AGM-88C HARM loses track on EWR 55g

[gasmate]

My apologies if this has been covered before.

 

Launched 2 HARMs at the EWR in TOO mode. They seem to start tracking then lose the track and overfly the target. See attached trackfile.

 

Edit: Also happens with the 1L13 EWR

HARM.trk

Edited November 4 by gasmate

[Northstar98]

Not really sure the HARM should be able to engage those radars.

Both the 1L13 and 55G6 are VHF radars, in DCS the 1L13 is defined as operating between 180 - 220 MHz and the 55G6 between 30 - 300 MHz

According to this, the AGM-88 (or at least the AGM-88B) has a conical spiral antenna (spirals are fairly common in ARM designs). The lowest frequency a conical spiral antenna can targhet is related to its base (outer) radius.

The same source states that the HARM can target the C to J bands - those radars operate in the A band and A-B band (just) respectively.

I'm not entirely sure of the equations that determine the minimum frequency of a conical spiral antenna, but for a planar spiral antenna it's f_min = c/2πr₂ where r₂ is the outer radius:

In order to target 220 MHz, r₂ would have to be at least 0.434 m and to target 300 MHz, it would need to be at least 0.318 m (and bear in mind, that's the upper limit of where these radars operate, at least as defined in DCS).

Those outer radii correspond to a diameter of 0.868 and 0.636 m respectively - the HARM has a fuselage diameter of only 0.254 m (and the seeker is even smaller still) - it simply isn't big enough to fit a conical spiral antenna big enough such that it can operate at the range these radars do.

Edited November 4 by Northstar98

[gasmate]

8 hours ago, Northstar98 said:

Not really sure the HARM should be able to engage those radars.

In which case you shouldn't be able to lock them up and the HARMs shouldn't start tracking towards the targets and then go dumb. 

 

I've attached another track file which shows HARMs being launched at the 55G6, 1L13 and the FPS-117 radars. The 117 gets hit but the other two get overflown. The EW page shows the radars don't stop emitting during the launch.

HARM2.trk

Edited November 4 by gasmate

[Hobel]

vor 2 Stunden schrieb gasmate:

In which case you shouldn't be able to lock them up and the HARMs shouldn't start tracking towards the targets and then go dumb. 

The Harm flies briefly in that direction because it uses this information from the host aircraft and tries to see an emitter in that direction, but finds nothing.

Tacview-20241104-221922-DCS-HARM2.trk.txt.acmi

[gasmate]

53 minutes ago, Hobel said:

The Harm flies briefly in that direction because it uses this information from the host aircraft and tries to see an emitter in that direction, but finds nothing.

Tacview-20241104-221922-DCS-HARM2.trk.txt.acmi 141.4 kB · 0 downloads

No, the HARM sees the emitter because it works exactly the same if you turn the RWR off. 

 

I don't have the F-16 to see how that would operate differently from the F/A-18c

Edited November 4 by gasmate

[Hobel]

vor 16 Minuten schrieb gasmate:

No, the HARM sees the emitter because it works exactly the same if you turn the RWR off. 

 

I don't have the F-16 to see how that would operate differently from the F/A-18c

 

you use TOO mode in F18. Yes, the Harm sees the emitter when it is on rail, but this should not really be the case if we assume that such emitters should not be recognised by the Harm.

It behaves exactly as I said, the AGM88 doesn't even see the EWR, it just flies briefly in the expected direction and then over it because it can't see anything.

 

 

Edited November 4 by Hobel

[gasmate]

Try it by turning the RWR off first, then select HARM and then TOO mode. The EWRs show up and are able to be fired upon.

 

Anyway I'm not trying to say whether the HARMs should or shouldn't be able to target the EWRs, just that the behavior within the sim is illogical.

Edited November 4 by gasmate

[Northstar98]

4 hours ago, gasmate said:

In which case you shouldn't be able to lock them up and the HARMs shouldn't start tracking towards the targets and then go dumb.

Then that's the bug here.

4 hours ago, gasmate said:

I've attached another track file which shows HARMs being launched at the 55G6, 1L13 and the FPS-117 radars. The 117 gets hit but the other two get overflown.

The AN/FPS-117 is a D band radar - it's within the range the HARM can target - the other two are not. Equation above works out to 0.191 m for the outer diameter of a planar spiral for the lower extremity of the D band, which would fit inside the HARM.

Edited November 5 by Northstar98

[gasmate]

5 minutes ago, Northstar98 said:

Then that's the bug here.

 

Yep.

 

It is slightly annoying when trying to sort out a clutter of HARM targets and wasting a missile on something that shouldn't be seen by the HARM. 

[Hobel]

vor 1 Stunde schrieb gasmate:

Try it by turning the RWR off first, then select HARM and then TOO mode. The EWRs show up and are able to be fired upon.

I have. :

Zitat

Yes, the Harm sees the emitter when it is on rail, but this should not really be the case if we assume that such emitters should not be recognised by the Harm.

 

As I said, if the missle in the  rail, the emitter is recognised and also displayed in the MFD, but this should not be the case.

[gasmate]

Ok so is this a bug with the HARM or specific to the F/A-18c? I don't have the F-16 module so am unable to test whether the HARM can "see" the EWR emitters while on the rail on the F-16.