Posts Tagged ‘bottle’

 

Triple Bottle Reinforced Stack – Hydrostatic Test

We have had our triple bottle stack of reinforced bottles ready for a while to hydrostatic test and finally got around to it this week.

Each bottle in the triple stack is reinforced using this method.  We had previously hydrostatic tested individual reinforced bottles to 180psi but not a stack of them. The 3 bottles in the stack are held together using robinson couplings.

Hydrostatic Test of reinforced stack

Our goal was to hydro test to 180psi. The bottles were filled with water, safety glasses were put on and being well back we pumped up to 180psi. This was a pic we took which says 177psi but we did put a few more psi in it to be sure we got to the 180psi. We left it for about 30 seconds before releasing the pressure with the abort valve.

177psi or 12bar

We didnt see any leaks which was good, so it was a successful test.

The triple stack has been fitted to the water rocket car ready for a test run. Based on the success of the last launch day we will probably need to fit a parachute to the car to slow it down, so we will turn our attention to that next.

Posted by on August 20th, 2010 Comments Off

Water Rocket Car – Demonstration Day

We were very fortunate this month to be invited along to Killara High School here in NSW to give a demonstration of our Water Rocket Car.

Murray Arnison contacted us through the HHWRSA website explaining he would  be  teaching his engineering class about water rocket cars this term and if we would be interested in coming along to do a demo. We were more than happy to oblige :) We organised for Mark to get the morning off school for this special science excursion.

We spent about an hour with the class showing the Green Hornet Water Rocket Car as well as the launcher and pump and how it all worked.

We used 100psi and 1L of water to ensure the car wasn’t travelling too fast across the quadrangle and several volunteers from the class waited on the other side of the quadrangle to stop the car plowing into surrounding  brick walls. Here is the short video of the launches.

A big thanks to Murray and the students, we had a great morning.  Good luck with your water rocket car designs and testing this term !!

Mark did a powerpoint presentation to his class the following week explaining about  water rocket cars and how we had developed it from a 1 bottle car to what it is now. He  even took the Green Hornet  in to show the class. Everyone including his science teacher was very impressed.

Posted by on August 18th, 2010 Comments Off

Water Rocket Mist Attachment – Static Test

An interesting development we saw on www.wra2.org from Jelo and Thunderrockets was a device called a mist rocket. This is an alternate method of mixing the air and water into the exhaust plume which produces a single air/water thrust and not the normal water then air pulse of a standard water rocket. Also when flown vertically there was a distinctive jet sound.

We though we would give this a try for our water rocket car.

The design uses a PVC pipe to funnel water from the second bottle to the nozzle. The air pressure in the top and bottle bottles are equal. The air in the top bottle pushes the water down the pipe and the air pressure in the bottom bottle forces air through two (2) small holes to mix air with the water just prior to escaping from the nozzle.

This is how we built it and tested it.

First we purchased some 20mm electrical conduit and a conduit cap. The 20mm conduit just fits in the 22mm bottle throat. A 10mm hole is drilled in the centre of the conduit cap and a 10mm internal diameter (ID) nut from our robinson couplings is carefully glued (with 24hr araldite) into the base of the cap, making sure no glue gets on the threads.

20mm Conduit Cap with 10mm ID nut - no glue yet

The conduit cap is then glued (24hr araldite again) to a section of 20mm conduit (longer than the bottle at this stage) and left for 2-3 days to set properly. Once this is set, this section should screw easily onto a standard 10mm robinson coupling thread.

Conduit connected to threaded rod (robinson coupling rod)

The next step is to cut the conduit so that it fits just inside the nozzle cap. The section is screwed onto the robinson coupling between two bottles then marked, unscrewed again and cut to size. The conduit shouldn’t protrude past the bottle lip as this will cause the bottle lip not to seat properly against the rubber washer in the nozzle and the bottle wont hold pressure.

Conduit cut to size of bottle

The conduit section then needs 2 holes drilled near the base of the rod. we used 6mm holes, these are to let air from the bottom bottle mix with water from the top, also if any water does get in the bottom bottle it allows it to escape.

Conduit section with cap and 2 holes drilled near the base

The completed conduit (now referred to as mist attachment) is then inserted into the bottle and screwed onto the robinson coupling. Note that about 10mm of thread was needed on the threaded rod to catch on the nut threads.

Robinson coupling ready for mist attachment

Mist attachment connected to robinson coupling

The the nozzle is screwed into place and its ready to test / launch. Here is the pic ready to test

2 Bottles with robinson coupling and mist attachment - Ready to test

The handy thing with this attachment is that it can be added and removed quite easily for test or launch.


Mist Attachment Test

The test we conducted was a vertical static test with 1L of water (no foam) and 100psi. The bottles used are 2.25L bottles. We were interested to see the following

– If we could reproduce the jet sound that thunderrockets produced on launch
– Examine the exhaust plume to see if it generate a good air / water mix
– Examine if there was any distinct air pulse after the water was ejected from the bottles

We did find that filling the top bottle a little more challenging to ensure water didn’t get in the bottom bottle. We used a small section of hose connected to a funnel to get the water past the 2 holes in the mist attachment, then gently pumped the top bottle.  Here is a video of the test

Conclusion

– We didn’t get the jet sound, even after 2 separate static tests – its a possibility that the rocket needs to be flying through the air to generate the sound, or possibly the holes were too big.
– The exhaust plume definitely had a good mix of water and air and produced a spray similar to a foam launch
– There was no distinct air pulse after the water was ejected
– An interesting observation was that there was minimal (a small amount) splash back in the bottle at the end of the thrust phase.

We will try this test again in a horizontal configuration to suit our water rocket car

Posted by on July 27th, 2010 5 Comments

Water Rocket Car MkXI – Launch Day

Even though it was a cold and slightly rainy winters day here, we were very keen to try out the Green Hornet with its new configuration, so we had a lunch day on Sunday afternoon.

The new rear end fins and low traction wheels were designed to make the water rocket car act more like a rocket for stability rather than a car, ie: The rear fins straighten the back of the rocket car. This means the rear fins need to overcome the friction of the rear wheels to effectively straighten the rear of the car.

Sounds good in theory .. time to try it out.

New Rear End of Water Rocket Car

Here is the video of the launch day. We managed only 2 launches due to the rain. We also had a father and his son on motorbikes stop to watch our second launch, that’s the noise you can hear in the background.

Results
Well we had partial success in that the launches were pretty straight, especially the first one, until there was any r/c steering input, as soon as the front steered, the rear of the car had no grip to follow and just fishtailed or did a 180 degree turn.  Obvious really after thinking about it, just like doing a handbrake turn in a normal car, …. On both runs we hit the gutter, we haven’t done this for a long time, even the r/c steering couldn’t control the cars direction when fishtailing.

Positives from the tests were the rear fins look to be working but we will need to put rubber back on the rear wheels, so we will see if there is enough force generated by the fins to straighten the car under thrust with the old wheels on.

The launcher updates worked great. The lightened chassis did work well as the car definitely accelerated quicker than the last revision.

We will keep working on it :)

Posted by on July 13th, 2010 Comments Off