Air Powered Rocket Launcher

In this Instructable I'll walk you through how to build an awesome air powered rocket launcher that can shoot paper rockets well over one hundred feet high. Parents and children alike always love building and launching the rockets. We take them to air shows and STEM events to help teach kids about aerodynamics. I designed these to be cheap, tough, and easy to use. Thanks to the 2 inch pipe design, the pressure never needs to go above 30 PSI.

The frame price is a little over $50 for a launcher, but this can be reduced when building multiple launchers.

This short video explains the reasons for my design decisions:

I made a very detailed video on how to build a launcher, but since it is such a long video, I made this tutorial as well since seeing the steps one at a time is sometimes easier. If you have any questions, more than likely they are in this video. Or if you just prefer video instructions, take a look here:

See the launchers on Fox 2 News!

Make sure all of the fittings you get are PRESSURE fittings.

I found most of the parts at Lowe's. With the exception of the Tee connectors and the SCH80 nipples, everything else was available at Home Depot as well.

See the attached parts list for URLs and more detail. It is a PDF so you can print it out when going to the store to pick up the items.

UPDATE:

After building many versions of this launcher, I've found the best cost vs performance vs transportability vs safety size of pipe is 1 1/2 inch PVC pipe and fittings. It's a little bit easier to work with, makes a smaller overall launcher so it's easier to transport/carry (quite a bit lighter weight), and the smaller pipe has a higher pressure rating. For the Tees I now use 1 1/2 inch Tees with a 1 inch threaded outlet on both sides. This makes the design symmetrical so it's a little bit easier to assemble. That means a 1 inch sprinkler valve is required which is a little bit more expensive/heavier than the 3/4 valve, but that additional diameter gives quite a bit more airflow and in my testing showed higher rocket launches. Keep that in mind when purchasing the parts, but all of the instructions still apply even if you change the sizes a little bit.

Parts:

• 36 inches of 2 inch diameter pressure PVC
• 4x 2 inch pressure PVC 90 degree elbows
• 2 inch smooth to 1 inch threaded Tee pressure PVC connector
• 2 inch smooth to 3/4 inch threaded Tee pressure PVC connector
• 1 inch threaded PVC plug
• 3/4 inch by 1 1/8 inch threaded SCH 80 nipple
• These were hard to find. Only one of the local Lowe's had them.
• 3/4 inch sprinkler valve
• 3/4 inch threaded street elbow3/4 inch threaded to 1/2 inch smooth PVC adapter
• 17 inches of 1/2 inch pressure PVC
• 8 inches of 1.25 inch diameter PVC pipe
• 2x 1.25 inch PVC caps
• 20 feet of 18 gauge speaker wire
• 3x 9v battery connectors
• 3x 9v batteries
• A button
• 2x 2 pin electrical connectors
• Valve stem
• The best local place for me to buy them was Autozone (part # 20128)
• Slime TR416 High Performance Valve Stems
• Bicycle pump

Tools:

• Drill
• 1/8 inch drill bit
• 1/4 inch drill bit
• 1/2 inch drill bit
• Miter saw or hack saw
• PVC primer and cement
• 120 grit sand paper
• Thread tape
• Electrical tape
• Tape measure

1. Cut four 2.5 inch long pieces of 2 inch pressure PVC pipe.
   1. Measure the inside of the sockets. For the Ts and elbows that I used, the depth of each was 1.25 inches. Double the length to figure out how long to make yours.
   2. Use a piece of wood with a clamp to use as an end-stop. on a miter saw. This makes it much easier to four short pieces of PVC that are all the same size.
   3. Push the PVC up against the wood, and then cut the pipe.
      • If using an electric miter saw, we found it best to put the PVC in place, start the saw off of the PVC, bring the saw down through the pipe, and then leave the saw down until the blade has stopped. Otherwise the blade could chip the pipe.
2. Cut two 13 inch long pieces of 2 inch pressure PVC pipe. These will make up the main portion of the compression chamber.
3. Cut a 17 inch long 1/2 inch pressure PVC for the launch tube. The launch tubes length doesn't matter much, but I made it this size to prevent it from being longer than the total length of the air chamber.

You will need:

• Power drill
• 1/8th inch drill bit
• 1/2 inch drill bit
• Threaded PVC plug
• Valve stem

If you're using a 3/4 inch sprinkler valve, then use a 1 inch threaded PVC plug. If you are opting for a bigger 1 inch sprinkler valve, then use a 3/4 inch threaded PVC plug. Start by finding the center of the PVC plug and drill a hole with the smaller drill bit. The size doesn't matter, it is just to keep the bigger drill bit from walking.

Using the smaller hole as a guide, drill the 1/2 inch hole.

Clean up the hole with a reamer or some sand paper.

Install the valve stem and ensure that there is a good seal.

Video Instructions: Install Valve Stem

• Lightly sand the outside of the connectors.
• Sand the inside of the sockets.
• I used 120 grit sandpaper.
• The sanded parts should no longer be shiny.
• This helps the glue join the pieces together.
• Don't forget to sand about an inch on one side of the launch tube, and then sand the inside of the 3/4 inch to 1/2 inch connector.

Video Instructions: Sand all the PVC

• Only glue the pieces in a well ventilated area.
• Do a loose dry fit of all the pieces. It's much easier to fix things now.
• Lay down something over your work area to to protect it from the primer and glue. I used a trash bag cut open.
• Make sure all of your pieces are close by and ready to join.
• Have some paper towels on hand to wipe up excess glue or primer.

Video Instructions: Prepare to Glue Connections

1. Start with priming the joints. Prime the entire joint surface on both the male and female side.
2. While the primer is still wet, apply the glue to both sides.
3. Quickly insert the connector into the Tee, twisting a quarter turn while pushing the pieces together.
4. Hold the pieces together firmly for 10 seconds while the glue sets. If you don't hold the pieces pushed together, they will push apart!
5. Use some paper towel to clean up any excess primer and glue around the joint.

First Detailed Gluing Instructions (gluing an elbow in the video, not the Tee):
Glue an Elbow to Each 13 Inch Pipe

The 3/4 inch Tee is slightly shorter than the 1 inch Tee, but that's okay.

Video Instructions: Glue the Other Connectors to the Tees

1. Only glue an elbow to one side of each pipe!
2. Glue the launch tube to the 3/4 inch to 1/2 inch adapter.

Video Instructions: Glue an Elbow to Each 13 Inch Pipe

1. This step can be tricky! Watch the video for clarification if you're unclear on anything.
2. Screw the launch tube into the 3/4 inch Tee before gluing the T assembly to an elbow. Use this to make sure the Tee is lined up with the 13 inch tube correctly.
3. Glue one of the elbows to the Tee and while pushing the pieces firmly together, and make the launch tube parallel with the 13 inch tube. Since the launch tube essentially multiplies the angle at the T and elbow joint, you should be able to get them lined up closely.
4. Glue the other elbowed tube to the Tee, this time using the table to keep the frame even. You don't need to use the launch tube to line things up since the other side should be even with the launch tube, then assuming your table is flat, the newly glued side should be parallel with the first side.

Video Instructions: Join the Elbowed Tubes to the 3/4 Inch Tee

• This side is harder to get exactly right, but since I am using it for the valve stem, it doesn't have to be perfectly parallel with the frame tubes.
• Glue one elbow to the Tee making sure that the threaded Tee opening is facing the same direction as the elbow opening.
• After gluing the second elbow to the Tee, I pushed the "mouths" of the elbows flat onto the table to try to get them as parallel as possible. If they aren't parallel, it will be very hard to fit this Tee assembly onto the rest of the launch tube.
  • You can also use the already assembled frame to help align the second elbow.

Video Instructions: Glue the Other Two Elbows to the 1 Inch Tee

• This is the hardest joint! Both pieces need to be glued at the same time, so it must be done quickly and it takes a lot of force to get both of the elbows onto the frame tubes.
• Apply the primer to all pieces first, and then the glue.
• After inserting the frame tubes into the elbows, I placed one end of the frame onto the floor, and pushed with all my weight on the other side to make sure both tubes go all the way into the elbow connectors.

Video Instructions: Glue the Two Frame Pieces Together

1. Get the valve stem plug and some thread tape.
2. Thread tape MUST be used!
3. When looking at the threaded side with the opening of the connector facing you, wrap the thread tape around the threads of the plug in a clockwise direction. Wrapping around clockwise makes it so that the thread tape won't unwind when screwing the pieces together. Make sure to cover all the threads! This will help seal the plug and lessens the friction on the threads to prevent damaging the PVC.
4. Screw the plug into the T. Don't over tighten, but make sure there is a good seal.

Video Instructions: Install the Valve Stem Plug

1. Wrap thread tape around the 3/4 inch nipple.
   • Wrap it halfway down clockwise, and then flip the nipple over and wrap clockwise from the other side.
2. Lightly screw the nipple into the T. No need to tighten it all the way because you will use the sprinkler valve to tighten it the rest of the way.
3. Take the solenoid off of the sprinkler valve (just unscrews by hand, see the photos). If you don't do this, the solenoid will hit the frame body and won't screw onto the frame.
4. Screw the sprinkler valve onto the threaded nipple.
5. Reinstall the solenoid.

Video Instructions: Install the Sprinkler Valve

1. Wrap thread tape around the male end of street elbow.
2. Screw it into the sprinkler valve.
3. Wrap thread tape around the male end of the 3/4 inch to 1/2 inch adapter on the launch tube.
4. Lightly screw the launch tube into the street elbow. This will need to be easily unscrewed later to transport the launcher.

Video Instructions: Install Street Elbow and Launch Tube

This is an optional step, but adding it prevents users from over-pressurizing the system to a point of failure. Thanks to aaron.linker for suggesting it! If the pressure goes over the max set on the relief valve, it will "pop" to relieve the pressure and then close again.

I modified the input side to connect a pop-off and the valve stem. Doing it this way allows the rest of the design to stay the same, but it does make the design more expensive and larger.

I used an 80 PSI pop-off (also called a safety relief pressure valve). 80 PSI should be more than enough pressure, since the two inch pipe designed launchers never really need to go above 30 PSI.

The other option is to account for the pressure valve in the design ahead of time. This keeps the design flatter so there is the potential to partially stack multiple launchers. It also keeps the valve stem and relief valve more inline with the design instead of hanging off of an elbow and tee connector. However, this design prevents the use of a 3D printed brace, but the depending on your priorities it could be worth it.

For the groups I usually deal with (Elementary children) not having a pressure relief valve is okay because the children are always monitored while using the launchers (mainly for eye safety), and a lot of the times the kids need help from an adult to pump the bike pump anyway. If you decide to use an air compressor or other "automated" filling system, then a pressure relief valve is a MUST!

1. AFTER a few hours, the glue should be fully set. It only takes a couple minutes for the glue to hold, but it doesn't hurt to be cautious. I usually wait a full day just in case.
2. Attach a bicycle pump to the valve stem and pump the air chamber up to 30 PSI.
3. Check for leaks.
4. Do NOT use the launcher in the cold. PVC becomes brittle when it gets cold, and it does not fail in a graceful way.

Video Instructions: Pressure Test the Launcher

This step shows how to make a launch button that will clip into the 3D printed holders, but the first launchers used a button assembly I found on Amazon that has an "arming" key and a big red button. I've included some pictures of how I assembled it. It was suggested by ringworld to include a "parent switch" when using the launchers with younger children. If this is wired in series with the other button, then the parent/mentor has to be pushing their button or else the launchers won't work. This is a great idea for the younger crowd to add some extra safety!

1. Wire three 9 volt battery connectors together in series.
   • Connect the first positive connector to the negative of the second.
   • Use electrical tape or heat shrink tubing to keep the between the two.
   • Connect the positive of the second connector to the negative of the third.
   • This adds the three 9v batteries together to make 27 volts total.
2. Wire the button to the positive side of the three 9v connectors.
3. Connect the positive side of the speaker wire to the other side of the button.
4. Connect the negative side of the speaker wire to the negative of the 9v connectors.
5. Cut the 1 1/4 PVC pipe down to 8 inches long.
6. Drill a small hole in the middle of the 1.25 inch pipe for the speaker wire.
7. Drill a hole in a the 1.25 inch PVC cap for the button. The size needed will be different for whichever button you use.
8. Put the speaker wire inside the pipe and through the small hole.
9. Connect 3 9v batteries to the connectors, and put the batteries into the pipe. Put the 1.25 inch caps on the pipe to protect all the batteries inside. No glue is required because you'll need to change the batteries eventually.
10. Connect the speaker wires to the sprinkler valve. The positive and negative do not matter for the valve.
11. Make sure there is nothing directly over the launch tube. Test the button. You should hear the solenoid on the sprinkler valve click.

1. Wrap a piece of paper around a piece of 1/2 inch pipe.
   • When we take the launchers to events, we have a lot of small 1/2 inch pipes at the tables so a lot of children can make rockets at the same time.
2. Use tape to keep the paper from unwrapping.
3. Tape over one end of the paper tube to hold in the air.
4. That's it! The rest is up to you. Add fins, a nose cone, paint, glitter, whatever!
   • If you're doing an event for a bunch of people, then having some nose cone and fin templates printed out ahead of time really helps out.
   • The kids usually really like picking out the different colors of paper, and drawing on their own designs.

This is not needed, but it does make it easier to transport the launcher, and helps reinforce the sprinkler valve. If you have easy access to a 3D printer, then this is a great way to add to the build.

The valve brace relieves any stress that might happen to the sprinkler valve connections, and will help make the launcher last longer.

The launch tube and launch button holder just makes all of the parts one piece so that it's easier to carry. I used hose clamps to hold the holders onto the frame tubes, but zipties would probably work as well.

Video Instruction: 3D Print Brace and Holder

• Always wear safety goggles!
• Only use the launcher in warm weather!
  • PVC will get brittle if it's cold.
  • PVC does not fail gracefully!
• This design doesn't need to ever be pressurized more than 30 PSI! I highly recommend close supervision to prevent users from over-pressurizing the system, or to add a safety relief valve.
• Always use thread tape on the threaded PVC connections!
  • Thread tape seals the connection and helps reduce friction in the joint so it's easier to turn
• Only put the paper rocket on when there is no pressure in the tank.
• When the PVC starts getting worn out (this is why I like painting the PVC, it shows the wear much easier), replace the body of the launcher! It's not worth saving a little bit of money if the PVC fails.
• Some users also suggest wrapping the PVC in duct tape to help reinforce it a little bit. Ideally this will allow the PVC to fail and release pressure, without sending PVC shards flying.

I want to make a full new Instructable about all of the design revisions I've made. The launchers have been used at many air shows and STEM events and are holding up well. Until I make the tutorial, here's the quick explanation:

1.5 inch pressure PVC turned out to be the best size, and it really works well. The parts are easy to find and the pressure rating far exceeds what the kids can pump the systems to.

I mounted the launch buttons in a box inside the frame for easier carrying and to have all the pieces inside. The launchers also stack somewhat, which again makes transportation easier. I use two buttons in series for the launch to help prevent accidental launches.

I finally added a blow off valve as well to prevent some high school kids from excessively pumping the systems up. The pipes should be fine, but I don't want to find out at an event. The safety valve is set to 60 PSI max, and is threaded into the schedule 80 nipple, and also held in place from the back side with a retaining nut. The brace design also ensures that it is pointing down in case of a blow out.

Some parts are now printed using TPU to increase their longevity. The brace that isn't supported the sprinkler valve isn't really structural, so it can be flexible. And the launch button box can be flexible too since kids kind of throw them around. With 3 nine volt batteries inside, there is enough weight to break PLA or PETG pretty easily.

Let me know if I left out some crucial details!