Posts Tagged ‘failures’


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.

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

Small Diameter Nozzle Failures

Testing new ideas plays a big part in water rocket development. While trying to keep the wrocket car straight the idea of reducing the diameter of the nozzle was an obvious choice to even out the thrust. So we tested a few different ways to create a smaller diameter nozzle.

Its often said you learn more by failing at something .. and whilst most of these attempts failed it has  taken us in the right direction to accomplish the result. We decided to post the details of these failures anyway to show the different approaches to solving the problem

1. Glued on Nozzle

We tried to glue the nozzle onto the outside of the bottle cap using 2 part Araldite and put a 6mm diameter hole in the bottle cap. This would in effect create a 6mm diameter nozzle as compared to the normal 9mm diameter of the gardena nozzle. There is a rubber seal between the nozzle and the bottle cap. Both the nozzle cap and the nozzle were sandpapered to create a rough surface for the glue to bond to. Here are some pics

Nozzle Parts before glueing

Nozzle Parts before glueing

The araldite was applied to the nozzle, both sides of the gasket and the bottle cap and left for 30hours to dry.

Held in place for 30 hours

Held in place for 30 hours

Here is the nozzle and bottle top glued.

Glued Nozzle

Glued Nozzle

View of the 6mm nozzle

6mm nozzle

6mm nozzle

It was attached to a 1.5L bottle and pressure tested

6mm Nozzle of 1.5L Bottle

6mm Nozzle of 1.5L Bottle

The results was the nozzle failed at 80psi. It was an explosive failure not just a leak, the bottle flew off and the nozzle section was left in the launcher. Here is a pic of the nozzle pieces after the failure

Failed Connection

Failed Connection

Reason for Failure:

The most likely cause of this failure was the rubber gasket itself. It looks like it failed in the rubber material itself possible as it was being stretched due to the air pressure. Its possible the glue may have bonded better to the nozzle and bottle cap directly without the gasket, however the bottle cap lid is slightly curved so we thought we would need a gasket.

2. Nozzle Filled with Araldite and Drilled out

Another method we used to try to obtain a smaller diameter nozzle was filling the nozzle itself with Araldite, waiting until it was set then drilling out a 6mm hole. The nozzle sidewalls were sanded prior to filing with Araldite.

Nozzle filled with araldite

Nozzle filled with Araldite

This didnt work out either as the whole section of Araldite turned and lost grip with the sidewalls of the nozzle when it was drilled with a 6mm drill bit. The slug of Araldite just fell out.

3. Nozzle filled with Araldite + 6mm drill bit

This attempt used the same process as above by filling the nozzle with Araldite but this time having a 6mm drill bit placed down the centre of the nozzle until it was nearly dry. The idea was to pull it out just before it was set. This didnt work out either as the Araldite went off quite quickly and it was too late to remove the drill bit. Again the whole Araldite slug came out as we puled out the drill bit.

4. Metal gasket inside bottle cap.

The obvious answer was to put a thin metal gasket with a diameter just smaller than the bottle cap inside the bottle cap itself. IT is placed between the nozzle and the rubber gasket, with of course a 6mm diameter hole through the centre. We tried this first with a 10c coin and drilled a 6mm hole through the centre of it. For non Australians this coin fits fine into the bottle cap but it is probably 2mm thick. This was too much and there wasnt enough thread left to do up the nozzle on the bottle.

We are currently searching for an alternative for this metal gasket, something in the order of 1mm thick or less and just under the diameter of the inside nozzle. This we think will be the best solution and as soon as we have one built and tested we will post some pics.

Having done all this preliminary work, its possible now that we may not need a reduced diamter nozzle as the rear fins have provided much better stability, however for distance record attempts it may come in handy :)

Posted by on August 1st, 2009 Comments Off