Tumansky R-25

The Tumansky R-25 is a turbojet engine, which is seen as the ultimate development of Tumansky R-11. It was designed under the leadership of Sergei Alekseevich Gavrilov.

Design and development
The Tumansky R-25 was designed as a replacement for the Tumansky R-13 in MiG-21 fighters. The R-25 is a two-spool axial-flow turbojet with a new compressor with increased overall pressure ratio and airflow, variable two-stage afterburner, and greater use of titanium.

An unusual addition to the R-25 was an emergency mode thrust boost which increased the compressor speed to 106% and also increased the afterburner fuel flow with the addition of a second afterburner fuel pump. Thrust was increased to 96.5 kN below an altitude of 2000 m. The time limit for its use was 1 minute during training and 2 minutes in wartime, as further use caused the engine to overheat and be irreparably damaged. Use of this WEP required the engine to be removed on landing for inspection. Use of WEP shortened the already limited time between overhaul typical of Soviet-made engines of that era compared to Western engines.

The R-25 engine was used on the MiG-21bis and the Sukhoi Su-15bis. A total of 3,200 R-25 were built between 1971 and 1975. The engine was also built under license by HAL in India for its fleet of MiG-21bis.