J-20 Radar Scattering Simulation

[Metal 0-1]

Introduction​

J-20 is the world’s third operational fifth-generation stealth fighter aircraft after the F-22 and F-35. It made China the second country in the world after the USA to operate a fleet of stealth fighter. By the time this article is published, it is estimate that there are around 208 J-20 produced.

Goals of the simulation:​

The aim of our simulation is to evaluate the mean and median radar cross section as well as the radar scattering pattern of the J-20 at 4 frequencies:

• VHF – 150 MHz
• L Band – 1150 MHz
• S Band – 3150 MHz
• X Band – 8150 MHz

.Because stealth aircraft tend to deflect radar signal away from the source, so a change in total arcs can have a big impact on median and mean RCS. So the mean and median RCS of J-20 will be simulated and calculated for 2 cases with different frontal arcs value.

• Case 1 simulates situation when the stealth aircraft have to face multiple radars located far from each others, thus they can illuminate the fighter from directions where the strong reflection lobes located
• Case 2 simulates situation when aircraft face small number of radars located close together so the stealth fighter can turn its nose toward targets

The details are in the following table:

Note: The contour map results for Case 2 is actually a part of Case 1 contour map, but it will be shown separately so that viewer can have an easier time visualize the radar lobes arrangement and how direction affect stealth fighter RCS.

Explanation of some terms:​

Median RCS is the middle RCS value of all RCS data. Which mean 50% of RCS spike inside the arcs will be higher than the median value, and the others 50% of RCS spike inside the arcs will be smaller than the median value

Mean RCS is the average of all RCS data.
It is very important to remember that both Median and Mean RCS does not tell the whole story, two object with the same Median and Mean RCS does not necessary equally visible to radar when viewed from the same direction ,thus we also need the contour map to see the arrangement of the reflection lobes.

RCS value illustrated inside the contour map will be measured in dBsm. To convert RCS between dBsm and m2, we can use the following guidance.

CONVERTING RADAR CROSS SECTION IN SQUARE METERS TO DECIBELS​

dBsm = 10 x log10(RCS/1m2)

CONVERTING RADAR CROSS SECTION IN DECIBELS TO SQUARE METERS​

RCS = 10(Decibels/10)

Basics Rules:​

Because not every information about J-20 is available in the public sectors, we will follow several rules in the simulation.

• In real life, J-20 skin has a layer of radar absorbing material (RAM) to absorbing radar energy. However, in this simulation, all external surface including the canopy will be treated as perfect electrical conductor (meaning they will reflect radio wave like metal)
• Stealth fighter will have trailing edge and leading edge treatment on its wings, horizontal and vertical stabilizers as well as inlet lips to reduce the magnitude of radar return from edge scattering and creeping wave return effect. But those effect were not added in our previous simulation for F-35 and Su-57 because there wasn’t enough information about their leading and trailing edge treatment. However, this time, the trailing edge treatment on the canard and main wing of J-20 in the form of edge serration will be simulated because they are very easily to identify visually
• J-20 radome is a FSS radome, so it will be treated as perfect electrical conductor for all frequencies except the bandpass frequency
• Luneburg lens which often used to increase stealth aircraft’s RCS will not be included in this simulation
• All cooling vents will be modeled
• The inlet , the radar blocker and the first 2 fan stages of 2 × WS-10C engine will be modeled
• Even though there is no current data on the absorbing capability of the RAM used by J-20. The inner surface of the inlet duct from the start of DSI bump leading to the engine stages and the radar blocker will be coated with a layer of MnZn ferrite RAM. This rule is made due to the fact that it is not possible to evaluate the RCS reduction effect of S-duct inlet without a layer of RAM added. The absorbing capability of the MnZn RAM will be based on actual real world measurement data. The current absorbing capability of the RAM used in our simulation is around -8 dB at 8.15 GHz and -4 dBsm at 3.15 GHz. Keep in mind though that actual RAM used on stealth aircraft may have absorbing rating of -15 to -25 dB depend on the actual frequency.

Software used:​

• Model of the J-20 is created using SolidWorks software, the model of the Infrared pod (Chinese EOTS) is created by Autodesk FBX. They are then converted to the same format to be added together.
• In most studies, radar scattering simulations are often done using POFACETS because it can run on most commercially available computer and provides convenient run–times. Unfortunately because POFACETS only rely on Physical Optics method to predict the RCS of target. As a result, it cannot take into account phenomena such as creeping waves return, thus lead to underestimation of target RCS value. Hence this radar scattering simulation will be done using Ansys HFSS. HFSS allows edge scattering, creeping wave, cavity return to be simulated accurately, thus it will be our chosen software.

Model photos:

OUTSIDE:

Top view

Side view

Bottom View

Head on view

Tail on view

SMALL PARTS AND REFERENCE IMAGES

EOTS window and pitot tube

​

​

Canard root hump and antenna hump​

Wing actuator humps and small humps near ventral fins

Humps on LERX, and belly DAS sensor

 

[Riz]

Tremendous achievement china , hope pak will get these birds after china getting its hands on 6th generation aircraft

 

[Metal 0-1]

Trailing edge serration treatment on main wing and canards

INTERNAL PARTS – S-duct Inlet and engine

Contour Map Result

• VHF band result of clean J-20 in Case 1 (-60° to +60° horizontal arc, -22° to +22° vertical arc)

• VHF band result of clean J-20 in Case 2 (-20° to +20° horizontal arc, -20° to +20° vertical arc)

• L-band result of clean J-20 in Case 1 (-60° to +60° horizontal arc, -22° to +22° vertical arc)

• L-band result of clean J-20 in Case 2 (-20° to +20° horizontal arc, -20° to +20° vertical arc)

• S-band result of clean J-20 in Case 1 (-60° to +60° horizontal arc, -22° to +22° vertical arc)

• S-band result of clean J-20 in Case 2 (-20° to +20° horizontal arc, -20° to +20° vertical arc)

• X-band result of clean J-20 in Case 1 (-60° to +60° horizontal arc, -22° to +22° vertical arc)

• X-band result of clean J-20 in Case 2 (-20° to +20° horizontal arc, -20° to +20° vertical arc)

3D Maps Result:

• VHF band result of clean J-20

• L-band result of clean J-20

• S-band result of clean J-20

 

[Metal 0-1]

• X-band result of clean J-20

SUMMARY:

From the simulation results, it is easy to note that J-20 has good signature characteristic. Even though, J-20 RCS is higher than F-35A RCS through the frequency range (approximately 3.5 times in X-band, 1.5 times in VHF band), it still has much better RCS characteristic when compared to Su-57. The canard return blended very well with the main wing return, and due to their high swept angle, the first high RCS spike of J-20 actually located at around 50 degrees boresight. This mean it is very easy for J-20 pilots to keep enemy adversary within their stealthy sector. Add to the fact that J-20 has very big antenna aperture, it can be highly lethal in BVR combat.

J-20 Radar scattering simulation

Introduction J-20 is the world’s third operational fifth-generation stealth fighter aircraft after the F-22 and F-35. It made China the second country in the world af…

basicsaboutaerodynamicsandavionics.wordpress.com

Source

Tremendous achievement china , hope pak will get these birds after china getting its hands on 6th generation aircraft

Could had a nice consistent thread. But no. You had to poke your freaking nose in there.

 

[m52k85]

Whats the source of this study? Looks pretty comprehensive.

 

[Horse_Rider]

ntroduction​

J-20 is the world’s third operational fifth-generation stealth fighter aircraft after the F-22 and F-35. It made China the second country in the world after the USA to operate a fleet of stealth fighter. By the time this article is published, it is estimate that there are around 208 J-20 produced.

Goals of the simulation:​

The aim of our simulation is to evaluate the mean and median radar cross section as well as the radar scattering pattern of the J-20 at 4 frequencies:

• VHF – 150 MHz
• L Band – 1150 MHz
• S Band – 3150 MHz
• X Band – 8150 MHz

.Because stealth aircraft tend to deflect radar signal away from the source, so a change in total arcs can have a big impact on median and mean RCS. So the mean and median RCS of J-20 will be simulated and calculated for 2 cases with different frontal arcs value.

• Case 1 simulates situation when the stealth aircraft have to face multiple radars located far from each others, thus they can illuminate the fighter from directions where the strong reflection lobes located
• Case 2 simulates situation when aircraft face small number of radars located close together so the stealth fighter can turn its nose toward targets

The details are in the following table:

Note: The contour map results for Case 2 is actually a part of Case 1 contour map, but it will be shown separately so that viewer can have an easier time visualize the radar lobes arrangement and how direction affect stealth fighter RCS.

Explanation of some terms:​

Median RCS is the middle RCS value of all RCS data. Which mean 50% of RCS spike inside the arcs will be higher than the median value, and the others 50% of RCS spike inside the arcs will be smaller than the median value

Mean RCS is the average of all RCS data.
It is very important to remember that both Median and Mean RCS does not tell the whole story, two object with the same Median and Mean RCS does not necessary equally visible to radar when viewed from the same direction ,thus we also need the contour map to see the arrangement of the reflection lobes.

RCS value illustrated inside the contour map will be measured in dBsm. To convert RCS between dBsm and m2, we can use the following guidance.

CONVERTING RADAR CROSS SECTION IN SQUARE METERS TO DECIBELS​

CONVERTING RADAR CROSS SECTION IN DECIBELS TO SQUARE METERS​

Basics Rules:​

Because not every information about J-20 is available in the public sectors, we will follow several rules in the simulation.

• In real life, J-20 skin has a layer of radar absorbing material (RAM) to absorbing radar energy. However, in this simulation, all external surface including the canopy will be treated as perfect electrical conductor (meaning they will reflect radio wave like metal)
• Stealth fighter will have trailing edge and leading edge treatment on its wings, horizontal and vertical stabilizers as well as inlet lips to reduce the magnitude of radar return from edge scattering and creeping wave return effect. But those effect were not added in our previous simulation for F-35 and Su-57 because there wasn’t enough information about their leading and trailing edge treatment. However, this time, the trailing edge treatment on the canard and main wing of J-20 in the form of edge serration will be simulated because they are very easily to identify visually
• J-20 radome is a FSS radome, so it will be treated as perfect electrical conductor for all frequencies except the bandpass frequency
• Luneburg lens which often used to increase stealth aircraft’s RCS will not be included in this simulation
• All cooling vents will be modeled
• The inlet , the radar blocker and the first 2 fan stages of 2 × WS-10C engine will be modeled
• Even though there is no current data on the absorbing capability of the RAM used by J-20. The inner surface of the inlet duct from the start of DSI bump leading to the engine stages and the radar blocker will be coated with a layer of MnZn ferrite RAM. This rule is made due to the fact that it is not possible to evaluate the RCS reduction effect of S-duct inlet without a layer of RAM added. The absorbing capability of the MnZn RAM will be based on actual real world measurement data. The current absorbing capability of the RAM used in our simulation is around -8 dB at 8.15 GHz and -4 dBsm at 3.15 GHz. Keep in mind though that actual RAM used on stealth aircraft may have absorbing rating of -15 to -25 dB depend on the actual frequency.

Software used:​

• Model of the J-20 is created using SolidWorks software, the model of the Infrared pod (Chinese EOTS) is created by Autodesk FBX. They are then converted to the same format to be added together.
• In most studies, radar scattering simulations are often done using POFACETS because it can run on most commercially available computer and provides convenient run–times. Unfortunately because POFACETS only rely on Physical Optics method to predict the RCS of target. As a result, it cannot take into account phenomena such as creeping waves return, thus lead to underestimation of target RCS value. Hence this radar scattering simulation will be done using Ansys HFSS. HFSS allows edge scattering, creeping wave, cavity return to be simulated accurately, thus it will be our chosen software.

Model photos:

OUTSIDE:

Top view

Side view

Bottom View

Head on view

Tail on view

SMALL PARTS AND REFERENCE IMAGES

EOTS window and pitot tube

​

​

Canard root hump and antenna hump​

Wing actuator humps and small humps near ventral fins

Humps on LERX, and belly DAS sensor

Looks like it's Frontal RCS is more than others. What's the rear? I couldn't find a sheet. I'm making this statement based on the wavelengths depicted in the images.

J-20 Radar scattering simulation

Introduction J-20 is the world’s third operational fifth-generation stealth fighter aircraft after the F-22 and F-35. It made China the second country in the world af…

basicsaboutaerodynamicsandavionics.wordpress.com

Source


Could had a nice consistent thread. But no. You had to poke your freaking nose in their.

I saw the excel, thank you. This was VERY informative. What's the REAR cross section? I always knew that it would have a bigger frontal RCS especially due to canard configuration. They gained some aerodynamic agility but made a bigger RCS. They could've achieved the agility with 2D TVC.

And yes, he's poking his nose in every thread, derailing them with hit PTI political agenda insulting our military. People like this need to be managed so they won't post such propaganda and hate against institutions.

 

[Metal 0-1]

Whats the source of this study? Looks pretty comprehensive.

Open the link

 

[m52k85]

Open the link

Thanks read it in detail.

Now the take away seems to be the J-20 sits somewhere between the F-35 and RCS reduced 4.5 gen planes (all in frontal aspect and x-band).

Official sources say the F-35 is in 10^-2 range (golf ball size). The linked website puts the number for F-35 at 0.06m2 - keep in mind they dont model material properties (e.g. RAM).

We don't know what the chinese claim the RCS of J-20 is but the simulation puts the same number at 0.21m2 - so if we apply the same RAM improvement as the F-35 we reach a number of 0.035 to 0.02 m2.

Ofcourse, this is all back of the envelop.

 

[ozranger]

https://twitter.com/x/status/1602989207194308608

 

[MajesticPug]

This seems like an excellent work, given that the RAM is unknown. Though I'm not an expert to judge the work, the RAM if known could change the RCS readings.

 

[siegecrossbow]

Looks like it's Frontal RCS is more than others. What's the rear? I couldn't find a sheet. I'm making this statement based on the wavelengths depicted in the images.




I saw the excel, thank you. This was VERY informative. What's the REAR cross section? I always knew that it would have a bigger frontal RCS especially due to canard configuration. They gained some aerodynamic agility but made a bigger RCS. They could've achieved the agility with 2D TVC.

And yes, he's poking his nose in every thread, derailing them with hit PTI political agenda insulting our military. People like this need to be managed so they won't post such propaganda and hate against institutions.

Dude did you read the summary?

SUMMARY:

From the simulation results, it is easy to note that J-20 has good signature characteristic. Even though, J-20 RCS is higher than F-35A RCS through the frequency range (approximately 3.5 times in X-band, 1.5 times in VHF band), it still has much better RCS characteristic when compared to Su-57. The canard return blended very well with the main wing return, and due to their high swept angle, the first high RCS spike of J-20 actually located at around 50 degrees boresight. This mean it is very easy for J-20 pilots to keep enemy adversary within their stealthy sector. Add to the fact that J-20 has very big antenna aperture, it can be highly lethal in BVR combat.

 

[Horse_Rider]

Dude did you read the summary?

No, I went directly to images. I have some background in that area so you always take a look at the details to find the devil..... The devil is always in details. I read his summary later, after I posted the message. I wanted to tell him about another software that's better than POFACETS he used, but will respond to him sometime.

 

[S10]

Thanks read it in detail.

Now the take away seems to be the J-20 sits somewhere between the F-35 and RCS reduced 4.5 gen planes (all in frontal aspect and x-band).

Official sources say the F-35 is in 10^-2 range (golf ball size). The linked website puts the number for F-35 at 0.06m2 - keep in mind they dont model material properties (e.g. RAM).

We don't know what the chinese claim the RCS of J-20 is but the simulation puts the same number at 0.21m2 - so if we apply the same RAM improvement as the F-35 we reach a number of 0.035 to 0.02 m2.

Ofcourse, this is all back of the envelop.

From PLA official requirement at the time when the program was still called J-XX, 0.1m^2 to 0.05m^2 frontal RCS was the goal. Both SAC and CAC designs were able to achieve this.

 

[SQ8]

So in conclusion - the J-20 is still worse off in RCS than the F-22 designed some 33 years ago and the F-35 designed some 20 years ago.

But, they do have some advantages in larger aperture options and in case of J-20 better transonic acceleration

 

[Horse_Rider]

So in conclusion - the J-20 is still worse off in RCS than the F-22 designed some 33 years ago and the F-35 designed some 20 years ago.

But, they do have some advantages in larger aperture options and in case of J-20 better transonic acceleration

I think the reason for that is when the Chinese designed this thing, they weren't sure of their engine tech's advancement. So they gave up some RCS / stealth on frontal due to canards to achieve agility. If I was to design it, I'd have used 2D TVC in achieving the agility. This option rarely is used, primarily in a dog fight for pointing the nose towards the opponent.