6-liter pop bottle rocket
Among the simplest rockets to build is the 2-liter pop
bottle with some fins and weighted nose cone. The longest lasting
rocket of mine is made from 3 2-liter bottles
connected
with
Robinson Couplers. That is, the bottles are connected together
with hollow, threaded lamp rod, with O-rings and washers to seal them
air-tight. The bottom (opposite nozzle end) of the lowest bottle is
connected to a bottle-cap. Select a washer size that is small enough
diameter so the second bottle can just screw onto this lid. The top
bottle is connected to the second bottle in the same manner. One nice
thing about this arrangement is that if the rocket ever lawn darts with no
parachute, it usually just crumples the topmost bottle. No problem
just unscrew and toss it, and screw a new one in place. Very easy.
I believe a 3-section rocket of this type is ideal. The lower section
gets filled with water and the top 2 are pressurized. Be sure to get
any water out of middle section before pressurizing rocket or the rocket
will have a very short flight - water does not go through the coupler
quickly enough during "the burn".
At the top of the rocket is a
separate payload section made from another bottle. It has room for the
"passenger" as well as
horizontal parachute
deployment system with Tomy timer. Robert Youen's
gets
credit for this (as far as I'm aware). The
right photo shows a loaded chute. This was my deployment system of
this type - Not too pretty with all the strapping tape and rubber bands, but
it works very reliably. I preload the timer with 1 full turn before
inserted the small eye-screw attached to the end of the rubber band.
It gets 3/4 of a turn more with the rubber band attached, and it is held in
place by the wooden trigger. This wooden trigger is connected to the
launcher with fishing line. When the rocket takes off, the trigger is
pulled and timer starts - delay is about 3 - 3.5 seconds before the rubber
band comes loose, unwinds rapidly and the chute is ejected out the side.
The 16" chute is made from a plastic garbage bag, cotton string for
parachute shrouds, and there is an elastic shock cord connecting the chute
to the top bottle cap. The holes in the chute, where shrouds are
connected, are reinforced with a bit of strapping tape on each one.
This rocket is a real crowd pleaser. While it doesn't
go as high as the FTC rockets, it sounds really cool, and is powerful.
