Is it possible to use one continuous fuse for lift charge and timing in small shells?

[JoeyMac]

So I've been a long time lurker. I've made fountains and ground salutes and small shells (<3").

 

I got a hold of some of these cute little 1-1/8" plastic ball shells with integrated lift cup. Should make neat bomettes/insert shells or just something small I can pop out of a 1-1/4" tube for fun without too much racket. They have this little lift cup molded onto the bottom with a 1/8" passfire hole for visco fuse. This will be my first time using plain visco for the time fuse. I usually use 1/4" chinese timefuse on my paper shells or 35mm film-canister type shells. On the 1/4" time fuse I use a diagonal cut, 25% NC laquer, BP slurry, and coat with 4Fg fine granules. Works well.

 

Due to the preexisting hole on these little 1-1/8" shells, after much reading, my initial plan for these little guys was to use 1/8" (3mm) visco with a couple wraps of aluminum tape and my typical BP priming. But looking at these little plastic shells with their predrilled hole and prenotched lift cup wall I got to thinking... what's to stop me from just using a long piece of visco fuse and continuously running it right through the BP lift charge cavity and then up through the passfire hole to the burst charge? I would think, with the fuse already being lit and being continuous, it should light the BP lift charge just fine and then continue right on burning. Basically, the type of fuse (slow american visco, standard chinese visco, medium cake, perfect pink, etc...) and the length of a passfire tube or wrapped aluminum foil tape is what controls the time delay.

 

Would this work? If not, why not?

 

It'd be cool to save some time on small shells (with small lift charges to pass through). I'm going to test a couple maybe tomorrow or the day after if the weather is OK. Maybe just a light BP load to report back and confirm it works. I don't have any stars made up at the moment, but I'm more interested to see if it works.

 

The shells that gave me the idea:

 

Concept applied to other small shells:

Edited June 21, 2020 by JoeyMac

[Arthur]

Remember that visco burns away, the length of visco inside the shell times nothing as the fire first passes through the shell wall it passes out of the visco, consider also the time/length of visco outside the shell, up the mortar and out to where you want to light it. I'd chose to make that no more than 4 seconds.

[JoeyMac]

Yes, the portion of fuse inside the shell will need to have a few wraps of aluminum foil (ducting) tape at its base cut to 3/4" wide and a ring of hot glue at the bottom. A bigger shell like a 2" might benefit from a small paper tube around the fuse. Even a few wraps of plain masking tape can shield the bursting charge from visco flame, and it's probably better for biodegradability consideration, but the paper masking tape adhesive can eventually rot and dry out if you're not going to use all the shells you make soon... so I prefer the adhesive aluminum foil tape. On these particular mini-shells, the 3/4" wide tape plus the shell's inside these little shells should give about 1" of shielded delay.

 

I hadn't thought about the fuse burn time outside in the tube. On these little shells the mortars are small, only like 6" long... but that's still at least a 12 second burn time. But on longer 2" & 3" mortars it could be a decent wait.

Edited June 21, 2020 by JoeyMac

[pyrokid]

Shell leader burn duration could be worked around with a quick match leader attached to a short piece of visco leading into the shell. My uncertainty is what happens after the lift charge is ignited. I'm concerned about reliability of the fuse when subjected to those violent conditions. Time fuses are typically reinforced somehow, and in this design there would presumably be more exposed fuse when the lift is ignited. To me, the production of timing elements for round shells is another unit process that exists in the assembly line. The simplifications that come with combining the leader and timing fuses seem to be accompanied by their own set of limitations or complications. In the end, test it, and if it works for you, that's great.

[SharkWhisperer]

Remember that visco burns away, the length of visco inside the shell times nothing as the fire first passes through the shell wall it passes out of the visco, consider also the time/length of visco outside the shell, up the mortar and out to where you want to light it. I'd chose to make that no more than 4 seconds.

This is a 6"-long cardboard mortar. The fuse hole goes through the bottom of the tube. And PK, there's no QM leaders used in 6" cardboard mortars by anybody I've ever met. But there could always be an exception...I guess you could use for timing a fan or barrage or something, but the QM certainly wouldn't directly connect to the lift charge. Might be difficult to easily slide QM between shell/inner mortar wall without either a super loose shell fit in that dinky tube or pinching the QM (or fast visco if you went that route) and risking trapping your shell. The lift charge is going to be tiny for a 1-1/8"--probably small enough that you won't blow out the burning end of your visco, and probably insufficient to burn through fuse coating ahead of the end and skip fire. But the distance/transit time from lift entry to shell entry is one unanswered question, as is the speed of visco to use for a continuous configuration. From the pix, it looks like your lift cup fuse hole-to-shell is almost an inch, which is a good distance for such a small shell. Also, in the pic at least, there's a pre-drilled hole on the top hemi of the shell (?!?), and at the angle shown one cannot see if there is a passfire hole from the lift cup to the bottom hemi (I'm assuming there is?). Or else somebody glued the wrong hemi half onto the lift cup, or drilled it wrong--where'd these very novel shells come from? Anyways, if no bottom passfire hole, a drill will solve that in moments, and epoxy will close the top hole (gonna top-light a 1-1/8" shell w/QM, hah ha? No reason not to mess around with a few configurations; apart from time, the materials expenditure is pretty minor.

 

Even with the teensy 1-1/8" shells that liftcup would require reasonably well-timed visco to get it to altitude/apex just when it passes fire through the bottom hemi towards the burst. Is regular slow green cannon visco (23-24 seconds/foot) going to work? Who knows? It would take around 2 seconds just to burn through the 1" lift cup zone--by that time, your tiny shell might be hovering around apex or it might be well on its way down already--hard to say til you launch it. How important is centering the fire arrival in a plastic shell that small anyways? If not so important, then hotglue and NC slurry priming the inside end might suffice. If standard Chinese green visco isn't fast enough and they start blowing up on the return trip or at your feet, you've got plenty of other fuse options to dial up burn speed w/o having to get too fancy inside the shell end. Plenty available at 15 or 20"/s burn rate. Al tape and/or paper wrapping is simple but kinda kills the time-savings you're hoping for.

 

They're tiny shells, so unless filled with hot flash and plutonium and you have very bad luck, the odds of an injurious blinding flowerpot, or mistimed/delayed ground burst on return shouldn't be particularly worrisome. They're cheap, tiny plastic shells. How much will the whole thing weigh once filled with your effects and ready to fly? Maybe launch a few in the air with burst and the shell filled with something inert or plain BP at the same mass as planned payloads--just so you can dial in burst timing and optimize lift. A few launches playing around to dial in the passfire visco type/hemi-insertion length/lift powder load within reason and you're golden!

 

Your old fashioned way with a piece of BM or visco end-primed with NC/BP slurry seems pretty simple, but not so simple as just pouring lift, covering with a paper endcap, dropping it into the mortar, and ramming a fuse through the fuse hole! The hardest part might be lining up the fuse hole on the mortar with the slot on the lift cup, hah ha! Like always, don't be standing right next to it during testing in case the tube ruptures if delay is way too short or directly underneath it lest it bounce off your melon if delay's too long...

 

Never considered building a 1-1/8" stand-alone shell before; doesn't seem like a job for fat fingers! Have fun & let us know how it worked out for ya! Eye protection, please.

Edited June 22, 2020 by SharkWhisperer

[JoeyMac]

These little shells came from skylighter. They looked neat and were only a few bucks. The little lift cup is only about 3/4" deep so a fuse coming down though the hole and out the side of the lift cup might only have 0.5" inches of exposed visco before it's up in the pass-fire hole.

 

The lift cup can hold like 4g of 2Fg BP (lol) but I plan to have the finished shells weigh about 15g, so lift charge will be tiny. I plan to start with 2g if lift and work from there. A 1/10th lift charge weight is usually pretty good for smaller shell diameters. I made a few practice shells just filled up with Goex 4Fg burst charge, foil time-delay wrapped visco running straight through the lift charge and out the side of the lift cup, super-glued the hemispheres together, and then poured in the lift charge before putting a piece of tape over the lift cup opening. Not sure what's up with the littel hole on top, but I just put a dot of tap inside and outside the top shell's hole.

 

Raining the next 4 days, so we'll see when I can test these.

Edited June 22, 2020 by JoeyMac

[SharkWhisperer]

They're cute, but seems to me the built-on lift cup is more of a hassle than a bonus--especially if you end up wanting to pack them together as inserts into bigger packages if you get bored with single launches from a mini-mortar. Glad at least it does have a drill hole already in the bottom hemi. That top hole must be for the eyebolt so you can string your quickmatch leader through it and be able to lower that monster shell straight down all the way to the bottom of your deep mortar til ya hear the "thud", hah ha! With 1/8" maximal clearance (1/16" all around if perfectly centered), you might get that oddball shell hung up in a 1-1/4" ID tube just from any QM or fast visco burn remnants from an attempted top fusing.

 

Might be fun to load up with a lil pile of well-primed microcrackle and burst with a slightly flash boosted BP, though. Careful with your payload selection til you get your timing figured out. Assuming the shell casings weigh maybe 2-3 grams, will be interesting how much mass of whatever effect you're able to cram into there. Crackle balls, whoo hoo!! Careful if you're using thin-walled tubes for mortars. I blow 'em up all the time when I don't feel like lugging my multibarrel steel stargun around ("just a few more stars...it can take it!" Boom!). 1+" OD tubes (thin or thick) might be more versatile for making single-shots (or even stacks) from your 1-1/4" tubes, and prolly half the price for twice the payload. Typical ignition. But you'd want a mortar with decent wall strength... Careful with the flash til your timing's repeatable.

 

Will look forward to your space launch results after the weather clears! Shoot some video if possible. Tiny is always interesting! See what kinda symmetry you can extract from that thar sphere!

[JoeyMac]

OK, lauched a few test ones today. Only 3 but they were 100% reliable. Anywhere from 3-5 seconds delay.

 

I put about a 1/2" wide strip of aluminum flashing tape around the base of the visco inside the ball and pushed it onto a little donut of hot glue and put another bead of hot glue around the fuse inside of the ball and in the lift cup. Then bent the fuse over, poured in about 2 grams of Goex FFg (that didn't even fill the lift cup halfway) and then I used a single layer of masking tape to close the liftcup.

 

Because the green visco is so slow, I only put a 4" fuse hanging out of the lift cup and drilled out one of my morter tubes so I could light the fuse from the bottom. Worked great.

 

 

I filled two of the shells with BP so they just popped open letting me know it worked. But one of the shells, just for fun, I completely filled with KP flash (about 8 grams). I don't think wasn't quite as loud as a proper thick paper ground salute. I'm not sure if it's because I'm not used to an 8g salute being so high in the air or because a thin plastic shell isn't as good confinement as a thick paper tube... although I'm not sure KP flash really needs much confinement at all. At any rate that one it was still pretty damn loud - LOL. Got two neighbors about 60 yards away to come out of their houses like WTH was that?

 

I might try a little less lift BP because after just 3 launches the spiral wrap inside of the 1-1/4 tube was delaminating. I might also try some 10-14 second medium cake fuse and jsut top load for easier reloads. Fishing the fuse though a bottom pilot hole could be tough in the dark. At any rate, I think cool this worked - IT WAS WAY FASTER than cross matching or even BP slurry priming. My only seconds thought so far is if the fuse fails to ignite the lift charge, the shell is bursting in the tube...

 

I didn't take a video but I took a pic of the fusing assembly... I'll get them uploaded shortly.

[Smokelvr]

Yes, the portion of fuse inside the shell will need to have a few wraps of aluminum foil (ducting) tape at its base cut to 3/4" wide and a ring of hot glue at the bottom. A bigger shell like a 2" might benefit from a small paper tube around the fuse. Even a few wraps of plain masking tape can shield the bursting charge from visco flame, and it's probably better for biodegradability consideration, but the paper masking tape adhesive can eventually rot and dry out if you're not going to use all the shells you make soon... so I prefer the adhesive aluminum foil tape. On these particular mini-shells, the 3/4" wide tape plus the shell's inside these little shells should give about 1" of shielded delay.

 

I hadn't thought about the fuse burn time outside in the tube. On these little shells the mortars are small, only like 6" long... but that's still at least a 12 second burn time. But on longer 2" & 3" mortars it could be a decent wait.

A piece of small straw, like a large coffee stirrer or something from a kids drink like a Capri Sun works great to shield visco, the plastic will take a lot of heat, even melt, but not pass fire

 

[Richtee]

Dip the tubes in water glass. Concrete sealer. Sodium Silicate.

[SharkWhisperer]

Seems to me the "mortars" are essentially disposable, so who cares?

 

Til dude wants to ramp up to larger projectiles, why bother?

 

They're currently less than 2" diameter, ffs.

 

I fail to see a problem that needs troubleshooting...

[Richtee]

Apparently he cares or he’d not have mentioned it, eh.

[SharkWhisperer]

Apparently he cares or he’d not have mentioned it, eh.

eh? eh. Thanks for the useful addendum. /s

[Smokelvr]

PL2020_x700.jpg

 

I looked at those too, I like them, but to me, the bottom is screaming for an effect, like a rising tail comet, press in or glue it, whole the center, or if you could, just save some visco, press it in the star then have fun.

though, by design, those are supposed to be headers on rockets.

[SharkWhisperer]

I looked at those too, I like them, but to me, the bottom is screaming for an effect, like a rising tail comet, press in or glue it, whole the center, or if you could, just save some visco, press it in the star then have fun.

though, by design, those are supposed to be headers on rockets.

Dinky little rocket headers on dinky little rockets are one possible use, but the built in lift cup and side hole (fuse hole) are for fusing the lift charge through a bottom-drilled hole in dinky 1.25" ID cardboard mortars.

 

But he's probably got enough space in the lift cup left over to add a small rising effect to the bottom of the shell, per his earlier experimentation (half full with BP and overlifted).

 

The hole on the top hemi is just funny to me. Top-fusing a 1.125" diameter shell? Mebbe not.

 

You could probably forget lift and just light and toss them nearly as high as a mortar will launch them. Unless you have a girly throwing arm like our good ferret-faced opportunist Dr. Fauci.

 

There's also thicker-walled cardboard tubes available for more durable mortars than the kid's stuff.

Edited December 22, 2020 by SharkWhisperer