Target aspect switch

[Kula66]

12 hours ago, IronMike said:

 

Perfectly normal. And similar to what happens if you change PRFs in more modern radars, where medium will let you see cold targets more likely and high hot aspect bandits etc. Think of it: if it isnt on the DDD, it cannot be on the TID. And ofc, all tracks will always be affected by this, which is why a good RIO will know when to use which.

 

Thanks IM, I'd always assumed the DDD was what the radar was seeing right now, and that the TID was your view of what the WCS HAS seen recently, ie. included things seen in the last seconds, but potentially, no longer visible at the current moment. I guess that's what comes from never having sat in the back!

Edited June 20, 2021 by Kula66

[sLYFa]

11 hours ago, Grater Tovakia said:

killing the missiles was a tested (and practiced) means of employment for the Tomcats and their AIM-54s.

Which is now impossible in DCS (at with PD) since an AS-4 flies well above 1800. Hence the original question whether the current implemention is really correct. Or is there another way to pick up fast targets head on in a look down situation? 

Edited June 20, 2021 by sLYFa

[gyrovague]

Added Jester option to set aspect switch, and defaulted the switch position to nose aspect. This should be available in the next openbeta.

[Naquaii]

13 hours ago, sLYFa said:

Which is now impossible in DCS (at with PD) since an AS-4 flies well above 1800. Hence the original question whether the current implemention is really correct. Or is there another way to pick up fast targets head on in a look down situation? 

 

 

According to the documentation we have this is correct. Adjustment of the aspect switch allows selection of +1800 to -1800 knots rate around own speed.

[near_blind]

3 hours ago, Naquaii said:

According to the documentation we have this is correct. Adjustment of the aspect switch allows selection of +1800 to -1800 knots rate around own speed.

 

So using the AS-4 scenario above, if the missile is cruising at ~2000 knots GS, the Tomcat should be able to see it so long as aspect is in NOSE and the aircraft has a GS of greater than ~200 knots?

 

Doing some quick tests, from the RIO seat of an aircraft travelling 450 knots and again at 550 knots with the aspect set to NOSE, the radar was unable to pick up targets with a closure of 2000 knots in PD modes. I was able to confirm the targets were within the scan volume and had detectable RCS by finding them in pulse search. If the gate is centered around the aircraft's own speed, I would expect the gate to be able to acquire targets up to 2250 or 2350 knots GS. 

Edited June 21, 2021 by near_blind

[IronMike]

3 hours ago, near_blind said:

 

So using the AS-4 scenario above, if the missile is cruising at ~2000 knots GS, the Tomcat should be able to see it so long as aspect is in NOSE and the aircraft has a GS of greater than ~200 knots?

 

This would give you a closure rate of 2200kts.

Calculating rate of closure is easy, when head on, you just add both speeds, that is lateral closure with a constant bearing and decreasing range, so 2000 + 200 = 2200kts. But not so easy when you have an offset. You need to first know the angle between aircraft 1 and aircraft 2, the speed of both aircraft and then you take the speed of each aircraft times the cosine of the angle between aircraft 1 and aircraft 2 minus each aircraft's heading and then substract both results from each other. Now, I know this because I just looked it up, haha, and honestly, math isnt mine, so no thanks on calculating that. But: what we can take from this is that if you would have two aircraft approaching parallel, but not head on, then the angle between the two increases, and thus the closure rate decreases, easily understood when the angle between both is 90° (cosine of 90 = 0), and thus no matter their speed, the closure rate is zero. (You would actually also take into account the vertical closure, yada, but let us save the headache with that, it doesnt make that much of a difference, if somethin is "cruising" I would say.)

Let me go further in being a total math idiot: we know that our radar can see 60° left or right, so we know that before the closure rate turns zero, we will not see the contact on the radar anymore, as it will be outside of the gimbals. We also know that offsetting ourselves too far right or too far left, without doing any math, will let the angle reach 60° faster than if we offset ourselves less. Conclusion: we want to crank or offset ourselves to either right or left of the shooting platform, in order to spot the object before it passes us. And because we do not want the angle to change, and have the maximum angle for the slowest possible closure rate, we do not just fly head on on the parallel, but we crank, this means we adjust our offest to the incoming missile, so that it is at max gimble or 59° at all times. 

Let us say the missile (aircraft 1) is heading 180° with 2000kts and we (aircraft 2) are heading 060° with 200 kts, our angle is 60° to the missile and the missile's angle to us is 0°. So we get 2000 x cos(0-180) = -2000kts (negative sign indicating the missile has a left closure on us). We also get 200 x cos(0-60) = -100 (also negative, because we are closing left on the missile, too). So we get -2000 - (-100) = 1900 kts closure. Let us proof it, if we are cranking on the right gimbal. The speeds are the same, the missile is still heading 180° with an angle of 0° to us, but we are heading 300° and we are putting it on our right gimbal at 60° again. So we get again 2000 x cos(0-180) = 2000 kts (positive, because closing right this time). We also get 200 x cos (60 - 300) = 100 (positive because closing right). So again 2000 - 100 = 1900 kts.

What this illustrated is that you need the offset as well, when cranking, just beaming the missile (say it would keep constant speed and keep turning on you), would not decrease the closure rate enough. But, ofc, when you crank you fly forward, while the missile does not adjust on you, so you keep increasing the offset and thus the angle between the missile (aircraft 1) and you (aircraft 2). Let us say we have flown for a short while in the cranking maneuver and the offset is now such, that the missile's angle to us is 10°. Then you would get 2000 x cos (10-180) = ~ -1970 and 200 x cos(10-60) = ~ -129, thus -1970 - (-129) = 1841 kts of closure. Means, we need to increase the offset even further. At 20° angle between aircraft 1 and aircraft 2 you'd get 2000 x cos(20-180) = ~ -1880 and 200 x cos(20-60) = ~ -153; so -1880 - (-153) = 1727 kts. As you see, the more you increase the angle, the earlier you will see the missile. Here is the funny bit: since you are in this case flying away from the missile (while increasing the angle from it to you, but let us neglect that as well as the fact that we would be adjusting our heading to keep it simple), the slower you are, the higher the closure rate. Thus if you fly with 300 kts instead, you would get 300 x cos(20-60) = ~ -230; so -1880 - (-230) = 1650 kts. At 350 kts you would get -1880 - (-270) = 1610 kts. The flaw in this calculation is that you are adjusting your own heading to keep a steady 60°, while increasing the angle of the missile to you, as you basically fly around it, so your rate would constantly adjust and decrease, and turn negative, once the missile has passed you. [Please any math geniuses around, correct me if I am wrong!] 

If I was the Navy, I would thus have had the bulk of my Tomcats attack the archers and have both left and right flanking Tomcats be maybe 30° - 60° (wild guess) off the missile trajectory to intercept the arrows before they can pass. (I am sure they would have crunched on numbers to guesstimate where best, I would say half way from the predicted intercept range of the archer's.) If you position yourself 90° off the missiles, you will have no issues spotting them, but you would likely miss them ofc. I think of it like an A figure: top of the A is the intercept point, or where you would expect the archers to fire latest, left bottom and right bottom of the A is where the Tomcats sit to intercep the arrows. The cross line in the A is approximately where they would both be able to spot them and intercept them. The bottom of the A pointing to the carrier and the top of the A pointing towards the archers.

 

Mind you, my math sucks and this is overly overly simplified. Also, I think I broke my brain while typing this one lol.

Personally I honestly just superimpose this in my head, crank full gimbal at 350 kts and wing it! #YOLO


The tools I used for this post:

1. I watched this video.

https://youtu.be/Wn8F_xlPslE    

2. I used this cosine calculator.

https://www.rapidtables.com/calc/math/Cos_Calculator.html

Edited June 21, 2021 by IronMike

[near_blind]

Hey, I appreciate the response @IronMike. My own math career peaked at Calc II so I'm not going to be the one to critique . 

 

I'm just a little perplexed is all. By every account I've read, the F-14 was designed to go fast, and to kill things that were going fast, be that ASCMs, highspeed bombers or fighters. 1800 knots as a hard limit is approaching speeds you could expect from a particularly hot commit versus another fighter or a backfire, much less something like a Foxbat. That sort of speed places serious hinderances on engaging the previous generation of ASCM and SSCMs, much less the AS-4 and AS-6 that the aircraft was purported to be a counter for. 

 

Solving the closure issue by cranking seems alright on paper, but contextually also seems odd. I've read on here before that cranking to reduce closer defensively simply wasn't a tactic employed during the 70s and portions of the 80s. As an interceptor, reducing closure allows the threat to approach closer to the carrier, and reduces the effective range of your weapons allowing them to approach closer still. Increasing off set against a very fast threat like a ASCM would also reduce the missile's PK by introducing another dimension your missile has to correct for, still further reducing range. Crew material I have read specific to the Tomcat emphasized preparations to shoot by getting high, and then fast, I don't recall any talk of having to massage geometry to maintain closure rates (besides considerations for the notch). 

 

I'm not trying to be combative, and I hate trying to fight lines in manuals with what is anecdotal assertion at best, but manuals can be misinterpreted and given the role and pedigree of the aircraft, this seems like an strange design decision, if on no one else but Hugh's part. Why would the DDD have a switch to display closure of up to 4000 knots if the system can only effectively use half of that? Have you guys discussed this with your RIO SMEs?

 

 

[IronMike]

9 minutes ago, near_blind said:

Hey, I appreciate the response @IronMike. My own math career peaked at Calc II so I'm not going to be the one to critique . 

 

I'm just a little perplexed is all. By every account I've read, the F-14 was designed to go fast, and to kill things that were going fast, be that ASCMs, highspeed bombers or fighters. 1800 knots as a hard limit is approaching speeds you could expect from a particularly hot commit versus another fighter or a backfire, much less something like a Foxbat. That sort of speed places serious hinderances on engaging the previous generation of ASCM and SSCMs, much less the AS-4 and AS-6 that the aircraft was purported to be a counter for. 

 

Solving the closure issue by cranking seems alright on paper, but contextually also seems odd. I've read on here before that cranking to reduce closer defensively simply wasn't a tactic employed during the 70s and portions of the 80s. As an interceptor, reducing closure allows the threat to approach closer to the carrier, and reduces the effective range of your weapons allowing them to approach closer still. Increasing off set against a very fast threat like a ASCM would also reduce the missile's PK by introducing another dimension your missile has to correct for, still further reducing range. Crew material I have read specific to the Tomcat emphasized preparations to shoot by getting high, and then fast, I don't recall any talk of having to massage geometry to maintain closure rates (besides considerations for the notch). 

 

I'm not trying to be combative, and I hate trying to fight lines in manuals with what is anecdotal assertion at best, but manuals can be misinterpreted and given the role and pedigree of the aircraft, this seems like an strange design decision, if on no one else but Hugh's part. Why would the DDD have a switch to display closure of up to 4000 knots if the system can only effectively use half of that? Have you guys discussed this with your RIO SMEs?

 

 

 

I understand where you are coming from, and I share your questions. We will inquire further, from a distant point of view, without having doven into the subject further, it makes sense that it would be designed to pick up targets at closure rates higher than 1800kts.

We will take a second look. Thanks.

[near_blind]

That's all I can ask. I appreciate it! 

[IronMike]

3 hours ago, near_blind said:

That's all I can ask. I appreciate it! 

 

We discussed it again and went through our documentation again, and this is the conclusion we draw from it:

The closure rate of course concerns TAS. This means if something flies with a TAS of 2000 towards you, it is doing M3.5 at 30k feet. To my knowledge only 2 missiles are affected by this, the AS-11 and the AS-4.

We have no knowledge whatsoever, and we haven't seen this concept for fighters in general (beyond theoretical discussions), that the AWG-9 or in principal the Tomcat's mission included or was meant for intercepting supersonic missiles. Nothing indicates that, and it is very likely that it simply wasn't. It was meant to intercept the bombers that were carrying them and to intercept cruise missiles that fly much slower than the Kitchen or similar (and of course fighters). We also dont know of other fighters who are intended to do that. Mind you we are talking about missiles reaching speeds of M4 or even higher, M4.6 in the Kitchen's case.

The X-4 setting on the DDD might have other reasons for going to 4000, like future proofing or scaling issues. We are continuing to look there, but thus far did not find anything.

The doppler filters are a finite resource, they have banks of filters which are each an overlapping band and there are only so many they can put in. It is not unlikely that especially older radars like the AWG-9 top out at around M4.

In conclusion, when set to nose, nearly all aircraft should be visible (unless two aircraft are going head to head both supersonic, which is ill advised anyway), but not all missiles will be visible. We do believe this to be indeed correct, as again, nothing states that the Tomcat was capable, or even meant to intercept supersonic missiles at speeds around M4 or higher.

I hope this helps.



 

Edited June 21, 2021 by IronMike

[Kula66]

Do fast high flying Iraqi Mig-25s come into this? There are examples of actual intercepts from Iranian 14s successfully intercepting these. Plus isn't one reason the 14 was purchased was to determine Soviet Mig-25s from over flying Iran?

 

From memory, these required a very small intercept window to be successful and I doubt that involved an off bore site shot from a slow 14 ...

Edited June 21, 2021 by Kula66

[IronMike]

17 minutes ago, Kula66 said:

Do fast high flying Iraqi Mig-25s come into this? There are examples of actual intercepts from Iranian 14s successfully intercepting these. Plus isn't one reason the 14 was purchased was to determine Soviet Mig-25s from over flying Iran?

 

From memory, these required a very small intercept window to be successful and I doubt that involved an off bore site shot from a slow 14 ...

 

 

They wouldn't fly at M3.2 but around 2.2... Their max mach speed of 3.2 iirc is not sustainable without causing engine damage, which would be between 1800 and 1850 kts TAS at between 35 and 45k feet. At M2.2 that would be 1250 ish kts and at M3.0 (also prolly only for a very short window) at 1730ish kts. Prolly not a factor/ issue at all. If someone presses supersonic, all you need to do is lay a phoenix in his path, it will love his closure very much. If he is very fast in the supersonic range, he will even help your full gimbal shots to have prime energy on him. On top of that, the MiG-25 didnt know if it can be seen or not. It did see the Tomcat nail however, at which point it prolly high tailed out of there.

Edited June 21, 2021 by IronMike

[Kula66]

22 minutes ago, IronMike said:

 

They wouldn't fly at M3.2 but around 2.2...

 

Agreed, but even a M2.2 Mig-25 closing on a M1.0+ F-14 ... wouldn't that put the closure over 1800kts?

[IronMike]

12 minutes ago, Kula66 said:

Agreed, but even a M2.2 Mig-25 closing on a M1.0+ F-14 ... wouldn't that put the closure over 1800kts?

 

Yes, and? Would be around 1800 exact indeed. Keep own speed below .85 and all good. Again, if he comes so fast to you, you shouldnt be storming at M1 towards him.

The idea to fly around in burners at M1 most of the time is a DCS thing. Tomcats cruised between 200 and 250 kts, capping far away from the carrier. Sure they may have engaged the burners to intercept something fast while being guided on, or to quickly close distance, but with such a fast moving target, and such shorter missiles with your opponent, why accelerate at all, turn nose on, shoot a phoenix, wait. When in engagement range, they would have settled for engagement speeds. Even if you lose a guy high at M2.2 - rl isnt like DCS in that he will suddenly decide to haul M 3.2 all the way to the ground or similar. Once you slow down, you will likely find him where you expected him to be: pressing on you.

Edited June 21, 2021 by IronMike

[Kula66]

Referring to 'Iranian Tomcats in Action', a successful engagement of an M2.3 25 at 70k' was prosecuted by 'the 14A accelerated to M1.5 and climbed to 45k' ... so keeping slow was not how they were used in RL combat

Edited June 21, 2021 by Kula66

[IronMike]

9 minutes ago, Kula66 said:

Referring to 'Iranian Tomcats in Action', a successful engagement of an M2.3 25 at 70k' was prosecuted by 'the 14A accelerated to M1.5 and climbed to 45k' ... so keeping slow was not how they were used in RL combat

 

 

What tells you that the shot was fired at M 1.5? Also this is not head on, there is a vertical angle, which matters at well. What is the source? I did not find Iranian Tomcats in Action. Maybe you mean Iranian Tomcats in Combat, by Tom Cooper and Farzad Bishop?

What tells you that it was a head on shot? That it wasn't offset additionally to the vertical angle? The vertical angle alone could have probably put the closure rate well below 1800. Or was it guided on by GCI/AWACS in the first place? Was it a TWS shot? That it didn't use PS and PSTT instead? In such a scenario you may want to fire an ACM shot within 20nm and just tail out of there, etc etc.

It doesn't change the fact, that the doppler filter had a range of 3600 kts closure, from -1800 to +1800.

 

[Kula66]

Ok, I give up

 

EDIT: Yes, it was Iranian Tomcats in Combat, my error

Edited June 21, 2021 by Kula66

[AH_Solid_Snake]

 

8 hours ago, near_blind said:

I'm just a little perplexed is all. By every account I've read, the F-14 was designed to go fast, and to kill things that were going fast, be that ASCMs, highspeed bombers or fighters. 1800 knots as a hard limit is approaching speeds you could expect from a particularly hot commit versus another fighter or a backfire, much less something like a Foxbat. That sort of speed places serious hinderances on engaging the previous generation of ASCM and SSCMs, much less the AS-4 and AS-6 that the aircraft was purported to be a counter for. 

 

Solving the closure issue by cranking seems alright on paper, but contextually also seems odd. I've read on here before that cranking to reduce closer defensively simply wasn't a tactic employed during the 70s and portions of the 80s. As an interceptor, reducing closure allows the threat to approach closer to the carrier, and reduces the effective range of your weapons allowing them to approach closer still. Increasing off set against a very fast threat like a ASCM would also reduce the missile's PK by introducing another dimension your missile has to correct for, still further reducing range. Crew material I have read specific to the Tomcat emphasized preparations to shoot by getting high, and then fast, I don't recall any talk of having to massage geometry to maintain closure rates (besides considerations for the notch).

 

I think there are a few misconceptions baked into some of this discussion, and while I'm by no means the final SME on the F-14, nor a math wizard I can offer the following points.

 

The F-14 is indeed designed to go high, and fast, and to kill other things that are also doing the same, but not necessarily all at the same time.

 

Geometry to manage closure is a huge part of running intercepts whether its a peace time stern conversion or a wartime weapons free, theres a reason when you see video of the F-14 doing TWS tests, or Phoenix tests in general that the wings are either full forward or in an intermediate (but still mostly forward) position - so long as you're high and pointed the right way the Phoenix will make up a lot of the range such that adding a few extra knots or breaking the mach prior to launch against a large number of targets just means you're going to end up ruining your TWS solution by the time you're getting to the 4th (or even 6th!) launch. Remember that your TWS scan volume is either wide or tall, again not both at the same time. Excess closure for this kind of shot means you're going to force some of the targets outside your allowable volume before going active simply by pushing that cone closer to them.

 

For single shots against the MiG-25/31 example these intercepts are incredibly geometry intense since you usually can't expect to be conveniently lined up right in front of them with a big rate of closure, and in this scenario we're going to be burning the Phoenix motor in order to catch them at all. F-15s with AIM-7 have even narrower margins for this type of intercept.

 

In these kinds of cases you're going to be going STT for a single shot, because against a target moving that fast a TWS scan is just not reliable enough to guide your weapon with much of a chance of hitting them.

 

TWS is more like guidelines than guidance for your missile. The best it can do is give your missile a box (usually referred to as cell) that the target is within, for the F-14, from memory these are 5 degrees wide and 5nm long...thats a lot of CEP for your Phoenix when both it and the target are doing mach 2+ in the terminal phase.

 

Secondly even with its big motor then depending on...that word again...the geometry of the intercept you are burning a lot of the missiles energy just maintaining a Pn lead pursuit course, if you were already on CAP the enemy is unlikely to just go CBDR right at your 12 oclock allowing for the perfect straight line course. And if you were scrambled to meet the threat your missile is also doing significant uphill work to meet them from a lower starting altitude.

 

In these cases you've got to manage 2 things with your geometry as usual. Range and angle off. Tracking 90 degrees or 180 degrees against a M2+ bandit will make even a Phoenix struggle, making your WEZ much smaller than the 100nm on paper.

 

Tracking nose on from below requires you to get as much height as you feasibly can before the enemy gets so close that your missile (and radar guidance) would have to do an immelman turn to maintain tracking, so you'll get whatever height you can, then get as fast as possible, then zoom climb so that at the optimum moment you are high / fast enough to catch them, followed by leveling off again before you stall out and again lose the STT guidance for the weapon.

 

All this was suffice to say that theres a hell of a lot of geometry involved and thank god there are RIOs for that

[Sandman1330]

Is this due to doppler gates? In my limited understanding, I know PD radars to transmit in harmonic frequencies, for which the spacing between them is determined by the radar's PRF. The doppler return needs to come in at 1/2 the PRF in order to be recognizable to one of the harmonics, otherwise it will fall into the "range" of one of the other harmonics, thereby giving an inaccurate speed. A faster closure will see more doppler shift, until such time as it falls into one of the other harmonic gates.

 

Is this what the target aspect switch does? Does it tell the radar which gate the return should be inside, thereby allowing a wider range of closure speeds? 

 

I think if we can get one of our many radar gurus to explain this better than I, it would clear up much of the dissention here...  I have a foggy enough understanding to know why this is a thing, but not enough to explain it well!

[near_blind]

8 hours ago, IronMike said:

I hope this helps.

Thanks for the effort!

 

So far checking the good old DTIC the "hottest" confirmed Tomcat shot I can find evidence of was that famous 110 mile Phoenix shot, which was from a M1.5 Tomcat against a M1.5 drone. Assuming they were both head on, that closure rate falls at or just below the 1800 limit. Reading through some early 70's vintage money requests capability reports, the anti ASCM language is certainly there, but it's more aspirational and less determinant than I remember. 

 

All this to say I still find the situation odd, but the AWG-9 was a system full of oddity. I can live with it.

For comparison, talking with a buddy who does Eagle stuff the contemporary, original APG-63 had a gate of 2100 knots.

[AH_Solid_Snake]

32 minutes ago, near_blind said:

Thanks for the effort!

 

So far checking the good old DTIC the "hottest" confirmed Tomcat shot I can find evidence of was that famous 110 mile Phoenix shot, which was from a M1.5 Tomcat against a M1.5 drone. Assuming they were both head on, that closure rate falls at or just below the 1800 limit. Reading through some early 70's vintage money requests capability reports, the anti ASCM language is certainly there, but it's more aspirational and less determinant than I remember. 

 

All this to say I still find the situation odd, but the AWG-9 was a system full of oddity. I can live with it.

For comparison, talking with a buddy who does Eagle stuff the contemporary, original APG-63 had a gate of 2100 knots.

 

Something relevant for this test shot is I would assume STT tracking unless otherwise specified and that the 1800 limit is irrelevant, the RIO has a lot more radar options than we do sitting in the front seat locked in TWS Auto.

 

 

[near_blind]

9 minutes ago, AH_Solid_Snake said:

Something relevant for this test shot is I would assume STT tracking unless otherwise specified and that the 1800 limit is irrelevant, the RIO has a lot more radar options than we do sitting in the front seat locked in TWS Auto.

 

The 1800 knot limit affects all PD modes, including PD-STT and PD-Search unless I've tested something horribly wrong. A 100 mile P-STT Phoenix shot would be... optimistic

[IronMike]

I think it doesn't make much difference if it was STT or TWS, since that shot fell within the 1800 kts closure, either would have been possible.

[AH_Solid_Snake]

For the purposes of the Vc / target aspect switch you're of course correct. I just have a somewhat ingrained reaction to the TWS unless otherwise attitude in flight sims when the reality that I'm aware of is fairly well the opposite, STT unless otherwise needed.

 

For the 100nm test if we are recalling the same one correctly then they spent time augmenting the radar signature of the drone and the test criteria was more around the Phoenix reaching that point and completing the intercept rather than the AWG-9 (I appreciate the two are linked), kind of proving that with some advances in electronics the system has some growth potential yet. In such a test with such a high closure single target I'd much rather put trust in STT to hold it than the (correctly modelled) reliability of TWS. Can you imagine getting half way through the intercept and having the little X appear and then the AWG-9 guestimating when to send the active signal for that run

[GGTharos]

On 6/20/2021 at 4:19 AM, sLYFa said:

Which is now impossible in DCS (at with PD) since an AS-4 flies well above 1800. Hence the original question whether the current implemention is really correct. Or is there another way to pick up fast targets head on in a look down situation? 

 

This is the correct result from what I could gather - these missiles were designed to go so high and fast that you can't reach them with any weapons unless you get them as they're launching or pretty much when they're terminal and forced to slow down.