PAK FA vs F22 Raptor : A Detailed Analasis

[gambit]

Thanks for an attention to my simple remark. Including quote from CV and basics for math methods of 3D objects modeling.
Guess next question will be on physical or geometrical optics.
So US researchers never use physical modeling?

Absolutely we do. A lot of it...

Technically speaking, it is 'RCS control'. Not 'RCS reduction'. In theory, if you can control something, you can manipulate its characteristics, behaviors, and appearance.

In RCS control, these things are in order:

- Prediction
- Modeling
- Measurement

With the advent of computers, we can swap Modeling and Prediction, but the final arbiter is always Measurement and the best is always with full scale. But back in my days, as in pre-historic (Internet), we first predict on paper on how a shape or combinations of shapes would behave under radar bombardment, then we would make scaled models, then we would subject all those models under real radar bombardment and take measurements. The closer that Prediction and Measurement are to each other, the more we know both mathematical and real models are accurate. In the early days of RCS control methodology, wildly off the mark was the norm, simply because we did not have Ufimtsev's work. We owe much to the good Doc, but in no way is he the 'father of stealth' as many tried to portray him. Even he did not know the practical utility of his work. Neither did the Soviets and that is why they let him published his work to the public. Ooopsie...

The above is just about my favorite illustration on how any radar system actually PERCEIVE any complex body, be it a human being, the Eiffel Tower, or an airliner. The regulars of this forum have seen it before and properly enlightened on the basics of radar detection processes.

Each one of the many spikes is actually a composite of many smaller voltage spikes produced by many smaller structures that make up many larger structures.

Two things:

- Destructive interference
- Constructive interference

The more complex the body, the higher the unpredictability of interference. Therefore, the first goal is to minimize the quantity of radiation points, or radiators, that could be conducive towards both types of interference. The second goal is to configure any radiator in any way possible so that the seeking radar will either receive no or very little radiation from those radiators.

For example...

The above is an absolute EM nightmare. So we can control it by enclosing weapons either inside the aircraft or inside a much more streamline carrier pod.

Anyway...Getting back to our airliner and its graph of voltage spikes. If below the graph is the 'stealthy' region, then our aircraft is obviously 'non-stealth'. We would not know this unless we actually perform measurement of full scale models, not just mathematical predictions.

In looking at our physical modeling and measurement data, the first target in our RCS control tactic would be that huge spike. We need to find out mathematically what caused it. On paper, we would reconfigure that area (Prediction), then we would make scaled models (Modeling) of our new complex body, then we would subject them to radar bombardment (Measurement). If our process is successful, that area of the aircraft would be inside the 'stealth' region.

While one team is working on that huge spike, another team could be working on the next highest, another team on the spike right below that, and so on...The danger here is that one team could find out no matter what, an area of the aircraft can only be reduced so much and that despite all the work, the spike from that area would still be prominent.

If the goal is to produce a 'stealth' fighter, we have to scrap our current design and start anew. Then the entire flow starts all over again: Prediction/Modeling, then Measurement.

Physical modeling is extremely important. Do you what is a 'radar range'?

National Radar Cross Section Test Facility (NRTF)

The National Radar Cross Section (RCS) Test Facility (NRTF) is the premier DoD facility for RCS testing. Formerly known as RATSCAT, which began measuring radar scattering in 1963, it is comprised of two complementary sites, Mainsite and RATSCAT Advanced Measurement System (RAMS). Assigned to the U.S. Air Force’s 781st Test Squadron, NRTF is located west of Holloman Air Force Base, New Mexico in a rolling gypsum region of WSMR. NRTF specializes in the RCS characterization of full-scale, aerodynamic vehicles and antenna radiation pattern development.

Do you know what is an 'EM anechoic chamber'?

Benefield Anechoic Facility - Wikipedia, the free encyclopedia

Benefield Anechoic Facility (BAF) is an anechoic chamber located at the southwest side of the Edwards Air Force Base main base. It is currently the world's largest anechoic chamber.

An EM anechoic chamber isolate the body from environmental EM contamination, even as low a signal as cosmic background radiation. The body is effectively sealed off from the outside world. Inside, we can have over 95% accurate estimate of what is the body's true EM behavior from many precise angles of radar bombardment.

A radar range is essentially an open field with completely uncontrolled EM contamination from space sources, radio, TV, etc. With both types of measurement of a full scale physical model, we will have the best possible data of our 'stealth' design. We can have the loop of Prediction and Modeling for several evolutions of our design, but we will never know for certain until we actually break the loop and have Measurement of a full scale model. Then starts all over if necessary.

No one is currently better than US at this process.

 

[Agnostic_Indian]

A question was asked about the possibility of a moving-target-indicator (MTI) radar to detect F-117 class bodies. The answer is 'Yes' but with serious caveats.

First...There is a misleading argument bandied about that goes: Since the F-22 has the RCS of a bird and no bird flies at several hundreds km/h, the US wasted a lot of money for nothing.

The argument is flawed in the fact that all radar systems have what is called the 'clutter rejection threshold', meaning stuff that are detected but whose electrical characteristics are known and filtered out. These stuff include cosmic background radiation, music radio, or TV signals. The classical concave dish just make their detection directional. All radars detect these things and installed filters raises that 'clutter rejection threshold'. Birds are usually filtered out so even if the 'bird' flies at Mach 10, it will be filtered out from the start.

Which lead up to the next point...

The above is an illustration of a typical radar signal.

There are four main very important characteristics:

- Amplitude
- Freq
- Pulse duration (or width)
- Pulse Repetition Interval

A series of pulses interrupted is called a 'pulse train'. We can change the above four characteristics from train to train but that is for another discussion.

From these four items we receive vital target 'resolutions' such as speed, altitude, heading, Doppler, and aspect angle. The last meaning how is the target facing us.

For an MTI radar, it is the Doppler component that is of interest. What an MTI radar does is to focus its data processing only on the Doppler shifts of a moving target. It does not care of heading, altitude, or aspect angle...

Doppler radar - Wikipedia, the free encyclopedia

The highlighted is a serious drawback when a radar system is purposely designed to process only the Doppler component of a moving body.

So for an MTI radar to be used against an F-117 class body, we would have to lower that 'clutter rejection threshold' to detect bodies smaller than birds then process EVERY SINGLE Doppler components of EVERY SINGLE moving bodies within the beam. Even with data processing of only one component out of many, the processing demand of so many objects is a serious technical hurdle. We can reduce this burden by narrowing the beam but this would increase coverage time over any given airspace volume. Then if some birds or a flight of F-35s just happened to be across our radar view instead of approaching or receding, the MTI system would not process them at all.

For the defender, there is another serious tactical disadvantage when facing a radar low observable adversary...

The B-52's RCS and its Doppler component will dominate the search volume and will mask the far smaller B-2's RCS and its Doppler component. Not completely but just enough to make an effective distraction and draw vital airborne resources to investigate. What if a flight of real birds take flight? The MTI radar could process different birds at different locations to be the one that flies at several hundreds km/h. More vital resources to investigate real birds instead of the one that matter.

So is an MTI radar an effective detector of an F-117 class body? Only if the conditions are 'just right'. But a knowledgeable adversary will do his best to create as 'wrong' the battlefield conditions as possible to maximize his technical advantage.

so if f 22 is heading straight to pak fa then dopular shift would be higher, but since it's front portion it offers less angles of reflection detection range will be lower..when within radar range, heading,speed etc can be acquired.

if heading angle is not straight then reflective surface on offer is more but dopular effect will be less..so detection will be early compared to straight heading but finding direction of heading, speed etc will be difficult..in the absence of data of speed the radar may reject it as a clutter..is that how it is ?

 

[gambit]

so if f 22 is heading straight to pak fa then dopular shift would be higher,...

Yes.

...but since it's front portion it offers less angles of reflection detection range will be lower..when within radar range, heading,speed etc can be acquired.

Frontal RCS is the lowest on any aircraft, not just the F-22. However, because the -22 is designed from the onset to have high RCS control quotient, effective detection range of the -22 will be even shorter than other aircrafts.

In mathematics, a 'quotient' is a figure denoting the number of times a quantity is contained inside another quantity. In the old days, RCS control as a factor was very low, in other words, when designing a military aircraft, its RCS quality was very low on the list of priority. For the -22, that is not so, RCS control tactics and methodologies combined have a very high presence. Every area of the aircraft must be precisely calculated for its contribution to total RCS, from major structures like the wings down to the allowable panel gaps. If a panel is secured by 50 fasteners, the orientation of the fasteners' heads, when flushed with the panel, will be measured to see how much each fastener contribute to total RCS. If a certain orientation is found to have a certain percentage of lower contribution in terms of reflected radiation output, then all 50 fasteners will be oriented that way. Fortunately for Maintenance, such was not needed.

This is the level of attention to details that should be applied if the desire is to compete against American 'stealth' aircrafts. This is why even when within visual range (WVR), weapons systems have difficulties acquiring radar lock on it. By the time any radar can acquire lock on the -22, that seeking radar would be well within the -22's missile range. In combat, that seeking radar would be long dead before it can acquire the -22.

if heading angle is not straight then reflective surface on offer is more but dopular effect will be less..so detection will be early compared to straight heading but finding direction of heading, speed etc will be difficult..in the absence of data of speed the radar may reject it as a clutter..is that how it is ?

In essence...Yes.

When trying to acquire a low radar observable body, all factors must be considered. Not necessarily at the same time. The greater the deviation from head on, the lower the Doppler component. If the target is moving across the face, or across the radar view, then the Doppler component is effectively zero. This is essentially looking at the aircraft's side. But if the aircraft is deliberately designed to produce as little reflection as possible, then any reflection from this perspective may not be enough to compensate for the lack of Doppler.

 

[waz]

The tech discusion is great but the fact remains that the USAF has operated this aircraft for eight years now, and it had its first flight in 1997. The US constantly assess its performance and has an assurance process going that seeks to not only better the plane but also rid it of any fault/weaknesses it endures. No other plane has been through this and the two other fifth generations jets have yet to undergo this.

There really isn't a comparison.

 

[victor07]

Absolutely we do. A lot of it...

Thank you for the comprehensive answer and interesting links.
"Neither did the Soviets and that is why they let him published his work to the public."
Ufimtsev's work is from applied if not fundamental physics area, so nothing secret was in it. Nobody payed attention to this work probably because at that time (1963) there were some other points of view to the air tactics. Corresponding Russian research facilities using physical modeling approach are in 2-nd Central Scientific Research Institute and in JSC Radiofizika.
Can not publish links, so only by replacing '*' with '/' in the following.
old.vko.ru*article.asp?pr_sign=archive.2004.18.02
radiofizika.ru*gallery*cam*

 

[massattack]

If you have no experience then how can you make that declaration? Because Rachel Maddow said so? Is she any sort of 'aviation expert'? Where did she got her information? That hack piece Maddow did on the F-22 has been debunked simply because she did not know what she was talking about and did not live up to her due diligence as a journalist. Maddow is now more entertainer than journalist.

i agree with you.. what do you have to say about Pierre Sprey analysis regarding the jet? and why the heck has this jet not been used anywhere in actual battle scenario?