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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.

Thampson WR-car record

Discussions about water rocket powered cars, sleds or boats.
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RaZias
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Re: Thampson WR-car record

Post by RaZias » Mon Oct 25, 2010 2:22 pm

Here are some ideas:

- The pressure vessels should be protected with something, like a half-pipe of PVC ? Balsa wood ?

- The inclination of the street should be measured.
I think there are cheap materials to makes this measure, the reason why is not for qualification purposes
but more for scientific studies of the impact of it.


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Re: Thampson WR-car record

Post by WRA2 » Mon Oct 25, 2010 5:38 pm

thampson wrote:Another Item I did think of was hot water/steam propulsion. This type of propulsion should not be included in this category.

> We should still discuss if a maximum is needed to keep the costs under control.
I think we could possibly have a 2.0L class and an unlimited class so that if cost was an issue you could still compete in the 2.0L class

> A car capable of going 400 meters "downhill" but only running 15 meters "uphill" on the same track will most likely go 200 meters on flat ground.
I dont think this is the case, If I had a nice downhill slope and a long enough road I could launch the current car at 20psi down the hill and steer it for 400m, whereas 20psi on the flat would go maybe 10m. I think having both runs within a percentage of one another will ensure this type of record attempt doesnt happen.

>What about containing the pressure vessel inside a wire cage mounted to the chassis
Thats an interesting concept, the cage will hinder any fragmented sections of bottles from flying off if there is an explosion, something like chicken wire would be light enough. It would need to be offset from the bottles slightly to allow for expansion of the bottles. I would recommend that this be as an addition to the bottle tethers. The question would be whether this type of protection is mandatory or not ?

>We should make this as part of the safety rules. We should also specify safe distance from the track that all spectators must be. I think that because the car travels horizontally, that this is even more important then with vertical rockets.
Agreed, When we launch everyone needs to be behind the rocket car and launcher.

>Could we take advantage of the "ground camera" to tell if the car is simply flying horizontally?
We currently have our camera mounted looking forwards and the front wheels are clearly in view and on the ground as a method of confirmation. As long as the onboard camera shows the wheel(s) on the ground I think that would suffice.

regards
-todd-
This is moving along great. Great ideas everyone. I'll try to have a 1st draft posted in a few days (depends on how many membership applications I have to process). We can take our time and do this right because inevitably some joker will come along 2 years from now and either try to cheat or find a loophole. Keep up the good work guys! TH:


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Re: Thampson WR-car record

Post by FredK » Thu Oct 28, 2010 4:35 pm

Why do we need all these rules anyways? Isn't who goes the furthest good enough? Why go through all the trouble?


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Re: Thampson WR-car record

Post by Spaceman Spiff » Thu Oct 28, 2010 5:21 pm

thampson wrote:Another Item I did think of was hot water/steam propulsion. This type of propulsion should not be included in this category.

> We should still discuss if a maximum is needed to keep the costs under control.
I think we could possibly have a 2.0L class and an unlimited class so that if cost was an issue you could still compete in the 2.0L class

> A car capable of going 400 meters "downhill" but only running 15 meters "uphill" on the same track will most likely go 200 meters on flat ground.
I dont think this is the case, If I had a nice downhill slope and a long enough road I could launch the current car at 20psi down the hill and steer it for 400m, whereas 20psi on the flat would go maybe 10m. I think having both runs within a percentage of one another will ensure this type of record attempt doesnt happen.

>What about containing the pressure vessel inside a wire cage mounted to the chassis
Thats an interesting concept, the cage will hinder any fragmented sections of bottles from flying off if there is an explosion, something like chicken wire would be light enough. It would need to be offset from the bottles slightly to allow for expansion of the bottles. I would recommend that this be as an addition to the bottle tethers. The question would be whether this type of protection is mandatory or not ?

>We should make this as part of the safety rules. We should also specify safe distance from the track that all spectators must be. I think that because the car travels horizontally, that this is even more important then with vertical rockets.
Agreed, When we launch everyone needs to be behind the rocket car and launcher.

>Could we take advantage of the "ground camera" to tell if the car is simply flying horizontally?
We currently have our camera mounted looking forwards and the front wheels are clearly in view and on the ground as a method of confirmation. As long as the onboard camera shows the wheel(s) on the ground I think that would suffice.

regards
-todd-

I like the idea of keeping people away from the track a certain amount. I think nobody should be directly ahead of the car on the track as well.

As far as protecting people from flying parts (batteries, servos, cameras, etc.) I think maybe we could make a call that says that no small parts can be closer than X centimeters from the pressurized bottles. I have noticed that when bottles explode the force drops off quite a bit just a few inches from the bottle itself. Parts mounted a distance away from the bottle will probably not get thrown very far.


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Re: Thampson WR-car record

Post by U.S. Water Rockets1 » Sat Oct 30, 2010 10:07 pm

FredK wrote:Why do we need all these rules anyways? Isn't who goes the furthest good enough? Why go through all the trouble?
If you don't have rules then what is the alternative? Do you really think anarchy is going to be any better?


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Re: Thampson WR-car record

Post by WRA2 » Sun Oct 31, 2010 3:11 pm

The fist draft is up for the water rocket dragster distance competition is up at:

http://www.wra2.org/WRA2_Dragster_Rules.php

Please comment here in this thread.

We are also looking for suggestions for a catchy title for the competition.


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Re: Thampson WR-car record

Post by WRA2 » Sun Oct 31, 2010 3:41 pm

FredK wrote:Why do we need all these rules anyways? Isn't who goes the furthest good enough? Why go through all the trouble?
Hi Fred,

The reason that we go through all the trouble is that a record is not a record without something to measure it against. The rules also keep costs down so that it does not become a competition as to who can spend the most money. Take the land speed record, there are rules requiring runs in opposite direction. All world records involving technology have rules so that new attempts can be measured against previous ones. Even human powered records like the 100 meter dash has a rule preventing the use of performance enhancing drugs by the athletes.

There also needs to be a finite set of classes for water rocket world records. There would be no incentive to compete without a defined set of classes. What we would wind up with is anyone wishing to claim a "world record" to promote themselves would simply find a "niche", custom build a rocket to fit in it, fly it and claim that they are world record holders. Next thing you know there would be people all over claiming records for 2-stage rockets, 3-stage rockets, rockets with blue fins, rockets made from specific materials, etc. etc. etc. Then chaos occurs when two teams dispute because someone treads in the others "niche".

With the WRA2 sanctioning the record classes for all water rocketry all of that is eliminated. Everyone gets to compete under the same rules and in the same classes.


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Re: Thampson WR-car record

Post by RaZias » Mon Nov 01, 2010 12:25 pm

A catchy title ? I don´t know :?: ...how about

Water Rocket Dragster Max Distance ------- WR-DMD

Water Rocket Dragster Max Speed ------- WR-DMS

So we would have a DMD and a DMS competition.


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Re: Thampson WR-car record

Post by Spaceman Spiff » Mon Nov 01, 2010 1:48 pm

RaZias wrote:A catchy title ? I don´t know :?: ...how about

Water Rocket Dragster Max Distance ------- WR-DMD

Water Rocket Dragster Max Speed ------- WR-DMS

So we would have a DMD and a DMS competition.
I like the idea of keeping them to short acronyms that are easy to type and easy to pronounce. I can get onboard with that!


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Re: Thampson WR-car record

Post by RaZias » Mon Nov 01, 2010 3:42 pm

We could also call:

Long Shot (for the max distance)

Max-G (for the max speed, altough Gs have a relation to accelaration and not to speed)

Onething about the one rule is that it doesn´t allow someone in front of the rocket...How the hell you going to put the "F-1 girl" there ?


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Re: Thampson WR-car record

Post by RaZias » Mon Nov 01, 2010 4:01 pm

Do rules allow for the use of PVC tubes ?

I am thinking in using one because some PVC tubes withstand 20 bar (I think) without reinforcement, that would make more cheaper the construction.

The PVC weight wouldn´t make to much difference compared with the PET in a Speed Record.


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Re: Thampson WR-car record

Post by WRA2 » Mon Nov 01, 2010 4:31 pm

RaZias wrote:Do rules allow for the use of PVC tubes ?

I am thinking in using one because some PVC tubes withstand 20 bar (I think) without reinforcement, that would make more cheaper the construction.

The PVC weight wouldn´t make to much difference compared with the PET in a Speed Record.
Because the pressurized part will be inside a wire cage (we still need to decide minimum specs for that) which would contain fragments PVC would be allowed.

We also need to come up with wording to eliminate pre-manufactured (like scuba tanks and fire extinguishers) and all metal pressure vessels.


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Re: Thampson WR-car record

Post by thampson » Tue Nov 02, 2010 10:32 am

Lisa,

thanks for putting out the first draft of the water rocket car rules. Here are my comments on the proposed rules so far

I. WRA2 Water Rocket Dragster General Design Parameters

Pressure Vessel of the Rocket Dragster must be constructed from lightweight nonmetallic materials.
> I would request that we can include an option for tethered metalic robinson couplings inside the cage. If the couplings are tethered to the chassis, the bottles are tethered to the chassis and they are inside the cage then there is a very small chance if any of them getting out of the cage. I am prepared to do two video recorded burst tests in this configuration to prove this is a safe configuration.
> I suggest that an additional rule of bottles needing to be tethered to the chassis be included. We use two per bottle for safety as we have seen thick cable ties break when the bottles expand under pressure, but I believe at least 1 should be used per bottle.

Rocket Dragster must be completely scratch-built. (with the exception of the Camera and Electronics)(manufactured items such as wind up toys are allowed)
> Can we assume electronics covers r/c receiver, servos etc. I think we can allow standard fitting ie: cable ties, screws, bolts, fittings in general for the chassis.


III. Safety Rules

All pressurized portions of the Rocket Dragster must be contained inside a wire mesh cage.
> I think we should add a maximum maximum sieve size of 9mm x 9mm ie: a 10mm x 10mm square cannot pass throught the mesh. Looking at standard chicken wire which has a sieve size of 12.5mm (1/2") x 12.5mm (1/2") (approx) the cage would require two overlapping wraps which would give an effective sieve size of 6.5mm x6.5mm which I believe is safer. Its also relatively cheap at $10 for a 5m roll x 900mm so there is no cost impact of two wraps.
> Also does the cage need to cover the nozzle ? Can we allow for a 2" diameter hole in the cage for the nozzle and exhaust ?


IV. Pressure Vessel Rules

Pressure Vessel and all external parts of the rocket may not be fabricated from metal. (see the WRA2 water rocket safety rules).
> As above I would request that tethered metal robinson couplings within the cage be allowed. We have a chassis to teher to, as well as a safety cage which is not taken into consideration in the standard WRA2 safety rules.
> Also parts of the chassis, steering, wheels etc should be allowed to be made from metal. ie: outside the cage.


V. Reaction Mass Rules
> Can we add a maximum of 40 degrees C for the water to exclude steam rockets


VI. Track Rules
> Can we add that runs need to be performed 180 degrees apart +-15 degrees across the same marked course


Additional Items whcih I believe should be added

> Rule to include car needs to remain on the ground 99% or more of the run
> Rule to limit surface to concrete, asphalt, dirt ie: not ice
> Rule to exclude any use of guide wires for steering
> Rule to limit the cars track to no wider than twice the length of the car

Also some comments
> is there any option to add the 2.0L class and the open class at this stage ?
> Im not convinced the PVC as a pressure bottle should be allowed. I am concerned that lower grade PVC will shatter at high pressures creating small shards that will get through the cage. There is no way to tether the PVC to the chassis unless it has a wrapping or coating like safety glass that will keep it together when it bursts.

regards
-todd-


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Re: Thampson WR-car record

Post by RaZias » Tue Nov 02, 2010 11:45 am

I am suggesting using a PVC tube that has written on it the pressure it stands. For example 20 bar or more.

I am aware of the shatereness of the PVC but I am thinking in surrounding it with the folowing options:

A - box of wood

B - a mesh cage surronded with another PVC half-pipe


I think since the chassis is made of wood, why should we use 2 mesh cage as Thampson proposed instead a wood box ?
A person who can make a wood chassis can make easly a wood box.

Remember, the use of a high pressure PVC tube can attract more persons to this competition because it won´t demand the use of expensive composites.


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Re: Thampson WR-car record

Post by thampson » Thu Nov 04, 2010 8:35 am

RaZias,

You are correct that a wooden box would contain pieces if the PVC pipe ruptured if it was well constructed and the wood thick enough, probably 10mm thick pine or similar I would imagine. It would add weight to the car though :(

I also checked out some of the high pressure PVC pipe ie: rated at 20 and 25 Bar (highest one I could find in Australia), they also have similar high pressure threaded fittings, but the pipe itself is very heavy. A 1 m section x 100mm diameter of the 20Bar PVC pipe weighs just under 4kg, the 25Bar one was approx 5kg per metre length. For comparison our whole car weighs only 2.6kg

The 20Bar PVC is 300psi rated so its not a huge amount more than what George is getting from his fibreglass wrapped bottles at 220psi and we are at 180psi with our double layer reinforced ones, which with further testing would go to 200psi I believe.

I dont want to discourage you from building one, but if you are after the speed record I think wrapping PET bottles with fibreglass/carbonfibre/kevlar etc is probably a better alternative.

-todd-


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