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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Water Rocket Car MkXI - The Green Hornet

Discussions about water rocket powered cars, sleds or boats.
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thampson
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Water Rocket Car MkXI - The Green Hornet

Post by thampson » Wed May 19, 2010 12:14 pm

Hi all,

We have steadily been making progress on our new water rocket car design. I have uploaded some pics and a writeup tonight to our website for those interested

http://wrocket.hampson.net.au/?p=1065

This version has a new rear end and fin design as well as being put on a pretty big diet to weigh about 45% less than the previous version of the car.

We are looking forward to trying it out in the next few weeks.

We are also working on a second nozzle / air amplifier which will sit behind the main nozzle. We will post some pics when we have done some initial testing.

I have added some pics here as well :D
100_0686.jpg
100_0683.jpg
-todd-
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RaZias
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Re: Water Rocket Car MkXI - The Green Hornet

Post by RaZias » Wed May 19, 2010 2:45 pm

It´s good that someone is giving some steps in WR-cars.

It´s that wood made ?

The wheels have no rubber...with the high-speed rooling it will surely damage the wheels...
Are they still radio-controlled ?

The diagonal wings give better handling ?


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Re: Water Rocket Car MkXI - The Green Hornet

Post by Tim Chen » Wed May 19, 2010 8:55 pm

Todd,

That's a sweet ride you got there! :cl: I don't get the wheels with no rubber on them though. I think it would hurt the ability to roll on anything but a perfectly smooth surface like a tennis court or interior hallway.


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Brian
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Re: Water Rocket Car MkXI - The Green Hornet

Post by Brian » Thu May 20, 2010 2:18 am

Looks Good!
the V-tale is lighter than vertical and horizontal stabilizers (sometimes) but the main advantage is that a vertical fin could get in the way of the exhaust where a V-tale wouldn't.
The wheels have no rubber...with the high-speed rooling it will surely damage the wheels...
I don't get the wheels with no rubber on them though.
Todd is probably yet to put the wheel tread on.

my question is, why do you have lots of space behind the nozzle?
i like the green!


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Re: Water Rocket Car MkXI - The Green Hornet

Post by thampson » Thu May 20, 2010 11:23 am

H Razias,

Yes chassis is plywood.

The rear wheels are quite strong plastic, un-powered test runs have held up with no damage. I expect some scuffing of the rims but not much else.

Diagonal fins are positioned to allow exhaust plume to go straight between them without hitting a vertical stabilizer. Do they give better handling ? I will let you know once I have tested it

-todd-


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Re: Water Rocket Car MkXI - The Green Hornet

Post by thampson » Thu May 20, 2010 11:39 am

Hi Tim,

Thanks for the clapping hands ;)

To answer your question, the lack of rubber tread on the rear wheels is deliberate. They roll just fine in this configuration, as well as they do with the rubber on them. The wear of the plastic (which is quite hard, not brittle) is the only concern, they will scuff up a bit when they roll on the asphalt road but I dont believe they will chip at all. Unpowered tests on roughish concrete so far are good. Also my wife probably wont appreciate me launching down the hallway and embedding the car in the drywall :)

The rear wheels have minimum friction with the road as I am trying to get this car to act more like a rocket than a car. My tests up until now were trying to get as much grip and down-force over the back wheels as possible to control the thrust steering problem we were having. I believe putting the nozzle well ahead of the rear wheels was a better solution to that problem. So now what I am trying to do it get the rear of the car to straighten like the rear of a rocket does when it flies vertically.

If the rear of the car get out of alignment with the front at speed, the air going past the car will hit the fins and try to push them back into line with the front. The force needed to do that will need to be enough to overcome the friction of the rear wheels and push them (plus the rear of the car) sideways on the road. With rubber on the rear wheels the friction between the road the the wheels is high, with no rubber and just plastic it is a lot lower, so the amount of force required to straighten the rear of the car should then be lower. This is my logic.

Whether the fins I have put on are big enough and the car is going fast enough to generate enough force to overcome this rear wheel friction I am not sure, we will have to take it to the test track to find out. This car is also a lot lighter than the last, and we are concurrently working on a new 3 x 2L reinforced bottle set to slide onto this chassis to generate more thrust ..

Should be interesting to see what results we get

cya
-todd-


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Re: Water Rocket Car MkXI - The Green Hornet

Post by thampson » Sat May 22, 2010 9:15 am

Hi Brian,

the area behind the nozzle is for an experimental device I am working on which is like a second nozzle or an air amplifier, I am attempting to draw in additional air moving past the rocket car into the exhaust plume.

I have a couple of designs I am working on. They will be removable so I can test different configurations.

-todd-


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Re: Water Rocket Car MkXI - The Green Hornet

Post by Brian » Sat May 22, 2010 8:17 pm

sounds interesting, here's a link to a small discussion which way help http://www.wra2.org/forum/viewtopic.php ... nted#p2468


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Re: Water Rocket Car MkXI - The Green Hornet

Post by U.S. Water Rockets1 » Sat May 22, 2010 9:57 pm

Todd,

It would be a pretty remarkable achievement if you can show that air amplifier nozzle concept works. It is an interesting idea. Good luck with the testing!


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Re: Water Rocket Car MkXI - The Green Hornet

Post by RaZias » Sun May 23, 2010 7:54 am

I have talked of that air-amplified concept in following the post:

http://www.wra2.org/forum/viewtopic.php ... nted#p2468

It´s a concept called "air-augmented rocket" I saw at Wikipedia:

http://en.wikipedia.org/wiki/Air-augmented_rocket
air augmented.jpg
I don´t know the drag it would creat but I have a concept diferent from this one.

Imagine you put a inverted air-plane wing right behind the nozzle, the fast air escaping from the nozzle by passing by the wing will creat a strong downforce that would even stick the rocket to the ground...but the problem would be the instability.
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Re: Water Rocket Car MkXI - The Green Hornet

Post by RaZias » Sun May 23, 2010 8:08 am

down force.jpg
The air expeled by the bottle by passing by the inverted wing would create a high down-force to stabilize the rocket during the kick-phase (technically it would be like a kick).

Even the down-side of the all chassis could be like in a inverted wing structure.
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Re: Water Rocket Car MkXI - The Green Hornet

Post by RaZias » Sun May 30, 2010 2:40 pm

Thampson,

You said that you have reinforced your bottles and they can hold 180 psi, could you show some photos ?

How did you reinforced the bottles ? (I am talking of the How To)


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Re: Water Rocket Car MkXI - The Green Hornet

Post by Spaceman Spiff » Mon May 31, 2010 8:37 pm

RaZias wrote:
down force.jpg
The air expeled by the bottle by passing by the inverted wing would create a high down-force to stabilize the rocket during the kick-phase (technically it would be like a kick).

Even the down-side of the all chassis could be like in a inverted wing structure.

I think the wing behind the nozzle idea is just extra work that could be accomplished much easier. For example, a second nozzle on the bottle pointing upwards would generate any amount of downforce you needed. The same could also be accomplished by angling the nozzle up, then creating a down going thrust angle and downforce.


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Re: Water Rocket Car MkXI - The Green Hornet

Post by Spaceman Spiff » Mon May 31, 2010 8:39 pm

On a different but related subject, has anyone tried making a water rocket powered hovercraft? Todds work to eliminate drag could be augmented by using a skirt and compressed air to get the car to hover and it would have almost zero friction.


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Re: Water Rocket Car MkXI - The Green Hornet

Post by RaZias » Tue Jun 01, 2010 5:52 am

A WR-Hover-craft would demand a complex system because how would you put air below the skirt ?
I have no idea how they do that in a real hover-craft...

For that matter it would be better to make as Anti-gravity...they just putted 3 ski pads below the rocket made of the same blue thing they use in their wings for their comercial WR.

But making a WR-tobogan is not as fun as a WR-car, the last one really demands the principle of this forum: technological challenges that releases the scientists one all of us :D


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