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PostPosted: Mon May 10, 2004 6:24 am 
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FirePower damage modeling explained

This is a general overview of the process we went through to bring the most realistic weapons and damage modeling into CFS3. Since realistic damage modeling (and the effects that go with them) is the foundation of any realistic air-combat experience, this is where FirePower development began.

In the initial stages of development, we tested many simulations on the market today against actual military data in terms of how many hits it typically took to take down a specific aircraft with a specific type of ordinance.

The two basic issues we immediately saw were:

1. Too many hits were necessary, with any given weapon, to down most aircraft
2. Large ground targets, including large warships, could be destroyed with small caliber weapons

With CFS3, we began the process by mapping out most of the objects, including aircraft, buildings, guns, ships, vehicles, and weapons to establish a base to work from. We researched archived military data in many areas and consulted with specialists including airborne weapon experts, Tony Williams and Emmanuel Gustin (their book “Rapid Fire” can be found here: http://users.skynet.be/Emmanuel.Gustin/volume1/. We asked specific questions about Allied and German intelligence information regarding their analysis of downed aircraft, and what was the cause of their destruction. From these studies, general guidelines and comparisons were made like, “3-5 hits from a 30mm cannon was usually sufficient to down a heavy bomber,” or “most B-17 wreckage was found to have no less than twenty 20mm hits.” This was all broken down to the various vulnerable systems in any given aircraft like the pilot, engine, fuel, hydraulics, control surfaces, etc.

Once we established a standard for all weapons and aircraft components, they went through a process of testing in CFS3 until the in-game results were identical to, or closely matched the real data we were using. The major hurdle we had to cross in CFS3 was achieving the right balance between airborne guns and heavy air-to-ground ordinance.

To generalize the process for CFS3, in the end, we had to increase the strength of the largest buildings, weapons, and ships as much as 5 Times to get close to historically accurate figures. We also took the time necessary to detail every single object, for example, the German R4M rocket housed ½ kilogram of high explosives, while the British R8 “60 pounder” rocket had a 27 kilogram warhead – FirePower reflects this. Here are a few more:

Rocket type Explosive weight
WGR 40 kg
R4m – HE - ground ½ kg
Brit 60lber 27 kg
FX1400 270-330 kg – armor piercing
Hs293 500 kg

HE / Kinetic Energy Analysis
The other issue is most games we’ve tested place too much emphasis on a weapons Kinetic energy, and not the high explosive content. Kinetic energy is the measured force a projectile can expend when it hits a target based on its speed and weight, and high explosive content is the amount of the explosive material inside the weapon.

Below is a picture from “Focke-Wulf– FW190 In Combat” by Alfred Price that states this type of damage was typical of only 1 or 2 hits from a 30mm. It can be seen that the HE explosive power far outweighs the kinetic energy considering a 30mm projectile weighs less than a pound and held in your hand.
Image

A common formula found for explosive energy is that of TNT, usually put at 4.2 billion Joule per ton, or 42000 Joule per gram. Most HE rounds used more stable and more powerful explosives.
For comparison, a 100g 20-mm round traveling at 850 m/s would have a kinetic energy of 0.5 x 0.1 x 850 x 850 = 36125 Joule. At a typical 20mm explosive content of 10 - 15 %, the explosive power is bound to be much larger than the kinetic energy. Also, the 30mm German 'Minengeschoss' HE shells were very thin-walled rounds with a lot of HE (75-85 Grams), to do damage purely by the blast effect.

The equations above indicate the ratio of a pure HE explosion to KE potential damage of a 20mm round could be as high as 10 to 1.

Here is a response from Emmanuel Gustin, a well-known airborne gun expert, who talked to us about large cannons and the damage they inflicted:

"Both the MK 103 and MK 108 were able to fire (Minengeschoss) ammunition, which carried a huge 75-gram explosive payload. German studies had determined that 500 grams of TNT would take down any aircraft if exploded on contact with any part of the plane (assumedly excepting fringe hits, such as wing tips), and this was reduced to 400 grams of the explosive used in German shells. Based on this it was claimed that 3-5 hits would down an American bomber."

Emmanuel talks about the different ways smaller (.303 cal) and larger (.50 cal) non-explosive projectiles damage an aircraft:

“Kinetic energy does its damage when the projectile hits the structure, but this too is a complicated story. A projectile can easily be destabilized by going through a thin plate (such as an aircraft’s skin), dramatically reducing its armour penetration. The heavier the projectile, the more stable it is, of course. On the other hand a heavy projectile with a lot of kinetic energy can expend it only when it hits something sufficiently sturdy; if it goes through thin plate—such as aircraft skin—it will only leave a couple of neat round holes, in and out, which may be irrelevant. Therefore some people have argued that kinetic energy is better spread over a lot of small projectiles than in a few large projectiles.”


Vehicles
We took into consideration the vast difference seen on the battlefield, for example a German Tiger tank could have almost a foot of frontal armor and a Sherman, just a few inches. FirePower uses actual armor thickness tables for all vehicles in the game, and scaled them accordingly. You would be surprised how well protected some of those German AA vehicles were.

Vehicles display damage based on their damage state, and content. Static vehicles with loose ordinance may display a little fireworks show (looks like a strip of firecrackers from high up), when each exploding round ignited a nearby round, in sort of a chain reaction. Tanks with tightly packed ordinance may explode. Gas trucks may erupt in a ball of flame. Radiators leak, engines can be damaged, and oil can burn, all resulting in different visual effects. Like the real pilot over a real battlefield, you can see what the state is at a glance.

Weapon Drag
We then addressed the complex subject of weapons drag. FirePower uses actual WWII data on specific airplanes, and matched their performance in the game. What FirePower reflects accurately is 2 smaller bombs of equal weight to 1 larger bomb will create considerably more drag than the larger bomb. IL-2 may be the only sim to model this (do not know, but suspect it might), but at this particular time, this type of drag modeling is new to CFS3. This is important to know, because if you want to pack the biggest punch with the least amount of drag, and you are playing FirePower, you want to carry the largest bomb possible. If you carry many smaller bombs, just like the real aircraft, you will be noticeably slowed down. Know this, it is important and gets more pronounced the faster you go. Jets are highly affected by weapons drag.

Me262 A-1a Jabo
From actual German test date (also applies to FirePower).
Bomb load Loss of speed test

Load % loss of speed
1 SC250 bomb 3.6% loss
2 SC250 bomb 7.3% loss
1 SC500 bomb 4.6% loss

Bomb blast radius
All bomb blasts were made in accordance to US military planning documents, and in the case of CFS3, resulted in a substantial lowering the blast radius of most weapons. Near misses do not count nearly as much as direct hits. The information we used gave detailed results based on HE type, kill distance prone / standing, material damage (brick, stone, wood, etc.), tree damage, distance debris is thrown, fireball size, crater size, etc. FirePower uses this type of realism to calculate how specific weapons damage specific targets and what visual effects are displayed.

Compatibility
The final issue we had to contend with is compatibility with other CFS3 airplanes. Our latest multiplayer utility will allow you to switch a FirePower installation back and forth from STOCK to FIREPOWER mode, to maintain compatibility with 3rd party aircraft. This utility serves two roles:
1. Full multiplayer compatibility
2. Compatibility for aftermarket aircraft that rely on STOCK values.

Please note that while FirePower can play in STOCK mode, the STOCK values are not accurate according to the data we have, and therefore the models that rely on these STOCK settings also suffer from reduced accuracy. The utility is there for your convenience, so you can easily go back to STOCK settings with ease.

This switching utility was the best solution, since it allowed us to break out of the box without stripping your FirePower installation of simple backwards compatibility. It is important to understand, while switching from STOCK to FIREPOWER is just a few clicks, there is a whole world of reality that is available to you while playing in FIREPOWER mode.

Scott.

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A2A Simulations Inc.


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