Agreed, the butterflies don't rotate. They have a mild comp with lots of titanium and not much propulsive force, and two holes opposite each other at the center point. The second video definitely shows these. I'm not sure about the first video, as those seem to be spinning, but I think they're hummers not tourbillons because they're spinning on the long axis.
Here's a butterfly insert, by (I think) Vulcan Fireworks. It would look exactly like the inserts in video 2 when lit. The tube is parallel wound (but not very good quality), 11mm ID, 2mm wall, 65mm long. The powder core inside is about 50mm long and the ends have paper plugs, glued in, indicating that it doesn't expect to have to hold much pressure. The grid on the paper is 5mm. I didn't make this so I don't know the composition, but I've made similar inserts and I would guess 60% KNO3, 20% charcoal, 10% sulfur, 10% fine titanium for a first try. Ram or press it solid like a rocket.
I think there is a definite difference between butterflies (farfalle) and tourbillions - the former have 2 opposed nozzles which gives a thicker (2x) trail and a straighter trajectory as there's little overall propulsive effect.
Edited by Peret, 16 July 2014 - 07:39 AM.
