Difference between revisions of "Chamber to barrel ratio"

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The C:B ratio of [[pneumatic cannon]]s is much less fixed, since factors like air pressure and valve performance play a greater part in determining overall performance. It is adviceable to use [[GGDT]] to determine the best design for pneumatic cannons.
 
The C:B ratio of [[pneumatic cannon]]s is much less fixed, since factors like air pressure and valve performance play a greater part in determining overall performance. It is adviceable to use [[GGDT]] to determine the best design for pneumatic cannons.
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[[category:Concepts]]

Revision as of 11:54, 15 April 2007

The chamber to barrel ratio, or C:B ratio, is the volume ratio between the chamber and barrel. The ratio determines how much of the available energy is transferred to the projectile, and a good C:B ratio is a major factor in combustion cannon performance. The goal of an optimal ratio is to have the barrel end at the exact point where the projectile stops accelerating.

Higher ratio cannons are louder, since more energy is wasted as noise when the projectile exits the barrel. Too low a ratio will hurt performance, since a vacuum is formed behind the projectile when the combusiton product cool. In extreme cases, it may even be sucked back into the chamber. [1]

Experiments have shown that a C:B ratio of about 0.6-0.8:1 is the most efficient for a given chamber. The ratio will vary somewhat depending on the weignt, friction and blowby of a certain projectile, but it's in that area for most common projectiles.

This does not neccessarily mean that the most efficient ratio is the best to use in a gun, if maximum power is the goal. If the chamber is designed around a certain barrel, a bigger than optimal chamber will give more power since more energy is available. When designing a barrel for a certain chamber though, one near the optimal ratio will make the most of the energy available in the chamber.

In short, C:B ratios are good for determining what barrel is most powerful for a certain chamber, but not what chamber is most powerful for a certain barrel. A near optimal C:B ratio is always good however, if the goal is reduced noise and/or fuel efficiency.

Burst disks can be used to increase the performance of high ratio cannons, since they let higher pressure build up before the projectile starts to move. They will not increase the performance in near optimal cannons. Source

The C:B ratio of pneumatic cannons is much less fixed, since factors like air pressure and valve performance play a greater part in determining overall performance. It is adviceable to use GGDT to determine the best design for pneumatic cannons.