Aerial Shells

[asilentbob]

I've pretty much neglected reading through this thread since it is so long... should probably get around to doing that sometimes... anywho...

 

Made some shells last night:

Made a 3" shell out of a medicine bottle. It has a central hopefully trimethyl borate proof plastic container with a few grams of polveroned crappy whistle. Then the rest of the space is pretty much filled with trimethyl borate. Don't know when I'll be able to test it. I also think it is leaking already :C... but taped up a bit and oriented so that it wont leak more.

 

Made a spherical 3" shell with just BP rolled up (poorly) on crackling ball dragon egg cores. Boosted with polveroned crappy whistle, BP/filler, and 1Fg GOEX.

 

Made a spherical 4" shell with pumped 5/8" C6. Boosted with a bit of polveroned crappy whistle and 1Fg GOEX plus BP/filler

 

Made a spherical 6" saturn shell with a 2 deep row of pumped old 5/8" D1 as the ring and the inner petal/planet being 1/4" win20. Boosted with a bit of polveroned crappy whistle + GOEX 1Fg + normal BP/filler.

 

Hopefully I'll get to fire them off near the end of the month. No idea though.

 

I REALLY need to get a star roller built. There is no way I'm going to sit around pumping stars for hours for just 1 6".

[Mumbles]

Oh no, don't worry about it. I actually responded with the volume vs area thing, but I guess it never got posted or what not. I am always willing to discuss pyro things, even if I'm wrong. I'd much rather have someone argue with me, and show that I am wrong or at least not 100% correct, than have everything I said assumed to be correct. I assure you it is not.

 

Here is the way I was thinking about it. I made two rather essential assumptions. They're not 100% correct, but they make it easier to conceptualize. I assumed that the lift burnt completely before the shell moved, and that the shell made a perfect seal. I was also thinking mainly about canister shells. With large multibreak canister shells, the assumptions almost become true actually.

 

The lift generates X amount of gas per unit weight. The amount of lift is directly proportional to the weight of the shell. So if it burns completely, and all gas is contained, then the pressure increases directly proportionally to the size of the shell (r^3 / r^2 = r)

[NightHawkInLight]

Made a 3" shell out of a medicine bottle. It has a central hopefully trimethyl borate proof plastic container with a few grams of polveroned crappy whistle. Then the rest of the space is pretty much filled with trimethyl borate. Don't know when I'll be able to test it. I also think it is leaking already :C... but taped up a bit and oriented so that it wont leak more.

Wow I hope you are able to capture it on video. I have never seen a green lampare shell. (<what they are called yes?)

 

Here is the way I was thinking about it. I made two rather essential assumptions. They're not 100% correct, but they make it easier to conceptualize. I assumed that the lift burnt completely before the shell moved, and that the shell made a perfect seal. I was also thinking mainly about canister shells. With large multibreak canister shells, the assumptions almost become true actually.

 

The lift generates X amount of gas per unit weight. The amount of lift is directly proportional to the weight of the shell. So if it burns completely, and all gas is contained, then the pressure increases directly proportionally to the size of the shell (r^3 / r^2 = r)

Ok, that makes sense using the assumptions you gave. More lift in not much more space = higher pressure. My assumption was that the shell moves before the gun reaches full pressure. Without math that is very far beyond me I doubt anyone will be able to accurately predict gun pressures. That is without sticking a pressure gauge on a very high quality and fast acting one way valve at the bottom of the mortar. That would be very interesting to see the results of. Variables through the roof though, even down to the paper the shell is wrapped in.

[hst45]

Mumbles, isn't it also true that applying force to a sphere is less likely to crush it than applying force to a similar diameter flat surface? It should be along the lines of an arch or dome carrying more load than a similar sized flat roof if I'm correct.

[Zmuro]

My first 6" shell with C8 stars: http://www.youtube.com/watch?v=kY7EXj0X19I

[oskarchem]

Nice shell, will be making one soon, anyway, you went hard on the lift and burst didn't you? Loved the two thumps.

 

I have a question: because I'm mixed up here I am making a 100mm shell, and the lift should be 16% of the total weight of the shell, or 1/16th of the weight? I'm asking this because I thaught it was 16% of the weight and I got 49g of lift... Wich I thaught is alot because if someone makes a 1000g shell he would come up with 160g of lift...

[qwezxc12]

I have a question: because I'm mixed up here I am making a 100mm shell, and the lift should be 16% of the total weight of the shell, or 1/16th of the weight? snip..

oskar,

 

The traditional amount is 1/16 (6.3%) the weight of the shell. This originates from the "one ounce per pound" rule...somehow saying 62.5g per kg doesn't have the same ring to it

 

Anyway, you better have GOOD lift if you expect to use the 1/16th ratio. Most home builders (using non-commercial BP for lift) start out at around 1/10 and dial it in from there.

 

Also, the smaller the shell is, you may need more lift proportionately. For instance, with my alder based BP, I can use 1/14 ratio (7%) on 6" and 4" ball shells, but when shooting 3" ball and 2in cans, I really need to use 10% to get them up there.

 

Hope that helps.

[TheSidewinder]

On my 3" cannisters, I need nearly a full ounce (26 grams actually) of lift for ALL of them that weight 1/2 to 1 pound.

 

 

From 1-10 pounds, yes, the formula is 1 ounce per pound of finished shell weight.

 

For shells more than 10 pounds, it's one ounce per pound for the first ten pounds, then a half-ounce per pound for the weight in excess of the first ten.

 

This is only a GENERAL guideline. You have to adjust up or down somewhat according to shell type.

 

It'll be a LONG time before I have to worry about a 10+ pound shell though.

 

M

[GalFisk]

Benzolift is nice for small shells, it's easy to make good quality lift (I suspect it's a lot less picky on charcoal quality than BP) and works well with a 1/16 ratio. It's probably not suitable for shells larger than 3" though. The largest I've fired with it as of yet is 2" canisters.

[oskarchem]

Ok, right so this is my first 100mm shell for the Bday of my step dad, hope it doesen't flourpot... Haven't quite finished pasting it just did a couple of layers. The Hemis were home made.

 

http://img389.imageshack.us/img389/9808/p100308204801wt0.jpg

[Frozentech]

Oskarchem,

 

Did you paste the lift cup with the same wraps as the ball shell ? I think I would avoid hard pasting the lift to the shell. It may go off more like a BP salute, fracturing the shell casing, instead of the (relatively) gentle lift you are looking for.

 

Let us know how it goes.

[oskarchem]

Shit, didn't think about that, well the good thing is that I didn't exactly finish the pasting, I'm half way through, anyway, maybe, I'll cut in to the pasting that attaches the lift cup to the shell.

[ST1DinOH]

Shit, didn't think about that, well the good thing is that I didn't exactly finish the pasting, I'm half way through, anyway, maybe, I'll cut in to the pasting that attaches the lift cup to the shell.

all you'd need to do is cut the bottom craft off the lift cup. throw a few layers of tissue paper over the bottom and you're good to go. you just want to be sure the lift cup has an easy out, usually the bottom.

 

if you do use tissue paper though be carefull that the tube doesn't have any moisture in it when you drop your shell in. it can soak through and foul your lift. that happened on NYE to one of my shells.

[oskarchem]

Well my lift cup is a 3oz plastic cup, so I'm not to worried about the humidity, but thanks

[ST1DinOH]

Well my lift cup is a 3oz plastic cup, so I'm not to worried about the humidity, but thanks

well this brings up a possibly trivial question but i'll ask anyway...

 

does partial confinement of the lift cup effect the lift in anyway or does it not matter?

 

i've made shells a few different ways, one set had a tissue paper bottom, the others had a loosly attached paper drinking cup...

 

would it make any difference at all if i had pasted in the cup a tad better than i had and just left the bottom of the cup bare?

 

in other words is there a perfered method for making lift cups...do they need some confinement of is it better to have the bottom as weak as possible to ensure that the lift gasses exit downward?

[NightHawkInLight]

I get much more height from my lift with the confinement of several turns of light kraft with a tied end. I'm sure it puts a lot more stress on the shell though so you gotta be careful with how much you use. It all depends on the shell also.

[qwezxc12]

Maybe it depends on the quality of the lift? I get plenty of height in 4-6" just using light craft cones taped on the shell bottom. As an opposite, Maltese builders sometimes use maroons made from rough powder with heavy twine spiking to launch their big multi-breaks, so I would think that the extra confinement can boost the effective power of a slower burning BP.

 

Theory: The confinement probably gives the lift charge the extra time needed to fully burn, thereby putting all of the gaseous combustion products to work lifting the shell. Either that or it increases the pressure enough to speed up the burn rate - either way, the lift charge is fully converted to gasses that provide the work soon enough to be applied to lifting the shell.

 

If the equivalent lift charge wasn't confined, perhaps it would still be burning (and generating wasted power) after the shell had already launched.

[psyco_1322]

Hay bob I finished that 3" bottle with trimethyl borate the other day, pasted and inserted that burst bag(that was PVC coated) and layed it on its side to dry by the stove that night. Next morning there is shit oozing out of teh cap area. Damn shit soaked into the double bag that was coated and soaked the fuse in alcohol. Pissed me off. I was really wanting to see it fly.

 

Oh Nighthawk, they arent quite the traditional lampare shell that your are thinking about. View:

http://s108.photobucket.com/albums/n3/psyc...pare%20Testing/

 

 

Oh Mumbles you should see this, its in response to that not many 8"+ multis made:

http://www.pyrobin.com/files/malta%20fireworks.jpg

[Mumbles]

I wasn't talking about Malta. I was thinking mainly from a hobby community sense. There are only a handful of people that have mastered the art of big canister shells.

[psyco_1322]

^Oh I see, Yah there isnt many hobbiests that make big multi break shells. I dont think that people have the patience for making them and the work required. Nevermind the special tools.

 

 

Nighthawk, what kind of purple did you use for that sun & planets? It looked like you had TT changing to purple, the way your desribeded it I thought they were seperate. Just wondering cause Ive been looking for a purple that burns with a nice deep color to it and isnt really slow burning.

[Mumbles]

If you are going to be firing off several of the same size of shell per night, specifically a mix of ball and canister, you may want to reconsider the lift cup. It may be different with you actually pasting it onto the shell, but generally plastic lift cups get left in the gun, and can cause a buildup of debris at the bottom which puts a standoff between the shell and the base of the gun. This can cause low breaks.

 

For my ball shells I put the lift into a plastic bag. I have been using the thin plastic bags that you put fresh produce in at the grocery store. However I have noticed them tearing a bit more than I would like. I will likely begin using a heavier gauge bag, such as the type common with sandwich bags. I then tape off the bag onto the leader. I find that if I tie it on, it tends to cut off the lift and give a bit of a delay which can be quite scary. I don't want to have a hang fire. This would likely be a non issue with multistrand blackmatch. I then tape the lift bag onto the bottom of the shell over the fuse with an "X" of tape. Readjusting the tape is where I had been having tearing problems. This is nice for it's water proofness, but you must be absolutely certain that there are no burning embers at the bottom of the gun. This will definatly set the shell off prematurely. As always load the shell by dropping it into the gun, and letting it lower under it's own weight. This will prevent you from being struck by it if it does go off, but you will likely suffer some burns.

 

For canister shells, I do it pretty similar to nighthawkinlight. The shell is spiked, and pasted in of course, and allowed to dry. After this a dry wrap is usually applied. I sometimes use the same setup with the plastic bag and leader, only top fusing the shell. Lately I have been going with a more traditional method. Tear off enough of the quickmatch paper to expose about an inch or so of bare match. Top fuse the shell, and tape it down to it stays put, and will be able to hold the weight of the shell as it is being lowered. Leave enough quickmatch to run down the side, and go at least halfway across the bottom of the shell. Roll up the dry paper(I use about 3-4 wraps of 30lb paper), quickmatch and all. Tape down the last flap. Tie a tight knot(generally clovehitch) around the very bottom of the shell, but still over the shell body. This prevents the lift from migrating up the side. Fill in the bottom with lift powder, and fold shut. This can be taped down. Alternatively, you can bunch it up, and tie it off. I prefer taped, but that is just me. Gather up the excess paper at the top of the shell. Tie it off at the base of the gathered paper, and again a couple inches above it. Cut off any excess paper and you're ready to go.

 

Just keep in mind the difference in the lift on ball shells and canister shells when comparing lifting methods. What works great on canister shells may not work the same with ball shells.

[NightHawkInLight]

Nighthawk, what kind of purple did you use for that sun & planets? It looked like you had TT changing to purple, the way your desribeded it I thought they were seperate. Just wondering cause Ive been looking for a purple that burns with a nice deep color to it and isnt really slow burning.

It's an ammonium perchlorate comp.

Ammonium perchlorate - 70

Charcoal - 15

Sulfur - 8

Copper(II) chloride - 7

Dextrin - +5

I use liquid starch to dampen the comp for cutting instead of adding dextrin. I form the wet composition into a cake and allow it to dry. I then break it up by hand into the stars. It leaves a rough edge that catches flame easily. With some slight scoring you can break them pretty evenly.

They were just thrown in with the TT in my shell. The two mix well.

[psyco_1322]

Where can one get some gummed craft? And what is it called/used for?

[ST1DinOH]

Where can one get some gummed craft? And what is it called/used for?

a lot of the online pyro suppliers have started to carry it. check around some of your favorites...odds are one of them now sells it along with the fiber strapping tape.

 

i was just thinking of ordering some this weekend myself.

[Mumbles]

It is called exactly what it is. Gummed kraft tape. Or gummed paper tape, something to that effect. It is used for many things. Some roll tubes from the wide stuff, some paste shells with it, some roll quickmatch tube, some use it for it's intended purpose and seal boxes. There are many things you can do with it.

 

Out of curiosity, why would you want any if you don't know what it's used for in the first place?