19 replies to this topic

[knocker]

I'd taken my son to an organised display on saturday evening in Huddersfield, of all things it was a thomas the tank engined themed display (it was so bad as to be brilliant) and whilst we were there I heard several extremely loud reports, when I say loud i mean they were so loud you could actually feel them and they seemed quite some distance away, there were quite a lot over the hour and a half we were there. On the way home there was one particular bang that physically shook my car, I honestly thought i'd run over something.

These carried on going off until about 10.30pm. Anyone idea what they could have been. I'm not entirely sure they're part of an organised display due to the lateness they were going off and the length of time they were being set off for ( about 5 hours)

We went to the same display last year and I noticed that the same thing happened then too. If it is an organsied display i'd love to find out where it is, anyone any ideas?

As for the thomas the tank engine display, that had to be seen to be believed, really was hilarious just wish i'd taken some video of it. Only bad thing about it was that maybe the firworks went on just a bit too long, never actually thought i'd hear myself say that

[Mortartube]

They may be 125mm plastic bottle ground maroons. They feel like a sledgehammer to the chest at a good distance

[David]

I assume you mean that the loud bangs were not actually part of the display you were at?

Probably pro stuff- but could just be loud Cat 3.

[Arthur Brown]

As the classification of some items changes then pro's are using them up! So may be putting stuff in shows just to get rid! could also be DIY Fx!!

[Asteroid]

I saw a few of these at a display last year, and they really are impressive, they got a great response from the crowd, but I always assumed they would just be flash or whatever charge inside a very thick cardboard tube, what's a plastic bottle maroon and why 125mm?

[pyroduck7]

there was a pro show on yestorday near me. i could see them in full from my garden so i dident have to pay the £6 or how ever much it was. but the finaliy ones where verry large reports. i could really feel them hitting my chest.

[Mortartube]

The maroons are just flash in a soft HDPE plastic bottle. The type chemicals that come in. The large version used for maroons is 125mm as a standard size. The soft plastic is torn into small shreds and is so light that the shreds don't travel very far. They are best fired suspended from string between 2 posts like a mini washing line. The hard plastic cap will then fly straight up if it is not destroyed. They are only electrically fired in my experience.

The bottles used are like the two on the left of the picture.

http://www.hdpe-cont...-containers.jpg

[wjames]

how much flash would you expect there to be in a 125mm maroon........i presume there is a filler of some type in there too.....

[Mortartube]

I can't recall how much is in there but it is a fair bit. A 125mm bottle would be about 1/8th full. Not sure about the filler. I never got to make them at the factory. I do know that they feel like a sledgehammer to the chest at 25-30m.

[wjames]

i presumed they wouldnt be full !!!!!

ive heard sand is sometime used for a filler.....not sure in what applications though.

[digger]

i presumed they wouldnt be full !!!!!

ive heard sand is sometime used for a filler.....not sure in what applications though.

Why not? If you are not going to fill them then you may as well use a smaller bottle. Containment makes no difference to the sound volume as they are above self confinement mass and effectively detonate anyway.

However 125mm does sound a little on the large side. A 4" spherical flash salute shell will have about 200 grams (ish) in it and they give on hell of a chest pounding thump.

On closer thought do you mean 125ml not 125mm as a 5 inch canister salute would knock you off your feet (well maybe not but it would be seriously powerful)

Edited by digger, 09 November 2008 - 09:41 PM.

[GZ22]

I recall seeing in several texts in the past that devices containing flash were never filled completely, in order to allow the blast wave to develop so that a more prominent report is produced.

[wjames]

really????


I presume thats as flash doesnt work by a rapid produduction of gas, and so the volume contained isn't all that important.....

he sits looking at his collection of old toilet rolls....and that Plastic tube in the corner....about toilet roll tube size......HMMMMM he thinks....




On another note......The general public wants to hear loud.....but doesnt want their ear drums to bleed.....

I'd love to see the db meter reading at 30 M away from a 125mm bottle FILLED with flash..........Or even better a pressure wave reading.

Ive heard some fairly loud ones....all of them were less than 25G.....just very very well confined......and all of them were remote, from 50M+......

I think this all depends on the flash people use..........Is it a perchlorate based flash in these maroons....or something slightly less powerfull....

[Asteroid]

I recall seeing in several texts in the past that devices containing flash were never filled completely, in order to allow the blast wave to develop so that a more prominent report is produced.

I've heard this too, on more than one occasion, and this is how I understand it:
Compressed air holds a lot of energy, and if the container is half full then lets say 300mls of air at 50bar can build up before the bottle bursts. If the bottle is full, then maybe only 10mls of air at 50bar will be abl to build up. The bottle will always fail at it's burst pressure, however depending on how much air can build up.

The bottle helps the report because the pressure it contains is released suddenly, faster than unconfined flash, and when the air suddenly expands 50x in a split second a shockwave is generated. With the 300ml or the 10ml, the 300ml can create a much larger shockwave.

Of course you do have to take into consideration that if a normal one were to be filled about 1/8th full, (maybe 50g) then a full bottle in this case probably would generate a louder report simply because of the HUGE amount of flash inside.

Edited by Asteroid, 10 November 2008 - 09:36 AM.

[digger]

I recall seeing in several texts in the past that devices containing flash were never filled completely, in order to allow the blast wave to develop so that a more prominent report is produced.

That is definitely one school of thought and some are produced in that manner, however I have seen both types of device and there seems to be no audible difference in volume for the same amount of flash(well on the larger ones anyway).

I have heard flash described as a negative explosive as the cooled reaction products occupy less volume than the reactants, however I am not sure that this is true during the reaction (I am sure that someone with more knowledge can chip in here). I believe that this is why people assume that a volume of air is required in the device so that it is heated to create some volume change.

really????

I presume thats as flash doesnt work by a rapid produduction of gas, and so the volume contained isn't all that important.....

he sits looking at his collection of old toilet rolls....and that Plastic tube in the corner....about toilet roll tube size......HMMMMM he thinks....

On another note......The general public wants to hear loud.....but doesnt want their ear drums to bleed.....

I'd love to see the db meter reading at 30 M away from a 125mm bottle FILLED with flash..........Or even better a pressure wave reading.

Ive heard some fairly loud ones....all of them were less than 25G.....just very very well confined......and all of them were remote, from 50M+......

I think this all depends on the flash people use..........Is it a perchlorate based flash in these maroons....or something slightly less powerfull....

Yep different types of flash are more or less powerfull than each other.

I am sure that with small amounts of flash containment can make a difference to volume, however I am sceptical (but prepared to be proved wrong) whether it makes that much of a difference when talking about larger amounts as it is the shock wave from the detonation (not deflagration) that creates the chest pounding thump and I am sure that confinement will make little difference to the detonation velocity.

If you take 1g of perchlorate flash and burn it on a flat plate (suitable safety precautions etc) it will burn very quickly, now put that same 1g of flash in an open ended tube and do the same. Even in the open ended tube it offers enough containment to cause the powder to detonate think air b*mb volume with very little containment.

Now if you tried that with some of the more dangerous flash mixes you would find that 1g can detonate with no confinement at all other than its own mass.

Most of this information and much much more is contained within the the flash thread I am sure.

Edited by digger, 10 November 2008 - 09:56 AM.