Posts Tagged ‘wrocket-car’


Green Hornet II – New Design

We have been working on several designs for new water rocket cars over the last 6 months and have decided on a configuration for our next water rocket car. It will affectionately be called  Green Hornet II and will be painted it in the now traditional HHWRSA Green and white colour scheme, carry a HHWRSA banner and the Australian flag .

The following are design features of the new water rocket car

  • Extending the pressure vessel stack from a 3 x 2L bottle stack to a 4 x 2L bottle stack, all stacks are held together with robinson couplings
  • Increasing the total  volume from 6L to 24L – 3 x 4 bottles stacks (2L per bottle)
  • Increasing the 9mm Gardena Nozzles to 15mm Gardena Nozzles
  • Increasing the number of nozzles from 1 to 3 (1 per 4 bottle stack)
  • All new chassis design based on two truss structures and cantilevered pressure vessel attachments to provide improved chassis stiffness to hold a greater volume of water without bending and scraping on the ground
  • Adding a removable parachute attachment and remote control R/C parachute deployment mechanism
  • Utilising fibreglass wrapping of the bottles to increase fill pressures
  • Changing the two rear fins from 45 degrees to vertical and increasing the fin size
  • Maintain the existing remote control steering

Here are the hand drawn designs for the new car

Green Hornet II - Profile View

Green Hornet II - Top View


To be able to fill the pressure vessel volume we will be using a 5hp petrol powered air compressor, which should be good for approx 120psi. After that we will cut over to the hand pump to increase the pressure beyond that level.

5hp Petrol powered Twin cylinder compressor

We will utilize the same external launch cage as the previous car. The new car design may increase the length of the car slightly, if necessary, we will simply extend the length of the cage and the launch rail to ensure the pressure vessels are maintained within the cage.

We will also need to modify the existing launder to accommodate the 3 nozzles and the bigger nozzle quick release connectors.

This cars main aim is to increase acceleration and velocity over the previous car to hopefully lower the water rocket dragster speed world record. It should also be able to increase the distance record significantly. Based on our calculations we should be able to break and push beyond the 100km/hr barrier with this car.

There is nothing radical in this design, there are a few new things for us to work on and engineer out the bugs, but we expect to have this car operational within a couple of months all things going well. Our more  radical design ideas we have left for the following car as these will require a bit longer to work out each of the components.

Keep a watch on our website as we will document our build progress as we go.

Posted by on April 20th, 2011 3 Comments

Launch Day – WRA Speed Record Attempt

Launch Day Preparation

After our latest car updates, camera and marker developments we were  finally ready to have a shot at a WRA Dragster record. We decided to try for the speed record first.

For a submission to qualify we need to meet the rules as layed out at

We prepared the car with two onboard cameras, one looking forward and one looking sideways. We also prepared our coloured cups to place on the 10m road markers so that it will be easier see the car pass the road markers.

MD80 Camera mount behind the front wheel

MD80 Rear Mounted Camera

We also decided for this launch day to use twitter to provide live updates from the launch day. We setup and tested a twitter client on our iphone and it worked well. Twitter updates are appearing on

Launch Day

We arrived at the launch site at approx 2:30pm and setup the launcher and the cage, at this point we realized we had forgotten our two normal camera to capture the run, so we decided just to use the iphone video camera and ty to hold it as smooth as possible.

We then measured out the course with our 50m tape measure and marked every 10 metres with a solid chalk line across the road. From the northern end we then marked the 45.7m mark with a dashed line. We then put the red cups every 10m, the blue cups every 50m and the green cup at the 45.7m mark.

We did some twitter updates, then turned on the two car cameras, turned on the electronics for steering, filled the car with water and bubble bath and locked it in on the launch rail inside the cage. Heres how our launch went



We were happy that all of the videos were ok. We used VirtualDub to calculate the time it took for the car to reach the 150ft marker. To do this we used the side looking camera and went through the video file until we found the first frame where the car launched, this woudl be  our starting time. Virtualdub works out what type of file it is and how many frames per second the camera captured. For the MD80’s  each frame was 0.032 seconds.

We then went through the video file frame by frame until we could see the coloured cups in the frame. We then took the used the time from virtualdub for that marker when we saw the white line and the cup one frame past the centre of the frame of the camera. We listed the time to pass each marker then calculated the following

– Relative time to pass each marker putting the first frame as 0 seconds
– Time to move from one marker to the next
– Time to reach the 150ft marker
– Average Velocity at each marker
– Instantaneous Velocity at each marker

This information is available in a spreadsheet for each run   Dragster Speed Record Attempt

The results were

Speed record
First Run 4.94
Second Run 5.32
Average 5.13
First Run 122m
Second Run 100.5m
Average 111.25m


Here are some graphs of the cars velocity as it made its way down the course

Run 1 - Velocity Graph

Run 2 - Velocity Graph

We think we have done enough to get the Dragster Speed Record with these runs. We  will submit the video and spreadsheet to WRA for peer review and hope that we get it accepted :)

Posted by on April 9th, 2011 Comments Off

Tweeting our Next Launch Day

This Sunday the 3rd April at approx 2:30pm Sydney time (GMT+10 or 04:30am 3/4/2011 UTC time) we will have a launch day to try the new updates on the water rocket car. We may even have a shot at the Dragster Speed Record if things go well.

We will try out something new for the hobby and use twitter to provide updates, commentary and photos in real time during the event.

Updates will be via our Twitter Page

If your a regular tweeter then you can go to our twitter page and follow us now then get our updates as we post them.

We will use the hashtag #waterrocketcar for all posts

If you are not a regular twitter user thats ok too, just go to our twitter page above about that time in your local area, or check out our HHWRSA web site (this site) and look in the sidebar to the right —-> under the Twitter heading and updates will be there too.

Here is a good time converter, remember our time is Sydney Australia Time, and no daylight savings tomorrow :)

Posted by on April 2nd, 2011 Comments Off

Rear Exhaust Deflector

One of the things we have noticed after raising the height of the rear of the car to give more ground clearance, is that it looks like some of the exhaust will be hitting the rear wheel supports.

While this may not impact speed or distance greatly, we have added a corrugated plastic deflector at the rear of the car to ensure the exhaust is deflected up and away from the rear wheel supports.

Rear Corrugated Plastic Deflector

The rear deflector is angled up towards the back of the car as can be seen from this picture. Yes the rear wheel attachments are not pretty but they are functional :)

Angled up exhaust deflector

This deflector is only really necessary due to too much  flex in the chassis. This caused us to raise the rear wheels to get the chassis of the ground, that then moved the rear wheel supports into the exhaust plume. So this deflector is a work around, but it will be interesting to see how it performs. It may also give us more downforce over the rear wheels which would improve stability.

The connection to the launcher still fits with the deflector in place and the female Gardena should just flick up over the top of the deflector as the car accelerates away after launch.

Posted by on April 2nd, 2011 Comments Off