Burst Testing With Berggren & Youens

Robert Youens

Bruce Berggren and I have been working with the National Association of Rocketry (NAR) to create a Water Rocket Safety Code. The results of our Burst Testing will be presented to the NAR to assist them in its development. Though our intial results are interesting, it is likely that additional testing will be needed before the WRSC can be completed.

This is the basic setup. We set up a test launcher on an abandond airport runway located north of Austin, TX, United States. Bruce built a series of 2 and 3 liter soda bottles with 10 fins evenly placed about the bottle. Fins were made from CD Discs. The material is dense and will shatter. We figured that these fins are a worst case because the fins could be thrown a long distance due to the high density of the material.

This is a view to the south down the length of the runway. The wind was variable from the south, and east. Wind velocity during the first few tests was east at less than 5 mph and increased to about 10 mph from the southeast during our latter tests. We marked the pavement every 5 feet from the launcher and made circles around the launcher at 20 and 30 feet.

Bruce documented the entire process with a video recorder. Each burst was recorded at various distances and zoom. We also did a video of the runway around the launcher demonstrating the fragement pattern of the bursts. Bruce got some incredible close video of the bottles as they burst. You could see the stretching and deformation of the bottle as pressure was increased. In the video taken a little further away, you got a good look at the dispersement pattern as the fins and bottle pieces left the launcher.

This is a picture of our pressurization rig. We pressurized with CO2 and slowly increase pressure until burst. We called out the launch pressures so they could be heard on the video. Bruce and I remained behind his car during pressurization.

Burst pressure ranged from a low of 140 psi on one of the 3 liter bottles up to 180 psi on one of the 2 liter bottles. We circled the fragments on the pavement and recorded the results. We were amazed to find fin fragments up to 81 feet from the launcher. The vast majority of fragments were found between 20 and 30 feet from the launcher. It is too early to draw conclusions from the results since we have not done a detailed analysis. It is likely that wind and other factors played a significant role in the results.