Report On The Design Of Physoc Air Pressure Rocket

report on the design of physoc air pressure rocket the basic principle behind this type of rocket is reasonably simple. a bottle about a q

Report on the design of Physoc Air Pressure Rocket
The basic principle behind this type of rocket is reasonably simple. A
bottle about a quarter full of water has air pumped into it, then you
release the rocket and the water shots out the back giving you thrust
via Newton’s Third Law.
A primitive rocket (a 500ml cola bottle say) of this type is very easy
to build, but in order to allow safe launch of a larger rocket, we
need to build a more complicated system.
This launching mechanism basically consists of the connector and
nozzle from a normal common or garden hose. This is attached to a hose
pipe in the normal way. At the end of the hose pipe is a bicycle tyre
valve. This is attached to the pipe by using a jubilee clip to squash
the hose pipe onto it. The valve will also have some araladite on it
also. This is very tight and will not blow out at the pressure we will
put inside the bottle. A bicycle pump can be attached to this and this
is how we pressurise the bottle.
Next we use looped pieces of a strong string (possible bale twine or
garden string) that go up through another jubilee clip around the hose
connector and down outside it. The jubilee clip is then tightened. We
use three bits of string in a equilateral triangle shape. This ensures
that when we pull on the string to pull the hose connector down, the
force down is equally distributed around the connector. This is
important as if only one side where pulled down the rocket would
launch crooked.
This is then mounted on a plank of wood and a bamboo cane put along
side it. This plank of wood is then attached to the base. This is
shown in the third diagram. The base is there to make sure it doesn’t
fall over and also to make sure the plank with the launching mechanism
is pointing straight up.
The rocket is a 2l cola bottle with the bottle top glued into the hose
nozzle. I used Araladite (excuse spelling), this is a really strong
super glue that can be bought in any car shop. On the side of the
rocket there is something like a toilet roll tube that will go along
the bamboo cane making sure it goes up straight at the start anyway.
To help the stability of the rocket after launch we use a rounded nose
cone at the top, this makes it more aerodynamic, so the air flowing
pass it will be close to the ideal of laminar flows. This means we
don’t get turbulence which cause exert a horizontal force on the
rocket and send it sideways. Along with this the rocket has a
cylindical plastic sheet (the middle of a cola bottle) attached at the
bottom using long sticks (I used kebab sticks). This is supposed to
improve stability further, I believe it works in two ways. One it
lowers the centre of mass moving it closer to the centre of pressure
which is a good thing for stability and two it must change the air
flow along the side of rocket.
Altogether the rocket should be stable.
That’s how the rocket will be made and launched.
The most important thing is that the rocket launches straight up. The
base stops the launcher falling over. The hose connector is pulled
down by three strings making sure the rocket is released evenly. The
bamboo makes sure that the rocket is still pointing up after the first
few seconds when most of the water is being forced out. And the rocket
is designed that it stays vertical.
Using the strings the rocket can be launched from a safe distance, so
none of the physoc committee get hurt. The students watching will be
kept a good distance back (e.g if it were launched on the rugby pitch,
students would be kept on the paths either side. This can be done with
the help of the security guards), so when the rocket comes down (this
technically should be back on top of the launcher but with a small
wind it could be up to 10m radius around it I’d estimate. I will know
more when I test it this weekend).
So in conclusion, I cannot see how anyone can be injured during the
launches (2 most likely but 4 max). Of course any suggestions are most
welcome and I will be happy to talk further will the college safety
officials.
Peter Elliott
PRO, DU Physoc
SSTP