Weapons .xpd questions

[Frosty]

Unfortunately, new weapons lead to new questions: I'd like to make the in-game damage effects of the weapon models shown in the P-47 development thread (https://www.sim-outhouse.com/sohforu...=1#post1325166) of at least similar quality as the AvHistory ones in ETO v1.50. Most of the weapon .xpd values are selfexplanatory or are sufficiently described in the CFS3 SDK. However, when it comes to what I think are the most important values, I am left with a lot of questions. For study and comparison purposes I have tabulated the most enigmatic values for a few ETO weapons (please ignore the VFX columns - I wanted to compare what weapon uses which FX to find a more consistent setup):



A few things in this table caught my attention:
- I would have thought that in ETO the 'stock' weapons (those with the "a_" prefix) would have been upgraded to AvHistory standards but apparently they are not when it comes to the "drag" value: Most are the same while the frontal areas or sizes of the weapons clearly aren't. Does anyone know/remember what the reason for this is?
- The weight values for the 'a_hvar' and 'a_m8a1' rockets are clearly wrong: The HVAR was way bigger and heavier than the M8A1. The AvHistory values are much more realistic.
- The "AvHistory_us_Bomb_1610lb" is an AP bomb. I suppose that it therefore has that very small blast radius compared to bombs of similar weight: It penetrates before exploding.
- The two AvHistory WP bombs have very large "ImpactOffset" and "BlastOffset" values but a relatively low one for "FireOffset" when compared to their GP counterparts. For a white phosphorus bomb I would have expected that to be reversed or at least show a higher value for "FireOffset", given a WP bomb's capability as an incendiary. But perhaps I misunderstand the use/effect of a WP bomb or the particular type depicted in ETO (one of my newly modeled weapons is a smoke bomb with WP as a major component). However, the VFX of the WP bombs in ETO are those of a classic WP bomb with white, smokey particle trails.



After thinking these values over, I am left with the following questions on

Offset values:
Q1a: Are the values under the "ImpactOffset", "BlastOffset" and "FireOffset" entries the actual damage(points) that the weapons inflict on other sim objects?
Q1b: If so, how are these values calculated/determined? Is there a general formula, spreadsheet etc. of any kind that would give consistent and reliable values?
Q1c: Comparing weapons of similar weight give different values for the three '-Offset' entries, as noted in the observations above. Is there a way to include real-life, known values (such as the type of explosive or the bomb's charge/total weight ratio) in the calculations?

"Drag" values :
Q2a: How is the drag coefficient of a weapon calculated in CFS3?
Q2b: Given that AvHistory internal weapons have a drag value of "0", is drag only used to influence aircraft flight behaviour or does it also influence the weapon's trajectory when dropped? (Which would make the zero drag weapons rather odd, so I guess not. Or they could be one of the many compromises necessary to make things work, given CFS3's half-baked state when published).

"Mass" values:
Q3a: Weapons labeled as 'containers' (eg. the triple rocket launcher) have two 'mass' values in their .xpds: "Mass" and "WeaponMass". I suppose the first value is the weight of the empty container and the second is the weight of the actual rockets or bombs?
Q3b: If so, is the "WeaponMass" the weight value of a single rocket/bomb or the weight of the total number of weapons in the container (so in case of the triple rocket launcher, 3x the weight of a single rocket)?
Q3c: "Mass" and "WeaponMass" can also be found in drop tank .xpd files. In this case the "WeaponMass" would be the weight of the fuel?
Considering the 'mass' values for the drop tanks, I am inclined to the idea of "WeaponMass" being the total weight of the container's contents (whether fuel, rockets or bombs) but those for both triple rocket launchers in the table are totally weird and completely off when compared to the values of the rocket .xpd (or their real-world counterparts), hence my confusion.

Decals:
Q4a: "WeaponCrater": Is this a floating point value (in meters) with the decal .dds as a prefix (eg. "crater_12")? There's only a single "crater.dds" in the "effects" folder. In the SDK there is mentioning of a "Radius" entry with a somewhat similar description.

So if anyone can shed some light on any of these questions, I am all ears! (Anyone of the old ETO crew that worked on the weapons around?)
Many thanks!!

[gecko]

I will answer what I can...

1 (all). This is a pretty grey area. In theory there might be some formula, but as far as I know nobody knows what it is. There is also the matter of no matter what you set, it must be balanced with the damage points assigned to everything that can be damaged in game. For realistic results you have to tune every xdp in game for consistent results..

2. In CFS3, this value only affects the aircraft's drag while it is attached to the aircraft. That is why weapons meant to be carried inside a bomb bay have zero drag. As to calculating drag of the weapons, that is rather more complex. Not only do you have to account for the form and friction drag of the weapon itself, but also the interference drag from the airflow around the weapon, pylon, and aircraft structure all running into each other. This will vary aircraft by aircraft, and on the P-47, I'll bet different combinations of stores under the wings interacted differently with each other. It can be a bit counter intuitive. On the under wing tanks for one of the Fw 190A variants, I actually used a very high drag value for the pylon, and a negative value for the drop tank itself. This is because the drag of that particular style of droptank pylon without the droptanks was greater than the drag produced by the pylon and droptanks together. So when you jettison the tanks on that model, you actually slow down. Thankfully I had flight test data for the drop tanks and pylons, so I adjusted the pylon drag until I got the correct top speed with just the pylons, and then added the drop tanks and adjusted the negative value until I was getting the correct higher top speed with the droptanks attached.

3. I used to know. I'll have to look when I have it in front of me again.

4. The crater_12 references an xpd in the objects folder in which you can set the size of the decal. Also, you can actually assign a 3D model to the crater instead of a flat decal. So 3D bomb craters are possible, and if your airfield is bombed and you taxi into a crater, it will destroy the aircraft. You can also use this method to create 3D crash wreckage for aircraft and assign it as a decal in the aircraft's xdp. I would not mind at all if you became inspired to create generic 3D wreckage models of various sizes btw.

[Frosty]

I will answer what I can...

1 (all). This is a pretty grey area. In theory there might be some formula, but as far as I know nobody knows what it is. There is also the matter of no matter what you set, it must be balanced with the damage points assigned to everything that can be damaged in game. For realistic results you have to tune every xdp in game for consistent results..

2. In CFS3, this value only affects the aircraft's drag while it is attached to the aircraft. That is why weapons meant to be carried inside a bomb bay have zero drag. As to calculating drag of the weapons, that is rather more complex. Not only do you have to account for the form and friction drag of the weapon itself, but also the interference drag from the airflow around the weapon, pylon, and aircraft structure all running into each other. This will vary aircraft by aircraft, and on the P-47, I'll bet different combinations of stores under the wings interacted differently with each other. It can be a bit counter intuitive. On the under wing tanks for one of the Fw 190A variants, I actually used a very high drag value for the pylon, and a negative value for the drop tank itself. This is because the drag of that particular style of droptank pylon without the droptanks was greater than the drag produced by the pylon and droptanks together. So when you jettison the tanks on that model, you actually slow down. Thankfully I had flight test data for the drop tanks and pylons, so I adjusted the pylon drag until I got the correct top speed with just the pylons, and then added the drop tanks and adjusted the negative value until I was getting the correct higher top speed with the droptanks attached.

3. I used to know. I'll have to look when I have it in front of me again.

4. The crater_12 references an xpd in the objects folder in which you can set the size of the decal. Also, you can actually assign a 3D model to the crater instead of a flat decal. So 3D bomb craters are possible, and if your airfield is bombed and you taxi into a crater, it will destroy the aircraft. You can also use this method to create 3D crash wreckage for aircraft and assign it as a decal in the aircraft's xdp. I would not mind at all if you became inspired to create generic 3D wreckage models of various sizes btw.

Thanks Daniel!

@1: So they are damagepoints?
@2:
@3: Please let me know, should it could come back to you.
@4: Ah, should have thought of that myself; found them and the "Radius" entry inside the file. I know about the possibility of adding 3D models. When I started modeling, I created a 3D crater model with the crater.dds as a texture for the exact reasons you mention but I never followed up on that. Maybe it's time to pick that up again... As for your suggestion: If you can pursuade someone to give me enough money to quit my dayjob for the rest of my life and and make it twice as long... (But I do find the idea intrigueing!)

I wish I was attracted to easier hobbies, like drinking beer and watching sports... [sigh]

[MajorMagee]

Having gotten myself involved with military aircraft construction in recent years, I found myself surprised about the amount of work (and years) it takes to integrate a new weapon into the overall air vehicle system.

[gecko]

1. I don't know. But because it's obviously related somehow (bigger numbers kill more damage points) the damage point values in the various objects need to be tuned to the damage the weapons can inflict or vice versa. I don't have a method other than "that seems about right." Generally I try to make sure bullets can kill soft targets without too much trouble but not take out a hanger with a quick burst. I think the biggest issue is that most buildings do not have nearly enough damage points and there is not a wide enough gap between the damage a 50cal round can do and what a 500lb bomb can do. Whatever scale the original developers were using was way off or at least applied terribly and without consistency.

2. Yep!

3a. For containers, Mass is the container weight in KG. I believe WeaponMass is actually the number of individual weapons it contains. The actual weight of the weapons themselves is defined in their own xdp. Also note that for something like rocket tubes, the rockets themselves should have no drag, since they aren't contributing to drag while inside the tubes. I expect the tubes create a lot of drag though.
3b. See 3a.
3c. For drop tanks, Mass is the empty droptank weight in KG. WeaponMass is the amount of fuel when the droptank is full, in liters.

4. Yeah, I'll get right on that.

*sigh*...yeah...these days it's a struggle to even have the mental energy for the stuff I'm trying to do in CFS3, but watching TV makes me feel braindead. So here I am, trying to stay awake and figure out why my code isn't working.

[Frosty]

Now you got me doing 3D bomb craters instead of aircraft stuff - okay, well, it's related

I found this rather interesting comparison of bomb crater sizes for various US GP bombs and some other ordnance:



This is the accompanying text:
"Crater diameters for a range of bomb types, air-launched rockets, and artillery shells used in WW2. Labelled whiskers show variation in crater diameter due to ground conditions; unlabelled whiskers show size range at ± 20% from quoted size. Data for US GP bombs is for drop heights of 10,000 ft (3,048 m), level flight and airspeed of 250 mph (402 km/h); crater diameters for equivalent bombs dropped in a 60o dive at 350 mph (563 km/h) and a release height of 4,000 ft (1,219 m) vary by ca. 0–8%. Key to source data: TBD – Terminal Ballistic Data (Office of the Chief of Ordnance 1945); WFIDE - Weapon Data - Fire, Impact, Explosion (National Defence Research Committee 1945); ORS – Operational Research Section (Copp 2000); Korhonen (2016)"


By the looks of it, the ETO crater decals are way to big, even with delayed action fuses taken into account: According to this survey, a 2,000lb bomb hittting soft soil may cause a maximum crater size of around 18m in diameter, while an ETO 1,000lb bomb already causes a 25m crater!

Thinking this and your info over, it should be possible to create differently fused bombs of the same size; The difference would lie in the distribution of damagepoints for the three Offsets, the blast radius and the crater model.

Oh my, what am I getting myself into...

[Frosty]

And a 3D crater in gmax looks something like this (57 polys):



Textured with the stock CFS3 crater.dds on the left, untextured on the right. Creating different diameters is merely a matter of scaling along the X/Y axes and raising/lowering the height of the lip. Add a rudimentary normal map and you're nearly good to go!

I already created one for the blue practice bomb in the P-47 thread and even managed to fiddle together some sort of white spotting charge smoke effect out of existing ETO effects.

[mongoose]

And a 3D crater in gmax looks something like this (57 polys):



Textured with the stock CFS3 crater.dds on the left, untextured on the right. Creating different diameters is merely a matter of scaling along the X/Y axes and raising/lowering the height of the lip. Add a rudimentary normal map and you're nearly good to go!

I already created one for the blue practice bomb in the P-47 thread and even managed to fiddle together some sort of white spotting charge smoke effect out of existing ETO effects.

3D craters seem a great idea for use in facility files and messing around with on airbases.

[gecko]

I see I'm to blame for causing a distraction. *whispers quietly about 3D wreckage*

I'm curious now how the model appears on a sloped surface. Does it angle to match, or does it remain flat?

[Frosty]

I see I'm to blame for causing a distraction. *whispers quietly about 3D wreckage*

I'm curious now how the model appears on a sloped surface. Does it angle to match, or does it remain flat?

LOL, yes; it's all your fault . What kind of wreckage did you have in mind? The odd wing, tail and a smoldering heap of twisted metal or something? Because I feel that since most WW2 aircraft shapes are pretty distinctive, it would be easiest to create them from the source models. If not, we can do it by modeling a new, less accurate version of the aircraft it is supposed to portray (it crashed anyway).

@2: I dunno, I have to bomb a slope first to see what happens. I'll let you know!

[NachtPiloten]

I would suggest that you make an attempt to contact Bear. He was a key player with AvHistory and a significant insider with the development of CFS3/4. Just search for him in this forum and you'll find a post by him from last April.

Also Greg Pierson at ww2aircraft.net-forum was very closely tied to CFS3 so reach out to him. I just don't remember the other AvHistroy folks......

[Frosty]

... @2: I dunno, I have to bomb a slope first to see what happens. I'll let you know!

The 3D crater model does not follow the terrain: bombing a slope results in the model displaying horizontally (as if the terrain is flat)

I would suggest that you make an attempt to contact Bear. He was a key player with AvHistory and a significant insider with the development of CFS3/4. Just search for him in this forum and you'll find a post by him from last April.

Also Greg Pierson at ww2aircraft.net-forum was very closely tied to CFS3 so reach out to him. I just don't remember the other AvHistroy folks......

Thanks! I didn't know that Bear was still around?

[gecko]

LOL, yes; it's all your fault . What kind of wreckage did you have in mind? The odd wing, tail and a smoldering heap of twisted metal or something? Because I feel that since most WW2 aircraft shapes are pretty distinctive, it would be easiest to create them from the source models. If not, we can do it by modeling a new, less accurate version of the aircraft it is supposed to portray (it crashed anyway).

@2: I dunno, I have to bomb a slope first to see what happens. I'll let you know!

I was envisioning more or less unrecognizable piles of twisted metal and churned up earth or something like that. I can't imagine the work of making wreckage of every type we have. Yikes!

It's a shame they don't match the contours, I was afraid of that.

[MajorMagee]

What does it look like if the 3D Bomb crater perimeter turns down so the edges are below the mating surface plane? Like when an aircraft sinks into a surface if the contact points are not set right, you only see what's above ground. I'm thinking that it might mask the mismatch for most slopes except for actual mountain sides.

[Frosty]

I was envisioning more or less unrecognizable piles of twisted metal and churned up earth or something like that. I can't imagine the work of making wreckage of every type we have. Yikes! ...

OK, I'll think that over and have a look on the web for inspiration!

What does it look like if the 3D Bomb crater perimeter turns down so the edges are below the mating surface plane? Like when an aircraft sinks into a surface if the contact points are not set right, you only see what's above ground. I'm thinking that it might mask the mismatch for most slopes except for actual mountain sides.

Good suggestion! I think the success would depend on the angle of the slope but the texture is gonna cause the most trouble because It can be stretched that much. I have to think that over too.