curiosity_cat - 14-7-2017 at 09:51
How many different ways can I say lame for those phony Hollywood fireballs posing as explosions ?
Clint Eastwood in pale rider. Anyone remember that ? Very rare to see the real thing in movies.
[Edited on 14-7-2017 by curiosity_cat]
Chisholm - 15-7-2017 at 06:33
The real thing in movies would be rather boring to look at: Over in a fraction of a second, and the overwhelming sound of the supersonic shockwave is
never replicated by the microphone, because showing a movie that damaged theatergoers' ears would be a bad business decision, to say the least.
In movies, what they almost always use to get that orange fireball is a fuel-air deflagration, typically ignited via an electric spark or a
pyrotechnic device. If there's a lot of black in the smoke, that means they used gasoline, kerosene, acetylene, or other overfueled mixture.
That's not to say they never use high explosives, because Jesus Fucking Christ, but even in that example they only used 24 kilos of HE total but 8,140 liters of kerosene. The HE serves only to heat and
disperse the fuel to ensure a large flame front, which you don't otherwise get from a fuel like kerosene, whose vapor pressure is extremely low.
Even on high-end studio productions, they typically use ANFO as the main charge, with a cap-sensitive AN emulsion dynamite for the booster, and a
commercial blasting cap containing a primary of styphnate-azide-aluminium feeding into a PETN charge.
Bert - 18-8-2017 at 14:07
Yup. If it's realistic, it is far too fast for the audience. I do this work for film and video productions occasionally, the artistic directors almost
never want realistic HE effects.
Rarely, some DO want the real thing... And a very high speed camera.
The original La femme Nikita? Watching her OUT RUN A SHOCK WAVE?! from some kind of rocket, running across a room and dive down a shaft... Damn. Made
a good scene for the audience, except me.
https://youtu.be/Hxg_DjlkaMA
Here at 5 minutes in is a scene using both some HE and the usual liquid fuel/low explosives fireballs. The crew shot the explosion with a high speed
camera, then slowed it down quite a bit to give audience time to see the truck go airborne and fall back down through the ice, in real time the
explosion and car flip from start to end took an eye blink.
https://vimeo.com/groups/4159/videos/21762564
[Edited on 19-8-2017 by Bert]
phlogiston - 18-8-2017 at 15:24
These tests of fireworks in a shipping container are very real and quite spectacular:
https://www.youtube.com/watch?v=1cBrB9T8BTY
https://www.youtube.com/watch?v=Nu6nmZBIWHM
https://www.youtube.com/watch?v=F55r0JL_lTQ
https://www.youtube.com/watch?v=7pthp9UEeHM
Unfortunately the video quality is rather poor, but man, that must have been a fun job.
[Edited on 18-8-2017 by phlogiston]
ninhydric1 - 18-8-2017 at 15:31
Wow, the clouds formed by the explosions look like mushroom clouds. As much as the irrational part inside of me wants to have the job, it just seems
too dangerous 
.
Dr.Bob - 16-10-2017 at 19:00
One of the EOD team nearby uses a block of C4 (on top of a piece of cardboard) with a plastic sack (mil spec thick trash bag) with 5 gallons of
gasoline in it to generate their fireballs. The cardboard protects the bag from getting poked by grass or weeds. They use those at air shows for
simulated bomb runs. They are a little more powerful than some other versions...
Another acquaintance used to make simulated atomic bombs for military drills in cbn training, same basic idea but often a few pounds of C4 in a drum
(or ten) of gasoline, often with some phosphorous grenades throw in to add more flames. Some of those old guys are a hoot to chat with.
cagce88 - 26-10-2017 at 01:59
The Hurt locker I think did use real explosives in the film. it's been a while since I've seen it.
LearnedAmateur - 26-10-2017 at 02:59
Not strictly related, but last air show at Duxford here in the UK had a pyrotechnics display for their WWI flight. The 'bombs' were obviously fuel
based but can anyone tell me what possibilities there could've been for the flak explosions?
greenlight - 26-10-2017 at 04:19
My best guess would be they are small shells with coloured chalk instead of pyrotechnic stars inside them and a burst charge situated in the middle.
They could be some sort of black smoke composition but I am sure that would leave a trail of black colour instead of what you have pictured.
LearnedAmateur - 26-10-2017 at 04:50
Yeah, I was thinking heavy particulates because they did hang around for a couple of minutes after detonation, pretty much intact before fading away.
There are a few relatively inert compounds that spring to mind - namely MnO2, CuO, and Fe3O4. I wouldn't suspect carbon due to its low atomic mass and
the fact that smoke dissipates in a matter of seconds, although I'm not sure about the behaviour of larger carbon particles spread by explosives so
it's still a possibility.
Bert - 26-10-2017 at 16:54
A couple of ways to do this... Did you notice if there was a bright flash at the center of the "flak" explosion? Or perhaps there was a brief, red
flame at the center?
Adding powdered napthalene to a report mixture, even to good old fashioned black powder leaves a cloud of excess carbon hanging like this. You would
probably notice a red flame hanging in the air very briefly after the explosion, as the vaporized napthalene burns.
Aluminum and Manganese dioxide thermite, if finely powdered and well contained will explode, there is a very bright white flame as the Manganese vapor
burns in the air, the black cloud is Manganese dioxide re formed from this.
English SFX people I have known had a liking for Copper oxide and Aluminum thermite as an effect. Many of the explosions in the original "Dr. Who",
vintage Monty Python & similar were Copper thermite charges. Fast enough to be used like perchlorate based flash, if ingredients are sufficiently
fine and mixed well. Leaves a BROWNISH cloud, not black, though.
LearnedAmateur - 26-10-2017 at 18:25
Watching the video I captured, there is a bright flash and a small pop accompanying each one, both black and white were pretty much identical in those
aspects so they must be similar compositions. I didn't manage to see or record any flames though so that doesn't rule out naphthalene for the black
clouds, it might be the only difference between the two with the same thermite base mixture since I'd expect different types to have varying report
and duration.
Bert - 26-10-2017 at 18:53
It is not impossible to make colored dust based "smoke" puffs, but it does not work particularly well in my experience.
I have watched several attempts to produce such effects by small flash powder charges in a canister shell filled with colored chalk line chalk, etc.
The effect is (relatively) tiny, and visibly falls before it dissipates, the particles of chalk are MUCH larger and less numerous than the aerosols or
fine particulates of real smoke.
A pyrotechnic smoke composition such as the chlorate, lactose and synthetic dye formulations gives a much larger effect, for an identically sized
device-
For ground based TNT/artillery shell simulations, I do like to put a gallon zip lock baggy of charcoal briquettes on top of a one pound tannerite
charge. THAT looks like the real thing... it disperses the black "smoke" FAST, most simulats are really slow compared to the real thing. Especially
realistic if you dump about half a 2 cubic foot bag of the largest sized bark mulch and some chunks of peat moss on top to simulate dirt being thrown
by the explosion.
For a civil war era, black powder charged explosive shell simulation, substitute a gallon baggy of barn lime (very finely powdered limestone) for the
charcoal.
LearnedAmateur - 27-10-2017 at 00:26
The clouds behaved a lot like the display smoke given off by one of the aircraft actually which I believe is oil based. The shape and size didn't
change much, especially the white ones which dissipate after roughly the same duration... It's only the black compound that lingers in the air, but is
easily blown by the wind and doesn't fall - in fact they appear to gain some altitude, although this could just be an effect of perspective since the
wind was blowing towards the flight line.
It would've been interesting to see those being used instead of the fuel based ground displays but the small, slow mushroom clouds give it away as a
liquid combustion. They still had quite a bang to them though, easily felt from 200-300 metres away despite how small they appeared. Not sure why they
didn't, but I guess the flying debris might disrupt the operation of the aircraft which are owned by the Great War Display Team and obviously very
old.
NedsHead - 27-10-2017 at 05:46
Do you think charcoal was used in this display to create the black smoke effect, there is a bright orange flash at the centre followed by the
dispersion of the black colour https://www.youtube.com/watch?v=qiJhGcylZxc
Edit: better footage of the display
[Edited on 28-10-2017 by NedsHead]