reported Harpoon Flight Profile

[Flagrum]

The flight profile of the Harpoon consists of 3 different phases:

1. cruise

2. sea skim

3. final

 

The DCS manual, and other sources I found, are not very specific about when the transistion from cruise to sea skim is supposed to happen. "Common sense" (yuck, bad word in DCS:W, I know!) suggests, that his should happen way outside of the typical air defense envelope of a war ship. My assumption: the transistion should happen, when the weapon either enters search mode or at least, after aquiring a radar lock.

 

The Harpoon in DCS does not show such behaviour. Instead this happens:

• R/BL, cruise alt = high: the weapon cruises at 10 000 ft AGL up to almost directly over the designated target. Then it dives towards the target. The terminal mode SKIM or POP is then obviously useless and makes not much of a difference in the flight profile. My assumption is here, that the search mode is only enabled when entering the SEEK distance - which is too small to allow an early enough descent to a sea skimming profile.
• BOL, cruise alt = high: the weapon dives straight down to ~160 ft AGL and cruises at this altitude until it gets a radar lock a few nm before the target. There it then goes down to ~50 feet and performs the correct TERM maneuvre.
  The problem here is, that the Harpoon does neither respect the FLT setting (high!), and also a set SRCH distance has no influence on the flight profile (see my assumption in the beginning).

 

R/BL FLT=high vs. BOL FLT=high

 

I have not yet looked into which influence a HPTP has on the flight profile in R/BL or BOL - it is already difficult enough to try to make sense of what the Harpoon does without it.

 

HPD BOL HIGH vs RBL HIGH.trk Tacview-20211003-005418-DCS-HPD BOL HIGH vs RBL HIGH.trk.zip.acmi

Edited October 3, 2021 by Flagrum

[BIGNEWY]

On 10/3/2021 at 1:13 AM, Flagrum said:

should happen way outside of the typical air defense envelope of a war ship. My assumption: the transistion should happen, when the weapon either enters search mode or at least, after aquiring a radar lock.

 

Do you have any evidence of this? 

PM me if required

 

thanks

[Chizh]

The SKIM and POP parameters set the terminal maneuver. SKIM - simple approach over the water, POP - pop-up.

[Flagrum]

4 hours ago, Chizh said:

The SKIM and POP parameters set the terminal maneuver. SKIM - simple approach over the water, POP - pop-up.

Yes, that is understood. But I am talking about the difference between the cruise phase and the sea skimming phase between cruise phase and terminal attack phase.

 

At it is now, in R/BL mode the weapon never really has a chance to execute a proper TERM maneuvre as it is still at cruise altitude when the terminal phase begins. It never gets close enough to the water to sea skim or even to pop up.

 

 

5 hours ago, BIGNEWY said:

 

Do you have any evidence of this? 

PM me if required

 

thanks

I think we agree, that the flight profile should basically consist of three distinct phases:

• Cruise, to initially cover the distance to the target
• Sea Skim, as low as possible without getting wet, something between 15 - 150 ft AGL
• Terminal, to perform the SKIM or POP maneuvre in order to hit the target

It also seems, that all three exists as distinct flight phases in DCS:W, just not merged into one flight profile. When you look at the BOL TacView screenshot: the weapon sea skims at ~150 ft and only a few seconds before the impact, it drops to 15 ft to perform the configured TERM attack (SKIM in that case - but I could also provide a POP example, where the maneuvre is clearly visible).

 

The whole goal of the sea skimming phase is to make the detection (radar horizon!) of, and the defense against the weapon (late detection = short reaction time) as difficult as possible for the opponent. If the weapon enters the sea skim phase too late (or not at all in our R/BL case at hand), this phase is virtually pointless. If it enters this phase too early, it's range is serverly limited.

 

https://navalpost.com/anti-ship-missiles-what-is-sea-skimming/

 

If the point, when the weapon enters the sea skimming phase, has any direct relation to when either ...

a) ... the weapon starts actively searching for a target, or

b) ... the weapon has eventually aquired a lock,

I can't say. There are probably arguments for both: target aquisition is easier at cruise altitude, but on the other hand, the weapon already knows more or less where the target is anyways and only needs a final lock a few miles out (s. the linked article which also elaborates a bit on that aspect).

 

 

 

Edited October 4, 2021 by Flagrum

[Northstar98]

Agreed.

While I don't have any solid evidence documenting the flight profiles this:

Quote

The whole goal of the sea skimming phase is to make the detection (radar horizon!) of, and the defense against the weapon (late detection = short reaction time) as difficult as possible for the opponent. If the weapon enters the sea skim phase too late (or not at all in our R/BL case at hand), this phase is virtually pointless. If it enters this phase too early, it's range is serverly limited.

Is dead right.

I think it should also be noticed that the RGM-84 (presumably RGM-84D Harpoon block IC), sea skims all the way to the target (though AI fired AShMs in DCS lack quite a bit of fidelity IMO, though that's not the subject of this thread).

Edited November 5, 2021 by Northstar98
formatting

[Flagrum]

Hi @BIGNEWY!

This is still in status "investigating" - do you need more input to get it "reported"? How can I help?

[GGTharos]

On 10/4/2021 at 7:52 AM, BIGNEWY said:

 

Do you have any evidence of this? 

PM me if required

 

thanks

@BIGNEWY I will check my docs (because I know I have seen this, details below), but I would argue that you don't need such evidence, and the reasoning is this:

The Harpoon is a digital missile whose various flight stages are defined by software.  I think it's clear why I emphasized this.

The 'average' ship this missile would have been aimed at could not shoot missiles beyond 10nm. 

Therefore, this missile should be sea-skimming by the time it's 10nm from target, perhaps closer - the point here being that missile retains its range but also maximized its ability to do damage.  In this case, fuel will be saved by the missile throttling down in the dive to sea skimming altitude.

 

Now, for the information that I have seen - it may have been B-52 delivered Harpoon manual or something else, I forget which.

1) The missile is launched with pre-loaded data for its flight and activation.

2) The cruise phase is executed.

3) If the missile is sea-skimming, it will climb to 5000'-6000' (don't quote me on this, it may have been 1500') to acquire target position at long range.

4) After this update, the missile will descend to sea-skimming altitude and initiate search for terminal homing

5) Terminal homing is performed and the selected terminal maneuver is executed.

Note #3 and #4.   This phase is not at all modeled, and in all cases it ends with the missile sea-skimming.   Anyway, I'll go look for the docs.

[BIGNEWY]

I have marked the thread reported as we do have a relevant one open already. We do have conflicting information so we will leave this with the team for now. 

thanks