4.5L Water Rocket Car

[thampson]

We had quite a bit of fun this weekend trying out the new 4.5L wrocket car. We
tried out our new launch site which we had to clean as there was heaps of small
rocks covering it, nothing a petrol powered blower couldnt fix. We cleared a 80m
stretch of the road which took about 30mins.

We tried water and foam launches at 125psi and 140psi and had some interesting
results.

Pressure Fuel Distance
125psi Water 60m
125psi Foam 75m
140psi Water 70m
140psi Foam 76m

There is a writeup going up tonight on our website but bottom line was that the
foam produced better distance and the speed to the eye (and the bike computer)
about the same. Surprisingly it also produced 1 long thrust. When we used water
only we had 2 distinctive thrusts as the water was ejected from each bottle.

We also discovered that the foam mixture makes quite a mess .... Although a
few minutes in the sun and it was dried out and dissapeared. Wife / Mother
warning, dont do this at home where you will make a mess.

We also found that with water ony there was between 100ml (140psi) and 300ml
(125psi) left in the bottles depending on the pressure used. With the foam there
was considerably less maybe 50ml but there was bubbles left as well.

The video of the launch day is here

[youtube][/youtube]

Today we did our record launch distance of 76m. Work is already progressing on our next 3 bottle water rocket car

-todd-
HHWRSA
http://wrocket.hampson.net.au

[Tim Chen]

Hey Todd!

Very nice experiments you have going on there. I am really interested in the way you are comparing the soap foam to the water. I see in your video that the foam seems to last a lot longer than the plain water does and you can see the car building momentum over the whole thrust period. The water powered car builds momentum faster but for a shorter time. The way that your car dampens the acceleration because of rolling friction makes the effect quite obvious.

Do you think that the foam is really better or is it possible that water would be more effective if you had a smaller nozzle? Could the effect only be prof that the foam worked better with a certain nozzle size?

Keep up the great work!

[RaZias]

Just tape fibeglass tape around the bottle (as seen in a bottle in air command), it burts at 260 psi.

Then you use those little black compressors for car tires, they go to 250 psi.

[U.S. Water Rockets1]

Just tape fibeglass tape around the bottle (as seen in a bottle in air command), it burts at 260 psi.

Then you use those little black compressors for car tires, they go to 250 psi.

It may be more work than that because the tape wrapped around the bottles will twist them as the bottles expand. If you try it yourself you will see the bottles being torqued. Our very first rockets were the first to use this reinforcing technique. It was going to be our "secret weapon". We noticed the effect accidentally when fast-forwarding through the time on the pad while pressurizing the rocket. The sped up video revealed the camera view rotating slowly through more than 45 degrees! When launched the rocket would uncoil violently and the rapid rotation would set off the parachute which was designed only for vertical g-forces. In a car application it could flip the car or cause it to veer off course.

[thampson]

HI Tim,

Thanks for the comments ... I think its hard to read any more into it other than for that nozzle size the foam is giving better distance .. I think the thing that was more interesting was that when using water only there is two distintive thrusts as water is ejected from each bottle, whereas with foam it just seems like 1 long thrust.

It would be interesting to try it with smaller nozzle sizes to see if the water is more efficient under those conditions.

-todd-

[thampson]

Hi Razias,

We will look at doing some higher pressure launches and reinforced bottles in future, at the moment its easier to add volume to get better distance. I would also want to test my launcher and hoses at the higher pressures before doing a higher pressure bottle test. At the moment our hoses and abort system is tested at 150psi . .so we will probably need to test this up to about 200psi before Id be happy to start reinforcing bottles.

Those small 12V compressors are fine but they really struggle over 120psi .. also they tend to heat the air that gets pumped into the bottles, this has the effect of reducing the volume of air at a particular pressure that the bottle will hold.

We use a Top Peak 3 stage hand pump which will go to 240psi, so we have plenty of headroom on the pump ... it does give a good workout pumping up these big volume rockets though

-todd-

[Aquafire]

Just tape fibeglass tape around the bottle (as seen in a bottle in air command), it burts at 260 psi.

Then you use those little black compressors for car tires, they go to 250 psi.

It may be more work than that because the tape wrapped around the bottles will twist them as the bottles expand. If you try it yourself you will see the bottles being torqued. Our very first rockets were the first to use this reinforcing technique. It was going to be our "secret weapon". We noticed the effect accidentally when fast-forwarding through the time on the pad while pressurizing the rocket. The sped up video revealed the camera view rotating slowly through more than 45 degrees! When launched the rocket would uncoil violently and the rapid rotation would set off the parachute which was designed only for vertical g-forces. In a car application it could flip the car or cause it to veer off course.

I never saw you discuss this idea before. Did I miss that?