AIM 120's

[Guest ruggbutt]

I spent an hour w/a client of mine discussing combat flight tactics and such. He's an F16 instructor at Luke AFB. I knew going into the conversation that certain info would be classified, such as most of the AMRAAM info. I posed several scenarios regarding LOMAC and 120's. High/High, High/Med, High/Low shots, closure rates etc......

 

The answer I requested from him was simple, is the sim (regarding the specific questions) under or overmodeled. The conclusion is that in LOMAC the 120's are undermodeled. I'm not trying to slag ED by any means, I understand that they have a limited amount of info that is "real world". I hope that in 1.1 the loft profile that we're supposed to get for the 120's will mimic more correctly accurate PK's at accurate distances.

 

As an aside he had no idea that communities such as this were as hardcore as we are. He was impressed that I understood F-Pole, notching, beaming, PK and other "fighterspeak". I'm going to burn a couple of LOC's flicks to DVD and drop them off to him. Maybe I can get him over to my place to try out the TrackIR, CH Hotas and pedals and his madskillz against the "bad guys".:D

[GGTharos]

Another thing we need is the following:

* Proportional Navigation for HoJ (All HoJ missiles)

* 5-g limit on missile turns until they reach close to terminal where they unlock to full maneuvering potential

* ARH TTA=TTI-10sec, NOT 10nm!

* ARH starts a search pattern in target 'probability box' when it goes active.

* More realistic ARH seeker modelling. The Seeker's FOV simply isn't limited enough ATM AFAIK - if someone launches without lock at 10nm, it should be likely that the missile will miss if the targetted aircraft goes defensive (it should be able to leave the seeker FoV) - also, there should be a 'search' warning from missile seeker as it searches for a target before lock tone. Depending on radar modelling, the lock could happen quickly or not at all.

* Better low-level performance than SARH (due to monopulse active radar)

* ARH switch to lead-collision at 2km from target, PN otherwise (prevents it from having its energy destroyed)

* Better Rmin implementation for all missiles (fuze not armed until Rmin cleared, typically via timer on missile - eg fuze not armed until 2sec in flight)

* More sensitivity to chaff, esp. for SARH

 

 

ED, I've got sources for all these deductions, but I think you must have similar sources for this as well - but don't hesitate to ask me for them! :)

[GGTharos]

Oh yeah ... Ruggbutt, could you ask him about ground-bouce/clutter and how it affects shoot-down and shoot-up from like 100'.

[Guest ruggbutt]

Some things I will not ask as I refuse to put him in a situation where he has to tell me no. I'm also very aware of National Security issues w/my country, so I can only put it in the context of this sim. I'll do what I can but I will not do anything that could potentially cause harm to myself, my client or my country.

[GGTharos]

I don't think we're asking for anything classified ... eg: Not asking for radar performance of AIM-120 vs. low alt targets ...

 

Just in general about how mcuh degradation or basically WHY is it bad to shoot from low alt to high alt long range ... or why is it good ... I'd just like to get an idea of what he can tell us because even though I've read up a whole bunch of this, someone who operates the equipment can basically confirm it - in other words, I'm asking for generalities.

 

Ie. You can't shoot up because your radar won't see suad, or his missile will get to you before your missile gets to his, etcetc.

[Guest ruggbutt]

Ok, I'll work out some questions for next time I see him.

[GGTharos]

RGR, thanks man :D

[SwingKid]

Another thing we need is the following:

* Proportional Navigation for HoJ (All HoJ missiles)

 

In light of the wingtip ECM emitters on the F-15 and (especially) Su-27, there seems reason to suspect these systems might be capable of "cross-eye" jamming, which can force even monopulse HOJ seekers onto incorrect trajectories. Lock On's pure-pursuit HOJ trajectory is modelled as a compromise to represent the average trajectory of a missile that is driven off target, then re-acquires, then is driven off again etc. without making things so complicated. Even so, by popular request Lock On provides the attacker with IMHO wildly generous burn-through range against self-protection ECM, making much of this a moot point.

 

* Better low-level performance than SARH (due to monopulse active radar)

 

Why "better," specifically? The fighter radars used to illuminate for the SARH missiles are also monopulse and similarly capable of tracking low level targets, no? They also feature sidelobe compensation horns that I don't think can fit into an ARH missile.

 

* ARH switch to lead-collision at 2km from target, PN otherwise (prevents it from having its energy destroyed)

 

Are "lead-collision" and PN not the same thing?

 

* More sensitivity to chaff, esp. for SARH

 

This one you should back up with sources. Everything I've ever read says that chaff decelerates instantaneously and pulse-Doppler radars are practically immune to it. The only way I could imagine chaff having effect is when used while (a) beaming or (b) bouncing rearward-transmitted ECM signals off of it.

 

ED, I've got sources for all these deductions, but I think you must have similar sources for this as well - but don't hesitate to ask me for them! :)

 

Interested,

 

-SK

[SwingKid]

Re: AIM 120's

 

I hope that in 1.1 the loft profile that we're supposed to get for the 120's will mimic more correctly accurate PK's at accurate distances.

 

I know this is going to sound ridiculous, but I think the F-16C may now be simply a more modern and capable user of the AIM-120 than is the somewhat more aged F-15C. According to the best and most recent information I've had the opportunity to review, the F-16C can loft the AIM-120, and the F-15C can't. (!?!) This will have a big impact on the missile's range and performance.

 

Any unclassified data to the contrary very welcome... First the "sort" mode, then RAM, now this. The more I research the Eagle, the more questions I seem to have...

 

-SK

[GGTharos]

Watch the Archer video. The AIM-120 fired in it lofts.

 

Also send me a PM with your email ... I'll send you a PDF.

 

I'll have to try and find the site I was reading up on radar again (also the F4 manual states that, after paying money for various research docs, they found out that ARH fares better in low level environments ... it had to do something with the monopulse radar and the fact that it is an ARH missile, but the explanation didn't go into details - it's basically possible that the ARH missile can use MTI more effectively IMHO)

 

You might be right on HoJ, I'll have to re-read about the cross-eyed jamming, though they definitely mentioned that 'the missile is the forced to swich to less efficient proportional navigation' ...

 

It also showed some burn-through graphs as well (indeed, the Burn-through range it'sn that great, but the key was that you don't need to actually completely overpower the jammer to get around it - one example graph had BT at 13nm or so)

 

This was on a NAVY mil site and it was used to help RADAR engineers, IIRC.

[GGTharos]

https://ewhdbks.mugu.navy.mil/contents.htm

 

Looking for other info that I had ...

 

Oh, BTW ... on the SARH being more susceptible to chaff: PD radars are nto necessarily 'immune' to it. The bloom might be rejected but it might also conceal the launching aircraft or otherwise mask the return (the cross section of chaff AFAIK is just ridiculous) and confuse it enough to either drop lock or lock onto the chaff - depending on conditions this may well not work, but it still -depends-. I suppose that you hit the nail on the head there, that it would be combined with beaming.

 

Additionally, SARH missiles may not have a way of telling accurately how much the doppler shifted so their seeker may attempt to look at the chaff - then it has to 'settle' and consequently when it finds the AC again is must 'resettle' and done at the proper time this may either take the aircraft out of gimbal limits or force the missile to pass out of lethal range when chaff is combined with a maneuver such as an otherogonal barrel roll as the re-settling seeker ends up preventing a completely optimal course.

 

An ARH might do better because it has its own emiter and could potentially be capable of gaging the doppler shift much more effectively, thus making it less susceptible to chaff at longer ranges (closer, the chaff might either completely be out of seeker view or the bloom might completely blind the missile for just long enough)

 

At the same time, an ARH at low altitude is capable of performing its own MTI - SNR is potentially lower for the less powerful ARH's radar than it would be for an aircraft radar in this case as well, and due to MTI it would likely not have issues with radar glint from the ground. This could be dependant on the missile's angle with the ground (the closer to vertical the better, IMHO, as far as the fuze goes)

At the same time, SARH will suffer more from radar glint at lower altitudes since it might not be as capable of performing its own MTI. This certiainly seems to be the case in the incident where 2 F-15's attacked a pair of landing MiG-25s in the GF - although I never got to verify this incident. According to the story the AIM-7's hit very close tot eh MiGs but no direct hits (about 10' away, ground impact) If any damage was caused to the MiGs it was unknown.

[Skywall23]

N00b question: what is lofting?

 

If you guys could get a picture I would apreciate. :)

[Chizh]

All this is very interesting.

Also it would be desirable to hear your opinion about special trajectories of AIM-120. In some situations analog R-77 execute complex maneuver. For example, at interception low-level target (such as cruise missiles) missile flies on a high trajectory (but it not loft) and then dives on the target. Due to it missile avoids strong ground noise and reduces risk to collide an obstacle. Except for that there are special trajectories for intercept target on pursuit. In this case the missile does lateral envelop to not get in a chaffs. There are also other ways.

[GGTharos]

I've tried looking - I have so far found a PDF descibing research into guidance laws for missiles, but it didn't cover special trajectories. It appears that such techniques are classified.

 

We coudl make our own deductions by simulating them - I've worked with such simulations before, however, I do not know enough about aerodynamics or radar physics to write proper simulation code :(

 

However, I have no doubt that such things are used - heck, iv'e thought of it myself! With something as advanced as an ARH having its own dedicated navigation section, it could choose a proper navigation algorithm dependong on the target - you may have to tell it what you're shooting at, but in many cases such trajectory cases could be automatic - for example, you mentioned cruise missile attacks. This may simply be a shoot-down algorithm and not specifically for cruise missiles. Lateral separation to avoid chaff also soudns very interesting.

 

It could also accumulate statistical data on the target in memory for the past x-seconds and analyze the enemy's maneuvering, and then for example, where hard weaving would, under the simplest guidance laws, have the missile going -left-right-left-right trying ot keep up, it could merely choose to go pure or just forthe 'center of the maneuver box'. I am continuong to research these topics :)

[GGTharos]

Interesting ...

 

http://www.rafael.co.il/web/rafnew/products/brochures/Python%205%20inside.PDF

[GGTharos]

No prob ;D

 

More research on the subject of missile attributes:

 

http://www.sal.tkk.fi/Opinnot/Mat-2.108/pdf-files/ehyt04.pdf

[GGTharos]

What I've found so far leads me to believe that while the specific trajectories used are classified, since they'd liekly reveal missile performance data among other things, computing them is an optimization problem (a difficult and numerically challenging one) ... ED could program different trajectories into the missiles, but given how difficult it is to do in RL, I suggest some trial and error - because you guys have the code handy, perhaps it would be useful to attempt programming several types of pursuit trajectories based on target behavior.

 

My suggestion is to model the following ocmponents of the missile:

Missile seeker (FOV, gimbals, RANGE, radar properties)

-Seeker Settling Time

-Search patterns

Missile CPU (handles logic)

-Choice of intercept trajectory

-Countermeasure rejection (might require some interesting radar modelling - are you guys using 3D objects for radar? same could be done for moving weather patterns!)

-Target reflection memeory (may be unrealistic, but why not?)

-Memory for statistical accumulation and processing of enemy fighter maneuvers (Computes generaql airspace the target has stayed in within the past 5 sec and goes for that airspace - this could prevent weaving aicraft from draining the missile's speed) and goes PN/Lead when homing or last 2km (whicever would be better!)

** Note that modern torpedos do such statistical accumulation of sensor returns but for different reasons ... so why not AAM's, right?

[SwingKid]

Watch the Archer video. The AIM-120 fired in it lofts.

 

Link?

 

Also send me a PM with your email ... I'll send you a PDF.

 

Sent. It's the same pdf as linked above?

 

I'll have to try and find the site I was reading up on radar again (also the F4 manual states that, after paying money for various research docs, they found out that ARH fares better in low level environments ... it had to do something with the monopulse radar and the fact that it is an ARH missile, but the explanation didn't go into details - it's basically possible that the ARH missile can use MTI more effectively IMHO)

 

It's suspicious that they emphasize monopulse, since the AIM-7M and the R-27R are similarly monopulse, making this irrelevant, but AIM-7F is not. It may be that they are comparing against AIM-7F?

 

You might be right on HoJ, I'll have to re-read about the cross-eyed jamming, though they definitely mentioned that 'the missile is the forced to swich to less efficient proportional navigation' ...

 

I think this may not refer to corss-eye jamming but rather HoJ performance against other types of jamming, e.g. pure noise. In this case the missile simply can't use loft.

 

It also showed some burn-through graphs as well (indeed, the Burn-through range it'sn that great, but the key was that you don't need to actually completely overpower the jammer to get around it - one example graph had BT at 13nm or so)

 

These would be interesting to see. It would seem to contradict:

 

 

-SK

[GGTharos]

I suggest looking at the radar link I posted. I don't understand it as well as you do most likely. Burn through is -consistently- more than this in their examples. I also think that the fact that they mention (somewhere) that an ARH seeker is expected to achieve burn-through at a point which will allow it to lock on for terminal guidance contradics that rather short range.

 

Also, it would appear, that according to what I've read, most ARH missiles are very resistant to most kinds of jamming ... in fact apparently once a missile's on its wya to you it turns out it's typically better to jsut shut the jammer off - but I don't think this applies to the more moderl SPJ's since I think it would be obviously that techniques to defeat them would be developed.

 

In some cases it was mentioned that the jammer needs to significantly overpower the radar to have a good effect as well.

 

The PDF isn't the same ... if you don't receive thwat I've sent you in a day or so tell me, I'll put it up for you to DL.

 

Their emphasis isn't based jsut on teh RECEIVER ... they seems to be basing it on the fact that monopulse rejects something (I forget what) or it mroe robust against some things, but the fact that you have an emitter onboard the missile and processing systems to process the signal with more accuracy than in the case of a SARH missile, you get better results in a number of cases. I really need to find and point you to this particular bit of info ... the only problem is that like a doofus I failed to bookmark it :P

[SwingKid]

I suggest looking at the radar link I posted. I don't understand it as well as you do most likely. Burn through is -consistently- more than this in their examples.

 

Well, setting aside the quote:

"Figure 1 is a sample graph - it cannot be used for data."

 

They still get the result:

 

"This required J/S line crosses the jamming line at about 2.8 NM which, in this example, is the burn-through range."

 

...i.e. significantly shorter than the burn-through we have in the sim, and approaching the minimum missile launch range limits. Note that this is with a radar cross section of 18 square meters (large), a radar power of 10 kW (high), and a jammer power of 100 W (weak but ok, not unreasonable). I think they exaggerated the numbers just to have something to show.

 

I also think that the fact that they mention (somewhere) that an ARH seeker is expected to achieve burn-through at a point which will allow it to lock on for terminal guidance contradics that rather short range.

 

I have doubts. The directivity and power of an ARH radar antenna are even weaker, biasing the burn-through equation further in favor of the jammer.

 

Also, it would appear, that according to what I've read, most ARH missiles are very resistant to most kinds of jamming ... in fact apparently once a missile's on its wya to you it turns out it's typically better to jsut shut the jammer off - but I don't think this applies to the more moderl SPJ's since I think it would be obviously that techniques to defeat them would be developed.

 

It is true that most monopulse missiles are very resistance to most kinds of jamming, but this is technically a different question from whether they are ARH or SARH.

 

In some cases it was mentioned that the jammer needs to significantly overpower the radar to have a good effect as well.

 

It's only ever necessary to overpower the skin reflections, and these are usually very weak.

 

The PDF isn't the same ... if you don't receive thwat I've sent you in a day or so tell me, I'll put it up for you to DL.

 

Ok standing by.

 

Their emphasis isn't based jsut on teh RECEIVER ... they seems to be basing it on the fact that monopulse rejects something (I forget what) or it mroe robust against some things, but the fact that you have an emitter onboard the missile and processing systems to process the signal with more accuracy than in the case of a SARH missile, you get better results in a number of cases. I really need to find and point you to this particular bit of info ... the only problem is that like a doofus I failed to bookmark it :P

 

Ok no rush. Don't take my grilling the wrong way, I appreciate your research into this as it supplements my own.

 

BTW I also wrote a mini missile simulator about a year ago for testing some of the trajectory concepts, but of course ran into difficulty collecting accurate data. If you're curious:

 

http://www.ecf.utoronto.ca/~pavacic/missiles/minizap.zip

 

So of course I'm extremely interested in this "Archer video" you mentioned... Searching...

 

Cheers,

 

-SK

[GGTharos]

No worries, any research must be scrutiinized ( did RL research into quantum chemistry at the National Research Council of Canada)

 

I'm jsut beating myself up over losing some of my sources :P

 

I'm gonna check out you rmissiles sim :D

[SwingKid]

Re: "Archer video."

 

Please, I need a hint. Where did you see this? Is it in a Lock On forum thread? It could be very helpful for miniZAP!

 

Thanks in advance.

 

-SK

[GGTharos]

Oh, sorry! It's on my hd ... not sure where to find a link to it..I'll try looking in the UBI or Frugal's F4 forums.

 

Edit: I like your missile sim. I wonder if you could add some features and wether the stuff I sent you would help at all to improve it?

 

There's also something wrong ... the 54C is supposed to have a confirmed kill at 145km ... but then again the friction coefficients could be different in reality to who knows ... perhaps there are some speed-preserving guidance optimizations etc.

[SwingKid]

Oh, sorry! It's on my hd ... not sure where to find a link to it..I'll try looking in the UBI or Frugal's F4 forums.

 

Ok, I think I found it in the Ubi forums:

 

http://forums.ubi.com/eve/ubb.x?q=Y&a=tpc&s=400102&f=94610606&m=12810897&p=14

http://www.pkbase.com/download/index.php?id=5

 

Downloading..

 

Edit: I like your missile sim. I wonder if you could add some features and wether the stuff I sent you would help at all to improve it?

 

Thanks! At first glance, I don't think so... The documents seem to deal with guidance. This might be more useful for Lock On one day. The missiles in miniZAP aren't really using any sort of guidance, PN or otherwise. Rather the simulator just tries to make them fly as far as they will go to calculate max range, and then adds on a non-maneuvering target motion vector with length proportional to the missile flight time, to compute "Rmax".

 

There's also something wrong ... the 54C is supposed to have a confirmed kill at 145km ... but then again the friction coefficients could be different in reality to who knows ... perhaps there are some speed-preserving guidance optimizations etc.

 

You can get some impressive ranges from miniZAP's AIM-54C with a high launch speed and altitude, and by turning on "Loft Glide Logic". Nevertheless this missile did give me the most trouble to model - such a fat, heavy missile, with motor burn approaching 30 seconds seems to give very slow acceleration compared to some of the others - I couldn't figure it out. In general though I found it odd that all the missiles seem to have verifiably similar propellant-to-weight ratios, yet we expect them to have very different flight ranges.

 

-SK

[SwingKid]

Watch the Archer video. The AIM-120 fired in it lofts.

 

Hmm... I think I have the right video here. The only definitive AIM-120 launch I can see is the one at 3:55, and there are only about three frames of video of it in flight - in the third one the AIM-120 flame is clearly seen pointing downward while going off-screen, not lofting but rather diving.

 

Skywall23:

"Lofting" is when a missile flies a high-altitude parabolic arc instead of a straight line to the target. This much more efficient trajectory allows the missile to greatly increase its maximum flight range, but it requires that the range to the target be known so that the correct loft trajectory be selected - therefore, lofting can't be used in HOJ mode, not even against simple noise jammers. It also cannot be practically used by purely passive-homing missiles like heat-seekers.

 

-SK