Lockheed Martin F-35 Lightning and F-22 'Raptor' : News & Discussion

[AbRaj]

I believe all of these aircraft are whatever these things claim until they are in combat load with weapons and pods then it's a shitshow.

But then combat load is highly variable parameter, so only Fighters with internal weapon bays can have uniform RCS and can mention it in simple form.
Gripen, F16 or Rafale are not expected to be LO/VLO while hanging dumb bombs,LGBs and other larger payloads required in various combat missions.

 

[zinswinsin]

But then combat load is highly variable parameter, so only Fighters with internal weapon bays can have uniform RCS and can mention it in simple form.
Gripen, F16 or Rafale are not expected to be LO/VLO while hanging dumb bombs,LGBs and other larger payloads required in various combat missions.

Heh, most aircraft are not expected to be LO/VLO in combat gear except the Rafale :O Active cancellation for the win.

 

[randomradio]

But then combat load is highly variable parameter, so only Fighters with internal weapon bays can have uniform RCS and can mention it in simple form.
Gripen, F16 or Rafale are not expected to be LO/VLO while hanging dumb bombs,LGBs and other larger payloads required in various combat missions.

It depends.

In A2A role, the RCS can be controlled by using missiles that have low RCS themselves. Like the ASRAAM has a lower RCS than the Eurocanards and won't contribute anything to the aircraft's RCS. Tanks have low RCS as well. The Meteor too has a very low RCS, with its shaped inlets and small fins. The ejector racks can also have low signature shaping. When it comes to modern designs, none of these add enough to make a dent to the aircraft's original RCS.

In A2G role, they go low, so they use nap of the earth profile to reduce detection range. In this case, the profile of the weapons when viewed from the top is rarely visible. So the external payload's greater RCS is circumvented this way. An aircraft flying at a height of 50m will only be detected at less than 40Km.

But the fact is with neither profile can they really hide themselves enough from air-based sensors, since their clean RCS itself is way too high, making the discussion irrelevant. So 4th gen aircraft are forced to use more expensive and sophisticated weapons to create an equivalent impact on the battlefield compared to 5th gen.

 

[john0496]

About the rafale: Each time you add a new weapon to the rafale, the plane is sent to the anechoic chamber to tune SPECTRA according to the new load...

 

[randomradio]

About the rafale: Each time you add a new weapon to the rafale, the plane is sent to the anechoic chamber to tune SPECTRA according to the new load...

Yeah, but when compared to the F-35, it obviously falls short, or so the Swiss and Finnish have discovered.

Obviously active cancellation is yet to reach the realm of the F-35. Even 0.01m2 is still 100 times more than the F-35's potential 0.0001m2. That's a 6 times difference in detection range, it's too much. If the numbers are true, the Rafale's RCS difference has to drop by 10 times before it can become even marginally competitive. Who knows how long that's gonna take...

 

[john0496]

I think the Finnish and swiss saw that rafale was detected at a quite long range.
But the main problem is not detection, it is to have a fire solution. Here come SPECTRA about.
You can see the rafale but you aren't able to fire toward it.
You can then use this fact to adopt unusual strategies of fight


PS:
SPECTRA: Système de Protection et d'Évitement des Conduites de Tir du RAfale
(translation with my poor enflish sorry : Protection and avoidance of fire guiding system of the Rafale)

 

[john0496]

Finally the year was good for two companies. LM and DA : 100% of the market

 

[_Anonymous_]

Finally the year was good for two companies. LM and DA : 100% of the market

Yup. No BAe or Eurofighter . Wonder when was the last time either figured in the list of contenders especially BAe , Paddy ? @BMD

 

[Picdelamirand-oil]

Yeah, but when compared to the F-35, it obviously falls short, or so the Swiss and Finnish have discovered.

Obviously active cancellation is yet to reach the realm of the F-35. Even 0.01m2 is still 100 times more than the F-35's potential 0.0001m2. That's a 6 times difference in detection range, it's too much. If the numbers are true, the Rafale's RCS difference has to drop by 10 times before it can become even marginally competitive. Who knows how long that's gonna take...

You do not fully understand the philosophy behind the use of the Rafale.
It is optimised to be effective when the parameters have average values, not extreme values.
Hence the fact that it is LO and not VLO, that its main air weapon is the MICA and not the Meteor, that it has two engines but only 7.5 t of thrust each, that its Radar is an AESA but of small size, and that its air-to-ground weapons do not break records in range.
This means that it will be able to approach at a medium range and find a firing solution, if not with the Radar it will be with the IRST or SPECTRA and above all it will be able to identify before firing.
In any case, from F4.2 onwards, we will be able to start developing a multistatic mode for the radar, which will completely cancel out the advantages of passive stealth, so there is no need to develop this type of stealth further, except to facilitate active stealth.

 

[_Anonymous_]

In any case, from F4.2 onwards, we will be able to start developing a multistatic mode for the radar, which will completely cancel out the advantages of passive stealth, so there is no need to develop this type of stealth further, except to facilitate active stealth.

Could you elaborate on this part ?

 

[BMD]

F-35s Could Get New Engines As Soon As 2027

Adaptive engine technology and other improvements could significantly boost capability but would come at a cost.

www.thedrive.com

You do not fully understand the philosophy behind the use of the Rafale.
It is optimised to be effective when the parameters have average values, not extreme values.
Hence the fact that it is LO and not VLO, that its main air weapon is the MICA and not the Meteor, that it has two engines but only 7.5 t of thrust each, that its Radar is an AESA but of small size, and that its air-to-ground weapons do not break records in range.
This means that it will be able to approach at a medium range and find a firing solution, if not with the Radar it will be with the IRST or SPECTRA and above all it will be able to identify before firing.
In any case, from F4.2 onwards, we will be able to start developing a multistatic mode for the radar, which will completely cancel out the advantages of passive stealth, so there is no need to develop this type of stealth further, except to facilitate active stealth.

You heard it here first gents.

The Rafale, optimised to be average.

 

[screambowl]

Could you elaborate on this part ?

Passive stealth like F35, F117, using RAM. The next coming advancement is more into active stealth technologies with active electronic countermeasures, and automated lamps on the fuselage according to the brightness around the plane, and dielectric composite materials. Which will not only cancel out the incoming detection but also camouflage their location with a different location. Due to development of cyber warfare which has become potent enough and other highly sensitive multi static radar, which I was talking about with @randomradio about the netted system along LAC, the passive stealth will lose it's potency.

 

[randomradio]

You do not fully understand the philosophy behind the use of the Rafale.
It is optimised to be effective when the parameters have average values, not extreme values.
Hence the fact that it is LO and not VLO, that its main air weapon is the MICA and not the Meteor, that it has two engines but only 7.5 t of thrust each, that its Radar is an AESA but of small size, and that its air-to-ground weapons do not break records in range.
This means that it will be able to approach at a medium range and find a firing solution, if not with the Radar it will be with the IRST or SPECTRA and above all it will be able to identify before firing.

Yep, a good balance between costs and capability. But it really depends on what the Finnish have discovered. We do not know the margin of victory yet, and it's unclear when we are gonna find out. But we can now say with certainty that the Finnish find the F-35 to be significantly superior to the Rafale.

In any case, from F4.2 onwards, we will be able to start developing a multistatic mode for the radar, which will completely cancel out the advantages of passive stealth, so there is no need to develop this type of stealth further, except to facilitate active stealth.

Yep. Not much of a future left for passive stealth.

I feel the future will be more about performance and EW than passive stealth. For example, the Mig-41 will be able to outfly and outrun any missile today. And missiles meant to defeat the Mig-41 will be way too big to defeat it, while at the same time the Mig-41 will have active stealth capabilities, along with passive.

 

[Picdelamirand-oil]

Could you elaborate on this part ?

Well I'll give it a try, we'll start with the basics:

In signal processing, cross-correlation is a measure of the similarity of two waveforms as a function of a time shift applied to one of them. For continuous functions f and g, the cross-correlation is defined as:



where f * denotes the complex conjugate of f and t is time.

As an example, if we consider two real functions differing only by an unknown offset in x. We can use cross-correlation to find out how much we need to shift the x's to superimpose them. The formula consists of calculating for each point x the integral of the product of the two functions. When the functions overlap, the value of the product is maximised. Indeed, if the extreme values are superimposed, they contribute strongly to the integral whether this value is positive or negative because the product of two negative numbers is positive.

If the functions have complex values, taking the conjugate ensures that the extremes with imaginary components will contribute positively to the integral.

The convolution product of two real or complex functions, f and g, is another function, usually written as "" and defined as :



We have



This equality is used in signal processing to reduce processing times. Indeed the Fourier transform of a convolution product is obtained by multiplying the Fourier transforms of the functions and therefore if f and g are integrable squares then:



The main interest of calculating the convolution product by Fourier transforms is that these operations are less time consuming for a computer than the direct calculation of the integral. The latter formula will allow the efficient calculation of the cross-correlation of two signals or the self-correlation of the same signal received at different times.

This specialised calculation was first performed by general purpose computers, but it is now possible to make massively parallel components dedicated to this single function. For use in GPS receivers there are now components that offer 1 million correlators.

Meanwhile, the E-1612-UB module series of Grove - GPS Module is a family of stand-alone GPS receivers featuring the high performance u-blox 5 positioning engine. The 50-channel u-blox 5 positioning engine boasts a Time-To-First-Fix ( TTFF ) of under 1 second. The dedicated acquisition engine, with over 1 million correlators, is capable of massive parallel time / frequency space searches, enabling it to find satellites instantly.

GPS Modules Selection Guide | Seeed Studio Wiki

GPS-Modules-Selection-Guide

wiki.seeedstudio.com

I will show some possible applications of this approach and technology

 

[Picdelamirand-oil]

The first application that comes to mind concerning the use of the correlators I mentioned in the previous post is the one concerning RWRs. As we know nothing about the threat we have to monitor all the frequencies and delays within the limit of the light propagation time between the antenna dipole we are using. The frequency/time plane is divided into elementary cells in which the correlation is tested.

The finer the cut, the more sensitive the detection: indeed, the superposition is never perfect because time is discretised and the frequency is subject to a different Doppler effect for each antenna. The finer the cut, the better the superposition, the stronger the correlation will be.

If we had only one correlator (or a general calculator), we would have to make the calculation successively for all the times and all the frequencies, which could take more time than the acquisition and we would thus be obliged to enlarge the mesh and thus reduce the sensitivity. We can therefore see the advantage of having a chip with 1 million correlators.

To achieve good precision in the measurement of the direction, there are two techniques: the distance between the antennas can be increased, but the size of the time/frequency plane element to be measured must be increased. Alternatively, one can make a phase measurement of the signal, which will give a precise delay and therefore a precise direction.

But it is not only RWRs. Radar can also use this technique. A radar knows very well what pulse it has sent, and is therefore well placed to test the return using the technique described above. Since what it is looking for is accurate it can spend a lot of time (fine tuning) on detection.

For example, if the radar has used a long pulse to spread the energy over time and increase its stealth, detecting the return with correlators means compressing the pulse as if it were short and with the same energy.

 

[Picdelamirand-oil]

Before explaining how these techniques could be used for on-board multistatic radar, a little more preparation is needed.

For this I will give explanations based on examples taken from navigation satellites. It is important to realise that from the point of view of detection, the performance of satellite navigation receivers is extraordinary. The satellites are 14,000 km away, the transmission power is a few watts, the receivers do not have big antennas, and yet it works.

The detection method is the one I have described, but for it to be effective, the signal must be coded with codes that are called "gold" because they give a strong auto correlation and a weak cross correlation. This is how the coding is done:

​

A pure frequency would not allow this correlation search principle. In addition to the coding, the signal can include data:

​

And this can be useful, as we shall see.

Why explain all this? First of all, it is necessary to understand that radars, transmissions, jammers and navigation satellites use electromagnetic techniques that can converge; and the military signal from navigation satellites has very interesting characteristics. First of all, we know how to reserve its use to allies: we know how to "encrypt" the signal so that it is unusable for those who do not have the key. You will understand that I will say no more. We also know how to protect it against jamming, spoofing, ... and all electronic warfare techniques. This is very important because it is an extremely weak signal.

Then the collaboration of several platforms to form an extended sensor comes up against a problem of precise time which is precisely at the heart of the resolution by the navigation system of the localisation problem. Indeed, if 4 satellites are needed to obtain coordinates, it is because the unknowns of the problem to be solved are the three spatial coordinates and the time coordinate. The users of a navigation system therefore have at their disposal a shared time base which has the quality and precision of an atomic clock.

 

[Picdelamirand-oil]

The aim of the TRAGEDAC study, notified in 2010, was to implement a networked passive 3D location for the Rafale and future combat drones in order to more easily establish a tactical situation and to improve the responsiveness of fire control and its coordination in the patrol. The solution must be able to operate in real time using information from the networked aircraft sensors.

The idea is to be able to increase the accuracy of locating an enemy by using non-emissive methods (Spectra and front-end optronics) and by sharing the information thus collected within a patrol. In particular to determine the distance to the target, which is the most difficult data to estimate using only passive means. This is a purely software modification but, according to the DGA, it would be especially complex to implement from the point of view of data synchronisation between aircraft.

What is the possible solution? The simplest solution seems to be to use link 16. But on link 16, tracks are transmitted, an ESM bearing is a track, but if nothing more is done, a lot of measurements will be lost because the track must be maintained by the best placed participating unit from the point of view of track quality. This is not what we want, we want measurements from the different aircraft to allow triangulations, we want to be able to feed all this into a Kalman filter so that it can give us a speed route position for the target. We don't want to lose any measurements.

If there was only one track it would be relatively easy, but as there are several, we need to be able to assign the ESM readings to each of the targets we want to track without making mistakes. For the Kalman filter to work properly it will be necessary to date the measurements with an accurate and common time base and I explained in a previous post how this was possible. In order to attribute the correct measurements to the target it will be necessary to rely on the technical analysis of the signal made by each of the aircraft.

The measurements will be transmitted on the new inter-patrol link because link 16 is not suitable for this.

But we can go even further, we can want to do auto-correlation between an antenna on one aircraft and that of another aircraft. The fact of having a dedicated link will facilitate this processing because we will not be constrained by the link 16 protocol.

The fact of considerably increasing the distance between the antennas will improve the accuracy, even beyond that which is possible with interferometry, because the position error will be small compared to the distance between the antennas. On the other hand, the processing must take into account a larger range of delays, which increases the computing power required to remain in real time.

The fact that the antennas are far apart also makes the difference in doppler significant and increases the volume of processing to be carried out. On the other hand, the doppler is a measure of the radial velocity which can greatly facilitate the convergence of the Kalman filter.

Once Tragedac has been completed, 80% of a multistatic radar has been completed. It is assumed that the AESAs are used as transmitters and passive receivers. The AESA emits a signal and transmits on the dedicated link the data allowing the receiver to build a replica of its signal, this one will be able to detect the direct signal (Spectra for example) and to reflect it by correlation with the replica that it has built. As we have seen, the signal is coded and can contain data. The signal may therefore contain the position of the transmitter (x,y,z,t) and the orientation of the antenna.

The delay of the reflected signal with respect to the date of transmission defines a locus of the target positions which is an ellipse and the orientation of the emitter's antenna defines a straight line whose intersection with the ellipse gives the target's position. Of course the common time base is still that of the satellite navigation system.

 

[_Anonymous_]

Before explaining how these techniques could be used for on-board multistatic radar, a little more preparation is needed.

For this I will give explanations based on examples taken from navigation satellites. It is important to realise that from the point of view of detection, the performance of satellite navigation receivers is extraordinary. The satellites are 14,000 km away, the transmission power is a few watts, the receivers do not have big antennas, and yet it works.

The detection method is the one I have described, but for it to be effective, the signal must be coded with codes that are called "gold" because they give a strong auto correlation and a weak cross correlation. This is how the coding is done:

View attachment 22049​

A pure frequency would not allow this correlation search principle. In addition to the coding, the signal can include data:

View attachment 22050
​

And this can be useful, as we shall see.

Why explain all this? First of all, it is necessary to understand that radars, transmissions, jammers and navigation satellites use electromagnetic techniques that can converge; and the military signal from navigation satellites has very interesting characteristics. First of all, we know how to reserve its use to allies: we know how to "encrypt" the signal so that it is unusable for those who do not have the key. You will understand that I will say no more. We also know how to protect it against jamming, spoofing, ... and all electronic warfare techniques. This is very important because it is an extremely weak signal.

Then the collaboration of several platforms to form an extended sensor comes up against a problem of precise time which is precisely at the heart of the resolution by the navigation system of the localisation problem. Indeed, if 4 satellites are needed to obtain coordinates, it is because the unknowns of the problem to be solved are the three spatial coordinates and the time coordinate. The users of a navigation system therefore have at their disposal a shared time base which has the quality and precision of an atomic clock.

Wow. I'd have to re read this again & go back to my engg course advanced mathematics curriculum to get a better understanding of what you've put out. Thanks a ton for the information & effort though. Much appreciated.

 

[screambowl]

In signal processing, cross-correlation is a measure of the similarity of two waveforms as a function of a time shift applied to one of them. For continuous functions f and g, the cross-correlation is defined as:

where f * denotes the complex conjugate of f and t is time.

As an example, if we consider two real functions differing only by an unknown offset in x. We can use cross-correlation to find out how much we need to shift the x's to superimpose them. The formula consists of calculating for each point x the integral of the product of the two functions. When the functions overlap, the value of the product is maximised. Indeed, if the extreme values are superimposed, they contribute strongly to the integral whether this value is positive or negative because the product of two negative numbers is positive.

If the functions have complex values, taking the conjugate ensures that the extremes with imaginary components will contribute positively to the integral.

The convolution product of two real or complex functions, f and g, is another function, usually written as "

" and defined as :

These are two riemann integrable continuous functions, but do we normally get continuous and integrable waves in real time when we deal with stealth?

 

[Picdelamirand-oil]

These are two riemann integrable continuous functions, but do we normally get continuous and integrable waves in real time when we deal with stealth?

One of the purposes of a program like Tragedac is to do tests to check that it works. The reason it works is that the signal does not go from - infinity to + infinity but exists for a very short time.