Water Rocket Recovery Systems Index

Sending several hours work up into the sky is a very exhilerating experience - especially if it stays up there for a long time. But, unless you find a way of sending them into orbit, they have to come down at some point and the higher they go, they harder they fall.

This index covers some of the so-called recovery systems that are used to allow a softer landing with, hopefully less damage to all of your hard work.

Ideally, your rocket will be aerodynamically sound. 2 x 2 litre rocket. Click here to see the pictures.Its low coefficient of drag will let it get to a great altitude but, having got it there, you need something to slow it down - not doing so lets the 1½litre 'Egglofter' rocket hit the ground at around 50mph and the 4 litre, 2 bottle rocket goes so fast that it is quite capable of bending the front bottle. Some way of increasing its coefficient of drag is required from the highest point of the flight (apogee) is one alternative, cushioning the impact is another.

Parachute Systems


There are three parachutes considered here;

  • Circular Bin-Liner parachutes (30 grammes weight - shroud + cords et cetera) - look at the pictures; and,
  • Circular Nylon parachutes (50 grammes weight - shroud + cords et cetera).
    The extra 20 grammes accounts for a loss of around 1% of height in the flight. It also amounts to less than 1/8th inch of water in the rocket - well within experimental error - look at the pictures.

Both are essentially of the same design but using different materials. The bin-liner type is quicker and easier to make but is not as strong. The nylon type is more of an investment of time and involves solving some techical problems regarding sewing (explained). Find your feet with the bin-liner and then move onto the nylon.

  • Parafoil chutes. Very interesting, esoteric design that could contribute to greater downrange distances if trimmed correctly - it is also possible to trim it so that it ends up at the launcher. Again, made from nylon - look at the pictures. This type of chute does not give such great 'in the air' times as a circular chute and it even weighs more (80 grammes weight - shroud + cords et cetera) but what it lacks in time aloft, it makes up for in wow factor.

Release Mechanisms

Deploying the parachute at the correct time is a great problem. Too early and it never gets as high as it was going to - too late and the might not have a chance to slow down the rocket's decent. Timing depends upon what you want. A long time in the sky (the object of some competitions) required deployment high up whereas a soft landing (always required) merely needs full deployment and a chance to slow down before impact. Read a discussion of the pros and cons of the various methods.

  • Nose Separates at Apogee (NSA) . Mounted in the nose cone, the parachute is deployed at the highest point in the flight and the rocket stays in the air for the longest time. Mounting the nose cone with the parachute inside it on the base unit is exceptionally easy as the operations of parachute packing and mounting are kept separate - it is as simple as screwing the top onto a bottle. Also discussed on this page are some parachute packing strategies and how to use Talcum powder or PTFE Sheet.

  • Non-metalic timers. Looking at the rules put out for Science Olympiads, metal is not allowed therefore some other ideas have to be used.

  • Wind Resistance Flap. A flap sticks out and at launch is pushed back where is stays until the wind speed drops sufficiently to allow it to move out - this time to deploy the patachute. This method is described on Dave Johnson's page which describes the release mechanism amongst other things.

  • Tomy timers. These small, spring/escapement mechanical timers are used to time the deployment of parachutes (second and subsequent stages in multistage rockets and so on). Bruce Berggren's pages show (amongst other things) how to use a small clockwork motor as a timer to deploy further stages as well as parachutes.

  • Balloon release. This has a balloon in the nose cone that is large enough to push the nose cone off the front of the rocket. It utilises the fact that the bottles used in water rockets come in slightly different sizes so, having a nose cone that will slip off the front of the rocket (forced by the balloon) allows the deployment of the parachute. The clever bit of this is that the pressurised bottle expands because of the pressure inside it trapping the nose cone on top.
    A flight would happen by putting the balloon into the nose cone, then the parachute and then pushing this down onto the top of the rocket. Then the rocket is pressurised thus gripping the nose cone. The rocket is launched and when sufficient pressure inside the rocket has gone, the balloon can start pushing the cone off as air starts to leak in. If this leaking action is timed correctly, (it can be speeded up by making more small holes in the nose cone) the parachute will be deployed at apogee. To see details of this device, look at Gary Ensmenger's Bigfoot site.

Drag Systems

These are systems for increasing the drag but are not strictly parachutes.

  • Ribbon. This is deployed at apogee and flaps in the air on the way down thus creating drag in the same way that a flag does in the wind. They can be deployed in the same way as the parachutes above.

  • Air Brakes are used to slow down the decent of the rocket. These large flaps are deployed at apogee and the rocket falls slowly to the ground.

  • Ball or cone. Destroying the aerodynamics of the rocket by using a ball or cone that falls off at apogee - the rocket floating down on its side.

Tumble Recovery

  • Nose Weight Loss. Simply, this is where the nose weight is water that allows the rocket to be stable on the way up but empties out on the way down so that the Cp - Cg stability is lost by the Cg moving aft by the loss of the weight of the water.

    To effect this, have the top part of a bottle on the top of a rocket (acting as a cone) and add sufficient water to make the rocket stable. The hole(s) in the cone should be large enough to let the water out quickly on the descent so that stability is lost well above ground level. If this occurs correctly, the rocket should lose stability and tumble to earth (remember that it weighs less as well so there is not quite as much energy to dispose of at impact due to two factors: loss of mass; and, loss of speed.


  • Wings. Adding larger fins, close to the centre of gravity allows a rocket to glide to earth by providing some aerodynamic lift. These are also good if you want to extend the downrange distance of the rocket

Cushioning Devices

The damage to the rocket happens because it has such a short distance to slow down - literally the height of the grass. The energy that has to be absorbed in such a short period of time causes plastic deformation of the front of the rocket. Lengthening this time period or allowing the energy to be stored in the form of elastic deformation will improve the longevity of the rocket.

  • Rubber ball nose. A rubber ball, such as a tennis ball, is taped to the nose of the rocket - couldn't be easier. On impact, the ball compresses, lengthening the duration of impact - the rocket simply bounces and lands from a lower altitude.

  • Foam rubber 'bounce' cone. A foam rubber nose cone that hits the ground first. Again, no problems regarding the timing of parachute deployment and the rocket retains its aerodynamic properties. Once again, the rocket bounces, landing from a lower altitude.

  • Retro-Rocket. A small water rocket mounted in the nose (a) is triggered by proximity to the ground, providing a short, reverse-thrust. A seal in a pressurised bottle is broken when the end of a rod attached to it touches the ground (b) - pushing it inside the bottle (c), releasing water to provide the reverse thrust and hopefully reducing the velocity of the rocket to one that will not damage the rocket by the time it hits the ground (d). Although I have not built this yet (soon, I hope - I am currently trying to find some 19mm plastic tubing that will withstand about 5 Bar), I have done some computer modelling looking at capacity, rod diameter, pressure, weight, mass of water and so on. You can download this to play around with yourself. Click here to download from this site the Lotus 1-2-3 97 spreadsheet (h2orretro.123) zipped up (h2orretro.zip - 32,630 bytes).

    MD5 hash = 4d961cce3f93aac3bca4216273abbf69

Thanks to the following group members (in alphabetical order) for their help and suggestions: Bruce Berggren; Bill Clagett; Ian Clark; Randy Crawford; Jim Gage; Carl Geisser; Clifford Heath; Bruce Johnson; Dave Johnson; Patrick Matthews; Gordon McDonough; and, Don Wilkins.
Prozac (tm) Rocket
Here's a rocket that you needn't worry about :-)

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