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    RCS of PAK-FA

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    RussianStalinist

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    RCS of PAK FA

    Post  RussianStalinist on Sat May 07, 2011 9:23 pm

    Sorry if something similar to this has already been asked, but here it goes:

    On the Sukhoi website, they state that the RCS of the F-22 is 0.3sqm. An Indian General (I believe) said that the PAK FA had an RCS of 0.5sqm.

    The 0.3sqm for the F-22 contrasts sharply what America has said the rcs of the f-22 really is (they said something like 0.0001sqm). Why is this? Is it because Russia calculates rcs differently?

    If that's the case, then what would the PAK FA's rcs be if it was calculated using the Western method?

    Thanks for any answers!
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    GarryB

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    Re: RCS of PAK-FA

    Post  GarryB on Sun May 08, 2011 3:13 am

    The US figure is likely the best figure for the aircraft at the specific frequency the design is designed to defeat.

    Unless it is a perfect sphere... which it clearly isn't, from different angles it will have different RCS figures.

    Needless to say it is perfectly visible in optical wavelengths and its cross section from above in optical frequencies is dozens of square metres... it is huge.

    The Russian figure is likely an average figure which gives an indication but is hardly accurate either.

    Average figures by their very nature are always wrong.

    If you have four people... two are 25 years old, one is 30 years old, and one is 6 years old... the average is 25 + 25 + 30 + 6 = 86 / 4 = 21.5.

    The average for the group is twenty one and a half years old yet none of the people are that age.
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    nightcrawler

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    Re: RCS of PAK-FA

    Post  nightcrawler on Mon May 09, 2011 2:37 am

    We can't speculate as of yet; these figures are so much surreptitious & Pak-FA test beds are tailored for aerodynamic testing & RCS figures aren't yet tested; that, one can plainly observe
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    Vladimir79

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    Re: RCS of PAK-FA

    Post  Vladimir79 on Mon May 09, 2011 6:57 am

    RussianStalinist wrote:Sorry if something similar to this has already been asked, but here it goes:

    On the Sukhoi website, they state that the RCS of the F-22 is 0.3sqm. An Indian General (I believe) said that the PAK FA had an RCS of 0.5sqm.

    The 0.3sqm for the F-22 contrasts sharply what America has said the rcs of the f-22 really is (they said something like 0.0001sqm). Why is this? Is it because Russia calculates rcs differently?

    If that's the case, then what would the PAK FA's rcs be if it was calculated using the Western method?

    Thanks for any answers!

    F-22 is far less than .3m^2. That is the RCS of a clean Rafale. F-22 is said to be marble to golf ball which is like .004m^2 at its largest. There is no official figure for F-22 but the references have been given by Lockheed. PAK FA RCS was stated by Sukhoi officials giving a debrief to Russian officials visting the production site on the dawn of their decision to sign the JV production MoU. Ajay Shukla reported they said .5m^2.
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    GarryB

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    Re: RCS of PAK-FA

    Post  GarryB on Mon May 09, 2011 9:05 am

    RCS is more than just shaping and materials.

    It is also about manufacturing quality and maintainence standard.

    An F-117 with a few screws not properly tightened can turn a tennis ball into a basket ball.

    Even water or ice on the airframe will effect RCS.


    It is very much governed by the law of diminished returns.

    It is a bit like speed... in the early 1950s designers started focusing on speed. Planes able to fly mach 3 and faster were designed in those years and it was simply thought that planes would just keep getting faster and faster and by the 1980s we'd have planes zipping around at mach 5 or more.

    The problem is that once you get to a certain speed things get harder... the best example is propeller driven aircraft. You get the biggest engine you can find and put it in your fighter. To get that plane to fly 100 mile an hour faster you need to double the engine power. If you double the engine power again you only get another 60 miles an hour faster. Double it again and you only get another 30 miles an hour in speed till eventually you double the engine power and the tips of the props are supersonic and instead of developing power or thrust they start developing noise and drag.
    The real unseen problem is that every time you double the engine power the cost goes up on a log scale.. first double in power = 10,000 dollars, second double in power is 100,000 dollars, third double of power is 1,000,000 dollars and the fourth is 10 million dollars etc etc.
    Pretty soon you are spending billions for a very small increase in performance.

    Look at the replacements for the F-15 and F-14... the F-16 and the F-18... they are both slower and shorter ranged than the aircraft they replaced and that was on purpose to keep costs down. The F-16 is a mach2 bird, and the F-18 is limited to mach 1.8 to keep the costs down... a choice was made at the design stage that the effort and cost to make both aircraft mach 2.5 birds wasn't worth it because modern fighters rarely travel at such speeds because it wastes fuel. By making them slower they possibly saved billions of dollars in design complication and operating costs.

    Clearly Sukhoi have decided that a super stealthy aircraft wasn't worth the extra cost and effort. The result is a much cheaper aircraft that might serve in rather larger numbers than the 189 odd F-22s.

    As technology improves reductions in RCS can be applied to further reduce the RCS of the design.

    Obviously there is also the possibility that the .5 squ m figure is a very conservative estimate, and of course being a single figure it is clearly an average anyway.
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    RussianStalinist

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    Re: RCS of PAK-FA

    Post  RussianStalinist on Tue May 10, 2011 4:09 pm

    How could the RCS of the PAK FA be that low? I think that Saab announced that the Gripen gets an rcs of something like 0.3sqm.

    I think that a plane designed with the intention of making it vlo would have a significantly lower rcs.
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    medo

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    Re: RCS of PAK-FA

    Post  medo on Tue May 10, 2011 4:24 pm

    How could the RCS of the PAK FA be that low? I think that Saab announced that the Gripen gets an rcs of something like 0.3sqm.

    I think that a plane designed with the intention of making it vlo would have a significantly lower rcs.

    We still don't know exact RCS. Maybe Sukhoi intentionally give to big RCS or that numbers go for shapes of the plane without coating when first prototype fly without colors. Also we don't know if PAK FA prototypes have RAM coating and if it is the same as the one for serial planes etc. We don't know even what will be actual RCS of serial Su-35, how than for serial PAK FA, which is designed for low RCS? The time will tell.
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    GarryB

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    Re: RCS of PAK-FA

    Post  GarryB on Thu May 12, 2011 2:10 am

    How could the RCS of the PAK FA be that low? I think that Saab announced that the Gripen gets an rcs of something like 0.3sqm.

    A Gripen clean with a RCS of 0.3sqm will be in trouble against a PAK FA armed with AAMs.



    The point is that the Gripen carrys weapons externally and while the PAK FA can it normally wont.

    Perhaps the 0.5sqm for the PAK FA is with external weapons?
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    IronsightSniper

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    Re: RCS of PAK-FA

    Post  IronsightSniper on Sat May 14, 2011 9:04 am

    Uh, Carlo Kopp estimates that RCSs are:

    F-22: 0.00004 m2
    F-35: 0.0001 m2
    PAK-FA: 0.001 m2


    Those are all in the Frontal Section with X-band radars. In general, the design philosophy of the T-50 is not to be the stealthiest plane in the sky, but rather just stealth enough to get close where it'll win almost all the time v.s. the F-35 and have a chance v.s. the F-22.
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    Stealthflanker

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    Re: RCS of PAK-FA

    Post  Stealthflanker on Sat May 14, 2011 1:12 pm

    IronsightSniper wrote:Uh, Carlo Kopp estimates that RCSs are:

    F-22: 0.00004 m2

    this is new to me... commonly quoted figure is 0,0001 Sqm
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    GarryB

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    Re: RCS of PAK-FA

    Post  GarryB on Sun May 15, 2011 3:20 am

    In general, the design philosophy of the T-50 is not to be the stealthiest plane in the sky, but rather just stealth enough to get close where it'll win almost all the time v.s. the F-35 and have a chance v.s. the F-22.

    Exactly... and the main purpose of setting the bar below the F-22 is so that it is not too expensive and while it is very unlikely that they will build as many T-50s as there are F-35s made, they will likely produce more than 189 T-50s.

    Mig and UAC keep talking about a light 5th gen fighter they are developing that is seperate from the Mig 1.42/1.44. They mention that actual production work will not happen till the T-50 is fully ready for production so that the new design doesn't delay the T-50. This perhaps suggests that by 2025 they might have a heavy and light 5th gen fighter pair... with UCAVs and probably a few Su-35/Mig-35.

    BTW isn't 35 a popular number... F-35, Mig-35, Su-35...
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    IronsightSniper

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    Re: RCS of PAK-FA

    Post  IronsightSniper on Mon May 16, 2011 12:42 am

    Stealthflanker wrote:
    IronsightSniper wrote:Uh, Carlo Kopp estimates that RCSs are:

    F-22: 0.00004 m2

    this is new to me... commonly quoted figure is 0,0001 Sqm

    Tbh, I forgot the last number in the F-22's Front RCS figure but I only remember that it starts with 4 0s Very Happy

    havok

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    RCS of PAK-FA

    Post  havok on Sun Jul 24, 2011 9:48 pm

    RussianStalinist wrote:Sorry if something similar to this has already been asked, but here it goes:

    On the Sukhoi website, they state that the RCS of the F-22 is 0.3sqm. An Indian General (I believe) said that the PAK FA had an RCS of 0.5sqm.

    The 0.3sqm for the F-22 contrasts sharply what America has said the rcs of the f-22 really is (they said something like 0.0001sqm). Why is this? Is it because Russia calculates rcs differently?

    If that's the case, then what would the PAK FA's rcs be if it was calculated using the Western method?

    Thanks for any answers!
    You are asking a very loaded question. There is no such thing as a 'Western' or 'non-Western' method of calculating the radar cross section (RCS) of a complex body. The RCS question/value rests on how many tools you have and how effectively do you use them.

    For starter...



    In radar detection, the simplest body is the sphere. On this body, there are only four possible behaviors:

    - Specular
    - Surface wave
    - Leaky wave
    - Creeping wave

    You can guess the matches from the illustration above. The fourth behavior -- creeping wave -- is conditional. There is a rule call the 'ten lambda' rule. Lambda is the Greek symbol for wavelength -- ANY wavelength. The 'ten lambda' rule states that if the diameter of the sphere (or cylinder) is greater than 'ten lambda' then the creeping wave effect will not occur. This is because of the leaky wave effect. The surface is called the 'electrical path' and the longer this path the greater the leaky wave loss mechanism, hence the creeping wave effect may or may not occur.

    In contrast, an aircraft is a much more complex body than a sphere...



    It is well known that Physical Optics (PO) is good only for specular reflections but not for anything else. Even the Iranians know this...



    For cavities such as engine inlet/exhaust tunnels, more sophisticated tools have been developed, such as Iterative Physical Optics (IPO)...

    http://www.jpier.org/PIER/pier.php?paper=07110803
    Abstract:
    It is always a challenge to predict Radar Cross Section (RCS) of a full scale military platform with a good accuracy. Most of the time antennas and cavities are the main contributors of aircrafts RCS. Several methods have been developed to compute the RCS of cavities such as analytical methods (modal methods) and asymptotic methods (geometrical optics (GO) methods and physical optics (PO) methods). This article presents the Iterative Physical Optics (IPO) method which consists in an iterative resolution of the Magnetic Field Integral Equation (MFIE) to compute the currents on the inner walls of the cavity. This method allows computing arbitrarily shaped cavity with a good accuracy even for cavity with a depth inferior to the wavelength. Comparisons of IPO results with Rays and Finite element methods show a better accuracy of IPO than Rays especially for cross polarization. But computation time represents one of the main limitations of the IPO method. We present here a new formulation of the Segmented IPO method which coupled with the generalized reciprocity theorem decreases significantly the complexity of the method and consequently the computation time. The S-IPO method has been validated by comparisons with Modal method and measurements. We have observed that the repartition of the electric currents density on the inner walls of the cavity is quite the same with IPO and S-IPO computations. Lastly we propose an evolution of the IPO method we have developed to compute the RCSof cavities under radome. This method has been validated by comparison with finite element results.

    Ufimtsev developed the edge diffraction method that gave US the F-117. Edge diffraction calculations is another tool.

    So your loaded question rests upon the tester's knowledge of how many behaviors are there on a complex body, how they interact with each other, how many tools available, and how good is the tester's usage of them. If there are deficiencies in any of those knowledge, and the problem here is that those deficiencies may not be known to the tester, in other words, he does not know he is wrong, the entire enterprise is compromised and a 'non-true' RCS will result. The next problem is that once as complex a body like an aircraft is considered 'complete' a project, meaning ready for volume production, you may not be able to make changes and/or corrections to that complex body without the possibility of creating negative aerodynamic compromises.

    So here is a possibility: You designed a 'stealth' aircraft using only Physical Optics (PO) as your measurement tool. You did not know about edge diffraction or surface wave behaviors. You shaped your aircraft in ways to deflect specular reflections away from the seeking radar's position. Then you publish the RCS value and call the design ready for production. On the other hand, your potential adversary spent a lot of money and much more time than you developing his 'stealth' aircraft with as many available tools, known and unknown to you, as he can. It is inevitable that he will create a superior 'stealth' aircraft than yours. His may not be as fast or may not carry as much ordnance as yours but because he can bypass radar networks with greater ease his 'stealth' aircraft can greater affect the war than yours can.

    Other considerations are the hardware used in running these tools. The more powerful the computers, the greater your knowledge on the interactions between these behaviors because these reflections and diffracted signals have to come off the individual bodies such as antennas or flight control surfaces some time. In a complex body, those signals will impact other surfaces at different angles and that may create a different behavior. Powerful computers can help you observe and record these complex interactions in a larger time span compared to breaking down the complex body into discrete segments and try to patch these smaller bodies together later.

    This is why it is not as easy in making and/or measuring a 'stealth' aircraft as many have come to falsely believe. The US have no problem with anyone making any claims about our 'stealth' aircrafts regarding their RCS values. The critics can make those values as high or as low as they wish.
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    Pierre Sprey

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    Those who question the stealth features of the PAK-FA

    Post  Pierre Sprey on Sat Feb 04, 2017 1:44 am

    There is a rather larger contingent of pundits out there who love to go over the Pak Fa's stealth features and look for holes. And they always compare it to the Raptor. If the Raptor has it and the Pak Fa doesn't then the Pak Fa ain't stealth is how it goes. They make these long blathering posts that question aspects of the Pak Fa. Most of them think, just by eye balling certain angles or little details, that they've uncovered a stealth deal breaker. When in reality, its usually just lame little details that they are totally blowing out of proportion. And they become so sure of themselves. I call them stealth absolutists.

    And the worst part is, that they don't even realize that they are questing the very stealth designation of the Pak Fa. Do they think that the Russian MOD was bluffing when they stipulated stealth or something ? Do they think that Sukhoi is lying when they say that the aircraft has met the terms of the tender ?

    One example is the air intake of course. That one famous picture that shows some of what they believe is the 1st stage of the engine. These guys say that this is a deal breaker. When in reality, the YF 23 had superior all aspect stealth than the F-22 Raptor and it has more engine exposed than the Pak Fa.

    Does anyone here question the stealth of the Pak ?
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    GarryB

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    Re: RCS of PAK-FA

    Post  GarryB on Sat Feb 04, 2017 8:50 am

    The design of the US aircraft (F-22 and F-35) are 100% compromised on favour of stealth.

    The PAK FA is from the start a stealth fighter hunter... hense it keeps the IRST despite the reduction in stealth, it has long wave radar antennas in its wings.

    Priority number one is manouver performance, stealth is important but it wont be the most stealthy aircraft that wins... when AAMs are defeated by jamming and cannons are the last resort my money would be on the PAK FA and Su-35 and MiG-35 with their cannon.


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    hoom

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    Re: RCS of PAK-FA

    Post  hoom on Sat Feb 04, 2017 9:43 am

    I do question the stealthiness, at least of the prototypes we've seen.
    There really are a bunch of obvious failures to align panel edges/minimise gaps & that means it clearly can't have as low an RCS as F-22/F-35.

    If the production version actually applies this level of detailing all over then T-50 should be well up there with the US fighters in RCS reduction


    On the other hand I also question widely thrown about RCS numbers 0.0x m^2 or lower for F-22/35 when you have ~0.4m^2 radar antennae like this on the front

    These are literally designed to be excellent Radar Reflectors & I really can't see any reason that they would bounce back significantly less than equal-area RCS (without severely limiting capability), certainly no way they can be orders of magnitude less than their literal area.

    But on the basis of what we've seen I don't think full effort at frontal RCS minimisation is a particularly important factor in T-50 design:
    F-35 puts nearly all eggs in the frontal RCS basket
    F-22 also has excellent manoeuvrability to fall back on.
    There is almost certainly enough RCS reduction to give T-50 the jump on T4 gen planes 1v1.

    T-50 shifts a lot of emphasis to 360deg situational awareness via cheek & rear antennae, extra Optical coverage & L-band wing leading edge antennae.

    (not sure there are actually antennae for all those lobes/frequencies Suspect)

    When you read scenarios where F-22/35 get their massive test/exercise victories vs G4 planes the G4 planes have no idea where the stealth planes are which allows the stealth planes to get on flank/rear & launch surprise attacks.

    I think the Russian intent is that they're going to have at least a rough idea where the stealth planes are via wing-embedded L-band radars &/or operating defensively in range of ground based L-band radar &/or will be facing enemy AWACS.
    Various articles over the years have pointed out that long wavelength radar with modern signal processing as seen on AWACS & Russian ground radar can easily locate stealth planes to within a few hundred meters which totally destroys those scenarios.

    Meanwhile those cheek radars allow a high range of defensive avoidance manoeuvre for the T-50 to dodge inbound missiles while still providing guidance to outbound missiles & maintaining strong warning/EW/ECM in direction of threat (F-22/35 lose a lot outside 120deg frontal AESA arc).

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