Intake design and general stealth discussions

[Ronny]

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.

You know, I have the English version of the book where that chart came from.
Firstly, as they admitted themselves, they use a perfectly conducting surface for their F-16 model while the real F-16 receive RAM and golden canopy from Have glass program
Secondly, judge by the number of parts in their model, they only make a very rough model of the F-16, that is hardly accurate
Thirdly, while their model suggest an F-16 with very high direct frontal RCS, when we go slightly off side between 15-65 degrees off side, the RCS value went below 1 m2 and even reach 0.1 m2 at some point. That pretty good for a perfectly conducting model.


I have also seen computer simulated radar scattering chart of stealth aircraft with very low value as well

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.

I didn't say they don't know how to make the chart correctly but there are things that will be impossible for them to model because they can't acquire the data to model them. For example: they can't know the absorbing capability of the RAM used on F-22 and F-35, and they can't know the exact inner radar absorbing structure without acquire the aircraft themselves. That why these radar scattering charts almost always assume a perfect conducting metal model. So if you see -10 dBsm or -20 dBsm on the chart, then the actual aircraft will have RCS less than that, but you can't know by how much
For your information, of the two radar scattering chart I posted, the F-35 chart came from Nanjing university of aeronautics and astronautics and the F-117 charts came from Deutsche Bremen anechoic chamber, it isn't a simulation but measurement of a metal F-117 model.
And I'm not saying that you can't put an arbitrary absorbing value on the aircraft skin, I am saying that it won't be correct.

​

 

[Scar]

judge by the number of parts in their model, they only make a very rough model of the F-16, that is hardly accurate

Ok, show me an accurate one. Coz i still don't understand where this 1sqm has came from and what does it mean, exactly.

 

[Cool ice]

{PS: i forgot to mention , if the thread continues on with the ''your source is wrong and the russians are lying because me and my eyeballs dont feel like it then i'm not continuing to take part in this discussion.This is just a message to any anonymous reader reading this thread to inform himself about the su-57 , not continuing to argue is not out of shortage of evidence , but because i dislike discussions where im bringing evidence and the other part uses guess work and fortune telling (which actually forms the basis of all su57 stealth criticisms).}


as i was thinking in not taking part of this discussion due to my absolute distaste for conversations in which gut feelings , personal guesses , and fortune telling based on pictures is put in the same regard and importance as actual legitimate sources , and official statements from the companies specialised in the matter (those , in return , get dismissed by more gut feelings and guesses that they are all conspiring and lying) , @1635yankee came in and injected a healthy dose of common sense , saying that no one has enough data to claim any thing about who is stealthier than who .

lets get to it ,

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.

a reduction of 10-15 sqm to 0.4 implies about twice less detection range. Very significant. Furthermore , 0.4 sqm stated by davydenko is an overall value , meaning that the actual RCS from the front is going to be significantly lower.

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!

Nno one said they are rounding up literally very angle. It can be perfectly reasonable that they are avoiding the two extremes , neither using an uselessly narrow , front only , one angle only perspective in which the rcs is obviously going to be pea sized , and not using literally every angle because the summation of deflected energy will then just add up. Think of it as aircraft weight , no one sees empty weight as a combat practical metric , and no one sees absolute max take off weight as an actually combat relevant metric , since aircraft burn fuel on their way , may drop their tanks , may have used their BVR missiles before dogfighting ...

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.

which is exactly what is done in the Su-57's design , and that is not my guess, the patent literally says so :

"........The shape of the theoretical contours and the layout diagram of the airframe made it possible to reduce the amount of energy of reflected EM waves in individual foreshortenings due to the redistribution of the maxima of the backscatter diagram to the minimum number of directions and to the least dangerous sectors......"

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.

frontal RCS is very important however beginning in equal hights is rather questionable. Even a slight difference in height can impact the angle of irradiation , and reveal things that are not revealed when looking directly from the front.Then thres the fact that certain aircraft can fly higher than others, and will not hesitate using that to their advantage , as the lesser drag associated with flying higher is attractive in terms of missile kinematics. The argument then may arise , you see an aircraft from above, then it sees you from below , also revealing details , but that just further bolseters my argument : a purely frontal value is very very unuseful. Lockheed , by ''giving away'' that its airplanes are pea size in RCS from the front , essencially gave nothing away.

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.

0.4 for su 57 is average , encompassing reasonable angles , 0.4 (or anything similar) for 4th gens is frontal. therefore , their average RCS will skyrocket if we put them in the same context.

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

Do you have a dental plan?

we've got you covered.

Firstly, the F-35 is certainly stealthier than the F-117 simply because the computer used to design the 117 filled the basement of an entire building and it still could not process radar returns of triangles smaller than what are visible on the aircraft. In both cases the same effort was put into construction (Sukhoi certainly stepped up their effort in fit and finish as both I and others have mentioned). The F-35 is simply billions of infinitely small triangles coupled together to form a round shape - such is the power of modern computers.

Let me quote myself :

" *the logic that states that the su57 is inferior in stealth to things like F-22 / 35 also implies that the F-35 is less stealthy than the F-117. The F35 has many rounded up shapes , such as the back of the engine , the massive cylinder where the gun lays, the countless lumps and bumps on its underside , by any means , the extremely faceted F-117 should be stealthier , but the F-35 actually is stealthier than it* "

therefore your statement goes to my advantage. I never claimed the F-35 is less stealthy , i claimed that the F-35 , by the logic used to bash on the Su-57 , would be less stealthy than the F-117 , due to looking more bubbly and less faceted ,that logic being guessing via photographs , and ignoring the fact that companies , with their hundereds of engineers and technicians will obviously find solutions to deal with RCS related issues , especially as technology advances. So why is it that the only plane receiving the photograph RCS treatment?

Secondly, the only source of aircraft specifications I trust less than propaganda outlets are manufacturers specifications they release publicly. Why would they smear their own product compared to its competitors in a public arena? The only reliable source would be an independent country evaluating say Su-57 and F-35 for acquisition. The bids handed to that selection committee will be the most accurate and they are also not public knowledge hence we can only speculate.

not trusting public manufacturer figures means not trusting the 0.0001 sqm claim from lockheed , the 157 kn engine power of the Su-57 , and so much more.
Publicly released figures may only be inaccurate in terms of being understatements of what the product can really do , as for inflations then its extremely inconceivable , how will sukhoi deal with customers finding out , in inevitable tests , that they lied about the RCS? what scandal will this cause? How will they deal with the MoD finding out that as well??
Also , the very statement that ''the only reliable source would be an independent country evaluating say Su-57 and F-35 for acquisition. The bids handed to that selection committee will be the most accurate" kills the ''su_57 is inferior based on this photograph" argument.

Thirdly, if Sukhoi managed to find such simple solutions to RCS issues using only coatings why didn't LM pick them up on F-35

No one said the su57 only uses coatings , its always a blend of coatings and shape. the Su-57 is very extensive in terms of using shape to reduce RCS , And how are you assuming that lockheed will directly pick up on literally any novelty coming into place? where is the study that takes into account the possible cost reduction of using less sawtoothed panels (if there is any , that also needs a study to prove) vs the cost increase related to changing the production line to adapt it to the new panels , and the modifications associated with t ?and is it worth it? where's the study?
also , since the patent , the official patent , the scientists involved into making the plane confirm that the sealant eliminates the parasitic reflections , why is this even put to question to begin with ?

Also , the point inversely works on the su-57 too , if the electrical conductive coating does a lousy job on the panels , why would they not pick on that and use sawtoothed panels more ? they did it for the landing gear ,weapon bays antenna fairings , what would prevent them from using that more ? thers literally a patent above saying they would eliminate all inhomogenities and focus energy to specfic sectors , if that is to be ruined , why didnt they do it ? or is it that hundereds of hours in anaechoec chambers will fail to notice that?

and why are the Chinese putting such effort into "Western" style details like faceted covers instead of just coating round shapes for optical sensors etc?

there is no western stealth and russian stealth. Stealth is stealth and it is up to the company and its sub contractors to see what fit them the most as long as they meet the objective , the principles considered by the russians are literally the same as the western side ,
i quote :
"
RCS of an aircraft consists of RCS of the following components: airframe; power plant; optical and antenna systems of the onboard equipment complex; suspended and retractable in-flight equipment.

The RCS of the airframe and the power plant is determined by three factors:

- the shape of the theoretical contours and the layout of the airframe, including the air intake and air duct;

- the design of the airframe assemblies, technological and operational joints of the skins, flaps, hatches and joints between the movable and fixed parts of the airframe;

- the use of radio-absorbing and shielding materials and coatings."

which is , by the one and only official source , at least F-22 level of stealth , an official statement , and sourced statements are not weighed the same as personal guesses.
now, the reverse argument , why is BAE systems envisaging a stealth aircraft with a round IRST , and doing what is considered by your logic , russian stealth ?


and even without the TAI-TFX argument , when was being copied a serious metric to determine who is right and wrong ?
no one has copied the kamov Ka-52 into making jettisoned rotor blades supporting the only combat helicopter ejection system on the planet , but it sure is the best solution out there.

instead of just coating round shapes for optical sensors etc? Like with nearly all LO details it is the combination of coatings and shape that give the end result. Ben Rich stated 60% air frame and 40% coatings for LO on the 117. The ratio undoubtedly has changed by today with advances in both RCS design and coatings but certainly not fully to either direction or we would see multiple solutions converging to simply using coatings and sealants. Instead we still see effort being put into both shape and coatings. If anything the big advance would have been in air frame design being able to calculate RCS for ever more complex objects instead of just for faceted objects.

regarding the IRST's on the Su-57 , all three of them , do you think the russians are oblivious to faceted IRST's ?
they are not :

then did they ruin themselves on purpose then ? obiviously not the patent describes focusing radiation is specefied sectors and making the RCS homogenous, if they are going to such lengths as eleminating the imperfections of the surface , and faceting small minute details as this :

then this a=can only mean there's a very good reason why the *optical* bulbs are round. And no this is not a compromise , not only due to the fact that it is ridiculously cost inefficient to spend millions on fine tuning every shape of the aircraft , its surface , its flaps and stabs , its weapon bay doors , the entire concept of weapon bays , advanced RAM and coating for the canopy , only to have all this ruined by two or three details. but also because , and i will repeat this point for as much as needed , the offical patent states that they aim at dircting radiation to specefic sectors while eleminating parasitic reflections , if there was no good engineering solution to reap the benefits of the superior round shape (superior for the performance of the optic) while keeping it stealthy , they wouldve easily faceted the optical panels like they, they are no strangers to it , and its actually *easier* considering how oval synthetic saphire is harder to make that tradition facets.

now to entirely put the nail in the coffin and make the IRST arguement even more dead than the air dut argument , have a look at the documentary :

View: https://www.youtube.com/watch?v=aDXNDA5xuS4

go to the part when they talk about placing every part of the aircraft to be testted in the anaechoic chamber , this part :

at 13:55 , they say that the tests show them exactly how much RAM needs to be added to the different parts , and how much isnt, now considering how the entire nose section , if we exclude the IRST , is faceted, and that the official patent above says that they want an uniform distribution of RCS , and to focus it on less dangerous , narrow sectors , how are they even bothering fine tuning the very thickness of RAM needed to the structure , if the elephant in the room , that massive orange sticking out of the cockpit , is there to ruin everything?

it is obvious that theres a solution , and the fact that we dont know it doesnt mean it doesnt exist , or else all of what is claimed in the documentary , the patent , and the interview, all of them being official sources , would just go down the drain. And its going down the drain through personal guesses and photographs , not even independant , third party testing in a bid or something.
the only unofficial thing is when a journalist adds a little spice and starts saying that the su-57 is great and lockheed is bad but i am not taking any claim like that as a source.

. Instead we still see effort being put into both shape and coatings.

Su-57 is no exception

These are the details pointing to Sukhoi being willing to accept less "stealth" which means their requirements were not "F-22 levels". Perhaps we could see changes when Su-57M with the new engines start production in a similar way to how the Chinese continually iterate their J-20.

there is no legit evidence pointing at that , if anything , again , we can only guess when there is no statement about what kind of stealth requirment is being presented, if an official source comes in and clarifies thatn then there is no place for guessing.

 

[Cool ice]

Su-57 doesn't use S-duct to hide the blade

it does

by the way , the argument literally ends here , no guess will ever be relevant infront of a legitimate source.

at best you can call it a extremely slightly curved duct, but the curve is negligible, the front part that might be mistaken with the curve is the inlet ramp used for pressure recovery, technically speaking, it can be used as a form of blocker to reduce the amount of radar wave hitting the turbine blade, but it isn't as good as an S-duct because the ramp is a discontinuity so there are some surface wave traveling back when they hit the gap

if it was negligable then the source i have gave , an official one , that is , would have never took it as a serious or significant constructive measure , i quote :
"...
of the engine, from the elements of which electromagnetic (EM) waves of the irradiating radar are mainly reflected, which makes up a significant proportion (up to 60%) in the EPR of the airframe-engine system in the teaching staff. The application of RSP on the walls of the air intake channel (VZ) allows to reduce the magnitude of EM signals reflected from the VNA and re-reflected to the channel walls, thereby the overall level of EPR of the inlet in the PTS decreases......."

it is *extremely* inefficient to compromise on a single element that makes up to 60 percent of the airframe engine combination.

a more accurate term to what are you trying to describe is less S-shaped , not ''non S shaped'. And being less S-shaped does not mean less stealthy , which i will explain after quoting your next statement , this :

While the advance on material science can help you make RAM with better absorbing capability, an S-duct is still better than a blocker from the signature perspective because it makes radar wave bounce multiple time and therefore accumulate the radar absorbing rating of the radar absorbing material (absorbing rating of 10 dB can be accumulate to 60 dB)

both use s shaped ducts with the duct of the su57 being less pronouncedly S shaped. Your argument of bouncing off the wave several times only works in conditions where the RAM on the walls is similar. If the wall is coated by superior RAM , you can get similar attention even if it bounces less , due to having a less s shaped duct. There are 10 years between the Su-57 and F-22 and no one claiming the su 57 is purely doing it just with coatings, its a combo of s ducts , RAM and blockers , if materials science advances to allow you to soften the curve , shaving off important weight, then you can go for it , as a matter of fact , this is exactly what they mention :

"...
Comprehensive implementation of the combination of the above measures provides the maximum effect on reducing the visibility with a minimum negative impact on the aerodynamic, weight, technological, operational and other characteristics of the aircraft. ...."

as long as you do not have any data on the absorbtion of each aircraft's RAM , the material behind it , and overall , an accurate test with appropriate equipment , you cannot claim the F-22 or 35 have more stealthy ducts than the su-57. Exactly like @1635yankee said. That point only stands if literally every other characteristic of the duct s the same.

A true S-duct look more like this:

it also looks like this


courtesy of yakovlev , rejected design.
and this

courtesy of sukhoi
it is not an extraordinary and unknown solution.
PS
every kilogram of weight shaved off via a less curved intake , can translate into another kilogram worth of RAM for the same weight. So again , where's the comprehensive study that encompasses all of these details , and that proves that sukhoi went the wrong way ? the only point besides that is that the requirement itself was "good enough" stealth , but i think ive said enough about explaining how this point is wrong.

unless the chamber also did a rather *massive* oopsie and
gave bad readings when specefically testing the engines and intakes to see if they check out or not.

The requirement of Su-57 isn't "at least F-22 level". What A.Davidenko said is " we have similar visual requirement" which can mean many things. For example: if the requirement is to have RCS lower than -20 dBsm and Su-57 has RCS value of -30 dBsm while F-22 has RCS value of -40 dBsm, then they both satisfy the requirement and they both have the same requirement, yet their RCS is still not the same.

that is not really true , for starters, to this point i still do not know what is so appealing in taking into account an extremely narrow aspect to base stealth upon it , the one in which lockheed states the RCS of the F-22 to be -40 decibels.
second of all , Dvidenko stated that the RCS of the F-22 had an average value of of 0.4 sqm , and then the patent states that the RCS of the Su-57 is also aimed at having an RCS within the magnitude of 0.1-1 sqm (it says within that magnitude , in other words , the 0.X figure) , no matter what would be the average RCS of the su-57 , if its in the the 0.X range , then its *extremely close* to the F-22 requirment ,which is , by their analysis , an average of 0.4 sqm , considering how very significan RCS reduction will ever result into a change in detection range , so being in the same magnitude means that their visibility requirments are very similar , *tightly similar* , not an entire order of a magnitude apart.

Source :
"....
The technical result to which the invention is directed consists in reducing the magnitude of the radar signature of the aircraft to an average value of the order of 0.1-1 m 2......"

something like "able to get within X distance from a specific radar system without being detected" then they can still have very different RCS and still the similar requirement. And to what extend can we count as similar? is the different of 5-10 dB still count as similar?

as the source above states , they were very specefic in the matter , tightly similar rcs is what is needed.

: S-duct is better for signature but take up more space and heavier, while blocker are not as good for signature but much lighter and allow a lighter aircraft and more space for fuel. But USA has many more aircraft carrier and tankers compared to Russia, so USA combat radius requirement doesn't need to be as high as Russia. In that case F-22, F-35 can scarify some fuel space for S-duct while Su-57 might opted to use a blocker because it must satisfy the range requirement as well. In the field of engineering

you never want the aircraft to have extra weight and dimensions. it can be regarded as extra range , but also , as i mentionned earlier , as extra weight that can be made into RAM weight , for much more absorbion , less space (physical surface) also equates into less RCS , especially in shallow angles.

The F-35 isn't randomly bumpier than F-117, it has the blended edges, the shape are still faceted but the edge where the facets connect are blended in a curve , it is done that way to reduce edge diffraction, which is an issue especially at low frequency. All stealth aircraft after F-117 use this sort of blended facets design so that their design can be VLO over a wider range of frequency.

But don't confuse a blended facets which make up of facets and only blended at the edge with circular or tube body, because a tube or spherical will lead to creeping wave return travel back to the source and it also have much wider specular lobes

This is the same point stated by black mamba and thus will have the same answer.
i never claimed that the F35 is less stealthy , i claimed the contrary , my point was that if we used the same RCS via a photograph argument + round shape bad logic then the F-35 would be less stealthy than the F-117 which it isnt, what solutions they used do not matter , thats not my point . Ttherefore , why is the su57 the only one getting flak based on photographs ?

and based on the photograph and guesswork logic , which i do not support ,
why are we ignoring whatever features the Su-57 has that are better for RCS reduction than its competitors ?
like the small , all moveable control surfacs ? which mean less required deflection , which in turn means less RCS?

".....
The use of an all-rotating vertical tail 4 makes it possible to reduce the total area of the AO and, as a consequence, reduce the level of the signal reflected from the AO, which, in turn, reduces the RCS in the BTS........"

why are we ignoring the fact that the Su-57 has a much thinner profile , especially the chin , as compared to the F22? (less surface is mathematically demonstrable to take part in RCS) Some targets are low RCS purely via dimensions.


why are we not taking into accouunt that the planform of the Su-57 sweeps at a steeper angle than the F-22's , so theres a wider arc before the RCS ''spike'' appears?



by that i mean the massive jump that inevitably comes in once we get more and more into being perpendicular with the planform alignment , the sweep of 48 degrees of the su 57 makes it so that the opposing aircraft need to be more widely spaced to exploit that

how about the fact that the SU-57 is sporting a very elaborate , 12 layer coating on its canopy ? and why are we not taking into consideration that Carbon Nano Tubes have been in the works for the Su-57 since a decade now? source :

View: https://www.youtube.com/watch?v=KvyAbM67yKI


i do not support photograph guesses but if you are about to do it then how are you factoring everything in ?

the Su-57 being ''unstealthy'' argument never had any back bone , guesses are not backbone , and was never legitimate from the start , where flight testing prototypes were being targeted for stealth criticism , all the way to right now.

 

[overscan (PaulMM)]

That’s a very long winded way of saying nothing very interesting.

Using averages for RCS is a great way to make substandard stealth tech look in the same ballpark as good stealth technology. Using averages is therefore suspicious.

Allegedly India were not impressed with the RCS values of the Su-57. It does seem that the basic shape is pretty decent for front quarter stealth, spoiled by detail design. As the program nears production, many of the detail design issues are being rectified. It will not ever match F-22 in all aspect stealth though - this is the “balanced stealth” comment.

 

[Cool ice]

That’s a very long winded way of saying nothing very interesting.

Using averages for RCS is a great way to make substandard stealth tech look in the same ballpark as good stealth technology. Using averages is therefore suspicious.

Allegedly India were not impressed with the RCS values of the Su-57. It does seem that the basic shape is pretty decent for front quarter stealth, spoiled by detail design. As the program nears production, many of the detail design issues are being rectified. It will not ever match F-22 in all aspect stealth though - this is the “balanced stealth” comment.

That’s a long winded way of saying i "understood nothing"

 

[overscan (PaulMM)]

That’s a very long winded way of saying nothing very interesting.

Using averages for RCS is a great way to make substandard stealth tech look in the same ballpark as good stealth technology. Using averages is therefore suspicious.

Allegedly India were not impressed with the RCS values of the Su-57. It does seem that the basic shape is pretty decent for front quarter stealth, spoiled by detail design. As the program nears production, many of the detail design issues are being rectified. It will not ever match F-22 in all aspect stealth though - this is the “balanced stealth” comment.

That’s a long winded way of saying i "understood nothing"

I understood fine. Your arguments were not very convincing.

The US spent large amounts of money on technology underpinning stealth, through three generations. Russia can't afford this and is trying to make something broadly competitive without similar resources or depth of experience. They might make more use of sealing tape on doors only opened on the ground, but that is annoying for maintenance - its a compromise based on realistic production tolerances, not a better solution.

A good analogy is jet engines. You can understand the principles of a jet engine perfectly at an academic level, but producing a modern engine in the EJ200/F119 class without having built previous generations of engines is still hard. Ask China. You don't have the institutional knowledge born from long design experience, the materials expertise, etc.

Take the example of electronics. The USSR had some of the most talented scientists and designers in this field, but they fell down because they couldn't achieve the quality control needed, nor the vast investment needed in new manufacturing tooling and processes. Beyond a certain point, no cleverness in design could compensate for their inability to productionise VLSI ICs. Cleverness alone isn't always enough.

Russia are making rational choices on Su-57. Doesn't mean its an F-22. In some areas its better, in others, worse.

 

[quellish]

why are we ignoring the fact that the Su-57 has a much thinner profile , especially the chin , as compared to the F22? (less surface is mathematically demonstrable to take part in RCS) Some targets are low RCS purely via dimensions.

Which of these two things has the larger RCS?

 

[quellish]

I have some questions for the Experts in this thread!

When the participants in this thread are saying "X is stealthier than Y" what does "stealthy" mean here? The lowest absolute RCS for all frequencies and any angle? Is it a "how low can you go" comparison?

The F-117 and F-35 were designed for different threats. If you are looking at the absolute lowest RCS achieved at any frequency the F-117 kicks the F-35's tailpipe. That doesn't mean I would send one into downtown Pineland tomorrow.

There is a lot of mention of RAM in this thread. If you applied RAM to a flat plate or sphere, how much do you think it would reduce the RCS?

 

[Firefinder]

There is a lot of mention of RAM in this thread. If you applied RAM to a flat plate or sphere, how much do you think it would reduce the RCS?

According to the Report of the time they Try to make the U2 stealth by covering it in RAM...

Not much since that experiment was a failure...

In my own honestly self educated AMAUTER opinion I rate the current stealth fighters as such.

F22
F35
SU57
J20 (base on what I know which isn't much)
F15SE (not an active design but I felt the need to add it for completeness)
Rafale (clean)
Typhoon (clean)
All the other fighters.

Basically to me the SU57 is a stealthy design, probably not as much as the pure stealth fighters like the 22 but it on the list. Does it have bad angles for stealthing?

Yes but so does the Raptor.

It all about the compromises that SU took for the Felon base on the RuAF prioties, just like Lockheed had similar for the Raptor for the USAF prioties.

Which needs to be stress ARE FUCKING DIFFERENT. If Russia want a F22 they would have gotten a F22. They probably know more about it then we do and easily could make a very good knock off. But they didnt cause the F22 does not match up with Russian needs, hell the F35 does a better fucking job for that. And those needs are a long range multirole with solid A2A and good A2G performance on a budget compare to the Raptors Stealthy Amazing A2A with A2G being an afterthought with barely a budget worth the title.

But as an artillery radar operator as my day job, I hope I will never have to face SU57s in combat. Cause odds are very likely that SU57 has enough stealthing to get close enough to end my life. It might not be able to almost over fly a radar like a F22 can but it doesn't need to.

Just needs to get close enough to lob an weapon to my area. Which I will bet anything it can do.

But that is if radar design and tech doesn't close the gap on stealth. We can do alot more with radars todays then we could even 10 years ago thanks to computer tech blowing up. We can do tricks that 15 years ago where consider impossible without an immobile supercomputer with something the size of my laptop. Hell we can see that now.

Most of the newer ship radars has specs literaly stating it is likely to detect a stealth object at X distance. It will not surprise me if the first time stealth craft goes up against a well man modern radar system it gets tracked further then the pilot will like. Cause remember, Stealth Planes are LOW OBSERVABLE, not invisable, and radars are getting better at seeing smaller shit all the damn time.

It will be amusing in way if radar closes the gab on stealthing before it gets a chance to be used in a big way...

 

[GARGEAN]

...

TBH don't care much about other people in this thread, but you kinda dissapointed me here. From some years of looking at current and dated threads you seemed to me as quite an intelligent and calm person, who most of the times goes into proper and deeper analysis in search of understanding things. Now... Now you just hooked yourself to some absolutely memetic promotional material and blindly dismiss whatever contradicts it. "LM is good, rest is bad", "Marble ball stealth", "Subpar stealth"... You even brought "India didn't liked it"!!! One of the dumbest arguments about whole Su-57 debate which has much better place in YT comments than on this forum. And you just dismiss any attemt into looking deeper than just shallow phrases with simple "nah".
Why?..

 

[Ronny]

it does
View attachment 647544
by the way , the argument literally ends here , no guess will ever be relevant infront of a legitimate source.
if it was negligable then the source i have gave , an official one , that is , would have never took it as a serious or significant constructive measure , i quote :
"...
of the engine, from the elements of which electromagnetic (EM) waves of the irradiating radar are mainly reflected, which makes up a significant proportion (up to 60%) in the EPR of the airframe-engine system in the teaching staff. The application of RSP on the walls of the air intake channel (VZ) allows to reduce the magnitude of EM signals reflected from the VNA and re-reflected to the channel walls, thereby the overall level of EPR of the inlet in the PTS decreases......."

it is *extremely* inefficient to compromise on a single element that makes up to 60 percent of the airframe engine combination.

The duct of Su-57 is pretty much just as curvy as F-15 and F-16's inlet duct. If the duct was truly S-shaped, it wouldn't need the blocker

a more accurate term to what are you trying to describe is less S-shaped , not ''non S shaped'. And being less S-shaped does not mean less stealthy , which i will explain after quoting your next statement , this :
both use s shaped ducts with the duct of the su57 being less pronouncedly S shaped. Your argument of bouncing off the wave several times only works in conditions where the RAM on the walls is similar. If the wall is coated by superior RAM , you can get similar attention even if it bounces less , due to having a less s shaped duct. There are 10 years between the Su-57 and F-22 and no one claiming the su 57 is purely doing it just with coatings, its a combo of s ducts , RAM and blockers , if materials science advances to allow you to soften the curve , shaving off important weight, then you can go for it , as a matter of fact , this is exactly what they mention :
"...
Comprehensive implementation of the combination of the above measures provides the maximum effect on reducing the visibility with a minimum negative impact on the aerodynamic, weight, technological, operational and other characteristics of the aircraft. ...."

as long as you do not have any data on the absorbtion of each aircraft's RAM , the material behind it , and overall , an accurate test with appropriate equipment , you cannot claim the F-22 or 35 have more stealthy ducts than the su-57. Exactly like @1635yankee said. That point only stands if literally every other characteristic of the duct s the same.

Firstly, F-35 coating get applied to F-22 recently to replace its previous coating

The F-35 and F-22 Teach Each Other New Tricks | Air & Space Forces Magazine

A dozen years after the F-22’s operational debut and two years after the F-35 was declared ready for c

www.airforcemag.com

even the F-35 itself also receive new type of coating recently

New and Old F-35 Coatings Compared in Recent Photo of Two Italian Lightning II Jets

The new coating was already applied to US-built aircraft since 2017, but this seems to be the first time it’s applied to aircraft assembled

theaviationist.com

So there isn't exactly 10 years of material sciences different between them
Secondly, if the shape of your aircraft need radar absorbing material with much higher absorbing capability to perform just as good. Then by definition your aircraft has an inferior shape for stealth is it not?.
Thirdly, having RAM with much better absorbing capability to make a semi curved duct to absorb as much radar energy as a curved duct is much easier said than done, because with each bounce the absorbing power applied again. Let put it this way, for example, in the S-duct inlet of F-22/F-35 the radar wave bounce 5 times before it goes out while in the semi curve duct of Su-57 the wave only bounce 2 times, let say the absorbing rating of RAM used on F-22/35 is only 15 dB while the RAM on Su-57 is 10 times better at 25 dB. After 5 bounces the accumulate absorbing rate from the S-duct is 75 dB while the accumulate absorbing rate from the semi curved duct is only 50 dB. In short, the more bounce it is the easier it is to reduce radar reflection.

it also looks like this
View attachment 647548

courtesy of yakovlev , rejected design.
and this
View attachment 647551
courtesy of sukhoi
it is not an extraordinary and unknown solution.
PS
every kilogram of weight shaved off via a less curved intake , can translate into another kilogram worth of RAM for the same weight. So again , where's the comprehensive study that encompasses all of these details , and that proves that sukhoi went the wrong way ? the only point besides that is that the requirement itself was "good enough" stealth , but i think ive said enough about explaining how this point is wrong.

unless the chamber also did a rather *massive* oopsie and
gave bad readings when specefically testing the engines and intakes to see if they check out or not.

You get it wrong, no one say S-duct is some unknown solution or that it is so extraordinary that Sukhoi doesn't know how to do. The point is that the Russia requirement are different from USA requirement, S-duct is better for signature but take up more space and heavier, while blocker are not as good for signature but much lighter and allow a lighter aircraft and more space for fuel. But USA has many more aircraft carrier and tankers compared to Russia, so USA combat radius requirement doesn't need to be as high as Russia. In that case F-22, F-35 can scarify some fuel space for S-duct while Su-57 might opted to use a blocker because it must satisfy the range requirement as well.
For example: a movable inlet such as the one used on F-14 and F-15 can have much better pressure recovery at high Mach compared to the fixed DSI used on F-35, so why doesn't F-35 use the movable inlet for better speed?. Because it has the VLO requirement to satisfy.
Or an engine with lower bypass ratio and higher wing sweep is much better for supercruising, and they have been used on F-22, so why F-35 doesn't use the same solution? Because F-35 has others requirement that it must meet and its set of requirement is different from the F-22.
There is no solution that is best in all every single aspect. The features of an aircraft is based on its requirements

that is not really true , for starters, to this point i still do not know what is so appealing in taking into account an extremely narrow aspect to base stealth upon it , the one in which lockheed states the RCS of the F-22 to be -40 decibels.
second of all , Dvidenko stated that the RCS of the F-22 had an average value of of 0.4 sqm , and then the patent states that the RCS of the Su-57 is also aimed at having an RCS within the magnitude of 0.1-1 sqm (it says within that magnitude , in other words , the 0.X figure) , no matter what would be the average RCS of the su-57 , if its in the the 0.X range , then its *extremely close* to the F-22 requirment ,which is , by their analysis , an average of 0.4 sqm , considering how very significan RCS reduction will ever result into a change in detection range , so being in the same magnitude means that their visibility requirments are very similar , *tightly similar* , not an entire order of a magnitude apart.

Source :
"....
The technical result to which the invention is directed consists in reducing the magnitude of the radar signature of the aircraft to an average value of the order of 0.1-1 m 2......"as the source above states , they were very specefic in the matter , tightly similar rcs is what is needed.

an average doesn't tell you anything because for a stealth aircraft, the distribution of the scattering lobes is very important.
One fighter with -30 dBsm at the front and -10 dBsm at the side vs another fighter with -20 dBsm at the front and -20 dBsm at the side might have the exact same average but the way they are used will be very different.

you never want the aircraft to have extra weight and dimensions. it can be regarded as extra range , but also , as i mentionned earlier , as extra weight that can be made into RAM weight , for much more absorbion , less space (physical surface) also equates into less RCS , especially in shallow angles.

RAM are generally not as wide band width as shaping and your aircraft is lighter doesn't mean you can keep adding thicker RAM on top, there are location that you can't add very thick RAM layer, and the RAM itself also doesn't have the same structure strength as normal aircraft skin

This is the same point stated by black mamba and thus will have the same answer.
i never claimed that the F35 is less stealthy , i claimed the contrary , my point was that if we used the same RCS via a photograph argument + round shape bad logic then the F-35 would be less stealthy than the F-117 which it isnt, what solutions they used do not matter , thats not my point .

If we consider purely specular return at high frequency then F-117 likely have lower RCS than F-35. But if we take into account edge diffraction, surface scattering, creeping wave return which become more dominant at lower frequency then F-35 RCS is lower than F-117 because it got the blended edge and edge treatment.
I already told you not to confuse the blended edge with round shape
This is a missile with blended edges

This is a missile with cylinder/round shape

Why are we ignoring the fact that the Su-57 has a much thinner profile , especially the chin , as compared to the F22? (less surface is mathematically demonstrable to take part in RCS) Some targets are low RCS purely via dimensions.

Because the impact of size is negligible unless you are half the size or something like that, Su-57 is only about 5-6% thinner than F-22, while having 2 additional corner between its two nacelles

 

[1635yankee]

Regarding RAM: a major operating expense of the B-2 is maintaining the aircraft's RAM; at least in early service aircraft, RAM was badly degraded by flight in precipitation.

 

[overscan (PaulMM)]

...

TBH don't care much about other people in this thread, but you kinda dissapointed me here. From some years of looking at current and dated threads you seemed to me as quite an intelligent and calm person, who most of the times goes into proper and deeper analysis in search of understanding things. Now... Now you just hooked yourself to some absolutely memetic promotional material and blindly dismiss whatever contradicts it. "LM is good, rest is bad", "Marble ball stealth", "Subpar stealth"... You even brought "India didn't liked it"!!! One of the dumbest arguments about whole Su-57 debate which has much better place in YT comments than on this forum. And you just dismiss any attemt into looking deeper than just shallow phrases with simple "nah".
Why?..

I am mystified why you would come to this conclusion.

I have no particular regard for Lockheed Martin. I think F-35 was misconceived and oversold.

The logic of my position is outlined below.

1) I assume that stealth works. There is a lot of evidence that it does. Some people don't believe stealth is real. I can't help that, it's conspiracy-minded nonsense. I don't believe the US (private companies and government) would have invested untold billions in a technology that doesn't actually work.

2) It is mathematically clear that RCS must be reduced by several orders of magnitude in selected directions and frequency bands.

3) Books on stealth note that there is an element of showmanship in the Lockheed "ball bearing" analogy. The F-117A has a tiny RCS comparable to a ball bearing from certain important directions in some frequency bands, but unlike a ball bearing, it doesn't have exactly the same RCS from all directions.

4) Considering analogies with other areas of complex engineering (electronics, jet engines) I find it unlikely that Russia has been able to catch up with the US capability in this area. To say "If Russia wanted to make an F-22 they could have" is true only assuming appropriate investment in the underlying technologies over a sustained period.

5) Statements by various Russian people involved in Su-57 seem to imply less emphasis on Stealth in the design.

6) Photographs of the Su-57 continue to show features apparently at odds with F-22 levels of stealth, while certain aspects improve. The overall design appears to be akin to the early ATF concepts of front-quarter-only optimised stealth.

You can argue that stealth capabilities are too expensive, make "hangar queens" with excessive maintenance or compromise other aspects of the aircraft performance, but doubting "marble ball RCS" is basically doubting stealth exists at all.

Globally, 6th generation concepts all seem to be travelling down the stealth path to greater or lesser degrees.

 

[quellish]

if we take into account edge diffraction, surface scattering, creeping wave return which become more dominant at lower frequency then F-35 RCS is lower than F-117 because it got the blended edge and edge treatment.
I already told you not to confuse the blended edge with round shape

You have made several statements in this thread along the lines of the F-35 has a "blended edge treatment" and the F-117 does not. The F-117 does have edge "treatments". All of the US stealth aircraft do, and in fact this is the primary, and most important role for RAM.

To quote Knott, et al:

The role of radar absorbing materials on low-RCS targets that have been shaped is typically to further reduce residual scattering in the threat sector. If shaping has been applied successfully, then the remaining fuzz ball signature is due to second order mechanisms such as edge waves, physical optics sidelobe energy, cavity returns, surface discontinuities, edge returns, or avionics sensors and antennas. Radar absorbing materials are then used to further reduce these residual scattering mechanisms. For air vehicles, RAM edges are utilized. The most critical location for RAM is at the tips and along edges.

 

[overscan (PaulMM)]

...

TBH don't care much about other people in this thread, but you kinda dissapointed me here. From some years of looking at current and dated threads you seemed to me as quite an intelligent and calm person, who most of the times goes into proper and deeper analysis in search of understanding things. Now... Now you just hooked yourself to some absolutely memetic promotional material and blindly dismiss whatever contradicts it. "LM is good, rest is bad", "Marble ball stealth", "Subpar stealth"... You even brought "India didn't liked it"!!! One of the dumbest arguments about whole Su-57 debate which has much better place in YT comments than on this forum. And you just dismiss any attemt into looking deeper than just shallow phrases with simple "nah".
Why?..

I am mystified why you would come to this conclusion.

I have no particular regard for Lockheed Martin. I think F-35 was misconceived and oversold.

The logic of my position is outlined below.

1) I assume that stealth works. There is a lot of evidence that it does. Some people don't believe stealth is real. I can't help that, it's conspiracy-minded nonsense. I don't believe the US (private companies and government) would have invested untold billions in a technology that doesn't actually work.

2) It is mathematically clear that RCS must be reduced by several orders of magnitude in selected directions and frequency bands.

3) Books on stealth note that there is an element of showmanship in the Lockheed "ball bearing" analogy. The F-117A has a tiny RCS comparable to a ball bearing from certain important directions in some frequency bands, but unlike a ball bearing, it doesn't have exactly the same RCS from all directions.

4) Considering analogies with other areas of complex engineering (electronics, jet engines) I find it unlikely that Russia has been able to catch up with the US capability in this area. To say "If Russia wanted to make an F-22 they could have" is true only assuming appropriate investment in the underlying technologies over a sustained period.

5) Statements by various Russian people involved in Su-57 seem to imply less emphasis on Stealth in the design.

6) Photographs of the Su-57 continue to show features apparently at odds with F-22 levels of stealth, while certain aspects improve. The overall design appears to be akin to the early ATF concepts of front-quarter-only optimised stealth.

You can argue that stealth capabilities are too expensive, make "hangar queens" with excessive maintenance or compromise other aspects of the aircraft performance, but doubting "marble ball RCS" is basically doubting stealth exists at all.

Globally, 6th generation concepts all seem to be travelling down the stealth path to greater or lesser degrees.

if we take into account edge diffraction, surface scattering, creeping wave return which become more dominant at lower frequency then F-35 RCS is lower than F-117 because it got the blended edge and edge treatment.
I already told you not to confuse the blended edge with round shape

You have made several statements in this thread along the lines of the F-35 has a "blended edge treatment" and the F-117 does not. The F-117 does have edge "treatments". All of the US stealth aircraft do, and in fact this is the primary, and most important role for RAM.

To quote Knott, et al:

The role of radar absorbing materials on low-RCS targets that have been shaped is typically to further reduce residual scattering in the threat sector. If shaping has been applied successfully, then the remaining fuzz ball signature is due to second order mechanisms such as edge waves, physical optics sidelobe energy, cavity returns, surface discontinuities, edge returns, or avionics sensors and antennas. Radar absorbing materials are then used to further reduce these residual scattering mechanisms. For air vehicles, RAM edges are utilized. The most critical location for RAM is at the tips and along edges.

I think he’s referring to complex curvature as opposed to simple curvature.

if we take into account edge diffraction, surface scattering, creeping wave return which become more dominant at lower frequency then F-35 RCS is lower than F-117 because it got the blended edge and edge treatment.
I already told you not to confuse the blended edge with round shape

You have made several statements in this thread along the lines of the F-35 has a "blended edge treatment" and the F-117 does not. The F-117 does have edge "treatments". All of the US stealth aircraft do, and in fact this is the primary, and most important role for RAM.

To quote Knott, et al:

The role of radar absorbing materials on low-RCS targets that have been shaped is typically to further reduce residual scattering in the threat sector. If shaping has been applied successfully, then the remaining fuzz ball signature is due to second order mechanisms such as edge waves, physical optics sidelobe energy, cavity returns, surface discontinuities, edge returns, or avionics sensors and antennas. Radar absorbing materials are then used to further reduce these residual scattering mechanisms. For air vehicles, RAM edges are utilized. The most critical location for RAM is at the tips and along edges.

I think he means complex curves with wing body blending versus simple constant radius curves like cylinders.

 

[riggerrob]

How does the RCS of an F-16 change when you compare a "clean" F-16 with one carrying external fuel tanks ...... versus an Israel F-16 with fixed external fuel tanks on top of the fuselage and a square box (full of electronics) along the spine?

 

[riggerrob]

Post #18 speaking of plasma stealth ... what does a radar "see" when it looks straight up the tail pipe?
Does the hot air distort the radar return?

 

[Ronny]

You have made several statements in this thread along the lines of the F-35 has a "blended edge treatment" and the F-117 does not. The F-117 does have edge "treatments". All of the US stealth aircraft do, and in fact this is the primary, and most important role for RAM.

To quote Knott, et al:

The role of radar absorbing materials on low-RCS targets that have been shaped is typically to further reduce residual scattering in the threat sector. If shaping has been applied successfully, then the remaining fuzz ball signature is due to second order mechanisms such as edge waves, physical optics sidelobe energy, cavity returns, surface discontinuities, edge returns, or avionics sensors and antennas. Radar absorbing materials are then used to further reduce these residual scattering mechanisms. For air vehicles, RAM edges are utilized. The most critical location for RAM is at the tips and along edges.

By edges treatment, I mean this:

 

[LMFS]

1) I assume that stealth works.

Me too, but I don't think the West has any right or any merit to dictate what is wrong and what is right in that regard, because they haven't either provided proof of their RCS levels nor have they values for the PAK-FA, in other words they have nothing but claims.

I tried to keep the discussion at least minimally constructive by referring to some concrete aspects that may be technically clarified by some people here and help check whether Western claims are the ones that need to be questioned:

> Angular width of the increased RCS regions created by the planform alignment, depending of frequency and propagation issues apart from plane design
> VLO design of a radar array that needs to be transparent in X band, which is the frequency at which the enemy fighter radars operate
> Presence on the fuselage of metal elements (pitot tubes) in roughly the same size as the claimed RCS of the whole plane.

Instead of getting a sound technical explanation, we jump to talk about conspirational mindsets and lean the discussion towards blaming people for daring to raise doubts. Some other people sit on the wings and make fun of the discussion, also without providing substance. I think we can agree that the discussion will not be settled that way.

There are many comments to be made to the rest of the post but I think the most important part is whether we agree that criticising the PAK-FA stealth without solid proofs about real RCS remains in the field of opinions and not of technical discussion. I am quite ok with anyone having their opinion, but trying to pass it for established facts is what gets a reaction from many of us.

 

[icyplanetnhc (Steve)]

With regards to overscan using Lockheed's stealth designs as "references", his posts are made in response to the OP's assertion that the Su-57's stealth "at least F-22 level" solely based on the wording of the Su-57's chief engineer.

On the subject of pitot tubes, the Su-57 appears to have more of them, and they appear to be untreated (bare metal) and not shaped for LO even in the production aircraft.

 

[quellish]

So yes, the F-117 has "edge treatments". So the did the Blackbirds, and even the "dirty bird" U-2!

 

[quellish]

Instead of getting a sound technical explanation, we jump to talk about conspirational mindsets and lean the discussion towards blaming people for daring to raise doubts. Some other people sit on the wings and make fun of the discussion, also without providing substance. I think we can agree that the discussion will not be settled that way.

I can only speak for myself, but my issue here is the overwhelming sense of deja vu.
Every discussion of radar cross section on the forum turns into a thread like this (i.e. old J-20 threads, etc.). People quoting "RCS" values they found on the interwebs that have no value (what frequency? what angle?). While RCS reduction can be a complex topic the physics are straightforward. Any discussion of the physics or engineering of RCS reduction falls on deaf ears. Attempting to counter interweb "wisdom" by educating, explaining, or providing data and sources gets nowhere.

without solid proofs about real RCS remains in the field of opinions and not of technical discussion. I am quite ok with anyone having their opinion, but trying to pass it for established facts is what gets a reaction from many of us.

This is what bothers me the most. The idea that there is no "solid proof" of an object's RCS. There is nothing preventing anyone on the forum from calculating the radar cross section of an object themselves (and, in past cases, this has been done and data has been provided). A typical argument used here is that "you can't account for RAM" or "you don't know what RAM they're using" but again this is not correct. You can model RAM, you can see what effect it would have. There are limits to what RAM can do (which is well documented).

I encourage those who are interested in RCS reduction or the RCS of a particular aircraft to read some of the textbooks on the subject and get POFACETS or similar software. You will find that almost all of the "internet wisdom" on the subject is wrong.

 

[bring_it_on]

Is someone keeping tally of how many screenshots one can cram into one post? I think this thread wins that by a lot.

 

[Ronny]

. A typical argument used here is that "you can't account for RAM" or "you don't know what RAM they're using" but again this is not correct. You can model RAM, you can see what effect it would have. There are limits to what RAM can do (which is well documented).

I encourage those who are interested in RCS reduction or the RCS of a particular aircraft to read some of the textbooks on the subject and get POFACETS or similar software. You will find that almost all of the "internet wisdom" on the subject is wrong.

To be fair though, if we don't know what type of RAM they use then how to estimate the absorbing capability of that RAM when they are all different?
F-22 model scattering chart at VHF with and without coating

 

[Acatomic]

I feel this whole discussion is like trying to figure out "what the recipe of the cake is, after it's been baked". Not impossible, just very hard.

You're going about this the wrong way, you are starting at the tail instead of the head. You should first ask yourself (our find out) what are the technical requirements for Su-57? What is it's main mission/goal that it's supposed to achieve?

A little help, we know what the main goal of F-22/F-35 was/is: Achieve Air superiority while operating over enemy IADS and (for F-35) to strike hard to get ground targets in IADS.

 

[LMFS]

With regards to overscan using Lockheed's stealth designs as "references", his posts are made in response to the OP's assertion that the Su-57's stealth "at least F-22 level" solely based on the wording of the Su-57's chief engineer.

He has consistently said that the Su-57 is not on par with the F-22 in regards of RCS, that assumes LM as a valid reference. But the reality is that the RCS profiles are closely guarded secrets and only some figures with a certain level of "showmanship" (totally agree on the term) have been published.

Regarding pitot tubes, the Su-57 appears to have more of them, and they appear to be untreated (bare metal) even in the production aircraft.

Do you know what is the treatment in F-22 for instance? The information I have is they are made of metal, heated in fact, and they are necessarily a cavity oriented forwards.

If your goal is a RCS equivalent to a sphere of 1 cm diameter (the area effectlively reflecting backwards is a tiny fraction of that!), then they are already equivalent and the rest of the plane needs to have RCS like zero or less than zero. This is the kind of claim that wakes up scepticism, but maybe there is a good explanation. If Davidenko says an average RCS of 0.3 sqm, then a pitot or two is no issue. So following such statements, 4 metal pitots in the production Su-57 would not contradict the Russian designers, but if you talk about 0.0001 sqm, two forward facing pitots would.

I can only speak for myself, but my issue here is the overwhelming sense of deja vu.

I can only agree there

While RCS reduction can be a complex topic the physics are straightforward. Any discussion of the physics or engineering of RCS reduction falls on deaf ears. Attempting to counter interweb "wisdom" by educating, explaining, or providing data and sources gets nowhere.

I know more than a bit about Maxwell equations and I am therefore in fairly reasonable conditions to understand reasoning about this issue, even when I don't make myself illusions of understanding this topic as a professional. But I don't think the physics about this are trivial, in fact it took some years and some contributions that are quite recent to make stealth planes possible. I am all ears if you are willing to educate us a bit, go ahead please.

This is what bothers me the most. The idea that there is no "solid proof" of an object's RCS. There is nothing preventing anyone on the forum from calculating the radar cross section of an object themselves (and, in past cases, this has been done and data has been provided). A typical argument used here is that "you can't account for RAM" or "you don't know what RAM they're using" but again this is not correct. You can model RAM, you can see what effect it would have. There are limits to what RAM can do (which is well documented).

I don't think amateur simulation and military grade research are the same thing. There are a number of strategies that can be used to address one particular RCS issue and without knowing exactly what the approach is, you are only trying to scratch the surface. For instance, you can have RAM, or you can have setups for destructive interference at a given wavelength of interest, without knowing the depth and characteristics of the RAM you are not going to be accurate.

I encourage those who are interested in RCS reduction or the RCS of a particular aircraft to read some of the textbooks on the subject and get POFACETS or similar software. You will find that almost all of the "internet wisdom" on the subject is wrong.

This is said at the site of POFACETS (bold font added by me):

POFACETS is an implementation of the physical optics approximation for predicting the radar cross section (RCS) of complex objects. It utilizes the scientific computational features of MATLAB and its GUI functions to provide an error-free encoding of input parameters and efficient calculation of RCS. POFACETS provides a convenient tool for a “first cut” at the RCS of complex shapes by representing its constituent parts by triangular facets.
The software calculates the monostatic or bistatic RCS of the object for the parameters specified by the user, and displays plots for the model geometry and its RCS. POFACETS calculations do not include multiple reflections, shadowing, edge diffraction or surface waves.

Well, I assume such simulation is going to be reasonable to assess the basic geometry of a plane, but to analyse real world complexity, or when people are discussing abut RCS of 0.0001 sqm for a house-sized plane, this kind of simplified approach is not accurate enough. Most papers I find deal with grossly simplified models, not accurate even geometrically, without gaps, unevenness, apertures, different materials, wear etc. To a certain level is helpful and interesting, to settle our discussions would it be enough? Some of these papers remind me of a certain study that analysed the aero parameters of F-22 and Su-57 on a water "wind" tunnel, with two models that were just "roughly" similar to the planes under simulation and where AoA measurements were done without even deploying aero surfaces like LEVCONS and LE flaps properly. What is the use of such studies?

 

[Ronny]

> Presence on the fuselage of metal elements (pitot tubes) in roughly the same size as the claimed RCS of the whole plane.

Is there anything stop these tube from being coated with radar absorbing material or made from a different material instead of metal?
They seem to have a top coat at very least.

 

[Trident]

The tip is going to be bare, due to the requirement of strongly heating it against clogging by ice accumulation (difficult to see on that image, but you can just about barely discern it if you know what to look for). Note the warning stencil "Caution Hot"! However, going by a close-up photo I can't seem to find anymore the F-35 and F-22 pitots appear to be shaped for LO as far as is practical, i.e. only the very tip is cylindrical.

As for the Su-57, early prototypes up to #055 had what appeared to be Northrop-style conformal air data sensors in addition to conventional pitots (the latter probably intended as a back-up). For some reason this solution appears not to have worked out though:

View attachment 606232

 

[LMFS]

Cylindrical front oriented metal pitot tube in the F-22. Keep in mind we talk about 0.0001 sqm so this means the rest of the plane is perfectly invisible to radar, gaps all over the place notwithstanding.

 

[overscan (PaulMM)]

The pitot tube is shaped to reduce RCS but is a compromise - the original ATF proposal used a flush air data system but it was axed to save money.

 

[Ronny]

So it seem like only the very tip is uncoated, the tip is very small, not even 1/10 the size of DAS bump, probably around the size of finger tip



I can't find any close up image of the F-35, F-22 tube head on though, but looking at a normal tube, the radar reflecting part should be even smaller because it has a hole (obviously), and it also not a flat plate or a parabolic dish

 

[tequilashooter]

So does the TAI TFX have a better canopy design than the Su-57 and judging by the shape of the IRST looking bulb on the Su-57, Is the TAI TFX with its IRST bulb shape better because it has that V shape (hard to see but it appears there) with it's IRST bulb? I have heard that besides new engines its getting new missiles and avionics, so hopefully those avionics have a better shape to them if those are the particular things that are getting replaced.

 

[LMFS]

The pitot tube is shaped to reduce RCS but is a compromise - the original ATF proposal used a flush air data system but it was axed to save money.

In the F-22 at least, it is a metal tube looking forward, like any pitot tube.

To be clear: I don't think for a second the pitot tube "ruins" the stealth of the F-22, but going by the claims, the modest savings in cancelling the flush air system would have a disproportionate effect on the plane's RCS of -40 dBsm. BTW, that is exactly the level of return such elements ("weak scattering sources") have:

When the order of magnitude of its RCS value is rather big, the requirements for measurement system and measurement method are rather low, and the rather accurate results can be obtained with the normal RCS measurement method. But when the order of magnitude of the RCS value of the target to be measured is rather low, for example, measuring the target whose RCS value is -40 dBsm requires that the error is 2 dB and that the background noise level reaches -60 dBsm, the measurement environment in an anechoic chamber cannot satisfy such requirements.

Typical weak scattering source
Conformal antenna
Crevices, staircases and rivets on the surface of an airplane
Angular points of airfoils,vertical fins and even tails
Nose cone and pitot tubes

Scattering mechanism
Traveling-wave diffraction
Diffraction caused by abrupt change in electromagnetic boundary
Diffraction of angular points
Diffraction from cuspidal point

High-precision RCS measurement of aircraft’s weak scattering source

The radar cross section (RCS) of weak scattering source on the surface of an aircraft is usually less than −40dBsm. How to accurately measure the RCS …

www.sciencedirect.com

Observe that such levels of return cannot even be properly measured without special techniques (!)
Reductio ad absurdum works well with absurd claims, like the whole plane having the level of return of one among many weak scattering sources. Leave one of those out and you "ruin" the whole plane (!)

So it seem like only the very tip is uncoated, the tip is very small, not even 1/10 the size of DAS bump, probably around the size of finger tip

Yeah but do you realize the size of the "metal marble" that creates a 0.0001 sqm return? It is a ball 1.13 cm in diameter, smaller than a finger tip. How big is the surface on such a ball, that will reflect the beam exactly backwards towards the source? It is a tiny fraction of that. Plus the pitot is an ideal source of edge diffraction unlike the ball. Now multiply that 2,000 times and you have a radar array. Now consider the 20 m long plane attached to it...

I can't find any close up image of the F-35, F-22 tube head on though, but looking at a normal tube, the radar reflecting part should be even smaller because it has a hole (obviously), and it also not a flat plate or a parabolic dish

See above about the scattering mechanisms and the level of return of a pitot tube.

 

[overscan (PaulMM)]

The pitot tube is shaped to reduce RCS but is a compromise - the original ATF proposal used a flush air data system but it was axed to save money.

In the F-22 at least, it is a metal tube looking forward, like any pitot tube.

To be clear: I don't think for a second the pitot tube "ruins" the stealth of the F-22, but going by the claims, the modest savings in cancelling the flush air system would have a disproportionate effect on the plane's RCS of -40 dBsm. BTW, that is exactly the level of return such elements ("weak scattering sources") have:

When the order of magnitude of its RCS value is rather big, the requirements for measurement system and measurement method are rather low, and the rather accurate results can be obtained with the normal RCS measurement method. But when the order of magnitude of the RCS value of the target to be measured is rather low, for example, measuring the target whose RCS value is -40 dBsm requires that the error is 2 dB and that the background noise level reaches -60 dBsm, the measurement environment in an anechoic chamber cannot satisfy such requirements.

Typical weak scattering source
Conformal antenna
Crevices, staircases and rivets on the surface of an airplane
Angular points of airfoils,vertical fins and even tails
Nose cone and pitot tubes

Scattering mechanism
Traveling-wave diffraction
Diffraction caused by abrupt change in electromagnetic boundary
Diffraction of angular points
Diffraction from cuspidal point

High-precision RCS measurement of aircraft’s weak scattering source

The radar cross section (RCS) of weak scattering source on the surface of an aircraft is usually less than −40dBsm. How to accurately measure the RCS …

www.sciencedirect.com

Observe that such levels of return cannot even be properly measured without special techniques (!)
Reductio ad absurdum works well with absurd claims, like the whole plane having the level of return of one among many weak scattering sources. Leave one of those out and you "ruin" the whole plane (!)

So it seem like only the very tip is uncoated, the tip is very small, not even 1/10 the size of DAS bump, probably around the size of finger tip

Yeah but do you realize the size of the "metal marble" that creates a 0.0001 sqm return? It is a ball 1.13 cm in diameter, smaller than a finger tip. How big is the surface on such a ball, that will reflect the beam exactly backwards towards the source? It is a tiny fraction of that. Plus the pitot is an ideal source of edge diffraction unlike the ball. Now multiply that 2,000 times and you have a radar array. Now consider the 20 m long plane attached to it...

 

[overscan (PaulMM)]

The "antenna problem" isn't really a big deal. The radome is designed as a Frequency Selective Surface, passing only the frequency range of the host aircraft radar. Therefore only your signal penetrates the radome, and other signals reflect away. There will also be RAM treatments inside and around the antenna elements, and angling the array is another simple countermeasure.

The only downside to FSS is if the enemy aircraft's radar uses the exact same frequency, it will pass through. It is possible to create a FSS which can be turned on and off by application of a voltage - this would reduce the vulnerability to only when the radar is in use.

I'll take bets the B-21 will not use an external air data system.

 

[Ronny]

Yeah but do you realize the size of the "metal marble" that creates a 0.0001 sqm return? It is a ball 1.13 cm in diameter, smaller than a finger tip. How big is the surface on such a ball, that will reflect the beam exactly backwards towards the source? It is a tiny fraction of that. Plus the pitot is an ideal source of edge diffraction unlike the ball. Now multiply that 2,000 times and you have a radar array.
See above about the scattering mechanisms and the level of return of a pitot tube.

I think the surface area of the marble that reflect radar wave straight back still bigger than the rim/edge of the pitot tube, which is already tiny.
about the radar, to add to what overscan said earlier, there are FSS made of diode with their band pass characteristic depend on whether they are on/off. You can probably stack 2 layers of FSS, the first block band apart from X-band and the second block X-band depend on whether the diode on/off then the on/off of the diode can be synchronize with your radar pulse transmission.
Like this for example:

 

[LMFS]

The "antenna problem" isn't really a big deal. The radome is designed as a Frequency Selective Surface, passing only the frequency range of the host aircraft radar. Therefore only your signal penetrates the radome, and other signals reflect away. There will also be RAM treatments inside and around the antenna elements, and angling the array is another simple countermeasure.

The only downside to FSS is if the enemy aircraft's radar uses the exact same frequency, it will pass through. It is possible to create a FSS which can be turned on and off by application of a voltage - this would reduce the vulnerability to only when the radar is in use.

I'll take bets the B-21 will not use an external air data system.

about the radar, to add to what overscan said earlier, there are FSS made of diode with their band pass characteristic depend on whether they are on/off. You can probably stack 2 layers of FSS, the first block band apart from X-band and the second block X-band depend on whether the diode on/off then the on/off of the diode can be synchronize with your radar pulse transmission.
Like this for example:

The issue is not what the B-21 will use or whether "plasma stealth" can be created inside the radome, the issue is what is done on current planes that claim surreal RCS values.

Tilting the antenna and surrounding the radar with RAM tells me they are far from getting a band-pass filter of almost infinite selectivity, what I have seen is something like this (and I am not even sure this is what F-22 or F-35 use, maybe you have references)

This is bandstop FSS:

So 10% attenuation at +/- 1 Ghz is not what I call letting pass only the "exact" frequency of the radar. Which, given the world has seen many times the array dish and antenna layout of both APG-77 and 81 is no secret to anyone either. The layout by ronny does not seem much more selective.

BTW AFSS seems far from being miraculous either:

The results show that AFSS technology can reduce the RCS of specular reflection of antenna inside the radome up to 10dB

Reconfigurable stealth radome using active frequency selective surface technology - IEEE Conference Publication

Probably the biggest part in the LO design of the radar is the optimization of the individual antenna elements to make them less conspicuous, ie. optimize their design to reduce edge diffraction.

Now you can ask yourself, if all these incredible X band RCS values were true, what is the sense of such effort and spending, when Russians are saying, openly and officially now, that they see the US stealth planes from as far as Iran with their Konteiner radar.

The more I read the clearer is to me that the discussion about the Su-57 stealth is based on unrealistic expectations and happy figures irresponsibly fed by the PR departments of Western MIC and armed forces to the public.

 

[Ronny]

I am not even sure this is what F-22 or F-35 use, maybe you have references)

From Have blue and the F-117A evolution of the "stealth fighter"

This is bandstop FSS:

So 10% attenuation at +/- 1 Ghz is not what I call letting pass only the "exact" frequency of the radar. Which, given the world has seen many times the array dish and antenna layout of both APG-77 and 81 is no secret to anyone either. The layout by ronny does not seem much more selective.

BTW AFSS seems far from being miraculous either:

The results show that AFSS technology can reduce the RCS of specular reflection of antenna inside the radome up to 10dB

Reconfigurable stealth radome using active frequency selective surface technology - IEEE Conference Publication

It all depend on which frequency selective surface you are talking about,
take this one for example: there is 10 dB attenuation at +/-1 Ghz, 10 dB is equal to 10 times reduction in signal, but even if radar wave penetrate the radome and reflected from the radar aperture underneath, the reflection will pass through the FSS radome once again and you have 20 dB reduction in signal (dB is exponential unit so 20 dB is 100 times reduction in signal power)



Or the sample of FSS that I showed earlier, when the diode is off the signal loss at 10 GHz is -30 dB ( 1000 times reduction in signal power), the signal loss at 11 GHz is 13 dB (19 times reduction in signal power), when the diode is on, the signal loss at 10 GHz is -1 dB and the signal loss at 11 GHz is -7 dB (5 times reduction in power). And you should also consider that radar wave will pass through this random twice

Now you can ask yourself, if all these incredible X band RCS values were true, what is the sense of such effort and spending, when Russians are saying, openly and officially now, that they see the US stealth planes from as far as Iran with their Konteiner radar.

Container (29B6) is a fixed and massive stationary over horizon radar, it can't be used to guide missiles to targets, it has a massive blind circular sector that is thousands km in length around it, you can't move it across the ocean or to locations half a globe away. US also has their own OTH radar such as AN/FPS-118 and AN/TPS-71 , France has NOSTRADAMUS, Australia has JORH and these radar can all see stealth aircraft (or anything really) from thousands km away, but they still have all the limitation of any OTH radars so they are kind of irrelevant to the development of stealth aircraft. Saying an OTH-B radar can detect a stealth aircraft from thousand kilometer away is the same as saying the Tsar bomb can destroy any main battle tank with a hit, ok sure, but it is irrelevant

 

[tequilashooter]

Some aviation forum users and boards get mad at the mentions of OTH radars that they bring up Naval and nuclear war related matters to take them out which of course ruins the purpose of discussing aerial combat, but there is no resolution as for stealth aircrafts to deal with HF waves in terms of stealth absorption material but maybe metamaterials might resolve it since it seems that China and Russia are making some recent headlines on those materials, or maybe using plasma that effects HF wave properties. Not many countries have them but some like Iran have developed theirs. Only news that I have heard of Konteyner is monitoring 5000 aerial targets and with doppler shifting the resolution to identify an aircraft taking off from a runway and telling the difference between a incoming cruise missile or aircraft. There are multiple Konteyner radar projects maybe you can distance them far enough for one to cover the other's blindspot or fill in ground radars to cover those spots to some degree. The only thing I see useful about them is to warn what kind of aircrafts are coming based on their altitudes, incoming speeds, etc to air defense units, along with maybe telling the air defense units ahead of time which was the original aircraft and that the additional objects coming out of one object are decoy's etc