A friend asked me to help
with his daughter’s science project. Of
course was my answer even before asking what the topic/subject was.
At least they didn’t
disallow a hand pump so I immediately started thinking about a compressed air
pumped rocket ‘engine’. Remembering coke
bottle rockets (2L bottles and a foot pump), I tried
to assemble a combination of easily available parts to make the power source.
A bicycle pump was a good
starting point. Complete with a pressure
gauge (alibi not very accurate), Home Depot supplied a pump for $7.00. It has a clip on fitting for the standard
tire valve which is nice because it provides a release mechanism (flip the
level and wiggle the fitting to launch.
Fitting the 2L bottle with a
tire valve turned out to be easier than expected. I bored a 7/16 hole through the cap and then
fitted a standard replacement tire valve from the auto parts store. The standard auto tire valve fits into a .453
inch hole which is close enough to 7/16 to fit just fine. Plastic is more forgiving than metal tire
rims. Don’t forget to unscrew and discard the valve stem otherwise the air
can’t escape!
The engine when pumped to
20# was able to send a plastic panel with 4 casters across the room. It was tried using water (half full) and a
dip tube. The launcher (person) got very
wet and the ‘car’ went way up the driveway.
Such a simple rocket engine
when under $20 (including pump) and I’m sure you can find many school projects
to power.