AIM-54 Hotfix PSA and Feedback Thread - Guided Discussion

[dundun92]

9 minutes ago, RustBelt said:

What do you mean by “addressed”? That’s clearly some modeling fudge factor that doesn’t actually have anything to do with an actual measurement of any sort if a change of that magnitude makes such a moderate difference. 
 

We come down this road a lot with DCS, where numbers in a LUA are dimensionless coefficients used to fudge the old game engine.

Exit area is a very specific and important IRL quantity, its not a fudge factor. It affects motor performance. This is the formula for motor thrust, Ae is exit area

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Edited August 3, 2022 by dundun92

[DSplayer]

3 minutes ago, RustBelt said:

What do you mean by “addressed”? That’s clearly some modeling fudge factor that doesn’t actually have anything to do with an actual measurement of any sort if a change of that magnitude makes such a moderate difference. 
 

We come down this road a lot with DCS, where numbers in a LUA are dimensionless coefficients used to fudge the old game engine.

That’s true. Fudging the numbers in DCS is kinda the thing to do. Just always wondered since it was the only 3rd party missile that had that low nozzle exit value and was kinda curious after reading a thread that mentioned the nozzle_exit_area value being something that could effect performance.

 

Just some food for thought.

[RustBelt]

No, in the real world there’s a thing called Exit Area. 
 

Never assume in DCS that “Nozzle_Exit_Area” has anything to actually do with that real world term. 

[dundun92]

11 minutes ago, RustBelt said:

That’s clearly some modeling fudge factor that doesn’t actually have anything to do with an actual measurement of any sort if a change of that magnitude makes such a moderate difference. 

you insisted that it "must" be a fudge factor because it has a significant effect; im saying IRL it DOES produce a significant change (the value is literally a coeffecient in the thrust formula), so that assertion is misguided.

Edited August 3, 2022 by dundun92

[RustBelt]

8 minutes ago, DSplayer said:

That’s true. Fudging the numbers in DCS is kinda the thing to do. Just always wondered since it was the only 3rd party missile that had that low nozzle exit value and was kinda curious after reading a thread that mentioned the nozzle_exit_area value being something that could effect performance.

 

Just some food for thought.

Most likely Heatblur needed to fudge that number in order to rectify some game engine issue with their actual data numbers build of the missile. 
 

Most of the LockOn vintage missiles are probably complete fabrications fudged to act convincingly. 

5 minutes ago, dundun92 said:

you insisted that it "must" be a fudge factor because it has a significant change; im saying IRL it DOES produce a significant change, so that assertion is mis guided

No I insisted its a fudge factor because it was a relatively small change for the difference of what 5 orders of magnitude?

As, I’ve said many times before, DCS is not a physics simulator, its a Simulacra. They aren’t just plugging values into real physics equations to get a simulated real output. 

Edited August 3, 2022 by RustBelt

[dundun92]

19 minutes ago, RustBelt said:

Most likely Heatblur needed to fudge that number in order to rectify some game engine issue with their actual data numbers build of the missile. 
 

Most of the LockOn vintage missiles are probably complete fabrications fudged to act convincingly. 

No I insisted its a fudge factor because it was a relatively small change for the difference of what 5 orders of magnitude?

OK, I definitely misread your statement, but its just as wrong either way. Do you even understand how nozzle exit area works, or are you just speculating based on what feels right?

As a TLDR... as you increase nozzle exit area, you expand the exhaust gasses more, which reduces the exhaust pressure. More expansion is good, up to the point where the pressure of the expanded gas is less than ambient air pressure; at that point, your gas is over expanded, and you no longer gain efficiency, AND you risk damaging the nozzle. Exit area will always have an optimum value such where exhaust pressure = ambient pressure. Its not a linear relation because increased exit area affects also exit pressure; the net thrust affect is gonna change a relatively small amount for changes in Ae, depending though on how close/far you are from the optimal value. To say it must be a fudge factor you cant just look at the order of magnitude, youd need to do the math to see what the expected values would be (or be an SME and have a "feel" for it)

 

For the record, im not saying it isnt a fudge factor, but that comparison of numbers certainly wouldnt tell you (perhaps someone more familiar with this stuff would be able to tell if the numbers actually make sense).

 

EDIT: Also, just from looking at the specific results from DSplayer... the fact that this change affects performance more at high altitude much more than low altitude, at the very least would seem to indicate its trying to model the actual affects of exit area, as thats the exact result you would expect. Whether its using an actual formula idk

Edited August 3, 2022 by dundun92

[RustBelt]

1 hour ago, RustBelt said:

Most likely Heatblur needed to fudge that number in order to rectify some game engine issue with their actual data numbers build of the missile. 
 

Most of the LockOn vintage missiles are probably complete fabrications fudged to act convincingly. 

No I insisted its a fudge factor because it was a relatively small change for the difference of what 5 orders of magnitude?

I sort of get nozzle area in that it’s a volume vs pressure deal since it’s 3rd law and mass going out the back with the most force is the goal so you balance flow vs pressure.

I just can’t buy that DCS is running that way, and best I see is it modifies exhaust plume drag or some other black box factor so all missiles don’t just behave with identical rocket dynamics. At its core, DCS just isn’t that sophisticated. 

[DSplayer]

17 minutes ago, RustBelt said:

I sort of get nozzle area in that it’s a volume vs pressure deal since it’s 3rd law and mass going out the back with the most force is the goal so you balance flow vs pressure.

I just can’t buy that DCS is running that way, and best I see is it modifies exhaust plume drag or some other black box factor so all missiles don’t just behave with identical rocket dynamics. At its core, DCS just isn’t that sophisticated. 

That's very possible that due to DCS simplifications that the nozzle_exit_area function is used for different purposes when compared to IRL but other air to air missiles (AIM-7s, AIM-9s, R-27s, SD/LD-10s, AIM-120s, and some of the newer A2G missiles like HARMs and Hellfires) in the DCS library still use that function with a value bigger than 1e-6 so I'm more inclined to think that it's being used to represent the nozzle exit area like it's supposed to.

Here is where I got my idea of editing the nozzle_exit_area function anyway:

 

A quick search for all uses of "nozzle exit area" in the forums brings up some posts as well:
https://forum.dcs.world/search/?q="nozzle exit area"&quick=1&updated_after=any&sortby=relevancy

Edited August 3, 2022 by DSplayer

[RustBelt]

Thing is, even the “other missiles. A nozzle area of less than 1 seems like a complete abstraction no matter. Unless it’s yet another dimensionless coefficient thing like we’ve run into before because all the real work is happening on the secret squirrel side of the engine. What units SHOULD Ae have? Even as square Meters those numbers for the sidewinder seem small.

[DSplayer]

17 minutes ago, RustBelt said:

Thing is, even the “other missiles. A nozzle area of less than 1 seems like a complete abstraction no matter. Unless it’s yet another dimensionless coefficient thing like we’ve run into before because all the real work is happening on the secret squirrel side of the engine. What units SHOULD Ae have? Even as square Meters those numbers for the sidewinder seem small.

I get what you mean. We don't know the units of nozzle_exit_area values and that leaves everything in the air and us in the dark. It reminds me of other values in the missile luas as well as War Thunder's (yeah ik) finAoA values being the percentage of a 90 degree angle. Perhaps other people more knowledgeable of the inner workings of the missile luas like @nighthawk2174 can perhaps help out if he knows what nozzle_exit_area's units is and how to calculate it.

[DSplayer]

23 hours ago, RustBelt said:

Thing is, even the “other missiles. A nozzle area of less than 1 seems like a complete abstraction no matter. Unless it’s yet another dimensionless coefficient thing like we’ve run into before because all the real work is happening on the secret squirrel side of the engine. What units SHOULD Ae have? Even as square Meters those numbers for the sidewinder seem small.

Little check up since a friend of mine pointed out to me that a value of 0.0068 being in square meters would make sense for a sidewinder. Considering the diameter of a AIM-9L is 5 inches. Shaving a bit off that number for material including casing, insulation, etc. could leave with a number around 3-4 inches (~0.09 meters) for a nozzle diameter that would allow for the 0.0068 sq meter value to make sense.

 

 

Edited August 4, 2022 by DSplayer

[_UnknownCheater_]

I just wanna say,King of BVR is back.

[draconus]

14 hours ago, DSplayer said:

Little check up since a friend of mine pointed out to me that a value of 0.0068 being in square meters would make sense for a sidewinder. Considering the diameter of a AIM-9L is 5 inches. Shaving a bit off that number for material including casing, insulation, etc. could leave with a number around 3-4 inches (~0.09 meters) for a nozzle diameter that would allow for the 0.0068 sq meter value to make sense.

Still holds for the R-33. 0,025 (DCS) vs 0,028m² calculated if you take 19cm for inner exhaust diameter.

Edited August 5, 2022 by draconus

[RustBelt]

Yea I reckon so then. New Missile model vs AIM-54 still waiting on missile api?

[IronMike]

Dear all, with the new update we are closing this thread, as the changes are significant and plenty, such that we want to start a new discussion in the new thread here:
 

We will of course keep this thread up for future reference, but any new feedback please post in the new thread. Thank you ever so kindly for your many great contributions thus far!