In 1945 the Soviet authorities instructed four bureaux to design fighters Mikoyan/Gurevich and Sukhoi were allocated responsibility for twin-engined types, with Lavochkin and Yakolev concentrating on single-jet aircraft. The powerplant was to be the Kolesov RD-10, an adaptation of the Junkers Jumo 004B developing 850 kg (1874 lb) of thrust. Primarily the responsibility of Yevgenii Adler and Leon Shekhter, development of the Yak-15 began in May 1945 around the captured German jet engines which were becoming available. The all-metal second-generation Yak-3 airframe was used as a basis and enabling the first of three prototypes to be completed in the following October. Taxying trials and short "hops" were performed, but flight testing was delayed while the possibility of the jet efflux attaching to the fuselage at high incidences was explored in the TsAGI T-101 full-scale wind tunnel. The Yak-15 retained most of the wing, rear fuselage, tail and undercarriage of the Yak-3, a new fuselage nose housing a Junkers Jumo 004B turbojet being introduced, and the main-spar being arched over the jetpipe.
Main longerons were strengthened to take the increased load. A stainless-steel sheet was attached beneath the rear fuselage to protect it from the hot exhaust gases, and a roller replaced the tail wheel, with protection against the jet blast being given by a shield.
The first prototype was ready in October 1945, but the first flight was delayed to 24 April 1946, just three hours after the Mikoyan-Gurevich OKB's I-300 (MiG-9).
The Yak-15 was demonstrated over Tushino during Aviation Day on 18 August 1946, and two days later, on 20 August, the NKAP (People's Commissariat for the Aircraft Industry) issued a directive that 12 additional aircraft be built to participate in the October Revolution Parade to be held on the following 7 November, 80 days later. Produced by hand, the first of these flew on 5 October and the last in time to participate in the Parade, which, in the event, was cancelled because of inclement weather.
State Acceptance testing was completed in May 1947, and, despite being structurally limited to Mach=0.68 below 3200m, 280 were ordered into production at GAZ 153 as an interim type single-seat jet conversion trainers. Flutter problems with an airframe which had been designed to accept a piston engine resulted in the Yak-15's top speed being limited to Mach 0.68, thus preventing full power being used below 3200 m (10500 ft).
One of the pre-series Yak-15s had meanwhile been adapted as a tandem two-seat conversion trainer under the designation Yak-21.
The initial production batch used the tailwheel undercarriage, but this proved unsatisfactory and the type was redesigned as the Yak-15U (Usover-shenstvovanny, or improved) with a tricycle layout. The nose wheel could not retract fully, since it was mounted beneath the air intake, so it was housed in a bulged fairing when in the up position. The change to a nose-wheel layout altered the Yak-15's balance, so the main undercarriage was modified to retract between the main spars instead of in front of the forward member.
The series Yak-15 carried an armament of two 23mm NS-23 cannon and was powered by a Jumo 004B turbojet which had been adapted by I F Koliesov of the Lyulka bureau for manufacture at Kazan as the RD-10 with a rating of 892kg. Production gave place late in 1947 to the Yak-17 after completion of 280 Yak-15s.
The Yak-15 was to achieve the distinction of being one of only two service jet fighters in aviation's annals to have been derived from a piston-engined service fighter (the other being the Swedish Saab 21R).
Span, 30 ft 2.25in (9,20m)
Length, 28 ft 6.5 in (8,70 m)
Height, 7 ft 5.5 in (2,27m)
Wing area, 159.85 (14,85sq.m)
Max speed, 435 mph (700km/h) at 8,200 ft (2 500 m), 500 mph (805km/h) at 16,405 ft (5 000 m)
Time to 16,405 ft (5000 m), 4.8 min
Max range, 317mls (510 km)
Empty weight, 5,1811b (2350 kg)
Loaded weight, 6,0291b (2735kg)