# How to launch a water rocket

What difference does the amount of water you put in the rocket make?

You will need a way of measuring the effect. One way to do this is to use your watch to time the number of seconds that the rocket is in the air.

First, try launching your rocket without any water in it. Try subsequent launches with 100 ml, 200 ml, 300 ml, 500 ml, 750 ml and 1000 ml.

Don’t use more than 1 liter of water (1000 ml) or the weight of it will bend and crush the fins before the rocket lifts off!

Which one stays up the longest? Why does the amount of water make a difference?

## What Effect Does Dish Soap Have?

Adding lots of foaming dish soap to the rocket water seems to make the rocket go much higher. How much soap makes it go the highest? And how much higher does it fly?

Just before pumping up each rocket with soap, make sure to really shake the rocket so that the soap foams up as much as possible. Launch your rocket with 300 ml of water (without soap) and measure how long it stays up in the air. Then launch it with 50 ml of dish soap and 250 ml of water and measure. Then 100 ml of soap and 200 ml of water and measure.

Why does the foamy water make a difference to how long the rocket stays up?

## Measuring Liftoff Acceleration and Velocity

Put a small stick in the ground right beside your rocket. Tape a meter-stick ruler to the small stick so that it is vertical right beside your rocket.

Set your video camera or smartphone to the fastest frame-rate possible and film the rocket lifting off. When you view the video later you will be able to see how far the rocket went from one frame to the next.

If you used a frame-rate of 30 frames per second:

1. Velocity will be Distance (cm) travelled per frame (from one frame to the next) * Frame Rate (in frames per second). The answer will be in units of cm/second. Try this at different frames.

2. To calculate acceleration, you will need to calculate the velocity of the rocket for two adjacent pairs of frames. For example, calculate the first velocity from frame 1 to frame 2. Then calculate the second velocity from frame 2 to frame 3. The change in velocity per frame at that point in the rocket’s flight will be (Second Velocity – First Velocity) / frame. Acceleration will be (Second Velocity – First Velocity) / frame* Frame Rate (in frames per second). The answer will be in units of cm/second². You can change this to meters/second² by dividing the answer by 100.
If you calculate acceleration for different pairs of frames, what do you notice about acceleration? Is it changing over time? Why?

## Launching Horizontally for Distance

You can make your rocket travel very far by launching it at an angle sideways. First make sure that the open field is still wide open where the rocket will land. This could be hundreds of feet away.

Pound a stick into the ground at a 45 degree angle, aiming in the direction you want the rocket to go. When the rocket has water and the launcher-cork in it, lay it on the angled stick. Now the rocket is aiming at a 45 degree angle sideways toward the target part of your field.

When you pump up and launch the rocket, it will go very far in the direction it was pointing, possibly hundreds of feet.

Measure this distance with a rolling distance counter. Try different stick-angles to see which one results in the farthest flight.

## Water Rocket Experiments: Make the Fins Spin the Rocket

Try gluing the fins on at an angle. All three fins should be at the same angle, so that when the rocket flies, the air going past the fins will make the rocket spin slowly (for a small fin angle) or vigorously (for a steep fin angle.

Try to think of your own experiments to do with your rocket. Always think ahead to keep in mind the safety of yourself and others.

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.

Instructions for Building the Launcher :

The launcher is simple and inexpensive to construct. Most needed parts are available from hardware stores. In addition you will need a tire valve from an auto parts store and a rubber bottle stopper from a school science experiment. The most difficult task is to drill a 3/8-inch hole in the mending plate. An electric drill is a common household tool. If you do not have access to a drill or do not wish to drill the holes in the metal mending plate, find someone who can do the job for you. Ask a teacher or student in your school’s industrial arts shop or the parent of a student to help.

Materials Needed

· 4 5-inch corner irons with 12 3/4-inch wood screws to fit
· 1 5-inch mounting plate
· 2 6-inch spikes
· 2 10-inch spikes or metal tent stakes
· 2 5-inch by 1/4-inch carriage bolts with 6 1/4-inch nuts
· 1 3-inch eyebolt with 2 nuts and washers
· 4 3/4-inch diameter washers to fit bolts
· 1 #3 rubber stopper with a single hole
· 1 Snap-in Tubeless Tire valve (small 0.453 inch hole, 2 inches long)
· Wood board 12 x 18 x 3/4 inches
· 1 2-liter plastic bottle
· Electric drill and bits including a 3/8-inch bit
· Screw driver
· Pliers or open-end wrench to fit nuts
· Vice
· 12 feet of 1/4-inch cord
· Pencil

Construction of the Launcher

1. Prepare the rubber stopper by enlarging the hole with a drill. Grip the stopper lightly with a vice and gently enlarge the hole with a 3/8 inch bit and electric drill. The rubber will stretch during cutting, making the finished hole somewhat less than 3/8 inches.
2. Remove the stopper from the vice and push the needle valve end of the tire stem through the stopper from the narrow end to the wide end.
3. Prepare the mounting plate by drilling a 1-3/8 inch hole through the center of the plate. (As safety precautions, hold the plate with a vice during drilling and wear eye protection.) Using a drill bit slightly larger than the holes, enlarge the holes at the opposite ends of the plates. The holes must be large enough to pass the carriage bolts through them.
4. Lay the mending plate in the center of the wood base and mark the centers of the two outside holes that you enlarged. Drill holes through the wood big enough to pass the carriage bolts through.
5. Push and twist the tire stem into the hole you drilled in the center of the mounting plate. The fat end of the stopper should rest on the plate.
6. Insert the carriage bolts through the wood base from the bottom up. Place a hex nut over each bolt and tighten the nut so that the bolt head pulls into the wood.
7. Screw a second nut over each bolt and spin it about halfway down the bolt. Place a washer over each nut and slip the mounting plate over the two bolts.
8. Press the neck of a 2-liter plastic bottle over the stopper. You will be using the bottle’s wide-neck lip for measuring in the next step.
9. Set up two corner irons so that they look like bookends. Insert a spike through the top hole of each iron. Slide the irons near the bottleneck so that the spike rests immediately above the wide neck lip. The spike will hold the bottle in place while you pump up the rocket. If the bottle is too low, adjust the nuts beneath the mounting plate on both sides to raise it.
10. Set up the other two corner irons as you did in the previous step. Place them on the opposite side of the bottle. When you have the irons aligned so that the spikes rest above and hold the bottle lip, mark the centers of the holes on the wood base. (For more precise screwing, drill small pilot holes for each screw and then screw the corner irons tightly to the base.)
11. Install an eyebolt to the edge of the opposite holes for the hold-down spikes. Drill a hole and hold the bolt in place with washers and nuts on top and bottom.
12. Attach the launch "pull cord" to the head end of each spike. Run the cord through the eyebolt.
13. Make final adjustments to the launcher by attaching the pump to the tire stem and pumping up the bottle. Refer to the launching instructions for safety notes. If the air seeps out around the stopper, the stopper is too loose. Use a pair of pliers or a wrench to raise each side of the mounting plate in turn to press the stopper with slightly more force to the bottleneck. When satisfied with the position, thread the remaining hex nuts over the mounting plate and tighten them to hold the plate in position.
14. Drill two holes through the wood base along one side. The holes should be large enough to accommodate large spikes (metal tent stakes). When the launch pad is set up on a grassy field, the stakes will hold the launcher in place as you yank the pull cord to launch the rocket.
15. The launcher is now complete.

Developer: David Mazza
Responsible NASA Official: Jo Ann Charleston

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. Any 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. An interesting variation of the two-liter bottle rocket is the whoosh rocket. This version of the whoosh rocket was developed by Roger Storm of Fairview High School and Mark Skor of North Royalton High School; both high schools are located in suburbs of Cleveland, Ohio.

The standard bottle rocket uses a two liter soda bottle as the frame of the rocket, and pressurized water as the propellant. The whoosh rocket replaces the heavy water with a much lighter, combustible, alcohol-air mixture. The pressurization of the bottle occurs during the combustion of the alcohol. Because the exhaust products are much lighter than water, the whoosh rocket does not generate as much thrust as a water rocket, and the flight trajectory more closely resembles a ballistic flight than a water rocket trajectory. Although the whoosh rocket does not normally fly higher than 50 feet, it is instructional for students because the thrust is generated by the combustion of a liquid fuel.

On the figure we show the launching of a whoosh rocket using a model rocket launch pad. A straw is attached to the side of a two liter soda bottle to guide the rocket along the rail during ignition. The bottle cap is drilled to create a 3/8 inch hole which serves as the rocket nozzle. Two or three drops of rubbing alcohol are placed in the empty bottle and the bottle is shaken to mix the alcohol with the air in the bottle. The rocket is then slid unto the launch rail and an igniter is placed near the nozzle exit. As the flame from igniter rises up through the nozzle, the mixture is ignited. Inside the bottle a chemical reaction occurs which converts the alcohol and the oxygen into carbon dioxide, water, and heat as described by this chemical equation:

2 C3H7OH + 9 O2 -> 6 CO2 + 8 H2O + heat

The reaction occurs very fast and the heating of the exhaust gases produces high pressure in the bottle. The exhaust gas is pushed out the hole in the cap and this produces thrust as described by Newton’s third law. When the thrust is greater than the weight of the bottle, the rocket accelerates up the rail as described by Newton’s first law. The powered portion of the flight of a whoosh rocket is quite short because of the speed of the chemical reaction. The majority of the flight occurs with weight and drag being the only forces on the rocket.

WARNING – Extreme care must be exercised in flying a whoosh rocket and students must be supervised when using this type of rocket. Do not attempt to build and fly this rocket without the assistance of your teacher. Only use soda bottles for the frame. Soda bottles are designed to withstand the pressure associated with carbonated liquids. Water bottles are not strong enough to withstand the pressure of combustion and may explode. The cap of the bottle must be drilled to produce a nozzle for the rocket. Do not make the nozzle hole smaller than 3/8 inch because this can produce excessive pressure in the bottle during combustion resulting in explosion of the bottle. Use only rubbing alcohol (isopropyl alcohol) for the fuel. Other types of fuel may cause the bottle to explode. Because the fuel is highly flammable, be sure to have a fire extinguisher available, keep the fuel containers capped when not in use, use safety glasses, and only fire the rocket outdoors in an isolated location. The rocket may be hot to the touch when it lands, so exercise caution in retrieving the rocket.

In a couple of hours (or less) you could make this water rocket! Water rockets use water and pressurized air to launch a soda bottle(s) 100’s of feet into the air. This instructable will NOT cover the launcher. I hope to later come back and write up an instructable for a launcher. There are many websites with water rocket plans (and launchers) part of the fun is to experiment and come up with your own designs. Feel free to modify, improve, experiment with this instructable and post your results in the comments. The original inspiration for this rocket was from the magazine called “MAKE Magazine” (makezine.com). Issue #5 has full instructions also.

## Step 1: Materials

List O Materials.

> 2 Soda Bottles (empty)
– Note: There are slight differences in the openings of the bottle depending on the soda brand. Pepsi is just a tad smaller than Coke. –
This Instructable is set up for 2 liter sized bottles – feel free to adjust for any size though.

> 1 sharp knife (kids get your parents help here!) I prefer X-acto brand for cutting foam core.

> 1 Large sheet of Foam Core (I prefer Black, but any color will do). Foam Core can be found at almost any arts and crafts supply store. To learn more about foam core try wikipedia: http://en.wikipedia.org/wiki/Foamcore

> 5 Min Epoxy (This stuff is nasty! Do not inhale, and use in a well ventilated area. Do NOT get it on your skin or eyes, or hair, etc. read all safety warnings before using.) Feel free to experiment with other glues. This can usually be found at any hardware store – kids, ask your parents for help with this glue.

> 2 (or more) Markers – I used Sharpies, one black and one Silver

> Clear Shipping Tape – It’s thicker than regular scotch tape and about 2″ wide.

> 2 (or more) cans of spray paint – Pick your own favorite colors!

## Step 2: Step One – Cut Bottle

Peel all labels off of the bottles.
Measure up from the bottle about a Third and cut the bottle. Try to keep your cut line as straight as possible. It may help to mark a straight line around the bottle first. Be sure to recycle or reuse any scrap pieces.

## Step 3: Bottle Merge

Take the cut bottle from the previous step and insert it directly over the bottom of the other bottle – this becomes the nose cone of the rocket. Try your best to keep everything straight. If you put the nose on crooked, your rocket will fly crooked. Place the nose cone on loosely at first, then gently press down until firm. Turn bottle upside down and let it drop on a hard surface several times. If you press the nose cone on too hard, you’ll start to get “crinkles” in the plastic. Crinkles are bad.

## Step 4: Tape Bottles Together

Once the nose cone is on tight (but not too tight) use the clear shipping tape to tape the seams. Try to keep tape smooth.

## Step 5: Cut the Fins

Next you gotta cut some fins to keep your rocket flying straight. I will attempt to upload a PDF file here, so that you can use it as a template. I used a Pepsi bottle, so again, you may need to adjust the curves to fit your bottle. Kids – this is the step that you will need your parents help. Parents. cutting foam core can be tricky. The key is to cut one time all the way through in a smooth motion. You’ll need to press hard to make sure the knife is all the way through the foam core. If you feel more comfortable using a utility knife by all means. Be Careful!

Please! Experiment with your own fin designs. I chose a more squared off design, but you can use curves if you like, etc. I chose 3 fins. You’ll need a minimum of 3, no more than 4 (unless you really really want to!). If you do 3, you need to split your bottle into 3rds, which equals 120 degrees. I’ll try to upload a second PDF file with a 120 degree template. 4 fins, you’ll just need 90 degrees.

## Step 6: Fin Supports

This step may not be needed, but I figured better safe than sorry.
Using some of the scrap pieces of foam core, I cut 6 small triangles. (approx 1″ x 1.5″). These will be added to your fins later for extra support.

## Step 7: Attaching the Fins

Prepare your next “glob” of glue for the next fin. REPEAT for all of your fins.

## Step 8: Glue Your Fin Supports

This is the added step for extra support. Glob out another dab of Epoxy and glue your triangle to the bottle and the fin. Glue the Supports on each side of each fin. Wait approx 10-15 minutes to be sure Epoxy has set.

Guess what. Your done all of the assembly at this point!!
You could take this rocket to the launcher at this stage and let it rip!
BUT. it’s kinda messy looking isn’t it?
One more step.

## Step 9: Paint and Details

This is where the spray paint comes in.
I used BLACK and a Bright Green so that the rocket would be easy to spot while up in the air!
Decorate your rocket any way you like! Flames, spots, checkers, glitter, etc.
Use your extra markers to add any fine details or words (I put H20 on mine so everyone would know this is a water rocket). Add some pin stripes, etc.

(note: as you can see from this photo, I also added some additional tape to the fins for extra support. Do this BEFORE painting.)

Perhaps, I should have mentioned this before, but this rocket has no parachute! What goes up, must come down.
WORDS OF CAUTION:
DO NOT launch this rocket near people, a crowd, small animals, streets or cars or houses. in other words. take your rocket out to the middle of nowhere and launch it in a safe place. Make sure everyone knows there is no parachute and that this rocket will be crashing to earth at a high rate of speed. I wouldn’t want to get hit by it! The rocket will probably fly higher and farther than you think.

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. The relative magnitude and direction of the forces determines the flight trajectory of the rocket.

On this page we show the events in the flight of a water rocket. Water rockets are among the simplest type of rocket that a student encounters. The body of the rocket is an empty, plastic, two-liter soda bottle. Cardboard or balsa fins are attached to the bottom of the bottle for stability, and a fairing and nose cone are added to the top as a payload.

Prior to launch, the body of the rocket is filled with water to some desired amount, typically about 40% of the volume. The rocket is then mounted on a launch tube which is quite similar to that used by a compressed air rocket. Air is pumped into the bottle rocket to pressurize the bottle and thrust is generated when the water is expelled from the rocket through the nozzle at the bottom. Like a full scale rocket, the weight of the bottle rocket is constantly changing during the powered ascent, because the water is leaving the rocket. As the water leaves the rocket, the volume occupied by the pressurized air increases. The increasing air volume decreases the pressure of the air, which decreases the mass flow rate of water through the nozzle, and decreases the amount of thrust being produced. Weight and thrust are constantly changing during the powered portion of the flight. When all of the water has been expelled, there may be a difference in pressure between the air inside the bottle and the external, free stream pressure. The difference in pressure produces an additional small amount of thrust as the pressure inside the bottle decreases to ambient pressure. When the pressures equalize, there is no longer any thrust produced by the rocket, and the rocket begins a coasting ascent.

The remainder of the flight is quite similar to the flight of a ballistic shell, or a bullet fired from a gun, except that aerodynamic drag alters the flight trajectory. The vehicle slows down under the action of the weight and drag and eventually reaches some maximum altitude which you can determine using some simple length and angle measurements and trigonometry. The rocket then begins to fall back to earth under the power of gravity. Bottle rockets may include a recovery system like a parachute, or a simple detachment of the payload section, as shown in the figure. After recovering the rocket, you can fly again.

You can study the flight characteristics of a water rocket by using the RocketModeler III simulation program.

On the graphic, we show the flight path as a large arc through the sky. Ideally, the flight path would be straight up and down; this provides the largest maximum altitude. But water rockets often turn into the wind during flight because of an effect called weather cocking. The effect is the result of aerodynamic forces on the rocket and cause the maximum altitude to be slightly less than the optimum. The parabolic arc trajectory also occurs if the launch platform is tilted and the rocket is launched at an angle from the vertical.

Water rockets are plenty of fun, but they can be even more fun if you go wild with the engineering. [The Q] is one such experimenter, who built a dual-thrust water rocket that even has a parachute for landing!

The testing took place in an area strangely reminiscent of a certain operating system.

The dual-thrust concept is an interesting one, and is well explained by fellow YouTube channel [Air Command Rockets]. The basic idea is to use several chambers on the water rocket, one which provides an initial short “boost” phase of high acceleration, followed by a longer “sustain” level of acceleration from a secondary chamber.

It’s a great way to send a water rocket ever higher, but [The Q] didn’t stop there. The build was also fitted with a wind-up module from a little walking toy, colloquially referred to as a “Tomy timer” in the water rocket scene. A rubber band is wound around the timer’s output shaft, holding a door shut containing a parachute. At launch, the windup mechanism is released, and its output shaft turns, eventually releasing the parachute. The trick is setting up the timer to release the chute just after the rocket is done with its thrust phase.

It’s a neat build, and one that would serve as a great guide to those eager to start their own journey down the rabbit hole of advanced water rockets. We’ve seen similar work before, too. Video after break.

## Introduction: Water Rocket With Easy Launching Pad (simple!)

By majjck Follow

Do you believe it? A water rocket launch pad with no PVC needed. In this Instructable, I will show you how to build a simple water rocket and launch pad that is very effective. Water rockets like these launch naturally rather than manually. Please try this simple project. This rocket usually launches around 30psi, allowing it to launch 100+ feet

## Step 1: Gather Materials

For Rocket:
-Plastic soda bottle (1 liter size is perfect)
-Thin Plastic (like from a gallon of water jug)
-Hot glue gun
-Glue for the glue gun (Duh)
-Plastic cup
-Electrical tape
-scissors
-utility knife
-permanent marker

For Launch system:
-Bottle Cork
-Electrical Tape
-Air pump with inflation needle
-Drill
-Smallest drill bit you can find
-Old can (like a 28 oz. can)

Some materials are shown in the following picture:

## Step 2: Fins!

Cut out a section of your plastic (using utility knife) and draw your desired fin shape in the piece of plastic. Cut this fin out, and use it to trace two more fins. When done tracing, cut out remaining two fins. Next, fold the edges of the fins over about 1/2cm where they will be in contact with the rocket. This provides a bigger surface area when glueing the fins. Discard the remaining plastic.

Use the images below for help:

## Step 3: Nose Cone and Fins

Glue the fins on to the bottle vertical with the bottle. (in other words, the normal way) Use the glue gun for this. Squeeze the glue on to the flap of each fin and attach to the bottle. Repeat this step for all fins. Finally, reinforce the fins with more glue to create a watertight seal to the bottle.

Next, it’s time to make your nose cone. Take a plastic cup, and cut down one side of the cup until you reach the bottom of the cup, then cut the entire bottom of cup out. Then, curl the cup to form a cone shape and glue. Finally, glue to the end of the bottle and tape to ensure that the cone is attached. Use pictures for help.

## Step 4: Finishing and Launch System

Now that you finished your rocket, do what you want with it. Spray paint it, add a recovery system, whatever you desire.

Now for the launch system
Materials:
Drill with TINY drill bit
Cork
Electrical tape
Big 28oz can
Air pump with inflation needle

Take your cork, and drill a LITTLE hole through the center. (where the inflation needle will be)
Next, tape around the circumfrence of the cork. Do this until it will fit very tight in the nozzle of the bottle.

To launch:
1) Fill the rocket 1/3-1/2 way with water
2)Stuff the cork in the neck of the bottle util pratically impossible to push any farther into the bottle.
3)Put the inflating needle through the cork (make sure the needle is already attached to the pump before doing this
4) Hold the hose alongside the rocket and place into can. Arrange the rocket so it is facing straight up or in the direction you want to launch. It should look like the pic below.
5) Start pumping and you should notice bubbles in the rocket. Make sure everyone is not near the launsh zone of the rocket. If you are pumping, stay as far as possibe from the rocket as you can (be ready to get splashed!) Once around 10 psi, you may hear a leaking noise. This is normal. The rocket should launch around 35psi (THE ROCKET WILL LAUNCH BY ITSELF). If it launches before 30psi, you need to put more tape around your cork. Replace cork every 20 launches, and every inflation needle every 50 uses or until it breaks. If your rocket is at 70psi, let the air leak out and try again.

Have fun and remember that I am not responsibe for your actions in this project. Be safe and ALWAYS do this outside.