need evidence AIM-120 Easily driven into terrain

[GGTharos]

On 6/23/2023 at 2:40 PM, Default774 said:

Unfortunately unless you manage to find a document that explicitly states the 120 will not in fact fly itself to intercept a predicted impact point that's 5000ft underground this is all a bit pointless sadly.

I would love to see Maestros thoughts on this (I cant figure out a way to tag his username, dont have a cyrillic keyboard)

 

Guidance laws helping missiles not fly themselves into the ground or sea have existed since the 50's, in particular there are research papers for USN warships using missiles vs sea skimming targets ( ... like other missiles  ).

Here it's purely ED's choice to implement or not, but I would hope they'd add such capability ... this is unfortunately subjective regarding which missile gets what without actual data but it's very, very far from being improbable.

Edited June 25, 2023 by GGTharos

[Mad_Shell]

On 6/26/2023 at 12:24 AM, GGTharos said:

Guidance laws helping missiles not fly themselves into the ground or sea have existed since the 50's, in particular there are research papers for USN warships using missiles vs sea skimming targets ( ... like other missiles  ).

Here it's purely ED's choice to implement or not, but I would hope they'd add such capability ... this is unfortunately subjective regarding which missile gets what without actual data but it's very, very far from being improbable.

 

The research I could find on the topic mention that a bias can be introduced to keep the trajectory high, or that different coefficients can be used for vertical and horizontal trajectories, but at close range (like in your video), it seems standard PN or APN are used because they deal better with target's high g maneuvers

[GGTharos]

2 hours ago, Mad_Shell said:

The research I could find on the topic mention that a bias can be introduced to keep the trajectory high, or that different coefficients can be used for vertical and horizontal trajectories, but at close range (like in your video), it seems standard PN or APN are used because they deal better with target's high g maneuvers

Yep, it's that easy.

3 hours ago, AirMeister said:

Why implement this if there is no proof that missile can actually do this or how it works. 

Also this only negatively affects those who fire from very low altitude. 
I doubt that in real life 90% of the aircraft engage eachother at 500 feet all the time so change your tactics or something 

What about NASAMs?  You might have trouble finding proof that any specific missile uses PN/APN as well.  This stuff isn't hard to implement.  It's a lot easier than some guidance capabilities that SAMs have for example, and easier than implementing loft as well.

[Mad_Shell]

17 hours ago, GGTharos said:

Yep, it's that easy.

No, what I mean is that it seems that in the terminal phase of the missile flight, only simple PN/APN is used, because they deal better with target's high g maneuvers. If you introduce a bias in the vertical acceleration, or decrease the PN coefficient in the vertical plane in the terminal phase, the missile will follow a not optimal trajectory. It will force the missile to pull more g to hit a highly maneuvrable target.

It really wouldn't surprise me that the AMRAAM behaviour in your video is correct/realistic. 

[DD_Fenrir]

Point 1: I would assume that the missile has to be aware of it's own barometric altitude, it has too many important ramifications on energy available vs intercept geometry to be ignored. How it measures that though...

Whether that is loosely via some kind of Inertial Measurement Unit (IMU) and makes estimate based on the launch altitude it was told by the launch platform, or a barometric device imbedded in the missile body... I don't know.

This could be enough - you have a logic switch that drives different guidance behaviour when under a set baro alt. This of course does not account for mountainous terrain so the missile could still potentially be driven into terrain, if this was the only method available to drive different guidance logic based on altitude....

Pont 2: It's an active missile: the radar will have to have some filtering to ignore ground clutter. Now that ground clutter needs to recognised in order for filtering to occur and if it's able to recognise it then it has the potential to discriminate and classify it, so that if the signal to noise ration reaches a certain level it recognises it is at a lower AGL altitude and this can be used to switch to a different guidance logic.

So it seems the feasibility is not that complicated... assuming @GGTharos is correct, and he has history of being a reliable authority on these topics, it is something that warrants further investigation.

 

[Hobel]

vor 2 Stunden schrieb Mad_Shell:

It will force the missile to pull more g to hit a highly maneuvrable target.

of course, but in the end that would still be better than a 2-3M missile just crashing into the ground, in many examples where it does just that it would hit the target.

have you ever seen an example where the Aim120 doesn't hit the ground? one thing i can tell you, the result looks very good.

Edited June 28, 2023 by Hobel

[GGTharos]

5 hours ago, Mad_Shell said:

No, what I mean is that it seems that in the terminal phase of the missile flight, only simple PN/APN is used, because they deal better with target's high g maneuvers. If you introduce a bias in the vertical acceleration, or decrease the PN coefficient in the vertical plane in the terminal phase, the missile will follow a not optimal trajectory. It will force the missile to pull more g to hit a highly maneuvrable target.

It really wouldn't surprise me that the AMRAAM behaviour in your video is correct/realistic. 

There's no magic here.  You can constrain PN until certain conditions are met, and then allow it full deflection.  You can also use different guidance algorithms for different phases of guidance, which again is not magic and has been done since the 50's.

[Mad_Shell]

2 hours ago, GGTharos said:

There's no magic here.  You can constrain PN until certain conditions are met, and then allow it full deflection.  You can also use different guidance algorithms for different phases of guidance, which again is not magic and has been done since the 50's.

ED already does that. The PN coefficient increases as the target is closer, to better deal with target maneuvers. In the example you provide in video, the missile is already close to the target (less than 3 miles) and in terminal phase, so the PN coefficient is 4 (research suggests the best coeff is between 3 and 5 for intercepting maneuvering targets, so that's plausible). Basically all the articles modelling air to air missiles use such simple PN/APN guidance for terminal phase, because that's the closest to optimal trajectory. Another reason is that it requires the missile to take into account very few variables. Other methods that use more variables induce a longer computing time, and a larger delay in the missile maneuvering.

So, maybe irl the AMRAAM uses some law to deal with diving targets, but it's just as plausible that optimal trajectory and reduced control delay were prefered and simple PN/APN is used irl, like in DCS.

 

[GGTharos]

10 hours ago, Mad_Shell said:

ED already does that. The PN coefficient increases as the target is closer, to better deal with target maneuvers. In the example you provide in video, the missile is already close to the target (less than 3 miles) and in terminal phase, so the PN coefficient is 4 (research suggests the best coeff is between 3 and 5 for intercepting maneuvering targets, so that's plausible). Basically all the articles modelling air to air missiles use such simple PN/APN guidance for terminal phase, because that's the closest to optimal trajectory. Another reason is that it requires the missile to take into account very few variables. Other methods that use more variables induce a longer computing time, and a larger delay in the missile maneuvering.

So, maybe irl the AMRAAM uses some law to deal with diving targets, but it's just as plausible that optimal trajectory and reduced control delay were prefered and simple PN/APN is used irl, like in DCS.

 

Yes, there may be more maneuvering depending on the situation.   The 50's sparrow already had guidance modes corresponding to certain altitude bands and other factors, I don't see the problem with an AMRAAM introducing a particular altitude guidance bias based on an easily selectable altitude profile.  And yes I'm aware about the varying coefficients, I happened to be one of the people who provided ED with evidence of their existence