Sukhoi Su-57 flight testing, development & operations [2012-current]

[Ainen]

That's a little dated, I mean, as in "delays" or "sanctions" or "that war with Ukraine".

Christ !

It's from a more civilized age, when F-35 blk.4 was still on time.
No one updates us this way on Su-57M and J-20B.
I personally don't think first contract was meant to include megapolis birds, but that's my speculation.
I.e. I'll be surprised to see them in series until 2028. Testing? Perhaps, for that we probably should get to see a full (not partial) prototype soon enough.

 

[paralay]

As far as I remember, during the discussion on your forum, the expert assessment of the forum members on the angle of the radio-transparent cone was in the range of 2.9 - 3.0 M.

It must be remembered once and for all:
- if the aircraft is duralumin, then the maximum speed is limited to M = 2.6 (2760 km/h)
- If the aircraft is steel or titanium, then the maximum speed is limited to M = 3.5 (3700 km/h)
- to increase the speed to M = 4.5 (4800 km/h), passive cooling of the structure
- is required to increase the speed further, active cooling of the structure is required

 

[F119Doctor]

As far as I remember, during the discussion on your forum, the expert assessment of the forum members on the angle of the radio-transparent cone was in the range of 2.9 - 3.0 M.
The patent for the air intake states that it is designed for speeds up to 3M.
If we consider the materials of the structure, then first of all it is necessary to consider the materials located in the most heat-loaded places, which are: the nose cone, the leading edges and the front part of the lamp.
The front part of the cockpit fairing is made of silicate glass, not plexiglass. Given that silicate glass is heavier but more heat-resistant, it is logical to assume that its use is caused by the need to withstand high temperatures.
If we consider the radio-transparent cone and the leading edges, then we see that the leading edges of the Su-57 cover the radars, therefore, they are also radio-transparent. Given that, for example, the materials used on the MIG-25 or MIG-31 were quite capable of flying at high speeds, it is logical to assume that the SU-57 should not have any problems with the selection of materials.
Of course, I have assumptions about why you mention a speed of 2.35M, but I leave them out of the brackets and focus only on the arguments.

The Su-57 intake may function up to M3, but the pressure recovery will fall off drastically with only 2 oblique shocks prior to the normal shock inlet throat. To get good pressure recovery at M3, you need multiple oblique shocks, and mixed compression with most of the oblique shocks inside the duct to keep the inlet size within reason. However, mixed compression inlets are notoriously susceptible to inlet unstart, especially under heavy maneuvering conditions.

I know you were specifically talking about the nose cone in terms of materials, but the MiG-25 / -31 primary structural material is steel to withstand the aero heating above M2.3. SR-71 structure was titanium. Composites and aluminum are often time limited above M2.1

 

[Squirrel]

is it really that hard to posts sources here? Christ
View attachment 768018

Nice and tnx....

So what they have for now? No more than 30 operational Su-57's with the first stage engine AL-41F-1.
That means they have almost 50 more fighters left to produce and where is the rush with the second stage engine? One more thing, did it occur to us that technically, technologically and structurally, the engine (and maybe even air intake? ) of the second stage might be completely different from the engine of the first stage? I've found some data that Izd 30's compressor is even 30-35cm wider then that of AL-31F where AL-41F-1's compressor is 27cm wider ( 932mm vs 905mm).

If I may, I will repeat some details about Izdeliye 30 from his 'father' Ye.Marchukov ( article from 2019):

''Specific weight in the aviation is the ratio of the engine mass to its full thrust. For the promising "Product 30" this figure is less than 0.1, i.e. the engine is capable of producing more than 10 times more thrust than it weighs. Specific thrust is the ratio of the full thrust to the engine's air consumption.''

Of course ,here we have a case of the max static thrust (not dynamic thrust) and I must note that even AL-41F-1 has that ratio ,more then 10:1. Again,that engine is 150kg lighter then AL-31F .So we have: 1530kg-150kg=1380kg of the dry weight where the max static thrust on the Full AB mode is 15000kgf.

''In the second stage engine for the Su-57, the developers applied a number of new design approaches and technologies, thanks to which the “Product 30” in terms of specific fuel consumption is approximately equal to the AL-31F dual-stream engine (670 grams per kilogram-force per hour in cruising mode), but surpasses it in terms of specific thrust.''

Specific fuel consumption is in opposition to specific thrust. The best fuel consumption is achieved on civil twin-circuit engines, but they have the lowest specific thrust due to the high bypass ratio. On the contrary, single-circuit engines have high specific thrust, but also high consumption.
“Due to the use of new designs and technologies in Product 30, the specific consumption remained at the same level, but the specific thrust increased,” said Marchukov.

The fifth-generation engine "Product 30" will differ from the AL-41F1 in its increased fuel efficiency and lower life cycle cost. Compared to the fourth-generation engines, the fifth generation has added the ability to cruise supersonic motion - for this, the engine must have a variable bypass ratio. This requirement added another specific parameter - specific fuel consumption at cruising supersonic speed.
The engine should also have significantly lower visibility in the infrared and radio wave range. This is achieved by a special design of the nozzle and air intake. Another important aspect of the new engine is the reduction in the life cycle cost of the machine - less maintenance costs, longer service life between repairs," Marchukov said about the new power plants.''

Source: https://nplus1.ru/material/2019/03/06/engines

Now some interesting data about Izd. 30 from famous military pilot Gen. Vladimir Popov. I already posted this but it's good to repeat and to make some comments and analysis.

Article from 2021 :

''According to the analyst's forecast, the second-stage engine will increase the Su-57's cruising speed to approximately Mach 1.5. At the same time, in a commentary to RT, Honored Pilot of Russia Major General Vladimir Popov estimated this figure at almost Mach 2. Little is known about the characteristics of "Product 30". Earlier, on air at Sputnik radio, UEC representative Anton Chechukov reported that, in comparison with the AL-41F1, the thrust of the second-stage engine will be increased to 17.5-19.5 tons. The engine will also feature increased fuel efficiency and a reduced life cycle cost.

In March 2020, an article was published on the website of the journal "Science and Technology" with an analysis of the technical solutions implemented in "Product 30". It reported that the oxygen-free ignition system is installed on modernized injectors that ensure ignition of the fuel immediately after it enters the combustion chamber.
This approach maintains an optimal combustion mode and eliminates the so-called flare - the ejection of a column of fire from the nozzle due to excess fuel in the combustion chamber. The second-stage engine is also equipped with a new nozzle with a thrust vector control function.
The material noted that the electronic digital control system of "Product 30" significantly simplifies the pilot's work and facilitates the engine tuning process. It receives a command from the pilot and then carries it out "taking into account the current parameters and various factors."
Vladimir Popov said that Russian designers have significantly changed the thermodynamic process used in previous generations of jet engines.

"This is due to the special ionization of the air flow, the air-fuel mixture. In the traditional combustion chamber there is an afterburner chamber.''

Note : both AL-41F-1 and AL-41F-1S have so called plasma ignition system for both chambers: the main and the AB chamber.

This was very interesting for me :

"Product 30" will not have an afterburner as such. Instead, it will have a ring system that will create fuel combustion without additional supply via pump systems, which will be more economical. The efficiency of fuel combustion is planned to be increased by 1.2-1.5 times," the expert said.

''Also, as Popov noted, the second stage engine is equipped with a new fuel automation system, which will regulate the flight mode due to thrust. According to his estimates, in the non-afterburning mode, the thrust of "Product 30" will be 1.5 times greater than that of today's engines.
"In addition, the new engine has improved technological and operational characteristics. The testing process is currently underway. Once completed, I think our industry will be able to set up production of the unit.
The design bureau and manufacturing plants work simultaneously, so there shouldn’t be any problems with production,” Popov explained.''

Source: https://russian.rt.com/russia/article/926444-su-57-dvigatel-izdelie-30

From P. Butowski article ( 2023)

In 2023, the engine was given the designation AL-51 .

Hm, w/o that ''F'' ( F for Forsirovanny or AB-mode).

Several days after flying tests of the Izd. 30 started ,site 'bpmd' released some data:

According to the manufacturer, the engine "Product 30" has a compression ratio of 6.7, the air consumption is 21-23 kg/s. The temperature of the gases in front of the turbine reaches 1950-2100Kelvin. ( about 1800°C).

Пара слов о двигателе "изделие 30"

В издании AirCosmos была опубликована статья Izdeliye 30 eqiupe le Su-57 , которая интересна взглядов из-за рубежа на испытания нового российского двигателя второго этапа изделие 30 для перспективного истребителя ПАК ФА. Так, в статье…

bmpd.livejournal.com

Many sources like this mentioned that max static thrust on the MP mode is 11000 kgf and max static thrust on the Full AB mode is 18000 kgf.

https://topwar.ru/155513-chto-izvestno-ob-izdelii-30.html

But those are only 'sources' ,now real question will be, is there AB chamber at all?

 

[F119Doctor]

It must be a translation problem….

1. Air consumption of 21-23 Kg/sec is 46-50 lbs/sec. A F414 is in the 175 lb/sec range, a F100-229 is 248 lbs/sec, a F110-129 is 270 lb/sec. The Product 30 figure BS.

2. The compression ratio of 6.7 only makes sense as the high compressor pressure ratio. That is way too high for a 3 stage fan, and way too low for overall pressure ratio. If you assume a OPR of 30 (about as high as practical for a supersonic engine with the TIT limit stated, a 6.7 HPC PR implies a Fan PR of 4.4, which is believable.

3. Magical “oxygen free plasma ignition” is the same as used in the USAF since at least the days of the J57. TF30-P-100 in the F-111F had plasma AB ignition. Earlier Soviet engines in the MiG-21 did have an oxygen bottle to assist with in-flight engine restarts, never heard of a western engine with that feature.

4. "Product 30" will not have an afterburner as such. Instead, it will have a ring system that will create fuel combustion without additional supply via pump systems, which will be more economical. The efficiency of fuel combustion is planned to be increased by 1.2-1.5 times," the expert said.“

More BS. The AB burns fuel, which releases heat based on the chemical reaction of jet fuel with oxygen. There is no 1.2-1.5x burn efficiency to be had. Maybe this is the improvement for non-AB supercruise vs AB fuel flow needed for supersonic operation on their previous engines.

5. If we take the 4.4 fan pressure ratio as correct, the engine should be capable of low supercruise, perhaps M1.2-M1.4. The real challenge is to maintain both airflow and high fan PR as the intake temperature increases past 100F at around M1.5. As the intake temperatures increase, the rotor speeds and the TIT have to increase to maintain the same airflow and pressure ratio. Is there sufficient rotor speed and turbine temperature margin to maintain supercruise thrust as the Mach and inlet temperature increases? This is extremely difficult to achieve, especially with their claimed 10:1 thrust to weight ratio.

It will be interesting to see if any further details are forthcoming on the configuration of the “Product 30” engine, and what Su-57 performance is actually attained with that engine, 2D vectoring nozzle or not.

 

[Null]

That's a little dated, I mean, as in "delays" or "sanctions" or "that war with Ukraine".

Christ !

2025 isn't over yet along with the deliveries that are coming.

 

[paralay]

Expected thrust izd.30, according to some reports:
afterburning 16300 kgf, maximum 10500 kg

 

[overscan (PaulMM)]

One more thing, did it occur to us that technically, technologically and structurally, the engine (and maybe even air intake? ) of the second stage might be completely different from the engine of the first stage? I've found some data that Izd 30's compressor is even 30-35cm wider then that of AL-31F where AL-41F-1's compressor is 27cm wider ( 932mm vs 905mm).

Jeez, what kind of maths do they teach in Bosnia?

932mm - 905mm = 27mm, not 27 cm.

"30-35cm wider" - yeah, nah.

 

[stealthflanker]

Expected thrust izd.30, according to some reports:
afterburning 16300 kgf, maximum 10500 kg

Not bad i guess. Certainly not "17500 KgF" as old expectation was. The maximum thrust seems a great improvement over Al-31F baseline (8800 KgF)

 

[Galaxy]

is it really that hard to posts sources here? Christ
View attachment 768018

The problem is the Russian press talks out of their behinds. The SU-75 was claimed to make a test flight in 2023, now it’s 2025 and still nothing. Now they claim 2027 is when it’s supposed to be introduced which is funny…some people really think in two years or less of testing an aircraft will be ready?

The conversation is of course about the SU-57 and the second stage engine but the idea is the same. 2025 is a reasonable timeframe for the new engines but I don’t think a single one has ever been put into a serial production SU-57. So far every single serial SU-57 has old engines, they are not second stage because they have old nozzles. The second stage engine is supposed to have flat nozzles or at minimum the round serrated ones as those were tested way back in 2017 and it doesn’t take 7+ years to create, test and manufacture a serrated nozzle.

The engines will come and will be a major improvement in IR and RCS but what I’m interested in is if Sukhoi will ever evolve the SU-57 in the way the SU-27 evolved into SU-30 and other variants. The SU-57 has a lot of room for improvement and if anything the war in Ukraine was a painful lesson on the importance to low RCS. Meaning will the MOD demand lower RCS? Will sukhoi ever reshape the IRST or any of the other round sensors? Will the canopy ever be reshaped from a round oval design to a trapezoid style canopy seen on US and Chinese stealth aircraft? Will the canopy ever be a one piece? Will the square access panels be changed to serrated ones? Will the coating be changed to something like the mirror like coatings being tested or used on F-22s, F-35s and J-20s? Will they add serrations around leading edges, intakes or squared panels like the Rafale did? The SU-57 has lots of potential and room for making improvements. Now will Russia take additional steps based on lessons learned in Ukraine due to dense SAMS networks, radars, aircraft and NATO global intelligence operation in and around Ukraine.

 

[Galaxy]

Not bad i guess. Certainly not "17500 KgF" as old expectation was. The maximum thrust seems a great improvement over Al-31F baseline (8800 KgF)

Not bad but not great either considering it 2025 already; I wonder if that is the figure with flat nozzles? With round nozzles the thrust may be much higher. Likewise if that figure is with round nozzles and they install flat nozzles it will degrade thrust further, which will be disappointing thrust output given the F-119 has similar numbers and it’s been operational since 2005…granted we don’t know if the F-119s thrust was with or without square nozzles.

I suspect that figure (if it’s a real figure) would be with flat nozzles since before the flat nozzles the figures floating around for the second stage engine were higher.

 

[Squirrel]

It must be a translation problem….

1. Air consumption of 21-23 Kg/sec is 46-50 lbs/sec. A F414 is in the 175 lb/sec range, a F100-229 is 248 lbs/sec, a F110-129 is 270 lb/sec. The Product 30 figure BS.

2. The compression ratio of 6.7 only makes sense as the high compressor pressure ratio. That is way too high for a 3 stage fan, and way too low for overall pressure ratio. If you assume a OPR of 30 (about as high as practical for a supersonic engine with the TIT limit stated, a 6.7 HPC PR implies a Fan PR of 4.4, which is believable.

3. Magical “oxygen free plasma ignition” is the same as used in the USAF since at least the days of the J57. TF30-P-100 in the F-111F had plasma AB ignition. Earlier Soviet engines in the MiG-21 did have an oxygen bottle to assist with in-flight engine restarts, never heard of a western engine with that feature.

4. "Product 30" will not have an afterburner as such. Instead, it will have a ring system that will create fuel combustion without additional supply via pump systems, which will be more economical. The efficiency of fuel combustion is planned to be increased by 1.2-1.5 times," the expert said.“

More BS. The AB burns fuel, which releases heat based on the chemical reaction of jet fuel with oxygen. There is no 1.2-1.5x burn efficiency to be had. Maybe this is the improvement for non-AB supercruise vs AB fuel flow needed for supersonic operation on their previous engines.

5. If we take the 4.4 fan pressure ratio as correct, the engine should be capable of low supercruise, perhaps M1.2-M1.4. The real challenge is to maintain both airflow and high fan PR as the intake temperature increases past 100F at around M1.5. As the intake temperatures increase, the rotor speeds and the TIT have to increase to maintain the same airflow and pressure ratio. Is there sufficient rotor speed and turbine temperature margin to maintain supercruise thrust as the Mach and inlet temperature increases? This is extremely difficult to achieve, especially with their claimed 10:1 thrust to weight ratio.

It will be interesting to see if any further details are forthcoming on the configuration of the “Product 30” engine, and what Su-57 performance is actually attained with that engine, 2D vectoring nozzle or not.

As I wrote '' ... to make some comments and analysis. ''

It was not mistake in transl but maybe ( and obviously ) in one 0 ? So we have 210-230kg/sec ??? Old AL-31F has 110-120 kg/sec ,AL-41F-1/F-1S ???

This was the original article :

Новый двигатель с плазменной системой зажигания для Су-57. «Изделие 30» и искусство компромиссов.
Source: https://ursa-tm.ru/forum/index.php?...-su-57-«izdelie-30»-i-iskusstvo-kompromissov/

Mistakes like : 20-23 кг/с, 1950 до 2100°K , 1700°K etc ....

About that plasma ignition ,yes but here we have ignition of both chambers, the main and the AB.

About AB chamber ,strange thing is that he said there is no AB chamber at all and then after that he mentioned some rings . AB chamber has usually several rings inside of it.

Expected thrust izd.30, according to some reports:
afterburning 16300 kgf, maximum 10500 kg

There is two AB-modes : combat/boyevoy and special/osoboy.

Jeez, what kind of maths do they teach in Bosnia?

932mm - 905mm = 27mm, not 27 cm.

"30-35cm wider" - yeah, nah.

Hehehe, obviously it was not mistake in math but in typing. Cheers and hallo from Bosnia!

The problem is the Russian press talks out of their behinds. The SU-75 was claimed to make a test flight in 2023, now it’s 2025 and still nothing. Now they claim 2027 is when it’s supposed to be introduced which is funny…some people really think in two years or less of testing an aircraft will be ready?

The conversation is of course about the SU-57 and the second stage engine but the idea is the same. 2025 is a reasonable timeframe for the new engines but I don’t think a single one has ever been put into a serial production SU-57. So far every single serial SU-57 has old engines, they are not second stage because they have old nozzles. The second stage engine is supposed to have flat nozzles or at minimum the round serrated ones as those were tested way back in 2017 and it doesn’t take 7+ years to create, test and manufacture a serrated nozzle.

The engines will come and will be a major improvement in IR and RCS but what I’m interested in is if Sukhoi will ever evolve the SU-57 in the way the SU-27 evolved into SU-30 and other variants. The SU-57 has a lot of room for improvement and if anything the war in Ukraine was a painful lesson on the importance to low RCS. Meaning will the MOD demand lower RCS? Will sukhoi ever reshape the IRST or any of the other round sensors? Will the canopy ever be reshaped from a round oval design to a trapezoid style canopy seen on US and Chinese stealth aircraft? Will the canopy ever be a one piece? Will the square access panels be changed to serrated ones? Will the coating be changed to something like the mirror like coatings being tested or used on F-22s, F-35s and J-20s? Will they add serrations around leading edges, intakes or squared panels like the Rafale did? The SU-57 has lots of potential and room for making improvements. Now will Russia take additional steps based on lessons learned in Ukraine due to dense SAMS networks, radars, aircraft and NATO global intelligence operation in and around Ukraine.

AL-41F-1, first flight on the Su-57 in 2010, serial production began in 2018. Before that test flights on the prototype Su-27M/T-10M-10 ( 710 blue).

''Т-10М-10 (б/н 710) — предсерийный экземпляр. Создан по образцу Т-10М-8. С 2004 года использовался как летающая лаборатория для испытаний двигателей АЛ-41Ф-1.''



Source: https://vpk.name/library/al-41f.html?images

R&D work on Izd. 30 began after 2010, static tests in 2016,flight tests from Dec. 2017. Serial production in 2024/2025 ?

 

[stealthflanker]

Not bad but not great either considering it 2025 already;

Well what are you expecting ? Give numbers not relativities.

 

[overscan (PaulMM)]

There is two AB-modes : combat/boyevoy and special/osoboy

Several Soviet & Russian engines back to the R-25-300 at least have had a "wartime" afterburner rating that was only usable for short periods without risking engine damage.

 

[Squirrel]

Several Soviet & Russian engines back to the R-25-300 at least have had a "wartime" afterburner rating that was only usable for short periods without risking engine damage.

Of course ,even RD-33 in the MiG-29 has special combat mode called RPT ( режим повышенной температуры).



From article :

Начались летные испытания двигателя второго этапа для истребителя Су-57

''«Изделие 30» – это полностью новая разработка российских двигателестроителей, созданная с нуля в постсоветскую эпоху.''

"Product 30" is a completely new development by Russian engine builders, created from scratch in the post-Soviet era.''
Source: https://2009-2020.oborona.ru/includes/periodics/priority/2017/1225/101423011/print.shtml

Interesting news from Oct. 2019 ( two years after the flight tests started) ...

''В октябре был выполнен очередной полет с проверкой характеристик изделия на разных режимах полета, в том числе проверялась работа поворотного реактивного сопла и проверка работы маслосистемы при отрицательных перегрузках. Всего на летающей лаборатории выполнено 16 полетов.''

''In October, another flight was performed to test the characteristics of the product in different flight modes, including checking the operation of the rotating jet nozzle and checking the operation of the oil system under negative overloads. A total of 16 flights were performed on the flying laboratory.''

 

[Galaxy]

Well what are you expecting ? Give numbers not relativities.

I was expecting something closer to 38,000 to 40,000lbs thrust given those were the figures being cited for years now. Moreover the relatively old F-119 puts out 35,000lbs (flat nozzle?) and yes I understand the F-119 is a bit larger if I remember correctly so it’s going to have more potential for more thrust.

I’m not saying the thrust is terrible, it may be respectable thrust given it’s the figure with flat nozzles that would reduce thrust by at least say 5%? Which would place it around 38,000lbs thrust. I understand this is not an F-135 sized engine so my explanations are not overly optimistic.

The thrust is important and seems adequate but the real advantage this power plant has is lower IR and RCS figures, super cruise, and reliability.

 

[MSV]

It must be remembered once and for all:
- if the aircraft is duralumin, then the maximum speed is limited to M = 2.6 (2760 km/h)
- If the aircraft is steel or titanium, then the maximum speed is limited to M = 3.5 (3700 km/h)
- to increase the speed to M = 4.5 (4800 km/h), passive cooling of the structure
- is required to increase the speed further, active cooling of the structure is required

The Su-57 intake may function up to M3, but the pressure recovery will fall off drastically with only 2 oblique shocks prior to the normal shock inlet throat. To get good pressure recovery at M3, you need multiple oblique shocks, and mixed compression with most of the oblique shocks inside the duct to keep the inlet size within reason. However, mixed compression inlets are notoriously susceptible to inlet unstart, especially under heavy maneuvering conditions.

I know you were specifically talking about the nose cone in terms of materials, but the MiG-25 / -31 primary structural material is steel to withstand the aero heating above M2.3. SR-71 structure was titanium. Composites and aluminum are often time limited above M2.1

In order not to answer similar arguments twice, I answer in one place.According to the patent for an air intake operating at speeds up to 3 speeds of sound. That's what the patent says. I have given this data as a reminder that it is indicated by 3M, not 2.35M. I'm not going to claim that the air intake ensures operation at speeds up to 3M, although it looks logical.According to the structural materials for operation at high sound speeds and the examples of the SR-71 and Mig-25.These aircraft are designed for long-term operation at high speeds, when the heat from the heated surface increases the temperature of the entire aircraft. Does the Su-57 require long-term operation at speeds close to 3M? No, it is not required at all. It is assumed that it will use supersonic without using afterburners. Would it be useful for him to be able to reach speeds of about 3M? Sure. If the main objection is not the design of the air intake, the aerodynamics of the aircraft or its engines, but rather the structural materials, then this is definitely not a problem for a not too long flight at a given speed. There is an example from the Su-27 above, which, due to the plexiglass in the glazing, could only go out at 2.35 M for a few minutes. But this does not prevent him from reaching this speed if necessary. The question is how fast the Su-57 can theoretically reach and how long it can maintain it.Let's look at the arguments.
1. Aluminum should not be used for high-speed aircraft. However, the Mig-25 had aluminum at 11%, titanium at 8%, and steel at 80%. As you can see, the presence of aluminum did not prevent him from making a long flight.
2. According to the latest information, the mass of composites in the Su-57 design is about 25%. At the same time, the wings of the Su-57 are a caisson, and in this case, the skin largely takes on the load, respectively, its share in the mass of materials is high. The Su-57's cladding is carbon fiber, so the information about 25% of the composites by weight can be considered quite reliable. Carbon fiber has a significantly higher heat resistance than aluminum. In combination with the radio-transparent materials of the nose cone and leading edges, as well as the silicate lamp, it can be argued with a high degree of reliability that a short-term exit at a speed of about 3M will not lead to the failure of surface materials. It takes a long flight to heat the entire aircraft. The question is, how long is it?
3. If we look at the statements about the maximum possible speed for titanium aircraft, we will see that the maximum speeds of 3700 and 4800 km/h are indicated. The second is when using passive cooling. It is logical to assume that if passive cooling is used for an aluminum aircraft, its maximum speed will increase by about the same percentage, namely up to 3,500 km/h. I leave out the need for this, because in fact the aircraft's design is a large caisson with a lot of kerosene in it, and in order to heat the aluminum structural elements located inside, you must first heat the kerosene. And it's definitely not fast. If we additionally organize the intake of kerosene to power the engines from heat-loaded areas, then perhaps the flight time of the Su-57 at high speeds will be limited by the fuel supply.
4. But good. Let's consider the option that there is no passive cooling. The plane reached high speed and went non-stop. The skin warmed up and began to transfer heat inside the aircraft. Kerosene evenly distributes the heat inside. What's happening? Do the structural elements inside immediately begin to collapse? No, as the temperature rises, their strength begins to decrease. He can no longer perform maneuvers with maximum overload. And if the strength is reduced by 40%, then taking the permissible maximum overload as 9G, then with a 40% decrease in the strength of materials, it will be able to perform maneuvers with an overload of only 5.4G. However, the Mig-25 is designed for 5G overload. If the strength does not decrease irreversibly, then in principle it's okay.

From my point of view, the Su-57 can easily reach high speeds and go at them for a long time even without any special frills. It's not a quick matter to heat this big barrel of kerosene. And its surface is made of very heat-resistant materials. At the same time, let me remind you that the Mig-25 has 11% of the weight of aluminum, and it was used just in the cladding, of course, not in the most heavily loaded places.The main question is – what speed can the Su-57 reach, taking into account the power of its engines and aerodynamics? That's an interesting question. Especially in modifications with new engines. At the same time, I would like to emphasize that any information on the maximum speed of the Su-57 provided by the manufacturer cannot be correct by default. It's all about the law on state secrets. Anyone admitted to it and who voiced the correct information before the moment of declassification will go to prison. Therefore, any values are called, but not exactly reliable ones.

 

[Squirrel]

That is the reason why we commented about the max possible real speed (Mach number) in conjunction with the windscreen and cockpit canopy limitations e.g . In fact, Su-57 has less aerodynamic drag then old Su-27 with more powerful engines in the acceleration phase ,of course in Full AB mode.This is valuable to count not only for the first stage but especially for the second stage engines.

 

[overscan (PaulMM)]

If planes were powered by the wishful thinking of some of the posters in this topic, the Su-57 would fly at Mach 4.5 powered by unicorn farts.

I'm not sure why there's this endless fascination with top speed. Flight above Mach 2.0 is likely to be rare.

 

[paralay]

Su-27, 57 degree angle, M=2.35
MiG-31, angle 63 degrees, M=2.83
Su-57, 59 degree angle,

M = 59 : 57 * 2.35 = 2.4
M = 59 : 63 * 2.83 = 2.65

 

[AGS-1787]

So the intake angle has impact on the speed?

 

[Galaxy]

SU-57s top speed will probably be similar to most fighter aircraft and it’s not even that important as fighters rarely ever reach their top speed and operate below the sound barrier most of the time. Ability to supercruise is far more important. The SU-57 was never designed with speed as a priority, if Russia wants speed (plus high altitude and long endurance) it would create a replacement for the MiG-31 and the only project I know about that might possibly replace and exceed the MiG-31 is the Mig-41…and who knows were that project is going.