IRST V F-22/35 and other stealthy aircraft

[kcran567]

http://theboresight.blogspot.com/2009/07/airborne-infrared-and-supersonic.html
https://foxtrotalpha.jalopnik.com/infrared-search-and-track-systems-and-the-future-of-the-1691441747

https://www.thedrive.com/the-war-zone/16381/rare-ghost-f-16d-toting-irst-pod-likely-based-at-area-51-spotted-in-jedi-transition

Early Fighter jets (Voodoo) IRST and others...has an F-22 ever been tested against some of these IRST systems? Maybe even against some Mig-29s and Su-27s at groom lake?

F-4, F-14 (Legion pod based on f-14D IRST) etc.

Legion IRST sensor—Lockheed's IRST21 based on an upgraded version of the AN/AAS-42 IRST that equipped the F-14D

Wonder how effective these systems are against F-22/35 and especially newer systems such as on the Gripen.

 

[stealthflanker]

The greatest problem to define effectiveness is that there are no real set of generic parameter to agree with.

As seen each manufacturer use different kind of targets, say Russian used either "Mig-29" or "Su-30" type targets while US and EU are even more vague with only listing (sometime) detection range and tracking capacity. Let alone any "standard" condition where the measurement is made.

There is a method i proposed for simple assessement but no real feedback.

General consensus however suggest that IRST might offer comparable performance to radar in high altitude and against high speed target where they experienced natural kinetic heating.

In lower altitude performance may decrease due to denser atmosphere. Another difficulties with IRST is that they are unable to accurately or directly measure target range.

 

[lastdingo]

IRST can be used for cooperative ranging (two aircraft triangulating).

IIR sensors do not make use of doppler effect, so it's tough to filter out a moving object from a similar background.
It's not impossible, but it's demanding.
Target aircraft will be detected more easily if they fly higher, or are heated-up by air friction (from supersonic travel).

All that I've seen points at IRST being promising against non-afterburning targets at 40 or 50 km or so, under rare conditions maybe 80 km.

IRST may thus become the decisive factor if two VLO aircraft attempt to detect each other. IRST won't change that a F-22 detects a Su-35 or Gripen first if said target is in the forward 120° or the F-22 is turning enough for all-round scans.

 

[sublight_]

There was some Air Force general that made the off hand comment they could detect the aircraft by its wake.

 

[LowObservable]

Stealthflanker is right to point out that there is no equivalent of RCS in the IR regime. This is an inherent problem given that your IR emissions will depend on speed and sunlight and propagation will depend on atmospheric conditions.

IRST can pick up IR signals at very long range - the problem is always that of picking out real targets from the background and getting decent range combined with low false alarm rates. Selex/Leonardo wrestled with this for a long time in the Typhoon program - where IRST was initially regarded as an anti-jamming device working cooperatively with the radar - and did well enough for the Swedes to find space for a derivative system on the JAS 39E. I would suspect that the Leonardo systems are more advanced than anything in the US, which is mostly derived from F-14D work.

 

[jeffb]

Doesn't the F-35 have active skin cooling?

I seem to remember that there was an effort made dump systems heat into the fuel tanks.

 

[Dragon029]

It does not (unless there's some classified system that's yet to be exposed). F-35s (and jets like the F-22 and Super Hornet) do dump heat heat into their fuel (which is then air cooled via radiators / heat exchangers), but that's not really for IR stealth purposes. Rather the F-35 just utilises coatings, the insulative qualities of its composite skin, exhaust nozzle design (the chevrons mix hot / cold air faster, reducing the IR output of the exhaust plume), it's relatively high military power thrust (vs AB), and the burying of the engine behind S-ducts, weapon bays and a ram-air cooled engine bay.

 

[icyplanetnhc (Steve)]

I recall reading a report a while back that the F-22 uses active cooling for the leading edges due to extended supersonic operations, though I'm not sure if this is done for the leading edge flaps (which also houses some antennas).

 

[Avimimus]

We could see high altitude clear weather combat driven by IRST and extended range BVR weapons... under the right conditions one might even be able to get the initial firing information from looking at the wake of heated air (if I recall correctly)?

But there are also poor weather conditions... clouds... where one would think radar would be critical to combat - where combat would happen at closer ranges, with less reliable interception and enemy contact... and would be much more dependent on the quality of the radars and how the radar data is processed.

So there could be a lot of asymmetries in combat. The infrequency of combat between modern aircraft also means that most testing for radar/missile systems is based on encounters with export models of surface to air missiles... so there must be a lot of uncertainty about real world performance of radars and datalinks against a modern foe... which means falling back on the high-altitude IRST strategy is a good option to have.

One thing I don't know is about the potential role of improvements in far infrared imaging (which can see through a certain amount of water vapour at short/medium ranges)... which might impact the above equation.

Any thoughts? Am I thinking along the right lines?

 

[bobbymike]

Lockheed's IRST Stealth Detection Pod Passes AF Milestones - Breaking Defense

"The Legion Pod uses an advanced IRST technology that gives 4th generation fighters the ability to 'see' stealth aircraft that traditional radar cannot," says an Air Combat Command spokesperson.

breakingdefense.com

 

[Avimimus]

There was some Air Force general that made the off hand comment they could detect the aircraft by its wake.

View: https://www.youtube.com/watch?v=58N6Plr17GU

 

[jsport]

a better configuration

 

[sublight_]

There was some Air Force general that made the off hand comment they could detect the aircraft by its wake.

View: https://www.youtube.com/watch?v=58N6Plr17GU

That is infra red footage. They were talking about being able to see a wake in the air the same way you would see a wake in the ocean.

 

[Foo Fighter]

Very handy but, does seeing the newer aircraft mean you can do anything about it?

 

[stealthflanker]

Very handy but, does seeing the newer aircraft mean you can do anything about it?

This needs a range measurement, after that. One can think of things that can be done.

One possible scenario is far above. cooperating with other aircraft. But if the carrier aircraft were happen to be alone, The the IRST could perhaps be used to "narrow down" the search sector. Radar can then be pointed there and spend more time on that sector.

Tripling the dwell time (e.g 0.025 second/beam to 0.075 second/beam) Is basically 1.3 times more detection range. The good thing about IRST is that it has great angular resolution, thus might narrow the search sector more. If it can narrow down the sector more thus allow the radar beam dwell time to reach something like 0.5 second/beam, the radar can pick 2.1 times of "range multiplier".

Still however the price to pay would be the possible increase of probability of enemy ESM detection as we are pointing our beam longer to enemy. Plus it would Rob scan time for other sector.

 

[AeroFranz]

Flanker, that's a useful relationship you mentioned - do you have the complete equation relating dwell time and detection range?
hmmm...looks like this is related to the radar range equation and the fourth power relationship, 3^(1/4) does equal 1.31.

 

[BDF]

A big problem is that IRST are not great at volume search and suffer a sizable reduced detection range when conducting volume search. As a stand alone solution they're only a modest improvement over radars against LO threats. That being said they benefit from cueing which is where those long detection ranges come in. In a sense they come into their own as a network enabled sensor. I would think that instead of them cuing radar it would be the other way around (or cued off of ESM detections.) My suspicion is that Russian and Chinese IADS strategies are for low frequency radars to cue airborne IRSTs as well as other air and ground based RF sensors.

 

[stealthflanker]

Flanker, that's a useful relationship you mentioned - do you have the complete equation relating dwell time and detection range?
hmmm...looks like this is related to the radar range equation and the fourth power relationship, 3^(1/4) does equal 1.31.

Yes it does. I developed my relationship based on George M Siouris's Book "Radar System Performance Modelling 2nd Edition". You can see the original "reference range" equation in section 5.3 page 70.

My relationship takes similar form except the N^3 variable for Active Array Radar


Apologize as it's made for Indonesian readers, some variables is in english, this is the one that in Indonesian :

N = Number of TRM in AESA radar
P = Emitted power of radar (Conventional)
Pe = Power per TRM
Tot= The dwell time (Time on Target) in seconds.
R= Range
G= Antenna Gain
Ref = Value taken from the reference radar.

I found it kind of weird tho that papers discussing merit of low RCS rarely touches the "other" thing a radar can do. With abovementioned relationship, one could see not only the factors affecting detection range but also able to make a simple tradeoff for a design.

Let's give an example of AESA radar with following :

N= 1524
Pe= 10 Watt per element
Tot = 0.025 seconds/beam
SNR or detectability factor required for the radar to make detection = 24 dB or 251 for 90% probability of detection.
Target RCS for the radar = 3 Sqm
Reference range for said radar against the target = 210 km
Pulsewidth of the radar : 1 microseconds or 1*10^-6 seconds

Now we wish to detect a smaller target say 1 Sqm. Based on RCS Only, one would get 159.6 Km range. But what if we tripling the dwell time ? Without changing the other parameters it would be yes 1.3 times or 210 Km. What if we double the amount of module, without changing other parameters ? Then it would be (2^3)^(1/4) = 1.68. So now the radar can detect target having 3 Sqm RCS at 353 Km.

Now we have a very low RCS target of 0.001 sqm. Based on RCS alone we will get about 28.4 Km. We are constrained in amount of module we can cram and power But what if we :

-Tripling the dwell time
-"Halved" the required SNR for detection by some maybe new sophisticated technique which still allow 90% PD but with only 20 dB (125.59) SNR
-Increasing pulsewidth by say 10 us, sacrificing some minimum range.

Then having all the required variable, the relationship would look as follows :

R=210 * ((1^3)*(1)*(3)*(.001/3)*(2)*(10))^(1/4)
R=210 * 0.376
R=78.9 Km.

So the Radar, providing it is capable of doing such changes, can allow increase about 3 times the "previous" detection range.

 

[AeroFranz]

Thanks for showing me this. Not being an EE, i can't really weigh in on the accuracy of this.
I will say, the math certainly seems to check out, but i will be the devil's advocate and offer that there may be potential pitfalls of one of two types with these types of analyses:

- The individual parameters can't be varied in isolation, that is, for one reason or another the physics link two of the parameters and varying one of those automatically results in a variation of another
- There are practical considerations that put constraints on how much you can actually vary the parameters (like minimum size of a TRM, or something else). I think you pointed to some of these.

Nonetheless, i am always looking for useful relationships like these. I will check out Siouris' book, thanks!

 

[stealthflanker]

Accuracy is, considering that it is entirely based on basic inverse square law is limited only to what kind of data available from the reference radar.

Additions can be made to take account of RCS Changes due to wavelength and other factors such as Path propagation factor. However in the excel spreadsheet i made for the equations. I choose not to include those factors as it would means increased complexity. The user itself is then have to be Fully aware about the limitations and constraint of the equations.

One example is the dwell time.

Increasing the dwell time, does increase range. However Care should be exercised (as i implied above) on the search sector. As increasing the dwell time means increasing the scan time too. If the scan sector is large, this will increase the scan time into impractical amount. Too much search time also actually reducing the probability of target being detected as the potential target might already travel to the another beam before it's visited.

Another example is increasing pulsewidth. This basically letting the transmitter to "fire" much longer. The benefit of longer pulse is increased energy per pulse or average power. But this also means reduction in radar minimum range. Minimum range itself is a "swath" of range where radar is blind as it transmit pulse. every micro seconds of pulse equals to about 150 m of range. Thus if a radar emit 1 microsecond pulse it has 150m of "dead zone" where it cannot detect anything. By making the pulse longer it would means this "blind range" getting longer. 10 us means the radar is Blind to whatever lies in 1.5 km in front of it. Increasing pulsewidth to 1000 us as what RRP-117 "Seek Iglo" Does means the radar cannot detect target lies within 150 Km from it. Thus a "cover pulse" or separate short range mode must be provided or scheduled on radar operations.

Lowering the amount of required SNR for detection would be limited fundamentally by current semi conductor and computing technology to shift real target from clutter.

While the amount of module and power is constrained physically by available space and cooling.

 

[jsport]

2021-06 | The Aerospace Advantage

The Mitchell Institute for Aerospace Studies is proud to present The Aerospace Advantage, with former Air Force weapons school instructor and Thunderbird Lt Col (ret) John “Slick” Baum as the host. Every week, Slick will take listeners into the world of ae...

mitchellinstituteaerospaceadvantage.podbean.com

Starts a bit slow, but LM claims to have doubled the RST rg since 2010, and alot on EOTS, DAS, Net-centric, DARPA TTNT, JADC2 are mentioned.