Mortar Explosions

[Joseph Nesbitt]

I was watching this extra in the Band of Brothers dvd set which mentioned alot about how they did the effects, the most interesting was this giant fan looking thing that threw dirt in the sky when you pressed a button, they buried it in the ground to simulate mortar explosions. Is this something they made themselves, or something that you can purchase? Or is there a more practicle way to simulate the effect? Any advice will help.

[Douglas Sunlin]

It's done with model rocket igniters (electrically triggered) and small bags of black powder or flash powder, with a pile of blackened cork on top. When this is lit off, it doesn't make a loud bang, so the sound of an explosion is laid over that.

[David Mullen ASC]

Usually those "air mortars" involve compressed air, I thought.

[Douglas Sunlin]

You mean no pyro at all? What's this world coming to? :)

[Leo Anthony Vale]

You mean no pyro at all? What's this world coming to? :)

 

Strangely enough, John Wayne's 'The Alamo' used wooden cannons with gas cylinders!

 

http://widescreenmovies.org/WSM02/alamo.htm

[Phil Rhodes]

You could do worse than:

 

http://www.detfilmshd.com/Collections_Explosions_02.html

 

Phil

[Toby L Edwards]

Usually those "air mortars" involve compressed air, I thought.

 

I have the box set and David is correct. They use air mortars and the flying chunks are foam. Excellent Movie by the way.

I think they used the same set up on Saving Private Ryan if memory serves.

 

Toby

[James Steven Beverly]

Is there a significant difference between an air mortor and an air cannon?

[Joseph Nesbitt]

definatly, try searching either on google and you'll get significant differnances, the air moratrs usually have lots of compressed air, usually a machine attached, the air cannons can often be these one time use spfx things to shoot out confeeti, or blood and guts for head shots if you want.

[Joseph Nesbitt]

oh yeah and Doug although I think toby might be right, where did you hear about rocket igniters? I'd like to see that, any clips or movies where they use that for this purpose or possibly another

[James Steven Beverly]

definatly, try searching either on google and you'll get significant differnances, the air moratrs usually have lots of compressed air, usually a machine attached, the air cannons can often be these one time use spfx things to shoot out confeeti, or blood and guts for head shots if you want.

 

Though, I like confetti, I was thinking Fullers Earth and painted Styrofoam chunks shot straight up out of a sawed off one with about 100 to 120 psi while either hidden in a depression, a hole or behind a bush, perhaps a pair used in tandem and set off at the same time to give a wider spread of dust and debris. That coupled with an electronic flash on the same circuit and possibly a sound effect in post would sell the effect. How would the blood and guts for head shots work, small one behind the actor aimed at the wall?

 

I've seen flash pots and concussion pots on stage shows I've done but never messed with them, THOSE are set off with some kind of electronic igniter, but I believe you need a pyro license to set them. I wonder if you set an amount of Fuller's Earth on top of a concussion pot charge if it would give you the desired effect?

[Brad Grimmett]

Though, I like confetti, I was thinking Fullers Earth

From what I understand, Fullers Earth is very bad to breath. Every time I'm on a set that is using it I ask for a mask so that I don't breathe it in. But actors can't wear a mask, so be careful and aware about Fullers Earth when using it.

[Douglas Sunlin]

oh yeah and Doug although I think toby might be right, where did you hear about rocket igniters? I'd like to see that, any clips or movies where they use that for this purpose or possibly another

I confess this is not an insider view. It's from various "Making Of" featurettes, notably one for Independence Day. It's an old technique, as far as I know; probably the pyrotechnics required extra insurance and a special technician.

 

Something like this:

http://library.thinkquest.org/10015/data/i...cts/stunts.html

Except that they spell primer cord as prima cord. Maybe that's a trade name.

[Dan Salzmann]

Are there any books that give detailed information on pyrotechnics for movies?

[James Steven Beverly]

From what I understand, Fullers Earth is very bad to breath. Every time I'm on a set that is using it I ask for a mask so that I don't breathe it in. But actors can't wear a mask, so be careful and aware about Fullers Earth when using it.

 

 

Yeah, it's a pain in the ass to deal with but it works. It will get the effect you're looking for. I suppose it's better than using a bucket of dirt, which is a HELL of a lot cheaper. :D

[James Steven Beverly]

Are there any books that give detailed information on pyrotechnics for movies?

 

There's a book called "Secrets of Hollywood Special Effects" by Robert F. Mc Carthy that has some stuff in it but I don't think learning Pryo from a book is a good idea unless you like the name "Lefty". :blink:

[David Mullen ASC]

Often they use a mix of Fuller's Earth (or crushed walnut shells these days) and broken-up cork for the chunks that fly up.

[James Steven Beverly]

Good to know. :)

[Bob Hayes]

I think ?Wind Talkers? had some of the most amazing pyro. It looked like huge amounts of earth were lifted into the air. I heard the used a lot of high explosive to achieve that effect. The explosive they used was so unstable they had to keep it refrigerated until they used it. I?m curious as to what they used.

[Greg Johnson]

I thought about getting one of these for my WWII short. Thunder Pipe.

 

I love how they demonstrate it with a massive fire ball in their drive way. I wonder what that dude's neighbors think.

 

We opted not to get that, and cut the scene. We ended up just throwing dirt clods near the actors,.. on set it was super lame,.. once I added sound it actually looked awesome.

 

- Greg

[Kevin Zanit]

I should have jumped in sooner, sorry.

 

I just did a big mortar attack scene for a Vietnam movie, the pyro guys used a mix of pyrotechnic solutions as well as compressed air. They buried large cone shaped metal mortars in the ground that they then padded with sand to absorb the shock of the explosive. They then placed the explosive (not sure what it was, though they were like 5" long by 2" in diameter) in the mortar. On top of this they filled it with various fine sands/ dirt (probably some fullers earth, though your not supposed to) and chunks of cork.

 

Here is a link to a video my 2nd AC Collin Cates took:

 

 

You can see me operating in this shot as well. The shot started hand-held on a crane; the first two mortars go off while the crane comes down. We get to the ground, and some of my guys get on the crane, I step off and then quickly move forward to the guys returning mortar fire. This is one of the later takes, and to complicate things our Preston went down, so you can also see my 1st Ken Bender running with us (as well as key-grip, Bobby Woo) when he meets me on the ground. Also in this take there was a larger delay between the last hit due to some earlier problems, we could not move forward until that one went, hence why everyone was asking if it went yet and we missed it or something.

 

The pyro guys used larger hits deeper into the camp so it would read better on film. As the hits walk in towards camera they get a little smaller (the first big one happens off camera, but you can hear it in the clip). They also shot air mortars filled with the same debris at me and the camera which looked great, though got me dusty as hell (hence me being so covered).

 

I shot this with a 90 degree shutter which helped freeze some of the debris, it looked cool.

 

Kevin Zanit

[Kevin Zanit]

To beat a dead horse/ thread:

 

Found another video of a different take of the above. This video shows very little of the mortar hits, but does show you how little pyro is needed to shoot the dirt into the air, you hear how quiet each hit is.

 

 

Kevin Zanit