Sukhoi Su-57 flight testing and development

Josh_TN said:
Lower frequency radars seem largely limited to ground stations. That seems like a bit of a win for low RCS aircraft. The one exception I know of is the E-2D, which is supposed to be a UHF band radar and apparently uses some form of computer black magic to generate target grade tracks. But we are still talking about a dedicated multi-engined platform with a huge fairing.

But the bigger question to me is whether a row RCS aircraft is really cost prohibitive in the first place. The F-35 is now at nearly the same price per copy as an F-18. There probably is a lot of sunk cost in R&D specifically related to composite materials and shaping, but that is spread across about 600 examples and counting. The main drawback the Su-57 seems to have in that regard is that the production rate and number of users of the aircraft are going to be much lower than F-35, which makes it harder to justify some program costs. This may or may not have influenced Russian attitudes and requirements for RCS; I don't think anyone definitively knows.
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Yes, this may have played a role. I doubt anything we've been expounding on as amateurs in this thread is news to the engineers at Sukhoi, but for reasons only known to themselves they deliberately elected to go a different route. That doesn't automatically make this choice correct (specifications and assumptions can fail to address reality), but it is something to be borne in mind by the likes of Justin Bronk.
 
Regarding ESM and aircraft detection, I believe I read an article that said one of the modes of operation for the F-22's radar was to stay passive except for spot lighting targets detected by the ESM system. The advantage here being while you will give away your presence, it should only be to the target(s) of your interest and anything else immediately down the bearing. The figure I read for the beam was on the order of 2 degrees, which if correct would mean that pretty much only the target or other aircraft in its flight would detect the illumination. But I've only read one source on that so I'm not positive this is an existing capability. I'd be a little surprised if the F-35 couldn't manage this with its newer avionics though.
 
Josh_TN said:
Regarding ESM and aircraft detection, I believe I read an article that said one of the modes of operation for the F-22's radar was to stay passive except for spot lighting targets detected by the ESM system. The advantage here being while you will give away your presence, it should only be to the target(s) of your interest and anything else immediately down the bearing. The figure I read for the beam was on the order of 2 degrees, which if correct would mean that pretty much only the target or other aircraft in its flight would detect the illumination. But I've only read one source on that so I'm not positive this is an existing capability. I'd be a little surprised if the F-35 couldn't manage this with its newer avionics though.
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I would assume this capability to exist in every modern fighter aircraft. It does not really needs AESA, but it needs accurate bearing. The one in F-22 might be more accurate than F-35 as AFAIK F-22 have more antenna in its ESM's. More antenna means more gain and potentially longer baseline distance (Separation between elements) required for Interferometric direction finding.

More accurate direction finding will allow narrow acquisition box which one can points its radar to and then acquire the target, narrow acquisition box would allow faster search as the radar only needs to dwell in few beams, few beams also means longer dwell time could be alotted for longer detection range and power can actually be reduced. Even better if range could be estimated, this would allow better power management to make it harder for opposing ESM to acquire the radar.
 
I think accomplishing that requires a fairly exacting ESM system and AESA. The more precise the bearing and azimuth, the tighter the search. And a mechanical search seems problematic- if nothing else, a mechanical antenna will illuminate a much wider arc, particularly considering side lobes. I assume it can be done in principle but I think the F-22 was the first to make this truly practical and automated.
 
flanker said:
overscan (PaulMM) said:
All the evidence points to a basic airframe configuration optimised for low RCS from the front only, with lesser regard for other angles.

The existing Su-57 airframes don't show the attention to detail needed for a truly low (VLO) RCS. We have no idea what the requirement was however - presumably it meets the requirements in the area.
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Considering the detailed changes between Phase 1 and Phase 2 frames (note the main weaponbay doors for instance) they have good understanding of the details and where they are worth it. According to the now chief engineer of the project, T-50 exceeded the stealth requirements. And someone who has worked on the stealth of F-22 and F-35 claimed T-50 is "metal marble class". Personally i dont think T-50 is as stealthy as F-22 - but i think it is stealthier than what most people give it credit for being.
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You are talking about djcross? I think he only worked on F-22.


He did have a interesting comment about it in 2018:

I have never seen an official document which states the design rationale for SU-57 low observables.

I can speculate that the SU-57 design provides an X-band detection advantage over western Gen 4 fighters. SU-57 edge alignment and RAM treatments likely provide effective X-band RCS reduction. This gives SU-57 first shot/A-pol advantage against Gen 4 fighters which would guard high value targets such as AWACS. NATO relies on AWACS directed Gen 4 fighters for air defense. Without the Air Battle Management coordination of fighters and long range L-band sensor capabilities of AWACS, NATO is vulnerable to air attack.

NATO has no effective SAM defenses, so SU-57 does not need RCS treatments to protect against S-band SAMs. SU-57 does not appear to possess S-band RAS features which some western fighters possess.

This speculative design philosophy is radically different that F-22 and F-35, where RCS was intended to counter the vast proliferation of Russian SAMs which would otherwise inhibit operation inside the IADS.
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Looking at the background behind Su-57 model, i guess they're using PCSR and their result might be similiar with Air Power Australia's Assessment
 
I haven't noticed it previously, but the KNS exhaust has perforations around the edge of the exhaust... Wonder if it is a similar system to YF-23's. Probably a better explanation but still curious, maybe others can chime in. There is another IR supression system on T-50 and it is basically aerosol dumping into the exhaust.
 

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What's the source of this image?
 

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I apologize if I did not look hard enough but what is this Aerosol Injection system that many talk about? I presume its some sort of IR signature suppression system but how would it work?
 
Your guess is as good as anybody else's in the public domain - the rather brief blurb posted by flanker represents the sum total of all information that is available, AFAIK. Based on the drawing, the idea is to create a sheath of aerosol-doped air around the nozzle and exhaust plume which is IR-opaque thanks to the properties of the substance.
 
Seems rather counterproductive to have to carry an aerosol supply in order to reduce IR plume visibility. Extra weight and complexity that could rather be dealt with by the F-35 like bypass air flow around nozzle.

Unless that measure only works with the lower cruising speed and higher BPR of the F135 and such.

Or that aerosol works well enough to warrant its adoption.
 
The nozzle serration is supposed to promote mixing between hot engine exhaust and the cooler ambient air. This reduces the amount of plume emmission coming from the engine. The aerosol takes the game bit further by "actively" cools the exhaust down to the point where its temperature would emit wavelength which be one strongly absorbed by ambient air.

bokeh_plot.png

For example. In 10000 meter altitude. If one desires to reduce the detectability of the engine or other infra red emmission he has to "cool" the emmission to the wavelength which have 0 transmittance. Means that the infra red energy emitted on that wavelength would be strongly absorbed by atmosphere. As seen at above chart from MODTRAN web app. One would wish to cool its engine emmission to about 6 micron wavelength or 9 micron or down to 14 micron. These wavelengths correspond to temperatures of 756, 595 and 480 Degrees Celcius. Typical Jet engine exhaust temperature is about 900 K or about 1173 Degrees Celcius.
 
stealthflanker said:
The nozzle serration is supposed to promote mixing between hot engine exhaust and the cooler ambient air. This reduces the amount of plume emmission coming from the engine. The aerosol takes the game bit further by "actively" cools the exhaust down to the point where its temperature would emit wavelength which be one strongly absorbed by ambient air.

View attachment 645014

For example. In 10000 meter altitude. If one desires to reduce the detectability of the engine or other infra red emmission he has to "cool" the emmission to the wavelength which have 0 transmittance. Means that the infra red energy emitted on that wavelength would be strongly absorbed by atmosphere. As seen at above chart from MODTRAN web app. One would wish to cool its engine emmission to about 6 micron wavelength or 9 micron or down to 14 micron. These wavelengths correspond to temperatures of 756, 595 and 480 Degrees Celcius. Typical Jet engine exhaust temperature is about 900 K or about 1173 Degrees Celcius.
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sound like a great solution, but how much aerosol in weight you need to carry to cool the engine that much though?
Is it better if aerosol is something that can block Infrared radiation ?
 
It's probably only in case of emergency. Just like the design emphasis on frontal and rear aspect stealth only, the aerosol shielding might only be for short duration (egress, Manpad...?).
 
Some form of thermoelectric cooling might be a possibility. Maybe combined with a gas/solid heat sink or something even more exotic?
 
Sukhoi OKB hasn't applied RAM coatings on the entire wet surface of the Felon. The surface may itself act as a radar absorbent structure due to the inclusion of some exotic stuff .

In here we see a thick ram layer around the gun port and cooling covers which extends right upto the radome .around the KS-U aperture just beneath the cockpit .

Is this the equivalent of boundary type magentic ferrite ram treatments we have seen in F-35? There are two small pitot tubes portruding from the sides.
 
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Samoderzhets said:
People appear to have missed the first glimpse at the actual radar blocker. I guess most of you watched the video in question (https://www.1tv.ru/shows/chasovoy/vypuski/glic-100-let-na-krylyah-chasovoy-vypusk-ot-18-10-2020) on youtube, where compression kills crucial details. I decided to check the footage at the source and here it is:
TbhsWb6.jpg


Here is the patent and fig. 3 certainly looks familiar, altough there are interesting differences.
https://findpatent.ru/patent/262/2623031.html
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Indeed interesting!

1607267703765.png
 
If I understand the patent correctly rather the device is of some length and the visible part is the leading edge and its purpose is to introduce multiple bounces into the radar path to and from the engine face to attenuate the signal. By reducing the duct into multiple smaller sections the number of bounces is greatly increased.
 
sferrin said:
That's a weird one. Looks more like a device for flow control rather than a blocker.
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It would actually function as both, just due to the nature of the flow going through the blocker. The problem is, you can only see the front face of it. You can almost see some curvature in the wall of the small section at the bottom, the sort of miniature s-duct forming. I was actually more interested in the fixed oblique ramps that are in the sides of the inlets now.
 
Guess the "real" blocker is behind it. Or maybe that's where the blocker would be attached, ahead of it. The blocker would be at front while that device "straighten" any flow distortion caused by the blocker to provide the engine the air it needs.

Or maybe yes it's the blocker itself, consulting from this patent image

v2-8ceedbba5e339d54f5da81a9e539e5a7_hd.jpg
 

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