Images have emerged of Russia’s Sukhoi Su-57 Felon advanced fighter equipped with a new type of thrust-vectoring engine nozzle. The radical-looking exhaust design aims to improve the Felon’s low-perception characteristics, although the future of the new mouthpiece is far from certain.
The videos and photos show the rear of the second flying prototype for the Su-57 program, the T-50-2, which was first flown in March 2011. It was subsequently used to build the improved AL-51F-1 ( also known as as izdeliye 30) turbofan, which first flew in December 2017 – with only one of the engines installed in the aircraft, next to one of the original AL-41F-1s.
What stands out about the turbofan mounted in the left engine nacelle of the T-50-2 is the nozzle, an example of the new flattened version intended to equip the AL-51F1 once it is installed in the improved Su-57M has been installed. version of the hunter. To date, no orders have been placed for this variant of the aircraft.
Another view of the flat version of the nozzle for the AL-51F1 (in the left engine nacelle), next to the original three-dimensional version (right nacelle). via X
The AL-51F-1 was developed as a ‘clean-sheet’ design, intended to provide increased thrust, reduced weight and lower operating costs compared to the previous AL-41F-1. Another disadvantage of the earlier engine is the Su-57’s inability to provide supercruise performance: it flies above Mach 1.0 for extended periods without the use of afterburners.
At this point it is worth looking at the AL-41F-1, the original engine for the baseline Su-57, and its nozzle configuration. This turbofan is also used in a simplified form in the Su-35 Flanker multirole fighter. The AL-41F-1 (also known as izdeliye 117) was produced by modernizing the existing AL-31F engine used in the earlier Su-27 and Su-30 Flanker series fighters.
Video of the Su-57, showing the original three-dimensional thrust vectoring nozzles:
An Su-35S and a prototype Su-57 over the Akhtubinsk flight test center in 2015. Mikhail Voskresenskiy/Sputnik via AP Mikhail Voskresensky
Video of the Su-30MKM, which uses a similar three-dimensional thrust vectoring arrangement as the Su-35:
In the Su-57 and Su-35, the AL-41F-1 is equipped with a thrust vectoring nozzle of the axisymmetric type. Also known as three-dimensional thrust vectoring, this provides control over pitch, yaw and roll.
In its original form, the AL-51F-1 also has a similar three-dimensional jet vector nozzle, but what we see in the new images is an alternative nozzle, this time of the two-dimensional type, which also provides pitch control. as limited roll control when asymmetrically engaged. It is not clear whether the angled installation of the nozzle is intended to provide additional control in the latter.
The original three-dimensional jet vector nozzle for the Su-57, seen above, compared to the new two-dimensional type nozzle, seen below. via X
These types of low-profile ‘flat’ engine jets are also used on the F-22 Raptor, for example, and are chosen primarily to reduce radar signature compared to an axially symmetrical nozzle design. It also offers advantages for infrared signatures.
A close-up of the F-22’s distinctive thrust vectoring exhaust nozzles in action. Their unique “hemispheric design” improves the F-22’s stealth, even from the rear. In fact, it is said that even the F-35 cannot match the rear stealth capabilities of the F-22. pic.twitter.com/9NHC8DECZQ
— Air Force (@RealAirPower1) September 16, 2024
According to Yevgeny Marchukov, CEO of the Arkhip Lyulka Design Bureau responsible for the AL-51F-1, in comments reported by Aviation weekWhen that program was launched, Sukhoi was not interested in using a flat nozzle for the Su-57. Only later was the two-dimensional nozzle ordered, after the Su-57 and the AL-51F-1 flew.
Since Sukhoi “resists changes to the airframe itself,” Marchukov explained, “we therefore came up with a rather complex planar nozzle.”
As shown in the diagram below, the nozzle has four independently controlled valves, which work by changing the cross-section of the air outlet and the thrust vector. Of these flaps, which are installed at an angle, two are reportedly tailor-made for use in the subsonic regime and two for supersonic flight. The images also appear to show the vectoring valves being vented, which, combined with air being forced through these areas, would help cool the exhaust gases and lower the aircraft’s infrared signature.
Two diagrams of the new nozzle from a company brochure. via X
Speaking in the summer of 2023, Marchukov confirmed that the new nozzle had been successfully used on a ground test field, including afterburning. He added that a first flight was expected before the end of 2023, although there is no data on whether that ever happened.
For the Su-57, the flat nozzle would provide notable benefits in terms of improving low-level visibility from the rear. The Felon’s original design optimized low visibility from the front, with less attention paid to the sides and rear. At the same time, the revised nozzles will reduce thrust to some extent, but this is clearly considered a valuable penalty based on the improved low observable aspects it brings, which are sorely needed for this type.
It is also worth noting that another flat nozzle design has been developed for the version of the AL-41F-1 engine used in the Sukhoi S-70 Okhotnik heavy subsonic unmanned combat air vehicle. In this case, the two-dimensional nozzle is intended to reduce the infrared and radar signatures, but it is much simpler, without any vectoring control.
via X
The Okhotnik was first flown with an intermediate engine, with a standard round nozzle, but the revised nozzle was fitted to the second aircraft, which was rolled out in December 2021, as you can read here.
As for the flat nozzle version of the AL-51F-1, its future depends very heavily on that of the proposed Su-57M.
Work on this improved version of the Felon was already well underway when the Su-57 entered production and service, although with only 76 examples of the original model under contract, it is far from certain that it will continue progress, at least in the near future. term.
Also known as the T-50M, formal work on the ‘deeply modernized’ Su-57M began when Sukhoi received a contract from the Russian Ministry of Defense in October 2018. At one point there were reports that a T-50M prototype was beginning flight testing. mid-2022 and series production at the end of 2024.
Clearly these targets have not been met, but if Russia – or an export customer – orders more Felons, it could also help ramp up the Su-57M. At that time, we may also see a production version of the two-dimensional thrust vectored version of the AL-51F-1 engine.
Contact the author: thomas@thewarzone.com
