Yak-44E - D-27 Engines
The power plant of aircraft consists of two D-27 TVVD, developed by the Zaporozh'ye machine-building design bureau ([ZMKB]) "Progress". Both key elements, which determine its high technological level, propfan and reduction gear, are produced in Russia. The propfan has a high-speed supersonic propeller with the wide scimitar-shaped blades. The main advantage of this screw was high efficiency at the high transonic speeds of flight, compared with usual propellers at the average flight speeds. Attempts at the creation of supersonic propellers were undertaken from the end the 1940s, but they ran into the impossibility of preparing the scimitar-shaped blades of the required strength. Only into 1970s, with the advent of of composite materials this problem was solved, and a number, the leading engine-building firms of the world approached the development of such engines. However, to complete this work - and with luster! - only ZMKB "progress" and Stupinskomu KB of Machine Building [SKBM] succeeded.
The selection of the engine for the aircraft Yak-44[E] was caused by the fact that with the sufficiently high subsonic cruising flight speeds it has considerably better efficiency than contemporary turbofan engines. Furthermore, as the analog of turboprop engine in the takeoff conditions it provides the best thrust characteristics and the thrust-weight ratio, sufficient for the takeoff from the springboard, and also an increase in the lift of wing due to the blowout. These qualities are important also because on the base of aircraft Yak-44E it was intended to create the entire family of the aircraft of deck and airport basing with different optimum cruising speeds, and in entire range of these of velocities the D-27 engine had the unquestionable advantages over TRDD and TVD.
The first tests of gas generator D-27 were carried out in 1988 ; and in 1990 it passed complex a study at the flying laboratory Il-76LL. For study and solution of some problems, which appeared with the design of aircraft with [TVVD] (acoustic and vibration loadings, level and the spectrum of noise at the work sites of crew and operators and others), on the base of aircraft Yak-42 ?525 was created the flying laboratory Yak-LL, equipped with one lateral D-236 TVVD, the experimental analog TVVD of the D-27 with smaller dimensions.
This work was important, also, for developing at this time in OKB im. A.S.Yakovlev was the design of passenger aircraft Yak-46 with two D-27 pushing propfans). The D-236 had the two-row pulling propfan SV-36 with a diameter of 4.2 meters (analogous to propfan SV-27, but smaller diameter). The quantity of blades in the front row was 8, and the rear 6. The takeoff power of the D-436 was about 12000 hp, equivalent thrust to 10.5-11 tons. The engine was installed on the special right pylon of the Yak-LL instead of one of three regular engines D-36. Since the takeoff thrust of the D-36 was less than the takeoff thrust of the D-236, in order to avoid the inadmissible turning moment, flight regimes were limited. In the takeoff conditions its equivalent horsepower was 9450 hp, and propfan - 8600 hp.
The development of aircraft Yak-LL began in 1987 ; and toward the end year was released design documentation. The ground tests of aircraft (race of engine D-236, taxiing with the measurement of vibration and acoustic responses) began in 1990 ; and the first flight took place on March 15, 1991. In June the same goal aircraft Yak-LL was demonstrated on the aviation coat in Le Bourget.
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