F-22 and F-35 RCS revealed by USAF

Anything goes, as long as it is about the Lockheed Martin F-22 Raptor
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sergei

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Unread post11 Nov 2014, 19:46

mityan wrote:
smsgtmac wrote:From a physics POV there is no 'teflection' per se, but conversion to heat or re-radiation. The direction of the re-radiation is controlled in the design.

Reflection and reradiation are the same.
What about heat?
For consuming the electromagnetic wave and revert it to heating the matching is required. The impedance of the canopy's metal plate should be equal to impedance of a free space - 377 Ohm in broad range of frequencies.
As for me, I think that's a bullshit, but maybe this is due to a lack of education.
Consider the matching is implemented. For very good high frequency design the voltage standing wave ratio (VSWR) of near 1.5 is an adequate value. It means that only 20% of energy is reflected back to space.
So divide the estimated value above by 5 and you get the rcs still greater than reported.
There is no magic.

And what I think also.
Nobody could think of russians as stupid dumbass.
And if the CEO of OAK (united aviation corporation of russia) Pogosyan tells Putin that PAK-FA RCS is about 0.3 sq.m. and this is close to Raptor, I think he's got his reasons. There are too many candidates for his chair to fell free in lying.


I think that talking about values ​​0.3 Pogosyan meant excluding anti-radar coating
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mityan

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Unread post12 Nov 2014, 07:37

KamenRiderBlade wrote:In reality, there will probably be very little reflection back, a lot more radiating away via the wave hitting the surface at a non perpendicular angle, some absorption into heat depending on what type of RAM coating is used.

Some estimations just has been made. Maybe the exact values we'll be reported after decades, but it definitely should be much greater than -40 dBsm. Canopy has no RAM cause its destination is to provide an outside view for the pilot. I think it's hard to coinside with absorbing option.
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mityan

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Unread post12 Nov 2014, 07:42

sergei wrote:I think that talking about values ​​0.3 Pogosyan meant excluding anti-radar coating

And I guess not. It's XXI century and radar capabilities (also using an optic band) eliminate the VLO advantage, so it's not worth to tend to perfection - too expensive (and maybe suffers some physical limitations)...
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smsgtmac

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Unread post13 Nov 2014, 03:54

mityan wrote:....It's XXI century and radar capabilities (also using an optic band) eliminate the VLO advantage, so it's not worth to tend to perfection ...


No.
You've made an assertion unsupported by fact. What is your case? By 'case', I mean a logical explanation, perhaps with supporting evidence from a credible source or sources that is specific enough to be proven either true or false. It is stated in the form of "This is true because_______________" (fill in the blank). A list of reasons is acceptable of course, but the reasoning and evidence must stand up to scrutiny and be free of logical fallacies.
--The ultimate weapon is the mind of man.
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mityan

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Unread post14 Nov 2014, 10:56

smsgtmac wrote:"This is true because_______________" (fill in the blank).

Thanks for the compliment. :)
But I've told that it's my guess.
So I'll try to explain further.
PESA Irbis can detect target of -20 dBsm at the range up to 90 km. AESA N036 supposed to have equivalent capabilities (at least).
As for me, I doubt that Raptor has its overall -40 (my apologies, guys), but if it has, it can be detected at only 28 km range.
This is very good. But location equipment in optic band provides now greater ranges. And what about a2a missile firing range?
I dont know values but it seems to be greater also. And the firing event could rather be seen from the greater distance.
So what good is of X-band stealthy if you are seen due to fire? Thus I conclude that I should provide stealthy up to firing range and that is enough. Or maybe up to optic/IR band detection range. No more.
There is a very very big challenge to reduce observability for 10 dB e.g., and seems to be excess in the case described above.
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hornetfinn

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Unread post14 Nov 2014, 15:01

Sergei, optical/IR bands are good but they have also serious drawbacks for wide area surveillance. They offer no accurate range information and work only if there is no obscuration between the sensor and target. This means they can not tell target speed, altitude or heading accurately. Radar offers all that information and can detect targets in any weather. If optical sensors are to have long range, they have to have very narrow field of view. They are very useful tools, just like low frequency radars, but are miracle systems against stealth aircraft.
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wrightwing

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Unread post14 Nov 2014, 15:36

mityan wrote:
smsgtmac wrote:"This is true because_______________" (fill in the blank).

Thanks for the compliment. :)
But I've told that it's my guess.
So I'll try to explain further.
PESA Irbis can detect target of -20 dBsm at the range up to 90 km. AESA N036 supposed to have equivalent capabilities (at least).
As for me, I doubt that Raptor has its overall -40 (my apologies, guys), but if it has, it can be detected at only 28 km range.
This is very good. But location equipment in optic band provides now greater ranges. And what about a2a missile firing range?
I dont know values but it seems to be greater also. And the firing event could rather be seen from the greater distance.
So what good is of X-band stealthy if you are seen due to fire? Thus I conclude that I should provide stealthy up to firing range and that is enough. Or maybe up to optic/IR band detection range. No more.
There is a very very big challenge to reduce observability for 10 dB e.g., and seems to be excess in the case described above.


Detected at 28km, tracked at an even shorter range. Meanwhile, the F-22 detected the Flanker at 200+km, and T50 at 100+km, well before their optical systems would be of use.
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mityan

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Unread post16 Nov 2014, 09:27

wrightwing wrote:Detected at 28km, tracked at an even shorter range. Meanwhile, the F-22 detected the Flanker at 200+km, and T50 at 100+km, well before their optical systems would be of use.

And that is all? Is it so easy in your way?
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disconnectedradical

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Unread post16 Nov 2014, 12:52

From optimal angles such as head on, the F-22's RCS in the X-band is as low as 0.0001 sq m. The F-35 is 0.001 sq m, possibly lower. I think some disclosures by Sukhoi and reliable journalists suggest an optimal T-50 RCS of 0.05 to 0.01 sq m, which is still pretty low. However, T-50's side RCS will probably be much larger than the F-22 and F-35, due to the nearly 90 degree joint between the rear engine nacelles and fuselage.
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arl8733

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Unread post16 Nov 2014, 19:00

One other element which contributes to the F-22 metal marble being hard to detect is that it is traveling at 1.8M.
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mityan

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Unread post17 Nov 2014, 08:02

arl8733 wrote:One other element which contributes to the F-22 metal marble being hard to detect is that it is traveling at 1.8M.

No way. It's not an issue. The band of doppler frequencies being analyzed in any fighter or ground military radar receiver is wide enough to deal with this speed.
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disconnectedradical

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Unread post17 Nov 2014, 08:13

On another note, according to djcross, IF the T-50's RAM and manufacturing tolerances are good enough, its frontal RCS can approach the F-22 and F-35 at optimal angles/frequencies. Again, big emphasis on the if. As for all aspect, the shaping of the sides and rear means that all aspect VLO is probably not going to happen, though that's probably Sukhoi's intent. Stealth and reducing RCS is really about money, and how much money you're willing to throw at manufacturing tolerances, RAM, etc. And Russia just doesn't have as much money to throw at these details as the West. Still, the T-50 is quite good for a first attempt at stealth, and it's an excellent design when you consider the circumstances. And remember, the T-50 doesn't have to match the F-35 and F-22 to perform its mission. Not to mention that it has some unique attributes of its own, namely high maneuverability in all axis (though its usefulness is debatable), very high fuel capacity and range (3,500 km on internal fuel), and quite large weapons bay.
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mityan

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Unread post17 Nov 2014, 09:18

disconnectedradical wrote:From optimal angles such as head on, the F-22's RCS in the X-band is as low as 0.0001 sq m. The F-35 is 0.001 sq m, possibly lower. I think some disclosures by Sukhoi and reliable journalists suggest an optimal T-50 RCS of 0.05 to 0.01 sq m, which is still pretty low. However, T-50's side RCS will probably be much larger than the F-22 and F-35, due to the nearly 90 degree joint between the rear engine nacelles and fuselage.

F-22's RCS in the X-band is as low as 0.0001 sq m for a very narrow angle span - it's just a local mimimum, which is not relevant to an average RCS in wide angle span.
Please, look at the previous page of the topic - I just took a good american book on RCS an calculated the reflections from a small cut of metallized cockpit glass. Got a value greater than marble.
And please dont attribute a wonderful absorbing option to the glass - it's just a glass to see through, very strong, termal resistant, UV-filtering, etc. tough glass - but it's not radio absorbing.
So the calculation is rather close to reality I guess.

Another consideration.
Here are the US patents on RAM for example.
http://www.google.com/patents/US5310598
http://www.freepatentsonline.com/5164242.pdf
If you look attentively to the graphs showing loss vs. frequency,
you will understand that the absorbing capability of 25 dB is a very good result (especially in wide X + Ka band).
Materials with such losses can be implemented in fighter design.
What does this value mean?
25 dB = 300 times.
Thus if the conventional fighter is given near 3 sq.m. RCS, than for VLO design 3/300=0.01 sq.m. is an adequate figure.

There are some RAMs, that have a much greater losses, but they look like this:
http://tdkrfsolutions.com/images/uploads/data-sheets/TDK-IP130BL.pdf
And you realize that they cannot be implemented in fighter design.

So I truly believe that F-22 is still the most VLO fighter in the world, but its wide angle span RCS should be about 100 times greater than a metal marble.
I can believe that cockpit glass RCS could be slightly greater than 0.001, I can believe that overall design could be near 0.01, I can believe that the local minimum of RCS could be actually 0.0001 - but in a very narrow angle span, maybe 0.5 degree.

What you think?
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mityan

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Unread post17 Nov 2014, 09:20

disconnectedradical wrote:Stealth and reducing RCS is really about money, and how much money you're willing to throw at manufacturing tolerances, RAM, etc. And Russia just doesn't have as much money to throw at these details as the West.

For a pity, money cannot fight physics.
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Unread post17 Nov 2014, 10:44

mityan wrote:
disconnectedradical wrote:Stealth and reducing RCS is really about money, and how much money you're willing to throw at manufacturing tolerances, RAM, etc. And Russia just doesn't have as much money to throw at these details as the West.

For a pity, money cannot fight physics.

No, it's not fighting physics. Closer manufacturing tolerances will result in lower overall RCS since it reduces the effects of surface discontinuity. How close you can get the tolerances is pretty much dependant on how much money you want to throw at manufacturing.
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