Soda Bottle Rockets!!

by Biodynamic

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Intro: Soda Bottle Rockets!!

this instructableWater Bottle Rockets are a terrific demonstration of Newton's Laws of Motion. I have been launching these rockets with my 7th graders for the past 10+ years. After a number of prototypes, I'm ready to share a project that anyone can build and test. The best part, it only takes about an hour to build! These rockets will easily fly 150 feet with some of the better projects traveling well over 300!

Warning! There is always risk involved when subjecting bottles to high pressure. There is also risk due to the uncertainty of where a rocket may land. Keep all spectators behind and away from the launch area / anticipated landing area.

STEP 1: Reduce, Reuse, Recycle

Want to know what's better than buying your own 2 Liter soda bottles? Raiding a neighbors' recycling or taking a few bottles home from a party you've attended/crashed. Although it only takes about 1 hour to build one of these rockets, I give my students 3 weeks notice (so they can find creative ways to collect the bottles). If your hunt for used bottles is a bust, you can almost always find a brand on sale. This year, I found a 5 for $5.00 deal on Pepsi products. I prefer the Pepsi bottles over the Coca-Cola brand bottles because of the shape of the bottles. We purchased A&W Rootbeer to make a few rootbeer floats and poured the rest down the drain.

STEP 2: Cut Bottles

Do NOT cut one of your bottles. This bottle will serve as the bottom of your rocket and must hold the water and air pressure. This bottle will not be referred to as the BOTTOM BOTTLE. Even the slightest pinhole in this bottle will cause the rocket to fail. Remove the label and set the BOTTOM BOTTLE off to the side.

Now that you've set your BOTTOM BOTTLE off to the side and PROMISE YOU WILL NOT CUT INTO IT, gather your remaining bottles.

1. Remove all labels

2. Find the line in the plastic where the factory joined the bottom of the bottle to the main cylinder.

3. Puncture the bottle on this line with a box cutter or knife. Be very careful! This is a good time to have some adult supervision.

4. Use scissors to cut along the line until you remove the bottom portion of the bottle.

Repeat these steps for the rest of your bottles so that you can assemble the body of your rocket.

STEP 3: Join the Bottles Together

Take one of your bottles (with the removed bottom) and fit it over the BOTTOM BOTTLE. The spouts of the bottles will be facing away from one another. Because the bottles have the same circumference it will be a tight fit.

Make the bottles as straight as possible.

Take your next bottle with the bottom cut off and place it on top of the previous bottle.

Make sure all three bottles are as straight as possible.

Repeat until your rocket is an ideal length.

Use packing tape or duct tape to join the bottles at the seams. (Helpful hint: Before taping the bottles into place, it's a good idea to roll them along a flat surface. If the bottles wobble, it indicates that they aren't straight.)

STEP 4: Cut and Glue the Fins

Determine the number of fins you want to add to your rocket.

Use a box cutter and a straight edge to cut your foam core into triangles.

Run hot glue (or superglue) down one edge of your triangle. *Caution! Burns possible. Adult supervision recommended. If using hot glue, be careful not to touch the glue or the nozzle of the glue gun. I'm all about experiential learning, but not when it comes to 3rd-degree burns.

Glue the fin onto your BOTTOM BOTTLE and make sure it's directly in line with the rocket. This is one of the more important steps in making your rocket fly super far!

Space your fins around the BOTTOM BOTTLE evenly.

Your soda bottle with fins should be looking like a real rocket! Although its currently ready for liftoff, one of the best parts of building the rocket is the decoration/personalization.

STEP 5: Decorate Your Rocket

An easy way to decorate your rocket is with spray paint. Keep in mind, you don't want your decorations to hinder the flight of your rocket. Covering the whole thing in decorative duct tape might look cool, but will add quite a bit of mass.

Many of my students will get together and have a rocket building/decorating party. Their creativity never ceases to amaze me!

STEP 6: Launch the Rocket


There are a number of different launch set-up kits that can be purchased online. I have used THIS KIT for many years and find the quality of the materials built to last.

First, add about one liter of water to the BOTTOM BOTTLE. (It's good to have a hose spigot close by and a 5-gallon bucket). This is approximately 2 Solo Cups worth of water.

Connect bottle to the launch kit (This can take some practice because it takes some leverage to get the rubber stopper into the mouth of the bottle).

After the bottle is secured to the launch kit, pressurize the bottle. The launch kit has a valve for pumping up the bottle (like you would find on a bicycle). You could use a bicycle tire pump, but it takes a lot of work and the time between launches increases. If you use an air compressor, getting the pressure up to around 90 psi only takes about 10 seconds.

Stand back, pull the string with a quick flick of the wrist, and watch it fly. You will need a large area to launch over (football field or soccer pitch).

When I do this activity with my students after everyone has had a chance to launch the kids can retrieve their rockets. If the rockets are in good shape (still have fins/nose cone can be straightened out) they can launch again. This is where I allow them to test out different amounts of water/different air pressures/different launch angles. If the rocket launched well the first time, I might bump the pressure up to around 100 psi.

I can usually go for about 3 years (launching 70-80 rockets each year) before the rubber stoppers wear out. I'm sure I could launch more rockets per year, but the rubber stopper tends to dry-rot after so many years. With the high pressure, the hoses have the potential to leak. This can be fixed by adding a few rubber bands (wrapped around) where the water or air is leaking to help create a better seal.

The major complaint about the launch kit (on Amazon) is stability. If you want to learn how to build an easy launch pad that will last for years, HERE is the instructable I created to take you through the steps.

Now go build a rocket!

STEP 7: Build a Launch Pad

36 Comments

paulsfo 4 years ago

No one seems to have mentioned safety glasses. Even if the possibility of the bottle exploding under pressure is very remote (unless it's damaged of course), you are talking about an object which can damage a car more than a hundred feet away. I'm sure that you agree that 8th-graders' eyes, much closer, are also much more valuable.
Sure, it's unlikely that it will go sideways and into someone's face, but that's not really how one thinks about whether or not to require safety glasses, is it?

Supernerd Sven 4 years ago

They use compressed air - there is no chemical propellant.

Eh Lie Us! 4 years ago

Wait, they got rootbeer floats before the hard work was done? I'm calling FOUL! :)

So, so, so great to see kids (especially the girls!) doing this. Thanks for posting and good luck. The sky is the limit.

Biodynamic 4 years ago

Thank you! One of the girls for my cover image is my daughter. My son wrote his name in big green letters across her project when she asked him to help decorate it. I love seeing all of the kids be successful, but it's especially satisfying when I can convince a young lady she's great at science/engineering despite her own preconceived notions.

Eh Lie Us! 4 years ago

Yes, indeed! We all have a lot more work to do. Every bit gets us closer and closer. Thanks again for what you do.

chhackm 4 years ago

A great reminder: I used to do this as a kid - a very long time ago. Back then I used a single bottle... which is the reason for this comment: it was only at the very end and on review that I realised there was no apparent purpose for any bottle other than the bottom one! Can you make it clear at the outset that the other ones are not going to have any propellant function, and also why they are there? My guess is for aerodynamic stability - which might also be achieved by angling the fins, but it's a trade-off between increased drag from angled fins and increased weight from adding length.

Biodynamic 4 years ago

After launching hundreds of these rockets I've found that 3-4 bottles work best. A single bottle doesn't have enough mass to fly very far. The weight of the fins on a single bottle makes the majority of the mass towards the back of the rocket so the rocket tries to flip around mid flight. You would have to add some weight to nose to get it to work. The center of mass of the rocket should be centered or a little towards the nose. Thanks for the feedback!

DavidR885 4 years ago

Tip 1: Before hot gluing the fins on, fill the bottle with water so the plastic bottle does not melt.
Tip 2: use ballast weights in the nose
Tip 3: Check out Air Command Rockets. They are boss at this. They show how to join multiple bottles to make a larger pressurised volume as well as multiple stages, parachute deployment and flight recording. http://www.aircommandrockets.com/

Biodynamic 4 years ago

I like the idea of filling the bottle with water before gluing the fins on. The bottles often warp due to the temperature change when they're empty.

I know some extra weight in the nose is great, but it also makes me nervous because it makes them a lot more dangerous on the way down!

I'm definitely going to encourage a few kids to try joining bottles next year. Thanks for the link.

LeeDr850 4 years ago

We did these with my Cub Scout pack with a few differences;

We figured out that a garden hose in some areas has about 90 PSI pressure so we just slide a bottle down onto a PVC pipe that we had heated up (like with a candle) and pushed to make it swell a bit. Push the bottle down pretty hard on to that and turn on the hose. You end up with about the right amount of water and compressed air in the bottle. The bottle releases once the pressure gets high enough. I know, it's not very accurate but it's super-simple. I'm sure there's instructables showing this technique.

I purposely angled all the fins on one bottle the same direction so it would spiral as it flew (like how a bullet goes through a rifled barrel). This seemed to make it fly straighter.

We generally used a single bottle for ours. We hot glued foam board fins on. We made nose cones out of paper and taped them on (they didn't last once they got wet but they also won't hurt anybody if they fall on you).

WARNING: A 2-liter bottle like these falling down on a car could put a small dent in it so make sure you're clear of parking areas.

Biodynamic 4 years ago

One year I parked under a big maple tree about 130 yards out. A rocket came straight down and knocked the grill out of the front of my car. Ever since, I have sent emails to all the teachers and staff not to park down range. I put up signs the week before. I still have teachers who park up on the nearby hill despite the warnings and the high probability they may end up with a dent in their car.

Dragonavionics 4 years ago

Hi
I have done these for many years as an introduction to powered rockets for students, the use of a compressor is one I used myself. The best tip I can give though (and I tested this Idea many many times) don't pour the lemonade or contents away but use it to power the rocket instead. I found a pretty significant gain in distance. I think the CO2 bubbles in the fizzy drink compresses a little.
Nothing to lose.
Best wishes
Chris

Biodynamic 4 years ago

Very interesting! As much as I'd love to try it, I'm not sure I want to get sprayed with soda all day. I'll probably test it with one or two rockets for comparison though. Thank you.

paskidog 4 years ago

Nice project! My only concern is your choice of launch sites. It looks like you sent the "rockets" up directly beside a 3-phase power line..... not a good idea! just sayin.

Biodynamic 4 years ago

Thanks for the warning! Since I know very little about 3-phase power lines, what could potentially go wrong? We don't have parachutes that might cause a rocket to get hung up on the wires.

charlessenf-gm 4 years ago

"Use packing tape or duct tape to join the bottles at the seams. "

I think the 'flimsy' plastic packing tape (that brown stuff) would prove a better/lighter choice than the thicker, heavier duct tapes I am familiar with.

That flimsy stuffs been good enough for UPS for decades!

Great project, looks as if you've inspired a few rocket scientists and creative 'types' too!
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