Fuel Air - adding fragments and as a source of propulsion

#1
What I was wondering about last night -

a) fuel air pretty much relies on overpressure, throwing the casualty into objects, or (less so) firing objects at the casualty. In bare-arse terrain you would think that fuel/air would work less well. Suppose the packet was surrounded by shot/foil blades/something similar. The packet pops and sprays the fuel and foil and then the spark initiates the bang. Would some of the foil blade (I'm thinking something the dimensions of razor wire) hang in the air long enough to be driven by the blast? Things fall 10m per sec ignoring air resistance, but air resistance can be significant with some things. Would falling through a cloud of fuel slow it down further? If it fell to the ground might it get usefully driven by the blast anyway? If it was light enough to work would it be too light to retain velocity?

It just seems to me that a fuel/air bang in open country looks impressive, but in the absence of fragments might not achive much.

b) How fast does the cylinder of a car engine move? Could you fire a mortar round with a tube and a bomb with a base plate acting as the "piston" in the cylinder, and a combustion chamber at the bottom, fuelled by a little bottle of petrol? I'm guessing that you wouldn't get enough velocity, and the weight of propellent saved would be low.
 
#2
gobbyidiot said:
What I was wondering about last night -

a) fuel air pretty much relies on overpressure, throwing the casualty into objects, or (less so) firing objects at the casualty. In bare-arse terrain you would think that fuel/air would work less well. Suppose the packet was surrounded by shot/foil blades/something similar. The packet pops and sprays the fuel and foil and then the spark initiates the bang. Would some of the foil blade (I'm thinking something the dimensions of razor wire) hang in the air long enough to be driven by the blast? Things fall 10m per sec ignoring air resistance, but air resistance can be significant with some things. Would falling through a cloud of fuel slow it down further? If it fell to the ground might it get usefully driven by the blast anyway? If it was light enough to work would it be too light to retain velocity?

It just seems to me that a fuel/air bang in open country looks impressive, but in the absence of fragments might not achive much.

b) How fast does the cylinder of a car engine move? Could you fire a mortar round with a tube and a bomb with a base plate acting as the "piston" in the cylinder, and a combustion chamber at the bottom, fuelled by a little bottle of petrol? I'm guessing that you wouldn't get enough velocity, and the weight of propellent saved would be low.
Try Horlicks in case it happens again. ;)
 

Biped

LE
Book Reviewer
#3
gobbyidiot said:
What I was wondering about last night -

a) fuel air pretty much relies on overpressure, throwing the casualty into objects, or (less so) firing objects at the casualty. In bare-arse terrain you would think that fuel/air would work less well. Suppose the packet was surrounded by shot/foil blades/something similar. The packet pops and sprays the fuel and foil and then the spark initiates the bang. Would some of the foil blade (I'm thinking something the dimensions of razor wire) hang in the air long enough to be driven by the blast? Things fall 10m per sec ignoring air resistance, but air resistance can be significant with some things. Would falling through a cloud of fuel slow it down further? If it fell to the ground might it get usefully driven by the blast anyway? If it was light enough to work would it be too light to retain velocity?

It just seems to me that a fuel/air bang in open country looks impressive, but in the absence of fragments might not achive much.

b) How fast does the cylinder of a car engine move? Could you fire a mortar round with a tube and a bomb with a base plate acting as the "piston" in the cylinder, and a combustion chamber at the bottom, fuelled by a little bottle of petrol? I'm guessing that you wouldn't get enough velocity, and the weight of propellent saved would be low.
Part of the problem is the speed at which you can disperse the fuel, against the speed at which you can disperse the 'splinters' - the fuel-air dispersal is pretty much immediate, whereas the fragments have greater mass and would need to be outside the fuel radius to get the full acceleration. Anything within the pressure or heat wave area will be bowlarked anyway, so the frag will just be OTT.

Also, fuel-air is more effective than anything else when getting around objects or through confined areas, such as tunnels, buildings etc. It's primary effect is a pressure wave, secondary being a heat wave - both of which can go around corners, whereas fragments can only richochet.

It's sort of gilding the lilly TBH, and probably more effort than it's worth.

Having said that - WTF is wrong with fuel-air anyway - pretty damned effective if you ask me.

As for point 'b' - stay off the drugs - mortars work just fine too.

Now, fuel-air mortars - NOW you're talking! :twisted:
 
#5
Which you can get delivered by the cheapo line of sight weapon delivery system you were thinking about on a different thread? Seems to me you are spending slightly too much time on the sofa wan*ing off to great big death dealing ideas, or you should maybe just get out more?

Interesting thought though, but beware what you wish for, when the 'enemy' build one and lob it in this direction...
 

Biped

LE
Book Reviewer
#6
Ta-da!

The thermobaric explosive warhead is aimed at creating an incredibly abrupt overpressure and heat in an enclosed space, followed by a deep vacuum. The overpressure can reach a value of between 2.5 and 3 Mpa while the temperature will soar to a mighty 3000 centigrade and create a blast wave that travels at a speed of 3000 metres per second, burning all available oxygen in the process. This explains the more than suitable choice of the word thermobaric to qualify this type of weapon, as it combines the Greek words of “thermo” (heat) and “baros” (literally weight, therefore pressure). Interestingly, the Russian also describe thermobarics as volumetric explosives, quite rightly one has to admit. A very common error made by the non-specialised press is to describe the performance of thermobaric warheads as a weapon that causes a huge vacuum; the vacuum, of course, comes after the huge overpressure wave and results from the combustion of all the oxygen in the vicinity.

That doesn't leave much work for fragments to do, unless of course you consider the number of high velocity projectiles made from objects in the area of the over-pressure wave - stones, walls, body-parts, personal weapons etc.

Edited to add:

60mm Thermobaric Mortar Cartridge

Under Solicitation R20030219, in February 2003 the US Army TACOM-ARDEC conducted a market survey to identify potential sources of a 60-mm mortar round that employs thermobaric explosive (TBX) technology to produce both blast and fragmentation kill mechanisms. This TBX projectile must have fragmentation capabilities equivalent to the US M720 60-mm mortar round and nominally a 40% increase in the M720’s blast output. The US Army was interested in industry submissions of items that were already in production or would be in production within 90 days of the announcement. The TBX projectile must meet all US military operational requirements for safety and handling. All respondents were required to demonstrate past performance as well as the capability to provide system engineering, integration and full-scale production.

There is no indication that this solicitation resulted in the aquisition of any thermobaric mortar rounds.
The Bulgarian VDMM 81mm Thermobaric is one such example.
 

Biped

LE
Book Reviewer
#8
Such a weapon in British hands would certainly mark the end of mortar round shortages. Just one might be sufficient to 'saturate' the enemy, or at least, saturate the surrounding ditches with taliban intestines.
 
#10
Send an e-mail to Mythbusters perhaps they'll try to construct a four cylinder mortar for you.
 

Biped

LE
Book Reviewer
#11
Tartan_Terrier said:
Send an e-mail to Mythbusters perhaps they'll try to construct a four cylinder mortar for you.
Nice idea, but 6 cylinders gives a far smoother and efficient area saturation.
 
#12
Biped said:
Tartan_Terrier said:
Send an e-mail to Mythbusters perhaps they'll try to construct a four cylinder mortar for you.
Nice idea, but 6 cylinders gives a far smoother and efficient area saturation.
What about a V-8? Hit two targets simultaneously!
 

Trans-sane

LE
Book Reviewer
#13
Did the man-packed LAW type thermobarric weapon being talked about at the start of Telic ever get developed/deployed at all?

As for adding shrapnel of some kind, it wouldn't work. The reasons mentioned above are all good reasons. Another is tiny bits of metal + lots of oxygen + sh1t loads of heat = meatal oxide. Your shrapnel would burn up before it got too your target...
 

Biped

LE
Book Reviewer
#14
Tartan_Terrier said:
Biped said:
Tartan_Terrier said:
Send an e-mail to Mythbusters perhaps they'll try to construct a four cylinder mortar for you.
Nice idea, but 6 cylinders gives a far smoother and efficient area saturation.
What about a V-8? Hit two targets simultaneously!
Well, you could go down the route of the rotary engine - I think it's called a 'dillon', but of course, you'd have to get the 'fuel' in REAL quick.
 

Biped

LE
Book Reviewer
#15
Trans-sane said:
Did the man-packed LAW type thermobarric weapon being talked about at the start of Telic ever get developed/deployed at all?

As for adding shrapnel of some kind, it wouldn't work. The reasons mentioned above are all good reasons. Another is tiny bits of metal + lots of oxygen + sh1t loads of heat = meatal oxide. Your shrapnel would burn up before it got too your target...
The daisy cutter uses aluminium dust of course.
 
#16
Hello gobbyidiot,


this may interest you:

http://www.aheloy-opm.com/images/(5).pdf


The engine cylinder will be doing whatever speed the rest of the engine is doing,the mean piston speed on the otherhand would be about one tenth the muzzle velocity of a typical mortar.


tangosix.
 
#18
tangosix said:
Hello gobbyidiot,


this may interest you:

http://www.aheloy-opm.com/images/(5).pdf


The engine cylinder will be doing whatever speed the rest of the engine is doing,the mean piston speed on the otherhand would be about one tenth the muzzle velocity of a typical mortar.


tangosix.
Ah, interesting. I'd still like to know what terrain they are using to arrive at their claims; looking at the slow-mo of fuel/air going off they must be relying on loose stuff lying about to act as shrapnel, I think.

And if I had cracked open Mary Webster's Essentials of Higher Physics ( :D ) I could have worked it out, but interesting to see that a pathetic 311m per sec gets you 5.4k at (presumably) 45 degrees. I knew mortar rounds came out slowly - an a grey sky you can watch the whole flight - but I didn't realise it was that slow.

On another thread people were talking about the effect of wind on mortar rounds. Significant, true, especially when it spends a long time in the air, but (obviously) a tiny fraction of the effect on small arms. The big old bomb obviously has a lot of energy for its air resistance.
 
#19
I've been looking at fuel/air "explosions" on the web. How sure is anyone that what you typically get isn't a big multi-directional incendiary? If it detonates properly you get a very quick flame front and the pressure. If it doesn't go right you get a longer flame front and no push. The A-bomb tests involved wooden blocks that would fly and they would calculate the yield. Presumably these days they can put pressure sensors some distance from the event and work out what happened nearer. But a lot of the stuff on the web seems, and I do admit it's hard to tell, to involve a big over-rich fireball rather than a good bang. And we all want a good bank (wibble, sneck, frapp...)
 
#20
gobbyidiot said:
There's nowt new, lad...., said Uncle Mort.
Quite apposite when you consider that when we first started experimenting with fuel air weapons around the end of WW2 we were working with coal dust. Evidently that didn't go much beyond the experimental stage and it was the Americans who took up the baton sometime later.

But coal dust was also what Dr Diesel first used as fuel for his diesel engines. So fuel air weapon have already been used for propulsion...after a fashion
 

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