The Saturn AL-31 (originally Lyulka) is a family of axial flow turbofan engines, developed by the Lyulka-Saturn design bureau in the Soviet Union, now NPO Saturn in Russia, originally as a 12.5-tonne (122.6 kN, 27,560 lbf) powerplant for the Sukhoi Su-27 long range air superiority fighter.

The AL-31 currently powers the Su-27 family of combat aircraft and some variants of the Chengdu J-10 multirole jet fighter.

With an emphasis on greater fuel efficiency over turbojets for longer range, the 12.5 tonnes-force (122.6 kN; 27,560 lbf) class turbofan engine was intended to power the heavy PFI (Russian: ПФИ, short for: перспективного фронтового истребителя, lit.

[1][2] After the collapse of the Soviet Union, design bureau and production plant distinctions realigned and gradually faded, and Lyulka-Saturn eventually merged with Rybinsk Motors to become NPO Saturn and was closely aligned with UMPO while Salyut became an independent entity; both Saturn and Salyut would make their own developments for the AL-31 family.

[3] This reorganization would result in serious disputes between Saturn and Salyut over intellectual property rights and royalties over AL-31 sales to China.

[2] The AL-31 was also used to assist Chinese engine designer and manufacturer Shenyang/Liming in developing the WS-10, with early examples directly using the AL-31F control system.

[7] The research on thrust vectoring would be applied to the production AL-31FP used in the Sukhoi/Irkut Su-30MKI for India as well as further derivatives including the Su-30MKM for Malaysia and the Su-30SM for the Russian Air Force and Navy.

AL-31FP is built by UMPO as well as in India by Hindustan Aeronautics Limited (HAL) at the Koraput facility under a deep technology transfer agreement.

[2] The AL-31FN variant was developed by Salyut to power the Chengdu J-10, with key differences including slightly more thrust of 12.7 tonnes-force (124.54 kN; 27,999 lbf) and gearbox relocated from the top to the bottom of the engine.

Later J-10 variants and production lots were equipped with the improved AL-31FN series 3, with thrust increased to 13.7 tonnes-force (134.35 kN; 30,203 lbf) and service life raised by 250 hours.

The engine also incorporated improvements to the combustor and turbine blade aerodynamics and cooling for higher entry temperatures.

[12][13][9] Salyut's developments of the AL-31 would result in serious disputes with Lyulka-Saturn's successor corporation NPO Saturn, which considers them unsanctioned and in violation of intellectual property rights.

Though the specifics remain classified, the AL-41F1's thrust was increased by 2.5 tonnes-force (24.5 kN; 5,510 lbf) over the AL-31 while the engine weight growth was reduced by 150 kg (330 lb).

The aircraft's powerplant, the NPO Saturn izdeliye 117S, or AL-41F1S, is a slightly simplified derivative of the AL-41F1 from the Su-57, with the key difference being the separate engine control system of the AL-41F1S.

The Su-35 and its AL-41F1S engines were originally developed by Sukhoi and Saturn internally for export, although the initial customer would be the Russia Defence Ministry.