AGM-88 HARM implementation FA18/F16

HARM on the Hornet is simplified for now. Howerver, it will be adjusted for the Viper standard in future. So, what depends on missile (detection rate, for example) will be the same on both planes. But, please keep in mind, that some things are aircraft specific and they will remain different.

Is that the same reason (will it be also changed) that apparently the agm88c alone can generate a stabilised and dead accurate box on your HUD for the targeted emitter?

Something that would normally take not one F16 with HTS, but actually 2 working together via L16?

Respect, cofcorpse .

There is a specific capability with F-16CJ HTS that threats are pre planned before flight so they show up as inactive emitters on the display even if the emitter never radiates the symbol is there. And when radiation does happen the system may associate the emission with a preplanned threat so it seems like the system located the emission perfectly but it just associated it with pre-planned. So accuracy of association depends on accuracy of the prepared expected threats.

HTS should be able to discover non-pre-planned emitters but accuracy is less.

Since the 90s figure was (I assume) taken from the AGM-88B documentation might the AGM-88C be expected to be a tiny bit faster?

Is that the same reason (will it be also changed) that apparently the agm88c alone can generate a stabilised and dead accurate box on your HUD for the targeted emitter?

Something that would normally take not one F16 with HTS, but actually 2 working together via L16?

I'm not convinced that is inaccurate on the Hornet as the HARM is looking for one radar in a very small area once you hand-off and get the box. Think of it like an 'STT' lock as opposed to regular radar search, the updates are now determined by the gaps between the target emitter painting the HARM seeker - much faster than the HARM searching about for an emitter.

By design the seeker would need to be able to determine the relative off-angles from its boresight to steer itself to a target radar and those offsets could be pushed back to the jet, thereby giving you a box on the HUD. Much like how the AGM65 triangle on the HUD lines up with where the seeker is looking.

The last comment on needing two HTS fitted F16s is more related to Geolocating an emitter in realtime (as opposed to simply telling you where the seeker is looking relative to your centre-line per what I've explained above).

Of note, the DCS Viggen can already geolocate emitters as a single aircraft, but it takes time to build the picture as you need to get multiple 'cuts' on the emitter from different locations.

Directional info and point locating of emitter are two different things. Getting the LOS right is pretty easy like Su-25T. Getting something which you can drop a CBU on through the clouds not so much.

F-16 HAS has a sort of two-step process. When a threat class is handed off it will still look for sub-threats so post designate it's still possible to step through

I'm not convinced that is inaccurate on the Hornet as the HARM is looking for one radar in a very small area once you hand-off and get the box. Think of it like an 'STT' lock as opposed to regular radar search, the updates are now determined by the gaps between the target emitter painting the HARM seeker - much faster than the HARM searching about for an emitter.

 

By design the seeker would need to be able to determine the relative off-angles from its boresight to steer itself to a target radar and those offsets could be pushed back to the jet, thereby giving you a box on the HUD. Much like how the AGM65 triangle on the HUD lines up with where the seeker is looking.

 

The last comment on needing two HTS fitted F16s is more related to Geolocating an emitter in realtime (as opposed to simply telling you where the seeker is looking relative to your centre-line per what I've explained above).

Of note, the DCS Viggen can already geolocate emitters as a single aircraft, but it takes time to build the picture as you need to get multiple 'cuts' on the emitter from different locations.

A Maverick will not generate you GPS coordinates for a JDAM drop either.

The seeker in the HARM rolls with your airplane and will not have the angular resolution that a camera for optical wavelengths (that are even constantly "transmitting" so to speak) has.

Imagine a search radar like a sometimes on, sometimes off laser spot. Now imagine a TPod without internal stabilisation and own INS and range information. (the JF17 tpod comes close as it can't generate range information above 20nm). As soon as the radar is no longer emitting (if you even find it quickly enough) your seekerhead will drift away from it's position. Yes, it will be in the neighbourhood to quickly find it again, but you don't get a solid fricking box pointing you at it. It just doesn't make any sense.

How else would you explain systems like the HTS (or the Hornets version, the TAS)?

They require - in the case of the hornet - two swapped out Pylons to generate range and precision azimuth information by ownship movement.

http://www.ausairpower.net/API-AGM-88-HARM.html

Interesting reading material there, as - for example - the HARM in the FA18 without TAS will not be able to get range information to the transmitter it's targeting, meaning it will not Loft unless you fire it in PRE-Mode "at" a waypoint and hope there's a transmitter closeby.

This means that the range of the HARM in non-PRE mode should be significantly lower than for the F-16C with HTS pod which can generate range information. But that's something for the future.

If a single HARM missile - which doesn't even have a stabilised seekerhead as Wags mentioned - can provide you a rock solid, non-jittery target box in your HUD then the USNAVY wouldn't have invested in the TAS. I would really like to know from where ED got the idea for that and if it's not just a debug feature. It defies every information that is out there on the reason why systems like the HTS and TAS exist.

If it's really just about showing that box, pointing a tpod at it .. using the planes internal terraion map to get the range to 0 AGL there then it could very well be automated, and AGM88s would be fired with range information and loft even in modes like SP or HAS.

The fact that this isn't the case and that they build HTS / TAS systems shows you that it's seemingly not an option.

So why is it that we can in DCS just slew a TPod across to the box, and have the coordinates for a theoretical PRE shot with lofting profile?

The public information is that TAS generates you information that is off by a few percent. Now that's a specialised system. And the HARM is supposed to give you a solid non-jittery box?

As for the Viggen, it's pod can pinpoint emission sources and then use angular triangulation using it's own course to guess it down to a box. But have you seen the ELINT exports? the "boxes" for the radar sites are quite big, and radars of the same type in close proximity are merged into one.

And seeing this quote in another thread:

Stations 4&6 are not wired for video. The only stations that can transmit video are 3&7. I'm saying this as a guy who ran those video lines the AGM-88 uses. I started on BLK 30s in 2001 and worked 16s for 13 years. Never saw a video line going to or from stations 4&6. Not sure who changed your mind, but it's worth taking a second look.

 

Edit for clarification: The station comm lines exist. Meaning jettison commands and such will go through and work. However there is no video, so the WPN page on the MFD will be blank. The 88 and LAU-118 will send the video, but there is no pin in the pylon disconnect on the wing to receive it on stations 4 & 6. Can't use a 88 without video. 65s and 88s use the same video line. Meaning that United States F-16s (can't speak for other countries) cannot support 65s or 88s on sta 4&6.

It makes me even wonder more how the FA18 would even get the information where the HARMs seeker head is looking at so steadily for it's HUD .. if the information coming from the weapon comes over as video feed.

Just to avoid confusion: The TAS doesn't exist anymore. It was a Navy project that never went anywhere AFAIK.

From my understanding of the TOO mode in the F/A-18C it does not use the missile itself as a sensor, it instead uses the RWR to generate the video image you see on your DDI. This is distinctly different from the method used in the F-16CM as it does use the missile itself as a sensor (HARM As a Sensor). This is where the disparity in compute power comes from.

When you hand off an emitter in the F/A-18C you are commanding the missile to then narrow its search pattern to that specific type of emitter in an a narrower azimuth/elevation scan (in effect analogous to an STT as some else suggested) that is commanded/steered/vectored by the RWR. This cross talk between the RWR and the missile is what is missing in the F-16C, and what the HTS remedied to some extent.

From my understanding of the TOO mode in the F/A-18C it does not use the missile itself as a sensor, it instead uses the RWR to generate the video image you see on your DDI. This is distinctly different from the method used in the F-16CM as it does use the missile itself as a sensor (HARM As a Sensor). This is where the disparity in compute power comes from.

When you hand off an emitter in the F/A-18C you are commanding the missile to then narrow its search pattern to that specific type of emitter in an a narrower azimuth/elevation scan (in effect analogous to an STT as some else suggested) that is commanded/steered/vectored by the RWR. This cross talk between the RWR and the missile is what is missing in the F-16C, and what the HTS remedied to some extent.

That's absolutely not how TOO mode works

From my understanding of the TOO mode in the F/A-18C it does not use the missile itself as a sensor, it instead uses the RWR to generate the video image you see on your DDI. This is distinctly different from the method used in the F-16CM as it does use the missile itself as a sensor (HARM As a Sensor). This is where the disparity in compute power comes from.

When you hand off an emitter in the F/A-18C you are commanding the missile to then narrow its search pattern to that specific type of emitter in an a narrower azimuth/elevation scan (in effect analogous to an STT as some else suggested) that is commanded/steered/vectored by the RWR. This cross talk between the RWR and the missile is what is missing in the F-16C, and what the HTS remedied to some extent.

You are thinking of SP mode in hornet, that uses the RWR for targeting and can fire outside of the HARMS fov, because its a LOAL (lock on after launch) mode. TOO uses the HARMS own sensor to target and is a LOBL (lock on before launch) mode.

That may be how F/A-18 "SP" works but TOO is the generic name for the "anti-radiation Maverick" mode which is called TOO in Hornet and HAS in Falcon.

USAF and USN names for HARM features are not consistent. There are behaviors which are in the same category with different names.

Pre-briefed: Pre-briefed (PB), Preemptive (PE), Position (POS), Equations of motion (EOM) is a kind of positional.

Target of opportunity: Target of opportunity (TOO), HARM as sensor (HAS), direct attack (DA)

Self-protect: SP, LOR

A Maverick will not generate you GPS coordinates for a JDAM drop either.

 

+ the rest of the text

The HARM doesn’t generate coordinates either, only the HTS does. But re the solid lock box I don’t really get the whole issue with whether a box in your HUD is solid/dashed/or whatever I don’t think that it really matters/is important. All it indicates is the last known emitter bearing as located by the HARM, it will just be in the rough direction indicator and not at a 100% accurate position marking

Considering the MSI implementation in the Hornet, it's not odd to think that the LOS to the selected emitter can be displayed on the HUD. It's not a position in 3D space, it's only in 2D. The missile seeker has no range info and generates no coordinates.

The HUD box can easily be generated by a 3 step process:

1) Translating the seeker's entire FOV into a surface area. Easy.

2) Marking the emitter's (x,y) position relative to that area. A 2D square and a point in that square. Easy.

3) Then, the missile's FOV area can be translated to fit into the HUD plane area and the box is generated using the relative position of the point from (2). Easy.

It all works in 2D and requires nothing more than calculating the (x,y) coordinates of the emitter relative to the HARM seeker's FOV area and then translating it to the HUD's area. All quantities are known and the entire algorithm is extremely easy.

The HUD box as we have it now is entirely possible in TOO mode.

And without interferometry, expect HARM angular errors to be in the sense of 2°. That means, at 25 nm, a 1.5 nm diameter circle of uncertainty. Right now the TD is deadly spot on

Could you tell what is the source of this information?

I mean, the diffraction limit is ~lambda/D; for a wavelength of a few centimeters, and an antenna diameter of ~20 cm, you get something slightly less than 1 degree. Assuming that the HARM seeker doesn't have particularly fancy optics, 2 degrees is not insane.

I suppose the HUD box could just be showing the center of the PSF, which can be arbitrarily small, and not bother with showing the uncertainty on that center. Even then, it should be slightly off rather than consistently being spot on whatever the HARM is tracking

Could you tell what is the source of this information?

I don't know what DOA accuracy in HARM is. But what I know is that for 1º or less you definitively need an interferometer, which is largely unavailable for a missile head:

https://basicsaboutaerodynamicsandavionics.wordpress.com/2016/03/02/rwresm-and-passive-geolocation/

Aircraft RWRs, which I would assume havemore sophisticated antennas and T/R modules than a missile, have DOAs around 5º, for example SAAB Gripen DASS system has 7º accuracy according to the manufacturer

https://saab.com/globalassets/commercial/air/electronic-warfare/radar-warning-receivers/bow/bow-product-sheet.pdf

So, even 2º RMS DOA accuracy for the HARM seems optimistic, if you ask me

Regards

And without interferometry, expect HARM angular errors to be in the sense of 2°. That means, at 25 nm, a 1.5 nm diameter circle of uncertainty. Right now the TD is deadly spot on

Perhaps ED could include a systemic random uncertainty in the system, based on the distance from the emitter, so the box is not always perfectly centered on the emitter.

I was just thinking an intentional random angular error to the LOS would be a cool and easy feature for DCS to implement. I was thinking 3 degrees max but that was entirely a guess. Every emitter could have a random offset associated with it (0-360deg, 0-3 deg). If you rolled the dice every relock then people would abuse the system by relocking a bunch to see the average. Even a simplistic conical random angular offset would go a long way.

If you really wanted to be fancy you should use a 2d Gaussian with a ~1 degree standard deviation. That's probably pretty close to reality actually.

Because at the moment what you have essentially gives you a box you can slew your TPOD on and got the emitter dead on.

And again .. this is if you even get the box visibly in the Hornet in the first place.

Afaik the HARM transmit an analog video signal for the HAS page that gets piped into your MFD much like the Maverick .. not really something that you can use to get azimuth etc. from easily.

Afaik the HARM transmit an analog video signal for the HAS page that gets piped into your MFD much like the Maverick ...

Not really, otherwise you would get the same interface in the f16, but you don't.

What comes over the video feed could well be analogue data that is utilised by the aircraft avionics to generate what we see in the displays as opposed to a 1 for 1 visual image.

From my understanding of the TOO mode in the F/A-18C it does not use the missile itself as a sensor, it instead uses the RWR to generate the video image you see on your DDI. This is distinctly different from the method used in the F-16CM as it does use the missile itself as a sensor (HARM As a Sensor). This is where the disparity in compute power comes from.

When you hand off an emitter in the F/A-18C you are commanding the missile to then narrow its search pattern to that specific type of emitter in an a narrower azimuth/elevation scan (in effect analogous to an STT as some else suggested) that is commanded/steered/vectored by the RWR. This cross talk between the RWR and the missile is what is missing in the F-16C, and what the HTS remedied to some extent.

This is the correct answer, TOO mode uses both the HARM and RWR as sensor and is not 1:1 analogous to the F16 HAS mode.

Also, the HARM can be launched both with LOBL and LOAL in TOO mode depending on where the emitter is in the seeker FOV.

(I really don't understand why people would assume that different employment modes in different aircraft with different EW suites, different RWR, and built for different services with different roles and doctrines would be exactly the same.)

I think the report by the Serbian SA3 commander near Belgrade was the most enlightening for HARM accuracy. If you read he tells you how far the harms were off. And they had over two dozen fired at his installation.

Something like 30 misses. But closer than the above suggests.

But... it reduced his ability to take time for better shots and thus suppression was actually happening, F-117 shoot down or not, it was happening.

This is the correct answer, TOO mode uses both the HARM and RWR as sensor and is not 1:1 analogous to the F16 HAS mode.

 

Also, the HARM can be launched both with LOBL and LOAL in TOO mode depending on where the emitter is in the seeker FOV.

 

(I really don't understand why people would assume that different employment modes in different aircraft with different EW suites, different RWR, and built for different services with different roles and doctrines would be exactly the same.)

How does the hornet TOO mode resolve vertical placement? If it was just RWR driven then it would only provide azimuth information, as SP and the RWR itself does.