1569 replies to this topic

[Amleth]

A small fact about flash. As you double the amount of flash its power is multiplied by 8. That means the 22 grams would probably be overkill.

That doesn't sound quite right to me. Exponential growth gets very fast, very quick. That's the same as saying that if you multiply the amount of flash by a thousand (say, from 0.1g to 100g), the power increases more than a billion times over.. i.e., it becomes over a million times more efficient...

If we start from the assumption that a tiny amount like 0.1g is enough for a small novelty cracker, then we end up concluding that a ton of flash is more powerful that all the nuclear arsenals in the world combined...

Scary.

[alany]

I dunno who came up with that stupid 3rd power law. It is complete crap, the energy scales linearly with the mass of reactants. The energy density is constant obviously, otherwise you get unphysical nonsense.

Its valid if you consider volume, in fact it may have been originally stated like that by someone who new what they were talking about, but I've never seen it stated like that. So lets just drop that old chestnut, or at least state it how it is.

Of course small amounts of flash deflagrate, and over a certian limit the mode of reaction transitions into a much more violent one (just ignore the bloody flash detonates arguement for a moment). There is definately a large difference in the scale of the physical effect produced above and below that "boundry", but that is because of the rate of energy release, the Power not the Energy. Two concepts than are widely misunderstood and used incorrectly as synonyms. The chemical energy of many HEs is the same order of magnitude as that of common pyrotechnic compositions, it is just that HEs release it a whole load more quickly, which is why they are brissant.

[Amleth]

I dunno who came up with that stupid 3rd power law. It is complete crap, the energy scales linearly with the mass of reactants. The energy density is constant obviously, otherwise you get unphysical nonsense.

Its valid if you consider volume, in fact it may have been originally stated like that by someone who new what they were talking about, but I've never seen it stated like that. So lets just drop that old chestnut, or at least state it how it is.

Of course small amounts of flash deflagrate, and over a certian limit the mode of reaction transitions into a much more violent one (just ignore the bloody flash detonates arguement for a moment). There is definately a large difference in the scale of the physical effect produced above and below that "boundry", but that is because of the rate of energy release, the Power not the Energy. Two concepts than are widely misunderstood and used incorrectly as synonyms. The chemical energy of many HEs is the same order of magnitude as that of common pyrotechnic compositions, it is just that HEs release it a whole load more quickly, which is why they are brissant.

Technically, it's not valid for volume either, since for a constant density, doubling the volume is the same as doubling the mass (either way could be thought of as doubling the "amount").

It is valid if you talk about the dimensions of an amount of flash, though. Double the dimensions of an object and it's volume (and thus mass if the density is maintained constant) increases eightfold (in 3D space, anyway). So for a sensible linear scaling of power with mass, 2x dimensions = 8x power.

You're probably right, though, in postulating that some perversion of that concept gave birth the the previously-mentioned 2x mass = 8x power rule-of-thumb. Though, it does put paid to my plan to gather a thousand tons of flash powder together in the desert somewhere, and then hold the world to ransom with my Doomsday Device, capable of releasing the energy of a million supernovas, almost certainly creating a black hole and possibly even collapsing the entire universe...

On the bright side, though, 6" flash salutes won't explode with all the force of a tactical nuclear warhead, killing everyone present at the show, so that's something, anyway.

[alany]

Yeah most people think of "bigger" or "smaller" as simple scaling. That means lengths scale linearly, surface area scales as the square and volume as the cube.

This physical fact is very important for biological machines, and is the reason cells are quite small. It is also why large animals run into all kinds of problems with cooling and structural rigidity.

For us pyros is means if you make a shell twice the size you will need four times the paper (of twice the weight) and eight times the chemicals. This impiles it will 8 times more dangerous and the effect is not in proportion with the increased danger, at least in terms of subtended solid angle at the observer.

[Rip Rap]

at least in terms of subtended solid angle at the observer.

What the hell is that!?

[Karl]

It's not quite a Cylindrical shell but here it is anyway. It's my first ever shell, so my first time at pasting something round. I used KP for the burst and Tigertail stars as the effect.

I plan to fire it sometime soon, maybe tomorrow. I'll make sure to get a video.



Being loaded into the mortar


Loaded, the fit is pretty nice!

[completebeginner]

nice looking shell karl hope it goes well can't wait for the video

[karlfoxman]

Nice looking shell, whats the details?

Lift weight, type?
Carrier for burst?
Weight of shell?
Nice job on the pasting, how many layers?
Pumped stars?

I am going to make some more KP on crispies soon as my 6" shell needs some. Post the vid of the shell if you can.

Edited by karlfoxman, 29 January 2006 - 12:25 PM.

[alany]

What the hell is that!?

Google is your friend, this excellent link being the first hit for me:

http://mathworld.wol...SolidAngle.html

[Rip Rap]

Google is your friend, this excellent link being the first hit for me:

http://mathworld.wol...SolidAngle.html

You're right Google is my friend - & that link was the first hit I got when I searched before replying to your post.

Now, I would say that I am of atleast average intelligence, but I am no maths scholar. So even though I read that "mathworld" page, I still could not understand your last sentence in that post.

[Karl]

The shell was fired last Saturday, with mixed results.

I forgot to mention that this shell was my practice shell, to see if my burst would be strong enough.

Lift : 15g 2F Granulated BP
Burst : BP on Crispies with 6g of KP in each hemi

The mortar was buried about ? way up the tube (This is hard to do when the ground is like ice!). The leader tube was unfolded and extended. Next was time to load the shell down into the mortar, nice and carefully.

I lit the Visco fuse that lead to the fast PIC and got away at a leisurely pace. I positioned myself about 200ft away and watched wit the camera recording.

?Thump?, the shell leaves the mortar but only to raise to around 10ft. The shell then dropped to the floor where the time-fuse continued to burn.

6 Seconds later the shell echoed all around with a nice deep boom as it burst.


So in conclusion, I found out that my BP should be strong enough. The lift sounded and looked ok but, but I think most of the pressure escaped around the side of the shell. More layers next time!
I now know that I definitely want either Whistle or Flash in there next time to shatter the shell rather than pop it apart.
Thanks for reading,
Karl

[Karl]

Heres some frames from the lift charge lighting, captured from my camera.

For some reason theres some sort of 'Fire Circle' that appears at the top of the mortar.



Heres the frames from the shell bursting.

[completebeginner]

I have almost finished a 3 inch shell to test a new star formula I posted in the formulas page I just have to add some more paste and I will launch it on thursday night.

[Frozentech]

From the pic of the shell fit in the mortar, I would agree that is where the problem lies. You might want to shorten the time fuse also, to about 3 secs. 6 seconds seems a bit long. I would be a nervous wreck waiting for a 6 second fuse in the dark ! Maybe add a comet for rising effect so you can keep the camera on the shell for the entire trajectory ?

[completebeginner]

Well my shell worked perfectly and the new stars were absolutely beautiful but the camera didn't focus and you cannot see the tails of the stars all you see is a few orange dots.