Water Rockets are great fun for kids of all ages. They are cheap to make, fun to launch and you might even learn a thing or two. It is especially rewarding if the rocket is safe, durable and can be used again and again. This water rocket is a design we came up with for the kids in our 4H club.
One of the unique features about this rocket is its flight characteristics. We use a section of hollow swimming noodle for the nose. This allows us to fill the nose with water to shift the center of gravity to the front of the rocket. When the rocket reaches its apogee it turns over and dumps out the water. The center of gravity is now changed so the rocket comes down sideways, using the area of the bottle and fins to slow the rocket decent. It flies up like a missile and comes down like a leaf. (A Heavy Leaf) The foam nose can also absorb an impact if it does come down like a dart. It won't put a dent in the car roof!
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Step 1: Materials and Tools
To build this rocket you will need
2- 2 liter bottles with the labels removed
1- Salad dressing bottle. The best bottles to use do not have the stiffening ribs molded into the large flat surfaces.
1- Foam swimming noodle with the hole in the center
Goop Brand Glue. This can be Shoe Goop, Plumbers Goop, RV Goop, any type they make. It all works fine.
Black vinyl electrical tape
Flexible measuring tape
Box knife or sharp pocket knife
A Rocket holder - this is simply a small board with a bottle cap glued and screwed onto it. We will use it to hold the rocket vertical while building it
Parts for a tool to make a nicely shaped nose you will need
1/2" PVC pipe
5/16 x 3 or 4" carriage bolt, 2 nuts and a flat washer
5 minute epoxy
A sheet of 80 grit and 150 grit sandpaper
Step 2: Make the Fins
Clean the Bottle
To remove the label from the dressing bottle, put some warm soapy water in the sink or a bucket. Fill the bottle with warm water and submerge it in the soapy water. In about 10 minutes the label will simply float off. Use some Goo Gone to clean up any glue residue.
Layout the Fins
I use a piece of cardboard from a cereal box to make a template. The shape I used for these fins was a retro style curved fin. I was able to follow the shape of the bottle and use the curve. I made the template so I could get two fins out of each side of the bottle. Trace around the template and begin to cut the fins. One thing I do is to cut them outside the line to start. Once I get the rough shape cut out, I trim it to the line and final size. I traced around the perimeter with a marker so I could see them better. The fins may have a slight curve and not be perfectly flat. That is OK. Bend them as flat as you can but don't worry if they are not perfect. A little curve or waver will not hurt anything. I was able to get 4 fins out of one bottle.
Step 3: Mark the Bottle for the Fins
The next step is to mark the bottle for the Fins. I measure the circumference of the bottle and divide by 4. In this case the bottle was 345mm. Divide that by 4 and it equals 86.2mm.
Next find one of the mold lines. Mold Lines run vertically on each side of the bottle across from each other. They are great to use as guidelines because they run straight and true. Put a box or something about 1/2 the diameter of the bottle next to the bottle and use it as a straight edge. Make a Sharpie line on one of the mold lines. This line should run 1/3 the length of the bottle at the nozzle / open end. Measure 86mm (1/4 the circumference) from this mold line and make a mark. Line this mark up with your guide box and make a Sharpie line down the bottle. Mark the opposite mold line using the box and sharpie and again measure 86mm from this 2nd line and mark a line. Your bottle should have 4 equally spaced lines drawn on the bottom half of your rocket bottle.
I make a mounting board by taking a bottle cap and screwing it fast to a board and securing it with Goop Glue.
Mount the bottle on the board Take one of the fins and put it up along the bottle and eyeball a nice height for the fin. The bottom of the fin should not interfere with whatever launcher you are using. When you are satisfied with the location, mark the top of the fin
Measure from the mounting board to your mark.
Use this same measurement and mark all the other fin locations. This will insure our fins are at the same height on the rocket.
Step 4: Attach the Fins (Step 1)
Take some 3/4" wide electrical tape and cut 1 1/4 long strips. The initial strips were 3/4 x 1 1/4. I then cut these into 1/4"wide by 1 1/4 long strips. You will need 12 skinny strips of tape for 4 fins.
Put two strips of tape on one side of the fin where it will attach to the bottle. Lay the fin flat against the bottle, line the top of the fin with your mark you made earlier, lay the edge of the fin on the line and tape it in place. (Fig 1)
Fold the hinge, using the tape you just put on as a hinge, place another piece of tape on the other side of fin, located in the center of the fin. (Fig 2) Do this for all four fins
Fig 3 shows the fin held on with the strips of tape. The purpose of the tape is to temporarily hold the fin in place while glue is applied. The fin should be held tightly against the bottle with a minimal gap between the bottle and the fin. It may take a little practice to tape it correctly.
Take a strip of scrap salad dressing bottle or Popsicle stick and put on a dab of Goop Glue about the size of a chocolate chip. (Fig 4)
Put a dab of glue in 3 places on the fin. One opposite the single piece of tape in the center of the fin and two dabs on the other side across from the top and bottom strips of tape. The purpose of this glue is to hold the fin in place until we can completely glue it.
Step 5: Attach the Fins (Step 2)
Now we have to align the fins. Look down the top of the rocket and make sure the fin is at a right angle to the rocket. You can eyeball this. It does not have to be perfect, but the closer and straighter you get it, the better it will fly. I used a AA battery on each side of the fin to hold it in place until the glue sets.
Once the Glue is set (At least 3 or 4 hours) Remove the tape. The glue is now holding the fin in place.
Now the fins need to be glued solidly in place. Put a fillet of glue between the body of the rocket and the fin. Do this on each side of the fin. This bead of glue should be at least 1/4 inch wide. Set it aide and allow it to dry for at least 12 hours before using it.
Step 6: Nose Cone Mandrel
There is a easy way to make a nice, symmetrical nose cone. Make a Mandrel out of a piece of 1/2 PVC pipe and a 5/16 x 3 or 4" carriage bolt, nuts and washer. Run one of the nuts about an inch away from the head of the bold. put in a flat washer and run the second nut up to the washer trapping it. Make sure the bolt head and washer slide into the pipe. You may have to grid them down a little to get them to fit. Mix up some epoxy and take a Popsicle stick and work the epoxy on the space between the washer and the bolt head. Slowly insert the bolt as you work in more epoxy. Once the second nut is inside the pipe, fill epoxy around the nut. We are trying to glue this bolt assembly into the pipe so we can attach a cordless drill to the bolt and spin the pipe.
Step 7: Spin the Nose
Making the nose is a lot of fun. For this rocket, a 12 inch section of foam noodle seems to work great.
Take the mandrel you just made and insert it into the Swimming Noodle. It should fit pretty snug. If it is loose, wrap some masking tape around the pipe in a couple of locations to build up the diameter until it fits snug.
Chuck up an electric drill on the bolt that is glued into the pipe. Make sure the epoxy is hardened!
I start with an piece of 80 grit sandpaper. Spin the foam noodle and start to work it along the sandpaper.
The pictures show the progression of the nose cone.
When you are near your final shape, go to a finer grit of sandpaper to smooth off the foam. The coarse paper tends to make a fussy finish. This will make a pile of foam dust, so be prepared to clean up a mess. Making the nose cone this way will take only a few minutes. It is possible to use a sanding block and do this without a drill and mandrel. It will just take more time.
Step 8: Finish the Nose
One thing we need to do is make the rocket nose able to hold water for ballast. Cut a plug from a scrap of noodle about an inch long and big enough to stuff in the hole of the foam noodle. Smear goop glue around the perimeter of the plug and then push it into the bottom of the nose. Leave about 1/8" of plug sticking out, this will help us glue it to the rocket. Make sure the plug is sealed well with the Goop Glue.
Step 9: Make the Transition Section
The bottle is a larger diameter than the noodle used for the nose. To make a smooth transition, take a 2 liter bottle and mark a line around it at its largest diameter before it starts tapering to make the top of the bottle (See the first picture). I find an easy way to make a nice mark around the bottle is to set the opening of it on the table, put a sharpie at a fixed point on top of some books or blocks or whatever is handy and carefully rotating the bottle against the marker.
When cutting it out, make sure not to cut to the line on the first cut. Cut outside the line and then trim it to size.
Then take a piece of foam noodle and put it inside the cone you just cut out. Carefully mark where the noodle touches the cone. We will have to cut this out so the noodle can go through the cone.
Step 10: Finish and Glue the Transition
Again, cut outside the mark and trim to the line. You may want to test fit to make sure the noodle goes through. It is OK if it is a little snug.
Put a bead of Goop glue around the large inside diameter of the transition piece
Glue this to the top of the rocket (Bottom of the booster section 2 liter bottle)
Step 11: Glue on the Nose
For all of this gluing, you will be using Goop Glue
Put a good sized dollop of glue right in the center of the bottle used for the Booster
Put a chocolate chip size drop on each of the five bulges on the bottom of the booster bottle
Press the nose in place and push it down until it meets the booster and glue.
Take the tube of glue and put a bead of glue between the nose and the transition piece
Make sure the nose is straight on the rocket and it looks true. This glue takes a while to dry so you have a little time to adjust.
NOTE: Goop Glue should dry for at least 12 hour before using the rocket!
Step 12: Launching
To launch the bottle rocket, fill the bottle about 1/2 full of water.
Put on the Launcher
Fill the nose cone with water. As stated earlier, the water will put the center of gravity (CG) in the nose of the rocket. This is where you need the CG for stable flight. When the rocket reaches its highest point (apogee) it will turn over, dump the water and become unstable. This will allow it to come down sideways, and not like a dart. If it comes down like a dart, try trimming off a little of the fin area. Snip off 1/4 inch of each fin and try again If it does not fly well on the launch, try adding a bit of clay in the nose for weight to see if it helps.
Pressurize the Rocket
3, 2, 1 LAUNCH!
Step 13: Variations
Here is a picture of a couple of variations. One rocket has 3 fins with a little more surface area, and the other is made out of a 20 oz bottles rather than 2 liter bottles. Experiment and make your own variations.
I hope you enjoyed this Instructable. Thanks for reading and Have fun!
If you want to build a launcher for these rockets, visit my Reliable Water Rocket Launcher Instructable. Thank you!