Central Aerohydrodynamic Institute
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TsAGI centenary in the history of aviation: the vertical and short take-off and landing aircraft Yak-36

25 July 2018

By the end of 1950’s, during the Cold War between the Soviet Union and the United States, military air forces of different countries needed to improve landing characteristics of combat aircraft and reduce the ground run. For a long period, military aviation was focused on the launch speed, causing fighters to lose low-speed mobility. The soviet attack aircraft Yak-36 could hover, as well as take off and land vertically, demonstrating Soviet technology of the time. Its first flight took place in July 27, 1964.

Specialists of the Zhukovsky Central AeroHydrodynamic Institute (TsAGI) participated in the development of a fundamentally new aircraft. Scientists proposed to redistribute the engine thrust in a way that vertical take-off and landing were possible through vectored thrust. This principle formed the basis of the Yak-36, using R-27-300 lift/cruise engine with rotating nozzles. The fuselage was substantial forward of the wing’s trailing edges to accommodate the engines, with cockpit, fuel tanks and equipment bays as close to the centre of gravity as possible, tapering sharply to the swept tail surfaces with a high-set empennage. Control of the aircraft was by conventional rudder, ailerons and elevators in normal flight and by compressed engine bleed air blown from control nozzles at the wingtips, rear fuselage tip and at the end of a long boom extending forward from the top lip of the air intakes.

Another distinctive feature of the Yak-36 was the tricycle landing gear with one wheel nose-mounted and two wheels toward the rear. A pilot ejection system was added to the rescue system device. The aircraft was equipped with an automatic control system for zero flight speeds. The airframe was typical for those years: fuselage, strengthened with power frame and wing spar with flaps.

The first four prototypes were intended for a different kind of research. One ran field tests with working engines in the large TsAGI wind tunnel where they simulated thrust vector control. As a result they obtained valuable data to ensure a safe take-off and landing, as well as transition.

In addition, while testing the aircraft aerodynamics at vertical take-off mode, the Institute specialists found two hazardous effects associated with engine blast at lift.

The first was associated with the following: the fighter jet surfaces were streamlined near ground, had depression, resulting in a decrease of efficient vertical thrust by 15-20%. Another effect were the hot gases flowing into air intakes. It reduced thrust possibly causing engine surge. TsAGI specialists constructed special model stands with screens to examine these phenomena and to develop a set of events, greatly weaken these harmful effects.

The first Yak-36 flight was in standard mode, and almost two years later, the first complete flight was made from vertical takeoff transition to horizontal flight deceleration to vertical flight and vertical landing. After much testing and practice the first public presentation of the Yak-36 was made on 9 July 1967 at an air show at Moscow-Domodedovo airport. Models of possible weapons were established on the wings of the airplane because of its low carrying capacity.

Later designers improved most of the aircraft systems. The result was a new Yak-38-deck fighter, the first in USSR serial vertical take-off and landing aircraft.

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