11 replies to this topic

[martyn]

One of my favourite effects is the horse tail shell.
I'm interested in how they are constructed, I've had a search online and not come up with any answers.
I'm guessing it's a very weak break and timed to burst just before apogee.
The commercial ones I have seen are ball shells, are there any construction details that anyone knows of that ensures that the stars seem to spit out from one end.
Could someone perhaps put a sketch up on pyrobin or something. I can imagine how it might be easier to get the 'linear break' effect from a canister shell just by popping a lid off and ejecting the stars, although I know this is not the technique used.
Would a ball shell softly broken appear to eject the stars in this linear fashion if it still had upwards momentum.

[portfire]

I believe it's the 'Poka' style construction (ball shell) how the Horsetail effect is achieved. The shell is filled from the top and sealed. I would have thought that as long as the casing can survive the lift you would get a similar effect.

[Mortartube]

I would imagine that it would be easier to make these with a heavy walled (A.K.A fairly thick card tube), cylinder shell with the time fuse disc heavily glued on and the other end fixed more weakly. This is basically what happens in a horse tail bombette cake. Break it with BP, so it gives more of a gentle bouquet effect.

Here is a horse tail formula from Dave Buell:

Brocade Horse Tail (Dave Buell)
Potassium Nitrate 36
Charcoal 29 then screen the metal in and pump the stars.
Charcoal (80 mesh) 14
Sulfur 9
Titanium sponge 7
Dextrin 5


I believe that you need to ball mill everything except the Titanium. There used to be a video on youtube but it's gone. It was a beautiful effect.

[pyrotrev]

I would imagine that it would be easier to make these with a heavy walled (A.K.A fairly thick card tube), cylinder shell with the time fuse disc heavily glued on and the other end fixed more weakly. This is basically what happens in a horse tail bombette cake. Break it with BP, so it gives more of a gentle bouquet effect.

Here is a horse tail formula from Dave Buell:

Brocade Horse Tail (Dave Buell)
Potassium Nitrate 36
Charcoal 29 then screen the metal in and pump the stars.
Charcoal (80 mesh) 14
Sulfur 9
Titanium sponge 7
Dextrin 5


I believe that you need to ball mill everything except the Titanium. There used to be a video on youtube but it's gone. It was a beautiful effect.

[pyrotrev]

I've tried the cylinder shell approach, but it is important to get the thing in the correct orientation when it breaks for the best effect. The commercial horsetail shells I've seen were all weakly pasted (2...3 layers), some with holes punched in the hemis as well - I guess for pressure relief? It seems to be important to either have a shorter delay fuse (or stronger lift) so that the shell is still moving upwards when it breaks.

Edited by pyrotrev, 08 September 2011 - 12:36 PM.

[Karl Mitchell-Shead]

Had a close look at some 150mm horsetails we fired at Plymouth that had come back to ground, it was clear the hemi's were in 3 pieces (one complete half and another which had been slit all the way around half way up the second hemi) like this:

(Was going to upload a photo but apparently this forum cannot handle that only able to link to URL?????)

Heavily pasted around the equator and lower half of the shell but VERY lightly pasted around the top 'skull cap'

[martyn]

Thanks for all the replys.
The slit and lightly pasted technique sounds promising.
I wonder how they ensure the 'weak area' is uppermost when it breaks, ot perhaps it dosen't matter?
Did you notice if the stars were occupying the 'top' part of the shell, with the burst in the lower part - behind them so to speak, or were they arranged as usual?.
I wonder it is a problem ensuring fire transfer to light all stars if they are all crammed in at one end and the pasting deliberately weak?
I'll had to look up poka style, found this not sure I'm much wiser. The rest of the site looks quite interesting.
So many questions.

[Mortartube]

I've tried the cylinder shell approach, but it is important to get the thing in the correct orientation when it breaks for the best effect. The commercial horsetail shells I've seen were all weakly pasted (2...3 layers), some with holes punched in the hemis as well - I guess for pressure relief? It seems to be important to either have a shorter delay fuse (or stronger lift) so that the shell is still moving upwards when it breaks.

Try compressing some clay in the bottom of the shell to keep it nose up. This can help with orientation.

[Bonny]

Thanks for all the replys.
The slit and lightly pasted technique sounds promising.
I wonder how they ensure the 'weak area' is uppermost when it breaks, ot perhaps it dosen't matter?

Commercial horsetail shells break in random orientations. Gravity ensures the effect as the burst is weak so the stars fall out rather than being thrown out.

Try compressing some clay in the bottom of the shell to keep it nose up. This can help with orientation.

That would probably work best if you break the shell AFTER it has started to fall. I have also read that horsetails can be broken on the way up, by shorteneing the timefuse so they break slightly earlier.

[seymour]

I have some experience with horsetail shells which I can share. Obviously everyone has their way, and other people do it differently, but this has worked for me.

I cut the time fuse about two thirds the length I normally would for this size shell. This is because I want to shell to burst BEFORE apogee, to give it the... well "horse tail" form.

The timefuse is then sealed to the shell using the normal strong and glue method.

I load the shells hemmies COMPLETELY with stars. Obviously the stars used depend on the effect desired, but as a point of reference, the shell in the video I'll show used brocade stars sized for a 6" Brocade Crown. Formula was SIMILAR to Slow Gold.

In a 4" shell I add ten grams of "grater grain" - BP granulated similar to the screen method, but using a kitchen grater instead. This just sits between the stars. It's not much, but not much is needed.

After closing, I paste the shell minimally. Two or three layers, depending on the paper, sounds about right. In fact, so long as the timefuse-hemisphere join is well sealed by the glued string, you only need a strip around the equator, as long as your hemispheres are the ordinary chinese chipboard or stronger.

All the construction of the case of this shell is purely to make sure the shell withstands lift. Strength does not need to be nearly as high as it does when your burst symmetry and size is affected by it, so sealing the shell from leaks that can cause a premature explosion are by far your primary concern.

Finally, I over lift it.

Instead of playing with inert weights, and fancy pasting, I fill her right up (I'm not keen on shells having anything inert in them unless it's really necessary). The form of the effect is created utilizing the fact that as the shell is weakly burst at significant speed, the momentum of the contents is the most significant factor in determining the trajectory.

Angling the mortars and firing salvos looks fantastic, as anyone who's seen this effect can confirm I'm sure.



Skip to 26 secs.

This was lifted with 100g of relatively low quality BP.

Edited by seymour, 23 September 2011 - 10:55 PM.

[martyn]

Perfect - thanks for that Seymour

[Richard H]

(Was going to upload a photo but apparently this forum cannot handle that only able to link to URL?????)

At the current time this function is disabled. If the forum moves to it's own dedicated server then this will change. User uploads soon eat up disk space from experience.