Tumansky R-15

The Soyuz/Tumansky R-15-300 is an axial flow, single shaft turbojet with an afterburner. Its best known use is on the Mikoyan-Gurevich MiG-25,

Design and development

The R-15-300 was designed at OKB-300 design bureau led by Sergei Tumansky in the late 1950s. The engine was originally designed to be used in the Tupolev Tu-121 high-altitude high-speed cruise missile. Due to lacking Soviet resources and funding the engine casing was mainly steel, and in areas exposed to high levels of heat, 30 micrometre silver-plated steel. At the time, the USSR did not have the resources to exploit metals such as titanium, or other composite alloys, which could have greatly reduced the engine's weight. The Tu-121 effort was later canceled, but its basic design was re-used to create the Tupolev Tu-123 reconnaissance drone.

Performance

At dry thrust the engine could produce 7,500 kilograms force (73.5 kN, 16,500 lbf); with afterburner the output is 11,200 kilograms force (110 kN, 24,700 lbf). This allowed speeds of up to mach 3.2 in the Mikoyan-Gurevich MiG-25 (which used two engines). However, at speeds above mach 3, the force of the engine sucking fuel through the pumps overwhelmed the pumps' ability to limit the flow. At this point, the engines effectively became ramjets, as air began to bypass the low pressure compressors, accelerating out of control until the pilot could regain throttle control through using firewalls or compressor stall, or the...
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