Anatomy of Explosions: Lethality, Blast, Fragments

The recent video about Dive Toss showed an F-4E Phantom II operated by Calir and Essah from the 86th Virtual Fighter Wing. They dropped at an extremely low altitude, raising a few questions about how dangerous such operations might be. So, in typical FlyAndWire fashion, let’s dive headfirst into the rabbit hole and see what happens when bombs go off in DCS.

This discussion covers topics such as:

• Understanding explosions. Featuring the most useful representation of an explosion I have ever seen;
• the visual representation of the explosions in DCS;
• whether the blast and the debris lifted are related to graphical representation;
• how dangerous is flying through such debris;
• the size of the blast wave for various iron bombs;
• a brief look at real data.

Eventually, the conclusions will help to improve Section and even bigger operations, as subsequent strikes require time deconfliction to maximise safety.

A real-life example

Let’s start with a boom. Usually, footage of explosions is taken from a certain distance, making discerning the behaviour of debris a bit more complex.
This example is, instead, the best representation of why explosions are dangerous even after a surprisingly long time. I am talking about the video of a whale carcass blown up with “slightly” too much explosive.

Timestamp: 01:49.

As we have seen, after 15 seconds, pieces of the whale were still falling, but the camera cut before the situation fully settled. This is, in my opinion, quite surprising. 15+ seconds is a long time for stuff to fall back down to Earth! This is why it is important to introduce a safety time interval between strikes, at least in real life.
Let’s see how DCS behaves instead.

DCS Visual Effects

These three shots show the blast effects of the Mk82, Mk83, and Mk84. These general-purpose bombs weight, nominally, 500lbs, 1000lbs, and 2000lbs. Circa 230kg, 450kg, and 900kg. As a side note, these bombs are slightly heavier than the weights I just reported.
As we can see, DCS shows debris, shrapnel, and other pieces of rocks and dust which are particularly nasty for any aircraft that travels through them. I have also measured, with some considerable approximation, the maximum area touched by the debris.

what are Blast waves

To better answer such a question, let’s introduce the concept of blast waves.
Focusing on a single bomb, in this case the almost ton-heavy Mk84, and slowing down time, we can appreciate the visual representation of the blast wave.
Simplifying a lot, a blast wave is an expanding area of high pressure, moving at extremely high speed. The blast wave is generally composed of a shock wave and a blast wind. The shock wave can move at supersonic speeds, and it is characterised by a pressure level much higher than the atmospheric pressure. The blast wind then follows and is constituted by air accelerated by the shock wave. The waves can also be reflected by ground or in closed spaces, increasing the pressure further.
On top of the phenomena discussed, additional dangerous effect follow and include debris, fragments, and other object dragged and accelerated by the expanding wave.
You can find more information at this link.

Flying through the blast

The next step is figuring out what happens to an aircraft that flies through the cloud of debris and the still-expanding blast wave. In this scenario, three F-14s are charging through the mess at M2. They are spaced by a few hundred meters.

Surprisingly, the blast effects are simply not there. The damage appears to be applied right away, and the following F-14s push through with no side effects.

Let’s investigate further.
In this scenario, four Gazelles spawn a second after each other. As we can see, the first arrives before the explosion, the others right after, but they don’t seem to care at all about the inferno raging around them.

These two examples allow us to draw the first preliminary conclusions: the debris appears to be a graphical effect only, and the blast wave seems to be a volume of space around the explosion itself, with subsequent damage applied instantaneously.

Blast size dimension

Now that we have a better idea of how the explosion works, let’s measure its effects. This stacked herd of Gazelles is spaced by 100ft, from 100ft to 800ft. Let’s toss a Mk84 in the middle and see what happens. Yes, many Gazelles have been sacrificed to Tzeentch, god of knowledge, to make these tests.

As we can see, every aircraft was damaged. But is this really the case? Inspecting the 3D models, we see no signs of damage. I guess it’s time to put our own life on the line!
My beloved Ka-50 will spawn a second before the explosion, starting at 450ft. Let’s have a look at what happens.

Curiously, we see the impact, we see the pieces falling off, but no actual damage. Spawning at 250ft see us blowing up as pop corn.
It appears that the graphical effects applied to the units not too close to the blast are just aesthetics: no damage seems actually delivered. It was probably introduced to smooth the appearance of the blast, as it would be weird if an explosion had a defined and strict cutoff. Another explanation might be that the damage is too negligible to impact the aircraft. I cannot tell for certain, for obvious reasons.

And here we go off like popcorn.
It appears that the graphical effects applied to the units not too close to the blast are just aesthetics: no damage seems actually delivered. It was probably introduced to smooth the appearance of the blast, as it would be weird if an explosion had a defined and strict cutoff. Another explanation might be that the damage is too negligible to impact the aircraft. I cannot tell for certain, for obvious reasons.

Blast size: Mk82, Mk83, Mk84

Following the modus operandi discussed before, here is an approximation of the blast dimensions. I assessed each value as you have seen before, lowering the spawn altitude until my Kamov blew up. Obviously, I cannot measure the damage itself if not visually, which is really not a reliable metre.

Mk-84

Starting with the Mk84, at 350ft the Kamov blew up. At 365ft, it did not. I then wanted to check whether the blast is a hemisphere, a rectangle, or something else. For this purpose, I placed a Kamov 300ft to the side and 300ft AGL from the centre of the explosion. Since the helicopter was fine, I suppose that the blast is indeed a hemisphere.

Mk-83

Next, the Mk-83. Weighting half of the Mk84, at 230ft the damage appears to be limited: there is no explosion. At 240ft, the same applies, but the decals are still limited to the lower part of the helicopter. At 250ft, the Kamov is untouched.

Mk-82

The smallest of the commonly used bombs used in DCS, it followed the pattern of the Mk-83 and the Kamov Ka-50 was safe at 250ft. At 240ft instead, minor damage affected the Kamov.

A Potential Bug?

I find interesting that the Mk-84 either blows up the Kamov or nothing at all, whereas the Mk-82 and Mk-83 have an additional layer of damage, represented by minor damage and external decals such as shrapnel holes. However, the Mk-84 was either all-or-nothing, which sounds odd. I wonder if this behaviour is intended, as it de facto reduces the damage range of such a bomb.
Moreover, the damage bubble of the Mk-82 and Mk-83 appears to be identical or at least very similar, as they both stopped applying damage at circa 250ft. The Mk-84’s damage zone is instead bigger, achieving the same effect until circa 360ft. This is not my realm of expertise, but I expected some sort of exponential progression.
Perhaps this is just a way to make the smaller bomb more effective, whilst containing the Mk-84, or perhaps it’s fine as it is. If you know the answer, please let me know!

Cluster shenanigans

What about cluster bombs, such as my beloved Mk20 Rockeye? I covered this bomb extensively in the past, but not from the perspective of the topic here discussed. In particular, I wanted to verify whether the falling bomblets could be detonated on impact by objects above the ground.

As we can see, some Gazelles receive damage, indicating that some were hit by the falling bomblets. This is quite interesting. For example, the Mk20s used in this scenario have been dropped at 10,000ft, and it took them circa 30 seconds from release to impact. So, if the odds of being caught by the explosion of iron bombs dropped by another aircraft are very low, given what we have seen so far, the chance of flying through a cloud of bomblets might be slightly higher. Ergo, it seems that, even if you are not interested in realism, a certain degree of time deconfliction should be applied when cluster bombs are operated.

A Real-life Example

In real life, debris, shrapnel, and blast are taken very seriously. As seen in the video of the whale carcass blown up, in fact, objects disturbed by the explosion can take quite a while to fall back down to Earth.
The following diagram approximates the dangerous area around the explosion as a function of time.

Conclusions

Even if a second aircraft can fly through the debris with impunity, I strongly recommend you avoid that. It’s a bad practice, which may become lethal if, at some point, those clouds of shrapnel are modelled more appropriately in-game.
Lastly, I want to stress that I do not consider the decoupling of blast volume and visual effect as a bug or unacceptable. No one asks ED to implement a fully physical simulation of blast and debris. It would kill any server instantaneously, especially considering how trigger-happy the average DCS player is, myself included. Hey, at the end of the day, we don’t pay for pixels, and explosions are fun!

Leave comments and feedback in the Discussion Forum thread.