AWG-9 velocity gating?

[Noctrach]

Feel free to move this to bug section if you want, but I'm curious if there's any sort of velocity gating implemented with the AWG-9.

It is really very easy to generate broken TWS tracks that share no semblance to the original locked return.

From the manual it seems relevant DDD information is missing for sure, so that's also why I wonder if it's implemented.

 

Attached a track in the PG BVR instant action displaying this. The two-ship flight splitting up is guaranteed to break the tracks. In most cases, the original track will even be flying backwards, away from both new returns. If the system was really this poor at resolving separating contacts, firing on 2-ships flying less than a mile apart would basically be pointless beyond 30 miles.

 

On top of that, the target doing a quick snake or barrel roll will almost definitely result in a broken track overlaid over the actual return, flying side by side. This happens even when MLC is disabled due to the altitude separation induced by my dive. (8000 ft at 23 miles is >3 degrees look-up) It should be getting returns just fine. The only likely explanation I can come up with is a poorly adjusted scan volume because it's trying to chase a broken track.

 

I know trackfiles are broken/nondeterministic for the F-14, but I see the behaviour appear on replaying this one with absolute consistency so maybe it helps. Note that this track is recorded in single-player. The problem gets a thousand times worse in multiplayer when latency starts getting involved.

 

While I fully understand broken tracks due to land-based clutter are a weakness of the real system. I find it hard to believe that this would be realistic behaviour for a system trusted to defend the fleet against cold war threats.

BrokenTracks.trk

[Naquaii]

According to our information the AWG-9 does not use velocity gating. It uses range-rate instead which is calculated from track position updates. This is what we've modelled in DCS.

 

I'm inclined to say that the weakness of the AWG-9/AIM-54 combo against fighters was the AWG-9 in TWS, not the missile itself.

[Noctrach]

Alright, it seems odd for it to be that easy to spoof. But fair is fair.

It would seem this weakness would restrict the usage of the Phoenix to mostly STT against fighters, which would essentially turn it into a big FOX-1.

That'd indeed mean the missile's capabilities would be quite severely limited by the platform.

 

Thanks for the reply.

[Northstar98]

FWIW, what is the difference between velocity gating and range rate gating? Up to now I thought they meant the same thing (range rate, i.e change of range over time, well that's just another way of saying velocity).

 

As I understand it, I would've thought PD modes would use a doppler speed gate and I thought that range-rate gating meant the same thing, obviously from the doppler effect. Pulse modes on the other should would use a range gate.

 

Any help?

Edited March 9, 2021 by Northstar98

[Naquaii]

Range-rate is calculated from positional updates, kinda like how a GPS works. Velocity gating on the other hand would use the speed directly, from doppler readings.

 

Edit: So to clarify, by specifying that it's range-rate it indicates that it's rate calculated from range updates, not velocity from doppler.

Edited March 9, 2021 by Naquaii

[Northstar98]

3 minutes ago, Naquaii said:

Range-rate is calculated from positional updates, kinda like how a GPS works. Velocity gating on the other hand would use the speed directly, from doppler readings.

 

Ah I see! So it's more or less the same thing, but instead differentiating between how it's measured. Thanks Naquaii!

Edited March 9, 2021 by Northstar98

[Naquaii]

Just now, Northstar98 said:

 

Ah I see! It's the same ball park, just different ways of measuring it. Thanks Naquaii!

 

Yes and no. Using range-rate isn't as good as it leaves the radar more susceptible to the described errors above as the AWG-9 might be unable to tell which return to use for the range-rate calculation. Velocity gating on the other hand would be better as it'd use the actual measured doppler so you would get rid of some of the false tracks.

 

You kinda need to remember that the AWG-9 was one of the absolute first examples of TWS and is a quite basic TWS system.

Edited March 9, 2021 by Naquaii

[Northstar98]

I should've worded it better, I meant that the 2 schemes are getting at essentially the same thing (closure rate), but different ways of getting it. Though once again, thank you for the explanation! 

[nobuttons]

3 hours ago, Noctrach said:

Alright, it seems odd for it to be that easy to spoof. But fair is fair.

It would seem this weakness would restrict the usage of the Phoenix to mostly STT against fighters, which would essentially turn it into a big FOX-1.

That'd indeed mean the missile's capabilities would be quite severely limited by the platform.

From my cursory reading I understood that the whole weapon system (radar and missile) was optimized for the threat of ship killing bombers? So maybe it's understandable that usage against fighters was deprioritized, or not even considered?

 

I'd love to learn more about this though, as I am basically ignorant here!

[Gunslinger22]

29 minutes ago, nobuttons said:

From my cursory reading I understood that the whole weapon system (radar and missile) was optimized for the threat of ship killing bombers? So maybe it's understandable that usage against fighters was deprioritized, or not even considered?

 

I'd love to learn more about this though, as I am basically ignorant here!

How does this myth of the Tomcat only being designed around being a bomber interceptor keep getting propagated? It was designed for fleet defence, which entails all threats, including the nimblest of fighters. 

[near_blind]

  

6 minutes ago, nobuttons said:

From my cursory reading I understood that the whole weapon system (radar and missile) was optimized for the threat of ship killing bombers? So maybe it's understandable that usage against fighters was deprioritized, or not even considered?

 

I'd love to learn more about this though, as I am basically ignorant here!

 

Kinda, or at least that's the impression I've always got reading through the early public materials for the F-14. 

 

30 minutes ago, Gunslinger22 said:

How does this myth of the Tomcat only being designed around being a bomber interceptor keep getting propagated? It was designed for fleet defence, which entails all threats, including the nimblest of fighters. 

 

I don't think that's what nobuttons is saying. The F-14 as an aircraft is certainly built to do more than down bombers, and whatever it's genesis the AIM-54 had excess capability enough to drop fighters. There are, however, a number of quirks about the AWG-9, especially the PD modes, that speak to the engineers working on it having definite assumptions on what it would be used against.

 

The AWG-9 has two distinct operating paradigms: PD and Pulse. All the PD modes focus on acquisition, tracking, and guidance at extreme ranges, the compromises chosen to get the radar functional with the technology available at the time seem to effect the radar least when the targets are flying straight at the Tomcat (like a stream of bombers trying to shoot missiles at the boat behind the Tomcat). These suit the Fleet Air Defense role, and those compromises were known as was the reality that the doppler notch and I guess other weaknesses like the rate gating left the system vulnerable towards small, maneuvering fighter type targets that the F-14 was likely to face in it's other primary role as an Air Superiority Fighter. That's why you have Pulse: compared to the quantum leap of the PD modes, it was a known technology with strengths and weaknesses that were well understood, and had proven at the very least capable in a combat environment. The Navy could also leverage a roster of crews that were experienced with the system after a decade of the Phantom being in service, and it was felt a good RIO could work the system such that he was more likely to be able to find a target than a contemporary noise filtering algorithm (the unspoken obverse not withstanding).

 

Remember that during period that the F-14 was designed and initially operated, there was a very different understanding of how air combat worked. The prevailing Navy experience from Vietnam was that against fighters at least, the fight was still very much a swirling, low level visual affair. Kills would primarily be made with the sidewinder and maybe the gun, the Sparrow would be used to grab whatever could be got on the way in and out, ROE and performance permitting. It's not the best analogy, the Navy of this period was more proactive about both missiles and the crew concept, but If you read materials and congressional briefings for the F-15 during this time the USAF is bending over backwards to insist that fighter is a primarily visual fighter and the ***giant*** APG-63 in the nose was merely there to provide situational awareness and guide the fighter to the merge for AIM-9 implementation. It isn't until AIMVAL-ACEVAL and the aftermath that the US Military seems to really grasp what the proliferation of capable all aspect missiles would mean, and begin to pivot from the idea of the swirling dogfight to tactics that exploit their superior sensors and missiles. 

 

It wasn't unreasonable thinking either: during the late 60s and early 70s the US has essentially monopolized the concept of the medium range missile. Of the three likely category of the opponent they would face: there was the Soviet VVS which was using cannon and AIM-9 knockoffs, the soviet PVO which was using all sorts of missiles of disparate use and short range compared to their size of cost, and export fighters, which were VVS aircraft but worse. RWRs were not widespread, and where they existed they were rather rudimentary. Neither was fighter launched chaff really a "thing", the concern was the ubiquitous rear aspect heat seeking missile. For this environment Pulse STT, the AIM-7E/F and the attitude that kills would be achieved via good ol' tail chasing isn't entirely unreasonable. 

 

 It wouldn't be until the mid 70s where you start to see increasing numbers of things like MiG-23Ms and MiG-25s with somewhat credible all aspect medium range missiles, escalating in the 80s with the Foxhound, Flanker and Fulcrum. During that time the role of the AIM-54 transitions from the silver bullet reserved for vital fleet air defense to a more ubiquitous tool. I don't have any specific literature from the 80s, but I've seen some things that suggest by the late 90s the AIM-54C was capable enough that the PD modes had become the primary tools for air supremacy, and the missile would make up for any deficiencies with the AWG-9. 
 

Two other thoughts I have, but couldn't figure out where to place. One, the two biggest weaknesses of the F-14: the engines and the radar, were originally supposed to be expedient stopgaps to get the type into service. The TF-30s were meant to be replaced quickly by the PW F401s (original F-14B), and the radar/firecontrol was supposed to be replaced by some to-be-determined digital set before the end of the 70s (F-14C). The Navy passed on both of these due to budgetary issues. Two, is that the nearest competitor to the AWG-9, the APG-63 was received a number of changes post AIMVAL-ACEVAL that transitioned it from a tool the fighter jocks were going to use to perform high aspect intercepts and shoot fleeing MiGs, into a capable, and more importantly flexible with all sorts of goodies and TWS and stuff. The Air Force had the political will and budget to force those upgrades through, and apparently the Navy did not. There is a reason the -63 forms the basis for most modern US mech sets post 1990.

 

alright, I'll stop talking out my ass now and leave y'all to it.  

[TLTeo]

Also in general, the DCS community obsesses over random 1v1, long range, TWS kills way too much, because that's how airquake works. I suspect in a real world situation where you're fighting as a coordinated 2-4 ship, falling back to STT launches if you suspect your target is a maneuverable fighter with a RWR better than an SPO-10 would probably work fine.

[AH_Solid_Snake]

Agreed, all the manuals regarding intercepts assume at least a pair performing the intercept and talk about staying in RWS to maintain awareness before going STT in the timeline for the attack.

 

I suspect radars more modern than the AWG-9 will be more reliable in TWS but not to the degree found in the other DCS teen-series.

 

another aspect to the air-quake is that it’s all about the kill, so maintaining stealth for the missile shot, IRL if you can force the attacking aircraft away from the territory or flight you are defending behind your CAP station then you’ve stopped them from carrying out their mischief while your friendlies have executed theirs unimpeded.

 

In servers more focussed on missions or dynamically taking over territory the mud movers are the guys really taking over the map and the fighters are just facilitating... it’s true in some ways that fighters make movies and bombers make history.

[nobuttons]

21 hours ago, near_blind said:

The F-14 as an aircraft is certainly built to do more than down bombers, and whatever it's genesis the AIM-54 had excess capability enough to drop fighters. There are, however, a number of quirks about the AWG-9, especially the PD modes, that speak to the engineers working on it having definite assumptions on what it would be used against.

Thank you, yes! That's the kind of education I was hoping for.

 

P.S. When I said 'weapon system' I should have specified I meant (AWG-9+AIM-54) not (F-14+AWG-9+AIM54).

One thing I recall, not touched on explicitly here is that the AWG-9+AIM-54 were in development and (relatively mature-ish?) by the beginning of the F-14 design (helping accelerate the F14 program), and they had been planned as the primary weapon system for other aircraft (including the F-111B which would have had more of a dedicated fleet defense/bomber interceptor role) than the  F-14?

[TLTeo]

Yep, correct on the F-111B. The origin of the system are actually in the AIM-47 missile and AN/ASG-18 radar that were supposed to equip the YF-12 and XF-108 .

Edited March 11, 2021 by TLTeo

[Naquaii]

Just to clarify. I'm not saying that the Tomcat or the AIM-54 are bad against fighters and that's certainly not how we've modelled it. What I'm saying is that the TWS in the AWG-9 isn't good enough to work reliably against small maneuvering fighter-sized targets and afaik that is more or less correct with real life.

 

What I was trying to say was that the percieved lack of performance against fighters likely stem from this imho while in reality the missile and STT were perfectly fine against fighters. Nothing we have points towards the AIM-54 in itself being unsuited for use against fighters.

[Noctrach]

1 hour ago, Naquaii said:

What I was trying to say was that the percieved lack of performance against fighters likely stem from this imho while in reality the missile and STT were perfectly fine against fighters. Nothing we have points towards the AIM-54 in itself being unsuited for use against fighters.

I think what's a bit of a thingy is that in DCS the interaction of chaff/notches with STT is mostly nonsensical. Even for targets that aren't anywhere near the notch, or against an AWG-9 in look-up mode, more than 50% of AIM-54C's fired as SARH will go for chaff if the target drops enough. Considering PD-STT warns the target through the RWR, that's anywhere between 30 and 100 seconds of opportunity to do a jink, dump some chaff and call it a day. Smart use of MLC or proper geometry will not help this at all, since it's not the AWG-9 getting spoofed but the missile itself.

 

What makes the AWG-9 seemingly stand out as such a poor platform in comparison to the modern ones is its very realistic radar modeling on one hand versus an incredibly simplistic countermeasure modeling in the sim. Though I would never ask for a change in the former, I'm hoping the latter becomes less of a pain as ED finishes the missile API in 2027.

 

Just feels like a lack of agency when you're simultaneously dealing with the inherent weakness of the system (fun) and the weird RNG of the sim (not fun).

 

 

Edited March 11, 2021 by Noctrach

[near_blind]

16 minutes ago, Noctrach said:

Just feels like a lack of agency when you're simultaneously dealing with the inherent weakness of the system (fun) and the weird RNG of the sim (not fun).

 

Agreed. As missiles and sensors gain more depth, the way CM works only becomes more glaringly problematic. I know ED and co has put in a lot of good work with the AIM-120 and AIM-7 last year, but with the latest changes to chaff and ECM it feels like we're right back in that 'gladiatorial combat' that they promised to move us away from. Hopefully it gets addressed sooner rather than later. 

[Naquaii]

Yeah, unfortunately spamming chaff currently gives the aircraft more "dice rolls" to negate the missile while IRL the cumulative effect would be much less. Tactics about how to release chaff and when is just inferior to spamming the chaff as each bundle give the aircraft a new "saving throw".

[Noctrach]

@Naquaii Out of curiosity, it's not possible for you to simulate the effect on chaff on e.g. Pulse mode right?

As far as my testing has indicated chaff and flares do not actually "exist" as much as they are simulated as subcomponents of the aircraft.

Uncaged AIM-9's for instance do not see flares until they've locked onto the host aircraft.

Neither can missiles see chaff/flares dropped by other hosts than the target they are currently intercepting.

 

Would be pretty cool to be able to see when the lock is being spoofed.

Edited March 11, 2021 by Noctrach

[Naquaii]

In a way yes, but like you say it we would need to do a lot of work on our side unless it's just gonna be that same "dice roll" to break STT. As DCS doesn't model the actual countermeasures as their own entities apart from visuals we'd need to somehow simulate all other effect on our side as chaff would show up on scopes and have the radar follow them and so on. We would in effect have to keep track of chaff and where it is internally in our module. 

 

In short it would be a lot of work for something that we might need to throw away if the DCS modelling of chaff changes down the line. And just adding a chance for the chaff to break an STT wouldn't be that realistic anyway as there are so many factors in a situation like that.

[Northstar98]

4 hours ago, Noctrach said:

What makes the AWG-9 seemingly stand out as such a poor platform in comparison to the modern ones is its very realistic radar modeling on one hand versus an incredibly simplistic countermeasure modeling in the sim. Though I would never ask for a change in the former, I'm hoping the latter becomes less of a pain as ED finishes the missile API in 2027.

 

Abso-friggin-lutely.

[nobuttons]

5 hours ago, Noctrach said:

...I'm hoping the latter becomes less of a pain as ED finishes the missile API in 2027.

 

At first I laughed and assumed you were being snarky...

Then I thought hard about this game and I was like, "ohmigoawd what if he's serious?!"

[near_blind]

14 minutes ago, nobuttons said:

Then I thought hard about this game and I was like, "ohmigoawd what if he's serious?!"

 

Two weeks^TM, be sure

[Noctrach]

@Naquaii Further question:

 

Edit: Ignore some of my reasoning below, I was over-analysing

The AWG-9 will start aggressively sweeping the antenna up or down if you are coupling roll with climb rates. Is this intented behaviour?

• Only descending -> No problem
• Only turning -> No problem
• Descending AND turning -> AWG-9 goes crazy and radically changes radar elevation

It does not matter how smooth you do this, the second you couple a bank with a dive you lose lock due to behaviour described below.

 

Edit2: This also happens if you don't couple them, bank first, dive second.

Upon banking, the radar elevation will go from +1 degrees to -20 degrees.

Rolling back upright sees the radar sweep back up from -20 to way past the target (> +10 degrees), losing the lock.

It doesnt really matter if you do this abruptly or smoothly.

 

Edit3: This also happens with a target flying perfectly straight and level

 

It seems like the AWG-9 is coupling its antenna elevation with its antenna train angle in PD-STT when the aircraft rolls?

Short video of it in action: https://streamable.com/76b19f

 

When PD-STT on a target in head-on aspect, MLC switch set to either on or off, the AWG-9 will still consistently lose the target with below result.

 

Target enters a 2G diving turn, Closure drops from 630 to 360 in about 8 seconds. The descent rate smoothly increases over this time from level flight to a peak of -22,800 ft/min. 

 

The AWG-9 responds to this by aggressively sweeping the antenna down to far below the target. It's  not related to target, it's related to the F-14/AWG-9 itself

Notice a -5.8 degree sweep, corresponding with a horizon-relative attitude of -21 degrees. The original attitude before we initiated the turn was about +16 degrees. Note that this is not a gimbal issue, the target is put on 45L, we are nowhere near the true antenna limits.

The AWG-9 sweeps the antenna back up about 3 seconds later. Notice a sweep angle of +11.3 which corresponds to an angle relative to the horizon of -3 degrees. Due to lost lock and MLC-off, the radar will lock onto the first ground clutter it finds during its upwards sweep.

The real target is currently elevated roughly 2 degrees above the horizon.

With MLC on we see the same behaviour, only the AWG-9 will never stop sweeping back up.

It actually gets a return hit at around +14 degrees, which is exactly the current target elevation relative to our aircraft attitude.

However, it does not correlate this back to the original track and continues sweeping upwards until hitting radar limits.

 

This seems like a genuine bug.

Edited March 13, 2021 by Noctrach
New information after further testing