Intake design and general stealth discussions

[Ronny]

At what aspect? At what frequency? With which emitting pattern?

Please, stop sticking to all those 0.0001m^2. You are a sane man after all! Thing has CANOPY. Huge perfect reflector visible from by far most relevant hemispheres. Yeah, metal coating, fancy material and what not, but it is NOT radar absorbant. It is a perfectly reflecting shape with quite huge forward profile and defined by basic reflection laws RCS. It alone is much bigger that all those numbers full of zeros.

technically speaking, there are transparent RAM

 

[LMFS]

The short answer is frequency selective radomes. Which are very difficult to get right.

Yes I am aware, they in the end are band pass filters with certain attenuation characteristics. For example:

Obviously they need to be transparent to X band, which is the frequency in which the radars of other fighters also work, so this "getting them right" so that the diffracted field created by 2,000 antennas is not visible outside of the radome looks tricky indeed.

The pitot tubes in both F-22 and F-35 are already similar in dimensions to the RCS given for the whole plane. I wonder why such values are not questioned but the Su-57 is.

I dont know about F-35(although im sure they do have a solution.) but the Su-57 is going to have an easy time giving the fact that it has a flat antenna tilted upwards.

I wouldnt get too carried away with the 0.0001 sqm idea , Lockheed is right about anything they specefy about their plane , but Lockheed states that as a frontal value. They never said anything regarding other angles.

Imagine any stealth airplane irradiated by enemies from above , like six different angles from the sides , possibly ground radars from below , all networked , one may understand why sukhoi likes to use more pragmatic values during their interviews. Im sure lockheed is just as knowledgable , the only entity blowing things out of proportion is the internet.

The Su-57 antenna will have the same potential issues, it is very similar to that on the APG-77 and 81 and tilted the same way, the radiating elements seem a bit different but that's it. I don't see how the diffracted backscatter from so many wedges as the radiating elements in the antenna is eliminated, that is why the values from Davydenko don't seem so crazy to me. He and Lockheed can be referring to different things when giving values.

Averaging the RCS in every possible direction isn't meaningful because the stealth aircraft RCS has large spikes in certain specific directions. Any radar energy not absorbed by RAM/RAS must reflect somewhere!

How wide are those spikes? Considering the (many) curves on planes like the F-35, the width of the illuminating beams and the effects of frequency, it seems to me they can be many tens of degrees wide, but feel free to correct me.

 

[haavarla]

If you believe the RCS requirement for F-22 was 0.3-0.4 sq m, then you may be interested in an investment opportunity in Nigeria I recently received in my email.

If you believe that RCS is a single value then then you might be interested in a post as a janitor in my recently built company over at Nigeria

Of course it’s not a single value. However stealth only works with reductions in RCS of multiple orders of magnitude. Reducing RCS from 10 sq m (F-15) to 0.4 sq m would not be tactically very significant.

Averaging the RCS in every possible direction isn't meaningful because the stealth aircraft RCS has large spikes in certain specific directions. Any radar energy not absorbed by RAM/RAS must reflect somewhere!

The art of stealth design is arranging the spikes in the least useful direction for the enemy, and also planning your flight to minimise the chance of your "spikes" pointing in tactically useful directions.

If you imagine a stealth aircraft with a large spike pointing directly down to the ground - this isn't tactically very useful to its opponent as you won't detect it until it passes directly overhead - and that assumes the radar even has a useable elevation capability of 90 degrees.

Every air-air fight is going to start at a certain geometry (roughly equal heights, heading at each other) which means frontal RCS is very important.

A frontal RCS of 0.3 to 0.4 sq m would be less ambitious than Typhoon or later model F-16/18 and result in no useful stealth capability at all.

Ehem.. Why did US reduce its RCS of F-18 intakes and HAVE BLUE on F-16's?
Ofc every reduction of RCS have its reasoning and value.
Pls stop being hyperbolic about stealth. That is what Fanboys does all the time on every Forum.

 

[kaiserd]

And evolving variations on “stealth’s not that important” becoming “stealth’s maybe important, but our stealth’s better than yours anyway, even though it might not appear to be...” also seen from predictable sections of “fanboys” on such forums.
Please bring back “plasma stealth” claims and we all can really get nostalgic....
All designs are a trade-off and only time and some actual objective information will tell where exactly that trade off for the Su-57 was made re: “stealth” aspects.
I would note that, very unlike the Cold War pattern for such programs, none of the new generation US or European fighter programs appear to be particularly flagging the Su-57 as a threat or as justification and/ or basis for these programs (re: the US programs some references made to the J-20 in the Pacific).

 

[Scar]

Reducing RCS from 10 sq m (F-15) to 0.4 sq m would not be tactically very significant.

Reducing RCS by 16 times decrease detection range by 2 times. Isn't it tactically significant when you can detect your enemy at a distance twice greater than that he detects you at?!

 

[Scar]

technically speaking, there are transparent RAM

Technically speaking, it has a horrible transmissivity and not used on the existing fighter jets.

 

[Evgeniy]

Now, if we talk really, then what one could cling to in terms of visibility in relation to the Su-57 is two KS-O balls from the bottom and top of the cockpit. Well, to the partition on the glazing.
With the air intake, I think everyone already understands everything (although this was not secretly before).
The serial view of the nozzles of the second stage, as it were, is known, it remains to wait for the sawtooth surface in the places where the nozzle itself sticks out of the airframe.

 

[Evgeniy]

The whole emotional incident in relation to the Su-57 RCS is connected with the fact that it is not matched with any specific aircraft, but with a "marble ball".
It is clear that Davidenko's figures are clearly not real either, because then he would have simply declassified the RKS PAK-FA.

 

[Ronny]

Reducing RCS from 10 sq m (F-15) to 0.4 sq m would not be tactically very significant.

Reducing RCS by 16 times decrease detection range by 2 times. Isn't it tactically significant when you can detect your enemy at a distance twice greater than that he detects you at?!

But that only applied when you compared to big fighter with already very big RCS such as F-15 and Su-35
When we take the 0.4 m2 value and compared that with fighter which has small RCS such as F-16 or F-18 at 1 m2 , then the value gain isn't very significant, only about 20% in detection range. The 0.3-0.4 m2 value is even more illogical when we take into account fighter with moderate RCS reduction such as F-18E/F. F=18E/F is said to reduce RCS an order of magnitude compared to F-18 C/D, if F-18 C/D RCS is 3 m2, that put F-18 E/F RCS at 0.3 m2. In short, F-22, F-35, Su-57, J-20 have no stealth advantage over the vanilla F-18 E/F?

 

[Ronny]

technically speaking, there are transparent RAM

Technically speaking, it has a horrible transmissivity and not used on the existing fighter jets.

I don't think canopy of stealth fighter have better transmissivity than 60-70%

 

[overscan (PaulMM)]

I'm sorry, but all these posts are just so many variants of argument from personal incredulity. "It doesn't make sense to me so it can't be true." Unless you are an RCS engineer, this isn't helpful.

Tactically meaningful stealth requires reducing RCS by a factor of 100 or 1000. No-one is going to call a 50% reduction in radar range revolutionionary.. Helpful, maybe, but no game changer.

If you don't believe achieving an RCS of say 0.01 sq m or lower in specific directions is possible, then you are simply saying "I don't believe stealth is possible".

The corollary of this is you believe multiple US corporations have committed industrial fraud on a massive scale for 30+ years and got away with it.

Whether Russia aimed to achieve "stealth" levels comparable to US aircraft is still up for discussion, but Davidenko's comment suggests not, to me. However, I'm not an RCS engineer either.

 

[GARGEAN]

F-16 or F-18 at 1 m2

o_0

 

[AGS-1787]

Well, lets just all of us pitch some money to buy one, and then we can test it to end the discussion

 

[stealthflanker]

So, what frequency we are working with ?

 

[Scar]

When we take the 0.4 m2 value and compared that with fighter which has small RCS such as F-16 or F-18 at 1 m2

No way F-16 or any other 4,5gen will have 1m2 with EFT's and missiles. Impossible.

 

[1635yankee]

If you believe the RCS requirement for F-22 was 0.3-0.4 sq m, then you may be interested in an investment opportunity in Nigeria I recently received in my email.

If you believe that RCS is a single value then then you might be interested in a post as a janitor in my recently built company over at Nigeria

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In the name of complete personal autonomy and libertarianism, self-service dental instruments will be supplied at a reasonable fee.

 

[framige]

Hi everybody,

I do not know if Su-57 is less, equally or more stealthy than F-22 and nobody knows really except its conceptors and the RuAF. However, as long back as 2009 (even before the first prototype took to the sky) at the MAKS aviasalon, M.Pogossian - at that time in charge of the project - said :
PAK-FA will incorporate many stealth features BUT NOT TO THE EXPENSE OF SPEED AND MANEUVERABILITY. In other words, the RuAF considered stealth a valuable asset but not the most important. And everyone having seen the flight demos of this plane knows that it is a very highly maneuverable machine.
So IMHO should the Su-57 turn out to be less stealthy than its US counterparts it would clearly be the result of a trade off and not to the Russians unability to build a stealth fighter.
Also keep in mind that this plane is a true multirole which the Raptor is not.

Just my little non technical pinch of salt in the debate. Sorry if it spoils...

Keep debating, it is very interesting.

 

[1635yankee]

In a more serious vein.

First, I was involved in LO analysis for the LHX project, in the early 1980s. I was not involved in F-117, B-2, A-X, F-22, or F-35 programs or their competitors, so my perspective is fairly narrow. My information is also about 35 years out of date, and any comments I make are solely based on public sources (which may include that long-term gift to foreign intelligence services, Aviation Week). Second, my LHX work was mostly on acoustic detectability, which is significant for helicopters, but completely irrelevant for high-speed aircraft.

The shape of small aircraft, like the F-117, makes very little difference to the longer-wavelength radars. A friend, who ended his USN career as a destroyer captain, said that the F-117's detectability by USN AAW radars was little different from any other current combat aircraft. This means that the B-2, despite being much larger probably has a lower RCS in some frequency ranges. Stealth is also not an invisibility cloak: many of the techniques to reduce RCS do not work against multistatic radars, exhaust streams are significantly hotter than the ambient air, and most engine combustion processes produce particulates.

As for the RCS of the Su-57 vs the F-22? Since the RCS values of both aircraft are closely guarded[1], it's not unlikely that nobody knows enough of about both aircraft to make a valid comparison.


[1] actually, the RCS of any serving US military aircraft is classified, or at least it was when I was working on LO. This meant that even an LO analysis of the T-41, essentially a Cessna 172 dressed up in USAF blue, was secret. We did a lot of analyses of the OH-57 (the same aircraft as the Bell JetRanger) and the OH-6 (same aircraft as the Hughes 500) that were classified as soon as they were run.

 

[Scar]

I don't think canopy of stealth fighter have better transmissivity than 60-70%

And i don't think you're right in your assumption. After all, studying transmissivity by photos is practically the same level of "expertise" as studying RCS.

 

[Ronny]

When we take the 0.4 m2 value and compared that with fighter which has small RCS such as F-16 or F-18 at 1 m2

No way F-16 or any other 4,5gen will have 1 m2 RCS with EFTs and missiles

I don't see why that would be impossible, air to air missiles have tiny RCS, especially one with tiny fin such as AIM-120. EFT have greater RCS values but they aren't always carried and can be dropped.
Keep in mind that stealth fighter are stealthy enough that they need to carry luneberg lens in peace time so that air traffic control can keep track of them whereas F-16 and F-18 even in clean configuration never have to carry these things.

 

[haavarla]

When we take the 0.4 m2 value and compared that with fighter which has small RCS such as F-16 or F-18 at 1 m2

No way F-16 or any other 4,5gen will have 1 m2 RCS with EFTs and missiles

I don't see why that would be impossible, air to air missiles have tiny RCS, especially one with tiny fin such as AIM-120. EFT have greater RCS values but they aren't always carried and can be dropped.
Keep in mind that stealth fighter are stealthy enough that they need to carry luneberg lens in peace time so that air traffic control can keep track of them whereas F-16 and F-18 even in clean configuration never have to carry these things.
View attachment 647436

omg...why don't Someone post that F-18 with its missile/hardpoint tilted in a akward angle, and then proclaim its a 1m2 rcs

 

[Ronny]

In a more serious vein.

First, I was involved in LO analysis for the LHX project, in the early 1980s. I was not involved in F-117, B-2, A-X, F-22, or F-35 programs or their competitors, so my perspective is fairly narrow. My information is also about 35 years out of date, and any comments I make are solely based on public sources (which may include that long-term gift to foreign intelligence services, Aviation Week). Second, my LHX work was mostly on acoustic detectability, which is significant for helicopters, but completely irrelevant for high-speed aircraft.

You talking about LHX remind me of the RHA-66 comanche. Detection range reduction over AH-64 is 80%, that equal to around 3 order of magnitude smaller RCS.
One famous story of F-117 that I have heard is when they put it outdoor on the RCS test pole, they thought they failed, turn out a little bird landed on the model and the radar picked up the bird instead of the aircraft.

The shape of small aircraft, like the F-117, makes very little difference to the longer-wavelength radars. A friend, who ended his USN career as a destroyer captain, said that the F-117's detectability by USN AAW radars was little different from any other current combat aircraft. This means that the B-2, despite being much larger probably has a lower RCS in some frequency ranges.

That partly due to F-117 smaller size but also party because it is fully faceted and lack the low frequency RCS reduction features that later generation of stealth aircraft has such as the blended edges and the trailing/leading edge treatment.

As a matter of fact, Northrop's XST (the competitor to Lockheed Martin's XST for F-117 program) actually have much lower RCS than Lockhead Martin design at low frequency, on the order of 20-30 dB (100-1000 times) even though their size are similar. Because Lockheed Martin F-117 pay no attention to low frequency

Stealth is also not an invisibility cloak: many of the techniques to reduce RCS do not work against multistatic radars, exhaust streams are significantly hotter than the ambient air, and most engine combustion processes produce particulates.

I don't think there are any multi static fire control radar yet, even now. The only multi static radar I can think of are these OTH radar, which too inaccurate to guide missile and are also a stationary station that is several km in length. Exhaust stream are hotter than ambient air but most stealth aircraft try to hide this stream from view by using engine with longer tube or serrated/square nozzle to create turbulent that mixed the stream with ambient air faster.
I don't think the unburned particles in combustion process will create much problem unless there are a massive amount of unburn particles such as in case of SR-71

 

[Scar]

I don't see why that would be impossible, air to air missiles have tiny RCS,

If their RCS wasn't a critical factor no one would hide them inside the fuselage. Even being tiny, they may produce huge parasite re-reflections, refraction and so being a "bright point".

EFT have greater RCS values but they aren't always carried and can be dropped.

Forget about the range, then. Especially on the Western fighter jets, they all relying on EFTs.

 

[Scar]

Keep in mind that stealth fighter are stealthy enough that they need to carry luneberg lens in peace time so that air traffic control can keep track of them

And?... By how much times, do you think, Luneberg lense can increase the RCS?

 

[Levsha]

I don't see why that would be impossible, air to air missiles have tiny RCS,

If their RCS wasn't a critical factor no one would hide them inside the fuselage. Even being tiny, they may produce huge parasite re-reflections, refraction and so being a "bright point".

EFT have greater RCS values but they aren't always carried and can be dropped.

Forget about the range, then. Especially on the Western fighter jets, they all relying on EFTs.

Neither the F-22, F-35, or the F-117 for that matter, rely on EFTs

That's quite a lot of aircraft.

 

[LMFS]

As for the RCS of the Su-57 vs the F-22? Since the RCS values of both aircraft are closely guarded[1], it's not unlikely that nobody knows enough of about both aircraft to make a valid comparison.

Appreciated dose of reality and common sense...

 

[Scar]

Neither the F-22, F-35, or the F-117

are 4.5gen fighter jets, which we were speaking about.

 

[1635yankee]

The Luneburg lens can be set up as retro-reflectors, sort of like a passive transponder.

 

[quellish]

I for one hope that any adversaries planning to develop stealth aircraft use this thread as a guide.

 

[Ronny]

I don't see why that would be impossible, air to air missiles have tiny RCS,

If their RCS wasn't a critical factor no one would hide them inside the fuselage. Even being tiny, they may produce huge parasite re-reflections, refraction and so being a "bright point".

If RCS of stealth fighter are actually around 0.3-0.4 m2 then the RCS of air to air won't be a critical factor. The fact that the RCS of missile is critical factor for stealth fighter indicate that their RCS values are smaller than 0.3-0.4 m2

Forget about the range, then. Especially on the Western fighter jets, they all relying on EFTs.

EFT can be ditched before going to the defensed air space. Secondly, 4 generation aggressor going without external fuel tank in Red flag exercise all the time along with the help ground ground based radar but I don't see them able to counter the 5 gen fighter

Keep in mind that stealth fighter are stealthy enough that they need to carry luneburg lens in peace time so that air traffic control can keep track of them

And?... By how much times, do you think, Luneberg lense can increase the RCS?

There are equation to calculate the exact maximum RCS of corner reflector.
L is length, λ is wavelength. Air traffic control radar operate at 2.5 GHz so λ = 0.12 m
Cross section diameter of the lens is about 20 cm at most, so L is about 10 cm = 0.1 m2
So maximum RCS at 2.5 Ghz of this luneburg lens is 0.02 m2 if it is the triangle type and 0.26 m2 if it is the hexagonal type

But that not the point, if F-22, F-35 advantage in detection range is only 20% better than a clean F-16, F-18 and equal to that of F-18E/F then they won't need to carry luneberg lens so that air traffic radar can track them

 

[Sundog]

I for one hope that any adversaries planning to develop stealth aircraft use this thread as a guide.

I was waiting to see if you were as entertained as I was, lol.

 

[Scar]

If RCS of stealth fighter are actually around 0.3-0.4 m2 then the RCS of air to air won't be a critical factor.

Wrong. Parasite re-reflections and refraction on elements of missiles, pylons and airframe are always generating huge RCS peaks, very similar to those we can see on the purposely designed corner reflectors.

 

[Scar]

EFT can be ditched before going to the defensed air space.

You say it like "defensed air space" is a relatively small area of few dozen kms, while IRL it's more like hundreds kms.

 

[Ronny]

If RCS of stealth fighter are actually around 0.3-0.4 m2 then the RCS of air to air won't be a critical factor.

Wrong. Parasite re-reflections and refraction on elements of missiles, pylons and airframe are always generating huge RCS peaks, very similar to those we can see on the purposely designed corner reflectors.

Huge compared to RCS of stealth aircraft, but not very hug compared to RCS of conventional fighter, even 6 MK-82 bombs with pylons only generate RCS above 1 m2 in very narrow direction

 

[Scar]

But that not the point, if F-22, F-35 advantage in detection range is only 20% better than a clean F-16, F-18 and equal to that of F-18E/F

Where did you get these 20% from?

they won't need to carry luneberg lens so that air traffic can track them

Who told you Luneburg lense is for air traffic?! This is a myth, coz even in Syria F-22 flew with them, knowning our Russian ELINT assets watching them. Luneburg lense prior purpose is to distort and increase the real radar signature, but this doesn't mean these lenses increase RCS by hundreds of times. The real multiplier is 10-15, in average. So if you belive in magic 0,0001sqm for F-22 and F-35, these lenses simply wouldn't help to civilian radars which has pretty crappy resolution, in comparison to military radars.

You, guys, are really overestimating stealth abilities.

 

[Ronny]

But that not the point, if F-22, F-35 advantage in detection range is only 20% better than a clean F-16, F-18 and equal to that of F-18E/F

Where did you took these 20% from?

Simple Math and radar equation, detection range is proportional to forth root of radar cross section
So if RCS of stealth fighter such as F-22, F-35, Su-57 is 0.3-0.4 m2 then they will reduce detection range by about 20% compared to F-16 and F-18 with RCS about 1 m2.
And they offer no improvement from F-18E/F which already have RCS an order of magnitude smaller than F-18C/D

Who told you Luneburg lense is for air traffic?! This is a myth, coz even in Syria F-22 flew with them, knowning our Russian ELINT assets watching them. Luneburg lense prior purpose is to distort and increase the real radar signature, but this doesn't mean these lenses increase RCS by hundreds of times. The real multiplier is 10-15, in average. So if you belive in magic 0,0001sqm for F-22 and F-35, these lenses simply wouldn't help to civilian radars which has pretty crappy resolution, in comparison to military radars.

You misunderstood how a luneburg lens work, they don't multiply the current RCS of the aircraft carrying them. If you take the luneburg lens on the F-22/F-35 and stick them on B-52, the RCS of the lens won't suddenly increase by a thousand times.
Luneburg lens are nothing more than a retro-reflectors made up of metal plate perpendicular to each others or a parabolic dish, it has a fixed RCS value. If you know the size of the len you can estimate its maximum RCS, as I already did for you above. Before you say: " how can true RCS be hidden if the RCS of the luneburg lens is a fix value?". The answer: You can only calculate the maximum RCS of the lens if you know the size, and the size of the reflecting lens can be smaller than the plastic cover outside

You, guys, are really overestimating stealth abilities .

I have seen more than a dozen radar scattering charts like that even the one measured in anechoic chamber, they all have the same problems:
1- The aircraft surface are treated as pure metal with perfect reflecting capability, RAM (radar absorbing material) and RAS (radar absorbing structure) aren't taken into account because there is no way for them to actually know the absorbing capability of the radar absorbing material and radar absorbing structure used on these fighter. This isn't a matter of taking an arbitrary absorbing value then applied to the whole radar scattering chart, because even when you used the same type of RAM on all location, the absorbing rating still isn't uniform. For example: the S-duct inlet will accumulate the absorbing capability of RAM by 5-6 times because it can make the wave bounce multiple time before reflecting back.

2- Leading edge and trailing edges treatment aren't taken into account
3- Most of them don't even model the inlet properly, this is important but also understandable because compared to the outer shape, there aren't many photo of the inlet and its exact curvature. The wave also bounce inside the inlet multiple time which is very resource consuming for a computer to simulate

 

[quellish]

I for one hope that any adversaries planning to develop stealth aircraft use this thread as a guide.

And here we go

 

[quellish]

So if RCS of stealth fighter such as F-22, F-35, Su-57 is 0.3-0.4 m2 then they will reduce detection range by about 20% compared to F-16 and F-18 with RCS about 1 m2.

Found these for you. You seemed to be missing them.

 

[Scar]

F-16 and F-18 with RCS about 1 m2

Again, what makes you think 4.5 gen fighter's real RCS is 1m2? And what does this 1m2 number exactly means? Average RCS or Peak low? In what aspect and/or sector? RCS isn't a constant number, it depends on angle and may change with every next impulse of radar, during countinuous scan.

 

[Scar]

I have seen more than a dozen radar scattering charts like that even the one measured in anechoic chamber, they all have the same problems:
1- The aircraft surface are treated as pure metal with perfect reflecting capability, RAM (radar absorbing material) and RAS (radar absorbing structure) aren't taken into account.
2- Leading edge and trailing edges treatment aren't taken into account
3- Many of them don't even model the inlet properly

I dont think guys working on one of the main Air Defense Research Institutes don't know how to make RCS chart correctly. BTW, above the F-22 RCS chart you can see a screenshot for RAM characteristics adjustment.