Multi Break Canisters - Mortar Tube Length - Drag Rope

[mkn]

Hi All,

 

I'm having some fun building some small muti break canisters ! looking to get them skyward from a mortar, and maybe a rocket or two ( love those rockets ! )

 

 

After some searching I have not found some answers to muti breaks. I am building some 1.75 " 3 break canisters, 7" - 7.5 " OAL, 1.8" diameter.

 

My questions:

 

Tube length calculations - I figure the mortar tube length will change ? is it 5 X length of shell ?

 

Tube materials: one thread stated only steel to be used on multi breaks, is this correct? I plan to build some 3" 3 break canisters when I am ready for that size after learning on the 1.75". Possibly 4" - We'll see on those, that's a lot of materials in one shot......

 

 

Drag rope, I understand them for use in lowering shell in tube and orientation of burst in sky, Are they necessary? will a canister tumble in flight without one, losing momentum? Is there a size when they become critical, if so what are rope sizes ( length and diameter ) for 1.75" , 3" and 4" canisters.

 

 

Thanks in advance guys and gals , I'll post some videos if I get some good shows !

PS what section should videos be posted if looking for feedback, or just want to show them ?

 

Matt

 

 

 

 

 

[pyrokid]

Tube length generally stays the same. If you look through some pictures from PGI, you'll see some of the larger shells sticking out of the gun.

 

Steel is used for some shells because it can tolerate the larger peak pressures generated by the lift charge of larger shells. It is critical that steel guns are buried in the ground. It is by no means mandatory that you use steel for all multi breaks. It's dependent on the weight of the shell. I'll let some of the more experienced members here chime in on where the relative cutoffs are.

 

Drag ropes are generally used for the two purposes you listed. Shell tumbling will have only a negligible effect on shell height. Look up some Dr. X videos on youtube for examples of this.

 

Nice looking shells!

[Arthur]

The Maltese, who are exponents of the big cylinder shell ( a metre LONG is not unusual) leave a lot sticking out of the mortar. however it's your design to perfect.

[nater]

Often, a slightly longer mortar is used for multibreaks. A standard 3" mortar is 18" long, wheras one for shells with more than 2 breaks is 24". Yes, with long shells they sometimes stick out.

 

As for steel vs anything else:

 

NFPA 1123 requires a steel mortar for all shells with more than one break. It also requires steel mortars to be buried at least 2/3 of their depth and fired electronically. Technically, this means peanut shells should be fired out of steel, but most operators fire them out of HDPE with no problems. True multibreak cylinders are rarely seen in public displays any more. 1123 is not the law in all States, but is the "industry standard"

 

What does this mean for you? Depending on weight of the shell, HDPE might be just fine. 2 breaks, I would not worry about at all. 3 is probably okay too if it is not too heavy. People are testing thicker walled HDPE to replace steel mortars and the results are promising so far.

 

Steel can be dangerous if the shell has a bottom shot. However a properly constructed bottom shot adds rigidty to the shell, making it more likely to survive the lift. (Really, they have a few purposes beyond a boom) So, when firing out of steel, make sure your construction is sound, bury the mortar and make a barricade. Use a long enough safety fuse or efire so you have time to retreat.

[mkn]

Thanks guys, I'll probably try my standard length HDPE tube, and leave out the drag rope on these small cylinders. When break orientation on the larger shell is more desirable, I'll have to try adding a drag rope !

 

Naters response just came in, my OAL is 7.5" 191 grams, so I think my HDPE is fine for now, but if I get to wondering, I'll strap it to a rocket !

Edited March 18, 2014 by mkn

[Mumbles]

I wouldn't worry about mortar construction until your shells get up into the 8-10lb region. That doesn't mean you can get away with sloppy construction. You also don't really need a bottom shot in smaller shells, particularly of only a few breaks. I'd be a little more comfortable firing multibreaks out of fiberglass, just due to their one piece construction. In the 2" size it wont make any difference though. I used to fire 3-breaks up to 4 and 5" without bottomshots out of fiberglass semi-regularly.

 

The lift rope primarily comes into play when your shells get too heavy to be supported by the leader. They really don't offer any orientation on heavy cylinder shells. They just carry too much momentum as it is. You can put one on, but it may not be necessary. You can usually control the break orientation just based on delay time. There is a pretty slow tumble, and you can get it close with experience. Also, any sort of controlled orientation will be thrown off after the first break anyway.

 

I generally use a standard sized mortar for all of my shells. It just makes things easier in the long run. When I go to club shoots, I don't need to worry about there being a special mortar available or lugging around heavy ones of my own. Generally firing out of slightly longer mortars just means that it breaks a little higher, which isn't always a bad thing.

[mkn]

oh yeah ! up to a meter long........that will be a ways down the road, but a great target to aim for !!!

[mkn]

Yes, I think I will stick to using standard length tubes as you suggest Mumbles, and that makes sense about too much momentum for a drag rope to help orient a shell. I may look into some fiberglass tubes to have on hand, I do have some fiberglass that came with consumer shells, but they are not one piece, they have a plug in the bottom.

 

ps posting a video of a weight test for my 1# rocket ( BP) I lifted a 1# payload plus sticks and motor., pretty neat , well for me anyway as I know now I can send up at least 3/4 of a pound no problem.

[mkn]

Shot my first build of a 1.75 inch triple break cylinder, not the build pictured above, that is my second. It was fabulous ! nice timing, all three breaks in the same area of the sky, I'm hooked on these triple breaks !!!

 

check it out: