Intake design and general stealth discussions

[vonstroem]

AIR FLYCAM, an Youtube channel.

https://www.youtube.com/c/A1RFLYCAM/videos

 

[flateric]

Don't look at other "more" stealthy airplanes up close or you'll be disappointed.

Can we leave this forum from another idiotic comparison of pre-production a/c to demo-team bird, that gives no fuck to RAM condition on certain reasons?

 

[QuadroFX]

I'm done, I feel like there is no point even getting excited about the maks 2021 airshow anymore.

510 and 01 comparison:

 

[tequilashooter]

Does RAM always have to be used or just on mission operations? I am being serious about this question. Great this even gives me more questions. As Confucius say, "The man who asks a question is a fool for a minute, the man who does not ask is a fool for life." I heard luneberg lenses are used for stealth aircrafts to hide RCS why not just use no RAM to get the same job done? Or is it because RAM coated aircrafts are still closer to the RCS figures of stealth aircrafts without them?

 

[flateric]

What did Confucius say about those who asking the same stupid questions for a decade?

 

[tequilashooter]

God bless the moderation on this thread(worth a screenshot), although I dont remember asking this question before for a decade? Got an answer?

 

[quellish]

Does RAM always have to be used or just on mission operations? I am being serious about this question. Great this even gives me more questions. As Confucius say, "The man who asks a question is a fool for a minute, the man who does not ask is a fool for life." I heard luneberg lenses are used for stealth aircrafts to hide RCS why not just use no RAM to get the same job done? Or is it because RAM coated aircrafts are still closer to the RCS figures of stealth aircrafts without them?

Shape is the dominant factor in RCS reduction. For example, an F-117 with no RAM applied and bare metal exposed will have a very low RCS. Almost as low as it would with RAM applied.

RAM can still make enough of a difference to be worth the maint. cost for operational missions, but the shape of the aircraft is what lowers the RCS to operationally significant levels.

 

[sferrin]

I'm done, I feel like there is no point even getting excited about the maks 2021 airshow anymore.

View attachment 660463

Its like that one animated clip where the F-35 pilot ejects from his seat to launch a rocket launcher at the Su-57 they might as well make an animation of the pilot grabbing the Su-57 wing with one hand and using a Philip screw driver to unscrew the wings off with the other hand. It doesn't even look like the screws are even RAM painted. Time for me to pay attention to other 5th gen projects more.

The fasteners are below the surface. Radar might not even see them.

 

[overscan (PaulMM)]

Wavelength is important to consider too. Very small surface features might not be important at operationally significant wavelengths. However surface discontinuities can be significant RCS contributors which is why its standard to align any doors with the primary alignment of wings etc. Its possible to use conductive or radar absorbing tape over the openings but that is maintenance heavy.

 

[MICAIR]

I think this great post by Stealthflanker should also be shared here
(no repost I hope, couldn't find it anywhere on this thread)

https://www.secretprojects.co.uk/threads/sukhoi-su-57-t-50-pak-fa-flight-testing-and-development-part-ii-2012-current.15626/post-455680

Su-57 intake 1 (without the patented blocker?): imgur.com/c72O4ir
Su-57 intake 2 (without the patented blocker?): s3.amazonaws.com/the-drive-staging/message-editor%2F1524527778030-su-57-fan.jpg

Su-57 radar blocker

https://twitter.com/x/status/1335604989922828290

View: https://twitter.com/RupprechtDeino/status/1335604989922828290/photo/2

 

[haavarla]

Been waiting for this.

View: https://www.youtube.com/watch?v=FhHPMfi3CII

 

[overscan (PaulMM)]

From https://pgs.aviationweek.com/awst-ebook-library

SPECIAL TOPIC - STATE OF STEALTH

http://images.link.pentonaviation.com/Web/PentonAv/%7B228918bb-c980-4679-9bc8-be8e5ed9b346%7D_State_of_Stealth_FINAL_121317.pdf

Pretty good primer on Stealth.

 

[Cannonfodder43]

Not sure if this was shared before but someone in cooperation with out fellow forum member StealthFlanker has created some nice articles regarding radar scattering simulations on some fighters. Most notably the F-35A, Su-57 and J-20.

Aircraft 101

aerodynamics , avionics , aircraft , missiles

basicsaboutaerodynamicsandavionics.wordpress.com

As always we can debate the accuracy and utility of such simulations and measurements but I see them as fairly informative. Especially given that the measurement criteria and analysis is clear and consistent with what I know and have read. Certainly the best around thus far.

 

[quellish]

This is a pretty cool paper

Odendaal, J. W., & Grygier, D. (2000). RCS measurements and results of an engine-inlet system design optimization. IEEE Antennas and Propagation Magazine, 42(6), 16–23. doi:10.1109/74.894178

https://ieeexplore.ieee.org/document/894178

 

[quellish]

Aviation Week "State of Stealth", a compilation of the "A Closer Look At Stealth" articles they published in 2016 on the website. This version was freely distributed (and is still available if you know the URL).

It has a pretty reasonable description of RAM, edge treatments, and inlet design.

 

[stealthflanker]

I wish it describe more about the material properties needed for Radar absorbers, as people do think one can simulate material with just Reflection loss.

 

[quellish]

I wish it describe more about the material properties needed for Radar absorbers, as people do think one can simulate material with just Reflection loss.

There are a number of textbooks that go into that in depth

 

[1635yankee]

Wavelength is important to consider too. Very small surface features might not be important at operationally significant wavelengths. However surface discontinuities can be significant RCS contributors which is why its standard to align any doors with the primary alignment of wings etc. Its possible to use conductive or radar absorbing tape over the openings but that is maintenance heavy.

The shaping of airframes becomes increasingly unimportant as frequencies drop; this means OTH radars, like Jindalee[1] are largely unaffected by many stealth design features.

-------------------
[1] Jindalee operates in the HF band, that is between 3 and 30 MHz, so its wavelengths are from about 10 to 100 meters.

 

[quellish]

The shaping of airframes becomes increasingly unimportant as frequencies drop; this means OTH radars, like Jindalee[1] are largely unaffected by many stealth design features.

-------------------
[1] Jindalee operates in the HF band, that is between 3 and 30 MHz, so its wavelengths are from about 10 to 100 meters.

At lower frequencies relative to the electrical size of the target the radar begins to see the volume of the object rather than object features (ie the whole thing is the scattering source rather than components)

Of course, a kill chain requires different radars at different frequencies to actually hit anything. Disrupting one or more parts of that chain increases your survivability.

 

[Scott Kenny]

Man, did this thread drift like a Ken Block video (RIP, Ken!)

Pardon me, got a lot of stuff to quote here.

This should interest both of you, though it's only supersonic, not hypersonic.

Boeing Stealth Inlet

Does someone have a copy of this file? 404 error.

But the serpentine duct with ram liner is around 60dB down from the straight metal duct without absorber
at 0 theta incidence and if you compare the bottom plot (the serpentine duct with ram lining) with the
straight metal duct without ram (the top plot) the strength of the reflection is significantly lower
across the board of theta incidence angle. There is a region at around 3 deg off nose-on incidence for
the E-field and 4 deg off for the B-field where the ram lined duct is as close as 30-35 dB as the straight
metal unlined duct, but most of the incidence angles are around 50dB down and very significant.

Wowza, though I should have expected that from multiple reflections.

In the early/mid 1990s Lockheed (now including General Dynamics) did an extensive study on intakes and found that new CFD (computational fluid dynamics) analysis could model and predict air flows with much greater precision, allowing the fixed Ferri type intake to be more efficient, to the point it could match a more traditional intake design while being 30% lighter, and with benefits in terms of stealth.

They first tested it on an F-16:

View attachment 619729

Does anyone make a conversion bit for the F16 DSI? I'd like to make a model of that...

The question then comes to, when you're running a modern stealth fighter in an arena where most competitors are running 4th generation aircraft, do you optimize for high-speed performance or do you optimize for low-speed performance? Remember, at the end of the day, the J-20 is currently slated to be equipped with only 6 missiles, two of them dogfight missiles. If you assume it'll take 2 missiles to knock down an enemy plane, would you prefer to dogfight or would you prefer BVR combat, where 5th generation aircraft excel in?

BVR, 100%. Save those two dogfight missiles for once you've cut the opposing numbers down.

The Russians are always going to say that the Su-57 is "at least F-22" level of stealth. They boast about this plane as "the best in the world" in their propaganda videos when there is plenty evidence they still committed a few stealth no-no's.

At the end of the day it comes down to their requirements which from an outsiders perspective is affordable stealth. They didn't fuss and spend millions on evey single feature of the aircraft to decease its signature. The spent the money where big gains are to be had and accepted the losses brought by other aspects. It simplifies production quite a bit if you don't facet every single joint on the airframe for example.

So yes, I have no doubt that Sukhoi met the requirements expected of them but those requirements were not "at least F-22 level" as they like to claim in the media.

This is a level I think we're going to see a lot more of in military aircraft. LO shaped but minimal RAM treatment, probably inlets, edges, and canopy. Probably have to use metal bonding or welding instead of rivets unless the discontinuities in the skin don't matter at that size.

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?!

Not if it only drops your detection range from 300nmi to 150nmi... You're still detected at any meaningful combat range. Even with most BRAAMs, if you're getting detected at 100nmi instead of 200nmi, it's no advantage. You need to be getting detected on radar at less than 50nmi, ideally less than 25nmi.

But I'll bite: what's the detection range for an F-15 from a Su27, and vice versa?

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.

Again, a halved detection range sounds great, till someone inconveniently points out that you're still detected from 100nmi away so have absolutely no surprise on the opponent.

just quoting this pic.
if stealth jets can't be detected until close range.
would this mean two stealth jets (say an Su-57 and an F-35) would both have to get up close to detect each other?
perhaps making WVR missiles more important than before?

Arguably, yes.

At least when depending solely on onboard sensors. Once you start adding offboard sensors as simple as AWACS or naval radars and some air traffic controllers your detection range under different frequencies really starts to matter.

Obviously this was a complete waste of time. The Tver RCS range in Russia uses cables to suspend models in the air from towers. Lockheed should have used espionage to discover what material these cables are made of. They must be very very special to not completely screw up measurements, especially those of low observable models. Otherwise any measurement taken there would be very suspicious, and if those measurements were used to validate an analytical model the whole model would be flawed. You might end up designing "stealth" airplanes with antlers and Happy Fun Ball!

That was the retelling of the Lockheed story when designing XSTs, how Lockheed and Northrop had to split the cost of the new pole that didn't reflect much/any energy back to the radar.

I don't think the deal is with F-35 market image since any countries that has F-35 and any radar will be able to test to see if its RCS is as advertised.
The deal with S-400 is different in the sense that country with both S-400 and F-35 can improve the S-400 by adding the exact signature characteristic (like exact scattering pattern) into S-400 library, which mean it easier to distingush F-35 from decoys, reduce false alarm, also they can test to see at exactly how far they can detect the aircraft, which is vital information as well. Then there is also aspect of its EW and radar system that can be exploited. A country like Turkey wouldn't mind selling all these information to Russia in exchange for additional technology transfer. Buying S-400 can be seem as a step toward Russia side.

Exactly.

But you can't have F-35 if you're not completely loyal to US. That's why Turkey or India will never get F-35, they didn't obey to US taboo on S-400. At the same time those who loyal and got F-35 will never tell something that contradicts to US advertising...because they don't want to make US sad and become another one Turkey.

This is a classic conspiracy of silence.

You mean like South Korea? Which is designing its own fighter that will be a competitor to the F-35? And is probably better in terms of pure air patrolling?

If the RCS is so small as they say, then the F-35 becomes simply "imbalance" and the air defense is useless. And with the mass production of the F-35, conflicts are inevitable in the near future. But air defense systems are being bought. Not stupid China, India, Iran, etc. Why are they spending huge amounts of money (Turkey - $ 2.5 billion) on useless air defense systems?

Because everyone, even the US, has hundreds to thousands of the 4thgen fighters that are quite vulnerable to things like S400s?

So how about some practical example ?

So this is a plot i made using my aircraft model.

View attachment 649395View attachment 649394

*eyetwitch*

Can you set that monostatic angle into 45/90/135/180etc? The 50/100 is giving me a headache trying to parse it...

I'm done, I feel like there is no point even getting excited about the maks 2021 airshow anymore.

View attachment 660463

Its like that one animated clip where the F-35 pilot ejects from his seat to launch a rocket launcher at the Su-57 they might as well make an animation of the pilot grabbing the Su-57 wing with one hand and using a Philip screw driver to unscrew the wings off with the other hand. It doesn't even look like the screws are even RAM painted. Time for me to pay attention to other 5th gen projects more.

Funny, that tells me a lot more. Deep countersinks in the skin, so it's likely composite with a healthy layer of RAM on top or baked in. I've seen 1cm-3cm thicknesses claimed for RAM types in this very thread, so that's simple enough. Those countersinks are also deep enough to allow for RAM putty to be added once the plane is out of primary flight testing and they're starting to work on things like weapons integration and defensive systems.

Ah so one of the ones that Russia said leave the stealthing out to save costs cause we want to see if it can even fly and drop weapons.

Eyeah figures.

Exactly. Don't waste the money on things you don't need at this stage in the process.