By Bill Kuhl
http://www.scienceguy.org
How it Works
An air-powered rocket is a rocket propelled upward by a blast of air.
No propulsion comes from the rocket as in a solid fuel rocket or water
rocket. Air is forced into a chamber that is a tube that the rocket slides
over. The pressure of the gas which is air, becomes much higher but
the volume is the same in the chamber. This forces the rocket upward.
The blast of air comes from another chamber that is quickly
compressed by stepping on it with your foot or feet.
The inspiration of the idea to
build this project came from a
rocket I purchased at a hobby
shop.
Building My First Rocket
I looked at the store-bought rocket and tried to think of materials that I could
use to build a rocket that was safe, light, and cheap. Foam pipe insulation
would fit over 1/2” PVC pipe, would be relatively light and absorb shock. A
ping pong ball cut in half would fit over the insulation, this would be light,
strong and not pointed. Cardboard could be for the fins and easily trimmed
with a scissors to experiment with different areas. Packing tape covered
the rocket for stiffness and to make it easier to attach the fins.
About the Construction
This project is so simple that I really do not think detailed construction
plans and article are needed. I would rather share ideas of how I
approached the project, some concerns, and where to find materials
needed. The educational value of this project would also be greater if
more creativity were used in the construction.
What Are the Basics?
Only a launcher and rockets are needed.
The launcher consists of a base to hold a tube vertical that the rocket will
slide on during the launch. I created a simple X-shape base structure
from strips of lumber. The PVC pipe was fastened to the base structure
with a cable tie that went around two wooden dowels that went partially
into the X-structure through holes drilled in the wood.
An “air bladder” is connected to PVC pipe with clear plastic tubing. The
air bladder is the portion of the project that I spent considerable time
experimenting with.
Safety Concerns
•The rocket leaves the launcher at a high velocity so it is important that no
one is hit with a rocket.
•There should be nothing sharp on the nose of the rocket.
•The rockets are light in weight thus relatively low in kinetic energy, but
getting hit in the eye with anything is dangerous.
•Stomping on the air bladder with one foot should be relatively safe but
jumping on the air bladder with both feet there is a danger of stumbling or
spraining an ankle.
Building a Launcher
The base for the launcher was built from some cheap lumber that
was leftover from home repair project.
PVC pipe is
relatively
inexpensive and
found at a lumber
or hardware store.
I just pressed the
pieces together but
you could certainly
cement the pipes
and elbow
together.
Holes were drilled through the base and then dowels were glued
into the base. Plastic tie wraps held down the PVC pipe.
This is Prototype #1 with 2-liter bottle for air chamber and a rocket
made from foam pipe insulation, a ping pong ball, and cardboard.
The 2-liter soda bottle was badly crushed after just a few
launches.
I am examining the crushed bottle,
what is needed is an air chamber
that has “elasticity”. That is the
physical property of a material to
return to its original shape after the
external force that made it deform
is removed. The external force in
this case is my feet jumping down
on the air chamber.
Prototype air chamber #2 made from heavy plastic shipping bag,
foam rubber and tape.
A couple of jumps on the bag blew out one side.
A science teacher friend had suggested a boat fender might work well
for the air chamber, and he was right. Cost was the only issue if
everyone in a group is building a launcher. On sale this fender cost
$6, normally it was close to $10.
I noticed the word “vinyl” on the label referring to the plastic
the fender was made of. This prompted me to do further
research into this material that worked so well for this
application.
The new air bladder is in place, it worked well but I kept wishing
to increase the altitude of the rocket. My approach to that was
to trying to change the air bladder hoping for greater altitude on
the rocket.
I tried a larger boat fender hoping for more altitude. It would be my
estimation that altitude might be only slightly higher, the smaller
unit appears to be a better value.
How I Attached the Tubing
At the spot where there is a small valve is where I drill a hole for
the tubing.
Plastic fitting is used to attach clear plastic tubing.
I used a hole saw drill bit to drill ¾” hole. Hole saw bits have
a round steel cylinder with saw teeth that are used for
cutting holes larger than drill bits that would normally fit in a
drill.
I wrapped the plastic insert with tape for a tighter fit and then used
hot glue to seal up the hole.
The clear plastic tubing needed a little stretching to slip on to
the plastic insert.
On the larger boat fender I used a longer length of the plastic tubing
which is a good idea to get the launcher further away when
launching.
More About Vinyl and Elasticity
The vinyl boat fender had good properties of elasticity. This means it has
the property to restore to its original shape after distortion. In this case it
is from stepping down on the fender with a foot that does the distortion.
Vinyl can be formed to be flexible or rigid depending on the ingredients
mixed with the vinyl resin. The vinyl record pictured below is very rigid.
Suggested Activity: to learn
more about elasticity research
Hooke’s Law.
Experimenting With Different Air Bladders
I was hoping to build a cheaper launcher so I attempted to build the
“air chamber”. This worked for a time but after repeated jumping
on the chamber leaks would develop.
This is how I built an air chamber using foam rubber, heavy plastic,
tape, and cloth. The cloth was to keep the plastic from ripping open.
Combining materials is the basis for composite construction.
Plastic was sealed together with duct tape, multiple layers of
plastic might have been more effective to sealing all leaks.
Cloth kept the plastic from ripping open, even when jumping on the air
chamber but there were still small air leaks detected.
I taped a board to the top of the bladder thinking it would more
completely press down on the air chamber.
Completed air chamber connected to the launcher.
Another Approach to the Air Bladder
I tried a plunger that used a “bellows” chamber which was not
enough pressure when holding it with one hand and pressing down
with the other hand. This got me thinking about how the bottom
section could be held and then you could push down with two
hands using upper body strength.
Wastebasket with
holes drilled for
bottom of the plunger
and an outlet for
clear tubing made a
good base.
Pushing down on the
top of the plunger
with two hands gave
a launch of good
height but not
wonderful height.
I replaced the half ping pong
ball with half a foam ball that I
found in a sporting goods store.
The ping pong ball was starting
to crack after hitting hard
surfaces many times. The
plastic would be fine if you only
launched over grass.
New Approach to Building the Rocket – Paper Rockets
A few of the first paper rockets I constructed.
New Approach
I decided to take a new approach to increasing the launch height and change
the rocket instead of the launcher. From heavy paper I created a rocket by
wrapping the paper around the launcher tube and taping. Paper fins were
taped to the bottom of the rocket. The nose of the rocket was created by
slitting the paper tube and putting more masking tape on the top of the tube.
I took it outside for some quick tests and it was
obvious that the launch height was much greater
than the foam rocket. This rocket weighs only
half as much and is much thinner also. After
launching repeatedly the paper rocket over a
hard surface, the paper tube was showing signs
of buckling.
Paper Rocket left 7 grams foam rocket 13 grams.
Color card stock paper held the round shape where it goes onto
the launch tube. Newspaper and magazine paper started to shift.
Launching the Rocket
Launching the rocket is so simple. First make sure the air bladder
has expanded back, then place the rocket over the launch tube.
Normally the boat fender air bladder comes back to shape rather
quickly, but if it is still partially deflated when the rocket is placed
over the PVC tube, the altitude will be much less.
It is safer for the person launching and easier on the rockets to
launch from a softer surface such as grass. Stepping down on the
air bladder with just one foot is safer then jumping down with both
feet as there is a chance of slipping on the air bladder.
The flight path of the rocket will normally be an arc. The highest
point in the flight is known as the “apogee”.
This is the paper I used, it will be found with office
supplies.
Building the Rocket Body Tube
Half sheet of bond paper is wrapped around ½” PVC pipe. Wrap the
paper carefully as it is rather stiff and tends to wrinkle.
Keep working the paper tightly around the tube.
The bond paper tends to wrinkle in places, so it helps to rub the
paper as it rolls around the tube.
It will be easier to tape the rolled tube with sections of tape
instead of one long piece of tape.
Completed
paper tube.
Fins at the bottom of the rocket help give the rocket stability, that is
keep it moving in a straight path. A straight flight path is more efficient
and the rocket will achieve a higher altitude. Fins can be made from the
card stock paper, tabs are bent in the paper and the fins are taped to
the body tube.
Most of the rockets I have constructed utilized three fins spaced evenly
around the body tube. I did build one rocket with only two fins that did
appear slightly less stable during launch . For an experiment I launched
one rocket with no fins, it did not get very high and tumbled to the
ground.
I draw one pattern for a fin on card stock paper with extra
material for support tabs.
After cutting out the first fin, I trace around it for the other fins,
normally I use three fins.
Use a straight edge to create the fold in the paper for the tabs.
Work the paper over until you have a nice 90 degree bend.
Cut slits in the section of paper that was bent up.
Bend half the tabs to the other side. Looking straight down
at the fin it should look like this.
I apply the tape to the tabs and then place everything on the
body tube at once, maybe another method will work better for
you.
Press the tabs and tape to the body tube making sure
the fin is pointing straight and that the fins are spaced
evenly around the body tube.
This was an
experiment in using
only two fins instead of
three.
Launching a rocket with
no fins tumbles on the
way down. The rocket
does not get very high
either due to unstable
flight path.
Without a shocking absorbing nose, the rocket tube will begin to
buckle when it hits a hard surface.
Parts used to make “shock-absorbing” nose. Plastic from a
bag is crumpled up for the padding and two layers of the
same plastic cover it to make a dome shape.
Cover the top end of the body tube with tape to keep the padding
from being pushed down farther into the body tube.
With the two layers of the plastic stacked together, press the
plastic wad into the center.
Work the plastic wad and the plastic covering on top of
the tape ledge so that it make a nice dome shape.
Then tape the plastic covering to the body tube.
The Nose of the Rocket
The finished nose should look like this.
Completed rocket ready
for launch.
With only single layer of plastic, nose came apart.
Space Shuttle
I tried to make a rocket that looked like a space shuttle using white
paper and foam plate material.
The space shuttle on the launch pad. The altitude obtained
was pretty good but not as high as lighter rockets with less
drag.
Space Shuttle coming down at steep angle, it never really
glided on the return trip.
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