An idea based upon the Copper Tube Launcher

This launcher comes from an idea from the following email extract.

Subject: Single hose Launcher

I am building my launcher.

I wanted something elegant, so all I want between my air bottle
and the launcher is a single air line.

I am using copper plumbing fittings for the business end, Bosch
air line fittings for all the rest and a scrap SCUBA regulator
that I can tweak to whatever pressure I want 30 - 200psi+

I am building the launcher to have a single air line to the
business end. The effect is to pressure the rocket, then
depressurise the fill line with a valve at my end. That will
(with the aid of a non return valve and an air piston) allow
the pressure in the rocket to activate the piston which releases
and then let it fly.

A solution

This (when it is built) will allow the pressurisation of the bottle and then release on depressurisation of the air supply line.

The diagram on the left shows the basic parts of the Copper Tube Launcher with the additional fittings that make it all function from one air line and the bottle in position (note that the 'o' ring and fins et cetera are omitted).

Construction

The copper parts (purple) are assembled as described on the Copper Tube Launcher page but omitting the cable ties, the copper ring and Jubilee clips that secure them and the plastic sleeve. The rest is as follows . . .

Fixed collar (a) is built to hold three of the latches (b) as shown in the smaller diagram at the bottom. There are three pins that secure the latches (b), allowing them to move freely. The fixed collar (a) can be made from 6mm brass or copper and the latches (b) from 3mm brass. The fixed collar (a) should be soldered onto the copper pipe and then end stop (d) is soldered into a hole made in fixed collar (a). End stop (d) can be made from 3mm brass rod but it should be remembered that it must be able to withstand the force from piston (h) at the highest pressure to be used.

Next slide spring (e) onto the copper pipe followed by sliding collar (c) which should slide freely. Into the bottom of sliding collar (c) are drilled two holes - one for piston (h) and one for the end of latch (k). Piston (h) should be soldered in place such that it is able to move up and down cylinder (g) freely. Cylinder (g) is soldered onto the side of the copper tube as is mount (j) - they may be mounted together. Mount (j) is positioned such that the end of latch (k) locates in a hole in the end of sliding collar (c) and allows for the disengaging of latch (k) and sliding collar (c) when sliding collar (c) moves upto and meets end stop (d). Lug (l) is positioned such that it holds the spring (f) in place on the side of the tube.

Spring (e) needs to be strong enough to overcome the almost neglegable friction force when latch (b) is holding a pressurised bottle in place.The cylinder (g)'s diameter needs to be great enough in order to compress spring (e) at the lowest working pressure used in addition to any frictional force derived from pushing sliding collar (c) along the tube and, disengaging the end of latch (k). The length of end stop (d) should be such that it allows enough movement to disengage the end of latch (k) whilst starting from a position of holding closed the latches (b).

Use

1. With latch (k) disengaged from sliding collar (c) which is slid down the copper pipe so that latches (b) are open, put the bottle in place, making sure that any seals are positioned correctly and that the water is at the correct level.

Hold latches (b) in to grip the flange on the neck of the bottle and slide sliding collar (c) against the pressure of the spring (e). Holding sliding collar (c) in place, push latch (k) against the spring (f) and allow sliding collar (c) to locate itself. This should now, all hold in place on its own. This is the position depicted in the diagram above.

At this point, make sure any tapes holding parachutes and so on are where they should be (on the rocket or in your pocket).
2. Increase the pressure in the compressed air delivery line. Air should pass through the one-way valve into the bottle and also go into the cylinder (g) and start to press against piston (h).

As the pressure increases, there comes a point when there is sufficient force against piston (h) to move sliding collar (c) against the spring (e) upwards to meet end stop (d). During this travel, the end of latch (k) becomes disengaged from the hole in sliding collar (c) and spring (f) pushes it out of the way. The launcher is now armed and pressure should be increased until it is at the required level.
3. To release the rocket, lower the air pressure in the air line. The one way valve will stop any water from leaking back down the delivery pipe.

On lowering the delivery pressure, the force acting on piston (h) is reduced and the force stored in spring (e) pushes sliding collar (c) down the copper tube. When the sliding collar (c) clears the ends of latches (b), the slight angle of the faces that are in contact with the bottle provide enough force to push them out of the way thus launching the bottle.

Esoteric Warning

If you are experimenting with different gasses in order to find the effects of the ratio of specific heat capacities of the gas at constant pressure and constant volume ( Gamma or compressability) on performance and are considering gasses with a low, you should not use Acetylene (it is dangerous enough gas as it is) NEVER PUT ACETYLENE IN CONTACT WITH COPPER. Try looking only at gasses with a high such as Argon.

Thanks to Jonathan Edge for writing to the group.


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