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Speculative/fictional Su-57 production version

Trident

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So I've always believed Sukhoi was fundamentally onto something with the T-50 configuration, but wasn't quite tapping its full potential. The implementation seemed a bit cumbersome, which is most un-Sukhoi-like really, when you consider the elegant simplicity of the Su-27 or Su-35S. Some of the criticism aimed at its stealth characteristics is apparently also based on this argument of excessive complexity.

These drawings represent my attempt to address these concerns while preserving the current structure and principal layout as much as practical. They are based on the high-res 3-view drawing from a patent describing the T-50 configuration (a comparison with the original in red is shown in the 3rd image). Changes include:

- SRAAM bays deleted One of the advantages of the Su-57 is the impressive size of its main weapons bays, yet oddly there appears to be no ambition to carry more than 6 AAMs (4 MRAAMs + 2 SRAAMs). Such a load could be easily accommodated in the centreline bays (the size of which is obviously driven by certain A/G munitions) alone, so the presence of separate SRAAM bays probably derives purely from an intention to provide good seeker FOV for LOBL missiles. With reliable LOAL becoming much more realistic thanks to near-field situational awareness sensors (EODAS) and modern SRAAMs equipped with datalink, this approach seems like poor choice to me. It burdens the aircraft with a very onerous feature that is rendered obsolete quite early into its service life, especially so if in this case the bays are actually sized to accommodate the very bulky R-73. With the F-35 making no allowance for internal SRAAM carriage at all, temporarily abandoning SRAAM capability pending the introduction of a successor missile seems more efficient. The benefits: more room for fuel, lower drag, reduced weight, fewer moving parts to maintain, lower RCS. More on the missile which might enable this change further down.

- LERX aspect ratio reduced The absence of the SRAAM bays offers an opportunity to slim down the span of the LERX, to maintain area & LE sweep angle (edge alignment) they instead extend slightly further forward. I took care to maintain approximately the same LERX and LEVCON areas with these changes. To be perfectly frank, this change was at least partly motivated by aesthetics ;)

- Single trailing edge flaperon The actuators move into the sides of the intake/engine nacelles instead of underwing actuator bulges. Benefits: fewer moving parts to maintain and gaps to RAM-treat, cleaner outer mold line.

- Fixed isentropic intake ramps Possibly one of the strangest aspects of the Su-57 is the presence of variable intake ramps. On an airframe obviously designed for low supersonic drag (high wing sweep angle etc.) and with a top speed goal of reportedly no more than Mach 2.0, a variable intake seems like an unnecessary RCS burden. My guess is that this is a consequence of a plan to rush the aircraft into service with the AL-31F-derived interim Izd. 117 engines, which might need this feature to achieve a useful supercruise capability. With the Su-57 now unlikely to enter service in any meaningful numbers before the definitive Izd. 30 engine becomes available, this feature can be dispensed with. Benefits: lower weight, fewer moving parts to maintain and RAM-treat.

- Modified intake boundary layer diverter/bleed system The upper BL diverter gap is eliminated in favour of a YF-23-like advanced bleed system to remove a cavity for RCS reduction. While the gap between the fuselage and intake remains, I've moved the ECS intakes into it - although the original location in the leading edge of the tailfin pedestal was pretty cleverly chosen (out of view of threats below the aircraft), the BL cavity exists & has to be treated anyway. You might as well kill two birds with one stone and take advantage of the inevitable effort to get stealthy ECS inlets 'free' (this is also the approach adopted by the F-22). Cooling air for the engine bay and engine oil heat exchanger are tapped off the main inlet duct (its area is slighter bigger due to the removal of the upper BL diverter gap anyway) instead, again as per the YF-23. The outlets for upper intake ramp bleed air are moved to the upper surface of the LERX (placing them out of view of most threats) and adopt a shape based on an 'intersected-pair' version of the current caret-shaped aperture on the outside of the nacelles. Those on the inside (facing the inlet tunnel) are retained but changed to the low-RCS caret-shape of the ones on the outside. Benefits: lower RCS, shorter ducting for the ECS heat exchangers.

- Serrated auxiliary intake louvres Later prototypes have a mesh screen over the intakes, but I think serrated louvres (essentially a reverse of the F-22 excess air bleed doors on the spine) would work better as they extend down to effectively form air scoops. Unlike the Raptor's spill doors (which are actively actuated and move during the pre-flight BITE sequence) they'd be spring-loaded as on the Su-27, making for an entirely 'passive' intake system. In up-and-away high-speed flight they'd be closed (again unlike the F-22), so the fact that they're located on the belly is probably ok. Benefit: better high-AoA intake performance at low RCS.

- FOD screens deleted This is a tough one... the current visor-like screens are a potential RCS issue with the straight ducts (blocker for engine masking). A study of nose gear FOD hazard for the C-130 which I read indicates the impact risk area starts about 2.4m aft of the nosewheels... on the Su-57, the forward-most point on the lower inlet lip is 2.5m aft, but about 0.2m higher off the ground than the lower fuselage of the C-130. Looking at the (Y)F-23 and the Hornet family, the inlets are further aft (considerably so on the F-23, moderately on the F/A-18), height above ground is pretty similar in all of them and the Su-57 inlets are wider apart than the Hornet's but closer together than the F-23's. On the latter, you can argue based on the C-130 study that they are far enough apart to be outside the FOD risk area, but the Hornet is at least as affected as the Su-57 is. As a result, with the Su-57 additionally having a nose landing gear mud guard that the others lack, it seems the adoption of FOD screens was driven by more stringent austere field requirements rather than a genuinely more FOD prone design. On these grounds, I'd get rid of the screens in exchange for greater restrictions on airfield apron/runway "hygiene". Benefit: lower mechanical complexity, reduced weight, lower RCS.

- Slimmed down tail fin pedestal to a pylon With the ECS/cooling air scoop gone, moving the taileron actuators into fairings below the 'waterline' (think F-35) allows the fat pedestal to be slimmed down to a narrow pylon. Benefit? It looks better ;) Especially as I actually like those spindle-shaped 'Kuchemann Carrots', so having deleted four of them from under the wings, introducing a new pair under the tail is a good compromise. More seriously, it does "free up" some cross sectional area for better shaping/blending of the engine/intake nacelles (see below).

- Re-shaped, more blended engine/intake nacelle fairing This isn't really visible in these drawings, but I would change the cross section of the nacelles to be more trapezoidal and blend more smoothly into the fuselage/wing, giving an OML rather like the J-20 engine fairings. The "spare" cross sectional area from an area ruling point of view for the change comes from getting rid of the SRAAM bays and fin pedestal described above, it also eliminates the break in the OML form the main landing gear door bulges (they just fair in smoothly). Benefit: Cleaner OML, lower RCS.

- Canted radar antenna bulkhead Flateric posted a CAD image of such a design sometime ago, so I included it. Benefit: lower RCS.

- Facetted IRST & DIRCM apertures Self-explanatory really. The IRST and both DIRCM windows are currently spherical domes which isn't optimal for radar signature (the IRST apparently has an elaborately treated backface which is exposed when it's not in use, but that forces the pilot to choose between stealthy passive sensor and stealthy airframe shape). Benefit: lower RCS, especially with IRST in use.

- Two rather than five nose landing gear doors, nosewheels without trailing link The doors open through substantially more than 90° to minimize destabilizing area in yaw (this problem apparenly caused the F-35 to switch from one door to split halves and may have driven the current Su-57 solution). An overall less bulky nose landing gear design (see fourth picture of the navalized variant) aids this approach. Benefit: fewer moving parts, lower RCS.

- Aligned taileron hinge line Currently the hinge is perpendicular to the aircraft centreline, I aligned it with the wing & taileron trailing edge angle. Benefit: lower RCS.

- Frangible covers for the gun muzzle & chaff/flare dispensers Currently they are hidden by actively controlled doors (though not serrated in the dispensers...). Needless complication IMHO, once a stealthy aircraft has to deploy expendable countermeasures or fire the gun, its cloak can be considered blown I'd say. Benefit: lower maintenance impact.

- Upper hemisphere MAWS/EODAS apertures repositioned They are currently placed into a small pyramidical enclosure like those for the lower hemisphere, though located quite a bit behind of the cockpit. I placed them into more Su-35S-like locations fore and aft of the canopy (the rear sensor actually on the moving part of the canopy). Benefit: the location of all sensors very close to the head of the pilot probably makes an EODAS-style near-field situational awareness function easier to implement.

- Serrated sundry RF apertures & access panels A surprising number of them are serrated anyway, but I tended to those that weren't already. Benefit: lower RCS.

- Wing & fin tips cropped at same angle as tailerons Benefit: purely aesthetical, really. On the wing tips it may give better edge alignment than before, but mostly it's just artistic license :)

In summary, the major items are the deletion of the SRAAM bays, re-shaped LERX, switch to a single-piece flaperon and numerous measures to simplify the intakes (fixed ramps, revised BL bleed system, auxiliary louvres and removal of the FOD screens). The rest is small change really, and even all together the scale of the modifications is smaller than what went on between the original T-10 and the production Su-27 (although there are a couple of remarkable parallels...).

The final drawing shows a navalized version which adopts the short tail sting from the patent drawing (representing the early prototypes). Ironically, it's closer to the current Su-57 in some respects, such as the wing and fin tip crops, the split flaperons (to accommodate the wing fold & enable inboard fixed vane slotted flaps) and the associated actuator fairings. I also re-introduced bulged main landing gear doors, to accommodate a possibly beefier gear. So if, looking at the comparison image, you were wondering what the original belly view (which was not in the patent drawing) would look like, the navalized variant provides a rough indication. The outboard flaperon actuator fairing is slightly closer to the wing tip though, to ensure it is outboard of the folding hinge. There is a tail hook compartment which partially intrudes on the rear weapons bay such that the middle slot can only hold a SRAAM (as shown in the drawing) and I assumed mission-adaptive flexible seal LE flaps as on the Su-27KUB. Finally, the brake parachute is gone, in its location is the chaff/flare dispenser displaced by the tail hook.

Whew... that's it - I think. If you've spotted something that I didn't mention, ask away: there's a pretty good chance that it's deliberate and was done with a specific purpose in mind. I'll add sources and sources of inspiration in another post later.
 

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TomcatViP

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SRAAM bays might not be bays at all. And Within visual range missile will probably fall off interest soon with the introduction of HEL and HPMW. Why would you have to carry rear aspect or a all aspect IR missiles when you can point your nose faster to beam out anything out of flight through Radar pulsed MW, an inboard Laser or Canon like HPMW mounted armament (notice how high AoA are determinant in this strategy)?

IR missiles will then be out of sight cheap discreet missiles used to gain surprise and ripple effects. They would need range hence will occupy a larger volume. This is why the dedicated side bay mounting such as in the 22 or their allegedly mounting on T-50 will make no more sense.

The "bays" presence will however probably settled since they are designed with aero effect in mind.
 

Trident

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Sorry, but they are definitely and confirmedly weapons bays - there can be no mistake on this point. Forum member flateric has seen them fitted with missiles with his own eyes IIRC, there are numerous other references to them in the press and finally, Sukhoi's patent covering the bays has been available for some time now:

http://www.findpatent.ru/patent/261/2614871.html

What aircraft do you think the above refers to, and does it look like anything other than a SRAAM bay to you?
 

overscan

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I believe they serve an aerodynamic purpose as well as housing the SRAAM missiles.
 

flateric

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They were identified as SRAAM bays by KnAAPO insider describing T-50_even before maiden flight_.
C'mon, this is 2018 already. Please stop that 'might not be'.
 

Dynoman

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Wasn't there a speculative naval version of the Su-57 with folding wingtips for the Shtorm carrier (I didn't notice wing-fold lines in the drawing)?

Also, from what I read the deal with the Indians fell apart because Sukhoi did not give up the codes and drawings to the aircraft's design so that India could manufacture the aircraft in India. Maybe an export version with the supercruise capable Izdelie-30 engine and serrated exhaust system.
 

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The SRAAM bays are in a good place structurally... I probably wouldn't touch them.

If I were imagining a late version... I think I'd go with the fancy 2d nozzel with the exhaust mixer (for IR reduction?) that was shown in a patent. Anyway, that is my 2 cents for what it is worth.
 

Trident

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PaulMM (Overscan) said:
I believe they serve an aerodynamic purpose as well as housing the SRAAM missiles.
Yes, they are going to be accounted for in the area ruling of the overall airframe, so I assumed at least some of the spare cross sectional area is put to to beneficial use in blending the engine/intake nacelle junction into the wing root. A bit like the removal of space reserved for thrust reversers in the YF-23 nacelles led to the trough between them having a reduced depth on the EMD F-23 design.

Dynoman said:
Wasn't there a speculative naval version of the Su-57 with folding wingtips for the Shtorm carrier (I didn't notice wing-fold lines in the drawing)?
Yeah, there is a wing fold line in my drawing too though. Perhaps I should update the side and front views with dashed outlines of the outer panels in folded position to make that more obvious.

Dynoman said:
Also, from what I read the deal with the Indians fell apart because Sukhoi did not give up the codes and drawings to the aircraft's design so that India could manufacture the aircraft in India. Maybe an export version with the supercruise capable Izdelie-30 engine and serrated exhaust system.
The Izd. 30 engines are in there already, including serrated nozzles. Although I'm reasonably happy with how the colourized drawing turned out given my crude methods, I'm not experienced or skilled at making camouflage profiles. I can change the national insignia to the Indian roundel and make it a uniform grey scheme (which conveniently matches modern IAF practise) if you want, but that's about as far as I'll take it :)

Avimimus said:
The SRAAM bays are in a good place structurally... I probably wouldn't touch them.
While they possibly are not as deleterious structurally as on the F-22/J-20, due to their semi-external nature, if 1) no demand for more than 6 AAMs exists and 2) you waive the requirement to accommodate legacy LOBL missiles, SRAAM bays just become excrescent (both literally on the Su-57 and figuratively) altogether. Why bother to accept even a reduced penalty if an alternative with zero impact gets the job done just fine?

Avimimus said:
If I were imagining a late version... I think I'd go with the fancy 2d nozzel with the exhaust mixer (for IR reduction?) that was shown in a patent. Anyway, that is my 2 cents for what it is worth.
IR signature reduction is an interesting point, we're still not quite certain how the Su-57 will handle this after all (will it get that mysterious aerosol system?). For the most part, I stayed away from the nozzle question beyond adding serrations of the kind that are visible on the Izd. 30 pictures we've seen to date. Currently, the engine appears to use a tilted-axis ball-joint TVC nozzle like Izd. 117(S), but personally I'd favour Salyut's KliVT/PYBBN-type 3D solution which is potentially lighter and less complex. For IR signature reduction, I'd consider an ejector effect as discussed for advanced F110 derivatives in this GE paper:

https://www.researchgate.net/publication/267483234_F110-GE-129_EFE_-_Enhanced_Power_Through_Low_Risk_Derivative_Technology

That again would give a simple yet effective route to 3-axis TVC with reduced IR signature (relatively low number of actuators required compared to a ball-joint, lower thrust penalty than a rectangular nozzle, no aerosol storage).
 

Trident

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Updated drawing of the navalized variant with folding wing panel indicated & "colour" profile of an IAF scheme.

I'll get round to the sources eventually.
 

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Trident

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As promised earlier, here's a collection of material that served as the basis for my proposed modifications.

-9M338K SAM This is perhaps the most crucial of them all, since what is likely the most significant among the changes (getting rid of the SRAAM bays) depends critically on it. Why does this missile potentially enable that optimization? First of all, it is very compact with an ASRAAM-like configuration and (in the SAM variant) even folding fins*, so its impact is dramatically lower than a R-73/RVV-MD, making it possible to carry one alongside 2 R-77/RVV-SD-size MRAAMs in each main bay alone. Secondly, it is VLS launched from the Tor vehicle, which has two important benefits: 1) in combination with its IR guidance, this means it should be inherently LOAL capable (indeed that would seem to be the default mode of operation), 2) it does not require rail launch, so should be able to use the same ejectors as the MRAAMs. Last but not least, according to flateric an AAM version WAS developed and entered into the competition for the next-gen Russian SRAAM, though the winner is not known. For the purpose of my drawings, I used the attached comparison with the legacy Tor missile which conveniently included a 1m scale, allowing me to size it accurately (it's about 2.8m long, in case you were wondering).

* If the folding fins are carried over from the SAM, things could potentially get even better: with launch rails mounted inside the doors of the forward main bay and assuming a 0.6m by 1.0m cross section for the bay as well as a 0.17m missile body diameter (similar to the R-73 and ASRAAM) it may be possible to carry 2 MRAAMs and 2 SRAAMs in the forward bay. With 3 MRAAMs in the rear bay that's just one MRAAM short of the F-22, with dramatically lower mechanical complexity (4 fewer weapons bay doors and 2 fewer extending trapezes). It's very risky in terms of safe separation of the MRAAMs though, as they'd require canted ejectors to put them on a diagonal trajectory between the wo SRAAMs on their door-mounted rails. See the attached sketch (to scale) and make up your own mind on whether that's tenable during manoeuvres, but it's an idea to consider.

-R-77 drawing I used this Yak-141 drawing with the missile's tail fins in folded configuration, scaled to a length of 3.7m.

-External tank When I saw the first photos of T-50-9 with drop tanks, I was immediately reminded of this early PAK-FA concept drawing. The tank is therefore based on the shape shown there, scaled based on the image I used for the digital camo scheme (see below).

-Kh-59MK2 ALCM The drawing is based on the attached advertising poster, scaled to the stated length of 4.2m. I cropped the wing tips at an angle and modified the tail fin trailing edges in a way that I would imagine gives lower RCS, but basically it's artistic license.

-Grom-E PGM The variant I drew is a fictional bunker busting version. Given its specs (upowered dual warhead variant with 65km range, rocket-assisted unitary warhead version with 120km range) I think it could potentially render the Kh-38M family moot if similar seeker and warhead options are provided. With a heavier payload the gliding variant achieves almost the same range, the one with a rocket motor flies almost twice as far - the dual warhead version seems to be aimed at soft targets with an airburst fuze, but it inspired me to speculate on a BROACH-type bunker buster. Body diameter is notably identical to the Kh-38M family, so I added an EO seeker based on the version displayed at various recent MAKS air shows. Source for Grom-E specs and geometry including dimensions: https://en.ppt-online.org/345832

-Deleted FOD screens Here's the paper I mentioned: https://www.aerosociety.com/Assets/Docs/Publications/OAPapers/4022.pdf
Also, this paper offers approximate angles of FOD impact threat: https://apps.dtic.mil/dtic/tr/fulltext/u2/a117587.pdf
Based on this, the Su-57 inlet is inside the danger area in beam view but almost entirely outside in the planform view, rather similar to the F-4 (Fig. 5). Since the Phantom does without FOD screens and the Su-57 has a mud guard on the nose gear, I think it should be ok.

-Flush air data system I forgot to mention this one in the original post, but I assumed flush air data sensors for lower RCS. On early prototypes (up to and including T-50-5) there were very interesting bare metal circles with what looked like numerous small holes on the nose, as shown in the attached image. They remind me a lot of the air data sensors on the B-2.

-Canted radar antenna bulkhead I've attached the CAD image I mentioned.

-Single piece flaperon, BL bleed on top of LERX, longer LERX, tail fin pylon These changes are all reminiscent of the well-known early PAK-FA CGI which surfaced on the NPO Saturn website even before the aircraft had first flown.

-Wing tip crop This apparent stress visualization shows a crop similar to the one I drew, albeit on an aircraft that is otherwise the same as the current Su-57.

-Digital camo scheme and EFT scaling Based on http://su57.mariwoj.pl/su57-T50-11(2).html

So many of the proposed modifications, which result in fairly dramatically reduced complexity while preserving much of the basic structure, are based on technology or ideas already available in Russia.
 

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Trident

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That the configuration from the NPO Saturn image was at one point seriously investigated is indicated by the TsAGI wind tunnel model in the this photo - it matches extremely well, although the forebody is generic.
 

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