Can AIM-120C lock a helicopter with 0 TAS?

[IVAN01rch]

Hi,

I have been playing on the Blueflag yesterday and was shot down by aim-120 while having 3.7 TAS. Is it a thing now?  I was hovering for quite a long time so it was not a moment low speed.

[Merlin_VFA34]

your helicopter is not moving but that thing above your head is moving close to the speed of sound.

[Badger1-1]

Thats not how filters work, yes the rotor is super fast but still the closing speed/rate is still close to 0.

[toilet2000]

1 hour ago, Badger1-1 said:

Thats not how filters work, yes the rotor is super fast but still the closing speed/rate is still close to 0.

That's exactly how Doppler notch filters work: that spinny thing has reflective material moving at a very high linear speed, both negative and positive.

The issue though is that the return, even though it might have a very distinctive Doppler shift, is fairly small, so in general it's hard to detect a spinning rotor at long range. The shorter range of a missile might actually still be able to see it though.

I would assume though that in this case, the AIM-120C just went directly for the last contact position with extrapolation as it should and hit the heli.

[Dragon1-1]

If set for small target size, the AMRAAM should see a helo just fine when it goes pitbull, rotors or not. Getting a lock in first place might be nontrivial, but once it goes pitbull, it should have very high PK against a helo.

[IVAN01rch]

I was sitting there for quite a long time. So it must have locked onto me without me moving relative to the ground. I find this weird.

[draconus]

11 hours ago, IVAN01rch said:

I was sitting there for quite a long time. So it must have locked onto me without me moving relative to the ground. I find this weird.

I don't know how DCS does this atm but depending on the radar and its software it certainly is possible to detect and track hovering heli - its fuselage can hide but its moving rotor cannot.

https://patents.google.com/patent/US7522089B2/en

[nighthawk2174]

Not just that but i'm sure that you could turn the doppler filters off as well and track purely in range.  Something an active monopulse seeker would be really good at given its absurd range resolution.  Now as to if the amraam can do this... your guess is as good as mine.

[QuiGon]

On 3/7/2022 at 4:22 PM, toilet2000 said:

That's exactly how Doppler notch filters work: that spinny thing has reflective material moving at a very high linear speed, both negative and positive.

Not in DCS, as DCS doesn't simulate the doppler effect of the rotor (unless something has changeded recently, which I doubt, as such a change wasn't mentioned anywhere).

Edited March 9, 2022 by QuiGon

[toilet2000]

4 hours ago, QuiGon said:

Not in DCS, as DCS doesn't simulate the doppler effect of the rotor (unless something has changeded recently, which I doubt, as such a change wasn't mentioned anywhere).

 

That’s not part of DCS but rather part of the radar code, which is most often per-module and not DCS-wide. I know Galinette (Razbam’s radar dev) has talked about it.

[Dragon1-1]

We're talking missiles, so it's part of DCS for them. How each individual aircraft module's radar handles it is another matter. 

[QuiGon]

6 hours ago, toilet2000 said:

That’s not part of DCS but rather part of the radar code, which is most often per-module and not DCS-wide. I know Galinette (Razbam’s radar dev) has talked about it.

Where did he talk about it? I would like to see that, because it doesn't make sense to me, as their code has to work with the values provided by the API and I don't think helos have doppler return values for their rotor. Maybe RAZBAM artifically multiplies the RCS for a target that is of the type "helicopter", but that's all I could think of.

[FiveWire]

sitting still should technically be irrelevant because you are not maintaining equidistant from the radar source so there is still a speed differential. If the missile has a reasonable line of sight behind you before the "clutter" interferes it will still track you. Basically it looks like you aren't close enough to the terrain to hide.