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

[Gloire_bb]

if you wanta write fiction here on SDF???

Basic knowledge of what fleet air defence / intercept is, is a fiction? Ok.
Then lets put it blunt and simple: priority list of f-35 is an opposite one to a proper interceptor.
The only saving grace here is what F-18E/F is even worse in this regard.

they my friend are putting their MONEY!

Of course we do. Now in Turkey we can literally hear how the free hand of the market works in NATO nations. Because nations are "free to face the consequences of their choices"(c), +/- quote.
Don't get me wrong, most allies are very happy with capability set of an f-35, because it delivers what they need. In case of US, AF(main customer) also gets exactly what it needs.
But Japanese case is a special one. They actually need an interceptor, and don't have one on their own(unlike,say, Britain).
Fighter-bomber is on their list too(maritime strike/air superiority and so on), but even they are expected to participate in defensive counter air.
Thus - result, they make their own F-3 to replace mainstream fighter force.

 

[TerraN_EmpirE]

Russia’s 5th-generation fighter jet starts flights with cutting-edge weaponry
Military & Defense
January 24, 11:44UTC+3
The protocols of information interoperability with almost all types of weapons have been agreed, according to Tactical Missiles Corporation CEO Boris Obnosov

MOSCOW, January 24. /TASS/. Russia’s Sukhoi Su-57 fifth-generation fighter jet has started flights with the most advanced air-launched weaponry on its board, Tactical Missiles Corporation CEO Boris Obnosov said in an interview with the TASS-published Bulletin of Military and Technical Cooperation.

"Tense work is underway. The entire set of precision weapons for this aircraft, both inside the fuselage and on an external sling, is being developed by the Corporation’s enterprises. We have switched to practical flights and I believe that we will see the result in the imminent future," Obnosov said, responding to a question about progress in implementing the program of developing air-launched weapons for the Su-57 fifth-generation fighter.


According to the Corporation’s chief executive, the protocols of information interoperability with almost all types of weapons have been agreed.

"The basic work, i.e. launches, is forthcoming," the chief executive said.


The Russian fifth-generation Perspective Aviation Complex of Frontline Aviation (PAK FA, also known as the T-50) fighter jet took to the skies for the first time in 2010. As was reported earlier, the cutting-edge fighter performed its first flight with a new engine on December 5.

Currently, the so-called first stage engine 117S is mounted on the Russian fighter. A new engine has not yet received its name and is conventionally designated as "the second stage engine."

It was reported earlier that Russia’s T-50 (PAK FA) fifth-generation fighter jet had received the serial index of Su-57. The experimental design work on the most advanced fighter jet should be completed in 2019 and its deliveries to the troops should begin at that time. As United Aircraft Corporation CEO Slyusar said, the pre-production batch will consist of 12 such planes.



More:

Please, Log in or Register to view URLs content!

Same factor(being fatty) makes f-35 surprisingly bad at loitering for amount of fuel it carries, so even small mistakes in timings, intercept control and so on will send fighters looking for fuel.
Well, at least F-35 is stealthy.

Just for the record F35 is not more "Fat" Then The Rafael And the Intakes would be almost twice as large as they flow into one engine vs the twin engines. That argument is total BS . The Fuselage is a lift generating body meaning it's easier on the fuel to.

 

[Gloire_bb]

While front pic doesn't give the whole picture(definitely so for supersonic) - do you even look at your own image? Sorry, but F-35 is exactly fatter on this pic, despite using only a single centerline engine.

Belief what you can just make a single engine fighter, put on it 8 tonnes of fuel and two huge and volumous internal bays near gravity centre and avoid sacrifices is remarkable, but unjustifiable.
And, honestly, I don't know why it hurts so much.
For airforce isn't a (skipped word) measuring contest.

 

[ougoah]

You have some real beef against F-35 it seems. Why are we even discussing this here again?

 

[Engineer]

Well, define "better" - that's conditional on the intended task. Better for the requirements of a pure air superiority fighter? Sure, a light-weight low-AR wing in conjunction with relaxed stability is best. For an aircraft with high demands on defensive patrol endurance? An unstable VG wing will look increasingly favourable the higher your loiter requirements go, until there eventually comes the tipping point beyond which fuel savings out-weigh the empty weight gain.

No real-world example required.

No real-world example means no proof for your claim that variable-geometry wing is better. Real-world engineering decisions have so far collectively decided against variable-geometry wing for modern fighter aircraft, and that's a fact. Real-world engineering decisions reflect what's better.

Relaxed stability decreases trim drag - what the aspect ratio of the base wing has doesn't fundamentally alter that effect. Even long-range airliners with their very high AR wings generally have a trim tank in the horizontal stabilizer to move their centre of gravity aft in cruise to take advantage of it (though for safety/certification reasons they again never become genuinely unstable - only "less stable"). Just because it doesn't exist doesn't mean it could not be done if there was the requirement for it (ask the USN how happy they are about NATF & A/F-X getting the axe in favour of short-legged Super Hornets, though).

All that says is that relaxed stability is good solution for decreasing trim (and enhancing endurance), thus proving my point. It does not support your view that endurance can only be achieved through variable-geometry wing.

Pitting a fixed high-AR wing with relaxed stability against a stable VG wing configuration is a contrived, intentionally biased comparison - there's no reason to apply relaxed stability to one but not the other.

No bias exists on my point, as the statement is about endurance achieved with variable-geometry wing can be achieved with relaxed stability; it is one versus another comparison. You are trying to attribute benefit of relaxing stability to variable-geometry wing to support your faulty assumption, and that's the real bias.

As DSI for fighter applications is a purely external compression intake, beyond triggering the terminating normal shock (which is about as easy as it gets) the cowl *contributes* basically nothing to pressure recovery though. The challenge is in designing it such that it *detracts* as little as possible from the theoretical optimum achievable with the chosen shock system and centers on managing and optimizing the boundary layer diversion. This is a bit harder to do than with a traditional intake (where the diverter and bleed take care of it) and accounts for the characteristic forward-swept shape to allow for BL air to spill overboard even downstream of the lip, but there's little scope here for improved pressure recovery over a well-designed conventional counterpart.

Not true, as the DSI is known to have higher performance than traditional fixed inlets, and that includes better pressure recovery. A simple conic or isentropic inlet is insufficient to explain DSI.

BTW, your earlier point about increasingly complex shock systems worsening inlet drag due to friction from higher wetted area at low speed & cowl drag due to larger flow turning angle at high Mach affects ALL external compression inlets - including DSI. Designing for shallower initial shock angles and greater total intake flow turning angle will result a longer, larger bump and a higher cowl projected frontal area - another effect which familiarity with the design method will make clear.

All streamline tracing method does is explain how the bump is generated. Design method for the bump tells you absolutely nothing about inlet drag and pressure recovery, nevermind performance of other inlet types.

Again, you are trivializing a very significant challenge - what kind of solution to that problem would not have been "already existing" in some way or other? Ion thrusters?

The Russian have dealt with instability before, and thrust vectoring isn't a new invention resulted from designing the Su-57. Instability is a problem which the Russian were already familiar with, and thrust-vectoring is an already existing solution.

Bit of an oversimplification, but fair enough - what about this:

"Indeed, but a conical shock system contributes to pressure recovery and the downstream behaviour is known to the Russians from earlier intakes with conical centre-bodies."

No further off the mark than what you said. I still don't see how designing a suitable cowl to both match the shocks (they already have that t-shirt) and accommodate BL diversion without a diverter & bleed (the only truly novel aspect) would defeat them.

Cute, but it doesn't work. LEVCON is simpler than canard as there is no canard downwash to deal with. DSI, as you admitted yourself "is a bit harder to do than with a traditional intake", and more complex.

 

[Tirdent]

No real-world example means no proof for your claim that variable-geometry wing is better. Real-world engineering decisions have so far collectively decided against variable-geometry wing for modern fighter aircraft, and that's a fact. Real-world engineering decisions reflect what's better.

The key phrase is "fighter aircraft", which implies requirements to which VG wings are a poor solution due to weight penalty - doesn't mean it's not an excellent choice for other jobs with differing priorities.

Does high aspect ratio (i.e. VG wings unswept) give better induced drag than a (fixed) low aspect ratio wing? Yes.

Does relaxed stability reduce trim drag on a high aspect ratio configuration just as it does with a low aspect ratio wing? Yes.

These technologies address different drag contributions (trim vs. lift induced), hence one is not a replacement for the other and they can be combined for added effect.

Can the VG wing be swept aft for low aspect ratio to match supersonic wave drag characteristics of the fixed wing? Yes.

So if you require excellent subsonic loiter while simultaneously needing a Mach 2+ dash capability, VG wings (plus relaxed stability, but in the 21st century that should really go without saying) are best. That the J-20 (and most other fighters) doesn't have subsonic endurance requirements this exacting is a moot point.

All that says is that relaxed stability is good solution for decreasing trim (and enhancing endurance), thus proving my point. It does not support your view that endurance can only be achieved through variable-geometry wing.

No bias exists on my point, as the statement is about endurance achieved with variable-geometry wing can be achieved with relaxed stability; it is one versus another comparison. You are trying to attribute benefit of relaxing stability to variable-geometry wing to support your faulty assumption, and that's the real bias.

The claim was certainly not that VG wings are the ONLY way to enhance endurance - nice try. I never denied that relaxed stability works - let's not forget, though, that your original point (which I DID disagree with) was that LERX / vortex lift helped in this regard.

Nonetheless, while relaxed stability is effective, it will get you only so far alone, because it does nothing to improve the inherently poor subsonic lift induced drag of a low aspect ratio wing. As I said, VG wings solve a completely different type of drag issue - these technologies are complementary and presenting one as an alternative to the other misses the point.

Not true, as the DSI is known to have higher performance than traditional fixed inlets, and that includes better pressure recovery. A simple conic or isentropic inlet is insufficient to explain DSI.

Better than historical fixed inlets? Sure, I can believe that - why *wouldn't* a fixed inlet (DSI or conventional) designed with today's methods and tools be superior to, for example, the 1950s F-104 intake? In the context of the Su-57 we are not talking about either a historical or a fixed inlet (given the caret-style shock sweep in two planes, even the "conventional" part is arguable), however.

Let's look at that rather vague statement in more detail:

Reference [3]



Only the abstract is available, so the specifics of the competing ramp inlet are not known to me, but if the number of shocks and inlet flow turning angle are the same as for the flow field used to generate the bump, it's not surprising that the DSI would come out on top. Under these circumstances a conical flow field will have shallower shock angles, meaning lower entropy rise, meaning higher pressure recovery - that's a consequence of using conical shocks though, not some magical property of DSI.

Reference [4]



Here the bump acts as a "drop in" compression surface replacement for a second ramp, so in this instance we really are replacing a 2D wedge shock with a 3D conical equivalent (though perhaps greater turning angle to maintain shock on lip without increasing length, i.e. higher static pressure rise for same loss). Again, no magical DSI effect required to explain the observed results.

Reference [5]

Same as [4], pretty much. Since the entire paper is available you can even see it by superimposing the two inlets in figure 5:



First ramp is parallel, the bump turns the flow through a slightly steeper angle to keep total length the same, with greater pressure rise for the same length (but also higher projected frontal area). Also, the ramp inlet was not fitted with a BL bleed system, so it suffers from stronger BL growth due to the adverse pressure gradient on the compression surfaces (the bump pushes most of that BL overboard without a bleed) - figure 6 illustrates that quite clearly.

Corroborates several of my points.

Reference [6] is in Chinese with only the abstract and figure captions in English, so I can't really comment beyond saying that none of the English parts and none of the images deal with conventional intakes. As the Chinese text is unfortunately not text at all but incorporated in the pdf as an image, you can't even get a machine translation without great effort, but given the experience with the other sources, I suspect any comparison will be similarly skewed. That doesn't make it necessarily redundant or even wrong (for the JF-17 as a real-world example the choice really WAS between DSI and a fixed ramp with diverter), it just isn't very applicable to our more general discussion.

For what it's worth:



(in addition to the NASA/USAF research project I posted earlier).

All streamline tracing method does is explain how the bump is generated. Design method for the bump tells you absolutely nothing about inlet drag and pressure recovery, nevermind performance of other inlet types.

Sure it does - the subsonic drag penalty of a complex, high flow turning angle shock system is due to the increase in wetted inlet area (longer compression surfaces) - happens the same way with a DSI designed to create a complex, high turning angle shock system as the bump size increases. OTOH the supersonic drag penalty comes from increased cowl angle which is directly related to the angle which the flow is turned through by the shock system, as the cowl should meet that air at low or zero incidence. DSI is therefore not exempt from any of these effects, and this does follow from an awareness of how the design methodology works.

Cute, but it doesn't work. LEVCON is simpler than canard as there is no canard downwash to deal with.

As I said, your canard analogy is an oversimplification. And while there is no downwash to deal with, in the specific case of the Su-57 the LEVCONs, due to their location, will interact very significantly with the engine inlets - unlike canards. This adds another layer of complexity which is at least as challenging, since what ordinarily is a purely aerodynamic design task is now coupled to a new set of constraints.

DSI, as you admitted yourself "is a bit harder to do than with a traditional intake", and more complex.

Yes, with respect to handling BL diversion and ensuring it really does keep the stagnant air out of the inlet as well as a conventional diverter (in an actual aircraft installation, DSI has to deal with the BL from the entire forebody, unlike the theoretical study in Ref. [5]). So the challenge is in *not worsening* the pressure recovery theoretically achievable from the chosen shock system, not so much improving it over a conventional (fixed - let alone variable) analogue.

Don't get me wrong, DSI is an extremely elegant solution with good pressure recovery at the design point and decent off-design performance spread, while offering advantages in weight and RCS - what's not to like? As I've said several times before, I *am* in fact surprised myself that Sukhoi didn't adopt it.

However I also realize it just isn't the answer to any and every requirement that you make it out to be, and that hence different priorities might favour another type of intake.

 

[Engineer]

The key phrase is "fighter aircraft", which implies requirements to which VG wings are a poor solution due to weight penalty - doesn't mean it's not an excellent choice for other jobs with differing priorities.

The context has always been about fighter aircraft. F-14 is a fighter aircraft. Variable-geometry wing will always come with weight penality, making it a poor solution when other alternatives already exist to provide the same benefits.

Does high aspect ratio (i.e. VG wings unswept) give better induced drag than a (fixed) low aspect ratio wing? Yes.

Does relaxed stability reduce trim drag on a high aspect ratio configuration just as it does with a low aspect ratio wing? Yes.

Can the VG wing be swept aft for low aspect ratio to match supersonic wave drag characteristics of the fixed wing? Yes.

These technologies address different drag contributions (trim vs. lift induced), hence one is not a replacement for the other and they can be combined for added effect.

They can be combined but they aren't. In the real world, other solutions replaced variable-geometry wing, proving that variable-geometry wing is obsoleted.

So if you require excellent subsonic loiter while simultaneously needing a Mach 2+ dash capability, VG wings (plus relaxed stability, but in the 21st century that should really go without saying) are best. That the J-20 (and most other fighters) doesn't have subsonic endurance requirements this exacting is a moot point.

No. As I said before, no real world example of such configuration exists, hence variable geometry wing being "the best" is merely your assumption. You are assuming variable geometry wing being the best to argue that variable geometry wing is best, which is a

Please, Log in or Register to view URLs content!

.

Endurance (range) is a requirement for J-20, stated by the chief aerodynamicist of J-20 in his very own paper. In fact, endurance is a basic requirement for all aircraft. "Our aircraft stays too long in the air" — says no engineer ever! We can agree to disagree on whether J-20 has Mach 2+ dash capability, but what about Su-27?

Please, Log in or Register to view URLs content!

exceeds that of

Please, Log in or Register to view URLs content!

. What excuse are we going to hear from you next?

Please, Log in or Register to view URLs content!

The use of fixed geometry inlets over variable geometry counterparts mirrors this development.

Characters limit reached. The rest of my response will go in a different reply.

 

[Engineer]

Better than historical fixed inlets? Sure, I can believe that - why *wouldn't* a fixed inlet (DSI or conventional) designed with today's methods and tools be superior to, for example, the 1950s F-104 intake? In the context of the Su-57 we are not talking about either a historical or a fixed inlet (given the caret-style shock sweep in two planes, even the "conventional" part is arguable), however.

Nice try, but the excerpt isn't about a comparison between modern designed inlet with historical inlet, rather a comparison between DSI vis-a-vis fixed inlet.

Let's look at that rather vague statement in more detail:

Reference [3]

View attachment 45107

Only the abstract is available, so the specifics of the competing ramp inlet are not known to me, but if the number of shocks and inlet flow turning angle are the same as for the flow field used to generate the bump, it's not surprising that the DSI would come out on top. Under these circumstances a conical flow field will have shallower shock angles, meaning lower entropy rise, meaning higher pressure recovery - that's a consequence of using conical shocks though, not some magical property of DSI.

Please, Log in or Register to view URLs content!

, and no, the paper did not attribute better pressure recovery to use of conical shock. The paper actually proves my point about how conical flow theory alone is insufficient in explaining DSI. First, the paper points out elimination of diverter allows DSI to have less inlet drag. Second, the paper states cowling design affects pressure recovery, with the reason given in the abstract:

The main thing to take away is that application is different from theory.

Reference [4]

View attachment 45108

Here the bump acts as a "drop in" compression surface replacement for a second ramp, so in this instance we really are replacing a 2D wedge shock with a 3D conical equivalent (though perhaps greater turning angle to maintain shock on lip without increasing length, i.e. higher static pressure rise for same loss). Again, no magical DSI effect required to explain the observed results.

View attachment 45106

Reference 4 looks at the effects of varying bump geometries. Geometry refers to the height and length of the bump:

The paper concludes about the importance of geometry details:

It follows from this study that streamline tracing method from Lockheed Martin's patent is insufficient in providing detailed geometry of the bump.

Reference [5]

Same as [4], pretty much. Since the entire paper is available you can even see it by superimposing the two inlets in figure 5:

First ramp is parallel, the bump turns the flow through a slightly steeper angle to keep total length the same, with greater pressure rise for the same length (but also higher projected frontal area). Also, the ramp inlet was not fitted with a BL bleed system, so it suffers from stronger BL growth due to the adverse pressure gradient on the compression surfaces (the bump pushes most of that BL overboard without a bleed) - figure 6 illustrates that quite clearly.

Corroborates several of my points.

Boundary layer is thicken by generation of shockwave. This is the reason why DSI outperforms ramp inlets. Such problem exists for conic inlets as well, and the underlying principles are explained by a different theory than conical flow theory. In short, conical theory is insufficient in explaining DSI.

This also proves my earlier point about how introducing more surfaces to improve pressure recovery sounds good only on paper. While pressure recovery lost can be mitigate by bleeding out the thickened boundary layer, this is not free and introduces inlet drag. Also, the complexity and weight introduced for extra surfaces will eventually become impractical.

Reference [6] is in Chinese with only the abstract and figure captions in English, so I can't really comment beyond saying that none of the English parts and none of the images deal with conventional intakes. As the Chinese text is unfortunately not text at all but incorporated in the pdf as an image, you can't even get a machine translation without great effort, but given the experience with the other sources, I suspect any comparison will be similarly skewed. That doesn't make it necessarily redundant or even wrong (for the JF-17 as a real-world example the choice really WAS between DSI and a fixed ramp with diverter), it just isn't very applicable to our more general discussion.

For what it's worth:

View attachment 45105

(in addition to the NASA/USAF research project I posted earlier).

The keyword is potentially, such as when the various interactions among pressure gradient, shock and boundary layer are not well understood. Theory only goes so far in explaining effects of these interactions and is meaningless without empirical data. This isn't just about DSI, as the Russian also didn't go with fixed Caret inlet. The Russian clearly sticks with they know best.

Sure it does - the subsonic drag penalty of a complex, high flow turning angle shock system is due to the increase in wetted inlet area (longer compression surfaces) - happens the same way with a DSI designed to create a complex, high turning angle shock system as the bump size increases. OTOH the supersonic drag penalty comes from increased cowl angle which is directly related to the angle which the flow is turned through by the shock system, as the cowl should meet that air at low or zero incidence. DSI is therefore not exempt from any of these effects, and this does follow from an awareness of how the design methodology works.

No it doesn't. You may try to make the connections between the design methodology and various things that you read up on, but that's you. The design methodology says nothing regarding performance. As we have seen from the above sources, many effects are not explained by the design methodology.

As I said, your canard analogy is an oversimplification. And while there is no downwash to deal with, in the specific case of the Su-57 the LEVCONs, due to their location, will interact very significantly with the engine inlets - unlike canards. This adds another layer of complexity which is at least as challenging, since what ordinarily is a purely aerodynamic design task is now coupled to a new set of constraints.

Yes, with respect to handling BL diversion and ensuring it really does keep the stagnant air out of the inlet as well as a conventional diverter (in an actual aircraft installation, DSI has to deal with the BL from the entire forebody, unlike the theoretical study in Ref. [5]). So the challenge is in *not worsening* the pressure recovery theoretically achievable from the chosen shock system, not so much improving it over a conventional (fixed - let alone variable) analogue.

Don't get me wrong, DSI is an extremely elegant solution with good pressure recovery at the design point and decent off-design performance spread, while offering advantages in weight and RCS - what's not to like? As I've said several times before, I *am* in fact surprised myself that Sukhoi didn't adopt it.

However I also realize it just isn't the answer to any and every requirement that you make it out to be, and that hence different priorities might favour another type of intake.

Actually, it is you who are trivilizing the problem for DSI. Every inlet design is about "not worsening the pressure recovery theoretically achievable from the chosen shock system". This isn't something that is unique for DSI.

 

[Tirdent]

The context has always been about fighter aircraft. F-14 is a fighter aircraft. Variable-geometry wing will always come with weight penality, making it a poor solution when other alternatives already exist to provide the same benefits.

The F-14 was not a typical fighter in that it had unusually demanding patrol endurance requirements and anyway, the only reason it didn't come with full relaxed stability (rather than the simplified glove vane solution it adopted) ON TOP of the VG wing is that FBW technology was not mature yet. As soon as the impact of carrying more fuel to offset the higher induced drag of a fixed low aspect ratio wing exceeds the empty weight penalty it will be worthwhile - whether that's the case or not for a specific aircraft comes down to requirements (see NATF and A/F-X).

Other solutions do not provide the same benefits - relaxed stability addresses trim drag, not induced drag.

They can be combined but they aren't.

Arguably they were - F-14 glove vanes (which was merely the nearest approach the FCS state of the art allowed at the time) as well as NATF & A/F-X.

No. As I said before, no real world example of such configuration exists, hence variable geometry wing being "the best" is merely your assumption. You are assuming variable geometry wing being the best to argue that variable geometry wing is best, which is a

Please, Log in or Register to view URLs content!

Not at all - I'm not assuming anything. I'm basing my argument on the FACT that a high aspect ratio wing provides lower induced drag in subsonic cruise.

Once more, define "best". VG wings are only "best" if your subsonic loiter requirement goes beyond that expected of a normal fighter.

Endurance (range) is a requirement for J-20, stated by the chief aerodynamicist of J-20 in his very own paper. In fact, endurance is a basic requirement for all aircraft. "Our aircraft stays too long in the air" — says no engineer ever!

No engineer ever says "XYZ is a requirement" full stop either. He'll prioritize clearly among conflicting needs and weight the importance (even if that means he gets accused of using weasel words by you...). As you say, endurance is a requirement for all aircraft to some degree, but how important is it relative to other performance aspects? There are no bonus points for insane endurance in a fighter if the measures you take to achieve it introduce prohibitive penalties on requirements that have higher priority for the aircraft's role.

BTW, the words "loiter" and "endurance" do NOT occur in the J-20 paper at all, as we've already established - it deals with subsonic L/D ratio only in the context of sustained turning (with a very passing reference to range). While relaxed stability does help in both respects, the fact that loiter/endurance wasn't chosen to illustrate the benefit indicates where the emphasis in terms of requirements is - improved endurance is a happy byproduct, not the primary objective.

Please, Log in or Register to view URLs content!

exceeds that of

Please, Log in or Register to view URLs content!

. What excuse are we going to hear from you next?

How long is a piece of string?

What is the payload? Your link says the mission for the F-14 is strike...

What is the flight profile? Your link says the F-14 missions assumes medium rather than high altitude in the target area...

What about the fact that the Su-27 has almost 30% more internal fuel capacity than the F-14?

What about the fact that the Su-27 has a significant weight advantage by not being carrier compatible?

What a useless comparison to make like that.

Let's do this properly, just to prove that you could have done better, ok?

F-14A combat range with 4 MRAAMs and no drop tanks (7350kg of fuel) is 2750km:

Please, Log in or Register to view URLs content!

(Fighter escort mission, at cruise altitude with 2min of allowance for combat @ Mach 1.0 & 3000m, 5% fuel plus 20min of reserves) -> 0.374km per kg of fuel.

Su-27 combat range with 2 SRAAM and 2 MRAAMs (9400kg of fuel) is 3530km:

Please, Log in or Register to view URLs content!

(all at cruise altitude, unknown allowance for combat or reserves but assumes missiles launched at half-way point) -> 0.376km per kg of fuel.

But we've forgotten something, the Su-27 is not navalized!

Su-33 combat range (9500kg of fuel) is 3000km:

Please, Log in or Register to view URLs content!

(load-out and flight profile not specified but probably same as Su-27) -> 0.368km per kg of fuel.

Alternatively, if we allow the F-14 to use 2x860kg drop tank fuel for a Flanker-like total of 9070kg, its combat range (based on the improvement in radius shown in the alternate loadings table) rises to about 3420km (0.377km per kg of fuel).

Still a lot of unknowns regarding the Flanker flight profiles (I suspect they might be more like the F-14's hi-hi-hi, only with 4 AAMs - in which case the Tomcat probably beats even the land-based Su-27), but the F-14A exceeds the Su-33 despite being stable and 15 years older.

The discussion is about how fixed geometry solutions made variable geometry obsolete through providing the same benefits without weight penalty.

They do NOT provide the same benefits. Relaxed stability does NOT reduce induced drag. DSI can NOT adjust to keep shock on lip at off-design Mach. They have OTHER advantages (e.g. relaxed stability: reduced trim drag; DSI: reduced RCS) that might make them more suitable to many requirements, but at the same time there remain purposes for which variable solutions remain superior.

The question is merely whether your needs warrant their use.

 

[Tirdent]

Please, Log in or Register to view URLs content!

, and no, the paper did not attribute better pressure recovery to use of conical shock. The paper actually proves my point about how conical flow theory alone is insufficient in explaining DSI.

The main thing to take away is that application is different from theory.

True, but not in the way you insinuate. Theory says pressure recovery of a DSI with one conical oblique shock should beat a ramp inlet with one planar oblique shock, and lo and behold - it does. The reason why it isn't attributed to conical shocks is because that would be trivial - what makes it worthy of a paper is that not having conventional means of handling the BL (diverter, bleed) means it is a challenge to translate that theoretical advantage into practical applications.

Conical flow alone doesn't address the BL diversion aspect of DSI, but it establishes an upper limit for the achievable pressure recovery (which was the subject).

Reference 4 looks at the effects of varying bump geometries. Geometry refers to the height and length of the bump:

The paper concludes about the importance of geometry details:

It follows from this study that streamline tracing method from Lockheed Martin's patent is insufficient in providing detailed geometry of the bump.

So?

Let's take a step back here and return to the basic arguments - we're starting to digress again by getting bogged down in too much detail.

You claim "DSI has equal or better pressure recovery than conventional fixed intakes".

I say this is both a moot point to a degree (in the context of the Su-57 we're dealing with a variable intake, after all) and too broad an argument (not all DSIs are created equal, and nor are all fixed inlets of conventional design).

The reason why I say so is that the sources you've cited to support your claim are unsuitable to prove it - the fixed inlet configurations they use for comparison with the DSI designs studied are of a nature which is at a disadvantage in theoretical pressure recovery from the outset. For the conventional counterparts to come out ahead in the more detailed analysis would therefore require the DSI to suffer larger penalties in translating the pressure recovery potential from theory into a practical design.

Since achieving acceptable BL diversion without conventional means of doing so (diverter, bleed) is a challenge, the result is indeed not a foregone conclusion, making the investigations performed sensible and pertinent. However, for them to act as proof of your point, DSI would have to be compared and found superior to a conventional fixed inlet configuration which is on par in theoretical pressure recovery potential. The results presented in the papers you've presented merely confirm the theoretical advantages over the specific conventional intakes chosen as benchmarks - they prove nothing about the universal superiority over all other fixed inlets which you keep postulating.

For the same deflection angle (ramp or cone body angle) conical shocks have shallower shock angles and better pressure recovery than oblique planar shocks - that's indisputable (in [6], using a ramp of the same angle as the DSI compression surface will actually result in a normal shock!). Another scenario relevant for practical purposes is same *shock* angle as the ramp equivalent (allows same overall compression surface length, used in references [4] & [5], possibly also [6] as far as the rather poor OCR translation indicates). This gives the same total pressure recovery as the ramp at higher static pressure rise and hence lower Mach after the normal shock, meaning a weaker terminating normal shock with better pressure recovery.

Run the numbers with the shock and cone angles at the design Mach of 1.6 quoted in [6] if you don't believe me (NASA has some nice online Java apps).

Boundary layer is thicken by generation of shockwave. This is the reason why DSI outperforms ramp inlets.

If you leave the BL bleed off the ramp inlet it'll be outperformed by DSI, sure. Not an entirely realistic scenario (nobody would implement a ramp intake without bleed unless the ramp angle is REALLY shallow), and it only adds to the choice of shock system already being an apples to oranges comparison. It's a reasonable means of demonstrating that unlike a ramp intake DSI gets away with out it, but the pressure recovery comparison is unrealistic and moot in the context of fixed intakes *in general* (as opposed to the singular case examined in these papers).

The keyword is potentially, such as when the various interactions among pressure gradient, shock and boundary layer are not well understood. Theory only goes so far in explaining effects of these interactions and is meaningless without empirical data.

It is the key word, because it indicates a recognition that not all conventional intakes are created equal (something Lockheed-Martin's publicity material in particular never really addresses). DSI pressure recovery (and even that is a bit of an oversimplification, since it can be based on different shock systems) beats some, matches others and is inferior to still others. Isn't it remarkable that you have as yet, over all these pages, not been able to provide an example which doesn't in fact fit the allegedly "meaningless" theory?

Have you notified the USAF yet that they are wasting their money because DSI in fact does provide pressure recovery comparable to the best 4th generation intakes?

No it doesn't. You may try to make the connections between the design methodology and various things that you read up on, but that's you. The design methodology says nothing regarding performance. As we have seen from the above sources, many effects are not explained by the design methodology.

It doesn't explain every little effect (which are beside the point), but it establishes a pretty good picture of the technological limits in terms of pressure recovery (which IS the point). Plenty good enough to prove your sweeping generalizations on that aspect wrong.