SUKHOI SU-57

HIGH-TECH, STEALTH, SUPER CRUISE

Dozens and hundreds far-sighting solutions have been implemented in the design of the Sukhoi Su-57 fighter. As a result, the Sukhoi design bureau has produced an airplane that can adjust itself to the level of pilot’s skills, one that is hard to detect by radio-electronic, infra-red, electro-optical and sound sensors. More than 50% of its airframe surface is made of composite materials. The flight suit can forecast g-loads and adjust to them so as to help pilot sustain maneuvering. These and other high technologies and engineering solutions have shaped the aircraft inside and out. But that is not the end of the Su-57 story. They also determined criteria whether to attribute a warplane to the fifth generation or not. Besides, the technologies and solutions attested on the Su-57 offer solid foundations for developing new designs.

The Su-57 is attributed to the fifth generation. There are certain criteria to make such an attribution. ‘Surely, such attribution is rather conditional,’ – admits deputy general designer at United Aircraft Corporation (UAC) with responsibility for combat aviation, director at Sukhoi design bureau, chief designer for Su-57. ‘Manufacturers in every country use their own criteria to attribute an aircraft to a certain generation. And yet, it is possible to select some features, so that positive answers to those would make it possible to attribute the aircraft to a certain generation.’

Speaking about fifth generation of fighter aircraft, Russian specialists name the following distinctive features for attribution. First, the ability to cruise supersonically (i.e. maintain ‘super cruise’ mode of flight). Second, requirements to aircraft signature: it should be lower for radio-electronic, infra-red, electro-optical and sound sensors compared to that for previous generation aircraft.

Besides, the fifth generation fifth generation fighters must meet requirements to do with onboard equipment. He explains: ‘It should be built to the principles of open architecture and make provision for modular structure in application to avionics set.’ Besides, the new generation comes with stricter requirements to automation and intellectual support for the flight crew. Multi-channel sensor equipment should extend the pilot’s situation awareness. Finally, the fifth generation aircraft should comply with the concept of network-centric warfare (NCW), and be an element in the armed forces’ NCW control structure.

Distinctive features

There are some distinctive features that each new aircraft has. Russia’s design differs from all other fifth generation fighters available anywhere else in having multi-functionality. The chief designer highlights this point: ‘There were certain requirements to our aircraft. It should be able perform ‘air-to-air’ missions which are becoming to an air-supremacy fighter, and, at the same time, perform strikes at surface targets, becoming to a fighter-bomber.’

The Lockheed Martin F-22A Raptor is not like that. It was designed from scratch as an air superiority fighter. Air-to-air missions prevail over all others, with a 90% share. Another U.S. design, the F-35 Lightning II is different. It was designed for strike missions, a fighter-bomber with focus on attacks at surface targets. Admittedly, both have some multi-functionality. Let’s take the Su-57 for comparison. The multi-functionality of the American designs has different distribution to various flight missions. It is, so to speak, less evenly distributed to them. In its turn, the Su-57 can solve air superiority tasks and strike tasks in roughly equal proportions.

Another point to notice is that the F-22A air superiority fighter is primarily intended for air combat at long ranges. That’s why stealth qualities were the top priority, along with carrying air-launched weapons in bays inside the fuselage. Comparatively, the Su-57 is good at air combat regardless of range. ‘We tried to find compromise between the respective requirements,’ he explains. ‘The first requirement was to ensure stealth operations for gaining advantage in the long-range air combat. In addition to that, the second requirement called for high super maneuverability so as to perform air combat at short ranges. As a result, we produced a fighter possessing the same or higher level of maneuverability compared to best fourth generation fighters.’

Cutaway model

Outwardly, the Su-57 is much different to fourth generation aircraft designs from the same manufacturer. This is because it was designed from scratch with the idea of stealth operations in mind. Stealth technologies were implemented in a big way. ‘Compared to previous designs, the airframe for the Su-57 was deliberately made to accommodate these technologies. That’s why it has such a characteristic shape with sloping sides, parallel edges and so on,’ the chief designer explains.

To make the aircraft low-observable, the Su-57 comes with bays inside the fuselage to accommodate air-launched munitions. This engineering solution required design team to pay much attention to the airplane’s force bearing structure.

The chief designer recalls this. ‘One of the critical technologies was to do with fuselage shaping. The fuselage comes with cutouts for very large weapons bays in which air-launched munitions should be placed. It was necessary to make a strong structure able to withstand forces that appear when the aircraft executes high-g maneuvers. It was rather challenging for the design team. Neither Russian, nor foreign aircraft designs had that challenging task solved before.’

The Su-57 aerodynamic layout is also very special. It comes with control surfaces never seen before on any operable airplane. For instance, let’s take the moving (deflectable) forward part of the fuselage-to-wing extension. 'This forward part provides for stability and controllability of the aircraft flying at high angles of attack. This surface acts under control from the common flight control system, integrated into it, so as to increase lift-to-drag ratio for the maneuvering airplane.’

Construction materials

Construction materials, that the Su-57 airframe is made of, are worth a few words. There are some traditional metallic alloys in use, and yet not without novelties. The number of parts in Su-57 airframe is four times less than the figure for the Su-27. The higher capability of modern metal cutting tools contributed to this achievement. Besides, a contribution was made by digital modeling and prototyping at the design stage.

The tendency towards larger milled airframe parts came in a big way. The number of small parts and fasteners went down. The chief for the scientific-research detachment for construction materials and technologies at Sukhoi design bureau, gives the following comment. ‘This enabled us to streamline the force-bearing structure. Engineers at the assembly lines say: thanks to larger airframe parts, the airplane has become easier and quicker to assemble.’

More than 50% of its airframe surface is made of composite materials. Introduction of composites made it possible to manufacture larger skin panels and to reduce the number of fasteners. New technological methods and ways helped cut time, albeit necessitated additional equipment and tools.

Wider application of new construction materials became possible thanks to close cooperation ties between the Sukhoi design bureau and manufacturers of composites. Those became tied up during materialization of previous programs including those on lightweight aerobatic airplanes. He recalls this. ‘Beforehand, we worked closely with a certain enterprise in near Moscow. In frame of the Su-57 program, our partners had to master production of many unusual airframe parts and also master construction materials they never used before.’

This was a challenge. And yet, he insists, wider application of composite materials enabled Sukhoi design team to execute control over qualities of airframe parts by applying various stacking layouts in the filler.

‘You may, well, place the whole pack of the material pointing in one direction. And yet it is also possible to place a part of that pack perpendicular, or at 45 degrees. By combining various stacking layouts you may influence the qualities of the ready-to-use airframe part. Today, the composite materials have one significant drawback: they are more expensive than metal. But as production output rises and so does the market for composite materials. Manufacturing costs will go down. If so, we hope for comfortable pricing.’

Prior to launching composite parts into production, a large number of specimens underwent testing. The partner companies managed to achieve the parameters required, so that the parts they manufacture fully meet the specification. To achieve this, companies had to observe strictly the prescribed procedures for the process of manufacture, and to introduce a vigorous system of checks.

During the process of panel manufacturing for the Su-57 skin, it is important to meet the strictest requirements to accuracy for one more reason. The chief designer explains: ‘The quality of airframe skin produces a considerable influence on stealth performance.’

To make the airplane low-observable, there were other measures applied. They included application of special radio-wave adsorbing and reflecting layers. Besides, screening materials were applied to antenna bays etcetera. ‘All pieces of onboard equipment that were attached to the leading edge etcetera, were designed so as to observe the requirements to lower radar visibility. For the infra red signature to go down, we had to apply certain measures. For instance, engine exhausts had to be screened, and heat exchangers had to be air-blown.’

Also, there were requirements to lower optical signature. In part, these were met with special painting for the airframe. ‘There were additional requirements to lower acoustic signature.’ When one attends an air show, he or she may notice that the Su-30SM, Su-35 and Su-57 perform differently. ‘The latter flies much quieter’, the chief designer insists.

Three into one

The Su-57 is a multifunctional aircraft. Pilot’s workload goes up with the number of tasks he solves. At the early days of the Su-57 effort, design team made estimations leading to the next finding. There should be three people aboard a multirole fighter, one for pilot, second for weapons officer, third for flight engineer. Such a result was no more than a joke. ‘To enable the pilot carry out his primary mission, it is necessary to reduce the workload by taking the second-tier functions away,’ the chief designer for supercomputer technologies at Sukhoi design bureau, says.

‘Putting all the mathematical models together has enabled us construct the digital system in such a way that it minimizes the pilot’s workload. And yet, the human remains responsible for making decisions.’

There were some aircraft types of the Soviet origin that featured digital systems. Digital processors were embedded in various subsystems of their on-board equipment set. With every new design rose the depth and complexity of the tasks these were solving, one generation after another. ‘Time can when we received a new assignment, that to create a single-seat multi-functional warplane. At this point, all considerations mentioned before went on top,’ says the designer for purposeful application at Sukhoi design bureau. ‘Some decisions we tried before on the Su-30MKI and Su-35. And yet the Su-57 became the tallest hill we managed to climb on in the past few years. Its onboard equipment set is completely digital. Some sensors are analogue, but they generate digital signals or their readings are converted into digitals. All data processing is digital.’

Since the Su-57 is a multifunctional aircraft, it comes with an enormous number of systems and subsystems operating in various wavebands. The design team faced a challenge to put all this under single control. He recalls: ‘It became apparent quickly that such a rich abundance, a tightly-packed systems set, is difficult to manage for a single pilot. On one side, we had multi-tasking, on the other side the multi-mode and multi-system features. And we made decision straight away, that the single crew member must be not so much of a pilot and not so much of an operator, but a warrior. He must act at the level of decision-making that calls for unordinary solutions.’

It seems that the design team could have automated every mode and regime of the Su-57 flight mission, every task to be solved. But all solutions would have been deterministic ones. High-tech opponent may have recognized these solutions and produced counter measures quickly. Therefore, in every intellectual system that was embedded in the Su-57 project, there always was a non-formalized human factor. That factor is for unordinary, unexpected decisions that would lead to victory.

Each pilot to have a Su-57 of his own

On one side, fifth generation fighter is rather complex a machine. On the other side, such airplane should be such that an average pilot can handle it. For that purpose, the Su-57 comes with several levels of automation. For less prepared crews, the airplane can solve all tasks in a flight mission all by itself, albeit with middling quality. For better prepared pilots, provision is made to vary systems, with which to perform this or that task. Those pilots who pretend to know much, can dive well into depths of the systems’ control.

In other words, even an average pilot with middling talents can operate this aircraft with a sufficient level of efficacy. As time goes, he can improve his skills and start using the Su-57 capabilities better in all situations possible.

Such an approach is important for those crews who previously mastered other aircraft types. He observes: ‘Historically, our system of crew training is tuned into solving certain routine tasks to do with air combat, ground strike, interception. Those pilots who underwent training this way, confess that solutions for certain mission type sit well and deep inside their brain. In the case of the Su-57 the whole variety of such tasks shall be solved by one man. That is why we decided to put the human well above those tasks. The pilot must be a warrior in the first place. The warrior who decides what to do in a particular situation with help of aids the system feeds him with.’ Inside the Su-57’s cockpit, the pilot has a complete situational awareness, while the system feeds him with deterministic hints. As a result, the human in control either agrees with those hints, or makes corrections. In the latter case, the system solves these tasks automatically, but following other threads.

Comfort and safety

The Su-57 boasts agility and high speed in cruise. But those qualities bring about the consequent problems for the pilot: he has to endure high g-loads. In order to make the pilot’s job easier, the design team applied special measures. For instance, the seat’s back is set at an angle of 22 degrees. This helps the pilot sustain the g-load.

Besides, a Sukhoi partner company has developed an improved set of pilot’s outfit. In particular, the company altered the logic for the pilot’s pressure suit. The suit compensates for pressure at high altitudes and also for the g-load factor. When the airplane executes high-g maneuvers, such a suit applies pressure to certain parts of the human body so as to keep blood in place. The new-generation suit is smart enough to react timely when the g-load is going up.

The ex-chief designer for comprehensive ejection system at Sukhoi explains. ‘The new suit acts in advance. When the pilot is making a move on, sending a command to the airplane’s control surfaces, the pressure suit begins acting in advance.’

The ejecting seat has been improved, too. Today, it can rescue the pilot in all situations: when the aircraft is parked, flying supersonically or maneuvering. Prior to ejecting the pilot out of the plane, the seat puts him into the pose for better protection against incoming air flow, and for safe ejection.

Complete picture in every dot

Digitalization made its mark in one more direction to do with the fifth-generation fighter. Digital modeling gave a boost to the Su-57 design process.

The chief for supercomputer technology recalls. ‘Since the very beginning of the design process, a larger work-share was being fulfilled with mathematic modeling. At first, we followed such an approach in order to reduce the number of errors possible during the design phase. Later on, we followed it during trials.’

Digital modeling proved useful in solving numerous design and development tasks. For instance, there was a need for the Su-57 to have an unusual airframe shape. ‘Mathematic modeling enabled us assess a few aircraft layouts. Had we gone for wind-testing in the wind tubes, these would have lasted for one or two years. Using a super computer, we made all necessary calculations within a week or a month. Besides, the mathematic modeling gave one more benefit: we can see a complete picture in every dot on the surface or out in the surrounding space.’ That data appeared useful for engineers to make decisions.

Mathematic modeling made it possible to prototype each and every system in the airplane. In turn, this opened the way to apply the concept of digital twins. In application to the Su-57 this enabled the design team to create an integrated digital model of the whole airplane.

‘This concept helps foresee how the airplane would behave in various situations. Or how to find causes to malfunctions, understand how they appear, and foretell consequences. These mathematical models are quite complex. We make them. This helps us understand the processes that go on both in standard, routine situations and in critical ones.’

The digital twins have become an essential tool in the hands of engineers, helping them better understand complex developments. Another application is to do with personnel training. Digital twins can show what sequence of actions shall be make in various situations to gain an upper hand.

Speaking of high technologies relevant to the fifth-generation fighter, we should make a point. They did not appear out of nowhere. Much rather, they are based on previous achievements made during development and testing of aircraft attributed to earlier generations. The chief designer draws a conclusion. ‘Anyone, even the revolutionary aircraft design comes into life basing on the scientific-technical experience amassed before. It is impossible to make a leap forward without having a backlog of technologies. Especially those technologies that can apply to newer designs so as to meet the new requirements and attain higher quality. All new qualities are rooted in technical solutions that are themselves found in the scientific-technical backlog.’