlev's OKB, took the best of what was available - a highly maneuverable yet powerful piston fighter Yak-3U and a German jet engine Junkers Jumo 004B, which the Soviet industry began producing under the designation Tumanskiy RD-10.
The wing, rear fuselage, tail surfaces, cockpit including instruments and controls, almost all electrical installation were taken from the original Yak-3U, the nose, wing spar, engine bed were completely new, the lower rear fuselage was covered by steel plates protecting the duralumin covering from hot exhaust fumes. The RD-10 turbojet engine was about the same weight as the VK-107A piston engine, plus no liquid and oil coolers were needed, only the cooling circuit cartridge weighed several tens of kilograms.
The first prototype was designated Yak-3 JUMO, and was ready for engine trials in October 1945. These tests were disastrous, the jet of gases exiting the engine immediately burned the tail wheel and the covering steel plates became so hot that they burned through the duralumin fuselage. The solution was simple in Russian, the tail wheel was replaced by a steel roller (this solution must have been very noisy and during takeoff and landing a literal tail of sparks must have formed behind the aircraft). Pads were inserted under the steel plates, thus creating an air gap that thermally isolated the duralumin fuselage from the hot steel plates. Armament was massive, with two NS-23 guns in the bow, each with 60 shells. The second prototype of the Yak-15 had a narrow-track landing gear - the wheels retracted from the fuselage towards the wingtips, this solution apparently did not work and other aircraft reverted to the original landing gear. Compared to the original Yak-3, the capacity of the tanks was increased, and the jet engine had much higher fuel consumption.


The prototype of the Yak-15 first flew on 24 April 1946, on which date the prototype of the twin-engine jet fighter MiG-9 had also taken off just an hour earlier.
Flight tests were quite satisfactory, it was found that the Jumo 004 engine did not have very good altitude characteristics, if the aircraft got above 6,000 m, the engine power began to drop noticeably and so the Yak-15 did not reach the calculated altitude of 13,500 m, but the pilots had to settle for an altitude of 10,000 m. The jet engine also had a very limited service life, originally it was calculated to have a service life of 25 hours, but in practice it was 15-17 hours and the engine was not allowed to be used in emergency thrust mode!
The new Yak-15 was introduced to the public at the Moscow May Day parade in 1947, a group of fifty Yak-15s and fifty MiG-9s flew over Red Square.


The entire production took place in the manufacturing plant No. 31 in Tbilisi, Georgia, and a total of 280 aircraft of this type were produced there. Most of the aircraft were used more for training pilots and ground personnel. The transition from the piston-powered Yak to this jet was quite easy for the pilots. Armament was often reduced to the installation of a single gun, or it was flown without weapons. Air defence of the state was provided by the more powerful twin-engined MiG-9.


Sources used:
Zdeněk Trávníček et al., Reactive Aircraft, Naše vojsko, Prague, 1965
L+K No. 9/1984, Monograph of the Yak-15, Miroslav Balous
http://www.airwar.ru/enc/fighter/yak15.html
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