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Chengdu J-10 Multirole Fighter Air Craft News & Discussions

>>>For this answer you must think in geometric terms because we are talking about radar deflection on certain physical planes (I wish I could draw this out but I will do my best to describe it instead). The design of a faceted airframe drastically reduces the number of specular directions from which large echoes are observed but this faceting creates a multiple of ''edges''. The scattering of radar signatures then is spread over the shape of a cone. When viewed from a normal incidence, the ''edge'' collapses to a disk and the intensity can be strong enough to be picked up by even relatively weak radar. Even if you manage to angle a surface so that the surface is never seen from a direction anywhere near the direction of its ''surface normal'', there still may be an edge with a large number of of specular directions spread over a plane perpendicular to the edge. So even though aviation manufacturers may rely on shaping to direct a specular surface reflection away from the radar, they must also rely on shaping to direct edge scattering away from radar. This means you choose the sweep angle of the wing to direct the edge diffraction out of the threat cone, which is usually centered on the direction of flight.

The only part of the frontal wing area that contributes to refelection is the space between slats... And then we talk about certain slats angles... You can add angles in the space between the slats to that to avoid it. The F22 has a good example how to do that. There is no impact for x degrees or more... Any fighterjet has sweep in its wing unless you talk about ww2 era... And even those have minor radar reflection if you take the wing. Just in case we do not have the same idea... RCS is often only the frontal section. So we talking about head on. If you talk about above or lower then you just might think about curving but it will have lots of impact on your weight cause making that stiff enough will cost you enough headache. Since you talk about sweep I guess you are talking about frontal area... I am looking forward to a drawing cause sofar there is no reason for me to change practice or theory.



>>>No arguments here, this is why I stated the key is in RCS reduction though nothing wrong with having the capability on your side when **** hits the fan.

If you have something like F22 and even then the plane is nothing without superb network of sats and radar. There is no **** that comes from India. They had some with Mig25 but if they had something like that now we would sit in bunkers in Islamabad. Don't go overestimating everyone... One side you talk about getting Mirage 2000 and the other side you think that even JSF is not good enough.


>>>If your AWACS goes offline in a variety of conceivable scenarios, it will not have dire consequences for the entire fleet if your top tier fighter aircraft have powerful AESA radars. Our AWACS should be used to direct the Thunder and F-16 among various others and that in itself is more than 300 aircraft being directed by a handful of AWACS platforms.

Do you think that anyone would add an awacs that could go offline? The AESA is not a magic stick... At the moment you are talking about development and not active. The power of awacs depend on size and computing power (often even related to cooling power). Good luck in adding something good enough is a "light" fighter. And just in cast you do not know... The radar is not that cheap that you would go for 100+... Otherwise everyone would have one.

Just for fun... Do you have technical or airforce background? Not to irritate you but I miss often facts in your theories.
 
The only part of the frontal wing area that contributes to refelection is the space between slats... And then we talk about certain slats angles... You can add angles in the space between the slats to that to avoid it. The F22 has a good example how to do that. There is no impact for x degrees or more... Any fighterjet has sweep in its wing unless you talk about ww2 era... And even those have minor radar reflection if you take the wing. Just in case we do not have the same idea... RCS is often only the frontal section. So we talking about head on. If you talk about above or lower then you just might think about curving but it will have lots of impact on your weight cause making that stiff enough will cost you enough headache. Since you talk about sweep I guess you are talking about frontal area... I am looking forward to a drawing cause sofar there is no reason for me to change practice or theory.

I think I have lost you.


Don't go overestimating everyone... One side you talk about getting Mirage 2000 and the other side you think that even JSF is not good enough.

I've never participated in the Mirage 2000 thread and this thread is about FC-20 not JSF which I have never mentioned before, so I guess you are pulling facts out of the air again.



Not to irritate you but I miss often facts in your theories.

What a coincidence! I often have the same problem reading your posts.
 
The I ask you to draw how you would explain that the frontal RCS is lower if the wing is more sweeped... Can't be that difficult cause you say that you know the facts. And if you could earn a few thanks then that would be an extra, wouldn't it?

So let us draw a frontal wing area... One is sweeped 30 degrees and the other 45 degrees... You are using a radar that is located in front of the plane... How much waves will be able to return to you dish? You can use any type of radar...
 
The I ask you to draw how you would explain that the frontal RCS is lower if the wing is more sweeped...

I will kindly re-state :

The scattering of radar signatures from the edges of a faceted surface (wing of an airplane in this case) is spread over the shape of a cone. This means you choose the sweep angle of the wing to direct the edge diffraction out of the threat cone. The more swept at a certain angle the less discernable clutter from these edges of the wing.
 
I do not think that more swept wing has lower rcs... Looking forward to get the theory on this...

About supersonic high agility... You can skip that in a nation with zero depth and where agility in subsonic speed and low altitude is far more important then mach 2 and a few g's...

About AESA... Nice to have on AWACS or ground but a fighter based AESA is hardly worth the extra costs. Netcentric is a solution. AWACS is a superb asset. For the rest AESA is at the moment not much wore worth then the normal dish...


Munir Sahib,

For head-on detection (frontal) - the more sweep a wing has, the less the detectability (or in other words lower RCS).

This has to do with scattering of reflecting radar waves. By have more sweep, you move the 'cone' of these reflected waves away from the emitting radar wave source.

For further details, including diagrams you may refer to the book "Aircraft design" by Jan Roskam page 142. You can preview the book (including the page referred to) on google books for free.


Do you think that anyone would add an awacs that could go offline? The AESA is not a magic stick... At the moment you are talking about development and not active. The power of awacs depend on size and computing power (often even related to cooling power). Good luck in adding something good enough is a "light" fighter. And just in cast you do not know... The radar is not that cheap that you would go for 100+... Otherwise everyone would have one.

True AWACS are not added for going offline, but in a war you don't want to end up in a situation where the enemy can shoot down your AWACS and you have nothing as a back-up.

Secondly, for offensive strike mission you will not have the support of AWACS. In such a scenario, it it will be wise for one or two of your striking unit to be equipped with a long range very powerful AESA Radar and be data-linked with the others to act as a mini-AWACS. Kind of what was missing in Cope India where the US had practiced 1:3 numerical deficiency with atleast 2 of their F-15 having a long range AESA radar. In Cope India, these radars were lacking and we all know what happened.

In my humble opinion, having very powerful AESA radars on 2-3 squadrons of FC-20 would be very handy both in strike mission as well as acting like a 'mini-AWACS' despite the cost involved. Hopefully, by the timeline (2014-15), China will have a functioning, tested and reliable AESA radar.
 
The I ask you to draw how you would explain that the frontal RCS is lower if the wing is more sweeped... Can't be that difficult cause you say that you know the facts. And if you could earn a few thanks then that would be an extra, wouldn't it?

So let us draw a frontal wing area... One is sweeped 30 degrees and the other 45 degrees... You are using a radar that is located in front of the plane... How much waves will be able to return to you dish? You can use any type of radar...

Try the attached file, it will help.
 
Try the attached file, it will help.

So as can be seen on the provided info none of the original waves returns to the receiver... And often people tend to think that wing contributes a lot to RCS... It is more the intake, the sensors, the canopy... Only if the slats are made of "composite" that do not reflect radar then the nextr layer is thick enough to do that... If something is printed doesn't mean that it is correct.

About the provided info... I am more intrested in these kind of info then the basic.

Fundamentals of EM waves

Electromagnetic (EM) waves are created by time-varying currents and charges. Their interactions with materials obey the boundary conditions of Maxwell’s equations. EM waves can be guided by structures (transmission lines) or by free space. An antenna is a material structure that directs EM fields from a source into space, or, by reciprocity, from space to a receiver. The shape and size of the antenna controls the transition from the near field to the far field.

The near field consists of the reactive near field, also known as the quasi-static near field, and the radiating near field also known as the Fresnel zone or Fresnel region. In the quasi-static near field we see fields that strongly resemble the electrostatic fields of a charge dipole for a dipole antenna and the fields of a magnetic dipole for a loop antenna. In large antennas the quasi-static field can be seen near edges.

In the Fresnel zone the waves are clearly not plane and may have phase shifts that do not vary linearly with distance from a (fictitious) phase center.

From the near field to the far field, EM radiation changes from spherical waves to plane waves. The far-field is sometimes called the Fraunhoffer region.

Common to all electrically small (less than a wavelength) antennas is that the near field excites the environment in which the antenna resides. It’s the antenna combined with its environment that radiates EM waves. Electrically small antennas include:

Before tackling the near field, it’s best to understand the behavior of the far field. Far from the source, the spherical EM waves flatten out and can be treated like plane waves. The power density is given by:

Ptransmitted/Area spread out = W/m2

In the far field, E-field and H-field are proportional to 1/radius. The Poynting vector (power/area) is given by E x H. Therefore, power density drops as 1/radius2.

Electrically large antennas are good sources of plane waves in the laboratory. A large antenna focuses the power, this is called directivity, or directive gain.

The antenna creates a large (D>>) area of electromagnetic field, with nearly uniform phase.

Then you go into more about reflections of radar beams...

An absorber with –12 dB return loss allows the scatterer to get twice as close to the radar before being detected, compared to an object with 0 dB return loss.

Radar cross-section is dominated by shape, because it's the shape that governs how much of the incident power is captured and sent back, as illustrated in the three examples below, where the objects are assumed to be large compared to the incident wavelength. For a cylinder, the reflected signal is proportional to 1/lamda. On the right is a sphere, which also reflects back a signal proportional to the radius of the sphere (and not a function of wavelength).

Orientation of the shape is critical. The worst case when the wave is incident perpendicular to a flat part of the surface, which results in specular reflection. Canting the surfaces redirects this echo.

Beware of "corner reflectors" when you are designing for low radar cross-section, as shown below. Inside corners can increase your radar cross-section much more than you'd imagine.

If the specular echo is redirected, the remainder is the next greatest contributor to radar cross-section. It is due to diffraction, which is caused by discontinuities of the surface. Discontinuities imply a change in the boundary conditions; and boundary conditions are what govern the distribution of the fields in the first place. Metals at radio frequency behave nearly like perfect electric conductors (PECs). This invokes a well-known boundary condition of Maxwell's equations: the tangential E-field must go to zero on the surface of a conductor.

Where did the energy go if total ETE =>0? It goes into the H-field:

On metal surfaces, E total is always perpendicular to the surface, and H total is parallel to the surface. On the shadow side the E-field attaches and travels along the surface at the speed of light. Equal and opposite charges created at the leading edge create almost no scatter. On the illuminated side we get a running (traveling) wave consisting of incident and reflected waves until it runs out of surface. Then it scatters strongly.

V-Pol, TM incidence on wing

For horizontal polarization (H-pol) it is the leading edge of an object such as of an aircraft wing that scatters strongly. The leading edge gets a very strong current induced in it whose job is to create the wave that exactly cancels the E field tangential to the metal. Clearly the radar cross-section reduction job is different for leading edges and trailing edges. Because Etotal = 0, there is no significant diffraction off the trailing edge.


I do not mind that you guys have a different opinion and it is good to have these kind of more technical discussions. As an engineer we know what to see as valuable informaton. As an engineer you need to think beyond the crap posted by journalists. The copy pasted text above pretty much explains why the theory of wingsweep is hardly worth to be seen as correct. It depends on other more complex factors. It depends on beam theory and how certain materials behave when being beamed... Maybe you know understand that some composites are nice to have when you want weight reduction but they are pain in the a when you need lower RCS...

I am not intrested in more thanks. Just trying to contribute.
 
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I don't know whether this was posted before, anyway i've posted it here.

Changes look good but an expert eye will know what effects they will actually have on the fighter capabilities, not me.:enjoy:

J-10AB.jpg
 
Is there any effect of DSI on maximum payload ?:coffee:
 
so can someone tell me if this improvement on j-10 is real or only a dream of chinese fanboys??? please
 

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