On recommendation of a co-worker, recently ordered the Skylab Water Rocket kit from Anti-Gravity Research. Got around to assembling it on a beautiful June day, accompanied by Miles and one of his friends. Downloadable instructions were super detailed with great pictures. Hardest part, of course, was finding a 2-liter pop bottle (who goes through that much soda, anyway?) I took a nip, and the rest went down the drain. The rest of the build was straightforward – snip off the retainer ring near the neck, attach the bumper with rubber bands (included), assemble the fins, and attach the guide tube (which slides over a stick to ensure a true vertical launch).
The included fins were really my only complaint about the kit – they’re finicky to put together, and they pop off on impact with every flight. Covered in soapy water, they get slippery, which makes putting them back together even more of a noodle. Have written the company asking why they don’t do a one-piece fin assembly.
Put about 1/2″ of “fuel” (water with 10% dishwashing soap for an extra fizzy vapor trail) into the bottle, attach the high-thrust bottle cap adapter, slip on the fin assembly, and insert the air pressure nozzle. For safety, the kit comes with a 20-foot connector hose, which runs to an ordinary bicycle pump. Start jacking! Immediately, the soapy water creates a foam visible inside the bottle. A few strokes later, the bottle is bulging with pressurized foam.
Pardon the bouncing camera as I was pumping with one hand and shooting with the other. Feel the expectation in the air? Love the kids’ commentary.
It’s impossible to know exactly when it’s going to go off – basically whenever the pressure-fit nozzle can no longer withstand the pressure of the foam. But when it does, holy mother of pearl! If I had to guess, I’d say the rocket flew between 100 and 125 straight into the air, majestic!
The 8-year-olds I was with weren’t able to pump hard enough to get it going so that remained a grown up job, but they were fully involved in the rest of the process, and love love loved it.
Update: I corresponded with Ken at Anti-Gravity, who saw this post and responded:
You estimated that the rocket had flown 100 to 125 feet up. If you pump quickly, the rocket will usually keep hanging on until about 60 or 70 pumps, and if the rocket has enough water in it (at these higher pressures it can carry up much more water without tipping over) the rocket can reach 400 feet altitude or more. In our development tests, using a high-strength bottle, the SkyLab has reached an altitude of 570 feet.