I will review my measurements, it was a long time ago when I did them. But I was careful and I was surprised with the results, I was expecting them to have quite similar capture areas
I've edited my attachment to highlight the capture areas with a red perimeter, for clarity. Again, inlet design consist of tradeoffs, and a larger area does not necessarily indicate superior supercruise performance for reasons of ram compression and spillage.
Intake throat area is the thing to measure for looking at performance vs mass flow rate and flight conditions. Throat is further downstream than the lips illustrated here.
The image I used was directly from Sukhoi’s patent on the T-50, RU 2440916 from 2012, and the F-22’s image is directly from Lockheed Martin. The details and resolution are frankly adequate, and the image you posted is of a lower resolution. In any case, actual frontal capture area doesn’t truly reflect the mass flow, as the streamlines being captured by inlet isn’t necessarily normal to the plane as depicted. The size of the difference that you’re claiming isn’t demonstrated.
Again, the size of the difference you’re claiming hasn’t been demonstrated, and besides trying to measure capture area, what other evidence have you presented? Just to make it clear, the F-22 and Su-57 do not have the same roles, especially if you’ve read about the goals and intents of the PAK FA program, compared to the ATF.
True, and the F-16’s larger inlet also increased critical Mach number. However, the Su-57’s inlet throat area is variable (it decreases as Mach number increases) so a direct comparison is difficult.
Where is the air captured by those lips at atmospheric pressure going to go, other than into the throat and to the engine? That capture area is not designed to be spilling air all of the time.
I posted because you questioned the values I got and I wanted to be transparent, I don't know for sure what the actual capture area is and never have claimed that I had official values. The image at the patent is a scarcely detailed schematic, not a blueprint. Maybe it is accurate re. the intake area, maybe not. Then there is the scaling and then the image from Lockheed, which seems rather ok but I have also not checked it in depth. After seeing so different values coming from you vs. the ones I measured, I would like to have very good graphical material before feeling that the question has been settled.
What is the deviation you are suggesting? The plane will normally fly with a very small AoA so this looks like splitting hairs, but at most it would only increase the effective capture area of the intake vs. the frontal views we are taking.
Never said it was, I just reported the measurements I had done.
My original argument was against the usual, tiresome claims about the propulsive shortcomings of the Su-57 vs F-22, trying to show that the known data indicate exactly the opposite. Since then and to be very honest with you, I have perceived you essentially denying and watering down every argument I make, not out of technical perfectionism (since some of these arguments are quite obvious to see) but out of some very evident bias. Your own measurements have also reported bigger capture area in the Su-57, plus higher reported thrust in the izd. 30, plus variable vs. fixed intakes. To you this does not prove anything about eventual propulsive advantages of the Su-57 and is due to "other" reasons. To me this is denial and is making me lose the faith in your good will to discuss further. The data are there, think what you want and as said already many times to many other people, let us wait for time and facts to settle the discussion.
Izd. 117S has 0.932 m diameter not frontal area, do not know what other engine you refer in the first line? And that has still does not say the whole story about the capture area of the intake...
LMFS, you have made a technical claim based on extremely flimsy foundations.
1. I never told this was a proven topic, since we don't have many cardinal data from both Su-57 and F-22, just that the hints pointed out to a higher mass flow consumption on the izd. 30, given higher thrust (almost obvious) and huge intakes as per my original measurements.
With all due respect, nothing of what you say below is new to me. You seem to be taking me for someone that does not know what spillage is or the vast effects of speed, air density and engine rpm on airflow availability and consumption. That is not the case.
I suppose Sukhoi knows how to size intakes and what their design point is, so they are not making them bigger just to make them worse.
Makes you wonder what the design point of the Su-57 is, when they state in the patent that this type of intake is designed for flight between 2 and 3 M
I don't see why me saying the Su-57 "may" have higher air flow needs to be proven, but your flow field "may" not be normal in Su-57 and F-22, changing completely the effective capture area, doesn't.
I provided my values and hypothesis and (naively?) expected people to contribute in finding the best values and explanations possible (i.e. being constructive), not to invest their effort in destroying them first and foremost, before even checking and without feeling the need to construct plausible alternative explanations. But I think with a little work (and time) this question can be clarified sufficiently for those who have interest.
Important in what sense?
It is an hypothesis, and one that makes sense at least, vs. "they did the intake big for the sake of spillage". I bet you many engine specialists here could give you a reasonable estimation of mass flow for a 18 tf engine with current technology, if they would want to.
I know that the full propulsive design of a fighter is infinitely more complex than what we are discussing here, but he is rebutting first order approximations and general common sense with third order effects, and that is easy to notice.
Well, that is why blow-in doors exist (Su-57 has them too), to avoid oversizing the intakes for regular flight. No need to spoil 99% of the flight time for the 1% take-off needs
Yes, from what we know the lower ones are blow-in doors while the side ones belong to the air bleed system for the boundary layer extraction
> Increasing inlet pressure thru ram recovery by itself does not increase RPM and turbine temperature by itself. If you doubled inlet pressure at the same temperature, you would have double the airflow with all the internal pressures doubled, fuel flow doubled, and thrust doubled (ignoring any nozzle pressure ratio effects), all with the same internal temperatures. At very low inlet pressures (upper left corner of the envelope) this relationship breaks down due to Reynolds number effects, and at very high inlet pressures (lower right corner) the combustor area pressures can reach the burst limit of engine and the control system will cut back fuel flow (lower RPM and airflow) to limit that burner pressure.
It’s not simply a matter of alpha, but also local aerodynamic effects such as those from the forebody. These aren’t values that are easily quantified just by simple visual analysis.
To be very honest with you, you’ve demonstrated a poor understanding of the propulsion principles that you are arguing so emphatically about. You are completely focused on correlating supercruise performance with mass flow and inlet sizing, despite so many sources and publications indicating that that’s not the case.
Airflow demand of the engine is not just at supercruise conditions. Again, inlet sizing is driven by worst case scenarios that demand maximum capture area, such as takeoff or maximum Mach; this was even demonstrated with data from the F-15, which you then handwave away as not applicable since it’s not a supercruising aircraft. Well, the propulsion principles don’t change, and in any case the afterburner is downstream of the turbines and its operation doesn’t affect airflow demand.
Again, evaluating propulsive performance through inlet capture area is pointlessly simplistic, especially without understanding all of the design considerations. I’m not stating that the Su-57 has better or worse supercruise performance one way or another. As Paul said, there isn’t enough information to draw a conclusion, whereas you seem to have your mind set using poor foundations.
If you are trying to judge the supercruise potential of a turbofan engine, a better place to start would be to assume that the airframe designers have made their best efforts to match the flow characteristics of the engine and maximized pressure recovery at their desired flight conditions.
Sure, I mean that with the same RPM the added ram compression will raise the inlet temperature and finally max TIT will be reached.
Interesting, that would surely imply that the engine may not have the same performance in other points of the envelope like subsonic acceleration as it may have been with other design temperature, maybe the FPR cannot be as high as in other designs? Would a VCE address that issue, allowing different FPR for different bypass ratios?
The FM3 is a modern variant by Salut of the Lyulka-Saturn AL-31F, but it has the same layout and basic characteristics. The izd. 30 is a totally new Lyulka design with a different layout (there were some references to stage count but I am unsure if they are official) and that will be the base for the new family of Russian military engines. No diagram has ever been published that I know.
You misrepresent what I say. I just claimed that the Su-57 was piling one element of supercruising performance on top of the other, among them the intakes being variable and bigger possibly allowing to ensure more airflow even at high supersonic speeds and high altitude, you decided that I was wanting to prove the direct correlation about the size of the intake and the thrust without considering other effects, maybe because that would allow you to skew the discussion away from the hardly disputable arguments I was making. I did not see you pursuing the same way all the guys making frivolous claims about the poor propulsion of the Su-57.
Since I am supposed to demonstrate every single statement I make, how about you demonstrating that high supersonic flight at max dry setting is not a design point of the intake and engine of Su-57 and F-22? Supercruising is an EXPLICIT design goal of both the Su-57 and the izd. 30 and in fact, the reason why AL-41F1 is not considered enough. Or do you expect they would design the izd. 30 if the mil thrust of the izd. 117 was enough? On top of that, max speed of 5th gen fighters seems to be quite low in comparison with 4th gen designs, so it indeed seems reasonable to think that the max speed in dry settings instead of max Mach on AB is a more relevant design point.
You prefer not to make any hypothesis about it, that is your decision but not mine. It is not so hard to understand what they try to achieve with the plane, the general requirements for a modern air superiority fighter are rather predictable and many of them have been stated in great detail in the plane's description and in the patents. You allege unknown design requirements that you may want to detail?
You are stretching it and you know it. I am saying that a bigger intake is a reasonable hint of a higher mass flow consumption of the engine, as a first order approximation, and suggested that the apparent strong overdimensioning may be an additional measure to help keeping a very high thrust at very high altitudes. Further corrections of our estimations of the capture area bring it to a much smaller size that may not require such explanation, agreed.
Still don't know what that has to do with the fact that the air captured by the intake will go to the throat but for the boundary layer extraction and eventual bleed doors (which I don't see clearly in the Su-57 intake).
You can work on scenarios based on requirements from similar planes, that would be the logical thing to do. In any case I am not surprised that a Western guy does not want to actively participate in making the case for the Su-57. I already know your opinion, so be it.
Trying to have the other side prove a negative?
It is not an attack, at all, just that I am not surprised about your lack of motivation. I am pretty sure if you were tasked to produce an engineering assessment of the Su-57's propulsive capabilities and a couple reasonable estimates you would be capable of saying more than "no idea". But it is ok.
If two engines have the same mass flow and same FPR / EPR / NPR at a specific flight condition, they will have similar thrust at Mil Power. The engine with the larger core (lower BPR) with more rotor speed and temperature margin will likely be heavier and have worse SFC that the engine will a smaller, harder working core that doesn't have that margin. There are some second order effects with exhaust temperature (higher temp means higher thrust), but basically the thrust would be similar.
I had heard that one of the main advantages of the VCE is that it allows to significantly reduce spillage at subsonic cruising speeds, wouldn't that go counter to what you say?
That is I think the key question re. izd. 30. Given the information provided by Marchukov (highest specific thrust + roughly same SFC of AL-31F which is ca. 0.67), what do you think is more feasible, to achieve that in a fixed bypass ratio engine or in a VCE? What do you make out of that, do you see it possible when the references are F119 and F135, both being 5th gen engines and the later specifically running substantially hotter than any known engine? On the one hand, the VCE option implies several technological difficulties and a higher technical risk but would be the logical, long term solution to the problems of supersonic cruising, on the other a fixed BPR would demand a very substantial and unlikely leap by Russian designers to go beyond the specific thrust of F119 as a low BPR engine and keep a SFC that is broadly considered equivalent to that of the F135. On top of that come the claims about TWR that you already referred as difficult to believe for a supercruising engine... do you make some sense of the data provided until now? Would you have some OPR, TIT and mass flow estimates for such an engine?
Have you ever wondered why the Su-57 has a large sweep wing, 48 degrees? This is more than any other fighter
That is interesting. None of currently known supercruising fighters (in the "light" sense of the word i.e. cruise supersonically even when below 1.5 M), that is, Su-35, Rafale, Eurofighter and quite probably Su-57 with the current engine, seem to have those louvers you mention in the F-22.
First question would be whether this buffeting issue applies to other planes with other intake layouts in the same way
Why is 1.5 M the critical speed? Was this F-15 specific or would it apply to other designs with other engines and intake design?
Can't other features like the variable ramps or the resonant design of the intake and air duct itself prevent buffeting too?
From the patent RU 2472956, maybe such solution is already present?
findpatent.ru
The fan "izd. 30" is called "izd. 129", one can timidly assume an air consumption of 129 kg/sec
The 1500km figure was assumed to be with first stage, naturally the range would be closer to your estimate with second stage engines.
All supersonic inlets have a maximum and minimum corrected airflow where they operate in a stable manner, with the shock waves properly positioned. The faster you go, the narrower spread between these values. For the F-15 and F-16, 1.4M was the speed where spread reached its minimum and the engine was maintained at Mil power to prevent dropping below that minimum corrected airflow. When the corrected airflow drops below the minimum, the normal shock is pushed forward out of the throat, and pressure recovery drops abruptly. With the pressure behind the throat decreased, the airflow in the inlet is momentarily increased, the shock is swallowed, pressure recovery increases, airflow drops below minimum, and the process repeats, many times per second. This is inlet buzz, and it can be very damaging to both the airframe inlet structure and the engine.That is interesting. None of currently known supercruising fighters (in the "light" sense of the word i.e. cruise supersonically even when below 1.5 M), that is, Su-35, Rafale, Eurofighter and quite probably Su-57 with the current engine, seem to have those louvers you mention in the F-22.
First question would be whether this buffeting issue applies to other planes with other intake layouts in the same way
The other, whether the speed that was scheduled for the F-15 applies to other designs.
I could imagine a supercruising plane (at least this should apply to current designs except F-22) progressively reducing thrust from mil (in the amount compatible with the intake's design) would slow down the plane by not only reducing thrust but also increasing spillage. That would slow the plane down and reduce ram gain, allowing further reduction of the engine's RPM wouldn't it?
Why is 1.5 M the critical speed? Was this F-15 specific or would it apply to other designs with other engines and intake design?
Can't other features like the variable ramps or the resonant design of the intake and air duct itself prevent buffeting too?
Also, there were other non-supercruising planes with bypass doors (F-14 for instance if I am not wrong), what was the reason for them? Maybe requirements for high speed at low altitude?
From the patent RU 2472956, maybe such solution is already present?
Stable operation of the air intake in all flight modes and engine operation is provided due to the presence of an air bypass in oblique jumps of the seal 28, a system for draining the boundary layer in the form of perforations on the stages of wedges 7 and 20 of the braking system and a transverse gap 13 between the front 11 and rear 12 adjustable panels. Draining of the boundary layer is additionally possible through an additional transverse slot, which is regulated by the flap 21 and located in the throat area behind the stationary braking wedge 20, which contains unregulated steps.
Сверхзвуковой регулируемый воздухозаборник
Interestingly, there have been design modifications to those additional inlets you mention during the development process, not clear if for RCS reasons or otherwise. It is also unclear whether they can operate as air bypass, though that function is not stated in the patents that I have seen.
We have not seen the Su-57M yet, so we cannot be 100% sure of how this issue will be solved with the second stage engine yet.
Question: wouldn't a VCE allow to address this issue by increasing the BPR? That may be a more elegant way to handle engine bypass than additional louvers
As to the hypothesis that the Su-57's design goal is a low supercruising speed, why it does not look likely to me:
- First, it is a both logical and also explicitly stated goal that the requirement for the PAK-FA was to at least match or surpass the (way older) F-22. Otherwise the development is failed from the beginning and therefore pointless.
- Why the variable ramps which start making sense from 1.5 M onwards and are a serious challenge to be designed with low RCS? You can see the considerable complexity of the design in patent mentioned above and also RU 2460892
- Why the new engine, specifically for supercruising, when the first stage one already allows for low supersonic speeds? (Supercruising, without further details, has been confirmed for the current engine by program officials)
- Why the highest specific thrust of any comparable engine?
- How can an engine with 12-15% more max thrust (hence higher mass flow in all likelihood) and higher spec. thrust not have higher mil thrust too than F119 (both uninstalled and at operational conditions, when it also has a more efficient variable intake?)
- Su-57 in the first stage has already been compared to Su-35 as accelerating much faster and going in supersonic regime almost without the pilot noticing (indicates both clearly higher excess power and higher supercruising capabilities than Su-35). Besides supercruising being one of the cardinal design requirements as stated in patents and other official documents (see below, "the T-50 is not inferior to the 5th generation F-22 aircraft as on subsonic, and at supersonic speeds")*. Hence its drag should be specially optimised and is difficult to justify that having more thrust it would be way slower.
I think that estimate is a bit low. On the one hand, the gain in thermal efficiency would need to be brutal to increase the thrust from 15 to 18 tf (20% increase) with the same airflow. On the other, the OPR of a supercruising engine is in the order of 35:1 (early supposedly official value for the F119), I do not think it is essentially wrong to take that as a basis value for the izd. 30 if it has higher specific. thrust than the F119, considering that the TIT is probably a bit higher (see roadmap below) and roughly in line with the F135 (which has a big reserve as per the reports). So IMHO a value around 140-150 kg/s is probably closer to the reality.
From what I read, the Su-57 is filled with fuel up to its ears, literally every usable space is fuel, in pictures for production it seems even the basis of the tails is sealed for that purpose. A natural design reference would be the fuel capacity of the Flanker, Su-57 has smaller linear dimensions but bigger surface and a more developed integral aerodynamic design, so it is not easy to estimate whether they reached or surpassed the 11.5 t of the Su-35. Those 10 t look reasonable to me, in the absence of a more definitive value.
I see. Reading the patent, there are many elements in the intake besides the most usual ones, I did not identify all of them with certainty yet. But some of them may damp a bit that resonant behaviour and help delay that inlet buzz, it would be intrinsically advantageous to ensure stable air feed to the engine with minimal complications in the engine control. Will keep looking for info about that issue.
The issue is that both F-16 and F-15 according to you have the same engine scheduling, despite completely different intake design. So maybe 1.5 M is indeed a natural barrier for supercruising, coherently with the old interpretation of the term (cruising speed above 1.5 M) and with the fact that the only known plane capable of achieving that is the F-22. So maybe specific design solutions are indeed needed to go beyond that point. The Eurofighter would be the closes competitor there, and its intakes have at least variable lips to manage the airflow
The F-22 in fact seems to have two bleed/bypass mechanisms, one inboard of the forward section of the intake and one additional at the subsonic diffuser, close to the engine inlet. I don't know if the first one is for the boundary layer extraction and the other the proper bypass door? With a fixed intake, there must indeed be some compensating mechanisms to ensure stable air supply to the engine across the whole flight envelope.
Yes, I know. The element that I referred to in the patent was talking about a bypass element, additional to the several boundary layer extraction devices (perforated surfaces plus gap at the variable ramps, connected to extraction grills in the external and internal faces of the intake). I still could not reliably identify it physically, the only drawing in the patent referring it is a diagram with the position of the inlet shocks
Ok thanks. That would be a great addition and would probably help increase engine operation stability, together with the reduction of the intake complexity and probably RCS too.
The problem there is that Russians normally do no state performance values for their hardware, if you notice the only values published are either those of utterly surpassed equipment or those of export versions for which Rosoboronexport discloses some data. Top cruising speed for the Su-57 with second stage engines are either leaked for the sake of some prestige claim or will remain secret for a long while, the same most of the data relative to the F-22 remain classified to this day, since that is relevant tactical information for a potential enemy. In any case, if performance claims are real aspirations, they need to be considered in the airframe and intake design
The variable intake is inherently superior in performance across a wider range of speeds and altitudes, but I know and I agree that the fixed intake design of the F-22 is most likely optimized for the flight regime considered most vital, probably max cruising speed. BTW, do you know how many shocks does the F-22 intake generate? And why can't fixed intakes be designed for speeds above 2 M, would they be too inefficient at lower speeds?
