Hypothetical Sukhoi "Su-52"

[Trident]

Su-52? Well, (47+57)/2 = 52

Which basically tells you what this is all about already, in a nutshell. An attempt to come up with a PAK-FA design on the basis of the Berkut airframe, taking advantage of ideas and solutions exemplified in the Su-57.

It strikes me that quite a few of the criticisms (legitimate as well as perceived) levelled at the T-50 configuration, particularly regarding LO properties, are avoided in the Su-47. Most prominently, it has fixed intakes with s-ducts which provide sufficient ground clearance and favourable positioning relative to the nose landing gear to obviate the need for FOD screens. The failure to adopt something like this is very commonly cited as a major RCS reduction shortcoming in the Su-57, though of course none of the critics has proved that a suitable blocker could not give similar results.

On the other hand, the unswept quarter circle inlet aperture is clearly not compatible with edge alignment requirements - the obvious solution would be to substitute a caret intake. I drew such a variant ages ago, but it would involve a considerable reshaping of the outer mold line on the lower fuselage flanks and in the meantime an alternative with good LO credentials has surfaced. In the NATF-23 carrier-based derivative of the Northrop/MDD ATF EMD configuration we find a layout that could replace the orginal Su-47 intake with far less impact. It basically involves serrating the inlet lip, adding a quarter shock cone to the upper inboard corner and removing the upper BL diverter gap (probably ok, as the shock cone acts as a semi-DSI). Orionblamblam got an eAPR sale out of this idea

Obviously, the forward swept wing, decidedly un-stealthy forward fuselage and empennage of the Berkut have to go. I've simply used suitably enlarged and adapted versions of the cockpit/nose section and flying surfaces of the Su-57 for this purpose, although the LEVCONs are not carried over.

I quite like the result, but it also gives a new appreciation for the real Su-57.

The most conspicuous feature of the "Su-52" in comparison is that it's naturally every bit as ginormous as the Su-47 was - quite a bit larger than even the J-20, we are talking MiG-31 territory here! It should therefore have greater fuel capacity and quite likely even greater fuel fraction, giving better range. Yet while the length & width of the main weapons bays are close to those of the Su-57 and it has a more elegant solution for carrying SRAAMs*, payload flexibility isn't really any better. Only the inboard part of each main bay could probably be made as deep as those on the Su-57 and they are slightly narrower, meaning it could likely only carry 2 heavy weapons internally as opposed to 4.

Therefore the more F-22-like** fuselage configuration that is proving so popular with other 5th generation fighter projects has a number of demonstrable drawbacks. And although the "Su-52" offers the same number of external hardpoints (6), the fact that all of them are underwing means the FOV for an external laser designator pod is more obstructed than on the T-50. Also, there is no straightforward place to put the rear high-band emitter that sits inside the Su-57 tail sting and closely-spaced engines might not offer the same roll authority with TVC. Last but definitely not least, the massive size increase would come with a correpsondingly painful hike in cost!

So, a certain lack of attention to detail in panel alignment and shaping of excrecences for LO not withstanding, the Su-57 emerges as a rather clever and efficient design in basic configuration.


* Or keeps them out of the main bays, compared to my "optimized Su-57" shown in these comparison drawings.

** Actually I'd say the closest analogue is arguably an early iteration of the naval variant of the F-23 which had conventional stabilizers (the definitive proposal got canards, of course). Wing config is quite different - trapezoid/diamond planform with fairly high aspect ratio and 3 flaperon segments as opposed to high-sweep delta with 2 segments - but this can be attributed to constraints imposed by carrier ops. In other respects, the resemblance is downright uncanny though: all but identical intake design (quarter-circle shock cone "semi-DSI" with serrated lip), framed canopy, same SRAAM bay layout, all-moving fins (though not reduced in area on the NATF-23)... All these things are markedly different on the F-22 which only really shares the lower fuselage aft of the intakes and the main weapons bay layout.

 

[Cool ice]

The concept looks pleasing to the eye .i like it , especially considering how the very even height of the fuselage gives potential to fold the vertical stabs horizontally in a carrier variant , and then stack them one on top of the other.i also love the resemblance to the somehow early concept drawings of the early stages.Great work mate!

i would just like to point out however that "criticism" towards the RCS of the 57 is largely based on hearsay, eye balling , and overall very simplistic and surface level observation. To this day , there isn't any actual credibility to this very long standing myth.From the "rivet" issues that werent actual issues since smoothing a surface for stealth is not required for a flight /weapons testing prototype , to magically assuming that the fans are a weakness without knowing the thickness , composition of the ram on the inlet walls , nor the materials and architecture of the blocker , and i can just go on and on.By all accounts , the chances for the su-57 being less stealthy than the F-22 are equivalent to those of it being stealthier than the F-22 , due to the fact that no one can actually prove this or that.Way too much info is needed , and classified.

 

[overscan (PaulMM)]

You can believe that if you like.

True stealth requires serious attention to details. The whole "you don't need stealth on the flight prototypes" - well, maybe you don't need to go the whole hog, but you do need for example planform alignment on gear doors, access panels, weapons bays, IR apertures designed for stealth, etc etc. Unless you believe the production Su-57 is going to alter all the detail design of the aircraft, the only way it will be truly stealthy is with a spray-on RAM coating to cover all the surface imperfections and seal the access panels etc.

 

[Trident]

The concept looks pleasing to the eye .i like it , especially considering how the very even height of the fuselage gives potential to fold the vertical stabs horizontally in a carrier variant , and then stack them one on top of the other.i also love the resemblance to the somehow early concept drawings of the early stages.Great work mate!

Thanks! Actually the un-even height of the fuselage is something I like about the Su-57, makes it look like the YF-23 which is rarely a bad thing, aesthetically speaking It's also indicative of close attention paid to area ruling (probably even differential area ruling on the Su-57), meaning it has a significance in practical terms as well. This is something where the "Su-52" might have issues in fact, it gains quite a bit of fuselage cross sectional area over the Su-47 behind the cockpit due to the larger LERX and its spine. I'm not certain the removal of the canards sufficiently compensates.

i would just like to point out however that "criticism" towards the RCS of the 57 is largely based on hearsay, eye balling , and overall very simplistic and surface level observation.

Although many of the criticisms are, like Paul says not all of them come into this category. As always, people seem unable to differentiate and divide into two camps, those who find problems even where there are none, and those who refuse to acknowledge any exist whatsoever.

I'm by no means an expert on RCS reduction, but the way I see it arguments against the Su-57 are of three basic kinds (in no particular order):

1) Non-issues. These include the lack of serpentine ducts and the infamous rivets, but that's not an exhaustive list, obviously. Numerous other aircraft designed to rigorous LO requirements have the same "problems", yet it only seems to matter on the Su-57...

2) Not problematic per se, but overly complex and removing at least some of them would probably yield useful improvements. Among these I count the SRAAM bays, or the nose landing gear mechanization (5 doors? Seriously?). By far the largest number of criticisms seem to fall into this category (variable intakes, two-piece canopy, the large number of control surfaces...).

3) Valid points. The lack of edge alignment on many access covers and panel joints which was already mentioned is an example, as are the spherical IRST and DIRCM transparencies.

Basically, my impression is that the outer mold line of the Su-57 is pretty much fine, but attention to surface details is lacking and the whole aircraft has too many moving parts. Although the vast majority of the latter are in fact properly aligned for stealth, each requires treatments for its edges that, if nothing else, add up to quite a weight penalty. I tried to demonstrate how I think most of the issues could be taken care of using established solutions proven on other aircraft (preferably Russian) with the "optimized Su-57" in my other thread.

EDIT: added a few more views, because why the hell not:

 

[LMFS]

1) Non-issues. These include the lack of serpentine ducts and the infamous rivets, but that's not an exhaustive list, obviously. Numerous other aircraft designed to rigorous LO requirements have the same "problems", yet it only seems to matter on the Su-57...

True, I am not seeing anyone saying YF-23 was a fake stealth plane, in fact it has gained a reputation of being actually stealthier than the YF-22, also no claims against X-32. Essentially, if it is Russian, suspicion and accusations without real evidence is considered the right approach. It is so silly it is not even worthy of attention anymore.

2) Not problematic per se, but overly complex and removing at least some of them would probably yield useful improvements. Among these I count the SRAAM bays, or the nose landing gear mechanization (5 doors? Seriously?). By far the largest number of criticisms seem to fall into this category (variable intakes, two-piece canopy, the large number of control surfaces...).

What is problematic with the SRAAM bays? They are small, give a great FoV to the missile's seekers and take almost no internal volume away. The solution in F-22 wastes a huge amount of internal volume, that in J-20 I am not so sure but why should it be better? It will complicate the air duct and have lots of internal wasted space. As to the landing gear gear doors, I don't feel confident to say it is an error to have five, and I don't know how you are so sure it is. Symmetry probably helps in handling the plane during take off and landing. Two piece canopy was not considered a capital sin against VLS when in the YF-23.

3) Valid points. The lack of edge alignment on many access covers and panel joints which was already mentioned is an example, as are the spherical IRST and DIRCM transparencies.

Some of them are aligned, some are not. If I remember correctly, it was Northrop that developed a system to keep the access panels in electrical continuity with the rest of the fuselage, if you notice the doors that open and close in flight have indeed properly aligned (and serrated) edges while the others don't. IRST aperture is taken as a spheric reflector when it could be transparent to RF. Just some examples of elements that may actually work differently than supposed.

Basically, my impression is that the outer mold line of the Su-57 is pretty much fine, but attention to surface details is lacking and the whole aircraft has too many moving parts. Although the vast majority of the latter are in fact properly aligned for stealth, each requires treatments for its edges that, if nothing else, add up to quite a weight penalty. I tried to demonstrate how I think most of the issues could be taken care of using established solutions proven on other aircraft (preferably Russian) with the "optimized Su-57" in my other thread.

How do we know the internal structure of the edges in the plane? Honest question. As to the finishing, I have never seen a plane so smooth and with so few joints as the dorsal surface of the second serial shown in the latest MoD visit to KnAAZ.

BTW, before PAK-FA was revealed, there were quite a bit of speculative drawings and some of them even seem to have originated in the same basic idea you have for this thread. Yours looks better, though

 

[Trident]

What is problematic with the SRAAM bays? They are small, give a great FoV to the missile's seekers and take almost no internal volume away.

Well, the fact that they are pretty much redundant if there is no need to carry more than 4 MRAAMs + 2 SRAAMs - that's a load which can be accommodated in the main bays alone. Good FoV is only really relevant when your missiles lack LOAL capability, which is becoming near-universal recently and is therefore likely to feature on Russia's next-gen SRAAM. Sure, you'd lose the ability to fire legacy R-73Ms initially, but is that temporary requirement worth permanently compromising the design for? The F-35 doesn't even have internal SRAAMs at all.

I can understand why it was done on the F-22, at the time when it was designed, LOAL was not yet available and remained unproven for several years even after it had entered service. Also, the USAF apparently insisted on 8 AAMs. But in an aircraft that first flew in 2010? With a missile that can be expected to come with the now established concept of LOAL from the outset? See my Su-57 thread for more.

No matter how efficient and well-designed for LO they are, the SRAAM bays are never going to be as light and stealthy as not having them at all.

As to the landing gear gear doors, I don't feel confident to say it is an error to have five, and I don't know how you are so sure it is. Symmetry probably helps in handling the plane during take off and landing. Two piece canopy was not considered a capital sin against VLS when in the YF-23.

Every gap requires treatment to prevent RF scattering. Fewer doors = fewer edges = less RAM = less weight (apart from the canopy, the F-23 is a perfect example of this smart minimalism). As I said, it (like the other problems in this class) is not a big deal, and all stealth aircraft have their share of such minor no-nos, but the Su-57 has markedly more than its peers. You don't need to get rid of all of them (I kept the two-piece canopy for example), but removing a few would help.

How many minor transgressions does it take to equal a capital sin?

Some of them are aligned, some are not. If I remember correctly, it was Northrop that developed a system to keep the access panels in electrical continuity with the rest of the fuselage, if you notice the doors that open and close in flight have indeed properly aligned (and serrated) edges while the others don't.

Having those aligned that move in flight is the absolute minimum requirement, but there's going to be a reason why all other stealthy designs without exception also align the others... even Northrop!

IRST aperture is taken as a spheric reflector when it could be transparent to RF. Just some examples of elements that may actually work differently than supposed.

That'd be even worse! Behind the aperture is the scanning mirror for the IR sensor, i.e. something deliberately designed to be a perfect reflector! You do NOT want enemy radar signals to encounter that. In fact the idea is to have the IRST dome turned 180° inside the fairing behind when not in use, exposing a thickly RAM-coated backside. That may offer a similarly low RCS to a F-35-style facetted enclosure, but forces an uncomfortable choice on the Su-57 pilot: he can EITHER use the stealthy passive sensor OR have a stealthy airframe configuration. Unlike the F-35 pilot, he can't have both at the same time.

As to the finishing, I have never seen a plane so smooth and with so few joints as the dorsal surface of the second serial shown in the latest MoD visit to KnAAZ.

Yeah, I never thought there were any issues with its manufacturing finish even on the prototypes, and seriously wonder what all those people deriding the build quality as shoddy were seeing. The number of joints (at least on the dorsal surface) is indeed something the Su-57 does exceptionally well BTW - fully more than a third of the top surface is covered by just 5 huge panels! If only they had applied that kind of rigour to other aspects (those landing gear doors, for example).

BTW, before PAK-FA was revealed, there were quite a bit of speculative drawings and some of them even seem to have originated in the same basic idea you have for this thread. Yours looks better, though

I know, it was an obvious starting point as it already ticked so many of the right boxes. All of those designs had one thing in common however: they were even worse (far worse, actually) than the real PAK-FA in terms of RCS reduction and edge alignment. None of them were credible, really.

 

[LMFS]

Well, the fact that they are pretty much redundant if there is no need to carry more than 4 MRAAMs + 2 SRAAMs - that's a load which can be accommodated in the main bays alone.

In the current configuration they need the wing root bays to carry the 2 SRAAM + 4 MRAAM. I personally see it much more structured and flexible to have two big bays were big ordnance can be carried and leave two small, well oriented ones for small missiles, otherwise in order to carry 2 self defence SRAAM you would lose ca. 1500 kg or half of the A2G payload, that would seriously compromise the operational effectiveness of the plane.

Good FoV is only really relevant when your missiles lack LOAL capability, which is becoming near-universal recently and is therefore likely to feature on Russia's next-gen SRAAM.

Dynamics are relevant to be the first shooting the opponent down, if you notice SRAAMs are all rail launched in the current 5G planes. FoV is relevant too, since with direct view there is less chance of the missile failing to acquire the target after launch. I don't currently buy that a missile that has to turn 180 deg AND find the target in the middle of vigorous manoeuvring and deployment of countermeasures has the same chances of success and be as quick at it as another one pointed directly at the target. Russian simulations seem to support that same understanding BTW.

No matter how efficient and well-designed for LO they are, the SRAAM bays are never going to be as light and stealthy as not having them at all.

Sure, there is no question about it, and the lengths they came to provide the plane with them, at least for me, is a sign that they are indeed relevant.

You don't need to get rid of all of them (I kept the two-piece canopy for example), but removing a few would help.

How many minor transgressions does it take to equal a capital sin?

That is the core of my problems with much of the criticism I see, the fact that nobody apart from the Sukhoi guys has actual RCS readings of the whole plane and is aware of the design compromises taken, in a quantitative and informed way. It is extremely adventurous to say what an alleged VLO "sin" actually means compared to the rest of the plane's RCS, at what frequencies and aspects, in what conditions, and much more what tactical relevance it has in the considered employment scenarios. To the point that I would not take them at face value even if the guy making them does have actual experience in VLO design, because even then he can ignore many things Sukhoi guys don't. Devil is in the detail and I have seen that proven time and time again in my own technical experience: anyone outside of the design team ignores 90% of what actually makes a difference.

Having those aligned that move in flight is the absolute minimum requirement, but there's going to be a reason why all other stealthy designs without exception also align the others... even Northrop!

Well the obvious goal of the invention was to turn the gap into a continuous electrical surface, but I would need to research more that solution before going deeper on the topic. But again the principle of prudence applies: why would Sukhoi ruin the stealth of the plane with such obvious blunders, and specially when they are taking such a structured approach with the gaps that cannot be sealed on the ground?

That'd be even worse! Behind the aperture is the scanning mirror for the IR sensor, i.e. something deliberately designed to be a perfect reflector!

A reflector in IR does not need, at all, to be a reflector in X band. If it is an essentially transparent surface to RF and the rear is covered with (thick) RAM then there is a big chance that no big signal is going to be reflected and their apporach would make full sense, since the spherical window is and easier, cheaper solution with better optical performance than the glazing in the F-35.

he can EITHER use the stealthy passive sensor OR have a stealthy airframe configuration. Unlike the F-35 pilot, he can't have both at the same time.

Under the hypothesis above that choice would not be necessary. It would be a really strong compromise actually.

The number of joints (at least on the dorsal surface) is indeed something the Su-57 does exceptionally well BTW - fully more than a third of the top surface is covered by just 5 huge panels! If only they had applied that kind of rigour to other aspects (those landing gear doors, for example).

They seem to have mastered manufacturing with very big composite panels, probably due to the vacuum infusion technology. It may have advantages in RCS return, but they may do it mainly for structural or manufacturing issues.

I know, it was an obvious starting point as it already ticked so many of the right boxes. All of those designs had one thing in common however: they were even worse (far worse, actually) than the real PAK-FA in terms of RCS reduction and edge alignment. None of them were credible, really.

That is true, before the PAK-FA was revealed there was no real faith that Russia would really try to design a VLO plane. After it, much of the scepticism remained, though

 

[Trident]

In the current configuration they need the wing root bays to carry the 2 SRAAM + 4 MRAAM. I personally see it much more structured and flexible to have two big bays were big ordnance can be carried and leave two small, well oriented ones for small missiles, otherwise in order to carry 2 self defence SRAAM you would lose ca. 1500 kg or half of the A2G payload, that would seriously compromise the operational effectiveness of the plane.

They do improve flexibility, but even without them the Su-57 would rival the F-35 for internal A/G weapons capacity and payload variability. You might legitimately wonder what practical use even better capability in this regard really is (and whether the benefit, if any, justifies the extreme airframe impact).

Dynamics are relevant to be the first shooting the opponent down, if you notice SRAAMs are all rail launched in the current 5G planes. FoV is relevant too, since with direct view there is less chance of the missile failing to acquire the target after launch. I don't currently buy that a missile that has to turn 180 deg AND find the target in the middle of vigorous manoeuvring and deployment of countermeasures has the same chances of success and be as quick at it as another one pointed directly at the target. Russian simulations seem to support that same understanding BTW.

Missiles can be made compatible with both rail and ejector launch, as seen with the AIM-120 on certain F-16 and F-15 hard points. With a clean-sheet missile especially there is no reason not to accommodate both methods.

LOAL simply means the missile seeker does not lock onto the target before launch, it does not necessarily mean that the target is far off-boresight (why on earth would that be *required*?). This mode of operation has actually been the norm for BVR AAMs like AIM-120 for ages, but in the more dynamic short-range dog fight environment was considered too risky for a time. As with MRAAMs, the addition of a datalink for targeting updates even after launch is part of the solution in several missiles.

Most new-generation SRAAMs (Mica IR, ASRAAM, AIM-9X Block II, Python 5) have now received LOAL as an upgrade, even if they did not already come with it out of the box. It would be an extreme oddity for the next-gen Russian SRAAM to lack this capability, so why not take advantage of it to drastically simplify the aircraft platform? Notably, the RZV-MD SAM for the TOR-M2 that I assumed as the basis operates according to the LOAL principle by default.

Again, when the F-22 was designed, the capability was still a relatively distant prospect and the sheer feasibility wasn't quite certain. This was/is not true of the Su-57, there is no good reason to tie its design to the same kind of (now defunct) legacy constraints.

Sure, there is no question about it, and the lengths they came to provide the plane with them, at least for me, is a sign that they are indeed relevant.

I'm sure Sukhoi in providing the SRAAM bays is faithfully executing the spec they were given which says the aircraft has to be able to launch legacy R-73Ms - that pretty much requires such a solution. Sometimes the spec is nonsense though (e.g. F-35, MiG-29) and you do the real world needs a disservice by adhering to it. Not Sukhoi's fault in that case, they don't get the contract unless they follow the customer's wishes, of course.

A reflector in IR does not need, at all, to be a reflector in X band. If it is an essentially transparent surface to RF and the rear is covered with (thick) RAM then there is a big chance that no big signal is going to be reflected and their apporach would make full sense, since the spherical window is and easier, cheaper solution with better optical performance than the glazing in the F-35.

It is true that generally what works in one part of the EM spectrum need not translate to significantly different wavelength, but I really struggle to see how the mirror could be IR reflective but RF transparent. High performance IR optics are typically gold-coated to ensure best possible reflectivity - that'll work just fine for X-band radiation too.

 

[stealthflanker]

Well the closest Russian could change Su-57 into something "stealthier" would be the Japanese 24DMU for F-3 fighter studies.

That takes care of every single Su-57 "stealth detractor"'s problem. If changes to be done to basic Su-57 design. Of course the Russian design may opt for smaller V tail and PcHN device ahead of the intake.

 

[donnage99]

Well the closest Russian could change Su-57 into something "stealthier" would be the Japanese 24DMU for F-3 fighter studies.

If you changes the center of gravity you basically changed the design. You're asking basically to go back to the drawing board/ground zero and restart. Why did you think boeing dropped the canted tail design modification from the f-15SE. That means years of flight testing and getting certified. And that was a simple change according to boeing. Making couple of photoshopped images is not airplane design. If that's the case, it wouldn't take decades to put a 5th gen into production.

 

[overscan (PaulMM)]

The IRST ball being 'transparent to radar' is the worst case scenario as it will allow radar to reflect off the internal optical mechanisms. If its treated to be reflective, as a sphere, it will give radar returns in basically every direction.

J-20, F-35 optical sensors use faceted blisters with treated transparencies to prevent radar signals entering.

F-22 and F-23 IRST (before it was cancelled on cost grounds) would have had the same.

 

[Trident]

That takes care of every single Su-57 "stealth detractor"'s problem.

... and, as donnage points out, becomes essentially a scratch-designed aircraft in the process (it represents a more radical departure structurally from the Su-57 than even this "Su-52" is from the Su-47). Since the basic shape of the Su-57 is fundamentally sound, I truly don't think changes of that scale are even necessary - which was the premise behind my "optimized Su-57". Take care of the valid criticisms (surface details, EO apertures) and cut the number of minor no-nos (basically reduce the mechanical complexity a good deal) and it becomes a perfectly legitimate VLO design.

 

[LMFS]

They do improve flexibility, but even without them the Su-57 would rival the F-35 for internal A/G weapons capacity and payload variability. You might legitimately wonder what practical use even better capability in this regard really is (and whether the benefit, if any, justifies the extreme airframe impact).

The payload capability is clearly one of the aspects Sukhoi is most proud about the plane, as highlighted by Strelets in his Zvezda appearance. I can only understand that, if you can have twice the A2G payload of the F-35 it will help a great deal, essentially doubling its tactical footprint. Added to potentially way bigger range and speed it is a relevant tool to compensate for higher NATO numbers. The available space can also be taken advantage of in A2A with weapons like izd. 810 or others that can be developed to maximize useful payload, or to carry internal fuel tanks.

Most new-generation SRAAMs have now received LOAL as an upgrade (Mica IR, ASRAAM, AIM-9X Block II, Python 5), even if they did not already come with it out of the box. It would be an extreme oddity for the next-gen Russian SRAAM to lack this capability, so why not take advantage of it to drastically simplify the aircraft platform? Notably, the 9M388 SAM for the TOR-M2 that I assumed as the basis operates according to the LOAL principle by default.

I have nothing against the capability itself, it is a logical and useful development, but I don't think it is 100% as good, fast or reliable as direct seeker targeting. Even the very modern J-20 can carry the SRAAMs outside of the bay with the doors closed.

I'm sure Sukhoi in providing the SRAAM bays is faithfully executing the spec they were given which says the aircraft has to be able to launch legacy R-73Ms - that pretty much requires such a solution. Sometimes the spec is nonsense though (e.g. F-35, MiG-29) and you do the real world needs a disservice by adhering to it. Not Sukhoi's fault in that case, they don't get the contract unless they follow the customer's wishes, of course.

That is an important point you mention, I can imagine the requirement in the F-22 was to carry the Sidewinder and that resulted in completely exaggerated bays for the SRAAMs. One of the things I like the most from the Su-57 approach is that weapons for internal carriage have been intended from the beginning, maybe to improve over designs like the F-22. So the R-73 is not internally carried but the izd. 760, also the R-37M is not carried but the new izd. 810 or even the R-77 also not intended for it,
but the izd. 180.

It is true that generally what works in one part of the EM spectrum need not translate to significantly different wavelength, but I really struggle to see how the mirror could be IR reflective but RF transparent. High performance IR optics are typically gold-coated to ensure best possible reflectivity - that'll work just fine for X-band radiation too.

I cannot say how this is done in the Su-57, all I know is there are optical reflectors that are RF transparent, so it is a possibility to be considered IMHO.

Well the closest Russian could change Su-57 into something "stealthier" would be the Japanese 24DMU for F-3 fighter studies.

Interesting that the original YF-23 did not use the same approach to weapons bays of the Sukhoi, having already the podded engine layout. Otherwise I find those two planes remarkably similar in many regards, especially for what we know of the F-23A

The IRST ball being 'transparent to radar' is the worst case scenario as it will allow radar to reflect off the internal optical mechanisms. If its treated to be reflective, as a sphere, it will give radar returns in basically every direction.

J-20, F-35 optical sensors use faceted blisters with treated transparencies to prevent radar signals entering.

F-22 and F-23 IRST (before it was cancelled on cost grounds) would have had the same.

Depends, what internal optical mechanisms are in the way of radiation from a frontal aspect? Only the mirror, which as said can be transparent itself. Eventual reflections from the lower mechanisms would have a multiple reflection path and be potentially damped by RAM. As said above it is just a possibility, but I am surprised that as such it has not been discussed more often.

The angled windows of reflective material are not the best solution from an optical point of view, there will be blind spots right where facets meet and also incident light will be reflected at certain angles much more than it would do if they were spherical.

 

[Trident]

The payload capability is clearly one of the aspects Sukhoi is most proud about the plane, as highlighted by Strelets in his Zvezda appearance. I can only understand that, if you can have twice the A2G payload of the F-35 it will help a great deal, essentially doubling its tactical footprint. Added to potentially way bigger range and speed it is a relevant tool to compensate for higher NATO numbers. The available space can also be taken advantage of in A2A with weapons like izd. 810 or others that can be developed to maximize useful payload, or to carry internal fuel tanks.

I don't think carrying 4 heavy weapons is a particularly useful capability - most of the conceivable load-outs are pretty odd (4 ALCMs + 2 SRAAMs but no MRAAMs?) and not very practical. OTOH with the main bays alone the Su-57 could carry 2 heavy weapons and potentially (with more efficient use of available space) up to 3 AAMs, still beating the F-35.

With the Okhotnik/S-70 heavy LO UCAV in the offing, there seems to be no reason to lean on the Su-57 that hard for A/G tasks. In fact the external LDP, which means laser guided munitions could only be employed in a permissive environment, indicates it's not a high priority.

I have nothing against the capability itself, it is a logical and useful development, but I don't think it is 100% as good, fast or reliable as direct seeker targeting. Even the very modern J-20 can carry the SRAAMs outside of the bay with the doors closed.

I'd say it's perfectly viable so long as the missile gets a datalink. Without post-launch updates I'd be skeptical too, but if such support is available, targeting should if anything work *more* reliably than conventional LOBL.

So the R-73 is not internally carried but the izd. 760, also the R-37M is not carried but the new izd. 810 or even the R-77 also not intended for it,
but the izd. 180.

The recently released footage of a SRAAM bay launch pretty clearly shows a R-73 variant.

 

[LMFS]

I don't think carrying 4 heavy weapons is a particularly useful capability - most of the conceivable load-outs are pretty odd (4 ALCMs + 2 SRAAMs but no MRAAMs?)

In a strike mission they make total sense IMHO, twice the weapons means twice the targets per sortie and that is a elementary metric to assess the military effectiveness of a platform.

With the Okhotnik/S-70 heavy LO UCAV in the offing, there seems to be no reason to lean on the Su-57 that hard for A/G tasks. In fact the external LDP, which means laser guided munitions could only be employed in a permissible environment, indicates it's not a high priority.

Still the big bays offer 4 LRAAM and as also other A2A configurations taking advantage of the big, regular shaped internal space available. Considering the new developments, Su-57 seems to rely mainly on stand-off weapons so the use of the external pod seems occasional at best. In any case, an internal EO targeting device like that on the Su-34 would be a nice addition for the second stage even when it would be difficult to find a place for it. Maybe unifying 101KS-U, -O and the said EO targeting system in front of the nose landing gear could be an option.

The recently released footage of a SRAAM bay launch pretty clearly shows a R-73 variant.

Yes, izd. 760 is a R-73 variant.

 

[stealthflanker]

Well the closest Russian could change Su-57 into something "stealthier" would be the Japanese 24DMU for F-3 fighter studies.

If you changes the center of gravity you basically changed the design. You're asking basically to go back to the drawing board/ground zero and restart. Why did you think boeing dropped the canted tail design modification from the f-15SE. That means years of flight testing and getting certified. And that was a simple change according to boeing. Making couple of photoshopped images is not airplane design. If that's the case, it wouldn't take decades to put a 5th gen into production.

Yes it is. Which why i think also the reason of why FGFA lies in limbo. The changes supposedly asked by Indian is far too great and amount to a new aircraft.

However should *any* lower RCS than what baseline Su-57 potentially has to offer. massive changes is obviously required.

 

[Trident]

Yes, izd. 760 is a R-73 variant.

Which means the Su-57 in this regard is following the example of the F-22 after all, even though it's so inefficient.

However should *any* lower RCS than what baseline Su-57 potentially has to offer. massive changes is obviously required.

Do you reckon? My (layman's) impression is that the changes I proposed in that other thread would suffice to bring it in line with its peers - why do you think deeper changes would be required?

 

[Cannonfodder43]

I largely agree with Trident that its mostly small no-no design choices (if that's the right way to describe it) that put the Su-57's RCS back a bit.

IMO just adding the serrations to more panels, faceting the DRICM and IRST, canted antenna bulkhead and a reformed lower aft engine nacelle profile would lower the RCS quite a bit. At least in my eyes. Those would be the minimum number of easy changes to make to be much more acceptable to me.

Although the SRAAM bays seem fine to me right now. I would much rather try and stuff another Izd-180 BVRAAM in each of the main bays instead.

EDIT: And I must say finding good analysis on the Su-57 is so hard with such junk reporting like David Axe's stuff proliferating online. When anyone with good researching skills and an eye for detail can see much of the online discussion is a bunch of crap IMO.

Also fantastic and well thought out design and illustrations, these hypothetical machines looks quite real compared to most.

 

[stealthflanker]

Yes, izd. 760 is a R-73 variant.

Which means the Su-57 in this regard is following the example of the F-22 after all, even though it's so inefficient.

However should *any* lower RCS than what baseline Su-57 potentially has to offer. massive changes is obviously required.

Do you reckon? My (layman's) impression is that the changes I proposed in that other thread would suffice to bring it in line with its peers - why do you think deeper changes would be required?

Well i think in Su-57 patent. It was described regarding the disadvantage of the "F-22" like platform.

My line of thought is that If Su-57 wants more "stealth" with its current configuration "philosophy" intact. Clearly the Japanese 24DMU studies is the way to go.

 

[Trident]

Well i think in Su-57 patent. It was described regarding the disadvantage of the "F-22" like platform.

My line of thought is that If Su-57 wants more "stealth" with its current configuration "philosophy" intact. Clearly the Japanese 24DMU studies is the way to go.

Not sure I understand what you mean here.

What I'm wondering is, would it be possible to bring Su-57 RCS broadly into line with its 5th generation peers (F-22, F-35, J-20) WITHOUT drastic structural changes, just addressing the obvious problem areas? My unscientific guess is that it might, by facetting the EO apertures, rigorously aligning those skin panel gaps which aren't already and markedly reducing the number of moving parts. Essentially, avoid making a 24DMUski, rather than a Su-57M.

I mean, by changing virtually everything other than the central fuselage box, you would hardly leave much of the current Su-57 configuration philosophy intact, right? Sure, RCS would be lower, perhaps even dramatically so, but the price would be astronomical and is that even necessary to simply match its competitors? Recognizing that those three are by no means going to be identical in the first place, of course.

 

[Trident]

All views in one handy graphic. There are some minor adjustments compared to the drawings posted previously, so those should be considered obsolete. For example, there is now a towed-decoy dispenser door on the lower surface between the engines, as a substitute for the aft EW installation in the tail sting of the Su-57.

A few notes on the re-designed forward fuselage:

- Depth at the windscreen frame location I made sure is the same as it was on the Su-47, this provides enough room to stack the nose landing gear well and cockpit above each other. If you "straightened out" the drooping nose on the Su-47 drawing and overlaid it with my design, they'd be very close in depth right to the aft end of the canopy. The Su-57 has a shorter nose gear hinged further aft, so can be more slender in this regard.
- Sight angle from the cockpit over the nose "in-flight" (zero AoA as shown) is the same as it is on the Su-57, so should be fine.
- On the ground, the nose-up attitude and lack of a drooping nose mean the angle is worse than on the Su-47 (droop) and Su-57 (nose-down stance on the ground). However it is slightly better than on the similarly-sized MiG-31, and therefore probably within acceptable limits.
- The large fuselage depth and nose-high attitude on the ground mean the canopy sill is *significantly* higher off the ground than in the Su-47 and Su-57, too - in excess of 10.5 feet high, in fact! Yet, as with the previous point, the MiG-31 cockpit is slightly taller still, so it should be ok.
- Radome aspect ratio is rather tall in frontal projection, but it should accommodate an antenna as wide as the Su-57's. The additional available height could actually be used beneficially for improved look-down performance, given the upward cant for low RCS.

 

[Trident]

And finally for something more fanciful (or actually less, depending on how you look at it)...

Ok, so given the existence of the Su-57, the 5th generation ship has obviously sailed. Russia's best course would be to modify that design in a similar manner to what I suggested in my other thread. But what about the next generation?

- Vertical tails eliminated altogether, as on this 5th generation MiG concept
- Frameless, rear-hinged rather than sliding canopy
- Fully diverterless intakes
- Gun, SRAAM bays & DIRCM replaced by retractable ventral/dorsal hard-kill laser turrets. Pew! Pew!

Given the trend toward greater persistence in US (and Japanese) future fighter concepts, the enormous size might be easier to justify for a 6th generation design, too.

 

[stealthflanker]

Well i think in Su-57 patent. It was described regarding the disadvantage of the "F-22" like platform.

My line of thought is that If Su-57 wants more "stealth" with its current configuration "philosophy" intact. Clearly the Japanese 24DMU studies is the way to go.

Not sure I understand what you mean here.

What I'm wondering is, would it be possible to bring Su-57 RCS broadly into line with its 5th generation peers (F-22, F-35, J-20) WITHOUT drastic structural changes, just addressing the obvious problem areas? My unscientific guess is that it might, by facetting the EO apertures, rigorously aligning those skin panel gaps which aren't already and markedly reducing the number of moving parts. Essentially, avoid making a 24DMUski, rather than a Su-57M.

I mean, by changing virtually everything other than the central fuselage box, you would hardly leave much of the current Su-57 configuration philosophy intact, right? Sure, RCS would be lower, perhaps even dramatically so, but the price would be astronomical and is that even necessary to simply match its competitors? Recognizing that those three are by no means going to be identical in the first place, of course

Well 24DMU has the sidebay and central Weapon bay. So it still retain the generic layout of Su-57's.


and we dont even know what the Su-57 RCS is and how to properly compare it with the others. So i would say it's better safe than sorry, wanna reduce RCS ?.. then might as well give the shape of the lowest possible RCS. If such cannot be done then i dont see it would be help to deal with "small things" like erasing the canoe side bay.

 

[Trident]

In uniform (Flanker-inspired three-tone blue scheme).

 

[TR1]

Comment by djcross I thought interesting regarding OLS spherical choice:

"The choice of materials for an EOIR window is a tricky engineering trade study. You have to choose a material which is transparent in the desired optical frequency band which matches the sensor. This isn't easy to do since a cool, optically transparent window in subsonic flight becomes a hot, opaque window in supersonic flight. Sapphire has good optical transparency across a wide range temperatures/mach numbers. Sapphire is grown in flat panes, which is why the F-35 window assembly is a conglomeration of flat panels. But sapphire is extremely expensive, and my guess is the F-35 window assembly probably costs in excess of $2 million apiece. Maybe as technology improves, the sapphire window can be grown in a curved shape and reduce RCS scattering over the baseline faceted design."

OLS-35 uses grown saphire vs glass of old OLS.
Given the "stealth mode" of the IRST internals, quite a bit of thought went into the design, not just an "oops, we don't know how to make faceted transparencies".

 

[stealthflanker]

Comment by djcross I thought interesting regarding OLS spherical choice:

"The choice of materials for an EOIR window is a tricky engineering trade study. You have to choose a material which is transparent in the desired optical frequency band which matches the sensor. This isn't easy to do since a cool, optically transparent window in subsonic flight becomes a hot, opaque window in supersonic flight. Sapphire has good optical transparency across a wide range temperatures/mach numbers. Sapphire is grown in flat panes, which is why the F-35 window assembly is a conglomeration of flat panels. But sapphire is extremely expensive, and my guess is the F-35 window assembly probably costs in excess of $2 million apiece. Maybe as technology improves, the sapphire window can be grown in a curved shape and reduce RCS scattering over the baseline faceted design."

OLS-35 uses grown saphire vs glass of old OLS.
Given the "stealth mode" of the IRST internals, quite a bit of thought went into the design, not just an "oops, we don't know how to make faceted transparencies".

So according to him the spherical OLS would have lesser RCS than faceted ? That's some confusion there.

So far the argument for faceted design was that it "throws" the strongest radar reflection lobe into a non threatening angle.

 

[Trident]

I don't believe that's what djcross meant, he was probably thinking of something like the IRST installation on Northrop's High Stealth Fighter concept for ATF that eventually led to the YF-23. This had the IR sensor looking through a curved panoramic window conforming to the outer mold line ahead of the cockpit windscreen (it somewhat resembled the flight deck windows of an airliner, but single piece).

Since Russia has apparently mastered curved (even double-curvature!) sapphire if they can make a spherical dome for OLS-35, there would seem to be even less reason to go for a shape poorly suited to stealth on that score. I think the answer is that LO wasn't really the primary driver in this decision at all, rather than optical performance, as LMFS alluded to earlier. A spherical window is really the only way you can completely avoid refraction (and possibly reflection) issues, the optical path traverses the transparency at right angles and uniform thickness no matter the direction. That would be a valid technical reason, but chances are it's a poor choice in order of priorities.

Anyway, to keep this post on topic, I've decided that the h-stabs were too large - this should be a highly unstable aircraft in pitch, like the Su-47 and Su-57. They are now some 5% smaller in area and that does make the whole thing look more well-proportioned, especially the 6th-gen derivative.

All in all, as cool as it is, I do like the "optimized Su-57" better - far more practical. The "Su-52" is just too damn big to have been a realistic option, it would certainly have priced itself out of the export market, even if Russia was willing to take the hit.

 

[Trident]

Another thought... Most of the Sukhoi FSW designs which ultimately led to the Su-47 envisaged the use of 2D exhaust nozzles, and had the intended R79-300 engines been available, the Berkut could conceivably have flown with them. Most of these were fairly exotic designs, for example with both engines exhausting through a common opening or incorporating an ejector configuration with intakes for secondary air. I've drawn a variant with a more conventional convergent/divergent setup with separate nozzles, the external shape is based on a n edge-aligned version of the layout on the S-22 mock-up.

 

[icyplanetnhc (Steve)]

Comment by djcross I thought interesting regarding OLS spherical choice:

"The choice of materials for an EOIR window is a tricky engineering trade study. You have to choose a material which is transparent in the desired optical frequency band which matches the sensor. This isn't easy to do since a cool, optically transparent window in subsonic flight becomes a hot, opaque window in supersonic flight. Sapphire has good optical transparency across a wide range temperatures/mach numbers. Sapphire is grown in flat panes, which is why the F-35 window assembly is a conglomeration of flat panels. But sapphire is extremely expensive, and my guess is the F-35 window assembly probably costs in excess of $2 million apiece. Maybe as technology improves, the sapphire window can be grown in a curved shape and reduce RCS scattering over the baseline faceted design."

OLS-35 uses grown saphire vs glass of old OLS.
Given the "stealth mode" of the IRST internals, quite a bit of thought went into the design, not just an "oops, we don't know how to make faceted transparencies".

I don't think his comment should be construed as a vindication of a spherical IRST bulb. As Trident mentioned, curvature doesn't necessarily mean spherical, but rather a smoothly blended continuous-curvature "fairing" or a curved window integrated into the OML as seen in one of the earlier YF-23 design iterations.

 

[Trident]

Dressed in what would've been its elder sibling's garb... and I couldn't be happier with the result, if I may say so myself! Looks properly villainous, with this combination of overall dark colour, sharp nose taper, fiercely serrated intakes and Red Stars!

The more eagle-eyed observer may note that a few other things changed as well: I reduced the wing and h-stab area a bit by cropping the tips and narrowing down the shelves, respectively. The shelves I had originally kept at the same size as they were on the Su-47, but there seems to be no compulsory reason to do that. Additionally, I re-drew the serrated inlet lips, which I felt didn't look quite right.

The wing and tail mods were prompted by measuring the wing area on the previous iteration and getting comfortably more than 100m²! It's now pretty much exactly 100m², which (despite the triple figures) should be a reasonably plausible value, if still rather on the high side. We are talking about an aircraft which would be 22.06m long and have a wing span of 15.45m, on that basis I'd estimate its OEW as somewhere between 22.0 and 23.0t.

So at least twice the weight of a Eurofighter Typhoon with its 50m² wing, giving a very similar wing loading - what I'm nonetheless a bit worried about is wetted area. Unlike the Typhoon, this fighter has capacious internal bays and large LERX, so wetted area could be disproportionately higher. Hopefully a size increase by a factor of ~2.0 is enough for the square/cube effect to mitigate against this somewhat. With a pair of 18tf engines its static T/W ratio would be comparable to the F-22, so that is acceptable too.

Oh well, at least it should have stellar high-altitude performance with that enormous wing!

 

[Trident]

Inspired by the Su-75 twin-seater posted recently, I lashed up a quick Su-52UB "Sparka" - and it's a beauty, if I may say so myself!

 

[paralay]