Water Rockets Launcher Discussion


There are many launcher designs available and you should have a look at each of them to come to a reasonable decision about which you want to build for your purposes and how seriously you take water rocketry at the time you build your launcher. There is nothing to stop you from building a simple launcher and trying out something a little more sophisticated later on.

Many launchers though there are, they can be split into groups according to seal position. There are (until someone comes up with another, valid idea on this subject) only four positions to seal a bottle onto the launcher:

  1. The inside of the neck;
  2. The end of the neck where the bottle cap seals;
  3. The outside of the neck where there is a flat bottomed groove; and,
  4. The flange.

Each of these potisions has advantages and disadvantages

Seal Position Pros Cons
  • Easy to set up each bottle, just push on;
  • No fiddling with o-rings on each bottle;
  • Sealing force is radial.
  • Surface is not machined and varies in shape;
  • Not a standard size - some bottles fit, some don't;
  • Expansion due to pressure can reduce seal pressure slightly.
  • Machined surface of standard size;
  • All bottles fit one launcher;
  • No fiddling with o-rings;
  • Bottles are designed to seal on this face.
  • Holding device has to hold sealing force as well as pressure from bottle - sealing force is axial.
Outside Groove
  • Machined surface with flat bottom;
  • Sealing force is radial;
  • Expansion of neck due to pressurisation will only make seal tighter if a metal launcher is used.
  • May vary in diameter - have to use different o-ring sizes;
  • Some bottles do not fit into launcher at all;
  • O-ring travels with bottle - although not too expenseive (15p (UK)) this is inconvenient if the bottle is lost.
  • Flat face therefore any bottle will seal regardless of the flange size or nozzle dimaeters.
  • High surface area means a large force required to hold on the launcher - sealing force is axial.

The launcher that you end up making will largly depend upon the materials that you have available and what facilities you have for assembling them.

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