A plastic bottle was taken as the rocket body. A plastic tube vertically mounted on a wooden frame was used as a launcher. A bottle filled with water about 1/3 is hermetically placed on this tube. At the bottom of the tube, there is a valve from the bicycle tube through which air is pumped in by a pump. When air is pumped into the bottle, high pressure is created above the water at the top of the rocket body. Air pushes water through the neck.
And when the bottle breaks off the launcher, the stream of water continues downward, creating jet thrust and pushing the rocket upward.
The take-off height of the rocket, made on the basis of a two-liter bottle, at launch was up to 50 meters.
Despite the fact that a rocket powered by a water jet engine is nothing more than a toy and such engines are not used in real life, the same principle is the basis for the operation of vessels with a Pump-jet propulsion. It is actively used on floating armored vehicles and small vessels operating in shallow water.
We will need:
Plastic bottle, water pipe (about 50 cm long), steel angle, two clips for installing pipes on the wall, valve, wood board and bicycle pump.
We make a support that will hold the tube in an upright position. To do this, we fasten plastic clips to a metal corner purchased in a building materials store. They can be used to place and remove the tube from the support.
We screw the corner for stability onto the bed – a piece of board.
Just before the start, it will need to be filled with water. Detachable clips will come in handy here. The tube can be removed, inserted into the bottle, without fear of spilling water, put on a tighter cork and then reinstalled.
To launch the rocket, you need to go to an empty space, away from windows and cars. The rocket flies very high, and the trajectory of its flight is practically unpredictable. In order to fix this, we could stick stabilizers on the bottle, but for now our first test was only a test of the launcher so the bottles aerodynamics weren’t tested yet. Due to the same unpredictability of the flight path, the person who will directly launch the rocket must be dressed taking into account the fact that the rocket pours a stream of water in flight, and it may well hit him.
- We pour water into the rocket. It should fill the bottle by about one third – this is the optimal ratio of water to air.
- We stick a tube into the bottle, putting it tightly on the cork.
- We connect the bicycle pump.
- We fasten the tube with the bottle put on it with clips to the support.
- Now you need to quickly and quickly pump air into the bottle. And after 10-20 seconds, it will break off under pressure and fly up. The flight does not last long, but it can always be repeated again by simply pouring a new portion of water into the bottle.
Materials + costs
- Small wooden pallet – free
Can be found at many shops as they are used to transport goods and usually thrown away
Pallet was broken down into planks to use to make the frame of the launcher
Alternatively, wood can be bought at DIY shops to assemble the frame, varied cost depending on the type of wood
- Bottle for rocket combustion chamber – 17p
2 litre fizzy drinks bottles are available in most food shops and supermarkets, and are usually very cheap
Important to use a fizzy drink bottle as they can hold significant pressure (fizzy drinks are usually pressurized at around 14 bar)
- PVC pipe (22mm diameter) – £2.50
Available in B&Q or other DIY stores
Used to create a relatively tight fit between the opening of the bottle and the pipe, and 22mm was a near perfect fit
- Tent pegs – free
Available in most outdoor shops, I used tent pegs I had at home but if you don’t have any available, they are available for under £5
Used to hold the bottle in place while it is pressurised and then pulled out to release the bottle
- Waterproof Silicone sealant – £10
Available from DIY shops
Used to create a seal between a bicycle valve and the PVC pipe. This is how we would transfer pressure into the bottle
- Bicycle inner tube – Free
We used an inner tube that was punctured to source the valve, however if you don’t have an inner tube, they can be bought for under £5 in stores like Halfords
We cut the valve out from the inner tube with some rubber left around it, to make it possible to use a standard bicycle pump to pressurise the rocket
- Assorted Screws – £2.50
Can be bought from any DIY store
Used to attach the wooden frame together
Results of the first tests
The general design concept worked well and is likely to be our final design
A few improvements we could make have been highlighted
Our first observation of the design highlighted an issue where screws extended from the wood beneath the launcher, where you would instinctively reach to pick it up. This is obviously a danger so our next design must not make this mistake. On our first test launch, the rocket released before we had secured it onto the launcher as we were not expecting it to be pressurized so quickly. When we tested again, the sealant between the pipe and inner tube valve failed. It is clear that it was not a suitable adhesive for the application, so we used a hot glue gun to secure the valve properly. This was not an ideal fix as a hot glue gun is not a common household item and doesn’t fit with our values of creating an easy and accessible rocket design.
After this repair, the rocket launched successfully multiple times, however, we noticed it would leak quite a lot of water at high pressure. To combat this, we overfilled the bottle to allow water to leak out and still be at 1:3 water to air ratio when the rocket launched. We also noticed it was quite difficult to release the rocket using the tent peg. The person releasing the rocket would have to hold the launcher firmly and pull the peg out with force, meaning the rocket could not be released from a distance. This means the person would get covered in water when the rocket goes up. On our last launch, the rocket released early without us intending for it to be released. We realized the problem could be due to the PVC pipe not being securely attached to the platform, allowing the bottleneck to bend away from the tent peg securing it in place.
Issues and potential fixes
- Screws protruding through the launcher base
Can be fixed by selecting shorter nails to attach the launcher together, however it is important the nails are long enough to properly secure the launcher together
- Bottle leaking water under high pressure
We need to slightly expand the PVC pipe at the bottle neck, to create a better seal. We tried Using an O-ring, however it was too wide to fit the bottle. We plan to slightly heat a ring of the pipe to expand it a bit.
Another solution is also to pump up the bottle quicker. We could use an electric pump or a bicycle pump with a bigger air chamber to pressurise the bottle quicker, therefore the water would have less time to leak out
- Quite difficult to release the rocket with the tent peg
The hole the tent peg is in needs to be slightly enlarged, to allow the peg to slide out easier. This would allow us to attach the peg to a rope, so the rocket can be released from a distance, and the person releasing it doesn’t get wet
- Rocket released without the tent peg being pulled out
This issue occurred due to the pipe bending to the left/right of the peg that secured it in place. This can be fixed by securing the pipe in a second location, currently the pipe is only secured at one spot, which can cause flexibility in the pipes orientation.
Another fix is to secure the bottle with a tent peg on either side of the bottle neck, however both tent pegs would have to be pulled out simultaneously
- Valve system requiring a hot glue gun to be sealed
We need to test/research a different way of sealing the valve to the PVC pipe
An alternative way is to buy a pipe connector to fit the end of the PVC pipe, and drill a hole to perfectly fit the valve, however this would make the design more complicated.