investigating Cruise missiles are invisible to the radar

[Northstar98]

Hi everyone,

Unlike other modules, anti-ship and cruise missiles (here tested with the YJ-83) are invisible to the radar.

Radar range is proportional to RCS to the 4th root - a MiG-21bis (RCS of 3 m² - see line 2025 of this) flying as low as the AI will let me at about mach 0.9 has it detected on the order of around 60 nmi. Based on this, a 0.121 m² target (see line 27 of this) such as the YJ-83, would be expected to be detected at approximately 20 nmi (ignoring other factors).

However, at no point during this mission (including using the ACM modes) are the missiles detected on radar. At one point I am following a missile close behind it and the APG-73 fails to acquire it. The AIM-120 on the other hand is able to acquire, track, home on and successfully intercept the missiles autonomously.

As for other modules:

• The Mirage 2000C detects the missiles at ~20 nmi.
• The F-14 detects the missiles at ~34 nmi.
• The missiles were clearly visible on the APQ-120's scope at 10 nmi.

Of course these modules all have different radars, with different antenna sizes, powers etc. Regardless though, the missiles are completely invisible to the Hornet's radar.

APG-73_YJ-83_no_detect.trk RDI_YJ-83_20nmi.trk AWG-9_YJ-83_34nmi.trk APQ-120_YJ-83_10nmi.trk

Edited April 14 by Northstar98
Grammar

[okopanja]

Idea: how about doing a calculation based on ED's white paper?

Also if I recall correctly phase 3 rework is not yet completed, so probably bug report should be checked afterwards.

[Northstar98]

9 hours ago, okopanja said:

Idea: how about doing a calculation based on ED's white paper?

The equation I’ve used is the same equation in the white paper both have detection range as being proportional to the 4th root of the RCS.

I’ve just treated all the other terms as being equal within the same radar because the gain, wavelength, average power, effective antenna area, dwell time etc wont be changing between the Hornet detecting the MiG-21 and the Hornet detecting a cruise missile. Given that the same radar mode, PRF etc were used in both tests.

SNR will probably change but I’ve got no way of determining what it is. A smaller RCS target will be producing a smaller signal, however as the distance closes that signal should increase to a detectable level, as it does in other aircraft.

Suffice to say however, the current implementation is a bug.

Edited April 14 by Northstar98

[okopanja]

This is all fine, but it still sounds like a table based approach, employed by FC3, and we should nit ecourage that with FF. Btw the range you gave hornet exceeds the range f15c(better radar) detected mig-29(higher RCS) in 1999.

So yes there are huge variations in practical range compared to what you get in ideal case.

Furthermore this will still be changed in future.

[Northstar98]

2 hours ago, okopanja said:

This is all fine, but it still sounds like a table based approach, employed by FC3, and we should nit ecourage that with FF

?

The approach is based on the radar range equation, from ED's own whitepaper. Something you yourself recommended I do.

Fidelity has nothing to do with whether the equation is valid. You may get a different result, as the variables may change (and its probabilistic in nature to begin with), but the equation remains the same and I'd expect any radar model to use it, at least at some point (as the current model does).

The numbers I used are not what I expect to get each and every time, I gave them as approximates for a reason, especially given this is one case of detecting low-flying, closing objects over calm, relatively open sea, radars are also probabilistic and RCS itself isn't necessarily a constant either. The numbers I gave are examples, based on current in-game behaviour.

All of this is perfectly consistent with ED's whitepaper.

But whether they're detectable at 20 nmi or 2 nmi, the point is they'd be detectable at some stage, but currently, they aren't at any stage, in any circumstance.

But what the ranges actually should be is besides the point - the problem is that the radar cannot detect these missiles at all. Not that it does so further or closer than expected.

2 hours ago, okopanja said:

Btw the range you gave hornet exceeds the range f15c(better radar) detected mig-29(higher RCS) in 1999.

Again, what the detection ranges actually are or should be is irrelevant to this bug report.

Using the same numbers I used in the OP, the Hornet's radar should detect a 5 m² target (what the MiG-29 is defined with in DCS) at ~70 nmi and that's exactly what happens in game with the same set up.

2 hours ago, okopanja said:

So yes there are huge variations in practical range compared to what you get in ideal case.

Yes, but again, this is irrelevant to the bug report.

If I was reporting things detected at unexpected ranges yes, but I'm reporting things not being detectable at all, under any case, as if they have an RCS of 0, so this isn't really relevant.

2 hours ago, okopanja said:

Furthermore this will still be changed in future.

The radar already has detection distance be proportional to the 4th root of RCS as it should be - this was the focus of the phase 2 upgrade (which concerned things like probabilistic detection and RCS etc).

The distances themselves may change, but as I've said previously the distances themselves aren't relevant to this bug report. The problem is that the radar simply cannot detect the missiles at all.

Edited April 14 by Northstar98

[BIGNEWY]

We will ask the team about this. 

thanks