Fundamentals of Stealth Design & Concepts of RCS Reduction

[mil-avia]

About sixth-generation combat aircraft

 

[The SC]

These systems will themselves be detected before they can detect any 'stealth' attackers who are aware of their presence.

Not when they are in passive mode.

 

[gambit]

Not when they are in passive mode.

Then they cannot detect anything. Please do not even attempt to 'educate' me on this subject.

 

[The SC]

Then they cannot detect anything. Please do not even attempt to 'educate' me on this subject.

Passive detecting mode... in combination with decimeter and mm radars.
Not trying to educate you. Asking pertinent questions. if you do not know the answer just say so.

 

[gambit]

Passive detecting mode... in combination with decimeter and mm radars.
Not trying to educate you. Asking pertinent questions. if you do not know the answer just say so.

Radar detection is a TWO-PARTS process: Transmission and Reception.

The word 'passive' is misleading.

You can be 'passive' as in doing nothing, or you can be 'passive' as in waiting to do something. There is a great difference, not just in semantics but also in technicality. If you are 'turned off', then you are truly passive. Nothing coming your way will provoke anything from you. But if you are 'passive' because you are waiting for something -- anything -- then that make you a part of a process. You are waiting for an activation to your job, whatever it is. Your response could be automatic or it could be analytical, meaning you are allowed to analyze the provocation before you do something else. If I poke you with a needle, your response would be to flinch and cry 'Ow'. That is an automatic response from a passive/dormant state. If I am your boss and give you something to analyze before you act, then you are an analytical reception, meaning you examine the provocation to see if it fits certain criteria before you do your job.

In radar detection, there is no such beast as a 'passive radar'. There can be a receiver half of the radar detection process that contains a transmission half. But if there is no transmission to produce reflections, then there can be receiver half of that process, that mean there is no such thing as a 'passive radar'. So when someone use the phrase 'passive radar', he really mean the system is a functional receiver half of a radar system that contains a transmission half that is somewhere else. The provocation here is a reflection from an object. If there is no reflection, there will be no provocation to you to do your job. In this two-parts process, none is more important than the other because without one, the entire process does not work. So just because you -- the receiver -- is number two in a chain, that does not mean you are less important than the number one process in the chain: (1) Transmit => (2) Receive.

Getting back to your argument...

The chain goes this way:

Transmission => Reflection => Receiver.

If this long wavelengths system is passive, then who/what is the active ? Someone must be able to produce a provocation -- a reflection. Someone must transmit in order to produce a reflection, which is picked up by the receiver who then will analyze the signal and alert the humans that there is an aircraft out there. So if the Transmitter is actively transmitting, then the 'stealth' fighter can do exactly what I said, which is to detect the transmissions and go around them. Without the aircraft, there can be no reflections, which mean there will be provocation for the receiver, which mean the receiver will remain idle.

Or I can drop a bomb on the Transmitter and silent it for good, rendering the Receiver forever passive. If you are the Receiver half, how can you analyze anything ?

 

[The SC]

I was saying it can work in combination with other radars with different wavelengths, even in passive detection mode.
In general, when you hear radar passive mode, you know it is activated , call it half or quarter, it does not matter that much.
Radars today linked to computing systems can be programmed to be automatic on specific targets let's say with an RCS of less than 1 square meter. Also the program can be linked to other types of radars working on different wave lengths.
The Serbs downed the US stealth bomber by activating their radars for very short periods of times , alternately turning it on and off. So this not as easy as you try to depict it, it just cannot be targeted and destroyed by the stealth plane that easily, In fact the plane has more chance of being destroyed once it is detected.

 

[gambit]

I was saying it can work in combination with other radars with different wavelengths, even in passive detection mode.

You do not know what you are saying. You are just throwing words out there just to pretend you have a credible argument.

If a system is designed to be a dedicated passive receiver, then by destroying the transmitter companion, the entire set up is rendered useless. It does not matter if the system is designed to operate with different freqs or not.

In general, when you hear radar passive mode, you know it is activated , call it half or quarter, it does not matter that much.

Make no sense, and am not going to waste my time trying to figure it out.

Radars today linked to computing systems can be programmed to be automatic on specific targets let's say with an RCS of less than 1 square meter. Also the program can be linked to other types of radars working on different wave lengths.

Any body that is definitively determined to have an RCS of one meter squared (or less) is either guesstimated or definitively measured. In order to measure definitively, the EM background must be as low as possible so that the body can stand out and this is where an EM anechoic chamber comes into play. The vast majority of objects with claimed to have so-and-so RCS are guesstimated. Who can afford to spend at least a couple thousands $$$ to rent a sophisticated EM anechoic chamber to measure his car or his own body ? For what purpose ?

This lead up to the can of worms call 'clutter rejection threshold' which am certain you know nothing about. For most practical purposes, if a body is less than one meter/squared, it is lost in the clutter rejection threshold. Every radar system have a clutter rejection threshold and every radar system AUTOMATICALLY reject any signal that do not go higher than that threshold. If that threshold is lowered and lowered and lowered, then the system will be overwhelmed by so many targets that it would be worthless.

A passive receiver is not a solution because it has its own clutter rejection threshold. The transmitter does not have a clutter rejection threshold. Why ? Because it is a transmitter, not a receiver. So if the passive receiver have a threshold that AUTOMATICALLY reject any body with an RCS of one meter/squared, then the 'stealth' aircraft will NOT be detected. Lower that threshold to pass through any target that is one meter/squared and the screen will be filled, thereby still masking the 'stealth' fighter.

So the problem is this: Either you reject the 'stealth' aircraft from the start, or you detect everything but then everything will hide the 'stealth' fighter anyway.

Again...Please do not attempt to 'educate' me on this subject.

The Serbs downed the US stealth bomber by activating their radars for very short periods of times , alternately turning it on and off. So this not as easy as you try to depict it, it just cannot be targeted and destroyed by the stealth plane that easily, In fact the plane has more chance of being destroyed once it is detected.

We lost one F-117 out of hundreds of 'stealth' sorties. NATO flew over 30,000 sorties, including 60 B-2s from the US, and we lost only two aircrafts: One F-16 and one F-117.

So please leave the Serbs out of this.

 

[The SC]

You do not know what you are saying. You are just throwing words out there just to pretend you have a credible argument.

If a system is designed to be a dedicated passive receiver, then by destroying the transmitter companion, the entire set up is rendered useless. It does not matter if the system is designed to operate with different freqs or not.


Make no sense, and am not going to waste my time trying to figure it out.




Any body that is definitively determined to have an RCS of one meter squared (or less) is either guesstimated or definitively measured. In order to measure definitively, the EM background must be as low as possible so that the body can stand out and this is where an EM anechoic chamber comes into play. The vast majority of objects with claimed to have so-and-so RCS are guesstimated. Who can afford to spend at least a couple thousands $$$ to rent a sophisticated EM anechoic chamber to measure his car or his own body ? For what purpose ?

This lead up to the can of worms call 'clutter rejection threshold' which am certain you know nothing about. For most practical purposes, if a body is less than one meter/squared, it is lost in the clutter rejection threshold. Every radar system have a clutter rejection threshold and every radar system AUTOMATICALLY reject any signal that do not go higher than that threshold. If that threshold is lowered and lowered and lowered, then the system will be overwhelmed by so many targets that it would be worthless.

A passive receiver is not a solution because it has its own clutter rejection threshold. The transmitter does not have a clutter rejection threshold. Why ? Because it is a transmitter, not a receiver. So if the passive receiver have a threshold that AUTOMATICALLY reject any body with an RCS of one meter/squared, then the 'stealth' aircraft will NOT be detected. Lower that threshold to pass through any target that is one meter/squared and the screen will be filled, thereby still masking the 'stealth' fighter.

So the problem is this: Either you reject the 'stealth' aircraft from the start, or you detect everything but then everything will hide the 'stealth' fighter anyway.

Again...Please do not attempt to 'educate' me on this subject.




We lost one F-117 out of hundreds of 'stealth' sorties. NATO flew over 30,000 sorties, including 60 B-2s from the US, and we lost only two aircrafts: One F-16 and one F-117.

So please leave the Serbs out of this.

I think you are out of sound arguments, so you start throwing in anything you find around you. You do not know what I know or do not know, and you have completely missed the mark in your answers, showing how narrow is your knowledge.

 

[mil-avia]

Aviones invisibles / Invisible planes

 

[mil-avia]

How to design an 'invisible' aircraft

Airplanes Invisible to Radar

Invisible Planes: China, US Race for Cloaking Tech

Researchers Cracked How to Make 'Invisibility Cloaks' the Size of a Fighter Jet

Stealth: Researches discover key to making an invisible fighter jet

Why are Stealth aircraft invisible to enemy radar?

Is there technology in which makes the air craft fighters invisible just say stealth with transparent?

 

[gambit]

Is the Horten 229 the world's first 'stealth' aircraft ?

The Ho-229 is often falsely attributed to be the world's first 'stealth' aircraft based upon equally false logic. Those who made such attribution do so, not out of any genuine technical understanding of even basic radar detection, let alone the tactical aspects of the same, but more out of simple petty jealousy: That the US is the first aviation power to field a fleet of operational 'stealth' combat aircrafts.

Basic radar detection comprise of two equally important elements: Transmission and Reception.

Without either element, there can be no radar detection. That said, when a body is inside a radar beam, or as many engineeers in the radar field would use the phrase 'radar bombardment', there is what is called 'radar observability'. With anything being observable, inevitably there are degrees of that body being perceived, and equally inevitable are the questions of and about factors that affects how that body is perceived by sensors. An analogy is that of how fog impairs visual perceptions and that impairment depends on the locations of the observers/sensors. Of course, the physically closer the observer is to the object, the less the impairment. Basically, fog is water droplets and/or very tiny ice crystals suspended in air and bends light waves, thereby distorting how objects are perceived in the visible light spectrum, and if the fog is dense enough, the distortion will be severe enough, and objects cannot be perceived at all. When a solid body reflects a medium such as an electromagnetic (EM) wave, temporarily that body is a transmitter. If the EM wave is in the visible spectrum, then the sensors can be biological such as the eye. The result: Transmission and Reception.

So what exactly is 'stealth' ? The popular conception is that 'stealth' equals to invisibility to radar, which is completely wrong according to those in the radar industry in general, let alone to those specifically in the defense industry. Simply put: In radar detection , NOTHING is invisible. If a body reflects, no matter how minute, those reflected signals can be received, and if they can be received, those signals can be processed into viewable forms. The distances in which those signals can be received varies according to signal energy levels. The higher the energy level, the greater the distance in which the signals can be received. From that perspective, a body under radar bombardment will have 'radar observability', meaning the body can be detected via EM wave processing.

The question remains: What exactly is 'stealth' ? Flying to avoid radar detection nets is, in a manner of speaking, 'stealth'. To NOT be under radar bombardment is to NOT reflects, and if the aircraft does not reflects, it cannot be under radar processing. So broadly speaking, 'stealth' simply means whatever means necessary to avoid radar detection. An aircraft can skirt radar nets by navigating around them in all 3 spatial axes. The most common tactic is to fly at an altitude below the seeking radar's scan altitude limit. So from this persepctive, the F-111 is a 'stealth' aircraft. Radar avoidance is a 'stealthy' tactic where the tactic places foremost the danger of radar detection in the flight calculus.

But what if the aircraft cannot employ radar avoidance tactics ? Obviously, the seeking radar is an adversary and not under one's control. The 'stealthy' solution is not in short term and situational tactic like 'flying below the radar' but to affect the aircraft's physical characteristics that responds to stimuli -- EM radiation. It is a technical tactic and because it is inherent into the aircraft itself, the tactic is long term and applicable to all situations where there are active radars.

The phrase 'low radar observability' stipulate three conditions:

- That the aircraft reflects EM radiation.
- That those reflected signals are measured.
- That those reflected signals are under a threshold.

It is given that all bodies reflects, but whether the reflected signals are measured is a matter of technical expertise.

FACT -- The Ho-229 was never under controlled radar bombardment and reflected signals measured.

The current record have three -229 aircrafts constructed for flight testing. One prototype crashed due to an engine mishap in its third test flight. One prototype damaged on landing due to too soon brake parachute deployment. The third prototype was under assembly when it was captured by the US. There is no record of any of the prototypes undergone controlled radar bombardment for cross section measurement.

FACT -- The Ho-229 being constructed of wood is irrelevant.

The de Haviland Mosquito was constructed of wood and its combat successes earned it the nickname 'The Timber Terror'. If material alone qualifies the -229 as a 'stealth' aircraft, then why not the Mosquito ? The reality and truth is that in aviation, weight is a penalty, and wood served the Horten Brothers' plan for a long range bomber that could make a Trans-Atlantic flight from Europe to the Americas, specifically to the United States. Wood was irrelevant, or at best a side interest, for the brothers when it comes to radar detection vulnerability. Wood was used because weight was the highest consideration.

FACT -- The flying wing design is not new.

Powered flight started at the start of the 20th century with the Wright Flyer in 1902 and by 1915 a powered all-wing design was at least theorized by all the world's major aviation pioneers, which included American Jack Northrop who had a flying wing model by the 1930s. The primary reasons for the attention on the flying wing design were its low drag and long range characteristics, not its any alleged low radar observability value.

Conlusion..

The logical error is apparent to those who are willing to exercise critical thinking. Just because modern day technology enabled a great deal of details on how an aircraft responds under radar bombardment, that does not mean the Horten Brothers made a great technological leap even deep insight back in WW II with their flying wing design. The brothers use of ferrite particles in the -229's design was merely a hope that the doping would affect reflectivity, but unless there were actual measurement data, there is no credibility in the claim that the -229 was as deliberately designed as the F-117 and later American 'stealth' aircrafts were so designed. Compare to conventional fuselage plus prominent flight control structures designs, the flying wing does exhibit much lower radar reflectivity, but unless the Horten Brothers had strict radar measurement regimes on the flying wing versus conventional designs, even as crude as radar technology was in WW II, it does not stand to reason that the -229 was a deliberate attempt to employ low radar observability tactic.

An aircraft maybe incidentally low radar observable, but in radar detection, the sphere is the standard for measurement. The sphere reflects the same quatity and energy level from all aspects. The sphere is a natural shape and naturally low radar observable. Part of what make an aircraft, a non-natural body, 'stealthy' is the intention to make the aircraft as low reflective as possible, which make measurement a non-replaceable component in the low radar observability triad. Non-replaceable also mean the component cannot be substitute with anything else.

This is essentially what the Horten Brothers did:

- That the -229 reflects EM radiation.
- Hope that the -229 will be missed by Britain's radar nets.

If the American 'stealth' fighter program came from the Nazis, as many charged, then why did the F-117 looks nothing like the -229 ? The truth is that if credit is to be shared, then the American 'stealth' aircraft program will share the credit with Russian mathematician Pyotor Ufimtsev, who formalized the behaviors of reflected waves off surfaces, not with the Horten Brothers who due to misfortunes of war never had the chance to see their creation into full fruition. Ufimtsev's math finally made measurements controlled and detailed, especially of complex bodies, and the only hope lies inside the engineers who hoped they have programmed their computers correctly in the complex calculations.

The F-117 is truly the world's first low radar observable aircraft. It met all the necessary criteria, from intent to design to measurement to verification to finally combat, the ultimate verifier.

 

[zahidiqbalrana]

I think now its time to replace with UAVs.. less collateral damages.

 

[Taygibay]

We lost one F-117 out of hundreds of 'stealth' sorties.

And it wasn't lost due to lacks in its stealth functions, BTW.
A mistake was made by command in allowing almost identical ingress flight paths repeatedly.
The plane was spotted once by eyesight and later geo-located by radio, triangulated if you will.
If the flight paths had been changed as per logic and rules, this would not have happened.
So human error, no deficiency in stealth characteristics?

Just sayin' Tay.

 

[mil-avia]

Is it time for a low-cost stealth fighter? Why air arms won’t see sense

 

[mil-avia]

Stealth and anti-stealth technology arms race