Flying model rockets is a relatively
safe
and inexpensive way for students
to learn the basics of forces and the
response
of a vehicle to external forces.
A model rocket is subjected to
four forces in flight;
weight,
thrust, and the
aerodynamic forces,
lift and drag.
There are many different types of model rockets. One of the first and
simplest type of rocket that
a student encounters is the bottle, or water rocket.
The water rocket system consists of two main parts, the launcher and the rocket.
On the figure we show a generic launcher, although launchers come in a
wide variety of shapes and sizes. The launcher has a base to support
the rocket during launch. A hollow launch tube is mounted perpendicular
to the base and is inserted into the base of the rocket
before launch. The launch tube is connected to an air pump by
a hollow feeder line. The pump is used to pressurize the inside of the
body tube to provide
thrust
for the rocket. We have attached a pressure gage to the feeder line to
display the change in pressure in the system.
This part of the system is very similar to the simple
compressed air rocket.
The other part of the water rocket system is the rocket itself.
Usually the rocket is made from a 2-liter soda pop bottle.
Before launch, the bottle is filled with some amount of water, which acts
as the "propellant" for the launch. Since water is
about 100 times heavier than air, the expelled water produces more thrust
than compressed air alone.
The base of the bottle is only slightly larger than the launch tube.
When the rocket is placed on the launch tube,
the body tube becomes a closed pressure vessel.
The pressure inside the body tube equals the pressure produced by the air pump.
Fins are attached to the bottom of the body tube to provide
stability
during the flight.
The
flight
of a water rocket is similar to the flight of a
compressed air rocket with one
important exception. The mass of the bottle rocket varies during the
flight because of the exhausting water plume.
There are
equations
which have been developed for
full scale
rockets that account for this loss of mass.
You can study the flight of a bottle rocket by using the
RocketModeler III
flight simulator. Because of the popularity of bottle rockets,
we have an entire section of this web site devoted to
water rockets.
Guided Tours
-
Types of Rockets:
-
Water Rocket:
Activities:
Educator Section: Grade 6-10
Related Sites:
Water Rockets
Rocket Index
Rocket Home
Beginner's Guide Home
