Fuel tank explosions here to stay?

[Hitcher]

Are the fuel tank explosions a feature or a placeholder for fuel system implementation? A 2 minute google search will show that gasoline doesnt explode in a way that would disintergrate an airframe yet these explosions account for a large portion of cannon kills.

 

Aircraft with multiple fuel tanks seem to be more susceptible with bombers and aircraft with auxiliary tanks exploding often from a few cannon hits.

 

If a dev could chime in and maybe give a short explanation it would be much appreciated.

 

Thanks

[453=SGII_Wotan]

I thought petrol plus high explosive round would equal boom

[Hitcher]

52 minutes ago, 453=SGII_Wotan said:

I thought petrol plus high explosive round would equal boom

You'd think so right? But gasoline doesnt detonate like an explosive, it deflagrates meaning the flame propagates at velocities far less than the speed of sound. In contrast to the shockwave of a detonation.

So more like a rapid combustion than a destructive blast.

Edited June 19, 2022 by Hitcher

[IckyATLAS]

If the fuel vapors (and the fighter piston engine fuel was very volatile)  gets mixed with oxygen but all this is contained in an envelope it will cause the envelope to explode.

Wings and fuselage are kind of containers and even if there is an internal "chemical" deflagration it will cause what looks like an explosion of the airframe.

[Jade_Monkey]

I believe the fuel vapors are now modeled, where the chance of an explosion is greater as the fuel tanks are emptier.

[354thFG_Panda_]

Its very cool they simulate all of this but I think they need to work on some force calculations or how they look a bit more. The planes fling around in comical ways. Example try the B25 or 110. 

Edited June 19, 2022 by [=RMAS=]theRedPanda

[EAF19_Marsh]

Fuel burns but rarely explodes. This is not only a physical property but is also easily observable with a quick internet search. Even when intended for rapid conflagration - such as napalm - it rarely explodes. Spreads and burns is more usual.

 

IMHO the DM is still too Hollywood. Most aircraft go down through system and crew damage / death, not massive and instantaneous structural failure. A 40mm-plus flak round might well cause this, but very rarely something fired from another aircraft. Even Luftwaffe 30mm footage vs. heavy bombers shows very little explosion or catastrophic failure. Some, yes, but still a minority.

[Avimimus]

Overall I agree the large fireball explosions are far too popular (and definitely less common for trucks than is depicted in game).

 

However, we're talking about a fuel vapour explosion in an enclosed space. A considerable overpressure should develop and propagate through the airframe until it can find (or create) sufficient openings to escape into the outside world. So we're not just talking about subsonic expansion of hot air and fuel in an open environment - but rather a situation where surrounding parts of the fuel tank and airframe are absorbing that energy from the overpressure and buckling or expanding as debris within the airframe.

 

[sevenless]

Images speak louder than words:

 

 

Start a 0:12 mark

 

 

[firdimigdi]

On 6/19/2022 at 12:54 PM, Hitcher said:

gasoline doesnt detonate like an explosive

 

1 hour ago, EAF19_Marsh said:

Fuel burns but rarely explodes.

 

Take a coke can.

Put about 50ml of gasoline in it.

Let it sit for 2 mins then throw a match at its opening.

 

Always a crowd pleaser around the farm. Alternatively, when used in rat holes:

 

Spoiler

 

 

I can also tell you we never found the top of the wood stove in the colonel's tent when some guy decided to use gasoline to start the fire when we were out on maneuvers.

 

Edited June 21, 2022 by Firdimigdi

[354thFG_Rails]

27 minutes ago, Avimimus said:

Overall I agree the large fireball explosions are far too popular (and definitely less common for trucks than is depicted in game).

 

However, we're talking about a fuel vapour explosion in an enclosed space. A considerable overpressure should develop and propagate through the airframe until it can find (or create) sufficient openings to escape into the outside world. So we're not just talking about subsonic expansion of hot air and fuel in an open environment - but rather a situation where surrounding parts of the fuel tank and airframe are absorbing that energy from the overpressure and buckling or expanding as debris within the airframe.

 

you mean to tell me the "explosion" wouldn't try to rush out the entry hole that caused the explosion in the first place? but would rather overpressure and blow out with enough force to cause the plane to rip apart? Not buying it.

 

8 minutes ago, sevenless said:

 

Start a 0:12 mark

 

 

 

That was probably an 88 flak shell and didn't look like what we're seeing in game. Not saying it didn't happen but that hit is a lot different than what's happening in game.

[sevenless]

Just now, 86th_Rails said:

That was probably an 88 flak shell and didn't look like what we're seeing in game. Not saying it didn't happen but that hit is a lot different than what's happening in game.

 

What you see is the gasoline ignition. Not more not less.

[354thFG_Rails]

what's being asked is this...

 

i don't think anyone is disputing whether or not fuel catches fire. it's the explosions that seem like michael bay levels of ridiculous.

[EAF19_Marsh]

29 minutes ago, Firdimigdi said:

 

 

Take a coke can.

Put about 50ml of gasoline in it.

Let it sit for 2 mins then throw a match at its opening.

 

Always a crowd pleaser around the farm. Alternatively, when used in rat holes:

  Hide contents
 

 
You certainly can cause a fuel-air explosion, it even has a BLU designation. However, that requires quite specific circumstances. Putting a given quantity in a container of a certain size, making a determined number of holes of a particular diameter, allowing a given degree of atomization / mixture and then specific ignition elements? Yes, it can happen, but it is a minority of circumstance.

 

Most fuel fires burn, they do not explode. Even more so in a multiple-100kt slipstream.

Edited June 21, 2022 by EAF19_Marsh

[sevenless]

8 minutes ago, 86th_Rails said:

i don't think anyone is disputing whether or not fuel catches fire. it's the explosions that seem like michael bay levels of ridiculous.

 

Yea, we are not there yet. My impression is, if they will find a way, they will include it.

 

Watch this. Real footage. At the 1:22 mark. Exploding belly tank of what seems to me like a 109. At the 1:28 mark wing hit of ammo box of a 190. At the 1:30 mark hit in fuel tank of a 109. Otherwise no exlosions or large ignitions to be seen.

 

 

[EAF19_Marsh]

There is quite a well-worn RAF doc online (name escapes me for now) that specifically states that the likelihood of a drop-tank exploding is very low, so they should be discarded only for the performance gain rather than potential danger.

 

In aircraft, fuel destroys through burning. Explosions are very much a minority though likely are overly-reported because they are memorable. That is not the same as a direct flak hit, that likely will cause an explosion as the aircraft ia blown into small pieces as the shell, onboard fuel, oxygen, ordinance and whatever all detonate. But even in such a case, the huge physical stresses of the airflow on a disintegrating structure should not be underestimated.

[354thFG_Rails]

Not only memorable but what other word would pilots use in the moment other than they saw the fuel explode or erupt. I mean I know if I saw a giant fire ball in that moment I would think the damn thing blew up too. 

[Jade_Monkey]

Sorry if I missed the comment, but these are not fuel explosions. They are ammo explosions.

[Avimimus]

I'm a bit disappointed by the lack of experienced pyromaniacs in this forum - I honestly thought it'd be higher for some reason.

 

Okay, so a few thoughts:

 

1) High altitude and high airflow speeds might lead to pressure regimes that produce much more rapid creation of vapours than we are used to at ground level

 

2) Aircraft are largely hollow, allowing the propagation of vapours and fuel throughout the wing

 

3) An aircraft under attack is likely to receive multiple perforations of a fuel tank. However, the number, size and distribution is likely to be highly variable.

 

4) The actual detonation would often happen in the context of either other spark or fire sources within the plane, or the detonation of incendiary or high explosive rounds from a second attack by an enemy airplane. There may also be considerable damage to the aircraft already prior to the explosion.

 

5) Aircraft have very specific structures designed to be light-weight and rigid while under fluctuating and relatively high aerodynamic loads. Ordinary ground vehicles are both overbuilt and experience much lower gee forces and smaller cantilever distances than is found in even a small civilian aircraft (let alone a large military aircraft).
 

I think all of these things mean that we lack a point of reference.

 

Yes, obviously Hollywood depicts vehicles blowing up far too often. I know this and even created a mod for Il-2 that removes the explosion fireballs from civilian ground vehicles. However, that doesn't mean this observation translates to aircraft.

 

Lots of aircraft burned and lost control without exploding. Lots of aircraft burned and underwent structural failures without exploding. Lots of aircraft endure flash explosions which blew themselves out and allowed the aircraft to return to base no longer on fire (as is now depicted in Il-2).

 

However, I also wouldn't discount the possibility that some aircraft had rapid vapourisation of fuel after being attacked and then detonated in a way where expanding debris powered by the over-pressure in the tank, when combined with the structural forces already on the aircraft, actually led to a structural failure.

 

I think any attempt to make simple categorical statements or generalizations is very silly.

 

 

1 hour ago, 86th_Rails said:

you mean to tell me the "explosion" wouldn't try to rush out the entry hole that caused the explosion in the first place? but would rather overpressure and blow out with enough force to cause the plane to rip apart? Not buying it.

 

The shock wave from the explosion producing the pressure would have to reach the other side of the tank and then propagate back to the hole before escaping through it. At a minimum that requires some time to happen.

 

Furthermore the pressure of the heated vapour escaping through the hole would have to be lower than the pressure in the rest of the tank before the vapour in the rest of the tank could escape through the hole. So you need to know the diametre of the hole, the rate at which the gas can escape through it, the pressure the gas is under during that process, and its relationship to the compressibility and temperature of the gas. Anyone with a physics degree (who was actually paying attention) should be able to work that out - but it will differ greatly depending on the size of the hole and the volume of the tank.

 

All of this does allow pressure to build up and potentially rupture the tank (thus creating new holes and chances for the gas to escape). Exactly how much force is involved is the question... but it should be calculable (within various assumptions, such as the completeness of combustion).

 

Anyway, your incredulity is pretty meaningless to me if you aren't planning on doing the work to show me the calculations proving that the overpressure would never become high enough in any tank configuration to be able to propel debris (or even rupture the tank and create additional holes - something you seem to be claiming).

[ACG_Cass]

1 hour ago, Avimimus said:

A considerable overpressure should develop and propagate through the airframe until it can find (or create) sufficient openings to escape into the outside world. So we're not just talking about subsonic expansion of hot air and fuel in an open environment - but rather a situation where surrounding parts of the fuel tank and airframe are absorbing that energy from the overpressure and buckling or expanding as debris within the airframe.

Absolutely agree but this should be pretty localised and at most cause the skin to rupture. Aircraft fuel tanks are nowhere near strong enough to contain the levels of pressure needed to cause a fuel explosion of that force and even then, fuel is not an explosive meaning as soon as there is a rupture the explosion will turn into a fire.

 

IL2s current implementation is what I would expect if a 500lb bomb exploded, not a mostly empty fuel tank.

 

 

Even outside of that we are talking about incredibly specific conditions for just that to happen. At the moment a plane with larger fuel tanks at low fuel levels can explode 10-20% of the time.

 

I really think this feature needs to be removed and replaced with regular fire until the fuel update allows for more nuance.

 

The fact there is zero footage available showing anywhere near the levels of explosion mean they should be replace with larger fires and at most, some structural failures.

[firdimigdi]

1 hour ago, EAF19_Marsh said:

However, that requires quite specific circumstances. Putting a given quantity in a container of a certain size, making a determined number of holes of a particular diameter, allowing a given degree of atomization / mixture and then specific ignition elements? Yes, it can happen, but it is a minority of circumstance.

 

Not that specialized really. All it needs is a way for the fire to make its way in to the container. So if you got one hole spewing out liquid and reducing pressure in the container and you got another hole sucking in air then you get very good conditions for an explosion.

 

Which is also a reason you should put distance between you and people squeezing any sort of flexible bottle with a combustible fluid over a fire in case they forget themselves and stop squeezing and it starts sucking back in.

[Avimimus]

30 minutes ago, ACG_Cass said:

Absolutely agree but this should be pretty localised and at most cause the skin to rupture. Aircraft fuel tanks are nowhere near strong enough to contain the levels of pressure needed to cause a fuel explosion of that force and even then, fuel is not an explosive meaning as soon as there is a rupture the explosion will turn into a fire.

 

IL2s current implementation is what I would expect if a 500lb bomb exploded, not a mostly empty fuel tank.

 

Okay, that sounds like a relatively plausible argument to me! Especially in the context of the pictures from the game.

 

That said, I wouldn't entirely rule out an explosion causing some kind of more significant structural damage. At least enough to damage control cables, set off oxygen tanks and oxygen lines (something which could destroy an aircraft) or damage structures already weakened by kinetic hits.

 

There are actually a bunch of studies out there if people want to look. Studies which produced real data! Rather than just speculation:

 

A report from Aberdeen Proving Ground may be worth a read (No.484 - in case the link dies):

ADA800109.pdf (dtic.mil)

 

This study may be interesting too - it shows up to 5.8 bar (85 Psi) overpressures. The study used jet fuel (but also didn't ignite with a 2000-5000 degree moving point of ignition from an incendiary round):

EXPERIMENTAL AIRCRAFT FUEL TANK VAPOUR/AIR EXPLOSIONS USING JET A AND JET A / GASOLINE BLEND FUELS | African Journal of Health, Safety and Environment (ajhse.org)

 

Wright Patterson Report AFB Memo Report No. TSEPP-144-1698 from 1946 also looks very interesting - but I wasn't able to find a copy.

 

Anyway, there are a lot of other studies out there if people are interested.

[357th_KW]

Some actual gun camera footage of cannons at work.  Good luck finding any big explosions like what we see in the game.

 

 

 

 

[EAF19_Marsh]

1 hour ago, Firdimigdi said:

 

Not that specialized really. All it needs is a way for the fire to make its way in to the container. So if you got one hole spewing out liquid and reducing pressure in the container and you got another hole sucking in air then you get very good conditions for an explosion.

 

Which is also a reason you should put distance between you and people squeezing any sort of flexible bottle with a combustible fluid over a fire in case they forget themselves and stop squeezing and it starts sucking back in.

Special in the sense that it requires an air-fuel mixture within upper and lower limits, specific temps and pressures, absence of external factors (such as rapid external air movement) and so forth. You can drop a match onto a patch of fuel and it will burn, but it will not explode. You can light a Molotov and it will burn but not explode. The latter will explode if the glass is broken rapidly, but only continue to burn if the neck is broken. There are conditions that need to be met (or avoided), and low oxygen conditions (above 10k ft) with slow leak (probable with <30mm and a self-sealing tank) and a high slipstream (net air movement) do not for good explosive conditions make.

 

Certainly can happen, but a rarity.

[SCG_motoadve]

All this explosions and fires which are way overdone  are killing immersion, making this Il2 series feel more arcadish, you can set a B26 on fire with just a couple of MG hits, then explodes,  bombers are fragile, planes explode too easy, P47 is a joke, earlier planes do much better.

[EAF19_Marsh]

What was the DM version, 3.xx? That was great because it was subtle. Alas, it was overridden by the perceived enthusiasm for greater visual drama.

[ACG_Cass]

1 hour ago, Avimimus said:

That said, I wouldn't entirely rule out an explosion causing some kind of more significant structural damage. At least enough to damage control cables, set off oxygen tanks and oxygen lines (something which could destroy an aircraft) or damage structures already weakened by kinetic hits.

Yeah that's fair.

 

I think the much bigger factor that isn't modelled is the damage fire can do to the aircraft structure and components. A serious fire should be reducing the structural strength of an skin/struts in range pretty quickly along with knocking out controls.

[1PL-Husar-1Esk]

Explosion are overdone plus I don't think is realistic  when few bullets in the fuselage or wing make ww1 plane start to shake like crazy or  few bullets in the wing of ww2 fighter make whole plane to roll like crazy.  

[Avimimus]

I feel like I should recommend to some people to try flying a greater variety of aircraft. Not seeing the world only through the Mk-108 or 0.50 calibre machine guns!

  

18 hours ago, SCG_motoadve said:

All this explosions and fires which are way overdone  are killing immersion, making this Il2 series feel more arcadish, you can set a B26 on fire with just a couple of MG hits, then explodes,  bombers are fragile, planes explode too easy, P47 is a joke, earlier planes do much better.

 

I agree that overdone fire effects and explosions tend to make things look arcade like. However, overall, large fire-plumes from burning aircraft are something that really occurs.

 

As for machine gun hits - it is worth noting that fighters with just two rifle-calibre machine guns did shoot down bombers on many occasions during the war. This is something which is exceptionally hard in the game (even when we are willing to expose ourselves in ways real pilots wouldn't want to in an actual life or death situation). So the combination of those facts makes me believe that rifle calibre machine guns are likely weaker in the game than they would be in real life.

 

[Denum]

11 minutes ago, Avimimus said:

As for machine gun hits - it is worth noting that fighters with just two rifle-calibre machine guns did shoot down bombers on many occasions during the war. This is something which is exceptionally hard in the game

 

Yeah, in the EARLY portions of the war. 

 

Aircraft armor wasn't a common practice. 

 

13mm HE in game is ridiculous. Someone put 6 of them on a mustang in game and it was hilarious. It was deleting planes.

 

 

[kendo]

19 hours ago, EAF19_Marsh said:

What was the DM version, 3.xx? That was great because it was subtle. Alas, it was overridden by the perceived enthusiasm for greater visual drama.

 

Grass is definitely greener with hindsight.

 

That DM was before the wings were fixed to stop them falling off every time a plane was hit. Probably more visual drama back then than now.

 

 

[EAF19_Marsh]

27 minutes ago, kendo said:

 

Grass is definitely greener with hindsight.

 

That DM was before the wings were fixed to stop them falling off every time a plane was hit. Probably more visual drama back then than now.

 

 

Maybe. Wing detachment and fires (about 5 mins ago in a QMB sortie) seem rather common. A few updates back and the most frequent occurrence appeared a shredded ship slowly slippping Styx-ward

[PatrickAWlson]

On 6/19/2022 at 5:11 AM, 453=SGII_Wotan said:

I thought petrol plus high explosive round would equal boom

 

It doesn't.  Fuel vapor + HE is what equals boom.  A full tank will not explode but it may leak all over the place and burn when it contacts something hot.

[453=Thornley]

I've spent the last 24 Years as a professional city firefighter. I've done multiple course on this over the years and attended countless car fires. 

 

Explosives are always oxygen independent, either by producing their own oxygen during the detonation process or by utilising a chemical reaction that doesn't require oxygen consumption.  Non-explosives can be made to detonate but to do this, they must dispersed into a fuel/air mixture so that lack of oxygen will not hinder the flame front speed. An example of this was exploding flour mills during medieval times. Finely ground flour dust would mix with the air inside the flour mills until they reached the correct fuel/air mixture. All it would take then was a ignition source and boom. Google dust explosions if you're interested.

 

Petrol is no more of an explosive than flour is. Liquid petrol lacks a built in source of oxygen and as such and will only ever burn at the boundary layer where the petrol and air mix. To make it detonate, like flour, we need to turn it into a vapour and mix it into a fuel/air mixture. This fuel/air mix can be found in the top of a partly empty fuel tank (if CO2 purging isn't available) and a incendiary bullet could cause this to detonate but the amount of energy in the tiny amount of fuel vapour in the fuel/air mixture is not going to rip a plane apart. Years ago, I attended an incident where an idiot was trying to weld up the top of a 44 gallon (200Lt) fuel drum that was still about 10% full of petrol. The resulting explosion of the fuel/air mixture ripped the seam of about half the lid and bent it upwards at a slight angle. The rest of the drum was not distorted at all. The I.I.Q. (Idiot in Question) was suffering concussion, minor injuries to his hands and sever hearing loss. What I found fascinating at the time was the petrol in the bottom of the drum had not ignited (probably from oxygen starvation due to all the oxygen inside the drum being used up in the detonation).

 

In the probably 100 car fires I've attended, I've never had a fuel tank explode in any form. I once had a burning car with a plastic fuel tank (that was a thing!) suddenly rupture, sending firies running like girls but there was no detonation at all. I can't see aircraft would be that different.

 

Bullets hitting the oxygen bottles in the fuselage of a burning plane, that however would be spectacular.

[Praetorious]

I love airplane crashes,what i mean is i find them fascinating and how they are analyzed on what happened etc, my Uncle who i never met,died in a airplane crash in 1947,he was playing in a soccer game and the school had chartered a airplane to take them to another state and on the way back the pilot got lost and they slammed into a mountain,he was 15 years old,this is a side story but the real reason i'm bringing this up is because for Christmas,i got the entire air crash investigation boxset (highly recommend it) and in season 17 there is that episode about TWA 800, that airplane blew up due to fuel vapors in the tank and faulty wiring igniting said vapors,i know this is highly unusual but its a very interesting episode and it took them years to figure out what had happened,its probably on Youtube to watch.

[EAF19_Marsh]

8 hours ago, 453=Thornley said:

I've spent the last 24 Years as a professional city firefighter. I've done multiple course on this over the years and attended countless car fires. 

 

Explosives are always oxygen independent, either by producing their own oxygen during the detonation process or by utilising a chemical reaction that doesn't require oxygen consumption.  Non-explosives can be made to detonate but to do this, they must dispersed into a fuel/air mixture so that lack of oxygen will not hinder the flame front speed. An example of this was exploding flour mills during medieval times. Finely ground flour dust would mix with the air inside the flour mills until they reached the correct fuel/air mixture. All it would take then was a ignition source and boom. Google dust explosions if you're interested.

 

Petrol is no more of an explosive than flour is. Liquid petrol lacks a built in source of oxygen and as such and will only ever burn at the boundary layer where the petrol and air mix. To make it detonate, like flour, we need to turn it into a vapour and mix it into a fuel/air mixture. This fuel/air mix can be found in the top of a partly empty fuel tank (if CO2 purging isn't available) and a incendiary bullet could cause this to detonate but the amount of energy in the tiny amount of fuel vapour in the fuel/air mixture is not going to rip a plane apart. Years ago, I attended an incident where an idiot was trying to weld up the top of a 44 gallon (200Lt) fuel drum that was still about 10% full of petrol. The resulting explosion of the fuel/air mixture ripped the seam of about half the lid and bent it upwards at a slight angle. The rest of the drum was not distorted at all. The I.I.Q. (Idiot in Question) was suffering concussion, minor injuries to his hands and sever hearing loss. What I found fascinating at the time was the petrol in the bottom of the drum had not ignited (probably from oxygen starvation due to all the oxygen inside the drum being used up in the detonation).

 

In the probably 100 car fires I've attended, I've never had a fuel tank explode in any form. I once had a burning car with a plastic fuel tank (that was a thing!) suddenly rupture, sending firies running like girls but there was no detonation at all. I can't see aircraft would be that different.

 

Bullets hitting the oxygen bottles in the fuselage of a burning plane, that however would be spectacular.

Thanks for the very interesting input. Somewhere in the back of my mind is an account from someone surviving what they thought was probably a hit on an oxygen tank as the aircraft simply became pieces with no sign of smoke or fire.

 

Would you expect chances of fuel detonation being even lower with the reduced oxygen level at altitude? Also, another benefit of using the high octane as it has a more stable burn characteristic and hence less explosive  propensity ?

[firdimigdi]

8 hours ago, 453=Thornley said:

In the probably 100 car fires I've attended, I've never had a fuel tank explode in any form.

 

Oh, I've seen one! But it wasn't a petrol fuel tank, it was a (probably badly installed without safety valves some have) natural gas tank. Was quite the sight and luckily happened before someone got near to put the fire out.

 

You can see one here as well, as part of firefighter exercises - if you track back to the first burning car you can also see a properly installed such tank with valves triggering and doing a controlled burn of the remaining gas, at some point the petrol tank ruptures as well and it spills out under the car:

 

Spoiler

 

 

[ACG_Cass]

7 hours ago, Praetorious said:

TWA 800, that airplane blew up due to fuel vapors in the tank and faulty wiring igniting said vapors

A 747 holds 100s of thousands of litres of jet fuel in enormous fuselage and wing sections. I don't think what happened to TWA 800 would be relevant to WW2 fighter aircraft.

[firdimigdi]

By the way, seems somewhat relevant: https://explodingfueltanks.com

[Retrofly]

For sure, since the last major patch explosions are happenign a lot more often.

Previously they were very rare for me, maybe once ever 20 or 30 sorties, now I expect at least 1 every sortie.

 

Im not here to argue if its realistic, just adding my own annecdotal observations.