Water Rocketry is a relatively unknown but awesome hobby. Why? Because you are able to build really good performing rockets without any expensive equipment or tools. We are a small team of students from Germany who have been building water rockets for almost seven years now. In this long time, we have learned a lot about building water rockets which brake the boundaries of what many thought is possible with water and a bit of air pressure. In this Instructable, we share with you everything we have learned in the past few years!
Step 1: See What You Can Expect From This Instructable...
Step 2: Planning the Construction of Your Water Rocket
The process of building a good water rocket doesn‘t start with the preparations of the bottles or with buying all the things you need. It starts with the planning phase, which is critical for the success of a water rocket. In this tutorial, we want to share with you the experiences we have gained in the last couple of years. We focus on giving some advice for beginners and explaining the different methods of construction.
Tips for building a good Water Rocket
- Do not overestimate your own capabilities. Start small and than slowly increase the level of difficulty.
- The size of your rocket depends on the number of joints between the plastic bottle sections. So, if you want to build a very big water rocket, that means you will have to deal with quite a lot with them. But watch out: Every joint is a potential week spot on the rocket.
- First of all, you have to decide how big your rockets should be.
- Keep it simple!
- It‘s very important to focus on the following aspects:
- Reducing weight
- Optimizing flight characteristics
- Increasing reliability
Methods of construction
- A single large vessel: The first method is the construction of a single large vessel. The parachute system sits on top and ejects the parachute sideways or upwards. Because there are no hollow spaces the chamber is very small and light
Two pressure vessel segments: The pressure vessel consists of two, differently sized segments, which are joined with a small adapter. This helps to optimize the center of gravity of the rocket, which results in better flight characteristics. The two-segment-vessel is a bit larger and heavier than a single vessel but it allows the use of radial parachute systems.
The fins are essential to ensure a stable flight of the rocket. Of course, they should be as light as possible, so choose a material which is very light but durable at the same time - like Corflute, for example. The fins of the rocket shouldn’t be too large, because that usually results in uncontrollable flight behavior. The typical shapes already used by many water rocketeers usually work quite well. We also recommend using only three instead of four fins on every rocket to save even more weight.
Step 3: Build Reinforced Pressure Vessels
Building the pressure vessel itself
Regardless which method of construction you go for, the principle of building the pressure vessel is always the same: Multiple plastic bottle sections are combined together. However, not all plastic bottles can be used for water rocketry. The bottles should be as strong as possible and should have a long cylindrical section. In this tutorial, we are using bottles from „Apollinaris“, but these bottles are maybe not available to you, depending on your location.There are many ways to combine the bottle sections. The most popular one is to cut off some parts and glue them together with polyurethane based adhesive. You can also put together multiple pressure vessels by using specific connectors. We are going to build a pressure vessel with six joints. However, the method of construction and the number of joints can be adjusted to your liking. But first of all, you have to prepare the bottles. Cut off both the lower and the upper sections from the bottles, but leave two bottles out and remove only the lower section from them but not the neck.
When cutting off the sections, it is useful to mark the areas with a pen and a piece of paper. You can also use a jig consisting of a drilling machine and a cutter. It is very important to ensure an even cutting edge.
To combine the bottle sections, you have to shrink them on one side. The bottle type we use in this video is a little bit conical, and so we choose the slightly smaller side. But before you are ready to shrink the bottle, you have to turn it on a hot iron. To shrink it, just put the bottle sections in about 2.5cm or 1 inch deep hot water. Depending on the water temperature, the process will only take one or two seconds. If you wait too long the bottle will shrink too much. Always keep in mind that it is important that you shouldn’t be able to put the sections together too easily. If this is the case, you should replace the section before continuing with the next step. Before you glue the bottle sections together, you have to sand the shrunken areas on the outside and the other bottle ends on the inside. Furthermore, you should also clean the bottle sections.
We recommend polyurethane based adhesive to glue the bottles together. But watch out: Not every adhesive is suitable for building water rockets. For example, we have good experience with PL Premium. Other adhesives like Sikaflex 11FC are very good to seal something - but not so much for holding together a rocket chamber. Nevertheless, you should choose this adhesive if you plan to reinforce your rocket with fiberglass or carbon fiber, because the reinforcement will hold the vessel together while the adhesive seals the joints . Thus, the pressure at launch can be increased up to 17 bars or 250 psi. We recommend using a jig which holds the chamber in place. It is very important to wear gloves, because you should not come in contact with the adhesive. We also suggest opening all the windows. Now, you can start applying adhesive on the sanded bottle areas. Be very careful when sticking the sections together and do not twist the sections while doing so. You can reuse some of the excess glue for the next section. If you have joined all bottle sections together, rotate the pressure vessel to make sure it is not crooked. After that, wait at least two or three days before you continue. In case you don’t plan to reinforce your rocket, you can now proceed with the pressure test. We explain how that works later in this tutorial. But if you plan to reinforce your rocket, we still have a lot of work to do: The whole chamber has to be sanded.
Reinforcement with fiber glass
To start with the reinforcement of your pressure vessel, you have to cut the fiber glass to size. We recommend using two layers of fiber glass. That means that the textile has to be wrapped two times around the chamber. Thus, the dimensions of the required fiber glass are:Length of the chamber x 6.4 bottle diameters.
Be very careful when cutting the fiberglass, because you do not want to pull out fibers from the cloth. At both ends of the fiber glass, we cut in little stripes so that the reinforcement can fit tightly at the ends of the pressure vessel. To reinforce your pressure vessel, you once again need a jig to hold the vessel in place. We simply use a PVC pipe for that. Don’t forget to mask the bottle thread with a little bit of tape. The resin is mixed in the ratio given on the packaging. Keep in mind that you should wear gloves and open the windows. After that, the resin can be applied to the pressure vessel using a roller. In case the bottle type you use has any patterns or notches you can use single fibers to fill them and make the surface of the chamber more even. Now you can start wrapping the fiberglass on to the chamber. For that, lay the cloth very carefully on the vessel. Use the roller to press the applied resin on the chamber trough the fiberglass until it’s see-trough. Every now and then you may have to add some resin, especially at the second layer. However, keep in mind that you shouldn’t use too much resin because that increases the weight of your rocket. Be very thorough at the ends of the pressure vessels. After completion, we suggest wrapping a single fiber around the thinnest part of the bottleneck. Wait at least a few days before continuing with the pressure test, we even recommend waiting a week. But that doesn’t mean that you can’t do anything in this time: You can remove protruding fibers and you can sand, if necessary, parts of the vessel using wet and dry sandpaper.
Now that your pressure vessel is nearly finished, you just have to test it before you can
use it for your water rocket. For that, fill the chamber almost completely with water and put it behind a barrier. You can use our launch pad to build up pressure, or you can build a dedicated system for it. A reinforced pressure vessel can hold up to 18 bars or 260 psi, most pressure vessels without reinforcement can hold about half that. However, that largely depends on how experienced you are and how conscientious you work. You should definitely test the chamber to a higher pressure than you plan to use it on your rocket. If your chamber has passed the test, it is ready to be used in your rocket.
Step 4: Building a Light and Reliable Recover System
The Tommy Timer
There are numerous approaches for parachute deployment mechanisms. In this tutorial, we show you how to build a mechanical system based on a Tommy Timer. Tommy Timers can be found in wind-up toys which are available in toy stores and on the internet. After removing the case you can cut off all protruding parts of the timer using pliers. You should also remove the plastic handle from the main axel by repeatedly clamping it in a vice. After that, bend the axel using two sets of pliers. The modified timer will later be the centerpiece of the system. You may wonder why we use these mechanical timers and don’t work with electronic systems. Well, the answer is pretty simple: Mechanical systems are way easier to build and repair, are significantly lighter and a lot more affordable when compared to electronic ones – this is especially important when a rocket crashes and you have to build a new parachute deployment mechanism. But luckily, this shouldn’t be the case all too often since the two systems we want to show you in this video have already proven their reliability with numerous flights.
Which system is suitable for my rocket?
The first system we want to show you is called Phoenix 6. It’s the latest version of our Phoenix Parachute Side Deployment System and is optimized for rockets with a single large pressure vessel. For rockets consisting of multiple pressure vessel segments we recommend building a Phoenix Radial Deployment System. This system was originally developed by our colleagues from U.S. Water Rockets, but we adjusted and optimized it for the use with a lightweight mechanical timer.
For the construction of the Phoenix 6 Side Deployment Mechanism you will need two bottles. It is necessary to use the same bottle type you have already used for your pressure vessel. Cut off the bottom of one of the bottles using scissors and remove the thread of the bottle with a saw. Now you have to cut a big opening in the cylindrical section of the bottle. In this case, the opening is about 10 cm / 3.9” wide and there should be about 3cm / 1.2” left to the lower edge. When you use bottles with a bigger or smaller diameter, you have to adjust the width of the opening. The bottle with the opening will later be the case of the parachute system. But of course, your case will need a nosecone. You can either glue a half table tennis ball on top with epoxy or you can use the nosecone of a fireworks rocket for that. Now take the second bottle and remove both the bottom and the neck. The remaining cylindrical section will be separated in two equally large pieces. One of these pieces will be the parachute door. If you want to paint your parachute system, you can do this now. First, sand and clean both the case and the door. We recommend using plastic primer before applying the paint. The spray paint can be applied as soon as the primer is dry. It‘s maybe necessary to spray several coats. After that, you can cut out two round base plates out of a thin plastic plate. You should be able to put the plates into the system, but they shouldn’t be too small and should remain in place without any glue. After you have placed the plates directly at the lower and upper edge of the opening, you can glue them in place using a hot glue gun. Please be careful and don’t use too much adhesive. Now it’s time to mount the Tommy Timer you have modified at the beginning. All you need are three small holes in the case located slightly above the lower base plate. Put the bent axel of the timer through the hole in the middle and use a small cable tie to fasten it. The parachute door, which is placed over the opening, can be fastened by using a rubber band. Just mount a loop slightly under the upper base plate on the case. Now you can wrap the rubber band multiple times around the system. Just hook the rubber band over the bent timer axel. To eject the parachute, you need a spring. For that, you can use a part of a thin walled plastic bottle. You can attach the bottle piece with wire on the case but you can also take the whole cylindrical section and glue it in place with a hot glue gun. However, if you use this method you have to watch out that the parachute will pushed out of the opening and not to the side. The parachute door can now be attached with a rubber band on the parachute.
But before we finish the construction of the Phoenix 6 mechanism, we want to take a look at the Phoenix RDS. The good news is, that it consists of even less components than the Phoenix 6. The most important component is a thin but flexible plastic cover. You can use a document cover or a thin walled bottle section for that. Mount the modified Tommy Timer at one edge of the cover using two little cable ties. On the opposite edge you can attach a rubber band loop. For the next steps, you will need a rocket with multiple pressure vessel segments. Wrap the cover around the connection between two segments, then wrap the rubber band around it and hook it on the timer axel. Another rubber band attached to the cover and the nosecone of the rocket will ensure that the cover will be pulled away when the parachute gets ejected. The Phoenix RDS is now already on the same level as the Phoenix 6 System, whose construction we described earlier in this video. The following steps are identical with both systems.
To prevent the rubber band sliding over the bend of the timer axel, glue a small cable tie head with epoxy or superglue directly at the bend. Now you can hook in the rubber band once again and wind up the timer. A few seconds later, the rubber band will be released and the parachute ejected. Please be very careful when testing the system because you do not want to get the rubber band flick into your eyes. Now, the only thing you need to complete the construction is a small trigger which holds the timer in place until the rocket launches. Luckily the construction is fairly simple. You just need a big cable tie! Cut the long part off so that the remaining cable tie is only 5cm / 2” long. Now wind up the timer and place the trigger underneath the small cable tie you used to attach the timer so that the timer can’t start running. Connect the trigger with wire and a rope to your launch pad and you are ready. But don’t forget to attach the parachute and the system to your rocket first.
Step 5: Build a Powerful Launcher
While smaller water rockets often use a launch system based on garden hose components, we want to show you the construction of a Full Bore Launcher (FBL) in this video. The advantage of a FBL is that the entire bottle opening of the pressure vessel can be used to push the water out of the rocket as quickly as possible, while other systems often require smaller openings.
First of all, let's talk about the main construction. In our case, this consists of 18mm thick plywood. This thickness is necessary to withstand the heavy forces during operation. The components of the launcher are a base plate and three feet of the same size, which are cut out of the plywood. The feet should have a hole on the underside, which will later allow it to secure the launcher to the ground. The base plate has some holes as well, so that the pipe system can be attached later. You can download a detailed technical drawing with all relevant dimensions of the main construction as a PDF file. Next, you should prime the construction and then apply external coating. After waiting a day, the feet can be screwed to the base plate.
Now, we can now take care of the core of the launch pad - the pipe system, which will later supply the rocket with compressed air and water. This consists of a set of fittings that are screwed together. Use some Teflon tape to seal the threads well. At both ends of the water and air supply there are fittings for garden hose couplings, so that hoses can be connected without any problems. Alternatively, you can also use pneumatic connectors. On the side of the air connection there is a non-return valve which prevents water from entering the air pump. On the other side there is a ball valve to manually disconnect the water filling system. In the middle of the system there is a T-piece into which a short pipe with a suitable thread has been screwed in. The system is now attached from below to the base plate of the launcher. We recommend using two pipe clamps and threaded rods. Next, we'll make the connection between the rocket and launch pad. It consists of a copper tube with a diameter of 22mm. An adapter is attached to one end of the tube system. On the other side, a reduction sleeve from 28mm to 22mm is fitted. They are attached by soldering them together. First of all, the parts are sanded with a special cleaning fleece at the corresponding points. Next, you should apply some flux to the soldering area. Wear gloves and do not to get in contact with the flux. Next, you should put some flux on the soldering area. Wear gloves and try not to get in contact with the flux. You can then put the parts together and heat them with a blow torch or a gas burner. It is best not to heat the joint directly, but to keep the flame at a nearby point on the pipe. After the tube has been sufficiently heated, the solder can now be held to the joint from above. Once you have applied the flux correctly, the solder runs around the joint and seals it. As soon as a small drop forms on the bottom, you can continue with the second junction. When the connector has cooled down, you can wipe off the remains of the flux and start placing cable ties around it. Put a bottle of the same type as you used on your rocket into the reduction sleeve. The cable ties should be placed directly against the collar. First you can use some tape to fix the cable ties. Then pull two hose clamps around the cable ties as tightly as possible. Now the connection can be screwed onto the launcher. Don't forget to use Teflon tape for that too.
To ensure a stable and straight launch of your rocket, we recommend the use of a launch tube. This is basically just a tube, which is inserted into the connector and has the effect that the rocket reaches a higher altitude. We recommend to wrap some tape around the launch tube before inserting it into the launcher. Unfortunately, conventional PVC pipes are often too weak to withstand the high forces at launch. Therefore, the PVC pipe with a diameter of 20mm should be reinforced on the inside with a steel pipe.
Now only the trigger for the launch pad is missing. You can use a short PVC pipe, which you put over the connector and the rocket. As soon as you pull the PVC pipe down, the rocket will launch. To prevent an unintentional launch, we suggest using multiple cable ties as a spring. Now you need a deflection. We use a U-piece made of bent aluminum for this purpose. Two nylon cords are attached to the PVC pipe. You can now attach your release line with a snap hook Before you can place your rocket on the launch pad, you will need to install an O-ring seal above the thread of your rocket. We use a O-ring with a diameter of 15.5mm and a thickness of 2.6mm, but slightly different sizes should also be just as good.
Water and air supply
The last thing we have to do before the launcher is completed is to take care of the air and water supply. The air is supplied using a 10-meter-long garden hose, which can be connected to the launcher with a coupling. If you have installed compressed air valves at your launcher, use a compressed air hose instead. On the other side of the hose you have to attach a car tire valve. Sand it, wrap it with teflon tape, put it into the hose and fix it with a hose clamp. You can now connect your air pump to this valve and build up pressure in the rocket. The water filling system is a bit more complex, but it allows a comfortable filling of the rocket. We use a pressure sprayer of which the nozzle is sawn off. Instead, we have attached a garden hose to it using a hose clamp. To use your filling system, simply fill water into the pressure sprayer and build up pressure using the integrated pump. Then open the valve of your launch pad and water will flow into the rocket. It is important that you fill the water into the rocket before you build up pressure with the air pump.
Step 6: Prepare and Launch Your Rocket Correctly
If you want to build a large and reliable water rocket, you do not only need good components – you should also assemble the rocket carefully and prepare it correctly before launch.
Assembly of the rocket
First, you should make sure that all components of your rocket are assembled correctly. The fins of your rocket, whose shape you should have planned at the beginning of the construction, can now be attached to the pressure tank at regular intervals with polyurethane based adhesive. Make sure that the fins are placed straight. If you haven't thought about the shape of your fins yet, we recommend that you follow our guide about the planning phase. If your rocket has several pressure vessel segments, it is important to check that the Tornado Tube which connects the segments, has been screwed on tightly. You can also attach the parachute to the Tornado Tube with a nylon cord. For rockets with only one segment you have to fasten the nylon cord at the upper end of the vessel. If your pressure vessel ends with a bottle neck, you can tie the cord around it. But if your pressure vessel ends with a bottle bottom, you have to glue the cord to the bottom with epoxy, and then lead it through a hole in the lower part of your parachute system. It makes sense to tie the cord at the end in such a way that it cannot slip through the hole in the parachute system. Afterwards you can attach your parachute system to the pressure vessel with epoxy resin and hot glue. If you plan to attach a camera to the rocket and you are looking for stable shots, we recommend a three-point parachute attachment. For this purpose, two more nylon cords are attached to the rocket chamber to prevent the rocket from swinging too much after the deployment of the parachute.
Where to launch
After you have assembled your water rocket, it’s important to find a suitable launch site. Your launch site should be located so that there are no roads, houses, trees or electricity wires nearby. You should also have a good view of the whole area. Make sure your launch site is large enough, as the rocket can drift in the wind.
But before you are ready to launch, let’s talk about the legal situation. Since we’re from Germany, we only know the legal situation here – and it’s pretty complicated. For example, you have to attach a sticker with your name and address to the rocket, and you have to get a license when flying higher than 100 meters. You can probably be happy about living in another country in this regard. But generally speaking, you will at least need the permission from the landowner. Besides that, there are often laws and additional regulations regarding the launch of model rockets. Please inform yourself.
After you have done this, the preparations for the launch can begin. We have created a checklist for you with all the important steps. It is important that you take a thorough approach and check all the steps several times. This increases the success rate of your rocket enormously. First of all, you should align your launch pad with a water level and then anchor it to the ground. Attach the release line, the air pump and the filling system. Before the rocket can be put on the launcher, you should fold the parachute and insert it into the system. The trigger, which prevents the timer from running, can also be inserted. Remember to put an O-ring seal on to your rocket. Now it’s time to place the rocket on the launch pad. Don't forget to attach the trigger for the parachute system to the pad. Once you've done that, you can fill the filling system with water and then build up pressure with the built-in air pump until the desired amount of water has flowed into the rocket. Then close the ball valve of your launcher and remove the filling system. A string attached to the ball valve can be useful if you have to abort the launch from a safe distance.
Tips for filming
For all of you who not only want to launch, but also want to make some nice videos, here are a few tips for you to get the best results possible.
• First of all, you don't need an expensive camera to take good shots of your rocket. Most mobile phones today have a camera that is easily capable of recording beautiful videos. Much more important than expensive hardware is the correct handling of it.
• One way to achieve this is to completely use the space available on the screen. That’s possible when filming in landscape - even if the rocket ideally starts vertically.
• If your camera or mobile phone does not have optical image stabilization (OIS), we recommend that you use a tripod for all shots or that you hold the phone firmly in place and do not pull it up when the rocket launches.
• If you have a slow motion function, use it! It’s awesome and you should definitely try it out.
• But the most important thing is to bring variety into your own video, and this can be achieved through different perspectives. Near, far, frog and bird's eye view are the classic ones here.
• The most spectacular shots can be made with an onboard camera attached to the rocket. We simply stick a small camera, which costs about 40€, to the pressure vessel of the rocket.
Launching your rocket
But let's get back to the launch preparations. You have now reached the point where you can build up pressure in the rocket. Once you have started, do not approach the rocket, as it may explode or launch unintentionally. Please always keep an eye on the surroundings so that nobody is endangered. You should also wear protective goggles. It is best to build up the pressure as quickly as possible using the air pump. Once you have reached your desired launch pressure, all you have to do is pull the release line and the rocket will launch.