H-Base for a Water Rocket Launcher

A H Base has the advantage that if the ground where you are launching is too hard to push a stake in, you can still set up your launcher. They are also lighter, and, arguably less dangerous.

Design Considerations

With summer aproaching, I decided to have a go at making a H Base for the launcher. The stake base, using the swing ball base is heavy and makes the launcher long to carry and taking into account the spike, fairly dangerous (thinking of someone falling on it while carrying it to the launch site). It is also difficult to drive into hard earth and in soft earth, is not as stable as I would like.

The H Base is made from 21.5mm od white PVC overflow pipe (the grey 22mm od overflow pipe will do although it is a little more difficult to assemble the base) with 'T' pieces to fix the bits together. Conection to the bottom of the business part of the launcher should be as easy and as reliable as possible.

Parts

To make one, you will need . . .

• 3 metres of 21.5mm od PVC overflow pipe;
• 4 'T' pieces;
• 2 Jubilee clips;
• A Dog restraint screw (optional);
• a pipe cutter (a pipe cutter won't cut the grey pipe very well but manages the white PVC pipe with little problem); and,
• a Stanley knife.

Construction

You need to have 6 equal lengths of PVC pipe and a short stem to mount the launcher on. I used around 6" (15cm) of grey pipe for the launcher stem but you can use the white pipe for this. Once you have cut your stem, divide the rest of the pipe equally into six using the pipe cutter or Stanley knife - if the latter, making sure that the ends are cut squarely.

Assemble the pipes with the 'T' pieces as in the diagram upper-right. To make it more stable (if you are going to launch a lot of heavy rockets), you can glue the joints marked 'G' - the joints fixing the cross bar of the H - taking care not to get glue on the other joints. Doing this will allow you to dismantle the base and pack it into a small volume suitable for carrying to the launch site by a child/slave/ground crew member, or by tying to a bicycle. If you are not going to use glue, then, whenever you dismantle the base, always leave the joints marked 'G' in place - doing this will not give them the opportunity to wear loose. The joints marked 'G' carry all of the rotational forces whereas the others are bending forces.

To fix the launcher (my Copper Tube Launcher with its 90º elbow at the bottom) to the H-Base, start off with the short, vertical pipe in one of the T pieces as in diagram a above-left (this will give you something to hold it with during the next step and make that operation safer for you. Very carefully, and using the Stanley knife, and, only cutting away from yourself, cut the part in digram b that is coloured blue so as to create a slit in the tube through which you can put the elbow of the launcher - just separate the two sides, there is no need to remove any material.

Once you have your slit, push the bottom of the launcher into the tube as in diagram c and then secure the launcher with Jubilee clips to make it sturdy. With the short piece of tube on the bottom, this can now fit into the H-Base that you have made.

To use any other launcher, you simply need it to have a length of pvc tube to attach it to the base as in the photograph on the left, showing the copper tube launcher and the hose connector launcher.

Use

1. At the site, assemble the H-Base as shown in the picture at the top of the page except for the central, vertical piece with the launcher attached to it;
2. Fill the rocket to the desired level and secure rocket to the launcher with launch tube if used;
3. Turn the rocket with the launcher attached the right way up and then push the launcher's tube onto the T piece at the centre of the H-Base as in the picture at the top of the page.
4. Pressurise and launch in the normal way.

Note that you should run the release string so that it is parallel with the cross-bar of the H-Base so that when you pull the release string, there are no twisting forces on the joints of the launcher base - only bending forces.

Variations

One problem is that the launcher is quite light and there is nothing fixing it to the ground other than gravity. When the release string is pulled sharply, it can lead to the launcher being pulled to one side resulting in a possible mis-firing of the rocket.

One solution to this problem is to use a tent peg or one of the corkscrew type dog securing skewers that you can use to secure a dog to a lawn. Knock the peg or screw the skewer into the ground and position the launcher over it so that the launch release string passes down through the metal loop. This will result in the only forces acting on the launcher to be downwards thus preventing a sidways movement at launch. Although this is sharper than the stake, it is nothing like as long and may also be protected (perhaps this should read 'the users may be protected from the point') by putting a suitable cork on the end of the point.

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