HHWRSA

Just getting the last few things done on the 2 bottle water rocket today to get it ready for its launch on the weekend. Two things built were a faring for the gap between the bottles and making a nozzle for the 1.25L cap and finally assembling the water rocket

Water Rocket Nozzle

The nozzle first. We had made nozzles for our 1.5L single bottle water rocket but it had a bigger cap so we had to make one to fit this size bottle cap. We used a gardena male adapter, its sold as a 12mm fitting in hardware stores to fit straight onto a tap. Its exit nozzle diameter is 9mm.

12mm Gardena male fitting

The part where it screws onto the tap was nearly all cut off leaving only a 2mm section. This 2mm section is still needed as it holds the fitting inside the bottle cap. It was cut pretty much right through the end of the last “A” in gardena in the pic above.  A file was used to then reduce the diameter of the ridge to get it to fit inside a bottle cap. After filing and shaping here is what I finished with.

Cut & shaped gardena fitting

Next a hole was drilled in the bottle cap to fit the size of the nozzle. The hole in the bottle cap needs to be big enough for the fitting to go through but still have the ridge that we just shaped inside the bottle cap. I estimate the hole in the bottle cap is ~ 18mm but I didn’t have a drill bit that big, so drilled a 12mm hole then used the end of a file to make it bigger. I had to make sure I cleaned up the hole of any plastic burs. I just used a sharp blade to do this.  Be careful !

Next I cut a washer from a bike inner tube, easiest way I found was to draw around the outside of the bottle cap on the rubber then cut just inside the mark so it will fit snugly inside the bottle cap. Also cut out a hole at least 9mm in the centre for the water to get out the nozzle.

Here is what we have

Nozzle Parts - (L to R)Â washer, bottle cap, gardena fitting

Assembly is easy, no glue is needed – first put the gardena nozzle through the hole in the bottle

Cap & gardena nozzle

The put in the washer and screw it to the bottle

Cap, Gardena fitting and washer

Here is what it looks like attached to the bottle. Just blow in the end to see if it leaks or put it on your launcher .. whichever is easier. If it leaks check the washer is in the correct place.

Nozzle attached to rocket

Bottle Fairing

I wanted to put a fairing over the space where the two bottles are joined to make it as aerodynamic as possible. I used a 1.5L P&N bottle and cut the middle section out of it. I realized the diameter of this bigger bottle would be slightly bigger than the 1.25L, so to make it a snug fit I needed to shrink it a little.

I don’t have any pics of this method as I don’t have a heat gun or a blowtorch so I used the hotplates to shrink the 1.5L bottle (this is not the recommended method). I filled a 1.25L bottle full with water, attached the pump and pressurized it to 20psi (the gardena quick release came in handy). This made the bottle nice and solid. I slipped the 1.5L section over the top of the 1.25L then rotated it over the top of the hotplate until it started to shrink. It did buckle a little but it did shrink. I will have to work on this procedure, but for the time being it worked. I depressurized the 1.25L bottle and slipped of the 1.5L section.

The 1.5L section was put in the space between the two joined bottles and taped on with strapping tape. Note there is only atmospheric pressure in this space, not pressurized air from the bottles. Once the fairing is taped in place the water rocket has a nice aerodynamic shape all along the length of the rocket. (see pics below)

Water Rocket Assembly

I finally got to the point of assembling the rocket. All the sections were put together with 3M strapping tape.

• PPNC (Ping Pong Nose Cone) Nosecone connected to pressure bottles
• Two bottles – Robinson coupled were tightened and pressure tested to 40psi
• 9mm nozzle put on the bottom pressure bottle
• Removable fin assembly (RFA) was taped to the bottom of the rocket.

Assembled 2 bottle water rocket

Last thing to do is fit another speed flap and test it on the timer prior to next weekends flight