TWS and semi-active guidance

[Poopskadoop]

My question partly relates to discussions in a previous thread I made on the "ode to Mongo" mission for the F-18C. I want to understand more about the TWS function of aircraft in general, and I'm sure there are some smart folks here that can answer my questions.

 

So, how does the AWG-9 radar of the tomcat simultaneously guide multiple AIM-54s and the APG-73 of the hornet guide multiple AMRAAMs but neither the tomcat nor the hornet can guide AIM-7 Sparrows simultaneously against targets? Both the AIM-54 and AIM-120 are effectively semi-active missiles until they are within range to engage their active seekers, is that not correct? My understanding is that semi-active missiles cannot be guided in TWS mode unless the radar is a PESA and literally splits the beams, such as on the MiG-31. So how does that work? Does the computer give the missiles "rough" guidance until the seeker heads go active? Is it just the fact that the software is not integrated to work with the AIM-7?

 

Further, why does ECM negate track while scan from a technical standpoint? Is there no provision for TWS to guide against multiple scrambled returns until the missile can engage some kind of Home-on-jam or otherwise get close enough to burn through the ECM?

 

Also, when did they introduce TWS mode 2 for the MiG-29S!? I had no friggin' idea it could engage multiple targets with the R-77 until I was messing around with the options yesterday. And would the J-11A, which can launch the R-77, really not have this functionality as well, given the similarity of the radars?

 

Finally, why does no aircraft in dcs (and I assume the real counter-parts) have the capability to guide a missile in STT while setting up a shot from an IR seeker? The AIM-9, R-73, and R-27ET do not require the radar to fire on a target, so why do aircraft not have such a simple functionality?

 

Many thanks for anyone who can answer my slew of (possibly) silly questions.:thumbup:

[LTRMcrew]

From what I understand (this only applies to hornet) the sparrow once you tell it "hey lock this target" tracks itself once launched. It's already actively seeking that target the moment you release it.

 

The amraam on the other hand if launched from further out (this distance... depends) has a till active count down on the hud. It requires your radar to maintain lock on the target and feed that info back to the missile until it goes active. Once active it tracks itself to the target.

 

This is the risk with amraam, if you launch it and it hasn't gone active yet and you lose lock with the target that missile will now go pitbull and just lock itself to whatever it sees first in front of it. Risk here being friendly fire.

 

So it the hornet with sparrow doesn't need to track multiple targets.

[Poopskadoop]

From what I understand (this only applies to hornet) the sparrow once you tell it "hey lock this target" tracks itself once launched. It's already actively seeking that target the moment you release it.

I'm confused by the term "actively seeking." From my understanding, the sparrow, being semi-active, has no guidance capabilities of its own without the target being painted by your radar, no? Is this not identical to the functionality of an AMRAAM before it goes pitbull? Otherwise, how is the AIM-120 guided prior to pitbull?

[AegisFX]

Cant speak for the Phoenix but the 120c has it's own radar. Your ship radar guides it until a point where that radar turns on and it handles itself. If you somehow lose lock, it turns on early and guides to the last known point while searching for the first target it finds.

 

The sparrow has no onboard radar.

 

TWS is like looking at something out of the corner of your eye. You may notice, track it, but your focus and the full radar strength, isn't on it. St puts all the focus and power on the one spot.

 

Like if you walked up to someone wearing camo, you may not notice in the corner of your eye but as you get closer while looking directly at them toy may begin to notice them a little more until you realize its actually a person.

[Poopskadoop]

I suppose I should rephrase part of my question. I understand why SARH missiles cannot be guided by TWS. What I don't understand is why the AIM-120 or any ARH missile can be guided if it is effectively identical to a SARH missile until the seeker goes active.

[will-]

all missiles act the same in dcs.

Semi active need a STT lock until impact.

 

https://en.wikipedia.org/wiki/AIM-7_Sparrow#Principle_of_guidance

Principle of guidance

The launching aircraft will illuminate the target with its radar. In radars of the 1950s these were single target tracking devices using a nutating horn as part of the antenna. This caused the beam to be swept in a small cone. Signal processing would be applied to determine the direction of maximum illumination and so develop a signal to steer the antenna toward the target. The missile detects the reflected signal from the target with a high gain antenna in a similar fashion and steers the entire missile toward closure with the target. The missile guidance also samples a portion of the illuminating signal via rearward pointing waveguides. The comparison of these two signals enabled logic circuits to determine the true target reflection signal, even if the target were to eject radar-reflecting chaff.

 

active ones can be fire and forget. How you choose to implement this can be in a STT mode, tws or bore.

 

ir can be fire and forget. stt, tws or bore.

[AeriaGloria]

The J-11A is “jerry rigged” to fire R-77, so it uses similar firing mode as R-27. MiG-29S 9.13S had the modification done to its upgraded radar N-019M to use R-77 and TWS for dual target engagement. More specifically the S is an upgrade of either 9.12 or 9.13, and with original R-77 only being used in numbers for export and not domestic Russian service, it was kind of a perfect match to sell the two together especially to those that already had 9.12. It was a new Ts101M processor which makes it able to do dual target track

 

There was just no changes for J-11A radar from original Su-27 but “hack it” to fire R-77. UBoats original J-11A post talks a bit about it.

[Poopskadoop]

I think I found the answer to part of my question in the wikipedia article for the AIM-120. Apparently, it does not continuously receive data from the aircraft's radar but rather is given a snap shot at launch and is then guided by INS (inertial navigation), with possible mid-course updates if the radar can afford it, until the seeker is active. Okay... that makes sense. So the radar doesn't do much of the work in TWS for an AMRAAM. I think what I was suggesting in my first post was more or less correct, that the missile is given a "rough" direction to fly until pitbull.

[GGTharos]

I suppose I should rephrase part of my question. I understand why SARH missiles cannot be guided by TWS. What I don't understand is why the AIM-120 or any ARH missile can be guided if it is effectively identical to a SARH missile until the seeker goes active.

 

 

Because it is not identical to a SARH missile in any way, shape or form.

 

 

The AIM-54 is the only missile that we have that is capable of SARH guidance as well as ARH, and it's usually SARH-to-ARH (ie. SARH reflections are substituted for some of the TWS guidance/INS or whatever) which aren't meant to guide to impact but rather to seeker activation.

 

The other mode is an STT SARH-only launch, and that AIM-54 will never transition to ARH, it is SARH all the way.

 

 

Further, unlike missiles with m-links for target position updates, the sparrow is home-all-the-way. It tuned to the radar on the rail, and when launched it performs a english bias maneuver then immediately searches for a target to lock on to within those radar parameters.

[Poopskadoop]

The J-11A is “jerry rigged” to fire R-77, so it uses similar firing mode as R-27. MiG-29S 9.13S had the modification done to its upgraded radar N-019M to use R-77 and TWS for dual target engagement. More specifically the S is an upgrade of either 9.12 or 9.13, and with original R-77 only being used in numbers for export and not domestic Russian service, it was kind of a perfect match to sell the two together especially to those that already had 9.12. It was a new Ts101M processor which makes it able to do dual target track

 

There was just no changes for J-11A radar from original Su-27 but “hack it” to fire R-77. UBoats original J-11A post talks a bit about it.

Thanks, that's very informative. :thumbup:

[GGTharos]

I think I found the answer to part of my question in the wikipedia article for the AIM-120. Apparently, it does not continuously receive data from the aircraft's radar but rather is given a snap shot at launch and is then guided by INS (inertial navigation), with possible mid-course updates if the radar can afford it, until the seeker is active. Okay... that makes sense. So the radar doesn't do much of the work in TWS for an AMRAAM. I think what I was suggesting in my first post was more or less correct, that the missile is given a "rough" direction to fly until pitbull.

 

 

It receives updates at the rate of target updates basically. In TWS, this depends on what the TWS revisit interval is (In an F-15 that's 2.2 seconds). In STT, you may as well consider them continuous.

[Poopskadoop]

Because it is not identical to a SARH missile in any way, shape or form.

 

 

The AIM-54 is the only missile that we have that is capable of SARH guidance as well as ARH, and it's usually SARH-to-ARH (ie. SARH reflections are substituted for some of the TWS guidance/INS or whatever) which aren't meant to guide to impact but rather to seeker activation.

 

The other mode is an STT SARH-only launch, and that AIM-54 will never transition to ARH, it is SARH all the way.

 

 

Further, unlike missiles with m-links for target position updates, the sparrow is home-all-the-way. It tuned to the radar on the rail, and when launched it performs a english bias maneuver then immediately searches for a target to lock on to within those radar parameters.

Yep, looks like the AIM-120 is INS to ARH. Thanks for explaining the AIM-54. I couldn't find any information that clarified it.

[AeriaGloria]

Original J-11A introduction post https://forums.eagle.ru/showthread.php?t=207147

[Poopskadoop]

It receives updates at the rate of target updates basically. In TWS, this depends on what the TWS revisit interval is (In an F-15 that's 2.2 seconds). In STT, you may as well consider them continuous.

Interestingly, at least according to the wiki article, some air forces didn't opt for mid-course updates for their AIM-120s, essentially making it a "let's hope the target is still somewhere around where we thought it was at launch when it pitbulls" kind of deal.

[Poopskadoop]

Thank you, gents. Now, the last question I am wondering about is the last one in my first post. It would seem to me that having the ability to guide a radar missile (either TWS or STT) and be able to utilize an IR seeker head while the other missile is still guiding would be a good capability to have. Imagine it: you're in your Su-27 and you launch an R-27ER. Meanwhile, you use the R-27ET's seeker head to acquire and fire on another target. Imagine the same for an F-18 , F-14, or F-15. It seems like it would be a simple software issue, not a technical limitation. Is the reality more complicated than it seems? I know most aircraft like to slave the radar to an IR target, but... I mean... does it have to? Why isn't this a thing?

[LTRMcrew]

Now that I think about it, I think the hornet when you launch a sparrow goes from TWS to STT automatically to give it that launch guidance then it's on it's own. Where in TWS the Aim-120 needs the feedback until pitbull.

[AeriaGloria]

In such a case you can fire your R-27ER and R-27ET one before the other and both will guide. You just usually want to fire IR first so it doesn’t lock on to a missile in front of it. You can use EOS to acquire someone then turn on radar and fire any missile or use radar and then turn it off keeping your EOS on target

 

If you mean firing on two targets with different types of guidance, it’s just how fast your are on the switches. In case of Su-27 the FCS can only handle one target at time. So if you want to fire a fox 1, you’ll have to stay in that mode until impact, so you leave it for after you fire your ET

Edited March 17, 2020 by AeriaGloria

[Poopskadoop]

In such a case you can fire your R-27ER and R-27ET one before the other and both will guide. You just usually want to fire IR first so it doesn’t lock on to a missile in front of it. You can use EOS to acquire someone then turn on radar and fire any missile or use radar and then turn it off keeping your EOS on target

 

If you mean firing on two targets with different types of guidance, it’s just how fast your are on the switches. In case of Su-27 the FCS can only handle one target at time. So if you want to fire a fox 1, you’ll have to stay in that mode until impact, so you leave it for after you fire your ET

Yes, unfortunately I tend to lead with an ER in a BVR scenario. I just wish I could fire the ER and let the computer track the target while I switch to a mode that will let me queue up an ET or 73 on a different target while we close in. I suppose the Su-27 has the advantage in this regard because an ET can be fired from a fair distance. But the F-18 has the same issue. I would be silly not to fire a sparrow first, yet there is no provision for queuing a sidewinder on another approaching target, supposing the seeker head is within range to acquire it. I'm just not sure why this is a limitation. Considering IR missiles are autonomous, I can't imagine it would be that much more work for the plane's computer.

[Poopskadoop]

Now that I think about it, I think the hornet when you launch a sparrow goes from TWS to STT automatically to give it that launch guidance then it's on it's own. Where in TWS the Aim-120 needs the feedback until pitbull.

It does go to STT, but the sparrow needs that feedback the whole way to the target.

[AeriaGloria]

Yes, unfortunately I tend to lead with an ER in a BVR scenario. I just wish I could fire the ER and let the computer track the target while I switch to a mode that will let me queue up an ET or 73 on a different target while we close in. I suppose the Su-27 has the advantage in this regard because an ET can be fired from a fair distance. But the F-18 has the same issue. I would be silly not to fire a sparrow first, yet there is no provision for queuing a sidewinder on another approaching target, supposing the seeker head is within range to acquire it. I'm just not sure why this is a limitation. Considering IR missiles are autonomous, I can't imagine it would be that much more work for the plane's computer.

 

The Fire Control System would have to do two things at once still, calculate DLZ and tracking information for two different points in space. I mean I don’t know about F-18 but the sidewinder doesn’t have to slaved right? Doesn’t that mean that if you have to fire on two targets with a sparrow first, couldn’t you fire the sparrow switch to AIM-9 keep it caged and point your nose on the bandit you want to fire on and fire while the FCR still maintains STT and semi active illumination. Would that work in F-18?

 

I guess with Su-27 you could try that this Phi0 mode, but I don’t know if it’ll maintain STT guidance for R-27.

 

I get why you think there’s obvious utility to it, but to me it seems like a pretty limited use case. These weapons have so many limitations already, if you have Fox 1 you are really have to focus on one at time. But if you can make it work go for it

[Harker]

Technically, you should be able to fire a Sparrow and switch to a Sidewinder "radar-less" mode, where the radar would maintain PDI on the initial target and the AIM-9 would be IR-only (either boresighted or slaved to the JHMCS). It's just that it's not a capability of the real jet, since the Hornet operates with dedicated A2A weapon modes. This seems like a software logic limitation more than anything else.

But to be honest, I just think it's a rare enough case that the MD or Boeing engineers figured there'd be little to gain and they'd have to redesign the whole A2A weapons selection logic. And with the AMRAAM's arrival, there was absolutely no point for something like this.

[bies]

 

Finally, why does no aircraft in dcs (and I assume the real counter-parts) have the capability to guide a missile in STT while setting up a shot from an IR seeker? The AIM-9, R-73, and R-27ET do not require the radar to fire on a target, so why do aircraft not have such a simple functionality?

 

 

F-15Cs during Desert Storm had this ability. Pilots were able to uncage and manually (without radar) steer and fire AIM-9 during constant AIM-7 guidance not interrupting STT - thus attacking two targets at once.

 

F-15Cs had also ability to shoot two AIM-7 to two different targets - not at once but second shoot to second target was being prepared 'in background' and pilot can shoot to second target immediately after the first was hit.

 

I assume Hornet having very similar radar and logic would be able to do the same.

Edited March 18, 2020 by bies

[QuiGon]

So, how does the AWG-9 radar of the tomcat simultaneously guide multiple AIM-54s and the APG-73 of the hornet guide multiple AMRAAMs but neither the tomcat nor the hornet can guide AIM-7 Sparrows simultaneously against targets? Both the AIM-54 and AIM-120 are effectively semi-active missiles until they are within range to engage their active seekers, is that not correct? My understanding is that semi-active missiles cannot be guided in TWS mode unless the radar is a PESA and literally splits the beams, such as on the MiG-31. So how does that work? Does the computer give the missiles "rough" guidance until the seeker heads go active? Is it just the fact that the software is not integrated to work with the AIM-7?

Originally SARH missiles like the Sparrow needed constant radar reflections from the target which their seeker could guide on, whereas the AMRAAM doesn't need that as it's guided by its own INS aided with data link updates from the host aircraft on the target position for the first phase of its flight before it goes active. I said originally, because AFAIK latter versions of the Sparrow do make use of INS/DL guidance as well, for the first flight phase, but they still require constant radar illumination for the final flight phase as INS/DL guidance is not precise enough for the endgame.

[GGTharos]

F-15Cs had also ability to shoot two AIM-7 to two different targets - not at once but second shoot to second target was being prepared 'in background' and pilot can shoot to second target immediately after the first was hit.

 

 

There is no such thing. This is a simple target switch, you have to scan/acquire again to shoot the other target.

[bies]

There is no such thing. This is a simple target switch, you have to scan/acquire again to shoot the other target.

 

Thanks for clarification.

I was wondering how it would work, it would require TWS with trackfile and STT at the same time with conventional array. But I believed what I've read since many F-15 monographs repeated this - looks like - fake.