2nd Cannon

removed · Tue Jun 20, 2006 2:54 am

Hey all.
I built my first combustion cannon a while ago and over time and with several problems it turned out to be quite good. It's reached the stage where where its just as easy/fun to build a new one rather than make futher improvements.
I'm fairly constrained by materials in NZ am stuck with what I think you guys call 4" pipe (~11cm) for the chamber and 2" pipe (~6.5cm) for the barrel.
Could someone please explain the C:B ratio thing to me and suggest appropriate lengths?
Also, just outta curiousity, are different electrodes for BBQ igniters any better? Eg: copper screws rather than steel or something.
Any ideas on what else I can with a simple(ish) combustion to make it more interesting?
Thanks!

rna_duelers · Tue Jun 20, 2006 5:38 am

Try a chamber fan,they are said to increase power by upto 60% and they are cheap if you ask and bargain to a computer guy about a old one they are dirt cheap and the C:B ratio is the ratio of the barrel to chamber so if you have a volume of 1.5L chamber the best size barrel to use has a volume of 1L.And the easyerst way to measure the volume is with water and measuring jugs.

Shrimphead · Tue Jun 20, 2006 12:18 pm

You are correct about the chamber fans rna, but you also have to realize that the optimal c:b ratio depends on what fuel you are using. The optimal ratio for propane is .6-.8:1. I think though, that 1.5:1 may be a good general rule for aerosols. But I'm not sure on that.

frogy · Tue Jun 20, 2006 1:14 pm

A chamber to barrel ratio is a simple thing really...

If the volume of your Chamber is 5 L (About 63.5 cm long peice of 4" Pipe)
You divide 5 L by 1.5 you get 3.3333, so your barrel should be 3.333 L in volume if your chamber is 5 L in volume...

To get a barrel to be 3.3333 L in volume made out of 2" pipe it needs to be about 164.5 cm long.