Source : Bulgarian Military
In 2024, Rostec’s UAC [United Aviation Corporation] is set to commence deliveries of the upgraded Su-57, now equipped with the cutting-edge AL-51F1 engine, formerly known as “Izdelie 30”. The revamped fighter has been rebranded as the Su-57M, with the “M” representing its modification year.
Rostec reports that the formidable AL-51F1 engine has passed all tests with flying colors, exceeding every expectation. The new engine delivers a robust thrust of 11,000 kg and an afterburner capable of 18,000 kg. Due to this upgrade, the Su-57 can now reach a cruising speed of Mach 2, while remarkably reducing its visibility within the infrared range — a decisive advancement over its predecessor.
Interestingly, the AL-51F1 does not just enhance the Su-57. It also revitalizes another promising fighter, the Su-75. Said by Russia’s Deputy Prime Minister Yuri Borisov at the Petersburg International Economic Forum [SPIEF], the Su-75 is scheduled to launch its maiden test flight in mid-2025. The initial model of this revolutionary aircraft is currently under construction at the esteemed Gagarin Aircraft Plant, KnAAZ.
AL-51F1 changes classification
Currently, the Russian Su-57s are powered by the AL-41F1 engine or its modified version, the AL-41F1S. This was a significant factor that led global aviation authorities to withhold their recognition of the Su-57 as a fifth-generation fighter. Enter the AL-51F1, a game-changing engine that propels the Su-57 firmly into the ranks of 5th-generation fighters.
The AL-41F1 engine was initially developed for the Mig-1.44 project. With time, it received an upgrade and evolved into the AL-41F1S that we see today, utilized in the Su-35S and later in the Su-57. ‘Experts’ argue that these engines don’t allow the Su-57 to attain a supersonic cruising speed without afterburning—a trait expected from a 5th gen fighter. [It’s worth noting that the F-35, too, doesn’t achieve supersonic cruise speed, but this doesn’t seem to disturb anyone].
However, this isn’t the full story. The Su-35C, carrying 75% fuel onboard, can reach a speed of Mach 1.15 without afterburning. This achievement is on par with the French powerhouse, Dassault Rafale. The Su-57, being a ton lighter than the Su-35S and equipped with a pair of AL-41F1 engines updated for increased thrust of 1,400 kg [700 kg each], logically suggests that the Su-57 should have no trouble cruising at Mach 1.25 – 1.31 speed—without afterburn.
The S-shaped air intakes
As time progressed, the Su-57 fighter transitioned from a basic fighter to a sophisticated piece of machinery. It underwent multiple enhancements in its avionics, and diverse systems, and received improvements in its gear and fuselage design.
Despite its advancements, critics began to express concern, particularly about the lack of S-shaped air intakes, which significantly boost the Equivalent Radar Cross-section [EPR]. However, the Su-57 deploys a different technical strategy to compensate for the absence of these air intakes.
By 2020, an intriguing practice was observed in photos and videos of the fighter – the air intakes were either meticulously retouched or entirely concealed because the turbine blades were not visible. But, that doesn’t imply they don’t exist; they’re just not conspicuously visible. The experts at the Sukhoi Design Bureau didn’t neglect the S-channel; they chose a different approach due to the engines’ specific characteristics. A part of the engine’s performance is vertical and the exposed turbine blades are shielded by what is known as a coaxial radar blocker [a specific type of grid], similar to the one found on the F-117.
Nozzles and turbines
There’s exciting news on the horizon as the updated Russian Su-57s are predicted to roll out in 2024, boasting a host of enhancements. These not only include a new engine, but innovative flat nozzles and ceramic turbines as well. Last year, we heard from Rostec and AUC, with the revelation that tests were underway for this novel configuration. Freshly in the news is that these firms report the test outcomes are aligning with the initially outlined technical specifications.
We had our first whisper about the Su-57’s flat nozzles when a slide from a presentation garnered attention. Swiftly, the Russian media began sourcing from this same slide during a talk by United Engine Corporation [UEC], hinting at ongoing developments. The work was not exclusively about flat nozzles—there was more. They spoke of the development of high-performance bearings, components termed “ceramic turbines”, and cutting-edge electrical systems.
But the conversation doesn’t end there. Discourse is also centered around the construction of a three-circuit power plant for the engine. Such progression could potentially lead to a notable improvement in subsonic effective fuel efficiency— perhaps an increase of up to 12.5%. Now, that is something to watch out for!
