The second stage engine with a flat nozzle and controlled thrust vector for the Su-57 fighter, known as ‘product 30’ or AL-51F1, is undergoing flight tests on a prototype aircraft with the flight number 052 (PAK FA T-50-2). At the same time, the second engine with axisymmetric circular nozzle remains standard – AL-41F1. This is told and shown in the documentary film of Channel One Masters of the Sky, dedicated to the 85th anniversary of the Experimental Design Bureau named after Pavel Sukhoi.
The engineering approach to the Su-57 implies modularity of its design, which makes it possible to quickly replace various components, including the propulsion system. As Mikhail Strelets, director of the Sukhoi Design Bureau and chief designer of the Su-57, noted, in the future combat aircraft fitted with the first-stage engines may be equipped with a new flat-nozzle engine, which will significantly improve their combat performance and also reduce the fighter’s visibility in the rear hemisphere.
The flat nozzle is a complex metal-composite construction. Unlike traditional axisymmetric nozzles, the flat nozzle is used on the aircraft to create new possibilities, including providing low visibility in the radar range due to the characteristic shape of the nozzle flaps, and allows its application in a wide range of altitudes and flight speeds. Thanks to this, the aircraft retains all its manoeuvring capabilities.
‘In essence, the flat nozzle complements the existing aerodynamic controls by allowing the creation of moments in three planes and thus pitch, roll and track control. And since the nozzle installation angle is preserved with axisymmetric, all the possibilities of super manoeuvring the aircraft are also preserved,’ explained Mikhail Strelets.
One of the key advantages of the flat nozzle is the reduction of the aircraft’s visibility also in the infrared range. The flat nozzle narrows the high-temperature exhaust jet, reducing the Su-57’s heat signature, making it less vulnerable to missiles with infrared homing heads.
On the foreign market, the American F-22 fighter has similar solutions. However, its flat nozzles can only deflect in the vertical plane, which limits manoeuvring capabilities compared to the Su-57.
In the USSR, a flat two-axis nozzle was designed in the second half of the 1970s for the Yak-41 vertical take-off and landing (VTOL) deck fighter. An original solution was used for its rotation – the nozzle was divided into three segments, which, rotating in opposite directions relative to each other, provided a deflection of the thrust vector in the vertical plane to an angle of 95° (at VTOL mode). For short takeoffs, the nozzle was set to 62°. This solution made it possible to use afterburner both in horizontal flight and in vertical mode.
Russia has brought to China the AL-51F1 engine for Su-57 and Su-75 fighters
In addition to modernising the Su-57 with the second stage engine, Sukhoi Design Bureau is working on improving the information display system. Data from the flight computer will be displayed not only on the cockpit displays, but also on the flight helmet visor. The helmet is equipped with an optoelectronic positioning system and a video display system. The picture is displayed on the face shield.
This helmet replaces several devices at once and is equipped with a large number of sensors. They detect the movements of the pilot’s head and, depending on where he turns his head, project the information he needs at that moment, such as target selection and acquisition. The helmet-mounted target designation system is being developed specifically for the Su-57 and will allow the pilot to receive information about the aircraft’s status, combat situation, speed, altitude and distance to the target.
According to Dmitry Korzinin, head of the optoelectronic systems department at the Sukhoi Design Bureau, if a missile with an infrared homing head captures a target, the pilot’s aiming marker on the helmet shield will change. He will know that the target has been acquired and will then see whether the launch is authorised or not. In which direction the pilot is looking, in the same direction the missile’s homing head is deflected. The helmet with the target designation system is now undergoing flight tests.
‘We see the aircraft as a platform that for at least 50 years can effectively fulfil its tasks. Including the gradual introduction of next-generation technologies, essentially turning the aircraft from generation 5 to 5 plus. This is the generation in which certain technologies of the sixth generation are already being implemented,’ Mikhail Strelets added.
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