How much Lift

[whitefox77]

I purchased a 1 7/8" HDPE mortar, and I'm going to my in-laws this weekend where it is at least semi legal to fire it off (not to mention they live in the middle of no-where, so no one will care). Per the book I have (Introductory Practical Pyrotechnics), I'm going to be using 20g of commercial FFg to launch the 20g-35g star mines.

 

However, I also made two comets. They are both 1.75" in diameter, about 1.75" long, and one ways 75g (charcoal based) and the other is 120g (Al based). I'm unsure of the amount powder I should use for these.

 

At first glance, the weight difference suggest a much larger charge will be needed, but at the same time, the comets should fit the mortar more tightly than the stars, so maybe I wont have to use that much after all.

 

Assistance would be appreciated.

[oskarchem]

Well, I don't exactly know the American powder sizes, but for Shells, it is 1/16 of the shell's weight, so I think you should go with that, but then again wait for someone ro verify that.

[TheSidewinder]

Yes, you will use less powder for the comets than the mines, and for the reason you mention: the "fit" of the comet in the mortar and, subsequently, the greater confinement of the lift charge.

 

I have very little experience with mines or comets, though, so I'll let someone chime in with some tips. I suspect you'll use ~15 grams for the comets if the mines work with 20, but that may be way off.

[KAP]

If there is only a 1/8 '' clearance to the mortar tube then 10 grams works for me. It also depends on burn rate of the comet.

I would feel safe with 10 grams lift to much could either turn it into a star mine or blow it blind.

[Mumbles]

Oh, 20g for a 35g star mine is way too much, especially for such a fine granulation.. I think you'd be fine with 5g, but it may be better to play it safe and use 10. For larger starmines (3 and 4"), I use 1/10th the weight of the stars/insert as lift. I also use a bit harder firing powder. I use 1Fg, where I use 2 FA for lifting shells. 2FA is approximatly -4+12, and 1Fg is approximatly -12+20.

 

Comets are hard to say as it depends on the burn rate. I'd go 10 for the charcoal, and 15 for the Aluminum. Should get them both up nice and high to make sure they burn out.

[whitefox77]

The Al is designed to burn quick. Sine the only Al I have is the Indian Dark, I figured I wouldn't be able to get much of a tail, the Indian Dark simply burns to quick, so I went for bright instead. The mixture is based on slow burn flash , but with more Al, and dextrin added.

EDIT: Oh, and I added a 1/10 of an inch layer of delay mix (green mix), and some BP primer to the bottom of the comet as I wanted it to leave the mortar before it starts burning like crazy. Probably not necessary, but it seemed like a good idea when I decided to do it.

 

The charcoal is designed more for a long burn with a good tail. I used Shimizu's Chrysanthemum 8 mix, but instead of using all 1 mesh of charcoal, it is a mix of sizes from fine powder to 15 mesh, with half of it being pretty fine powder, and the other half being a mix of different larger mesh sizes. From what I've read so far, that should cause it to have a very nice tail.

 

I don't have a comet pump or a hydraulic press, so I jerry rigged something with some PVC and a very large C-clamp. Hopefully the comets will burn properly and hold together. If they don't work right, well, it's hard to shoot any kind of fire into the air and not have it look at least a little cool So long as I don't blow my mortar up, I wont be too disappointed.

 

The stars I made are all the standard Shimizu's Chrysanthemum 8 mix.

 

Oh, and as a result of getting ready for this weekend, I'm now almost out of powdered Al, potassium nitrate, dextrin, and powdered charcoal.

[TheSidewinder]

Well, be sure and get videos of them all.

 

Then post them here for us to see!

[whitefox77]

Sorry, no pics or video,

 

The first mine (30g of 1/2" stars) at 10g FFg lift didn't go very high, so I upped all the lift numbers by 5g. The aluminum comet worked quite well at 20g FFg lift, it was VERY bright, went up very high, very fast. However it didn't last very long. The charcoal comet worked great. At 15g FFg lift it just barely reached it's apex when it burned out, and it left a tail that was probably 3 to 5 feet long.

 

The mines were are very impressive. My last shot was a 55g star mine with 20g FFg lift. It was made of two different size stars, some 3/4" cube, some 1/4" cube, with the smaller stars above the larger ones. The effect was cool as the small stars came out and burned out quickly, with the larger stars shooting past them up to a much high level, and burning much longer. The larger stars went up to tree top heights.

[Bonny]

The lift charges sound pretty heavy, but as long as they worked to your satisfaction that's most important.

[Mumbles]

One thing I probably never mentioned is that a perforated disk or sabot below the stars, but above the lift helps to make more efficient use of the lift gases. It also prevents the lift from mixing with the stars, which is detrimental to it's efficiency.

[whitefox77]

Mumbles: Nope, the book didn't mention that... Sounds like a good idea though. My lift and stars were wrapped separately in little "sacks" that were single layers of tissue paper. Does using a disk like have a detrimental effect on the stars lighting?

 

The aluminum comet definitely had more lift than needed, it was still moving up very fast when it went out. But considering how bright it was, and how short lived, I think the speed with which it was moving enhanced it. The most common response I got to that was "WOW!".

 

The charcoal comet could have worked with less, but it looked very nice going out just as it arced over. Over all I think that one worked just about perfect.

 

The first star mine really didn't have enough. I know at least one of the stars made it back to the ground. The other smaller star mines all worked well, with the stars starting to arch back to the ground, but only getting about half way back.

 

The last mine was probably a bit much. The smaller stars were still moving up when they went out, and the larger stars had only just started to arch over (not even to the point of falling) when they went out. It would have been nice if they'd fallen a few feet before going out. However, it was still a nice effect, and my family was talking about how cool it was for 20 minutes after. Considering my complete lack of experience with a mortar, I'm going to call that a success .

 

One question I have, I really like the effect of the one set of stars shooting past the other, but for my mine, I only used one lift change, and it happened very quickly. I think the effect would be more dramatic if I could have delayed the large stars be a 1/2 to 1 second. Could I do that by using two separate lift charges? One at the very bottom under the large stars, one smaller one under the small stars, but on top of the large stars, and use a piece of fast fuse going from one to the other so that the larger stars were delayed by a half second or so? Or would this be best done by using two separate mortars and just carefully timing how they are fused?

[TheSidewinder]

Using a perforated disk will have have no effect on lighting. Trust me, the burning gases will do their trick. And it can help the overall height of the mine, too.

 

As to the mines where star groups pass one another in-flight, are you sure that's not done with 2 seperate mines fired milliseconds apart?

 

I can't say I've seen a single-mine shot do that.

[whitefox77]

As to the mines where star groups pass one another in-flight, are you sure that's not done with 2 seperate mines fired milliseconds apart?

 

I can't say I've seen a single-mine shot do that.

I guess that is what I'm asking. Is there a reason why you couldn't do it with one shoot?

[TheSidewinder]

Well, I'm not sure the way you describe it will work.

 

Lift gases expand and ignite things *SO* quickly that I don't think you'll get ANY delay between the bottom and top lift charges. The first one to go will immediately light the other one.

 

But I can't say for sure. Firing two mines electronically would allow you to fire them precise timing, if you put the e-match directly into the lift of each one.

 

If you try your method, post the results.

[Mumbles]

The easiest way is to probably give the effect of the stars rising through another. That is use two star types. One should be a relatively fluffy tailed glitter, streamer, or charcoal type of tail. This will in effect conceal the other stars. Time them so they burn out relatively quickly, and you will see a set of color stars rise over the top. I'd suggest metal fueled stars when working with glitters or streamers. You could probably get away with organic when using charcoal or lampblack fueled stars. Another possibility would be the use of propelled inserts. They won't neccesarily all rise through the stars, but they will shoot off in random directions after they have slowed a bit.

[hst45]

whitefox, I'm not sure that I can help you with stars that actually pass one another, but what about rolling a color-change star for a mine? Let's say they take fire red and change to glitter. Perhaps you could roll some glitter cores to 1/2". Take half of these and finish rolling them red, and finish the other half in glitter. This MIGHT give the effect of red rising change to glitter, which MIGHT seem to pass their red brethren, even though in actuality the red just dies away early. I've never tried it, just a thought.