Some of you that have followed me for a while might recognize this project as an upgraded version of my water bottle rocket launcher, seen in this video. While the old design was the cause of quite a few singed arm hairs, this new model is much more pleasant to use due to the new blast shield as well as the distance from the rockets that has been achieved by having the igniter on a longer leash. Even so, safety glasses are a required precaution, just in case.
I recently participated in leading some science based activities for grade school aged kids and these bottle launchers were a big hit. The kids had a lot of fun attaching craft foam fins onto the bottles with duct tape and hot glue. The launchers themselves only take about 20 minutes to put together, so it's a quick and easy project that offers a ton of entertainment.
The rockets are fueled by the combustion of rubbing alcohol, which is ignited by the spark from a barbecue igniter. I used rubbing alcohol with a concentration of about 90% in the video, but any concentration of 70% or greater should work just as well. When fueling the bottles, the most important step as shown in the video is to whip the last drops of liquid alcohol out the open end. This brings the fuel/air mixture to the proper level for a good combustion, and reduces the liquid alcohol particles expelled from the rocket upon launch that otherwise could melt the plastic blast shield or cause minor burns.
A neat trick I did not mention in the video is that once the bottles have been fueled, rather than pushing them onto the launcher the cap can be put back on the bottle to have it ready to fire later.
Parts for this project:
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