18 replies to this topic

[Mortartube]

Yellow igniter cord burnt around an inch per second from memory. It had a copper wire core which was surrounded by composition. This copper wire transferred heat from the flame front to control the burn rate.

The whole lot was covered in a yellowish/green plastic sheath which rendered it waterproof. It produced quite a large hot flame which would ignite a small rocket core very easily.

ICI ceased production in the last few years.

Here's a picture of some, you can see the wire, composition and plastic sheath. Being wire cored, it was easily bent over and would hold itself in a rocket. It did light easily from touchpaper.

http://www.yorkshire.../user/PIC_s.jpg

There was also a brown gunpowder based version with no copper wire, this was the fast PIC, about 8 inches a second and a blue version which was very slow, probably around 0.25 inches a second. I never had call to use the blue.

PIC was originally designed for blasting and special detonators were available that had the back part open. You put the end of the pic in this opening and taped it in. The PIC lit a delay compositon which then set off the detonator.

For use on shell racks etc special connectors called beanhole connectors were available. They were designed so that visco could be lit end on reliably with PIC. Malcolm Armstrong at TPL used to sell them.

Crimped chokes are an easy form of construction if you have a crimping machine (which looks like an iris in a camera lens. Lots of plates close down around the tube when you pull a handle). Crimped chokes are often less accurate than a clay choke, because the tubes are often still damp with glue so they can be crimped more easily. The choke can shrink as the tube finally dries.

Another method of choking tubes without a crimping machine is to use a wire, like a thick guitar string for instance and make a loop in it around the tube to be crimped. Put a drift the size of the choke hole in the tube and pull the wire tight. The tube needs to be damp to do this by hand or it will be impossible to do and probably it would also tear.

Edited by Mortartube, 20 July 2008 - 05:23 PM.

[maxman]

Mmm sounds like the crimped nozzle would of made unreliable or rockets of variable performance if some tubes shrank more than others. Is there any reasons that core burners are no longer sold? I assume its down to cost again is it? I found a picture of a Standard rocket with some PIC hanging out Here I can't really remeber much detail about these rockets from my youth except I could only afford the smaller ones. Did these rockets have a slower take off than ones sold today? (preasure build up) I made some 4oz ones recently with 80/20 meal/C but they were too fast to enjoy when fused with blackmatch up the core but with just visco shoved in a short way up the core, some were fast and others much slower with the same comp batch hence my original questions regarding fusing core burners.

[BrightStar]

Is there any reasons that core burners are no longer sold? I assume its down to cost again is it?

I'm guessing that it's simply economics. My traditional 7.5" long 1lb core burners only take 40g of composition - there's a lot of empty space. They're not too fussy on charcoal quality or tube strength and can be reliably rammed by hand.

Given repeatable machine mixing and pressing and stronger plastic tubes, I suppose an end burner is more practical. The Estes 'D' engine is probably the refinement of this design.

Re ignition, I was surprised to read about the use of PIC until I thought a bit further. From experience, the greatest risk when fusing BP rockets is that the partially burnt remnants of the fuse will compress in to a ball and block the nozzle as the motor fires. This usually causes catos when I try to use 'visquick' etc. A hooked strand of 1.8mm slow visco works fine. Although the PIC will leave a strand of copper wire behind, it seems unlikely that this will completely clog the nozzle.

Having said that, I have a BP cluster rocket on the drawing board, so if anyone has a reliable method of igniting BP core burners instantly without risk of cato please let me know!

[sui]

@Brightstar

I had very good luck with just a pinch of granulated bp in the core along with the fuse. I normaly use this methode only for hard to light motors like the colored MgAl rockets,but then again .., i use fine Ti around 40 micron in that pinch of bp. It never failed me on these motors and with normal bp coreburners bp is all it needs. To keep the bp from falling out of the core i just push some wadding around the fuse and let the granulated bp do its thing. The Wadding get pushed out very relyable. So waht do you think ?

Regards

Sui