MANPADS Guidance

[Vekkinho]

 

And another wish that I forgot to mention: IR missile guidence - no interceptions, only tail chase.

 

Why?!!

 

:huh:

 

Than you can forget about R-73 'cause it's an all aspect IR missile.

[Renato71]

All aspect yes, but it cannot intercept (lead) the target, just go straight towards it (dog chase).

(I have misused term "tail", sorry)

[GGTharos]

Heat seekers (really, any modern AAM) use proportional navigation in the terminal stage of guidance. That means constant collision course, of if you prefer, intercept.

 

All aspect yes, but it cannot intercept (lead) the target, just go straight towards it (dog chase).

(I have misused term "tail", sorry)

[Renato71]

Yes, but are they using it from the moment of the missile launch?

Namely, I've observed many times that Strela (any type), Igla and Stinger are intercepting me throughout of their flight. I don't think that those missiles have any algorithm for interception. I'm sure that Strela does not have any. Some (very) later types may have such guidance, but are those among SAM/AA missiles that are modeled in FC?

[GGTharos]

All of those use proportional navigation. Some older SAMs (SA-2) use beamriding but they fake proportional well enough by steering to collision to start with.

[Renato71]

Strela 2 cannot do that. As far as I remember its manual, it says something like "while it is rotating, seeker is pointed towards the target, and it tries to align seeker with missile body". However, I'll try to ask a buddy that shot a few of them (for real, hehe :D ).

And I do not think that logic in IR missiles can do that good job in predicting the targets position. Currently, they are intercepting at the same rate as any SARH missiles - way too much in front of the target :(

It is most obvious in tacview with vectores turned on. You can see the intersection point of missile and your plane.

[GGTharos]

Missile seeker logic can do it as easily as you can, and it has been doing it since AAMs went into mass use :)

 

Proportional navigation is a very simple concept, though perhaps not so simple to implement in practice.

 

Imagine you are driving down the road towards a T-intersection. From the right a car is moving towards the intersection as well. Now, you're a crazy bumper-car driver, so you want to hit him.

 

What do you do?

 

You make sure he remains motionless, fixed in your FOV. The angle at hiwch you turn your head towards him (We ignore the eyes) must remain steady. If the engle changes, someone has either sped up or slowed down - you adjust accordingly to freeze the LOS again.

 

This is a very simplistic explanation of PN, but all AAMs and most SAMs use it. There are limitations like the angle to which the seeker can deflect (which may force the missile into a tail-chase eventually and it is the reason for which you should absolutely put missiles on your 3-9 line to defeat them, among other things) but ignoring all that, there's nothing stopping a missile from running a collision course on you. The technology isn't even new or new-ish. It's some of the oldest stuff in the book.

 

If you read the stinger manual, that requires the shooter to set the launcher with initial lead and elevation to give the missile maximum range (ie. it is already launched on a collision range) because it will not have to correct on its own. The missile lead dot on the F-15 serves the same purpose, helping to conserve missile energy.

 

Strela 2 cannot do that. As far as I remember its manual, it says something like "while it is rotating, seeker is pointed towards the target, and it tries to align seeker with missile body". However, I'll try to ask a buddy that shot a few of them (for real, hehe :D ).

And I do not think that logic in IR missiles can do that good job in predicting the targets position. Currently, they are intercepting at the same rate as any SARH missiles - way too much in front of the target :(

It is most obvious in tacview with vectores turned on. You can see the intersection point of missile and your plane.

[Wilde]

Excellent explanation GG. :thumbup:

[Renato71]

Excellent explanation GG. :thumbup:

Not quite :)

 

If you read the stinger manual, that requires the shooter to set the launcher with initial lead and elevation to give the missile maximum range (ie. it is already launched on a collision range) because it will not have to correct on its own. The missile lead dot on the F-15 serves the same purpose, helping to conserve missile energy.

Strela-2 manual also mentions "leading", but "leading during launch", not that missile has a "leading ability during flight", which is totally different thing. Lead on launch is when a person moves launcher in front of the target and then fires a missile at an angle, in relation to the target (not directly toward the target). After launch (at an angle) missile will turn toward the target. Missiles seeker will NOT try to intercept the target. It will go straight towards the target. NOT THE SAME.

 

IR missile cannot intercept target properly cos it has no info on distance. In FC they chase the aircraft the same way SARH missiles do it. Keeping your head on target cannot give you exact distance. You can only calculate it or guess it, based on your own speed (which you have to measure [strela cannot], or guess)

 

Combine that with your example with cars - Strela 2 is NOT doing that. It is not keeping its head toward the target, while its body is going other way (toward intersection). No, Strela is trying to align its head and body. Meaning, it will try to keep other car in the middle of its windshield. That is pure "chasing".

[GGTharos]

Not quite :)

 

 

Strela-2 manual also mentions "leading", but "leading during launch", not that missile has a "leading ability during flight", which is totally different thing. Lead on launch is when a person moves launcher in front of the target and then fires a missile at an angle, in relation to the target (not directly toward the target). After launch (at an angle) missile will turn toward the target. Missiles seeker will NOT try to intercept the target. It will go straight towards the target. NOT THE SAME.

 

Not the same, but it doesn't matter; it's done for all missiles to improve their Pk.

 

IR missile cannot intercept target properly cos it has no info on distance.

 

Utterly, totally, and completely incorrect. No distance information is required for PN, only LOS angle rate measurement :)

 

In FC they chase the aircraft the same way SARH missiles do it.

 

Because SARH, ARH, and IRH all use PN. In the case of modern versions of all of those, they can do some extra tricks for long range shots, but pretty much everything you mentioned doesn't fall into that category.

 

Keeping your head on target cannot give you exact distance. You can only calculate it or guess it, based on your own speed (which you have to measure [strela cannot], or guess)

 

You don't have to measure speed or distance or anything for any other reason than to know you're in range. The missile has no need to know it.

 

Combine that with your example with cars - Strela 2 is NOT doing that. It is not keeping its head toward the target, while its body is going other way (toward intersection). No, Strela is trying to align its head and body. Meaning, it will try to keep other car in the middle of its windshield. That is pure "chasing".

 

If strela is pure-pursuit, then it sucks ... so I would guess it isn't ;)

[Renato71]

Strela is pure pursuit and yes - it sucks, and immensely. I repeat, it is trying to align its seeker with its body. Thats the whole point - it cannot intercept.

 

(topic got split while I was writing this)

Edited March 18, 2010 by Renato71

[GGTharos]

Actually it does use PN. It's problem is not the pursuit curve; it's that the seeker is rear-aspect only, or capable of engaging only slow targets head-on.

[Vekkinho]

Please bear in mind that experienced (trained) Igla/Strela/Stinger operator makes manual intercept, pulls some lead before letting the missile go hence the "lead effect" with those missiles.

[GGTharos]

This is done for all MANPADS, AFAIK.

[Frederf]

It seems GG and Renato are at an impasse ^.^

 

We should ignore the operator practice of reducing missile workload by giving a favorable launch angle since it is entirely an unrelated distraction from the topic of the missile's guidance behavior. The question of the behavior of the missile's guidance is in no way answered by discussing the operator launch angle technique. Both parties are guilty in participating in this distraction.

 

So far it is two persons saying "It is A" and the other "It is B" neither of which is too convincing without an appeal to a more authoritative source of evidence.

 

My understanding of electronics leads me to believe that achieving lead pursuit guidance in a package small enough to fit in and be affordable to a MANPAD is well within believable. Theoretically such a benefit is very plausible. That's not to say that I actually know how the MANPAD guidance units are made, but that they would be so "simple" as to be pure pursuit is nearly unbelievable.

 

The argument that rear-aspect seekers cannot benefit from lead pursuit is flawed. Partial lead could be well accomplished such that some benefit was had while keeping inside the rear aspect position cone.

 

The only believable rationale for making a pure (or even lag) pursuit behavior instead of leading is that the Pk might benefit. A "dogtail" missile encounters a target with lesser tangential velocity than one approaching abeam (as might be the case with a lead pursuit). However the "dogtail" missile encounters more problems with energy and time-to-impact. Which is the overriding consideration probably varies by situation.

 

I can only speculate on why Renato states his position but if "IR missile cannot intercept target properly cos it has no info on distance." is critical to his stance, then his stance is suspect. Constant bearing = collision course is a concept at least as old as wooden sailing ships. A great deal can be done mathematically with the geometry knowing only angular information.

 

Wiki is a terrible source to quote but it does say this of the Strela_2

The guidance system tracks the movement of the seeker relative to missile body, and uses proportional convergence logic, also known as angle rate tracking system, to guide the missile towards the target on the basis of this information. In practice this means monitoring the seeker's angular velocity, and issuing steering commands to turn the missile towards the direction where the seeker is turning to (not necessarily where it is pointed at), in an attempt to bring the seeker-to-body angle rate to zero. Given constant missile and target velocities and non-maneuvering target, the angle rate is zero when the missile is headed straight towards the intercept point.

[GGTharos]

Yeah, I wasn't going to quote wikipedia - I went hunting for a real manual instead but I couldn't find one.

[Renato71]

I did further reading as per GG's explanations, and I have to apologize - I was very wrong about this.

My error was toward descriptions regarding Strela 2 usage that were given to me long time ago, where I was told that guidance equipment is trying to align the guidance head (which is trying to align itself toward the target) with missile body, not to keep it a t a constant angle. Meaning, it cannot intercept, only dogchase. I assumed that this is a general method for all IR MANPAD missiles, and that PN was used for radar guided missiles only.

I was trying to contact the person(s) that told me that info, but no luck. Also, I was not able to find a manual (from Yugoslav Army). Either lost or given away to someone.

 

Terribly, terribly sorry.

Very, very grateful for clarification and understanding.

Again :)

[GGTharos]

No worries - most people just stick to it without ever going to actually check, so I think you're one leg up on many of the masses :)

[mig29movt]

I found something in German (or better something from East-Germany) maybe it helps you:

http://www.flak11.de/9K32-Start.htm

 

It describes the details of the IR seeker and it's function but I really don't know if it's useful for you guys

Your discussion sounds interesting but it's way too comlicated for me^^

 

I think you're searching this:

Der IR Zielsuchlenkkopf empfängt die Infrarotstrahlung des Luftziels, bestimmt den Fehlerwinkel zwischen der Längsachse der Fla-Rakete und der Strecke Fla-Rakete-Ziel und erzeugt die für die Lenkung erforderlichen Fehlersignale.

 

Erm... :blush:

The IR seeker receives the infrared emission of the airtarget, specifies the "Error"(?)-angle between the length axis of the missile and the missiles target and it generates the necessary "Error"(?)-signals for the guidance.

 

I hope it's the Strela-2 you were talkin about :blush:

[GGTharos]

Sounds right. :)

 

It is IIRC called an 'error' because it causes a voltage difference against the reference voltage.