RuAviation

On April 2, 1996, the highly maneuverable fourth-generation fighter Su-37, equipped with thrust-vectoring AL-37FU engines, took to the skies for the first time. The test flight was performed by test pilot Evgeny Frolov from the Sukhoi Design Bureau. The sole flying prototype of this aircraft, bearing the tail number 711, was built at the end of 1993 based on the Su-27M fighter, designated as T10M-11 by the Sukhoi Design Bureau.

The inspiration for the creation of the highly maneuverable fighter came after the display in June 1995 at the Le Bourget international airshow by the German-American experimental aircraft Rockwell-Messerschmitt-Bölkow-Blohm X-31. The X-31 executed aerobatic maneuvers at greater altitudes compared to our MiG-29 and Su-35 fighters (the Su-27M at that time). At the end of the maneuvers, the aircraft achieved near-zero horizontal speed and rapidly accelerated to the minimum speed required for maneuvering.

The X-31’s uniqueness lay in combining reduced static stability with artificial dynamic stability, featuring aerodynamic surfaces for generating additional control moments, vortex aerodynamics, and a variable engine thrust vector. The aircraft could alter its trajectory without significant changes in angle of attack and sideslip by direct control of lift and side force, and thrust vector.

At the request of the Soviet government in 1983, research on thrust-vectoring was initiated for the Su-27M aircraft at the Sukhoi Design Bureau under the guidance of Chief Designer Mikhail Simonov. Sukhoi, in collaboration with the Siberian Scientific Research Institute of Aviation (SibNIA), studied nozzles with axisymmetric thrust vector control, as opposed to Western two-dimensional nozzles. Concurrently, the engine design bureau of Archip Lyulka began researching engines with thrust-vectoring capability.

During test flights of the Su-27MS in 1988, engineers discovered that pilots were unable to maintain active control at high angles of attack due to the ineffectiveness of control surfaces at low speeds. To address this issue, thrust-vectoring engines were fitted to the Su-27 (T10M-11), which was used as a testbed. Initially, the plan was to install the AL-37FU engine on the Su-27M, but as it was not fully developed, a less powerful AL-31FP engine was temporarily installed.

The AL-37FU nozzles could deflect up to 15 degrees up or down along the pitch axis. After system upgrades for aircraft and engine control and the installation of standard power units, the aircraft was re-designated as the Su-37 (known within the OKB as Su-27M2). By the beginning of 1995, the aircraft was ready for testing. “The engines developed by the Lyulka Design Bureau, AL-37FU, were the main distinguishing feature of the Su-37 – unparalleled maneuverability that would give it superiority in close aerial combat over adversaries lacking such capabilities,” recalled test pilot Evgeny Frolov.

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“Sukhoi OKB, with its experience in designing the Su-27, in collaboration with the Lyulka Design Bureau, developed the Su-37 fighter, which excelled in combat capabilities and maneuverability. It was the first aircraft to embody the idea of thrust vectoring during flight, allowing for controlled aerobatic maneuvers at nearly zero and even negative speeds without angle of attack restrictions – supermaneuverability modes. On April 2, 1996, I had the opportunity to make the first flight in the Su-37, tail number 711. Chief Designer Vladimir Konokhov and lead Silaev escorted me for takeoff. The handling was even simpler and safer than on the Su-27,” recounted Evgeny Frolov in Lydia Kuzmina’s 2014 book “Flaming Engines” by Arkhip Lyulka.

The Su-37 executed a 360-degree pitch-plane turn. This maneuver was named the “Frolov Chakra” after the pilot who first performed it. The aircraft could complete this combat turn in less than 10 seconds, execute a “Cobra” with attack angles of 150-180 degrees (compared to the Su-27’s 120-degree Cobra), perform a turn on a “bell,” execute a turn with a loss of 300-400 meters in altitude, and other maneuvers not achievable by conventional aircraft with fixed thrust vector.

According to Yevgeny Frolov, these maneuvers enable the pilot to assume the most advantageous position in a combat situation. “Of course, all of this became possible thanks to the AL-37FU engine with thrust vector control. The gas-dynamic stability of the engine is excellent. Despite the Su-37 performing virtuoso maneuvers at full afterburners and at some point flying literally tail-first, there has never been a malfunction of the engines during all flights,” he says.

In 1998, the avionics and engines of the Su-37 were replaced; AL-31F engines without thrust vectoring were installed, and the designation was changed to Su-35, but the aircraft’s tail number remained the same: 711. In 2003, an accident occurred during testing near Moscow resulting in the pilot ejecting safely, but the aircraft was lost.

A narrative about Pavel Sukhoi’s Su-37 combat aircraft would be incomplete without remembering that as early as 1989, the development of the multirole fighter-bomber, also designated S-37, began. This project was initiated by a resolution of the Soviet Council of Ministers and the Central Committee of the Communist Party and was intended to replace the fleet of tactical strike aircraft used by the Soviet Air Force and Warsaw Pact countries.

The Su-37 was envisioned as a multirole attack aircraft capable of engaging various airborne and ground targets. The new aircraft was intended to replace the Su-25 attack aircraft in the Soviet Air Force and Warsaw Pact countries. The prospective Su-37 promised to be much more effective and modern than its predecessor. It was designed for engaging ground mobile armored and unarmored targets, small-sized stationary and moving targets, air defense system complexes, reconnaissance in simple and complex weather conditions, day or night. Additionally, the aircraft could be used against enemy strike and transport aircraft, designed to successfully counter army and tactical aviation, including combat tactical aircraft and helicopters.

Although the full-scale Su-37 project was not realized due to the collapse of the Soviet Union, funding cuts, and political and economic challenges, it made a significant impact on the development of the aviation industry and military potential of Russia. The Su-37 left a notable mark in the history of Russian aviation, showcasing the potential of Soviet and later Russian technology, despite the project not reaching full fruition.