Sukhoi Su-57 / T-50 / PAK FA - flight testing and development Part II [2012-current]

LMFS

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I said that capture area isn’t driven by cruising conditions. There is a lot that goes into inlet design aside from capture area. You were using capture area as evidence of superior supercruise capability, when that condition isn’t what drives inlet capture area. You’re welcome to verify this with publications from Raymer or Nicolai.
You said so, but you did not provide reason or evidence or any other design point which is more demanding for a supercruising aircraft, just that there are many factors and refer me to books. Essentially you are not proving anything.
 
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icyplanetnhc (Steve)

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The table shows that at 35,000 ft, airflow at M=0.8 is close to the maximum airflow of the engine.
I am sorry, but there is no way to make progress if you keep dodging my questions. But if you insist on the table, explain please why the thrust in intermediate at 35 kft is one fourth of the static thrust at sea level, despite the advantage in mass flow.
I don’t see how I’m dodging your questions. Thrust is not determined just by air mass flow, but also the ambient pressure and temperature (which varies with altitude), and their ratios with stagnation properties.

Note the effect of ambient temperature and pressure on thrust for a turbojet; similar principles apply to turbofans.

I have given you examples of what drives inlet capture area size, such as takeoff, or maximum Mach. These are conditions that would demand maximum airflow that requires large capture area.
 
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LMFS

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Thrust is not determined just by air mass flow, but also the ambient pressure and temperature (which varies with altitude), and their ratios with stagnation properties.
http://www.stengel.mycpanel.princeton.edu/MAE331Lecture7.pdf
Note the effect of ambient temperature and pressure on thrust for a turbojet; similar principles apply to turbofans.
That is a nice lecture indeed

I have given you examples of what drives inlet capture area size, such as takeoff, or maximum Mach. These are conditions that would demand maximum airflow that requires large capture area.
This case is max Mach, only with AB off (no difference for mass flow because of that), because the whole point here is to have a cruising speed as high as possible. I really don't get why this is a point of contention.

This is not peace time cruising, it is a combat condition where the plane tries to fly as high and fast as possible to gain a kinematic advantage for itself and its weapons without needing to switch on the AB.
 

icyplanetnhc (Steve)

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This case is max Mach, only with AB off (no difference for mass flow because of that), because the whole point here is to have a cruising speed as high as possible. I really don't get why this is a point of contention.

It’s unlikely maximum Mach is what the inlet is sized to; the inlet design is external compression, and with the density increase from the shock compression (even a normal shock at M=1.5 increases density by a factor of 1.862, and isentropic compression to the same Mach number is even higher) mass flow is generally not the limiting factor for fighter engine at high Mach numbers. Again, at higher Mach numbers, specific thrust (exhaust velocity, generally) becomes the limiting factor, not mass flow.

From the inlet’s perspective, maximum Mach does not matter if it’s with afterburner or not. If capture area is driven by maximum Mach, it factors more into the corrected airflow and mass flow ratio in mixed (external and internal) compression inlets; this generally wouldn’t be a driving factor for supercruise.


Normally supersonic intakes are sized for the cruise condition, but with emphasis on the maximum acceleration during the take-off from sea level and subsonic climbs. A supersonic intake has to cope with the engine airflow demand over the required flight envelope, see figure 8 on page 11. All supersonic aircraft have to fly at subsonic speed, therefore the intake must be able to handle flow at subsonic speed, this includes take-off from sea level, subsonic climb, descent, land, and taxi. In addition to sizing the intake for engine demand allowance should be made for boundary layer control, environmental control and the engine cooling system.
An intake sized for subsonic operation will be too large for the cruise condition and therefore will generate excess drag.

I'm not sure why you're so insistent on using capture area to argue for superior supercruise performance. There are plenty of merits to the Su-57 design and the airplane represents a set of requirements that differ from other stealth fighters, so I find this insistent need to try to argue for its superiority in every aspect strange.
 
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LMFS

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It’s unlikely maximum Mach is what the inlet is sized to
It remains you making a supposition and applying common knowledge from your field, but with the caveat that high flying supercruising fighters are not the topic of those documents. I guess only topic specific articles or actual calculations can offer a more conclusive take and this is not the easiest topic, but it it is what it is and if I have the time I will do th required research and calculations to settle it.

mass flow is generally not the limiting factor for fighter engine at high Mach numbers. Again, at higher Mach numbers, specific thrust (exhaust velocity, generally) becomes the limiting factor, not mass flow.
There are compression losses too and your article points precisely to that and to the need of a variable intake for maximum performance.

As to the limiting factor, again, with the same specific thrust, the higher mass flow provides more thrust. You say the Su-57 intake is designed not for max cruising but for other undefined requirements, but still this is not so easy to determine and besides the PAK-FA does have additional intakes for low speed and/or high AoA operation. In any case, it is clear that the engine of the Su-57 has much more air available than that of the F-22.

Correct me if I am wrong, but the speed adds ram compression quadratically and removes thrust roughly linearly (more with turbofans, much less with turbojets), but the altitude takes density away in an exponential manner and the intake losses apply on top of all that. Why are you sure that the first effect is dominant at a given flight condition? Density at 60 kft is roughly ten times less than at sea level, more than the effect of ram compression at M = 2. You seem to disregard supersonic maneouvering too, which is a requirement for a fighter aircraft and which will restrict the airflow to the intake. Again, a requirement mentioned in the article to accommodate for a wide range of flight regimes is a variable intake.

From the inlet’s perspective, maximum Mach does not matter if it’s with afterburner or not.
Yes, this is what I said too.

I'm not sure why you're so insistent on using capture area to argue for superior supercruise performance. There are plenty of merits to the Su-57 design and the airplane represents a set of requirements that differ from other stealth fighters, so I find this insistent need to try to argue for its superiority in every aspect strange.
I made the point that the propulsive design of the Su-57 is more advanced and capable than that of the F-22 and you attacked it from the intake approach, but IMHO you still did not prove that the bigger intake in the Su-57 does not contribute and I therefore continue to dispute your position. I am just trying to bring a technical argument to its logical outcome.

In turn I find it strange that, in light of a bigger capture area, more effective variable intakes, a shorter diffuser without S duct, a similarly sized more modern engine with higher specific thrust and almost necessarily higher mass flow (18 vs ca. 16 tf max thrust), more fuel to burn at max mil, more lifting area, lift-generating trimming surfaces ideal for supersonic flight and more efficient nozzles, you dispute the fact that the Su-57 is indeed clearly ahead in propulsive design. Based on those elements, it is basically a fact.

The question is not to defend some absolute lack of shortcomings of the plane (that is never the case), it is to address groundless attacks that are done very lightly and that are an insult to intelligence, specifically when, like in propulsion, it is not one aspect where the Su-57 is ahead, is practically all of them, and not by a small margin. When people state dismissive oversimplifications about the F-35 which are outright false I do the same, I am as stubborn as that
 

overscan (PaulMM)

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Look at the N+1 interview with Marchukov
Thank you, https://vk.com/@pakfa-plazmennyi-motor-n-1-pogovoril-s-razrabotchikom-izdeliya-30 now just a random question to any viewers

"In the engine of the second stage for the Su-57, the developers applied a number of new design approaches and technologies, so that the "Product 30" in terms of specific fuel consumption approximately corresponds to the al-circuit engine AL-31F (670 grams per kilogram-force per hour in cruising mode), but surpasses it in terms of specific thrust. The AL-31F and its variants are among the most fuel-efficient combat aircraft engines in the world; such engines are put on the Su-27, Su-30 and Su-34 fighters, as well as on the Chinese fifth-generation fighter J-20."


View attachment 661063

random google search gives me the Max weight on the Su-57 of 35,000kg and internal fuel of 10,300kg. Su-57 is a little heavier but has more internal fuel. Will the Su-57s max range be higher than the Su-27 along with the addition to supercruise? Trust me my curiosity for the F-22s ferry range on another thread was not of bad intention, I just love technology. :p
This is utter drivel from start to finish.

The Su-27 manuals are freely available and will give you the correct information.

Placard max speed is Mach 2.35 but limited to 5 minutes maximum above Mach 2.15.

Maximum takeoff weight: 33,000 kg (when KN-41 wheel with model 017A tyre and KT-156D wheel with model 2A tyre are installed)
Maximum takeoff weight: 28,000 kg (when KN-27 wheel with model 016A tyre, KT-156D wheel with model 2A tyre are installed)
Design takeoff weight: 23250 kg (2 x R-27 + 2 x R-73E, 5090 kg internal fuel, full non-removable equipment suite,150 rounds for gun).
Max fuel takeoff weight: 27,380 kg (2 x R-27 + 2 x R-73E, 9220 kg internal fuel (density = 0.785)
Maximum weight of load of R-27 and R-73E missiles – 1950 kg

The Su-27 doesn't use external fuel tanks. It doesn't have a Flash Dance radar or a TV sensor or a 'balistic bombsight". Ranges are all different from the ones quoted.

In short, any arguments made using figures from this page are utterly without foundation.
 

tequilashooter

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This is utter drivel from start to finish.

The Su-27 manuals are freely available and will give you the correct information.

Placard max speed is Mach 2.35 but limited to 5 minutes maximum above Mach 2.15.

Maximum takeoff weight: 33,000 kg (when KN-41 wheel with model 017A tyre and KT-156D wheel with model 2A tyre are installed)
Maximum takeoff weight: 28,000 kg (when KN-27 wheel with model 016A tyre, KT-156D wheel with model 2A tyre are installed)
Design takeoff weight: 23250 kg (2 x R-27 + 2 x R-73E, 5090 kg internal fuel, full non-removable equipment suite,150 rounds for gun).
Max fuel takeoff weight: 27,380 kg (2 x R-27 + 2 x R-73E, 9220 kg internal fuel (density = 0.785)
Maximum weight of load of R-27 and R-73E missiles – 1950 kg

The Su-27 doesn't use external fuel tanks. It doesn't have a Flash Dance radar or a TV sensor or a 'balistic bombsight". Ranges are all different from the ones quoted.

In short, any arguments made using figures from this page are utterly without foundation.
I guess I received the wrong info from a few sources on the 1st google search results. You got a source I can look for to get this correct information on the range and internal fuel please?
 

stealthflanker

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DWG

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The Su-27 doesn't use external fuel tanks. It doesn't have a Flash Dance radar or a TV sensor or a 'balistic bombsight".

HUDs can (no idea if it does in the Flanker) function as a ballistic weapons release computer, generating a continuously computed impact point or release point. Replacing older bombsights with something better was a big part of the retrofit HUDWAC market in the mid-late 80s. So 'balistic bombsight' may just be extrapolating from 'it has a HUD'.
 

icyplanetnhc (Steve)

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It remains you making a supposition and applying common knowledge from your field, but with the caveat that high flying supercruising fighters are not the topic of those documents.
There is no reason that somehow supercruising fighters aren’t held to the same principles. Principles of supersonic flow don’t change between aircraft and aircraft. Frankly, it is you who is trying to make a “supposition” that supercruising fighters don't have to follow these inlet principles.

There are compression losses too and your article points precisely to that and to the need of a variable intake for maximum performance.

As to the limiting factor, again, with the same specific thrust, the higher mass flow provides more thrust. You say the Su-57 intake is designed not for max cruising but for other undefined requirements, but still this is not so easy to determine and besides the PAK-FA does have additional intakes for low speed and/or high AoA operation. In any case, it is clear that the engine of the Su-57 has much more air available than that of the F-22.
Again, specific thrust is not some static value, it varies across the flight envelope. It's not as simple as designing around higher mass flow; mass flow will be driven by what the engine needs and can accept, not the other way around. Inlet capture area is just one area that goes into the inlet design, and I never said that it isn't designed for supercruise. I'm skeptical that capture area is necessarily driven by maximum Mach at military power. For instance, the F-22's aerodynamics and inlet likely have a design point of Mach 1.5 for supercruise, even though it can reach about Mach 1.8 in military power; a variable geometry inlet has some more flexibility around its design point, but even this inlet is an external compression inlet where the ramp varies the throat area (contrast this to the F-15 or SR-71 inlet that can vary both the capture area and throat area).

This table from Leland Nicolai's aircraft design book, page 410, for turbine engine inlet sizing shows the airflow and capture area demand of the F-15's F100-PW-100 engine at different points in the envelope. Here, A_inf_E (the fourth column) represents the demand capture area, while A_C (the fifth column) is the actual capture area.

engine and secondary airflow​
A_inf_E​
A_inf_E/A_C​
Mach​
Altitude​
(lbm/s)​
(ft2)​
0.25​
2,000​
205​
10.9​
1.76​
0.5​
4,000​
220​
5.9​
0.95​
0.75​
5,000​
245​
4.53​
0.73​
1.0​
30,000​
130​
4.56​
0.74​
1.2​
30,000​
154​
4.53​
0.734​
1.4​
30,000​
183​
4.62​
0.749​
1.6​
30,000​
217​
4.76​
0.77​
1.8​
30,000​
257​
5.01​
0.81​
2.0​
30,000​
300​
5.26​
0.853​
2.3​
30,000​
388​
5.92​
0.96​

Here you can see that despite the variable in airflow, the demand capture area is the largest at low speed. The demand capture area in supersonic flight wouldn't overtake the low speed demand until well past Mach 2, which is beyond supercruising at this point. Furthermore, as you increase airspeed, engine required airflow increases, but as you increase altitude, the engine's required airflow decreases. For instance, at 45,000 ft, with the F100-PW-100, the required airflow at around Mach 1.9 is only about 150 lbm/s (Nicolai, Figure 14.8g page 377).

A supercruising engine won't have the exact same curves, but will follow the same trends; they both turbine engines and optimizing for supercruise won't somehow make it follow different principles.

Correct me if I am wrong, but the speed adds ram compression quadratically and removes thrust roughly linearly (more with turbofans, much less with turbojets), but the altitude takes density away in an exponential manner and the intake losses apply on top of all that. Why are you sure that the first effect is dominant at a given flight condition? Density at 60 kft is roughly ten times less than at sea level, more than the effect of ram compression at M = 2. You seem to disregard supersonic maneouvering too, which is a requirement for a fighter aircraft and which will restrict the airflow to the intake. Again, a requirement mentioned in the article to accommodate for a wide range of flight regimes is a variable intake.
I don't think you quite understand compression. In incompressible fluids, dynamic pressure increases with the square of the velocity, but that is not how it works in compressible supersonic flow; you'll need to use oblique and normal shock tables/equations, and then isentropic equations in the subsonic section (for approximation). There's a reason that dynamic pressure calculations for anything higher than low subsonic take Mach number into account.

I made the point that the propulsive design of the Su-57 is more advanced and capable than that of the F-22 and you attacked it from the intake approach, but IMHO you still did not prove that the bigger intake in the Su-57 does not contribute and I therefore continue to dispute your position. I am just trying to bring a technical argument to its logical outcome.
Frankly, you need to prove that larger inlet capture area automatically translates to superior supercruise; capture area is but one factor in supercruise performance. Larger capture area can provide greater airflow if the engine demands it, but it also increases weight and drag. You're using a larger capture area as proof of something that requires far more information. Advanced is also rather subjective here. If the propulsion system is mainly beneficial at conditions beyond the limits of the airplane from other factors (such as materials), can we really say it's more advanced? I'm not saying it's the right or wrong choice, but there are many tradeoffs and aspects to consider before declaring something as unconditionally superior. Not everything Sukhoi (or Lockheed, Northrop, any designer) does should be treated as infallible or beyond reproach.

I don't understand why you think I'm somehow attacking the Su-57's supercruise capability. It's clear that supercruise is one of the main design drivers of the aircraft. I wouldn't declare it as outright superior to all competitors in all parts of the envelope, and since you're demanding proof, you frankly haven't presented an argument with rigorous technical merit (it would be difficult to do so in any case because of lack of important data that would be necessary for calculations). For what it's worth, with the right engines I think the Su-57 can be excellent at supercruise, and likely has more range than the F-22.
 
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LMFS

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There is no reason that somehow supercruising fighters aren’t held to the same principles. Principles of supersonic flow don’t change between aircraft and aircraft. Frankly, it is you who is trying to make a “supposition” that supercruising fighters don't have to follow these inlet principles.
Of course they are held to the same principles, but the numerical values used as reference have a context in which they are valid, the flight regime and associated demands of the supercruisers are different. See more below.

I'm skeptical that capture area is necessarily driven by maximum Mach at military power. For instance, the F-22's aerodynamics and inlet likely have a design point of Mach 1.5 for supercruise, even though it can reach about Mach 1.8 in military power;
This is not quite clear to me: if the design point is 1.5 M, how does it reach 1.8? There would be not enough air for the engine...

This table from Leland Nicolai's aircraft design book, page 410, for turbine engine inlet sizing shows the airflow demand of the F-15's F100-PW-100 engine at different points in the envelope. Here, A_inf_E (the fourth column) represents the demand capture area, while A_C (the fifth column) is the actual capture area.
The airflow in the third column is the demand or the actual?
The plane is in steady horizontal flight?
I assume the 5th column represents the relationship between the theoretical demand capture area divided by the actual one, is that correct?

Here you can see that despite the variable in airflow, the demand capture area is the largest at low speed. The demand capture area in supersonic flight wouldn't overtake the low speed demand until well past Mach 2, which is beyond supercruising at this point. Furthermore, as you increase airspeed, engine required airflow increases, but as you increase altitude, the engine's required airflow decreases. For instance, at 45,000 ft, with the F100-PW-100, the required airflow at around Mach 1.9 is only about 150 lbm/s (Nicolai, Figure 14.8g page 377).
There are a few comments and questions here:
> Starting at low speed, the actual intake provides less airflow than what the engine could take (1.76 more demand than actual airflow?) In this case the plane does not seem to be designed with that demand in consideration. In the Su-57, additional intakes exist that should need to be considered
> @30 kft, as the speed starts increasing, the engine is already working in AB and as it spools faster, the airflow demand increases and the use of the capture area is almost maxed, up to 0.96 at 2.3 M. This is interesting, because the increase in speed at the same altitude should help the intake, but the effect we see is is not enough (the added compression due to speed does not compensate the additional airflow demand?). This is quite significant and I was not even counting on that. Actually it seems to strongly support my point that the capture area indeed is an issue, and is not only driven by altitude but also by speed. So the bigger intakes of the Su-57 would help not only at extremely high altitudes, but at way lower ones already.
> In this example the engine must be using AB, if those speeds were to be attained on dry settings, the airflow would need to be substantially higher, correct? So the same intake design that would allow to attain 2.3 M in AB for the F-15 would not be enough for doing it on mil power, even if the engine was theoretically capable of delivering the necessary thrust. The comment you make about the demand in supersonic only overtaking subsonic one beyond 2 M strongly depends on this.
> As to the airflow reduction at higher altitude, I am assuming it refers to the demand for steady flight and is related to the reduced drag, does that make sense?
> What would be the factor of use of the intake in those conditions, considering the air is way less dense at that altitude?

I don't think you quite understand compression. In incompressible fluids, dynamic pressure increases with the square of the velocity, but that is not how it works in compressible supersonic flow; you'll need to use oblique and normal shock tables/equations, and then isentropic equations in the subsonic section. There's a reason that dynamic pressure calculations for anything higher than low subsonic take Mach number into account.
True, I was not aware of that and it explains my assumption that the main use of the bigger intake was the very high altitudes only. This is a complex topic indeed, thank you.

Frankly, you need to prove that larger inlet capture area automatically translates to superior supercruise; capture area is but one factor in supercruise performance. Larger capture area can provide greater airflow if the engine demands it, but it also increases weight and drag. You're using a larger capture area as proof of something that requires far more information. Advanced is also rather subjective here. If the propulsion system is mainly beneficial at conditions beyond the limits of the airplane from other factors (such as materials), can we really say it's more advanced? I'm not saying it's the right or wrong choice, but there are many tradeoffs and aspects to consider before declaring something as unconditionally superior. Not everything Sukhoi (or Lockheed, Northrop, any designer) does should be treated as infallible or beyond reproach.

I don't understand why you think I'm somehow attacking the Su-57's supercruise capability. It's clear that supercruise is one of the main design drivers of the aircraft. I wouldn't declare it as outright superior to all competitors in all parts of the envelope, and since you're demanding proof, you frankly haven't presented an argument with rigorous technical merit (it would be difficult to do so in any case because of lack of important data that would be necessary for calculations). For what it's worth, with the right engines I think the Su-57 can be excellent at supercruise, and likely has more range than the F-22.
Fair enough. Since I cannot provide true numerical values I am referring to the kind of information that is available and which is of qualitative nature. The elements that, to the best of my knowledge, determine the supersonic performance, are essentially maxed in the Su-57. The radar blocker will have an impact, the weight of the plane is unknown and by the numbers that I have seen, the cross sectional area of the plane should be very similar to that of the F-22, other than that I don't see elements that could strongly skew what seems a setup consciously designed to go beyond the limits of the F-22. I really think the effort put by Sukhoi in this regard is easy to perceive, as they seem to have been very systematic in addressing every aspect that could give them an advantage. But I agree that any platform as a whole and the compromises taken in different aspects are are very difficult topic to analyse and compare in fairness.
 
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Cannonfodder43

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An interesting article about RAM on the Su-57 shared on Reddit courtesy of user Foxhoundbat

Perhaps machine translating of the article will prove more cooperative to some of you compared to me, but I have shared translations of key sections.

Each layer of a special coating has a special functional purpose and its own unique thickness, which depends on the area of application. Compounds - compositions based on various polymers - eventually form a kind of layer cake, the properties of which make it possible for the Su-57 to significantly reduce radar signature.

“We apply, process, measure the thickness, apply again the next day, and so on,” explains Svetlana Latyshova. - The quality of the coating and its service life during the operation of the aircraft depend on the thoroughness of all operations. The Su-57 has a very long warranty period and service life. We are obliged to do everything to ensure that the radio-absorbing coating is of high quality, in compliance with all the rules and regulations laid down in the design documentation. Marriage is unacceptable in this matter. "

“The work is laborious, physically and technically challenging, but very interesting and promising,” says Konstantin Lachkov, painter of the area of radio-absorbing coatings. - The center of competence for radio-absorbing coatings in Russia is us, our plant named after Yuri Gagarin. Coating booths like ours are nowhere to be found. You will not find such knowledge as that of our brigade outside Komsomolsk-on-Amur. All are trained and certified. Taking into account the growth in production volumes, new personnel are being trained. Our team is ready for the serial production of the new aircraft. We have everything for this."
Mastering the technology of applying radio-absorbing coatings of the Su-57 aircraft is only the beginning of the journey. A lot of work is underway to improve the process. According to today's technologies, the entire cycle of stage-by-stage application of radio-absorbing coatings takes just over a month. According to experts, technological capabilities and scientific developments to reduce the time of this process make it possible to do it faster.

“We have developed a good connection between production and technological service,” explains Svetlana Latyshova. - Production raises questions of where and what can be done better, and the technological service works through them and gives answers. We are moving towards making the process more processable in order to reduce the time required for coating on downstream aircraft. ”

Serial production with a gradual increase in the output of fifth-generation aircraft poses new complex, but interesting tasks for the coating department staff. One thing remains unchanged - the quality of work must always remain at its best.
 
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Avimimus

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Err.... what happened to those central weapons bays tho??? The bay doors are shaped differently.
That is just a marketing stand by KTRV
That has much more problems than just bay doors. This pseudoKAB in internal bay...

Yeah... what is going on with that? I get that the KAB-500 is a tad on the impossible side... but also, what is going on with the KAB-1500?
 

Grey Havoc

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Some sort of weapons rack or similar mounted externally, including over the main weapon bay doors, leaving the bay for additional fuel tanks only?
 

icyplanetnhc (Steve)

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This is not quite clear to me: if the design point is 1.5 M, how does it reach 1.8? There would be not enough air for the engine...
Because supercruise isn’t flying at maximum military power, as that would still be very inefficient even without afterburner. You would want your supersonic cruise design point to be somewhat lower than that (around 80-90% or so) and try to maximize your efficiency there. Of course, the inlet also has to be able to handle off-design conditions. Inlet and engine airflow matching is quite a complicated process, and variable geometry will grant you more flexibility, but it still has its limits, especially if it’s only external compression with fixed capture area.
The airflow in the third column is the demand or the actual?
The plane is in steady horizontal flight?
I assume the 5th column represents the relationship between the theoretical demand capture area divided by the actual one, is that correct?
The third column is the demand from the engine as well as airflow demand from oil cooling, nozzle cooling, and so on. Your other assumptions are correct, although steady flight is not really relevant from the engine’s perspective.
This is interesting, because the increase in speed at the same altitude should help the intake, but the effect we see is is not enough (the added compression due to speed does not compensate the additional airflow demand?). This is quite significant and I was not even counting on that. Actually it seems to strongly support my point that the capture area indeed is an issue, and is not only driven by altitude but also by speed. So the bigger intakes of the Su-57 would help not only at extremely high altitudes, but at way lower ones already.
There is much more that goes into the airflow for the engine than just the mass. You’ll also need to take into consideration pressure and temperature. Pressure decreases steadily with altitude, while temperature decreases with altitude from sea level until the tropopause, 36,000 ft, above which it remains constant until about 66,000 ft when it increases again. With increasing speed and altitude, your may reach your turbine temperature limits before your airflow limits. Again, all these factors are why you can’t just look at the capture area and declare superiority in supercruise. A larger capture area can provide greater airflow, but it also increases weight and drag at Mach numbers like 1.5 where you’d be spending most of your time, so there’s a tradeoff for how large you want that area to be.
In this example the engine must be using AB, if those speeds were to be attained on dry settings, the airflow would need to be substantially higher, correct?
No. These numbers are all at maximum power, but again required airflow generally doesn’t depend on afterburner as it is downstream of the turbines. So the problem for military power here is not merely air mass flow, but exhaust velocity, nozzle pressure ratio, and other factors. An engine that tries to reach that thrust in military power settings can’t simply do that just with more airflow; more important is exhaust velocity, which enables better dynamic thrust at higher Mach numbers.
> As to the airflow reduction at higher altitude, I am assuming it refers to the demand for steady flight and is related to the reduced drag, does that make sense?
> What would be the factor of use of the intake in those conditions, considering the air is way less dense at that altitude?
There are many factors that goes into this. At higher altitudes and Mach numbers, you may run into temperature limits. The ambient pressure also continues to drop, which affects engine performance; there’s much more than just air density at altitude to consider.
 
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The third column is the demand from the engine as well as airflow demand from oil cooling, nozzle cooling, and so on.
So this demand is met at all points but the slowest speed in the table. Interestingly @ 0.5 M, 4kft and 2.3 M, 30 kft the demand of the intake is similar (0.95 vs 0.96). It seems in subsonic, the increase in speed indeed improves the airflow. From M=1 to 1.6 roughly, the intake is under relatively steady demand, at higher speeds the demand raises quickly. Maybe because the pressure recovery of that particular design starts not working that good?

With increasing speed and altitude, your may reach your turbine temperature limits before your airflow limits. Again, all these factors are why you can’t just look at the capture area and declare superiority in supercruise. A larger capture area can provide greater airflow, but it also increases weight and drag at Mach numbers like 1.5 where you’d be spending most of your time, so there’s a tradeoff for how large you want that area to be.
But remember we talk about mil power, the turbine temperature should not be as high as that suffered at the higher speeds attained with AB, so should be below the tolerance of the engine. I wonder what is the mil cruising speed goal Sukhoi established for the plane, when they equipped it with such complex and big intake. Why to do that, if you expect to fly 1.5 - 1.7 M, to name a figure the F-22 already manages well with the fixed inlet?

No. These numbers are all at maximum power, but again required airflow generally doesn’t depend on afterburner as it is downstream of the turbines.
You mean, the aircraft is accelerating? I have difficulty understanding that the engine is demanding so different mass flows at the same power setting...

On the other hand, I know the airflow is not affected by the AB, but the thrust indeed is. So, if you want to reach in mil power the same speed reached in the table with AB, that same engine would need (if it could handle it) substantially increased airflow. Because the AB should provide a very fast gas jet that is most effective at high speeds, compared to a turbofan in mil power. And at that point, the capture area demand would already be well above the subsonic demand at 0.5 M, 4 kft and well above 1.

So the problem for military power here is not merely air mass flow, but exhaust velocity, nozzle pressure ratio, and other factors. An engine that tries to reach that thrust in military power settings can’t simply do that just with more airflow; more important is exhaust velocity, which enables better dynamic thrust at higher Mach numbers.
Yes I know it is very complex, but I am making the supposition that the variable we are modifying is the mass flow only, to illustrate one of the dependencies that I am interested in exploring, I know an effective supercruising engine should try to increase the exhaust velocity rather than trying to have a huge, slow mass flow. But in the case you had a F119 and a F119 v2 with same exhaust velocity and rest of parameters, but higher overall size and mass flow in the second, that one would generate more thrust. Wouldn't it be supported to assume izd. 30 requires a higher mass flow vs. F119, when the max thrust is ca. 2 tf more? The reference we have to the thrust level of both engines is a bit indirect, but reasonably solid.

There are many factors that goes into this. At higher altitudes and Mach numbers, you may run into temperature limits. The ambient pressure also continues to drop, which affects engine performance; there’s much more than just air density at altitude to consider.
Pressure and density vary very similarly with altitude from wat I have seen. If the engine can handle the temperature, would the intake be under higher demand at higher altitude for the same amount of thrust? I assume clearly yes, and that would be a second factor complementing the first (speed) pointing to the convenience of increasing capture area.
 

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I'm not being facetious but it seems like only one side of this discussion really understands the topic.

if you want to reach in mil power the same speed reached in the table with AB, that same engine would need (if it could handle it) substantially increased airflow

That's not how it works, you can't just force extra air in to make the engine generate more thrust. You need a differently designed engine.

Supercruise-optimised engines have a larger core and smaller bypass ducts, so that they generate a greater proportion of thrust in dry thrust.

Alternatively, variable cycle so the amount of air going to the core and bypass can be varied.
 
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But remember we talk about mil power, the turbine temperature should not be as high as that suffered at the higher speeds attained with AB, so should be below the tolerance of the engine.
No, afterburner is downstream of the turbines, so turbine temperatures are no different in full military power or in afterburner. As for Sukhoi's rationale for the inlets, it may be a way for Sukhoi to maximize the capabilities of the AL-41F1 in the Su-57 while providing growth margin for future variants in the long term. I think it's important to remember that this engine was never actually meant to be "interim", and when the aircraft was designed in the 2000s, it was expected that a sizable fleet of Su-57 would be using the AL-41F1; Sukhoi's T-50 submission for the PAK FA competition had the izdeliye 117 (AL-41F1). See Piotr Butowski's book on the Su-57.

You mean, the aircraft is accelerating? I have difficulty understanding that the engine is demanding so different mass flows at the same power setting...
At the same power setting (i.e. zone 5 afterburner), the engine may demand different airflow due to different limits being reached first depending on the conditions, whether it's rotor speed, turbine temperatures, airflow, etc. This is not at all straightforward and can be difficult to predict. Thrust is dynamic, and the rated thrust at you see is often uninstalled, sea level thrust.

So, if you want to reach in mil power the same speed reached in the table with AB, that same engine would need (if it could handle it) substantially increased airflow. Because the AB should provide a very fast gas jet that is most effective at high speeds, compared to a turbofan in mil power. And at that point, the capture area demand would already be well above the subsonic demand at 0.5 M, 4 kft and well above 1.
No, if afterburner is required to reach a certain speed, then the same engine in military power can't reach the same speed, even if you try to increase airflow. Especially at higher Mach numbers, airflow isn't the limitation, exhaust velocity is. Greater mass flow is of no use if the exhaust velocity isn't high enough.
Wouldn't it be supported to assume izd. 30 requires a higher mass flow vs. F119, when the max thrust is ca. 2 tf more? The reference we have to the thrust level of both engines is a bit indirect, but reasonably solid.
It may, or may not. Greater mass flow isn't something you would arbitrarily want, and there are various tradeoffs that we don't have the data to draw conclusions for. And in any case I don't know why you would be comparing maximum thrust when supercruise involves military power. Furthermore, comparing maximum thrust isn't helpful since it doesn't provide information about dynamic thrust at different speeds and altitudes. I'll also note that lower bypass ratio can result in a smaller thrust increase from military power to afterburner, as there is less unconsumed oxygen for the afterburner combustion.
 
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I'm not being facetious but it seems like only one side of this discussion really understands the topic.
I take absolutely no offence that some guy that links in his profile to AIAA student branch at UCLA knows more about such a thorny issue like inlet design than some random guy in the internet like me. That he wants to actively contribute with myself proving my point is a different story, and he is fully entitled to not doing so BTW. I appreciate (a lot) the information and links he is providing regardless, this is a topic I wanted to research for a long while but it is not easy to do 100% on your own with very limited time.

That's not how it works, you can't just force extra air in to make the engine generate more thrust. You need a differently designed engine.

Supercruise-optimised engines have a larger core and smaller bypass ducts, so that they generate a greater proportion of thrust in dry thrust.

Alternatively, variable cycle so the amount of air going to the core and bypass can be varied.
Maybe I am not explaining myself properly, the considerations you make are common knowledge even to me and not what I am referring too. The trend in the table above is that increasing speed places an increasingly high demand on the intake. In that particular case at 2.3 M, the capture area is already almost fully used up, and that engine is not supercruising and therefore is generating thrust with AB, so it uses less airflow for that generated thrust that it would be necessary for generating it if AB was off. That is true, no matter what other complications and considerations you want to introduce in the discussion. I know no single current fighter engine where AB cannot add some thrust without increasing airflow. And that proves that the airflow demand on a supercruising plane @1.5 - 2.0 M is higher than it would be for a plane flying at that speed using AB and that the table above is understating that demand.

No, afterburner is downstream of the turbines, so turbine temperatures are no different in full military power or in afterburner.
They are, if the speed is higher because AB is on...

As for Sukhoi's rationale for the inlets, it may be a way for Sukhoi to maximize the capabilities of the AL-41F1 in the Su-57 while providing growth margin for future variants in the long term. I think it's important to remember that this engine was never actually meant to be "interim", and when the aircraft was designed in the 2000s, it was expected that a sizable fleet of Su-57 would be using the AL-41F1; Sukhoi's T-50 submission for the PAK FA competition had the izdeliye 117 (AL-41F1). See Piotr Butowski's book on the Su-57.
That at least is one take on the issue. It is a possibility, and I am thinking in future 3 stream engines where airflow would need to be very high and that should be also better handling spillage as a reasonable possibility. Still izd. 30 was started relatively early on (early 2010's), since then there have been modifications on the airframe, if that huge intake size was going to be a handicap for 10 or 15 years I don't think it would have made sense to keep them that big, similar changes are done on other planes (i.e. F-16) when different engines are used and they don't seem to be the end of the world. Still, interested to understand what you mean by maximizing the capabilities of the AL-41, since I don't think anyone out there would be making intakes wilfully small not to use their engines as optimally as possible.

At the same power setting (i.e. zone 5 afterburner), the engine may demand different airflow due to different limits being reached first depending on the conditions, whether it's rotor speed, turbine temperatures, airflow, etc. This is not at all straightforward and can be difficult to predict. Thrust is dynamic, and the rated thrust at you see is often uninstalled, sea level thrust.
I admit I don't understand it either. RPM should be max in all cases, turbine temperature should be progressively increasing due to the increasing speed, and still the airflow grows and grows. That's why I referred to the increasing pressure recovery losses as an possible explanation...

No, if afterburner is required to reach a certain speed, then the same engine in military power can't reach the same speed, even if you try to increase airflow. Especially at higher Mach numbers, airflow isn't the limitation, exhaust velocity is. Greater mass flow is of no use if the exhaust velocity isn't high enough.
Sure, therefore I am talking about a bigger engine with more airflow capacity and the same exhaust velocity, and saying it would need more air. I referred to izd. 30 as that engine, once we have decently reliable information about its max thrust. What would be your static mass flow estimation for a modern engine with those 18 tf thrust? I don't know what values do you handle or take for reasonable for F119, but taking 16 tf, that would be already 12% more thrust in max settings and the airflow would need to match that from what I understand.

It may, or may not. Greater mass flow isn't something you would arbitrarily want, and there are various tradeoffs that we don't have the data to draw conclusions for. And in any case I don't know why you would be comparing maximum thrust when supercruise involves military power. Furthermore, comparing maximum thrust isn't helpful since it doesn't provide information about dynamic thrust at different speeds and altitudes. I'll also note that lower bypass ratio can result in a smaller thrust increase from military power to afterburner, as there is less unconsumed oxygen for the afterburner combustion.
I compare max thrust because I understand that it gives a good estimation of the mass flow of the engine. As you say, lower BPR means less AB boost, because the limiting factor is the oxygen that goes through the engine without being used at the core. So in the end and excluding what would seem to my limited knowledge as second order effects, AB equalizes the differences in layout and BPR and allows us to know what is the rough comparison in mass flows for two engines.

As to your second comment, we know from the lead designer that izd. 30 is claimed to have the highest specific thrust of any comparable engine, so I take F119 as lower bound reference in that regard. It should be then both an engine with higher exhaust velocity and higher mass flow and hence ideal for supercruising.
 

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That he wants to actively contribute with myself proving my point is a different story
Frankly, this discussion has not proven your point.
In that particular case at 2.3 M, the capture area is already almost fully used up, and that engine is not supercruising and therefore is generating thrust with AB, so it uses less airflow for that generated thrust that it would be necessary for generating it if AB was off. That is true, no matter what other complications and considerations you want to introduce in the discussion.
Again, no. If you are at Mach 2.3 in afterburner, and then you pull out of afterburner and are on military power, your thrust will decrease and you’ll start decelerating, but the engine’s airflow and turbine temperature will remain the same at that condition. Remember that the afterburner is downstream of the turbine. If you want to generate the same thrust without afterburner, you can’t simply just increase airflow, if your nozzle pressure ratio and exhaust velocity aren’t sufficient. You’ll literally need a differently designed engine for the task, and the airflow is just one factor, not something you design the whole system around.
I know no single current fighter engine where AB cannot add some thrust without increasing airflow. And that proves that the airflow demand on a supercruising plane @1.5 - 2.0 M is higher than it would be for a plane flying at that speed using AB and that the table above is understating that demand.
No. At a given airspeed, an engine will demand the same airflow with or without afterburner. Exit mass flow is increased slightly because of fuel injection from the afterburner, but the airflow demand at that condition remains the same, and you’ll just accelerate because of excess thrust. The table is not relevant to your assertion here at all, and in fact shows that there are other conditions that drives the capture area, such as low altitude subsonic or takeoff.
They are, if the speed is higher because AB is on...
No. You’re changing the conditions. Again, at a given airspeed; the afterburner doesn’t change your turbine temperatures. An engine that can produce the same amount of thrust at military power as another engine in afterburner would have entirely different characteristics, airflow may or may not be greater.
Still izd. 30 was started relatively early on (early 2010's), since then there have been modifications on the airframe, if that huge intake size was going to be a handicap for 10 or 15 years I don't think it would have made sense to keep them that big, similar changes are done on other planes (i.e. F-16) when different engines are used and they don't seem to be the end of the world. Still, interested to understand what you mean by maximizing the capabilities of the AL-41, since I don't think anyone out there would be making intakes wilfully small not to use their engines as optimally as possible.
Again, you don’t simply take an airflow and design your engine and propulsion system around it. A bigger inlet may not even be necessary for better supersonic performance. The F-16/79 had the J79 engine which has lower airflow than the F100, but while subsonic performance was worse, the supersonic performance was actually better. Engine and inlet matching fits into an overall system, you don’t just design one around the other.

I admit I don't understand it either. RPM should be max in all cases, turbine temperature should be progressively increasing due to the increasing speed, and still the airflow grows and grows. That's why I referred to the increasing pressure recovery losses as an possible explanation...
Turbine and rotor temperatures depend on speed, altitude, and compression. Every engine will behave differently, you’ll need to know the characteristics of the specific engine to know the airflow requirements, what limits are reached first, etc. It’s definitely not as simple as looking at an inlet capture area to make determinations.
Sure, therefore I am talking about a bigger engine with more airflow capacity and the same exhaust velocity, and saying it would need more air. I referred to izd. 30 as that engine, once we have decently reliable information about its max thrust.
Is that actually the case with the izdeliye 30, or are you just assigning attributes that matches what you want to believe? Additional mass flow may not even be necessary for improved supersonic performance, see the example with the F-16/79, and there are conditions other than supersonic cruise that drives inlet capture area. Also compare the J79-powered F-4 Phantoms with the Spey-powered ones; the latter’s greater airflow enabled better efficiency and subsonic acceleration, but worse high altitude and supersonic performance.

In any case, the mass flow and specific thrust of the production F119 and F135 have never been disclosed, as far as I know, so I would not put much stock into statements claiming the best attribute of any known engine.
 
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@icyplanetnhc

My point is that the increasing mil thrust requirement of a higher supercruising performance is coherent with the increased specific thrust and air flow we see in the combo Izd. 30 / Su-57, and that other explanations for those features are simply weak or non existing. You seem to demand a numerical demonstration of the compared performance, which none of us will have for any of those two planes. I did not prove my point beyond any reasonable questioning (that was already known from the beginning, since we don't have the actual, complete data), but there is abundant evidence supporting my understanding. You focused more in the methodological weaknesses of my claims, but not in the actual, reasonable evidence I was providing. I can perfectly understand your position, and still think that I am on the right track. We will hopefully get to know not too far from now.

Above you are repeating to me issues that were already clear (AB and airflow, or AB and turbine temp for instance) and misunderstanding my point. I rest my case, I said what I had to say and the data in the discussion is enough evidence of the strong dependence between speed - airflow demand. It would be great to go further but I think I will have to do this on my own as I progressively acquire the theoretical tools needed to do it properly. In any case I thank you for the information and patience.
 

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If your point is simply that Izdeliye 30 needs greater mass flow than Izdeliye 117, and the intakes for Su-57 were oversized intentionally, then that is certainly possible.

Late 1980s AL-41F (Izdeliye 20) was a larger and heavier engine in general with significantly greater diameter than AL-31F due to its supercruise optimised enlarged core, which is why it wouldn't fit in the Su-27 family.

Izdeliye 30 however seems to have the same diameter as the AL-31F/AL-41F1 family and is significantly shorter. It could be that the core is larger, but this would mean a lower bypass ratio to fit in the same diameter, so it's not clear that mass flow would increase overall - just that more of the air passes through the core and less goes around it.
 

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Izdeliye 30 however seems to have the same diameter as the AL-31F/AL-41F1 family and is significantly shorter. It could be that the core is larger, but this would mean a lower bypass ratio to fit in the same diameter, so it's not clear that mass flow would increase overall - just that more of the air passes through the core and less goes around it.
I believe there have been explicit mentions to the izd. 30 being exchangeable with the AL-41F1, and the same was said for the upcoming 3 stream version under design for the 6G. So I am not convinced it is shorter, I wonder if you have seen any solid evidence of that?

As to the mass flow, OPR is one of the parameters subject to technological improvement over engine generations, so it is logical to expect that the airflow is going to be increased because of that, and also enabled because TIT is increasing too. In fact I think that the max thrust reasoning I did above as a way to compare airflow of different engines has merit despite probably not being 100% accurate, and the AB thrust increase in izd. 30 vs previous engines of the AL-31F family is very substantial and difficult to explain without a serious growth in mass flow.
 

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There have been mentions of a potential five missile A2A internal readout on LTS. This makes me wonder if the update the su57 is supposedly going to get in a few years might also include an eight missile internal loadout.
 

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Izdeliye 30 however seems to have the same diameter as the AL-31F/AL-41F1 family and is significantly shorter. It could be that the core is larger, but this would mean a lower bypass ratio to fit in the same diameter, so it's not clear that mass flow would increase overall - just that more of the air passes through the core and less goes around it.
I believe there have been explicit mentions to the izd. 30 being exchangeable with the AL-41F1, and the same was said for the upcoming 3 stream version under design for the 6G. So I am not convinced it is shorter, I wonder if you have seen any solid evidence of that?

As to the mass flow, OPR is one of the parameters subject to technological improvement over engine generations, so it is logical to expect that the airflow is going to be increased because of that, and also enabled because TIT is increasing too. In fact I think that the max thrust reasoning I did above as a way to compare airflow of different engines has merit despite probably not being 100% accurate, and the AB thrust increase in izd. 30 vs previous engines of the AL-31F family is very substantial and difficult to explain without a serious growth in mass flow.
Afterburner thrust increase compared to 117 could the result of a higher bypass ratio leading to more oxygen in the exhaust. This would decrease dry thrust but increase afterburner thrust, at a cost in fuel burn. Given we have no figures for mil thrust, only maximum, this is a plausible scenario.
 

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Afterburner thrust increase compared to 117 could the result of a higher bypass ratio leading to more oxygen in the exhaust. This would decrease dry thrust but increase afterburner thrust, at a cost in fuel burn. Given we have no figures for mil thrust, only maximum, this is a plausible scenario.
The SFC is roughly that of AL-31 family, that does not combine well with a higher BPR, it would mean that they have gone backwards in terms of efficiency.

Moreover, the way you say you would loose military power, so where would the overall increase in thrust come from? You can see that high BPR engines do not have prortionaly higher max thrust than low BPR ones, just a bigger jump from mil to max. And on top of that, the designer has said the specific thrust is the highest around, even if they don't have the 100% values from F119 that means they reach a very low BPR.
 

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As to the mass flow, OPR is one of the parameters subject to technological improvement over engine generations, so it is logical to expect that the airflow is going to be increased because of that, and also enabled because TIT is increasing too.
Overall pressure ratio (OPR) improvement is not tied increased mass flow, you can't simply assume one will cause the other.

Keeping in mind that thrust is the product of mass flow and exhaust velocity, as well as pressure differences between the inlet and exit, higher OPR can increase the stagnation properties of the gas, which in turn can result in more work being extracted by the turbine and greater exhaust velocity from higher nozzle pressure ratio, depending on how the system as a whole is designed. I don't know why you're fixated on mass flow, and to be frank it's looking like circular reasoning at this point.
 
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Afterburner thrust increase compared to 117 could the result of a higher bypass ratio leading to more oxygen in the exhaust. This would decrease dry thrust but increase afterburner thrust, at a cost in fuel burn. Given we have no figures for mil thrust, only maximum, this is a plausible scenario.
The SFC is roughly that of AL-31 family, that does not combine well with a higher BPR, it would mean that they have gone backwards in terms of efficiency.

Moreover, the way you say you would loose military power, so where would the overall increase in thrust come from? You can see that high BPR engines do not have prortionaly higher max thrust than low BPR ones, just a bigger jump from mil to max. And on top of that, the designer has said the specific thrust is the highest around, even if they don't have the 100% values from F119 that means they reach a very low BPR.
The primary improvement to Izdeliye 30 is the raising of the turbine entry temperature from 1745K to 2000-2100K. This puts it close to the F135 class (2200-2300K)
 

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Overall pressure ratio (OPR) improvement is not tied increased mass flow, you can't simply assume one will cause the other.

Keeping in mind that thrust is the product of mass flow and exhaust velocity, as well as pressure differences between the inlet and exit, higher OPR can increase the stagnation properties of the gas, which in turn can result in more work being extracted by the turbine and greater exhaust velocity from higher nozzle pressure ratio, depending on how the system as a whole is designed. I don't know why you're fixated on mass flow, and to be frank it's looking like circular reasoning at this point.
How would you increase mass flow through an engine of the same diameter if you don't improve the compression and thermal characteristics?

BTW I am addressing both exhaust velocity and mass flow, being both the main manageable factors of thrust as you say. It is obvious that improving any of those two is of immediate use in a supercruising engine.

The primary improvement to Izdeliye 30 is the raising of the turbine entry temperature from 1745K to 2000-2100K. This puts it close to the F135 class (2200-2300K)
I don't know what the source for that temperature is?

The points I made about the izd. 30 are all sourced at the designer, it is a supercruising engine with higher claimed specific thrust than F119 or F135 and that is hardly compatible with the high BPR you are referring, unless it is so much ahead of them in TIT that it can compensate a big difference in bypass ratio.
 

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Overall pressure ratio (OPR) improvement is not tied increased mass flow, you can't simply assume one will cause the other.

Keeping in mind that thrust is the product of mass flow and exhaust velocity, as well as pressure differences between the inlet and exit, higher OPR can increase the stagnation properties of the gas, which in turn can result in more work being extracted by the turbine and greater exhaust velocity from higher nozzle pressure ratio, depending on how the system as a whole is designed. I don't know why you're fixated on mass flow, and to be frank it's looking like circular reasoning at this point.
How would you increase mass flow through an engine of the same diameter if you don't improve the compression and thermal characteristics?

BTW I am addressing both exhaust velocity and mass flow, being both the main manageable factors of thrust as you say. It is obvious that improving any of those two is of immediate use in a supercruising engine.

The primary improvement to Izdeliye 30 is the raising of the turbine entry temperature from 1745K to 2000-2100K. This puts it close to the F135 class (2200-2300K)
I don't know what the source for that temperature is?

The points I made about the izd. 30 are all sourced at the designer, it is a supercruising engine with higher claimed specific thrust than F119 or F135 and that is hardly compatible with the high BPR you are referring, unless it is so much ahead of them in TIT that it can compensate a big difference in bypass ratio.
Saturn (Lyulka) have given the temperature figures. No dry thrust figures for Izdeliye 30 are available, so conclusions on bypass ratio are purely speculation. Better fuel economy is claimed, but in cruise, dry, reheat? All three?

Higher temperatures should reduce SFC across the board. If its truly optimised for supercruise, then bypass ratio would be 0.3 or close to it. Afterburning thrust is irrelevant for supercruise.

I'd expect it to be lower bypass ratio than AL-31F, which means for the same external physical diameter it has a proportionately larger core, which will help increase dry thrust. Low bypass ratio engines get a smaller thrust boost from afterburning however, so a high afterburning thrust says nothing much about bypass ratio - the best clue to that is the relative thrust of military to afterburning.

There's not enough data points to do more than speculate though.
 
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