S-400 and F-35

Discuss the F-35 Lightning II
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outlaw162

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Unread post08 Apr 2020, 18:12

(Ancient) History Lesson:

Contrary to some of the statements in that Combat Tree thread above, F-4 WSOs did not 'guide' AIM-7s among other things.

Radar targets could be locked on to by the WSO, or by the pilot auto-acq switch on the outboard throttle. The AIM-7 CW guidance illumination requirement was the same for either type of acquisition, the difference being the pilot boresight auto-acq system was limited to 10 miles, and was switched to by the WSO when requested by the pilot, often in cases where the WSO was having some difficulty, generally during maneuvering. No tilt and gain required if the pilot could see and boresight the target, front or rear aspect, inside 10 miles on the front with closure being problematical for tuning and settling times.

With respect to BVR shots, you could not lock on to an APX return. In the F-4D, you had to have the raw analog radar return, which involved azimuth, distance AND ELEVATION to lock on to a target. The displayed APX lines gave rough azimuth and distance, so at least one knew 'something' was out there to refine the radar antenna direction to, while trying to nail the elevation. Looking down, gain was particularly critical. Tilt and gain, tilt and gain, range gate, lock, wait, wait....shoot....hope.

It was a primitive beginning, just like the AIM-7E itself, but without those small steps, no slammer. Ritchie may have been a great dogfighter also, but his real strength was his absolute knowledge and mastery of how to employ his weapons successfully, even with their somewhat severe limitations.

F-35 and slammer, who could ask for more? :D
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Unread post08 Apr 2020, 18:37

Outlaw,

Generally how far out could the F-4D APQ-109 radar see a fighter sized type target? I have a book that says the Solid State pulse F-4E radar (the APQ-120) with the smaller sized 28 inch dish was from about 25 miles and beyond. However, for a bomber sized target it was around 80nm or more (I think a 57th FIS F-4E WSO said it was approx. 80 or 90nm for a Soviet Bear).
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Unread post08 Apr 2020, 19:40

I think it was advertised as 30ish, which was optimistic from what I saw. And not PD, so it was well advised to stay low. With the APX, advertised at 60ish to get initial range and azimuth bracketed, more time to massage tilt for elevation and gain while pointing in approximately the right direction, and the APX would show all targets....but once you switched back to scan you lost that additional SA and had to pick one and go for it....if you could find a raw return again at all.

Without AWACS, I recall being very happy with the rare 20 mile contacts (actually even with AWACS), but there was a bell curve of WSO ability....with some guys I'd just be happy to have a contact at any range, but I had 20/12 eyes also. I once picked up a lizard F-5E at 13 miles looking down, really. :shock:

Without TWS capability, from 20ish miles you could afford to break lock and sample the APX maybe once if you dared before you committed. In the canned training situation, you could generally expect to find at least two (or more) in mutual support, even running on one contact out of necessity. Not good real world thinking. As I said, it was primitive.

But it sure was fun. :D

edit: BTW the modern radar capabilities of 'sorting' and cross-targeting, etc. and all these type luxuries, were just not usually available to you. You played the cards you were dealt as it were.

edit #2: The F-35 drivers will never have to deal with the 'blind' and 'clueless' concept we were familiar with.
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Unread post08 Apr 2020, 21:53

Salute!

Thanks for the great stuff, Outlaw. My feeling is that Ritchie's or Lodge's kills were due to better SA than finding and poking a bandit with the Tree gear. OTOH apparently Lodge had two HO shots/kills using it to verify ID, despite ROE a for most of the war. We had just gone back up north and needed some kills, plus we had much better GCI than in 1968.

The piece brings back good and bad for this old fart. They were both friends and classmates from the Zoo.

Image
Ritchie upper left, Gums center bottom
Steve, Gums and the two guys on far right got fighters outta UPT

Image
Gums and Steve at an airshow 25 or so years later

Bob lived down the hall in Vandenburg, so I knew him better. I went thru "pilot indoctrination training" with Steve in 1963, when I gave up summer leave for the chance to see what UPT was be like. We both got 12 rides outta the T-37 syllabus, but they wouldn't let us solo. It was obvious from the IP's talk that Steve had great hands. Ditto for Karl Richter, another classmate that I flew with in UPT the next year. No mystery that the three of us graduated very high from UPT and got front seat fighters ( the Double Ugly was just coming aboard, but UPT grads could only be "pilot systems operators" until late '67 or '68.) Bob Lodge was in the quickie Master's degree program, being brainy, so didn't go to UPT for almost a year after Steve and I. But he had good hands and got a Thud assignment.

Steve was a very good pilot, and knew the Sparrow and the Double Ugly better than most, even when he took long shots for tactical reasons. Bob Lodge was "brainy" and I think he may have been involved in in the genesis of Teaball along with Steve.

Lottsa opinions about Bob being shot down, and Steve was in the flight. Despite calls that he had a trailer, he either didn't hear or pressed on to get another kill. I could ask Steve at next reunion, but he will likely remain quiet.

The Locher rescue in the link was one of our case studies when I became a Sandy. We tries a similar rescue with the A-7 in December that year, but too close to Bullseye and we had to abandon the effort after two tries and a shot up Jolly that crash landed on a Lima Site in Laos. We then destroyed the thing ouselves to prevent the PL or Vee from getting the classified stuff.
Long link, but has many good pages about the folks we're talking about:

https://books.google.com/books?id=BxT6h ... ge&f=false

Gums sends...
Gums
Viper pilot '79
"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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Unread post08 Apr 2020, 23:07

Gums you were a handsome devil.
We love the history, please keep it up.
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spazsinbad

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Unread post08 Apr 2020, 23:09

:devil: I always imagine GUMS looks like his avatar! :doh:
A4G Skyhawk: www.faaaa.asn.au/spazsinbad-a4g/ & www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/videos?view_as=subscriber
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ricnunes

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Unread post09 Apr 2020, 13:20

spazsinbad wrote::devil: I always imagine GUMS looks like his avatar! :doh:


LoL, me too :mrgreen:

Anyway, great stories there Gums and Outlaw! Keep them coming :thumb:
“Active stealth” is what the ignorant nay sayers call ECM and pretend like it’s new.
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Unread post26 Oct 2020, 10:34

charlielima223 wrote:Its funny when Russian fanboys/trolls claim that the S-300/400 can detect the F-35 and F-22. Yet when pressed as to how their usual response comes out reading like this after awhile...

Usually it uses a different frequency bands - L-band, UHF-band, "optic"... For example, S-400 has L-band surveylance radar - 91N6. Low and middle range systems always has optic/thermo visors. All clear, it's magic only for persons who knows nothing about this complexes and physics. For L-band (15 - 30cm wavelength) radar you need to cover stealth plane comparable layer thickness of half radar wave lenght (half-legth antenna/vibrator), or such cover is uneffective. Plane form like F-117 we don't see, so much stealth it is a coverage. Stealth planes has so thick coverage? :oops:

Defence area minimum limit - 2 large complexes, normal -3 large complexes. It means that stealth will be surveylance from very different angles.

If stealth use their radar or open bays/gears off - it's not a stealth anymore, so it can't survey and attack immediatly by yourself without fired at own, and must use only full self-guided ammunitions. Or stealth will be fired on instantly.

So, what I am wondering - why nobody speacking about land decoys and jammers? Do you all really belive that air-defence complexes hasn't any protection? :D Whithout any strict aviation limits for weight, sizes, forms, energy consumption, logistics? Every SDB, or, my godness - CRUISE MISSILE - and complex takes a direct hit, of course, into complex HQ or surveylance radar? :D
Let me suggest - because you are knowning nothing about that, aren't you? :wink:
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Unread post26 Oct 2020, 11:41

hocum wrote:
charlielima223 wrote:Its funny when Russian fanboys/trolls claim that the S-300/400 can detect the F-35 and F-22. Yet when pressed as to how their usual response comes out reading like this after awhile...

Usually it uses a different frequency bands - L-band, UHF-band, "optic"... For example, S-400 has L-band surveylance radar - 91N6. Low and middle range systems always has optic/thermo visors. All clear, it's magic only for persons who knows nothing about this complexes and physics. For L-band (15 - 30cm wavelength) radar you need to cover stealth plane comparable layer thickness of half radar wave lenght (half-legth antenna/vibrator), or such cover is uneffective. Plane form like F-117 we don't see, so much stealth it is a coverage. Stealth planes has so thick coverage? :oops:

Defence area minimum limit - 2 large complexes, normal -3 large complexes. It means that stealth will be surveylance from very different angles.

If stealth use their radar or open bays/gears off - it's not a stealth anymore, so it can't survey and attack immediatly by yourself without fired at own, and must use only full self-guided ammunitions. Or stealth will be fired on instantly.

So, what I am wondering - why nobody speacking about land decoys and jammers? Do you all really belive that air-defence complexes hasn't any protection? :D Whithout any strict aviation limits for weight, sizes, forms, energy consumption, logistics? Every SDB, or, my godness - CRUISE MISSILE - and complex takes a direct hit, of course, into complex HQ or surveylance radar? :D
Let me suggest - because you are knowning nothing about that, aren't you? :wink:


Weapon bays open very few seconds, it is not enough for get firing solution on it. And after you need guide the missile very near.

You do not understand all these phases.

And of course, radar will stay ON all time....for telling to everybody, "hey i am here". :D

It is so easy destroy a stealth airplane that everybody wants one, included Rusia or China. :roll:
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Unread post26 Oct 2020, 13:07

hocum wrote:Usually it uses a different frequency bands - L-band, UHF-band, "optic"... For example, S-400 has L-band surveylance radar - 91N6. Low and middle range systems always has optic/thermo visors. All clear, it's magic only for persons who knows nothing about this complexes and physics. For L-band (15 - 30cm wavelength) radar you need to cover stealth plane comparable layer thickness of half radar wave lenght (half-legth antenna/vibrator), or such cover is uneffective. Plane form like F-117 we don't see, so much stealth it is a coverage. Stealth planes has so thick coverage? :oops:

Although that theory gets recycle and brought up every now and then, it is sadly an oversimplify and incorrect representation of fact. If only countering stealth aircraft can be that easy then no one would be researching them. The way waves interact with objects are far more complex.
Firstly, the total radar reflection of a complex body such as aircraft made from several different kinds of reflections:
Image
Specular return: this is the most significant form of reflection in optical region (when structure circumphere > 10 times wavelength) ,surface acts like a mirror for the incident radar pulse. Most of the incident radar energy is reflected according to the law of specular reflection ( the angle of reflection is equal to the angle of incidence).This kind of reflection can be reduced significantly by shaping
Traveling/Surface wave return: an incident radar wave strike on the aircraft body can generate a traveling current on surface that propagates along a path to surface boundaries such as leading edge, surface discontinuous …etc, such surface boundaries can either cause a backward traveling wave or make the wave scattered in many directions .This kind of reflection can be reduced by radar absorbing material, radar absorbing structure, reduce surface gap or edges alignment ( so that their lobes occur in low priority region )
Diffraction: wave striking a very sharp surface or edge are scattered instead of following law of spectacular reflection.
Creeping wave return: this is a form of a traveling wave that doesn’t face surface discontinuous and not reflected by obstacle when traveling along object surface ,so it is able to travel around the object and come back at the radar. Unlike normal traveling wave, creeping wave traveled along surface shadowed from incidence wave (because it has to go around the object). As a result, the amplitude of creeping wave will reduce the further it has to travel because it can’t feed energy from the incident wave in the shadow region. Creeping wave mostly traveled around a curved or circular object. So, stealth fighters and stealth cruise missiles do not use tube fuselage. Nevertheless, the creeping wave return is much weaker than the specular return.
The percentage which each type of return will contribute to the total RCS value of an object depending on which region that object located in.
A high-frequency regime (or optical region) applies when the circumference of the object is at least 10 times longer than the wavelength of the incident radar wave. In this regime, specular mechanisms dominate the radar reflection ,(the angle of reflection equals the angle of incidence), like billiard balls colliding. Reflection towards the emitting radar – is reduced by angling surfaces so that they are rarely perpendicular to radars and suppressing the reflections from re-entrant structures such as engine intakes and antenna cavities with combinations of internal shaping, radar-absorbent material (RAM) or frequency selective surfaces. In this regime, “surface wave” mechanisms are small contributors to RCS, but are still present. If the wavelength is small relative to the surface, these waves are weak and their overlap will generate maximum backscatter when the radar signal is at grazing angles. When these currents encounter discontinuities, such as the end of a surface, they abruptly change and emit “edge waves.” The waves from different edges interact constructively or destructively due to their phases. The result is that they can strengthen the reflection in the specular direction and create “sidelobes” – a fan of returns around the specular reflection which undulate rapidly and weaken as the angle deviates from the specular direction. Surface wave reflections are generally very small in the optical region.
Mie region or also known as the resonance region : applies when radar wavelength*0.1 ≤ object circumference ≤ radar wavelength*1 in this region the surface wave can also swing around a structure’s back side, becoming “creeping waves” that shed energy incrementally and contribute to backscatter when they swing back toward the threat radar. This creeping wave can interferes constructively or destructively with the specular backscatter to produce a variation in the object’s RCS. Creeping wave doesn’t follow mirror like reflection rule, thus the common angular shape of stealth aircraft doesn’t help deflect them away from the threat radar
Image
So why is stealth less effective at low frequency? As the radar wavelength of radar grows, the intensity of specular reflections is reduced but its lobes width are widened (the same phenomenon also happened to radar, if aperture size remained the same, the reduction in frequency will increase radar beamwidth). Because the specular reflection lobes are widen ,shaping become less effective because it will be harder to deflect radar wave away from the source ( it is important to note that, while this lobe widening phenomenon making shaping less effective, it also reduce the intensity of the reflection because the energy will be distributed over a wider volume )
Image
Specular reflections from flat surfaces decrease with the square of the wavelength but widen proportionally: at 1/10th the surface length(approaching Mie region) they are around 6 deg. wide.

At lower frequency, the effect of traveling wave and diffraction is also more pronoun. For flat surfaces, traveling waves grow with the square of wavelength and their angle of peak backscatter rises with the square root of wavelength: (at 1/10th the surface length, it is over 15 deg). As the power of surface wave grow, the power of creeping wave return also grow. Tip diffractions and edge waves from facets viewed diagonally also grow with the square of wavelength. The end result is that the net value of stealth aircraft’s RCS often increases in Mie region. Maximum RCS is often reached when the wavelength reaches the circumference of the structure
There is a common misconception that any low-frequency radar can render stealth aircraft useless regardless of their transmitting power or aperture size (Ex: Tikhomirov NIIP L-band transmitter on the leading edge of Flanker series are often cited by enthusiasts as a counter stealth system) , that is wrong however. While it is true that stealth aircraft will often have higher RCS in Mie region. It is important to remember that given equal radar aperture area, lower frequency radars will have much wider beam compared to high-frequency radars, thus, the concentration of energy is much lower making them more vulnerable to jamming, lower gain also result in lower accuracy. Moreover, as mentioned earlier lower frequency also resulted in wider reflection beamwidth, hence weaker reflection. As a result, most low-frequency radars have much bigger transmitting antenna compared high-mid frequency radar (to get narrow beamwidth) ,it is also the reason that fighters fire control radar still work in X-band, because a L-band, VHF band radars of similar size would be too inaccurate for any purpose others than early warning.
So, is there any way for modern stealth aircraft to reduce their return even in Mie region?. The answer is YES
To begin with, the negative effect of traveling wave and diffraction can be reduced by: aligning discontinuities to direct traveling waves towards angles of unavoidable specular return, such as the wing leading edge, thus limit their impact at other angles.
For example: serrated edges are used in places where there is current discontinuity such as weapon bay door so that traveling wave return reflected toward less important aspect
Image
Image
Another common method to reduce the effect of surface wave is designing airframe facets with non-perpendicular corners and so radars view them along their diagonals, at low angles and across from the facets’ smallest angles, limits the area of edge-wave emission. Surface wave diffraction can also be reduced by blending facets. The first stealth aircraft, the F-117, was designed with a computer program that could only predict reflections from flat surfaces, necessitating a fully faceted shape, but all later stealth aircraft such as B-2 , F-35 , F-22, X-47 use blended facets. Shapes composed of blended facets are not only more aerodynamic but also allow currents to smoothly transition at their edges, reducing surface-wave scattering. Therefore, blended bodies have the potential for a lower RCS than fully faceted structures, especially at low-frequency regime. And blending the curves around an aircraft in a precise mathematical manner can reduce RCS around the azimuth plane by an order of magnitude. The penalty is often a slight widening of the specular return at the curves, but in directions at which threat radars are less likely to be positioned. This was one of the great discoveries of the second generation of stealth technology.
Image
Image
Image
It is, however, important to remember that, even though a blended body shape can benefit stealth characteristics because they reduce surface scattering compared to sharp facet design. A full circular (tube) body is extremely bad for stealth application, the reason is that the surface wave doesn’t get scatter but will travel a full circle around the object and come back to the source (also known as creeping wave return).
Image
While it is possible to reduce the number of sharp edges with blended edge design, it is not possible to get rid of them all, for example an aircraft will always have wing and inlet edges. Thus, there are the need for trailing edge and leading edge treatment. As mentioned earlier, the edge diffraction is more pronoun at lower frequency. To reduce the effect of edge diffraction, the wing and inlet leading edge can be made to be a soft electromagnetic surface, to achieve this, a tapered resistive sheet can be stuck or painted on the edge. Additionally, the edge can be made from bulk absorber to improve the result. Similar to the previous example, the resistivity of the sheet will reduce from the maximum at the front tip of the edge to near zero at the rear. The resistivity of the sheet can be increased by adding holes and reduce by adding metal particles in it. This allows the surface current to transition slowly rather than abruptly as well as be absorbed and thus reduce the edge diffraction as well as surface waves
Image
Image
Image
Image
As mentioned earlier, the resistive strip/tape must have a WIDTH at least half the wavelength of the lowest frequency of interest to be effective (read image carefully, the width not the thickness) , so it is plausible to estimate the lowest frequency where the edge treatment can remain effective.
For example the inlet edge strip/tape treatment of F-35 has a width between 22- 25.4 cm, which would indicate the lowest frequency where the treatment can still be effective is around 0.5-0.7 GHz
Image

Finally, Rayleigh Region applies when the circumference of the object is smaller than the radar wavelength. A common misconception is that the lower the operating frequency of the radar ( longer wavelength ), the better it would perform again stealth assets. That is wrong, however. It is important to remember that aircraft RCS does not necessarily grow linearly with an increase in frequency. Once the radar wavelength grows past the target’s circumference, the specifics of target geometry cease to be important and only its general shape affects reflection. The radar wave is longer than the structure and pushes current from one side of it to the other as the field alternates, causing it to act like a dipole and emit electromagnetic waves in almost all directions. This phenomenon is known as Rayleigh scattering. At this point, the RCS for aircraft will then decrease with the fourth power of the wavelength and can get exponentially smaller as the frequency reduced.
Image
There is a common misconception that any low-frequency radar can render stealth aircraft useless regardless of their transmitting power or aperture size (Ex: Tikhomirov NIIP L-band transmitter on the leading edge of Flanker series are often cited by enthusiasts as a counter stealth system) , that is wrong however. While it is true that stealth aircraft will often have higher RCS in Mie region. It is important to remember that given equal radar aperture area, lower frequency radars will have much wider beam compared to high-frequency radars, thus, the concentration of energy is much lower making them more vulnerable to jamming, lower gain also result in lower accuracy. Moreover, as mentioned earlier lower frequency also resulted in wider reflection beamwidth, hence weaker reflection. As a result, most low-frequency radars have much bigger transmitting antenna compared high-mid frequency radar (to get narrow beamwidth) ,it is also the reason that fighters fire control radar still work in X-band, because a L-band, VHF band radars of similar size would be too inaccurate for any purpose others than early warning.
Image
https://basicsaboutaerodynamicsandavion ... ermeasure/
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Unread post26 Oct 2020, 13:58

eloise wrote:
hocum wrote:Usually it uses a different frequency bands - L-band, UHF-band, "optic"... For example, S-400 has L-band surveylance radar - 91N6. Low and middle range systems always has optic/thermo visors. All clear, it's magic only for persons who knows nothing about this complexes and physics. For L-band (15 - 30cm wavelength) radar you need to cover stealth plane comparable layer thickness of half radar wave lenght (half-legth antenna/vibrator), or such cover is uneffective. Plane form like F-117 we don't see, so much stealth it is a coverage. Stealth planes has so thick coverage? :oops:

Although that theory gets recycle and brought up every now and then, it is sadly an oversimplify and incorrect representation of fact. If only countering stealth aircraft can be that easy then no one would be researching them. The way waves interact with objects are far more complex.
Firstly, the total radar reflection of a complex body such as aircraft made from several different kinds of reflections:
Image
Specular return: this is the most significant form of reflection in optical region (when structure circumphere > 10 times wavelength) ,surface acts like a mirror for the incident radar pulse. Most of the incident radar energy is reflected according to the law of specular reflection ( the angle of reflection is equal to the angle of incidence).This kind of reflection can be reduced significantly by shaping
Traveling/Surface wave return: an incident radar wave strike on the aircraft body can generate a traveling current on surface that propagates along a path to surface boundaries such as leading edge, surface discontinuous …etc, such surface boundaries can either cause a backward traveling wave or make the wave scattered in many directions .This kind of reflection can be reduced by radar absorbing material, radar absorbing structure, reduce surface gap or edges alignment ( so that their lobes occur in low priority region )
Diffraction: wave striking a very sharp surface or edge are scattered instead of following law of spectacular reflection.
Creeping wave return: this is a form of a traveling wave that doesn’t face surface discontinuous and not reflected by obstacle when traveling along object surface ,so it is able to travel around the object and come back at the radar. Unlike normal traveling wave, creeping wave traveled along surface shadowed from incidence wave (because it has to go around the object). As a result, the amplitude of creeping wave will reduce the further it has to travel because it can’t feed energy from the incident wave in the shadow region. Creeping wave mostly traveled around a curved or circular object. So, stealth fighters and stealth cruise missiles do not use tube fuselage. Nevertheless, the creeping wave return is much weaker than the specular return.
The percentage which each type of return will contribute to the total RCS value of an object depending on which region that object located in.
A high-frequency regime (or optical region) applies when the circumference of the object is at least 10 times longer than the wavelength of the incident radar wave. In this regime, specular mechanisms dominate the radar reflection ,(the angle of reflection equals the angle of incidence), like billiard balls colliding. Reflection towards the emitting radar – is reduced by angling surfaces so that they are rarely perpendicular to radars and suppressing the reflections from re-entrant structures such as engine intakes and antenna cavities with combinations of internal shaping, radar-absorbent material (RAM) or frequency selective surfaces. In this regime, “surface wave” mechanisms are small contributors to RCS, but are still present. If the wavelength is small relative to the surface, these waves are weak and their overlap will generate maximum backscatter when the radar signal is at grazing angles. When these currents encounter discontinuities, such as the end of a surface, they abruptly change and emit “edge waves.” The waves from different edges interact constructively or destructively due to their phases. The result is that they can strengthen the reflection in the specular direction and create “sidelobes” – a fan of returns around the specular reflection which undulate rapidly and weaken as the angle deviates from the specular direction. Surface wave reflections are generally very small in the optical region.
Mie region or also known as the resonance region : applies when radar wavelength*0.1 ≤ object circumference ≤ radar wavelength*1 in this region the surface wave can also swing around a structure’s back side, becoming “creeping waves” that shed energy incrementally and contribute to backscatter when they swing back toward the threat radar. This creeping wave can interferes constructively or destructively with the specular backscatter to produce a variation in the object’s RCS. Creeping wave doesn’t follow mirror like reflection rule, thus the common angular shape of stealth aircraft doesn’t help deflect them away from the threat radar
Image
So why is stealth less effective at low frequency? As the radar wavelength of radar grows, the intensity of specular reflections is reduced but its lobes width are widened (the same phenomenon also happened to radar, if aperture size remained the same, the reduction in frequency will increase radar beamwidth). Because the specular reflection lobes are widen ,shaping become less effective because it will be harder to deflect radar wave away from the source ( it is important to note that, while this lobe widening phenomenon making shaping less effective, it also reduce the intensity of the reflection because the energy will be distributed over a wider volume )
Image
Specular reflections from flat surfaces decrease with the square of the wavelength but widen proportionally: at 1/10th the surface length(approaching Mie region) they are around 6 deg. wide.

At lower frequency, the effect of traveling wave and diffraction is also more pronoun. For flat surfaces, traveling waves grow with the square of wavelength and their angle of peak backscatter rises with the square root of wavelength: (at 1/10th the surface length, it is over 15 deg). As the power of surface wave grow, the power of creeping wave return also grow. Tip diffractions and edge waves from facets viewed diagonally also grow with the square of wavelength. The end result is that the net value of stealth aircraft’s RCS often increases in Mie region. Maximum RCS is often reached when the wavelength reaches the circumference of the structure
There is a common misconception that any low-frequency radar can render stealth aircraft useless regardless of their transmitting power or aperture size (Ex: Tikhomirov NIIP L-band transmitter on the leading edge of Flanker series are often cited by enthusiasts as a counter stealth system) , that is wrong however. While it is true that stealth aircraft will often have higher RCS in Mie region. It is important to remember that given equal radar aperture area, lower frequency radars will have much wider beam compared to high-frequency radars, thus, the concentration of energy is much lower making them more vulnerable to jamming, lower gain also result in lower accuracy. Moreover, as mentioned earlier lower frequency also resulted in wider reflection beamwidth, hence weaker reflection. As a result, most low-frequency radars have much bigger transmitting antenna compared high-mid frequency radar (to get narrow beamwidth) ,it is also the reason that fighters fire control radar still work in X-band, because a L-band, VHF band radars of similar size would be too inaccurate for any purpose others than early warning.
So, is there any way for modern stealth aircraft to reduce their return even in Mie region?. The answer is YES
To begin with, the negative effect of traveling wave and diffraction can be reduced by: aligning discontinuities to direct traveling waves towards angles of unavoidable specular return, such as the wing leading edge, thus limit their impact at other angles.
For example: serrated edges are used in places where there is current discontinuity such as weapon bay door so that traveling wave return reflected toward less important aspect
Image
Image
Another common method to reduce the effect of surface wave is designing airframe facets with non-perpendicular corners and so radars view them along their diagonals, at low angles and across from the facets’ smallest angles, limits the area of edge-wave emission. Surface wave diffraction can also be reduced by blending facets. The first stealth aircraft, the F-117, was designed with a computer program that could only predict reflections from flat surfaces, necessitating a fully faceted shape, but all later stealth aircraft such as B-2 , F-35 , F-22, X-47 use blended facets. Shapes composed of blended facets are not only more aerodynamic but also allow currents to smoothly transition at their edges, reducing surface-wave scattering. Therefore, blended bodies have the potential for a lower RCS than fully faceted structures, especially at low-frequency regime. And blending the curves around an aircraft in a precise mathematical manner can reduce RCS around the azimuth plane by an order of magnitude. The penalty is often a slight widening of the specular return at the curves, but in directions at which threat radars are less likely to be positioned. This was one of the great discoveries of the second generation of stealth technology.
Image
Image
Image
It is, however, important to remember that, even though a blended body shape can benefit stealth characteristics because they reduce surface scattering compared to sharp facet design. A full circular (tube) body is extremely bad for stealth application, the reason is that the surface wave doesn’t get scatter but will travel a full circle around the object and come back to the source (also known as creeping wave return).
Image
While it is possible to reduce the number of sharp edges with blended edge design, it is not possible to get rid of them all, for example an aircraft will always have wing and inlet edges. Thus, there are the need for trailing edge and leading edge treatment. As mentioned earlier, the edge diffraction is more pronoun at lower frequency. To reduce the effect of edge diffraction, the wing and inlet leading edge can be made to be a soft electromagnetic surface, to achieve this, a tapered resistive sheet can be stuck or painted on the edge. Additionally, the edge can be made from bulk absorber to improve the result. Similar to the previous example, the resistivity of the sheet will reduce from the maximum at the front tip of the edge to near zero at the rear. The resistivity of the sheet can be increased by adding holes and reduce by adding metal particles in it. This allows the surface current to transition slowly rather than abruptly as well as be absorbed and thus reduce the edge diffraction as well as surface waves
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As mentioned earlier, the resistive strip/tape must have a WIDTH at least half the wavelength of the lowest frequency of interest to be effective (read image carefully, the width not the thickness) , so it is plausible to estimate the lowest frequency where the edge treatment can remain effective.
For example the inlet edge strip/tape treatment of F-35 has a width between 22- 25.4 cm, which would indicate the lowest frequency where the treatment can still be effective is around 0.5-0.7 GHz
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Finally, Rayleigh Region applies when the circumference of the object is smaller than the radar wavelength. A common misconception is that the lower the operating frequency of the radar ( longer wavelength ), the better it would perform again stealth assets. That is wrong, however. It is important to remember that aircraft RCS does not necessarily grow linearly with an increase in frequency. Once the radar wavelength grows past the target’s circumference, the specifics of target geometry cease to be important and only its general shape affects reflection. The radar wave is longer than the structure and pushes current from one side of it to the other as the field alternates, causing it to act like a dipole and emit electromagnetic waves in almost all directions. This phenomenon is known as Rayleigh scattering. At this point, the RCS for aircraft will then decrease with the fourth power of the wavelength and can get exponentially smaller as the frequency reduced.
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There is a common misconception that any low-frequency radar can render stealth aircraft useless regardless of their transmitting power or aperture size (Ex: Tikhomirov NIIP L-band transmitter on the leading edge of Flanker series are often cited by enthusiasts as a counter stealth system) , that is wrong however. While it is true that stealth aircraft will often have higher RCS in Mie region. It is important to remember that given equal radar aperture area, lower frequency radars will have much wider beam compared to high-frequency radars, thus, the concentration of energy is much lower making them more vulnerable to jamming, lower gain also result in lower accuracy. Moreover, as mentioned earlier lower frequency also resulted in wider reflection beamwidth, hence weaker reflection. As a result, most low-frequency radars have much bigger transmitting antenna compared high-mid frequency radar (to get narrow beamwidth) ,it is also the reason that fighters fire control radar still work in X-band, because a L-band, VHF band radars of similar size would be too inaccurate for any purpose others than early warning.
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https://basicsaboutaerodynamicsandavion ... ermeasure/


I have been getting into home theater recently and it’s mind numbing just to start figuring out how sound waves interact with the room and other sound waves. That’s in a room you know the dimensions of in a very narrow audio bandwidth and you still get all kinds of issues with frequency cancellation etc. Referencing what Gums just said about the F-4 and the AIM 7 is about where audio is currently, now fast forward 50 years to stealth, EW and general tactics and FOW, I’m starting to believe the military industrial complex lies more about abilities than snake oil charlatan hi fi companies!
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spazsinbad

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Unread post26 Oct 2020, 15:36

Rather than repeat all of the above quote I'll just quote the text part of the quote:
"I have been getting into home theater recently and it’s mind numbing just to start figuring out how sound waves interact with the room and other sound waves. That’s in a room you know the dimensions of in a very narrow audio bandwidth and you still get all kinds of issues with frequency cancellation etc. Referencing what Gums just said about the F-4 and the AIM 7 is about where audio is currently, now fast forward 50 years to stealth, EW and general tactics and FOW, I’m starting to believe the military industrial complex lies more about abilities than snake oil charlatan hi fi companies!"

This will be an interesting read for you 'tank-top': https://socratic.org/questions/how-are- ... etic-waves
A4G Skyhawk: www.faaaa.asn.au/spazsinbad-a4g/ & www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/videos?view_as=subscriber
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Unread post26 Oct 2020, 16:23

spazsinbad wrote:Rather than repeat all of the above quote I'll just quote the text part of the quote:
"I have been getting into home theater recently and it’s mind numbing just to start figuring out how sound waves interact with the room and other sound waves. That’s in a room you know the dimensions of in a very narrow audio bandwidth and you still get all kinds of issues with frequency cancellation etc. Referencing what Gums just said about the F-4 and the AIM 7 is about where audio is currently, now fast forward 50 years to stealth, EW and general tactics and FOW, I’m starting to believe the military industrial complex lies more about abilities than snake oil charlatan hi fi companies!"

This will be an interesting read for you 'tank-top': https://socratic.org/questions/how-are- ... etic-waves


No argument there, I was simply making a comparison even if it was apples to space ships. My point was claimed abilities vs real world abilities and I was really making the statement toward our broken English friend. In response to your article, EM waves don’t need physical particles to travel through but they are affected by it, hence stealth. I had the opportunity to chat with some people who work with our latest radar technology and emerging radar technology, from the little they told me we can do some really cool stuff, like tracking individual rotor blades on multiple drones under less than stellar conditions.
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Unread post27 Oct 2020, 04:14

Salute!

@Tank !!!!!!

PLZ attempt to simply extract a few words to make a point and avoid a complete duplicate of a previous post!!!

GASP! I almost passed your post up as I thot it was a keystroke mistake by Eloise.

@eloise
A super tutorial about radar and such. I hope there's a lot more about the LO plane design that you will keep quiet.

Gums sends...
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"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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Unread post27 Oct 2020, 11:34

eloise wrote:Although that theory gets recycle and brought up every now and then, it is sadly an oversimplify and incorrect representation of fact.

Really? So much words and pictures from you, and all about radar waves, with simple book theory, without any your own mindwork. It is showing something, I suspect. :wink:

Do you reject that stealth plane exellent visible by human eye, don't you? Optic/thermovisors scopes/cameras can easyly observe and tracking stealth aircraft. Buk, Vyitaz, Osa, Pantsir, Thor, Tunguska, Strela-10, Kub/Kvadrat has it. Su and Migs has it. Is it incorrect representation of the fact?

But you did "incorrect representation" (more correct that you just missed uncomfort question) that normally in position area has THREE main complexes in very different places. Plane can absorb wave from any direction with high cedenbals must looks like an electromagnetic anechoic chamber, reversal outspace. It hasn't even hint of aerodinamics at all. So it isn't especially against stealth even - complexes need to reload their rockets after launches, refresh personnel, stops for maitenance and repair... 8)

Antenna geometry can't cheat by any materials or computer modelling. In another case, nobody would construct miles/kilometras length antenna arrays for submarine linking, for example. Just special materials and computer modelling "phasets surfaces", implement in reversal direction - from absorbing to emitting waves.

It is a matter of fundamental metric of our Riman space. If object is too small/thin - there is no any inluence on wave, that's all. If you can manipulate this - you can manipulate with our space, create hyperdrives, warp portals and so on. If the steals lost its coverage - it becomes much more visible, even by all another complex measures.

Complex countermeasure, such as another band seekers/trackers, different angles of emitting WITH information exchange, radar modes such accumulative informations from special sectors of space instead of regular round obeserving makes every stealth full visible. No any tricks, or "incorrect representaions"... :wink:

And if recall that russian long range complexes in Siria placed nothern Masyaf, so its can't observe air space of Lebannon and Israel because mountines southern and western, placed like so especially for unavailable tracking israely planes... It is obvios that potential danger exists, even for new israely stealth planes.

eloise wrote:If only countering stealth aircraft can be that easy then no one would be researching them.

Why do you mean that it is so easy? Enemy must design, produced, full tested and deploy new radars/optic, upgrade links between them. For fighter planes all it is worse, it is more difficult. Onboard fighter/interceptor radars really has very low capabuilities against stealth, because it is must much more compact then landing/naval, and it isn't so easy to change its band without creating much disadvantages.

For radio guidance missile (especially air-to air) requirements for giudance precisions grows very high, and no ways to go its back so easily too. In another case nor Russia, neither China woudn't create their own stealth planes. But in Russia stealth conception differs: against very problematic unsurveylance (but very temting for first looking, of course) much more measures trying to reach untracking, and radio/proximity fuse correct working problems. This is more difficult to going back, because tracking needs more precisions, and more length waves just fail requirements. For radiofuses, for example, I just don't know good decision at all.

So, stealth is advantage - but against what? Another planes/fighters? Yep, that's true, exellent measure. But against land/naval multi-echeloning air defence position area??? :shock: :D Are you serious? Think again. 8)
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