When the weather gets nice, a sprog's thoughts turn to rocketry. Photos of the first mission of the bottle-rocket season after the jump.
First, giving credit where credit is due: The rockets were built by our friends the Visiting Mathematicians who, with their sprogs Double Trouble, were picnicking with the Free-Ride family. We just got to share in the fruits of their awesomeness. The Visiting Mathematicians, in turn, credit Make Magazine as the source of the technological know-how. (There's an instructional video, too.)
T-10 minutes: On-site rocket assembly commences. Despite my urging, we did not, in the end, include the watermelon in the rocket payload. Note for future launches: park water fountains are ill-suited to fill bottle rockets.
T-5 minutes: The rocket is mounted on the launch pad. Launch angle set perpendicular to pad after we remembered that the three supporting lines ought to be 120 degrees from each other. Nearby picnickers seem relieved at launch angle.
What propels a bottle rocket, of course, is the release of water that is in the rocket at high pressure. The rocket is filled 30-50% with water. Then, on the launch pad, the rocket must be brought to about 70 psi. This takes a good deal of pumping.
Quite a lot of pumping. This is a good reason to bring a large flight crew for the launch. (Some members of our flight crew were larger than others.)
Seriously, 70 psi requires some muscle!
So, with all that pressure in the rocket, you need a mechanism to keep it from launching until you want it to launch. For this mission, the mechanism involved a release pin held in place by a small ring of PVC pipe. While the initial design put a pull-cord just on the PVC O-ring, a modification added a pull-cord to the circular part of the release pin. This is another good reason to have a large flight crew.
Ready to launch!
Note for future missions: A wee digital camera is not the best tool for documenting the flight path of a clear bottle rocket, especially when the sound of the launch makes the photographer jump. Witnesses noted the rocket shooting past the top of the tree pictured here.
I managed to snap a shot of the rocket during reentry (it's that whitish blob near the high tree branches on the left side of the frame).
The sprogs judged the mission successful, and their parental units concurred.
Sudden Death
I never guessed that the offspring were girls until I saw their shoes. This, in my mind, makes your kids even more remarkable for their love of all things gross and awesome. Way to counteract cultural programming! (Also I am totally jealous of the bottle rocket.)
That's an oddly shaped bottle in the last shot. Was there some effect of the sudden depressurisation through a confined nozzle which caused the plastic to deform?
I'm so building one of those.
Jess, that's why all the nieces get taken fishing. Also it tends to triple my, err, our limit.
Hey Dr Freeride
We had a second round of launches at a secret Santa Cruz proving ground with our crackerjack crew: Chief Linuxian BCboy, 40's starlet and guidance expert Hedy Lamarr, their crew of three rocket-retrieval sprogs, and launch director and chief documentarian MediaMike. The improved launch mechanism worked great, but we discovered a tendency for the hoses to break loose above 125psi. I'd strongly suggest that anyone who tries this at home not stint on the hose clamps: a faceful of sea water at 150psi is no fun!