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[RESOLVED] AIM-54 inconsistency with CFD whitepaper


dundun92

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2 hours ago, IronMike said:

It is still there? We didn't remove anything.

http://media.heatblur.se/AIM-54.pdf

It wasn't there at the moment of posting, and several hours afterwards. Maybe i should have taken a snapshot? Not that it mattered, i'm sure pretty much everyone that needed it, had already downloaded it, or at the very least had the relevant pages captured 😄 

1 hour ago, Aisxos said:


Right now I'm super curious to see what the end result will be. Will the phoenix end up being more or less an amraam? How will I fight more modern jets with it if that's the case. Is the SD10 ever going to get changed or will it slowly become the best missile in the game simply because its not being remodeled? Maybe it's realistic as it is? Will everyone soon be flying eurofighters because 'best bvr missile' or will the f15-16 amraam become the king of bvr with the new changes? Who knows! One thing for sure is there's a long road ahead before DCS becomes stable and ED/Heatblur/any other dev is satisfied with the simulation level detail of things. And that's exciting!

Like mentioned in a recent discussion about how certain airplanes perform and how their performance in DCS is portrayed, i have zero interest in comparative performance. The missile needs to perform accordingly to its own benchmarks, not how the other missiles perform. The AMRAAM is mess right now. The other missiles haven't been touched since the last time Wooly Mammoths walked the earth. Are you gonna base your missile on their performance? What happens when/if their performance changes? 

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 Found this gem in the youtube video suggestions for some reason, did HB change it to mirror the white papers more accurately now and due to ED's scuffed atmosphere modelling its now super slow...which it overperforming the white papers were to counteract in the first place? 

 

Coz I defiantly haven't experienced the issues he states but I have also not played in like 2 weeks so. 

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14 hours ago, Gypsy 1-1 said:

If you knew anything about aerodynamics you wouldn't even mention the size. Ever seen a large russian SAM missile? It all comes down to L/D, thrust and pressure as well as lift. Especially in the end game the Phoenix should technically have more lift than a 120C with it's large fins and body. The same people who make this argument will then praise the R-33 even though it is aerodynamically very similar and of nearly the same shape and size. And what you think the Phoenix was designed for based on hearsay and wikipedia does not change the fact what it was actually designed for and what its requirements were - especially once the C comes into the picture. The current changes were a band-aid fix for down low, which everyone who understands the physics involved will agree that a NEZ of 15nm at 100ft is pretty unreasonable. However, as a result the NEZ at higher altitudes is now just as unreasonable. Someone above me mentioned the atmosphere model in DCS - this is very much one of the main issues as it does not even come close to ISA, hence why various people comparing EM diagrams which are based and calculated on ISA conditions will simply not apply to DCS when you set it to 15C and 29.92. So simply matching CFD pressure and drag components to X altitude in DCS based on a table will often times just be a brute-force method when it comes to various temp and pressure changes. 

Yes, agreed. However, the main issue here is with the fact that most missiles use completely different physics and guidence comparatively speaking. If most or all missiles were on the same API we would not have this inconsistency across the board. It's like comparing SFM to an EFM or PFM. This has been on-going for about 3 years now when ED decided to "rework" the AMRAAM. There is no sense of urgency to adress and fix literally one of the most important aspects of modern air combar - AAM's.

Not saying it is completely broken or unusable but it's inconsistent and sometimes defies physics - often times coming down to a random diceroll whether something is going to work or not.

 

This is a very insightful (and refreshing) post ... thanks.


Edited by Kula66
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17 hours ago, captain_dalan said:

Like mentioned in a recent discussion about how certain airplanes perform and how their performance in DCS is portrayed, i have zero interest in comparative performance. The missile needs to perform accordingly to its own benchmarks, not how the other missiles perform. The AMRAAM is mess right now. The other missiles haven't been touched since the last time Wooly Mammoths walked the earth. Are you gonna base your missile on their performance? What happens when/if their performance changes? 

I think you missunderstood me.  I just said it's an interesting problem to solve, how to go up against other planes right now. Requires new tactics, which I find fun. I do agree with you, comparative performance is not a measure by which anything should be designed or tweaked, but as a player, developing strategies is something I enjoy.

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20 hours ago, Gypsy 1-1 said:

 Someone above me mentioned the atmosphere model in DCS - this is very much one of the main issues as it does not even come close to ISA, hence why various people comparing EM diagrams which are based and calculated on ISA conditions will simply not apply to DCS when you set it to 15C and 29.92. So simply matching CFD pressure and drag components to X altitude in DCS based on a table will often times just be a brute-force method when it comes to various temp and pressure changes. 

Do we know for certain EDs atmospheric modeling doesn't follow ISA? All I see is unsubstantiated claims. Here's an ISA chart and table. Can anyone corroborate that EDs modelling doesn't match what's below?

@mattag08
Edit: In fact, I've found evidence to the contrary that EDs atmosphere actually does simulate the tropopause temperature inversion layer.

Pressure Altitude - an overview | ScienceDirect TopicsWhat are ISA +10, ISA -15 and ISA -30? - Aviation Stack Exchange

Edit 2: Also the speed of sounds seems to match up almost perfect in DCS with the above chart which tells us that the ingame atmospheric simulation is a close match to reality as the speed of sound is largely a factor of temperature and air pressure (ie air density). Seems like pretty good atmospheric modeling to me so far.

The tropopause can begin anywhere from 30,000' to 56,000' depending on where you are located on earth (Its pulled higher toward the middle latitudes due to the centrifugal force from the rotation of the earth. It appears DCS simulates the tropopause at 36,000' to follow the ISA chart. This is great atmospheric modeling in my opinion.
image.png


Edited by Hawkeye91
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20 hours ago, Gypsy 1-1 said:

1. The current changes were a band-aid fix for down low, which everyone who understands the physics involved will agree that a NEZ of 15nm at 100ft is pretty unreasonable. However, as a result the NEZ at higher altitudes is now just as unreasonable. 

2. Yes, agreed. However, the main issue here is with the fact that most missiles use completely different physics and guidence comparatively speaking. If most or all missiles were on the same API we would not have this inconsistency across the board. It's like comparing SFM to an EFM or PFM. This has been on-going for about 3 years now when ED decided to "rework" the AMRAAM. There is no sense of urgency to adress and fix literally one of the most important aspects of modern air combar - AAM's.

 

1. Indeed. And by fixing one edge-case scenario of dubious tactical usefulness unless you are counterstr...... i mean air-quake-ing (in full honesty, i can recall ever tail-chasing someone at sea-level in a tactical scenario only once, and it wasn't because it needed to be done, but because i wanted to see if it can be done), we essentially broke the vast majority of other non-WVR tactical scenarios. Was that worth the effort? Can you remember the last time you shot a Phoenix bellow 15000ft? Or merged with one still on your rails? And if so, what in good God's creation made you do it? So yeah......right now they are great as long as you and the target fly straight and level.........at sea level. Like i said in that other post...... Hooray!......? 

2. No quarrel here. And the move to the new API is long overdue. Like more then a year. And as someone who was a lurker here long before engaging in any discussions or even installing the game, i know perfectly well of what you speak off. The status quo has been around for at least a decade back and probably longer. What boggles my mind more then anything else is the cultural inertia of the community, that resists any changes the the "BVR" representation in DCS. It's almost as if they fear a time table that involves anything more then Fire at 10 miles and Split-S out of Dodge. 

As a result, the changes are slow and to make things worse, for any step forward, often two are made back. Is it so because of community backlash? I can't say. But my hopes for the missile performance being solved anytime soon aren't high. But hey, we'll always have the Dogfighting and aerobatic servers, right? 😄

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Im not sure why everyone is assuming the high altitude NEZ is "just as unreasonable". It matches (indeed, slightly overperforms due to lack of plume effects in the CFD) straighline NEZ from the whitepaper at all altitudes. Like, the AIM-54 NEZ wasnt just broken down low, it was way overperforming high. Not as much as down low (1.7x vs 2.5x), but it wasnt fine before at either high or low altitude. With the new loft profile the AIM-54 at high altitude is arguably more dangerous in long shots, now that it lofts to 90-100kft in really thin air, and conserves a ton of energy; in many cases like this the current 54 is better than the old one. This is hardly a "band aid" fix for low altitudes when HB themselves have states that for the most part the FM is fine, it was an attempt to match more closely to the CFD at all altitudes; the problem is guidance issues causing too aggressive turns, pulling too many Gs too far away, etc. Unfortunately, years of the old AIM-54 have set some false expectations, which is becoming really apparent. Hopefully, the guidance issues get fixed on EDs end as soon as possible; but those expecting a significant increase in pure kinetics, that just isnt happening.

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21 minutes ago, dundun92 said:

 With the new loft profile the AIM-54 at high altitude is arguably more dangerous in long shots, now that it lofts to 90-100kft in really thin air, and conserves a ton of energy; in many cases like this the current 54 is better than the old one. 

The issue is now that the AWG9 has problems weighting its fired missiles appropriately, and will move the TWS-A cone outside of its active track in order to pick up something it just saw on the extreme other side. I'm unsure if this is the correct behavior, but I assume it is not and it should be ignoring new contacts while there are 1-6 missiles out. It certainly shouldn't be putting your only active target on the absolute edge of your radar cone.

You cant hit a target when you have all sorts of issues with small perturbations in network trashing locks, weird bugs where the TTI indicator doesn't show up and the missile is stupid off the rail, and hold-tracks not working because they are implemented as a hack rather than a complete feature due to needing the new API to function properly. 

INS guidance and the other features we should have available should help- But this has been the long tent pole for a while. Who knows when ED will get around to making that stuff, but maybe this will light a fire under the move to the new API instead of fooling around with the old one which is essentially wasted time. 


Edited by DoorMouse
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13 minutes ago, DoorMouse said:

The issue is now that the AWG9 has problems weighting its fired missiles appropriately, and will move the TWS-A cone outside of its active track in order to pick up something it just saw on the extreme other side. I'm unsure if this is the correct behavior, but I assume it is not and it should be ignoring new contacts while there are 1-6 missiles out. It certainly shouldn't be putting your only active target on the absolute edge of your radar cone.

Yeah, when I last RIO'd in the F-14 that was a big issue. I would have a perfectly good TWS-A track with a good AIM-54 in flight and suddenly it would move the cone to a target near the edge and then show the dreaded X on the active track. Meanwhile it has a perfectly good track on that edge contact 😄

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1 minute ago, dundun92 said:

Yeah, when I last RIO'd in the F-14 that was a big issue. I would have a perfectly good TWS-A track with a good AIM-54 in flight and suddenly it would move the cone to a target near the edge and then show the dreaded X on the active track. Meanwhile it has a perfectly good track on that edge contact 😄

If it does that that's a bug. The radar should never let go of a track with a missile in flight even if only a held track. If you have that happen you should try to reproduce and report it as such.

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25 minutes ago, Naquaii said:

If it does that that's a bug. The radar should never let go of a track with a missile in flight even if only a held track. If you have that happen you should try to reproduce and report it as such.

This happens on a daily basis but ive been trying to isolate and replicate it. I think I have it.  I can provide lots of videos though. 


Its hard to get tracks because it usually happens on GS or somewhere crowded but i've been planning to make a separate thread.

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2 minutes ago, Gypsy 1-1 said:

Try different altitudes - the density coefficient is usually way off and said inversion layer is static and doesnt change with temp afaik. This really comes into effect once you put any AOA o the jet/missile. To truly be certain someone would need to pull these raw values from DCS itself and also compare how ISA deviation affects them. 

Said high altitude NEZ was purely based on someone making a comparison with the current 120, which turned out to be pretty close - I think most these issues come down to guidence (aggresiveness, AWG-9 issues, and active phae "wiggle") more than anything else.

the temperature shouldn't be changing in the tropopause. It remains constant until you hit the stratosphere....

International Standard Atmosphere (ISA)

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15 hours ago, Southernbear said:

 Found this gem in the youtube video suggestions for some reason, did HB change it to mirror the white papers more accurately now and due to ED's scuffed atmosphere modelling its now super slow...which it overperforming the white papers were to counteract in the first place? 

 

Coz I defiantly haven't experienced the issues he states but I have also not played in like 2 weeks so. 

Sounds perfectly reasonable from 3:00 up to 3:15 . 

 

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21 minutes ago, Gypsy 1-1 said:

Yes and this is not what I said. 

Ah I see, I thought you were inferring that the temperature model was incorrect. I don't know of way to get a raw data readout of the air pressure, but currently it matches almost exactly to ISA from my testing because as I said, the speed of sound is mostly a factor of pressure and temperature and from the real world data I can find, DCS match up. I've still yet to see any evidence to the contrary other than pure speculation. I'll see if I can reverse engineer something more scientific.


Edited by Hawkeye91
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43 minutes ago, Gypsy 1-1 said:

Yes and this is not what I said. 

ok so I fired a AIM54 up to 80,000' to get a mach speed messurement. This missile reached a speed of Mach 2.56 with a true airspeed of 1619 knots.

image.pngimage.png

1619/2.56= 632 knots for the speed of sound at 80,000' or 727 MPH. 
image.png

Plugged the 727 MPH gives a speed of mach 1.1 at 80,000. So its 0.1 Mach different from what this tool from what NASA's speed of sound calculator says the mach number should be at 80,000 meaning the temperature and pressure model has to be pretty damn close even at that altitude. Its not far off.


Edited by Hawkeye91
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1 hour ago, Hawkeye91 said:

ok so I fired a AIM54 up to 80,000' to get a mach speed messurement. This missile reached a speed of Mach 2.56 with a true airspeed of 1619 knots.

image.pngimage.png

1619/2.56= 632 knots for the speed of sound at 80,000' or 727 MPH. 
image.png

Plugged the 727 MPH gives a speed of mach 1.1 at 80,000. So its 0.1 Mach different from what this tool from what NASA's speed of sound calculator says the mach number should be at 80,000 meaning the temperature and pressure model has to be pretty damn close even at that altitude. Its not far off.

 

Without getting too far off topic, I was curious and measured the atmosphere in DCS using the standard DCS api for EFM's (in this case I just used a modified A-4E mod because it already had the logging functionality).

 atmosphere.png

I only plotted the pressure and temperature against the ISA values. Also you will note that the ISA values above 20km are not correct because I didn't have time. From what I can see it seems that DCS model matches the ISA atmosphere.

 

Attached are the raw data that I recorded if anyone wants to do any plotting, contained is time,height,Temp,speed of sound,density, pressure.

 

Edit for full disclosure I added the script I used to calculate the ISA values and plot them.

atmosphere.csvatmosphere.py


Edited by JNelson
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5 minutes ago, Gypsy 1-1 said:

Has anyone tested whether these public and official speed numbers are achievable under normal conditions?

 

 

423432.PNG

 

Source: https://www.f-16.net/forum/download/file.php?id=36652

 

Currently the 54s do reach the stated max altitudes and then some more on top of that. However, the biggest problem I see when comparing that table to what we have for DCS is that the drastic increase for speed that it gives to the 54C, something that we cannot achieve ingame thanks to the motor’s performance. The guidance should hopefully fix some problems with the lofting since sometimes it will overloft the target and then the battery dies.

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2 minutes ago, Gypsy 1-1 said:

I stand corrected. Have you taken a look at ISA deviation as well by chance? I am pretty sure this is what causes most issues once you get in the hot and cold region as far as peformance goes.

No I didn't have time, although given that ED has clearly implemented the ISA atmosphere I see no reason why it would be incorrect.

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Just now, nighthawk2174 said:

It was an issue identified in the past I don't know if its been fixed or if its still an issue.  The issue was above 50k feet the atmospheric density was way off and I think the error reduced as you went below that altitude.

You might want to check the units again 😛

 

I went up to 70,000 ft. Or about 21,000 metres.

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4 hours ago, dundun92 said:

...Unfortunately, years of the old AIM-54 have set some false expectations, which is becoming really apparent...

Woe to the all the souls that were briefed to consider their 35 mile launches as kill shots then 

11 hours ago, Aisxos said:

I think you missunderstood me.  I just said it's an interesting problem to solve, how to go up against other planes right now. Requires new tactics, which I find fun. I do agree with you, comparative performance is not a measure by which anything should be designed or tweaked, but as a player, developing strategies is something I enjoy.

Ah, roger that. My bad then!

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15 hours ago, captain_dalan said:

Woe to the all the souls that were briefed to consider their 35 mile launches as kill shots then 

Ah, roger that. My bad then!

I disagree I think the missile will still perform well as before. 70% Of my missiles miss because of bad guidance logic. Over AOA ect. Launch from low altitudes I suspect will be rough because it’s so draggy.


Edited by Skarp
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