Aerial Shells

[InRainbows]

That black match looked great! It has way longer spark trails than mine. I couldn't really understand, that had volfram(tungsten) in it? I actually think tungsten is used in delay compositions, so that could make it slower, but the sparks looked way longer lived than than my blackmatch, made it look great. I know blackmatch is for fusing, but I hate fuse that doesn't do anything cool.

[Mumbles]

From what I understood, the tungsten is the "string" to the blackmatch, not actually in the composition. Tungsten has an incredibly high melting point, and I am unsure if the BP could actually ignite it if it were in the powder.

 

Your blackmatch was exploding because you bound it with NC lacquer, which makes it much more reactive. If you used dextrin or some other water based binder, I think you'd find it is much more manageable.

 

I would also still suggest tying the lead wire off to something. You may think it will never catch, but it is better to be safe than sorry and wreck a firing board, or accidentally set off everything at once. Both are entirely realistic possibilities.

[vice]

in tis bm i used win26 composition insted of bp it looks even cooler at night

about the dextrin ... i dont like it becose it driese of a very long time so i use nc ... but this ear i will use dextrin becose i'll try to roll stars and in this case i think dextrin will be better than nc ...

[psyco_1322]

Well your quick match doesnt need to burn fast, its jsut a leader to the shell. Unless you are needing instantanous firing than slow leaders isnt really a problem, just not that exciting. But good bp in several stands of match in weak tubing could cause it to explode, which isnt really a bad thing. Thats just saying the its burning fast, really fast! It'll still work fine. And dextrin isnt that bad, its cheap and teaches you to wait, <which will be usefull later on.

 

But yah you lift "bag" will not blow into pieces, it will just blow off and hop out of the tube or be left in the bottom of it. Like Mumbles said - stake down them wires, put a screw into your rack or base plate and wrap it around the screw several times.

 

Where do all these noobs get these KMnO4 ideas? Thats not the easiest thing to get ahold of, if your ordering it than you more than likely have access to other chems, if its OTC than you should find a better oxidiser thats OTC, like KNO3, you can also get sodium chlorate which is about useless and potassium chlorate which is not the best stuff to use do to its reactivity, although it makes good and easy stars.

[NightHawkInLight]

I finally finished work on a 5" sun & planets shell I've had planned for almost the last 4 months.

Here are some pre-fires:

I don't know when I'll get around to firing it, I still must find a suitable mortar. If all else fails I will simply dig a hole, bury a sheet metal tube and let the ground support the walls. There is a lot of clay in the soil here.

[oskarchem]

Wow, now that's a shell... Hmm... I'll be making those in a long time... Anyway, it's butiful.

[Mumbles]

Looks pretty good. How big did you make the planets? I use a 1 1/4" former and can fit 7 per ring. I'm also curious as to what kind of stars you used in the shells? I am leaning toward purple and win 13 sun. The last one was 7 different colors and a win 20 sun which looked very good might I add.

 

I should hopefully have a sun and planets shell ready myself this spring. The last one broke at a bad angle and didn't look as pretty as possible.

[NightHawkInLight]

I don't supposed you got it on video? I was looking forward to seeing yours. I am also afraid this shell will break at the wrong angle to get the full effect. Guess it's just a chance you have to take. (Actually it sounds like some new ground that needs to be broken...How to get a shell to always break in the correct orientation. Hmm..)

I also used a 1.25" former for the planets. I'm guessing your shell was a 6" to fit 7? In my planets I am using purple and TT. I did a test of one of them in this video:

I think they look quite nice.

 

For the sun I am using just straight up TT and a very hard break the should end up in a disc shape. Not the typical design, but I thought it would be a spectacular finish. Had I thought about it at the time I would have thrown in a hand full of Mg turnings, it gives a bright glittery heart to TT shells that I really like.

[Mumbles]

Nope, 5" shell, 7 to a ring. It was a tight fit, but they fit none the less. Talk to me on AIM sometime and I'll send you my insert diameter spread sheet. My inserts are about 1 3/8" OD after spiking and pasting, and they lock in TIGHT.

 

Unfortunatly, as usual the pyro and camera gods conspired against me. I shot 6 shells that night, and of course the two good ones somehow missed getting captured.

[NightHawkInLight]

Alright turns out I was able to get a mortar after all. A neighbor had one a pro left after last years display. Lucky me, here's the video:

I was only disappointed with the somewhat weak initial break that didn't throw the planets properly.

[ST1DinOH]

Alright turns out I was able to get a mortar after all. A neighbor had one a pro left after last years display. Lucky me, here's the video:

I was only disappointed with the somewhat weak initial break that didn't throw the planets properly.

very nice...

 

hopefully i'll be making cool stuff like this soon. got some 6 inch hemi's on thier way.

[Mumbles]

It may seem counter intuitive to some, but bigger shells are far easier to build than smaller shells. They may take more time, and supplies, but they are far more forgiving and preform much better and more consistently.

[ST1DinOH]

It may seem counter intuitive to some, but bigger shells are far easier to build than smaller shells. They may take more time, and supplies, but they are far more forgiving and preform much better and more consistently.

man i hope so.

 

thats a lot of chems to "waste" if the shell doesn't work right.

 

it's also a waste of a good HDPE gun ($20) if my 6 decides to flowerpot.

 

is there any school of thought here on building 6 inch ball shells...do you still orientate the time fuse twords the lift cup, or would the lift gasses be so strong they'd push the fuse in and CATO my shell in the gun?

 

are you supposed to top fuse the shell in the gun and passfire to the time fuse with the QM leader on the way to the lift cup?

 

or is it still safe to have the lift gasses passfire to the time fuse in the cup?

 

man i can't wait to build a 6

[Mumbles]

Ball shells are almost always bottom fused. About the only top fused ones I've seen were 36" ball shells, and a few specialty japanese 12" shells. The curved nature of the shape takes much of the stress off the fuse. You will have no problem with blow through assuming you seal around the fuse adequately, and don't have 2" of fuse sticking out. The lift will light the time fuse. Again, it's up to you on how you prime the fuse if at all, or crossmatch or any of that fun stuff.

 

HDPE is pretty resilient. Even if the 6" does flower pot, unless the shell is broken pretty hard it should withstand the force, especially if buried.

 

Are you making paper or plastic 6" shells? Plastic I won't be able to help with as much, but I hear they generally need some flash or whistle boosting.

[NightHawkInLight]

The size of the shell shouldn't effect whether or not top fusing is necessary at all. The force shouldn't be any different for large shells. Same amount of psi.

[ST1DinOH]

Ball shells are almost always bottom fused.  About the only top fused ones I've seen were 36" ball shells, and a few specialty japanese 12" shells.  The curved nature of the shape takes much of the stress off the fuse.  You will have no problem with blow through assuming you seal around the fuse adequately, and don't have 2" of fuse sticking out.  The lift will light the time fuse.  Again, it's up to you on how you prime the fuse if at all, or crossmatch or any of that fun stuff. 

 

HDPE is pretty resilient.  Even if the 6" does flower pot, unless the shell is broken pretty hard it should withstand the force, especially if buried.

 

Are you making paper or plastic 6" shells?  Plastic I won't be able to help with as much, but I hear they generally need some flash or whistle boosting.

 

The size of the shell shouldn't effect whether or not top fusing is necessary at all. The force shouldn't be any different for large shells. Same amount of psi.

 

sweet...thanks guys. you hear all sorts of contradicting "facts" from people when you talk about shell building. thats why i came here. most of the guys i know and shoot with don't build shells, they shoot 1.4, so when i talk with them about building shells i get all sorts of warnings and advise from them that is rather suspect. it's nice to have a place to come to to get these questions awnsered propperly, and more over, to dispell myths.

 

having never built anything larger than a 3, and only a handfull of thoes, i want to be sure and learn as much as i can before building anything serious. i'd hate to spend all that time, and cross all thoes fingers, only to have a very loud starmine (now with %20 more plastic schrapnel).

 

lol

 

i should be making my own cut stars soon, waiting on a price check on the chems i need, and then i'm ordering away. i'm so close i can take it.

[justanotherpyro]

I started with three inch shells for a long time, then moved up to four inch ones. The difference is pretty big. I have only recently bought the stuff for six inch so I am definitely looking forward to jumping up two inches this time instead of one.

[ST1DinOH]

I started with three inch shells for a long time, then moved up to four inch ones. The difference is pretty big. I have only recently bought the stuff for six inch so I am definitely looking forward to jumping up two inches this time instead of one.

well i'm trying to learn fast, so the jump from 3's to 6's should save me time and money...but i just don't want to move to fast and screw up.

 

i have been hearing quite a bit lately though that the mid sized shells are the easiest to build. 3's and under are tough to get looking good...and 8's and up can get uber complex.

 

6's sound like a happy medium.

 

now i just need a place to shoot them

[Mumbles]

6" is a pretty happy medium. They're large enough you can do some of the more complex effects such as double petal, saturn, etc. They also are definatively more impressive than class C materials, something that is not always true with 3 and 4" shells. I would start smaller than 6" for canister shells however. 4 or 5" is a good happy medium there. 6" canisters take significantly more composition, and don't really offer much of an advantage over the smaller ones.

 

I do have to disagree with the size of the shell not mattering however. I used to bottom fuse 3" and 4" shells, but I would never do anything larger than that. I currently topfuse everything as it is, canister wise. As shells get larger, the forces do get exponentially larger to lift the shells. Heavier shells give more resistance to movement, and thus generate higher chamber pressures. The area is also larger, and is thus more susceptible to failure. This is one of the main reasons you rarely see multi-break canister shells above 8", and when you do there is a high failure rate. They are certainly a skill that takes considerable amounts of practice and knowledge.

[ST1DinOH]

6" is a pretty happy medium. They're large enough you can do some of the more complex effects such as double petal, saturn, etc. They also are definatively more impressive than class C materials, something that is not always true with 3 and 4" shells. I would start smaller than 6" for canister shells however. 4 or 5" is a good happy medium there. 6" canisters take significantly more composition, and don't really offer much of an advantage over the smaller ones.

 

I do have to disagree with the size of the shell not mattering however. I used to bottom fuse 3" and 4" shells, but I would never do anything larger than that. I currently topfuse everything as it is, cansiterwise. As shells get larger, the forces do get exponentially larger to lift the shells. Heavier shells give more resistance to movement, and thus generate higher chamber pressures. The area is also larger, and is thus more susceptible to failure. This is one of the main reasons you rarely see multi-break canister shells above 8", and when you do there is a high failure rate. They are certainly a skill that takes considerable amounts of practice and knowledge.

so are you suggesting i should top fuse a 6 inch ball shell???

 

by your post i wasn't %100 sure if you meant for can's or ball's or both.

 

i'd bet can's take a ton of beating during the lift (flat surface) but would a ball shell still be just as suseptable to blow through of the time fuse?

 

i'm usually hot gluing the inside very well and the outside i give a nice thin coat. i hope tht's enough...as i said 6 inch HDPE guns are running around $20 so i'd hate to risk damaging it when i could just as easily top fuse the thing.

[Mumbles]

You can still bottom fuse the ball shell. I was talking about canisters. They are much less susceptible to lift related blow through. Up to you though, top or bottom fuse, it will still work just fine. It's harder to top fuse a plastic hemi as you lose the use of the leader ring for lowering the shell. All it takes in a bit of tape to make up for it though.

[qwezxc12]

FWIW, I bottom fuse all of my plastic ball shells...up to and including 8". I've only made 4" and 6" cans and all of those were top fused in the traditional manner of Italian construction.

[NightHawkInLight]

I do have to disagree with the size of the shell not mattering however. I used to bottom fuse 3" and 4" shells, but I would never do anything larger than that. I currently topfuse everything as it is, cansiterwise. As shells get larger, the forces do get exponentially larger to lift the shells. Heavier shells give more resistance to movement, and thus generate higher chamber pressures. The area is also larger, and is thus more susceptible to failure. This is one of the main reasons you rarely see multi-break canister shells above 8", and when you do there is a high failure rate. They are certainly a skill that takes considerable amounts of practice and knowledge.

I was speaking of ball shells with my statement. The extra surface area does offer more points for failure, but I have to disagree that higher pressures build because of more shell weight. Because of the extra surface area the pressure has much more room to work, far more than enough to make up for the extra weight. You may increase the weight of the shell by a pound or two, but you have extended the bottom surface area by 10 square inches or more. At 100 psi, there's another thousand pounds of force on the shell, more than enough to overcome the shells weight before pressure builds. For that reason I don't think a large ball shell has any more chance of failure at the fusing. The entire wall is more likely to fail, but the tiny point at the fuse entry undergoes no more force.

I think a likely cause for failure of those large 8" multiple break cans is the bottom of a shell over accelerating the top and just plain folding in half. I had that problem building multiple break 2" cans.

[GalFisk]

I was speaking of ball shells with my statement. The extra surface area does offer more points for failure, but I have to disagree that higher pressures build because of more shell weight. Because of the extra surface area the pressure has much more room to work, far more than enough to make up for the extra weight. You may increase the weight of the shell by a pound or two, but you have extended the bottom surface area by 10 square inches or more. At 100 psi, there's another thousand pounds of force on the shell, more than enough to overcome the shells weight before pressure builds. For that reason I don't think a large ball shell has any more chance of failure at the fusing. The entire wall is more likely to fail, but the tiny point at the fuse entry undergoes no more force.

I think a likely cause for failure of those large 8" multiple break cans is the bottom of a shell over accelerating the top and just plain folding in half. I had that problem building multiple break 2" cans.

That's not correct, the volume (and therefore weight) of the shell increases cubically, while the cross section (which is what counts when it comes to how much upwards force the lift can impart on the shell) only increases quadratically.

 

Example (rounding to nearest integer): a shell wiah a diameter of 4" has a volume of 4/3*pi*r^3 = 268 in^3 and a cross section of pi*r^2 = 50 in^2

 

shell volume to cross section rato: 268/50 = 5.36:1

 

for 6" shell you have

volume: 905 in^3

cross section: 113 in^2

 

volume/cross section ratio: 8:1

 

So for a 6" shell the lift must impart 8/5.36 = 1.5 times as much force per in^2.

 

 

This of course is a very simplistic view, we have factors such as mortar length, inertia, differing amounts of lift and different lifting heights for different size shells. I don't know enough about those factors (or enough of the math) to take that into account. It would be interesting someone can do that math, and prove or disprove the point I'm making.

[NightHawkInLight]

Alright I can understand that. Although I think that even with an 8/1 increase in volume over cross section, the 1 can overcome the 8 easily. With another square inch of area you can get many tens of pounds of force, but with another 8 cubic inches you get maybe several ounces of weight? At a certain size with the ratios getting more widespread I suppose the pressures would need to be stepped up. But for up to 8" or so I don't think the change is very drastic. Maybe another 5 psi is reached between an 8 and 3" shell.

 

I suppose I could be totally wrong when taking inertia into account. Even with the huge amount of gas pressure the time it takes to impart energy into moving the shell could compound with the weight. Not sure about that.

 

Anyway, sorry about arguing with you Mumbles, it really is irrelevant I think. However if anyone does know the calculations I would be interested in knowing for sure as GalFisk said.