Water Rcoket Car Development

[thampson]

I thought I would share the development videos so far on our wrocket car. There is a writeup on each video with accompanying explanations of the developments on our website at http://wrocket.hampson.net.au

Just a note that this started out as a science experiment for my sons second grade science expo and has just moved along from there .. We have found this is great fun and surprisingly we dont end up destroying wrockets if tests dont go so well, which is what we have previously experienced building water rockets. Dont get me wrong, they are great fun but destroying a wrocket that took a week to build on its first launch when a test fails is a little depressing. With the wrocket car even if it rolls or snaps hooks into the bushes, we just drag it out, brush the dirt off and go again ...

Most of the development so far has been working on stability and controlling the direction of the wrocket car, which I believe is a big part of the science and engineering of wrocket cars. For those staring out and havent built water rockets before, you may wish to at first use a string to run the wrocket car along while working out the propulsion part of it.

For those that already have build water rockets and have worked out how to make them go straight then the string is not needed and you can enjoy engineering a water rocket car to go straight by itself.

Enjoy the videos

Water Rocket Car MkI - 1.5L angled down Bottle
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Water rocket Car MkII - Upgrade from 1.5L to 2.25L Bottle
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Water Rocket Car MkIII - Lower Centre of gravity - Narrow Nozzle
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Water Rocket Car MkIV - Rear Fins at 120psi
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Water Rocket Car MKV - Rear Fins + Bike Computer at 140psi
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More development to come

cya
-todd-

[The Mooseheads]

Todd,

Thanks for sharing your water rocket car videos and experiments. Has anyone suggested using a multi-stage design?

Not long ago. 4 or 5 years max. I saw a toy car that was made by one of the big name toy companies. The car had a pressure vessel inside and you would pump it with a pump station. There was a gear system connected to the axle that would release the air in the tank after 20 feet or so of rolling. The purpose was to get the car rolling and then the air pulse would come out and give it a thrust of turbo boost and it would pick up speed and really go far.

You car reminded me of this and I thought I would toss out the idea of a multi-stage car. If you put a small nozzle on the first stage then you could get rolling up to speed before the main motor kicks in. I think the less abrupt acceleration of a rolling start would help you car go farther.

I will try and remember the name of the toy car I saw.

[RaZias]

More faster ? It´s easier !! Try to make a car with 4 rockets so you will end up with 4 nozzles, you will need a four nozzle launcher.

Then try thin wheels and surrond them with Teflon tape.

Does a 1 wheel in the back and 2 in front may make less drag ?

[RaZias]

More faster ? It´s easier !! Try to make a car with 4 rockets so you will end up with 4 nozzles, you will need a four nozzle launcher.

Then try thin wheels and surrond them with Teflon tape.

Does a 1 wheel in the back and 2 in front may make less drag ?

Anyway, I saw the video of your static test, it remained a lot of water inside the rocket...that is heavy, you need to make something about it.

I know that someone putted an vertical bottle in a WRC and connected it to a nozzle by a curved tube.

Otherwise you need to open the bottle, put something to divide it inside verticaly so you will create a compartement for the water.

[WRA2]

More faster ? It´s easier !! Try to make a car with 4 rockets so you will end up with 4 nozzles, you will need a four nozzle launcher.

Then try thin wheels and surrond them with Teflon tape.

Does a 1 wheel in the back and 2 in front may make less drag ?

Anyway, I saw the video of your static test, it remained a lot of water inside the rocket...that is heavy, you need to make something about it.

I know that someone putted an vertical bottle in a WRC and connected it to a nozzle by a curved tube.

Otherwise you need to open the bottle, put something to divide it inside verticaly so you will create a compartement for the water.

What about using a different container like the ones that have the neck on one side to make pouring easier (motor oil comes in this type in the U.S.) but I have also seen detergents in similar containers. The idea would be to place the nozzle as low as possible to allow more water out.

[thampson]

The static test doesnt reflect what actually happens when a water rocket car is launched. Under launch conditions the bottle accelerates horizontally faster than the water itself and the water is pushed back / sloshes against the nozzle. At this point the compressed air pushes against it to expel it.

Interestingly this provides a good mix of air and water when it is expelled and you typically dont get the familiar laminar water exiting, then the air pulse, you just get a constant air/water mix.

Also 90-95% of the water is typically expelled from the bottle during a launch. If you setup the car to have the bottle angled down slightly all the water will come out. However in this situation under high thrust, the vertical vector of the thrust can lift the rear wheels off the ground, loosing traction and loosing directional stability.

The use of water drain pipes integrated into the nozzles for water as well as air vent pipes for air only are something we are working on at the moment, so we will post videos when we have something that works.

There is some interesting science involved when you lay the water rockets down horizontally, you dont always get the results you would think based on typical vertical water rockets.

-todd-

[thampson]

Lisa,

we have tried different shaped bottles before and they dont seem to hold the pressures we use even with reinforcing. The drain tubes will do the same thing whilst letting us keep the current bottles that will go to 150-160 psi

-todd-

[thampson]

Rick,

We have been toying (excuse the pun) with the idea of multi stage. We are working on a restricted nozzle, a few failures so far but we are getting there. Also the addition of boosters to get the car off the line then let the main bottle take over from there.

The idea of using the wheels / axle as a timer is interesting though. Our car doesn't use axles but others Im sure will so if you could hunt down some pics Im sure this would be interesting to all developers of water rocket cars.

thanks
-todd-

[Spaceman Spiff]

How about this idea to make it more efficient. What if you were to use a smallish nozzle on the water rocket motor but instead of using the entire thrust to propel the car, you would have some of the thrust hitting a "paddle wheel" type of thing connected to a drive axle on the wheels?

The thrust would turn the wheels and propel the car in addition to the rocket motor thrust.

The idea of the axle as a timer could also be used to perhaps open some kind of variable nozzle valve in a more standard design too. There are a lot of possibilities to explore here.

[Tim Chen]

I've seen water rocket cars before that used multiple bottles connecting through pipes to a common outlet. The people who made it said that they could angle the bottle so that gravity plus acceleration would keep the water at the exit of each bottle and they could use all the water completely.

[thampson]

Thanks for the suggestion spaceman .. but thinking about it, wouldnt that turn the paddle wheel the opposite way to the direction of travel . .you would needs a second gear to turn an axle the right way. The water would also exert a force on the paddle wheel in the opposite direction to the way the car is travelling ....

-todd-

[RaZias]

Thanks for the suggestion spaceman .. but thinking about it, wouldnt that turn the paddle wheel the opposite way to the direction of travel . .you would needs a second gear to turn an axle the right way. The water would also exert a force on the paddle wheel in the opposite direction to the way the car is travelling ....

-todd-

Not necesseraly, if you put the axle above the nozzle then the air jet would it in the paddle in the right way

[Spaceman Spiff]

Thanks for the suggestion spaceman .. but thinking about it, wouldnt that turn the paddle wheel the opposite way to the direction of travel . .you would needs a second gear to turn an axle the right way. The water would also exert a force on the paddle wheel in the opposite direction to the way the car is travelling ....

-todd-

Not necesseraly, if you put the axle above the nozzle then the air jet would it in the paddle in the right way

Yep. That's exactly what I had in mind! Thanks for helping me out!

[Chonchielopez]

I would use cds for wheels with balloons around them less drage more traction.