fake explosions

[bob]

Just a quick update, fired of a fire ball effect and it was ok but nothing great, I used three liters of gasoline in a plastic ice cream pail, and 30 grams of bp in a pill bottle.

Picture and video below.

http://m.youtube.com/channel/UCm2gITr8ZiRVvYgFNg3aEzA#/watch?v=jyHc4ZLVLF0

Edited March 25, 2014 by bob

[MWJ]

That looks pretty cool!

[christinegiles]

Hello, everyone . . . my name is Christine, and I am a film student in Oklahoma City.

I am working on a project that involves choosing a special fx scene in a movie, then describing how I would pull them off.

I am not building anything.

 

Would anyone be willing to answer some questions?

I'm researching air mortars, specifically in the ground to simulate an explosion with debris.

Here's what I've got for that, based on the research I am doing:

 

Smaller explosions with debris – Air mortars hidden in depressions in the ground, firing a mixture of coffee grounds and sawdust using black powder from Schedule 80 PVC arm with a 4” opening, shot at 150psi.

 

I don't actually know how big the opening should be . . . I just estimated. So . . . how big should it be? Am I missing anything? Am I totally off here or on the right track?

 

I really appreciate the help!

Christine

[bob]

Hi there,

I am afraid I do not have any experience with air cannons, however a few other people on here do.

First of though a four inch piece of pvc pipe is going to produce a lousy effect in my experience. PVC is not to be used if you are using a lift charge ie black gun powder for safety reasons, however with air it would be fine. I don't see the point in using coffee grindings but I guess if you have access to them in bulk for cheap it would work fine, and yes they do use say dust in many of these effects, although you don't want to use fine saw dust combined with a lifting charge as there is a strong possibility of it turning into a fire ball. Some easy to find materials would be flour, cement powder, peat moss, clay powder, powdered chalk, sand, ect. Also pipe as a general rule doesn't work very well, a cone works much better.

Hope this helps.

 

bob

Edited April 6, 2014 by bob

[FlaMtnBkr]

Edit: nevermind, didn't realize it was so old. Edited April 6, 2014 by FlaMtnBkr

[christinegiles]

We had a lecture on special effects. We went over how they make rain, snow, explosions, fog, breakaway glass, etc. But we didn't get very technical; we are supposed to research. We don't have any lists to use, other what we covered in class (my notes). The main problem I'm having is that everything folks write is written in pyro-ease - they use abbreviations and terminology that I just don't know, so I can't decipher it. I'm using the first 1:05 minutes of the movie "Sahara", the one with Matthew McConaughey. There are lots of explosions, some with fire, smoke, and debris .. . some without fire . . . white smoke, black smoke . . . a trail of smoke from a cannon . . . stuff like that. I meed to figure out what equipment I would use to create each effect. Right now I'm working on the explosions on the ground with debris and white smoke.

 

So, the air is enough, no powder needed - got it. I just need debris and some smoke coming up from the ground about 4 feet or so, like something dropped and BOOM! Would you use an air mortar? Is an air mortar and an air cannon the same thing? Do you use cones when you need fire as well? I'm searching the web, but, again, there's a language out there that I just don't know.

 

Thanks for your help!

 

Christine

[bob]

Yes the cones are still used when there is to be flame, the only time that would not be true is if you wanted a fire ball that just keeps going up and up, in which case a tube is used.

If the stuff that the explosion throws up is dark it is probably compost or peat moss, but if it is gray it is most likely cement powder, and if it is white then it would be flour. If it is a lot of flame and white dust it is a type of powdered creamer and a black powder lift charge. If there has to be flame then an air cannon/air mortar is not used, instead an explosive lifting charge must be used ie black gun powder, flash powder, or a high explosive, this is because the flammable material that is to be added such as gasoline must have a source of ignition.

For the flame, gasoline is the most common, however if you also need black smoke then naphthalene (moth balls) is used.

For dibres things such as fabric, foam, and bark chips are used.

As far as white smoke I have heard that a mixture of flour and diesel works well.

The blast from the cannon, is it an old fashioned cannon or a piece of modern artillery? If it is an old fashioned cannon I would suggest plain old black gunpowder,

and perhaps some flour and diesel. If it is a modern piece of artillery some sort of high explosive (HE) and flour might work.

bob

[bob]

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CDIQFjAA&url=http%3A%2F%2Fwww.pyrodirect.com%2F&ei=sspAU7_LIOzgsATFpIH4BQ&usg=AFQjCNGOO5EU9sGETeDFRRgtyiizQ5I4tA&sig2=KYhl2vV1vbPhfDWcH-cPEg&bvm=bv.64125504,d.cWc

This place has some videos on pyrotechnic special effects, might be worth checking out.

This guy http://www.amateurpyro.com/forums/user/12911-wiley/ would be able to tell you about gasoline fire balls.

bob

Edited April 6, 2014 by bob

[bob]

Another way of creating a sort of half ball looking explosion is to actually use a plastic or paper ball with an explosive charge in the center and filler (ie peat moss) of your chose to fill up the rest of the ball.

Look at this video In this video

at 2 minute and 7 seconds you see the effect I am talking about. I believe they used Creamora for the filler, and the explosive charge would have been black gunpowder or more likely HE.

bob

Edited April 6, 2014 by bob

[bob]

Ok so I set off another explosion simulation a few days ago, here is the video

So here are a few details.

I used a protein powder container to hold the black gun powder lifting charge, which I wrapped in a little bit of rope.

The lifting charge was 2400 grams of 4-13 mesh bp, and a bag in the center with 100 grams of 13-17 mesh bp.

That steel cone I used last time was again used.

I used compost and a little bit of peat moss to fill the cone.

I didn't use any gasoline because of the fire hazard (hay bales were near by)

The guy that gets blown up was a dummy made out of grass clippings and two by fours, he was blown into 3 pieces despite the rugged construction, although his head which was a balloon remained intact!

the debris was just one of those foam mates, like these. https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcRO9efkL6cul_Cg2l0dm7xrX-85zGITykqwQjt0WWXhgFIYGOmfeHRVT6f5 I placed it on top of the compost (in one piece) and put just a little bit of dirt on top of it to hide it from the camera.

Now as far as the rocket, well it was just a nozzle less core burning sugar rocket (50/50 ration of sugar and KN03) that was guided down from on top of three bales with fishing line.

The first picture is of the rig that held the fishing line on top of the bales, and the rest are fairly self explanatory

I was fairly happy with the compost as opposed to my previous mix of clay powder and peat moss, particularly because it took about an hour and a half to screen compared to ten plus hours to grind the clay.

Well I can't think of anything else at the moment so I guess I leave it at that, please let me know what you think and don't hesitate to ask any questions.

bob

Edited May 27, 2014 by bob

[psyco_1322]

Looks like you're having some fun! That's one heck of a cone, makes that protein jug look tiny.