How-To Tuesday: Compressed air rocket

Fun & Games Rockets
How-To Tuesday: Compressed air rocket
airRocket-1.jpg

Photograph by Gabriela Hasbun

PAPER, TAPE, COMPRESSED AIR … LIFT-OFF!

Blow your friends away as you send this 25-cent rocket hundreds of feet in the air. You can build this easy launcher and rocket with common hardware store items in an afternoon.

All the parts for this simple but impressive air rocket and launcher are cheap and easy to find. Building it is a breeze and the modifications are endless. It’s legal in a big city, reusable, clean, and can be launched even in high winds on a small field.

Believe me, folks are quite taken by the 200- to 300-foot flights fueled by 18 or so bicycle pumps of compressed air. Whether you’re launching on your own or with a whole group of rocketeers, watch the crowds gather … 3, 2, 1, and away!

! CAUTION: DANGEROUS PROJECT

At normal temperatures, standard Schedule 40 PVC has a working pressure of around 150psi, but heat, sunlight, solvents, scratches, and time make the material lose strength, and even at the 75psi used for this project, it will eventually fail. When it fails, it will break into fragments that can be thrown with great force by the compressed air. For added safety, wear safety goggles and wrap PVC elements in several layers of duct tape (not shown) to minimize any possible shrapnel. For a bomb-proof model, you could also build the entire system out of galvanized steel pipe at a greater expense.

PUMP IT UP, UP, AND AWAY!

airRocket-2.jpg

Illustration by Nik Schulz

AIR ROCKET ANATOMY

  1. Bicycle pump ~18x
  2. Tire valve Allows PVC chamber to be pressurized.
  3. 3/4″ inline electric sprinkler valve Releases the pressure in an instant burst.
  4. Paired wires Connect the battery button and sprinkler valve.
  5. Button Triggers the sprinkler valve for the launch.
  6. R/C toy or power tool battery Provides the juice necessary to trigger the valve under pressure. 4.8V 600mAh

My 5-year-old son demonstrated the physics of an air rocket recently at a hamburger joint when he shot the wrapper off his soda straw. That’s basically how this air rocket works.

The launcher is made from PVC pipe, and has a chamber that’s pressurized using a bicycle pump. The pressure is released in a split second through an electric sprinkler valve, sending the paper-and-tape rocket into the sky.

What’s unique about this design (as opposed to a solid-fuel model rocket or soda-bottle water rocket) is that the force of the air propelling the rocket upward is applied all at once. It still blows my mind that just this initial blast of air can send the rocket so high.

If you want more info on the basic physics of the air rocket, this NASA link gives a nice simple description: makezine.com/go/airnasa. NASA’s description of how air-powered rockets work also includes a nice Flash animation.

SET UP.

MATERIALS

[A] 3/4″ PVC slip end caps (2) see below

[B] 3/4″ PVC adapters, 3/4″ male threaded x 3/4″ female slip (2)

[C] 3/4″ PVC reducers: 3/4″ male slip x 1/2″ female threaded and 1/2″ female slip x 3/4″ male slip

[D] 2″ PVC slip tee

[E] 2″ PVC slip end cap

[F] 2″ PVC reducer bushings, male slip x 3/4″ female slip (2)

[G] 2″ PVC pipe, 10″ length

[H] 3/4″ PVC pipe, 3″ and 4″ lengths

[I] 1/2″ PVC pipe, 16″ length for launch tube

[J] 48″ length of 1 x 3 pine board to be cut to various sizes for the launch tower

[K] 10′ length of paired wire I used speaker wire.

[L] Button momentary switch RadioShack part #275-609

[M] Tire air valve

[N] Teflon tape

[O] Electrical tape

[P] Wood screws, size #6 x 1 1/2″ or similar (8)

[Q] 10′ length of 5/16″ (outside diameter) x 3/16″ (inside diameter) flexible vinyl tubing

[R] 1/4″ hex bolts, 2″ long (2), wing nuts (2), and washers (4)

[S] PVC cement and primer

[T] 24″ x 24″ piece of 1/2″ plywood as a base for the launch tower

[U] 3/4″ inline 24V electric sprinkler valve Cheap is fine, just make sure you get an inline one.

[V] Hose clamps: size #4, 7/16″–1 1/16″ (2) and size #72, 31/2″– 5″ (2)

[W] 1/2″ male threaded x 1/8″ female threaded brass reducer bushing

[X] 3/16″ hose barb x 1/8″ male threaded brass fitting

airRocket-3.jpg

Photography by Rick Schertle

[NOT SHOWN]

Battery connector Connectors can be the standard R/C toy type used for rechargeable batteries, or a generic bullet type.

Power tool or R/C toy battery to trigger the sprinkler valve. Under pressure, the valve requires higher amperage: a power tool or R/C toy battery will work, minimum 4.8V, 600mAh.

Bicycle pump and pressure gauge Use a pump with a built-in gauge, or just use an ordinary pen-type tire pressure gauge.

ROCKET BUILDING MATERIALS

[AA] Paper napkin

[BB] Glue stick

[CC] 2″-wide masking tape

[DD] 3/4″-wide masking tape

[EE] Printed rocket template Download it from makezine.com/15/airrocket and print on 8 1/2″ x 14″ paper.

[FF] 13″ length of 1/2″ PVC pipe for rocket-building stand

[GG] 51/2″ length of scrap 2×6 lumber

TOOLS

[NOT SHOWN]

Hacksaw or PVC cutter A cheap PVC cutter is a super handy tool for cutting hose, PVC pipe, etc.

Fine sandpaper

Rubber mallet

Utility knife

Screwdrivers

Drill and bits: 3/32″, 1/4″, 1/2″, 13/16″

Saw for cutting lumber to various sizes

Soldering iron and solder (optional)

Socket set (optional)

Scissors

Wire cutters

Adjustable wrench

Channel-lock pliers

Large C-clamp

airRocket-4.jpg

Please note: Only Schedule 40 PVC should be used.

MAKE IT.

BUILD YOUR AIR ROCKET LAUNCHER AND ROCKETS

START>> Time: An Afternoon Complexity: Easy

1. ASSEMBLE THE PRESSURE CHAMBER

1a. Use PVC primer, then cement, to glue the 2″ male slip x 3/4″ female slip PVC reducer bushing into the 2″ slip tee. Next, prime and glue the 3/4″ male slip x 1/2″ female threaded PVC reducer into the 2″ male slip x 3/4″ female slip PVC reducer bushing.

airRocket_1a.jpg

1b. Apply teflon tape to the threads of both brass fittings. Screw the brass barbed fitting to the brass 1/2″ x 1/8″ reducer bushing. Screw the 1/2″ x 1/8″ brass reducer bushing into the 3/4″ male slip x 1/2″ female threaded PVC reducer. Tighten all connections with an adjustable wrench.

airRocket_1b.jpg

1c. To complete the pressure chamber assembly, prime and glue the 2″ end cap onto the 10″ length of 2″ PVC pipe. Next, glue the 10″ piece of 2″ pipe into the other end of the 2″ tee as shown.

airRocket_1c.jpg

2. BUILD THE LAUNCH SYSTEM

2a. Wrap teflon tape around each of the 3/4″ male threaded x 3/4″ female slip PVC adapters. Thread the adapters onto the 3/4″ inline 24V electric sprinkler valve and tighten with channel-lock pliers.

airRocket_2a.jpg

2b. Cut a 3″ length of 3/4″ PVC and a 16″ length of 1/2″ PVC. Glue the 3″ piece into the “In” side of the sprinkler valve. Glue the 3/4″ male slip x 1/2″ female slip reducer and the 16″ length of 1/2″ PVC into the “Out” side of the valve.

airRocket_2b.jpg

2c. Glue the 2″ male slip x 3/4″ female slip PVC reducer bushing into the tee on the pressure chamber.

airRocket_2c.jpg

2d. Glue the completed launch assembly into the pressure chamber. Your air launch system is complete.

airRocket_2d.jpg

! WARNING: Wrap the pressure chamber with several layers of duct tape (not shown) to prevent injury in case the chamber shatters under pressure.

3. BUILD THE LAUNCH TOWER AND ATTACH THE LAUNCH SYSTEM

3a. Cut your 3/4″ x 3″ lumber to the following lengths: 15″ (1), 3 1/2″ (2), and 12″ (2).

3b. Clamp a 3 1/2″ length to the 15″ length as shown. Pre-drill 2 holes with the 3/32″ bit and then screw in the 1 1/2″ screws using a drill/driver. A bit of wood glue would be good too, if available. Repeat with the other 3 1/2″ length on the other side.

airRocket_3b.jpg

3c. Mark a 3 1/2″ piece 1″ from the bottom, mark a 12″ piece 2″ from the top, line them up, and sandwich them together using a C-clamp. Drill a 1/4″ hole through both pieces, then slip a 1/4″ hex bolt through, with washers on both sides and a wing nut on the outside. Repeat on the other side.

airRocket_3c.jpg

3d. The 24″ x 24″ piece of plywood will provide a sturdy base for the launch tower. Measure and mark a line down the center of the plywood, 12″ in from either side. On your centerline, measure and mark 4 1/2″ in from both ends. Place the legs of the launch tower with their edges on the inside of the marks, then trace a line around each leg. Drill two 3/32″ holes in each traced area.

airRocket_3d.jpg

3e. Turn the whole thing upside down, line up the launch tower on the marks, and then finish drilling pilot holes into the launch tower legs, through the existing holes in the plywood. Screw into place.

airRocket_3e.jpg

3f. Once your base is secure, attach the pressure chamber/launch system to the horizontal board using the 2 large hose clamps. Your launch tower is complete.

airRocket_3f.jpg

4. MAKE AND WIRE THE LAUNCH BUTTON

4a. Drill a 1/4″ hole in the middle of one 3/4″ PVC slip end cap, and drill a 1/2″ hole in the middle of the other to accommodate the button switch.

4b. Thread the paired wire through the end cap with the smaller hole, from the outside, and tie a knot about 8″ from the end, so the knot is inside the cap. Now thread the end of the wire in the following order — through the 4″ piece of 3/4″ PVC, through the nut and washer for the button, then through the 1/2″ hole in the other 3/4″ end cap, from the inside.

airRocket_4b.jpg

4c. Solder the wire ends to the leads on the bottom of the button. Slip the washer and nut over the button, inside the PVC cap, and tighten the nut using a pair of needlenose pliers. This can be a bit tricky.

airRocket_4c.jpg

4d. Push everything together to complete the button assembly. Don’t glue it, in case you need to make repairs to your button later.

airRocket_4d.jpg

4e. Connect the wiring. Solder connections when possible, and insulate them with electrical tape.

1. Use bullet connectors or something similar to connect the battery leads to the button and the electric valve.

2. Connect 1 wire from the button to 1 lead on the sprinkler valve. Twist, then solder and/or tape.

3. Connect the other wire from the button to one of the bullet connectors on the battery leads (red or black, it doesn’t matter).

4. Connect the remaining battery connector to the remaining lead on the sprinkler valve.

airRocket_4e.jpg

4f. Tape the wire for the button to the vertical support of the launch tower. Test your launch button. When you press the button, you should hear the sprinkler valve click open and closed. You’ll do more testing later when the system is under pressure.

airRocket_4f.jpg

5. MAKE THE AIR HOSE AND TEST THE LAUNCH SYSTEM

5a. Now we’re going to assemble and attach the air hose to the launcher. First, strip the rubber off the tire valve. You can use fine sandpaper to clean off the valve so it’s shiny.

airRocket_5a.jpg

5b. Slip the tiny hose clamp over the hose and insert the tire valve into the hose. Push it in as far as you can. Tighten the hose clamp over the tube and valve using a socket or screwdriver. This connection was the Achilles’ heel in my prototype launcher. Granted, it was exciting to have the hose explode off at 75psi, hissing wildly like a snake, but, for the sake of reliability, I’ve strengthened it by using the mini hose clamps.

Slip the second mini hose clamp over the other end of the hose, and push the hose end onto the 3/16″ hose barb. Tighten the clamp over the hose and barb. If you find the clamp too big and you’re not able to get it really tight, wrap the barb in rubber from a bike inner tube and then tighten the clamp over that.

airRocket_5b.jpg

5c. Attach the bicycle pump to the tire valve and pressurize the system to about 75psi. Keep an eye on the gauge and listen for any hissing. The pressure should stay at 75psi. If you find leaks, fix them and try again.

Release the pressure by pressing the launch button (with the battery connected). Be careful when you do this — wear eye protection and stand clear of the pressure chamber.

If the pressure doesn’t release when you press the button, tighten down the solenoid (the black thing with the wires coming out) on the sprinkler valve. You may also need a larger battery (one with more amps) to trigger the solenoid under pressure.

If you’re still having problems with your electrical system, most valves have a manual trigger you can flip to release the pressure. If you’re up this close to the valve you may want hearing protection as well. Be very careful that your head is away from the launch tube.

6. BUILD THE ROCKET ASSEMBLY STAND

Mark the center of a 5 1/2″ scrap of 2 x 6 lumber. Drill a 13/16″ hole 1″ deep in the center. This is where a drill press is really handy. Then twist a 13″ length of 1/2″ PVC pipe into the hole. Add masking tape to the base of the pipe, if needed, to get a snug fit.

airRocket_6.jpg

7. BUILD THE ROCKETS

7a. Download the rocket template from makezine.com/15/airrocket and print it out on 81/2″x 14″ paper. Cut out all the pieces on the solid lines as shown.

airRocket_7a.jpg

7b. Wrap the body tube around the assembly stand and tape it in 5 places with the 3/4″ masking tape. The smoother your tape, the more aerodynamic your rocket will be. Now wrap the body tube with 2″ masking tape, working your way down. Slide the body tube to the top of the PVC stand. Tape the pressure cap on top of the body tube by crisscrossing 3/4″ tape over the top, and smooth it down.

NOTE: Make sure to overlap the tape, making it about 2 layers thick everywhere. If you miss a spot, you’ll have a dramatic blowout!

airRocket_7b.jpg

7c. Curl the nose cone around to overlap the dotted section, and tape it in place. Stuff the nose cone tightly with the napkin. A full napkin should fit in. Use a pencil to pack it tightly.

airRocket_7c.jpg

7d. Place the nose cone on top of the body tube, tape around the tabs, then cover the nose cone in tape.

airRocket_7d.jpg

7e. Wrap the fin guide around the PVC pipe at the base of the body tube and mark on the 3s for a 3-fin model or the 4s for 4 fins.

airRocket_7e.jpg

7f. Fold the fins on the dashed lines, then stack them together and trim the tops and bottoms at an angle.

airRocket_7f.jpg

7g. Glue the fins together with a glue stick, and pinch them to adhere them. Make sure you don’t glue the tabs that will be used to attach the fins to the rocket.

airRocket_7g.jpg

7h. Line up the fins with the marks on the bottom of the body tube. Tape all fins securely in place.

airRocket_7h.jpg

Your rocket is now complete and ready to launch. The great thing about these rockets is that no matter how they’re built, they will fly! Some of course will fly better than others, but they all will fly to some degree.

FINISH | NOW GO USE IT »

USE IT.

ROCKET SAFETY, SITE SELECTION, OPERATION, AND CONTESTS

SAFETY

As with any air-powered device, you have to use caution. Eye injuries are your biggest danger. Safety goggles for you and any spectators are required.

SITE SELECTION

Because these air rockets have no recovery system, you can launch them in a fairly small area even with wind. They will go very high but then come right back down.

A small field would be an ideal launch site. The rockets are light and soft, so while it’s not ideal for them to land on cars, the chance of damage is slight.

OPERATION

Set the launcher on the ground and lay out the air hose and launch button wire away from the launcher.

Slide the rocket down the launch tube until it stops at the pressure cap. This is a tight fit and you may need to smooth down the inside bottom of the rocket with your fingers to get it on. You may also bevel the top of the PVC launch tube with a file to make it easier.

Connect the air pump to the hose and pump up to about 75psi. If you go above 75psi, you may blow out the side of your rocket.

Count down and then launch! With a good launch, the rocket will go nearly out of sight and then free-fall to the ground.

The rocket will get crumpled as it hits the ground, but can simply be pinched back into shape and launched again and again.

If for some reason it does not launch, follow the pressure testing instructions in Step 5c.

CAUTION: When placing the rocket on the launcher, make sure your head is never over the launch tube. Wear safety goggles. Make sure everyone is clear from the area before launching, and do a countdown once everyone is at a safe distance.

airRocket-5.jpg

CONTESTS

» Tilt the launch tower, then place a trash can 100yds away and see who can get the closest.

» Build a simple clinometer (wikihow.com/Make-a-Clinometer) and have contests to see whose rocket can get the highest.

OTHER RESOURCES

If this MAKE project really grabs you, here’s a great article on air rockets and some more sophisticated setups, by two professors at Southern Illinois University: makezine.com/go/airrocket.


Rick Schertle (schertle@yahoo.com) is a master at the craft of teaching middle school in San Jose and a novice maker at home. His diverse interests include backyard chickens, adventure travel, veggie oil-fueled cars, and geocaching — all made more fun with the enthusiastic support of his wife and the crazy antics of his young son and daughter.


References:


Make 15

From MAKE 15 – Page 103. To get MAKE, subscribe or purchase single volumes.

48 thoughts on “How-To Tuesday: Compressed air rocket

  1. Eddie says:

    “… When it fails, it will break into fragments that can be thrown with great force by the compressed air. For added safety, wear safety goggles and wrap PVC elements in several layers of duct tape (not shown) to minimize any possible shrapnel …”

    Followed by illustrative pictures of a young lady, and two small children, all using the device with no protective gear whatsoever.

    Safety fail, as they say.

  2. Marc de Vinck says:

    @Eddie

    You are right, thanks for the additional warning. We did mention the importance of duct tape in step 2.

  3. Shawn! Waite says:

    A friend and I made this with our kids. A great project. We made a fast-forward video of the process.. sorry there is little in the way of flight video.

  4. Dave says:

    Great project, and well written-up!

    You commented that if the sprinkler valve fails to open, you may need a larger battery, “with more amps.” I’ve found that insufficient voltage is more often the problem with these valves. They’re designed for 24 VAC sprinkler systems, so they often require more than say, 18V from a tool battery. Three 9V batteries clipped in series have worked great for me. 27 VDC, but very low maximum current.

  5. Big Dave says:

    I’ve built Pneumatic Air Cannons before (the premise of this setup), but I’m thinking this project needs a little fire in its belly.

    I’m planning to try this using a traditional combustion cannon using hair spray.

    Fun stuff. Great instructions!

    +1

  6. Ev Quink says:

    I built one of these several months ago to use with our cub scout den. The boys had a fantastic time with it and learned quite a bit in the process.

    The rockets have a bonus feature in that if you shoot them enough times, the body tube will weaken enough and fail on the launch pad. What is more fun to a fourth grader than a paper rocket that you can shoot hundreds of feet? One that blows apart on the launch pad!

  7. Jon Anderson says:

    You can get bolt-on tire valves to connect directly to the pvc end cap. I made a similar project once, and got the valve from a tire store – I think it was a Belle Tire. You drill the right size hole through the cap, then slide the valve through and tighten down a nut on the inside. It has rubber gaskets to form an airtight seal.

    I also used the nozzle from a hose instead of a sprinkler valve to save money. It gets plenty of air flow very quickly, so it worked out well.

  8. Anonymous says:

    ABS plastic doesn’t shatter like PVC, so it might be a safer choice.

  9. Scott Benners says:

    Would you see any problem with rigging up the low-voltage speaker wire to an adapter that plugs into a 110 wall outlet? Would that be too much juice?

    I ask because I’ll already be using my compressor and hose instead of the pump tire valve for faster, easier, and more consistent air refill. So, an electrical outlet will already be needed.

    I’m just looking for a way to make it less dependent on a depleting resource such as battery juice. Running out of power in the middle of fun would be a bummer.

    1. Peter Holley says:

      Don’t use 110V Wall electricity. It is too much for the valve and is dangerous. Just buy the sprinkler system power adaptor at the hardware store. It is the correct voltage.

    2. Leland Sindt says:

      I use a compressor as well, but have found that the 3, 9 volt batteries I use are still running strong after almost a year of use. I would not worry too much about wall warts..

      1. Trinity Patterson says:

        I’m not much in the way of electronics. Can you provide brief instructions on how you ran your 3 9V batteries in series? That seems like a really nice solution!

    3. Theo Aukerman says:

      I took apart a ryobi flash light and soldered the ends of the speaker wire to the wires inside. Electrical tape or small wire nuts would work if you don’t have a soldering iron. The 18 V from that battery is perfect and rechargeable. The kids (even us old kids) love having an actual trigger.

  10. John De Ryckere says:

    Amateur pyrotechnicians long ago realized that PVC was a poor choice for their mortars. Instead they use high density polyethelene (HDPE) which is both somewhat stronger but also more ductile. The increased ductility means that in the event the mortar fails it’s more likely to fail like a seam rather than as shrapnel.

    Here is one article describing HDPE v.s. steel, paper and PVC.

    [http://www.pyropage.com/HDPE/HDPE.vs.steel1.htm]

  11. lmerk says:

    The solenoid and battery seem to add a fair bit of cost, complexity, and inconvenience. Isn’t there any option to have a mechanical valve that could release the compressed air to fire the rocket? I can see that a regular valve would be too slow to open, but maybe a spring-loaded valve that opens quickly when ‘triggered’? (I’m also picturing a cable release, like with the old SLR cameras). Does anyone know of such a valve?

  12. Steve Davee says:

    Thanks for such a fantastic project and such thorough documentation, Rick!

    Here’s some pictures of a black pipe, copper and brass version, and the use of a presta valve.

    http://www.flickr.com/photos/14770793@N05/sets/72157625453345459/

    I’ve been meaning to thank you for his article especially as I got a lot of use and inspiration
    from your designs this past summer for various tinkering camps, parties and workshops:

    http://www.flickr.com/photos/14770793@N05/collections/72157625586029588/

    Once again, thanks for such a useful, fun and inspirational project.

  13. realmadrid says:

    I am going to make this launcher for a science fair project and I was wondering if you need to charge the battery before you attach it to everything for use. Any reply would be very helpful.

  14. Tom Price says:

    I followed these instructions exactly. It’s a very simple project. However, I cannot for the life of me figure out why a 4.8v 600mAh battery is part of the plan. I installed a 3/4 inch Orbit 24v sprinkler valve. It does not trip the valve at all. I then daisy chained (3) 9v batteries and voila, valve trips. But, it won’t trip if I pressurize beyond exactly 30 psi.

  15. Pneumatic Valves says:

    Hey, interesting article & you are a good tutor. Thanks for sharing these important tips with us. Its really very helpful to assemble a air rocket.Its great keep sharing with us.

  16. Hydraulic Valves Suppliers says:

    Awesome dear.Using pressurized air as it’s only fuel, the rocket might rise as high as five meters. No fire and no explosives are used – it’s perfectly safe for indoor use.

  17. Anonymous says:

    I would like to use an air compressor and launch more than one rocket at a time.  Do you have any sugestions?

  18. Anonymous says:

    I would like to use an air compressor and launch more than one rocket at a time.  Do you have any sugestions?

  19. Dave says:

    First, the launcher is a thing of beauty. I wonder how you came up with the volume/circumference ratio? It’s perfect.
    My son and I are having a blast with this launcher (I swear he found this site and has been dogging me for a year to make it for him (he’s 8)). But…
    We’re having rocket… longevity problems.
    I made your rocket and it’s awesome. It lasts about 2-4 launches…
    2nd attempt, I reinforced the tube with a ton of tape… 4-10 launches.
    3rd I figured it all out (ha ha) and made a tin nose cone with wood spines running down the sides for support. It’s very nice but it’s like a killer javelin… and it’s still around 18 or so…

    My question is… has anyone tried some kind of recovery system with this and how?

    Thanks again. This is a ton of fun.

    1. Bryan says:

      My family just went to a “fund raiser” for a local youth detention facility where they had this system working. My kids purchased a rocket where the cone was made out of foam rubber. That way it could still be shaped and it would hold the point, but it was forgiving enough that when it returned to earth from it’s great trip they ran to get it and away it went again. I did notice a little buckling on the body of the rocket after about 10 launches, but it was still going the same after 15 or so launches. May be look at that as an option.

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