Russian Su-57 Aircraft Thread (PAK-FA and IAF FGFA)


halflife3

New Member
Registered Member
Why did they not design an S-duct into this fighter. Does it mean the fan blocker is definitely effective? Western commentary on this S-duct issue seems to suggest that Russian engines are not able to deal with the "turbulence" from S-ducts or they just simply can't do it. This is obviously hard to believe given how many other fighters in Soviet and Russian arsenal had S-ducts, not to mention the J-10 and J-20 both fly with S-ducts while using AL-31s.

Seems like a real oversight but there's gotta be more to it. Radar blockers? Offset fan surfaces? If it's possible to design stealthy bomber and fighter airfoils, it's possible to design stealthy fan surfaces. Personally I think given the slightly offset angle of the engines and the position they occupy from almost all frontal angles, the blades are designed to bounce energy off some internal sections which either absorbs and/or reflects the energy further away from source.
Lack of money. Russia's defense budget is only a fraction of what it was during Soviet era. Developing a brand new jet fighter costs tens of billions of dollars and decades of research. Russia's economy also isn't going to get better anytime soon with the sanctions and falling oil price.

To put into perspective, Russia has not constructed a single warship from a destroyer class and above. Most of Russia's hardware such as T-72, T-90, Su-27/30/33/35 series, Mig29/35 series, were all developed during Soviet times. After Soviet Union dissolved, Russia's economy was crippled, however it inherited vast numbers of weapons and defense research whose costs were written of as a result of the collapse, benefitting Russia immensely.
 

ougoah

Captain
Registered Member
Lack of money. Russia's defense budget is only a fraction of what it was during Soviet era. Developing a brand new jet fighter costs tens of billions of dollars and decades of research. Russia's economy also isn't going to get better anytime soon with the sanctions and falling oil price.

To put into perspective, Russia has not constructed a single warship from a destroyer class and above. Most of Russia's hardware such as T-72, T-90, Su-27/30/33/35 series, Mig29/35 series, were all developed during Soviet times. After Soviet Union dissolved, Russia's economy was crippled, however it inherited vast numbers of weapons and defense research whose costs were written of as a result of the collapse, benefitting Russia immensely.
I disagree. If you bother to build a ground up new fighter which the Su-57 is, then why be penny wise pound foolish? Do not buy this theory at all. So they went 99% of the way to design, engineer, test, build every single new piece of technology on this fighter but didn't have the pocket change left to "properly" do the intakes and ducts? No way.

If one is to suggest that Su-57 is just a flanker... again bullshit. It's about as much of a flanker as the F-22 is a F-15 rebuild. These clueless guys have no idea about engineering. They probably also think J-20 is Mig 1.44 since both have canards, two engines... they're also both big I guess. This isn't to say Su-57's components are every bit as advanced and capable as leading counterparts but surely it differs internally from the flankers as much as it does externally, a lot! While it may look like a boxy, stealthified flanker because it uses a similar wing-intake arrangement for lift, there is a whole world of engineering difference as soon as you include different weight distributions, internal bay structures... to say nothing of all moving V shaped vertical stabilisers and LEVCONS.
 

Tirdent

Junior Member
Registered Member
Why did they not design an S-duct into this fighter. Does it mean the fan blocker is definitely effective? Western commentary on this S-duct issue seems to suggest that Russian engines are not able to deal with the "turbulence" from S-ducts or they just simply can't do it. This is obviously hard to believe given how many other fighters in Soviet and Russian arsenal had S-ducts, not to mention the J-10 and J-20 both fly with S-ducts while using AL-31s.

Seems like a real oversight but there's gotta be more to it. Radar blockers? Offset fan surfaces? If it's possible to design stealthy bomber and fighter airfoils, it's possible to design stealthy fan surfaces. Personally I think given the slightly offset angle of the engines and the position they occupy from almost all frontal angles, the blades are designed to bounce energy off some internal sections which either absorbs and/or reflects the energy further away from source.
Because an s-duct did not fulfill their requirements as well as a short, straight duct with a radar blocker.

The notions that Russia would be unaware of the fundamentally important requirement to deal with engine face radar signature or incapable of designing an s-duct for lack of money are indeed risible. As you say, a number of Soviet/Russian aircraft have curved inlet ducts and even if in most of these the reason isn't RCS reduction (so you could be tempted argue there is some "secret sauce" they lack), that is not true for the Su-47. In a document on LO work performed at Sukhoi, its s-ducts are not only mentioned, but specifically described as a deliberate RCS reduction measure - they were certainly no accident. So there is institutional experience with s-ducts in the company, and in terms of engine matching it was a success too, with the Su-47 flying at high angles of attack during air shows (despite its D-30F6 engines which were hardly intended for such antics).

So how does/will the Su-57 solve this issue? All indications are that it will use a blocker of some type - there is a Sukhoi patent on inlet blockers but it is (probably deliberately) vague and describes a multitude of possible configurations. For the most part it only serves a further good clue that this is the kind of solution which will be adopted - although it can be interpreted as hinting that the blocker will not be integrated with the engine fan IGVs. That's a bit of a surprise given the rather exotic shape of the Izd.30 fan IGVs (photos of which were leaked a while ago) that are reminiscent of the GE YF120 configuration for the YF-23, which despite s-ducts had incomplete engine face masking. Possibly the separate blocker is only intended for the interim Izd.117 engine, so it retains maximum commonality with the 117S on the Su-35S?

Anyway, this begs the question of how an s-duct is inferior, given its widespread adoption elsewhere. While it's definitely an elegant solution there are certain drawbacks:

- Introducing sharp bends into an air duct inevitably increases flow resistance, i.e. causes pressure loss. Careful design can minimize but never eliminate this effect.
- One solution is to make the duct very long, so complete engine masking can be achieved even with gentle, large radius bends. Longer ducts increase pressure loss from wall friction, however.
- The offset between intake aperture and engine face may increase maximum cross sectional area which can cause drag issues from poor cross sectional area distribution and increased wetted area.
- Particularly if the duct is long, it takes up a lot of internal volume that is already at a premium in stealthy aircraft due to internal weapons bays and high internal fuel fraction (to avoid drop tanks). This can drive up weight.

None of these are show stoppers and by careful packaging the F-22 and J-20 have dealt really well with the third point in particular, but it gives an indication how a short, straight duct with a blocker could be an attractive alternative. If the pressure loss penalty from the blocker can be kept low enough (for example by integrating it with the fan IGVs) to ensure competitive engine performance it might well yield a handsome weight saving at the aircraft level. So why has nobody else done it? Well, they have - the Super Hornet is operational with a blocker, the YF-23 would likely have required one for complete engine masking, the Boeing ATF entrant and JSF design certainly had one (the latter beating MDD's s-ducted design)...

All we know is that Sukhoi did its homework on the subject and apparently came away convinced that they were better off without an s-duct.
 

ougoah

Captain
Registered Member
No doubt Sukhoi knows and does better than armchair engineers on this matter. Given the arrangement of the internal bays, the Su-57 really couldn't realistically employ S-ducts the same way an F-22 does. So alternative solutions must have been explored and now used. I think the blockers may be how they decided to go since it appears easier than making rotating blades deflect radar waves away from source. There are bound to be some positions at certain angles of incidence where the blades show up and in rapid rotation the returns will almost be continuous.
 

bruceb1959

Junior Member
Registered Member
The climb aircraft appears to be the same aircraft that launches the side bay SRAAM because it has the same paint job. May not have been in the same sequence of events and the missile does appear to be "ejected" into a firing position at 1:19 if you slow it down to 0.25x speed. Then again it could have been in that position and was just hidden by the clouds before the moment it becomes visible but this is unlikely since we can see every other aspect of the plane clearly so what mysterious cloud hides just the missile which is right under the wing.

The sticking out position of the SRAAM is a curious sight though. The side bay mechanism is still shrouded in secrecy. I would sooner believe it's a drop away cover than some mechanism that extends the missile forward and holds it there but who knows.

Does anyone know what these bubble looking things in the canopy glass could be? Appears around 1:03. Maybe air bubbles in the canopy?

View attachment 58684
The bubbles are unlikely to be within the structure of the canopy as they can be seen to move, but beyond that I'm at a loss
 

Inst

Senior Member
Any news on potential PLA purchases of the Su-57? The current unit cost of the Russian contract is THIRTY ONE MILLION. It literally makes more sense for the PLA to purchase the Su-57 than the Su-35 at this point, given that the Su-35 flips at 50 million (probably closer to 40 million).

The Su-57 is literally an aircraft where if you're getting a 1:2 KD ratio vs the F-35, you're winning.
 

siegecrossbow

Brigadier
Staff member
Super Moderator
Any news on potential PLA purchases of the Su-57? The current unit cost of the Russian contract is THIRTY ONE MILLION. It literally makes more sense for the PLA to purchase the Su-57 than the Su-35 at this point, given that the Su-35 flips at 50 million (probably closer to 40 million).

The Su-57 is literally an aircraft where if you're getting a 1:2 KD ratio vs the F-35, you're winning.
On the contrary I think this is a once in a life time opportunity for Russia to market the Su-57 to India.
 

anzha

Junior Member
Registered Member
On the contrary I think this is a once in a life time opportunity for Russia to market the Su-57 to India.
If India believed Russia would stick to that price. The Russians came back to the trough several times with the FGFA development stating there was going to be more money needed.

I really don't understand why folks think the Chinese would want to buy the Su-57. China is intent on moving forward with its own 5th+ gen birds. They have more J-20s in service than Russia has all of its Su-57s. The su-57 is clearly not done with its development, whatever the russians are saying.

So, why? why would the Chinese be interested?
 

dankris

Junior Member
Registered Member
If India believed Russia would stick to that price. The Russians came back to the trough several times with the FGFA development stating there was going to be more money needed.

I really don't understand why folks think the Chinese would want to buy the Su-57. China is intent on moving forward with its own 5th+ gen birds. They have more J-20s in service than Russia has all of its Su-57s. The su-57 is clearly not done with its development, whatever the russians are saying.

So, why? why would the Chinese be interested?
If China is just interested in the engines and avionics of Su-35, then as long as Su-57 is mature enough buying Su-57 is not that bad of a deal as you'll get what the Su-35 has and with a cheaper price, if what @Inst say is true. It also comes with an added benefit of giving the Chinese engineers a chance to inspect the plane with all their sensors, probably giving them intel on a potential future RuAF backbone. That said, it's only a good deal if Su-57 is considered mature. I think China looked at it and deem it not mature enough to justify the risk.
 

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