Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 65 users online :: 4 registered, 1 hidden and 60 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

A question about chamber length

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
Sponsored 
  • Author
    Message

A question about chamber length

Unread postAuthor: elad311 » Mon Nov 17, 2008 9:52 am

Is it ok to use a 2" dia 36" length PVC,
or a 4" dia 18" length PVC as a chamber, because
I can't find any PVCs with a bigger diameter than 3".so.. will the long
2" work good as the short 4"?
  • 0

User avatar
elad311
Sergeant
Sergeant
 
Posts: 94
Joined: Sat Oct 04, 2008 7:48 am
Reputation: 0

Re: A question about chamber length

Unread postAuthor: Ragnarok » Mon Nov 17, 2008 10:16 am

What you're not seeing here is that volume is proportional to the square of the diameter of the pipe. As such, each inch of 4" diameter pipe has the same volume as 4 inches of 2" diameter pipe.

Remembering this, the 36" long 2" ID pipe only holds half the air of the 18" long 4" ID pipe, despite being twice as long, and thus the cannon will only be able to support half the length of barrel.

For a combustion cannon, I wouldn't normally recommend a long thin chamber as it slows burn rates and hampers fuel mixing.
For a pneumatic, it's quite another matter, and in this case, I would almost certainly recommend a longer and thinner chamber, sometimes at the expense of overall chamber volume, as there will be less flow restriction at any reducing bushings/parts.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: starman » Mon Nov 17, 2008 10:20 am

Actually, 9" of 4" PVC = 36" of 2" PVC or = roughly 18" of 3" PVC. Use for pneumatic chamber would be fine. I wouldn't try to use a 36" x 2" pipe as a combustion chamber.

You can always just do the volume math for a cylinder to find these things out for yourself.

V = pi * Radius * Radius * Length. Be sure to use the inside dimension of your pipe.
  • 0

User avatar
starman
Donating Moderator
Donating Moderator
 
Posts: 3041
Joined: Wed Dec 12, 2007 12:45 am
Location: Simpsonville, SC
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Mon Nov 17, 2008 10:53 am

Apparently the perfect chamber would be a sphere, however this is an impractical shape so it would seem that the ideal is to have chamber that is as long as its diameter.

This is to say that a 4" diameter chamber 4" long is better than a 2" diameter chamber 16" long, even though they have the same volume.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: psycix » Mon Nov 17, 2008 2:04 pm

Jack, you are completely correct, UNLESS someone is using more then 1 sparkgap.
When using multiple evenly spaced spark gaps, your chamber may be longer then its diameter: theoretically the optimal length is the amount of spark gaps times the diameter.
  • 0

Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

Spudfiles steam group, join!
User avatar
psycix
Donating Member
Donating Member
 
Posts: 3684
Joined: Mon Jun 25, 2007 7:12 am
Location: The Netherlands
Reputation: 0

Return to Combustion Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'