New launcher

To launch the new rocket I definitely needed to build a new launcher because the other one was way to small for this rocket and you couldn't really call it a "launcher".
The new launcher should contain the gardena quick release and a launch rod to guide the rocket. I wanted to make it a tripod so it would be stable on uneven surfaces. Beneath is an image I made with Blender (a free open source 3D creation program) just to see what it would look like.

I had some leftover plywood which would function as a base for the launcher. For the launch rod I used 2 pieces of 10mm glass fibre rod fitted over a piece of 8mm carbon fibre rod, this makes the rod easy to transport because it can be divided into two parts. The legs of 50cm length where sawed from a mounting rail and are mounted on the base with bolts and nuts, so they can easily be removed for transport. The gardena quick release is pulled down by a pair of springs, during pressurization the quick release is held in the locked position by a piece of wood. At launch this is pulled out, the springs pull the collar down and the rocket is released.

Ready to launch some rockets!.... or isn't it...

 

Proven techniques

After the disappointing results of the last few launches I decided to build a new rocket. I just wanted a rocket that worked so I chose to use common techniques and materials that have been proven to work.
I Chose to use a "Robinson coupling" to splice the bottles, this is probably the easiest way to connect bottles. A Robinson coupling consists of a hollow threaded tube that joins the bottles together, the hollow thread allows water or air to pass from one bottle into another. "HHWRSA" has a great video on how to make a Robinson coupling: http://wrocket.hampson.net.au/?p=1081  and that is exactly the way I did it.

The recovery system is based on the side deployment mechanism from Air command water rockets but without the electronic timer and the servo, instead of them I used a so called "tommy timer" which I've taken out of a cheap wind-up toy. At the launch pad the gears of the timer are jammed by a piece of plastic wire, at liftoff the wire is pulled out and the timer starts.

The pressure vessel consists of three 1.5 liter (labeled) bottles, so the total volume will be around 4.7 liters, and it is equipped with a 9 mm gardena nozzle.

The rocket will use a 1.6 meter long external guide rod to keep it stable during the first part of the flight, by the time it leaves the guide rod the rocket should go fast enough for the fins to keep it stable. The fins will be made and attached the same way as on the sov-4-20 rocket (see:SOV-4-20 part-1). 

With the great videos of the side deployment mechanism and the robinson coupling building the rocket was pretty much straightforward. 

I'm looking forward to launch this rocket, but a bigger rocket needs a bigger launch pad...

SOV-4-9

This is actually the same rocket as in the 2 previous posts but with a 9 mm gardena nozzle. the reason I added this 9 mm nozzle is that I wanted the rocket to have a longer thrust phase and fly slower. I made the nozzle from a soap dispenser cap and a gardena quick connector, the reason that I used this cap is that it has a longer thread so there's enough space to hold the connector and a washer, and it already has a hole in it to put the nozzle through. 

It had been a cold and wet summer but there were a couple of good days at the beginning of the fall so I made some time to launch the rocket again.
After a 10 minute drive and a 5 minute walk we arrived at launch site. I assembled the launcher, prepared the rocket and another 10 minutes later we were ready for the first launch. The plan was to launch the rocket at 100 psi again but (as always) things didn't go as planned. The rocket took off spontaneous at 60 psi leaving the nozzle and his adapters on the launcher. We got the rocket back and reassembled it but the second launch it had the same problem again, we tried a third time again with the same results. Probably the stress from previous launches had made some cracks in the thread of the cap so it couldn't hold the pressure anymore. I had no tools and materials to fix this in the field so we went home a little discouraged by the failed launches. 

Well, at least there's a nice onboard video that shows the kids had fun...