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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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thampson
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Re: Thampson WR-car record

Post by thampson » Thu Nov 04, 2010 10:28 am

I went and had a good look at available wire mesh products today and purchased a 6.5mm x 6.5mm mesh product to make our rocket car cage. Here are some pics
launcher-upgrade 001.jpg
launcher-upgrade 003.jpg
This is a welded mesh as apposed to a twisted mesh like chicken wire. Also this size mesh will only require 1 wrap of the mesh to meet the 10mm x 10mm mesh size requirements. Being welded its very solid and makes a cylinder very easily. This product is manufactured in Australia by Whites Wires - http://www.whiteswires.com.au. It purpose is to keep mice and snakes out of aviaries so I expect a similar product should be available in other countries.

The chicken wire which has a hexagon mesh shape would suffice with two carefully overlapping wraps as well, although I preferred the 6.5mm mesh (personal choice) as it will provide a sturdier cage to do burst tests in.

-todd-
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Re: Thampson WR-car record

Post by air.command » Thu Nov 04, 2010 10:55 pm

thampson wrote: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-
I would suggest rather than building the safety cage into the car that it should be built into the launcher. If the car is going to blow up it is most likely going to do it during pressurisation or just as you launch. It is very very unlikely to explode when it is already moving as the pressure is dropping rapidly. I am yet to see a rocket/car explode after it's been launched. If the launcher say used a 2m tunnel made from wire mesh, or wood as Razias suggested then there is no weight and drag penalty for the car and you retain the safety factor. You can then use what ever material you like and what ever weight you want to make the cage.

To simplify the staying on the ground and keeping within a certain direction rules, I'd suggest requiring the car to pass through a simple and standard frame (like soccer goal posts with a couple of vertical and a horizontal bar) that would be set up a set distance away say 10 or 20 meters from the launcher. Inexpensive to make and easily verified on video. Sure the car could still deviate from the path afterwards, but it would only be only to the detriment of straight line distance. It would be difficult to make the car fly like a rocket at such low level without having to be in contact with the ground for most of the trip through the frame.

- George


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Re: Thampson WR-car record

Post by RaZias » Fri Nov 05, 2010 1:24 pm

I agree with AirCommand about using a protection in the launcher because it removes weight from the car.

About the PVC pipe it´s sad that they have those weights...I was thinking in using one because it allows me to insert several 9mm nozzle, that would give a nice thrust for a speed record.

By using PET bottles I have to use serveral ones to get a lot of noozles...

- Solutions for several nozzles:

A - development of a new technic to glue several nozzles in one single PET bottle.
B - use a low weight PVC pipe reinforced with kevlar/fiberglass


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Re: Thampson WR-car record

Post by WRA2 » Fri Nov 05, 2010 6:45 pm

air.command wrote: I would suggest rather than building the safety cage into the car that it should be built into the launcher. If the car is going to blow up it is most likely going to do it during pressurisation or just as you launch. It is very very unlikely to explode when it is already moving as the pressure is dropping rapidly. I am yet to see a rocket/car explode after it's been launched. If the launcher say used a 2m tunnel made from wire mesh, or wood as Razias suggested then there is no weight and drag penalty for the car and you retain the safety factor. You can then use what ever material you like and what ever weight you want to make the cage.
That is a good suggestion George. Why not allow competitors to use either method as long as the cage covers the pressurized portion completely. Some teams might not want to transport a cage large enough to cover the pressurized rocket car.
air.command wrote: To simplify the staying on the ground and keeping within a certain direction rules, I'd suggest requiring the car to pass through a simple and standard frame (like soccer goal posts with a couple of vertical and a horizontal bar) that would be set up a set distance away say 10 or 20 meters from the launcher. Inexpensive to make and easily verified on video. Sure the car could still deviate from the path afterwards, but it would only be only to the detriment of straight line distance. It would be difficult to make the car fly like a rocket at such low level without having to be in contact with the ground for most of the trip through the frame.

- George
It would be kind of like shooting a ball through a wicket. Would a run be disqualified if the car touches the sides on the way through? The only downside of this idea might be if there is a collision with the posts which could destroy the car (or damage it a least). The cross bar could be mounted low enough to prevent a flying car too.


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Re: Thampson WR-car record

Post by WRA2 » Fri Nov 05, 2010 6:51 pm

thampson wrote:I went and had a good look at available wire mesh products today and purchased a 6.5mm x 6.5mm mesh product to make our rocket car cage. Here are some pics
launcher-upgrade 001.jpg
launcher-upgrade 003.jpg
This is a welded mesh as apposed to a twisted mesh like chicken wire. Also this size mesh will only require 1 wrap of the mesh to meet the 10mm x 10mm mesh size requirements. Being welded its very solid and makes a cylinder very easily. This product is manufactured in Australia by Whites Wires - http://www.whiteswires.com.au. It purpose is to keep mice and snakes out of aviaries so I expect a similar product should be available in other countries.

The chicken wire which has a hexagon mesh shape would suffice with two carefully overlapping wraps as well, although I preferred the 6.5mm mesh (personal choice) as it will provide a sturdier cage to do burst tests in.

-todd-
The welded mesh was what I had in mind when I suggested this. 10mm is probably a good size as the maximum for the squares in the mesh as the maximum allowed. The teams would be welcome to use smaller of course.


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Re: Thampson WR-car record

Post by WRA2 » Fri Nov 05, 2010 6:58 pm

RaZias wrote: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.
The only problem with using a solid box as the shielding is that the rapidly expanding gas cloud from an explosion may not be able to escape the box fast enough causing the box itself to explode. Also someone might be able to disguise some form of spud gun cannon as their shielding.


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Re: Thampson WR-car record

Post by WRA2 » Fri Nov 05, 2010 7:23 pm

thampson wrote: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.
With the addition of a cage over the pressurized parts we could allow metal couplers and nozzles. I think that all metal pressure vessels and manufactured pressure vessels still should not be allowed.
thampson wrote: 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.
The idea here is common single components like screws, nails, wheels, an RC steering rack, etc would be allowed but attaching a WR pressure vessel to a RC car that was purchased would not.
thampson wrote: 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 ?
See my earlier post regarding allowing even metal nozzles if you used George's suggested external cage that was part of the launcher. Also remember that a wooden (or other solid material) chassis counts as part of the cage.
thampson wrote: 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.
If the coupling is contained inside the cage then I believe that the tethers will not be necessary. You are correct about the parts outside the cage. Metal should be allowed. Since our pressure vessel is contained by the cage it should not be a safety issue.
thampson wrote: V. Reaction Mass Rules
> Can we add a maximum of 40 degrees C for the water to exclude steam rockets
The WRA2 rules have always not permitted "phase change" rockets which includes steam rockets and LCO2. I'll make sure it is still listed on the draft
thampson wrote: VI. Track Rules
> Can we add that runs need to be performed 180 degrees apart +-15 degrees across the same marked course
The "opposite direction" was supposed to cover it but I can add that 180 degrees to the text on the draft.
thampson wrote: 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
Ill look at adding those items as well.
thampson wrote: 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-
Once we get the basic rules set for WR car distance we might be able to spin off a class with a volume limit similar to our "Altitude challenge" for rockets.

I think you might have proven that PVC will be too heavy to be useful as a pressure vessel but maybe it would be allowed if wrapped with reinforcement such as fiberglass tape.


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Re: Thampson WR-car record

Post by WRA2 » Fri Nov 05, 2010 7:26 pm

Should we add a rule that covers sharp edges and pointed edges on the car as part of the safety rules?


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Re: Thampson WR-car record

Post by WRA2 » Fri Nov 05, 2010 7:28 pm

I would like to thank everyone for the input here. We are designing a new class in the traditional WRA2 way and everyone's help and ideas are appreciated. Keep the ideas coming! TH:


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Re: Thampson WR-car record

Post by thampson » Sat Nov 06, 2010 8:37 am

Thanks everyone for the continued discussion, looks like we are getting closer :)

> Safety Cage & guide rail
This is a good idea from George to have a cage attached to the launcher. I agree this should be allowed as long as the pressurized portion is covered. There will need to be an opening in the cage at the end for the car to get out but this will be pointed away from the spectators. In our case the rear fins are quite big, so the cage needs to be wide as well as long. As the cage is so long (1.4m) a guide rail I believe will be needed for the car to leave the cage safely without the fins collecting the cage on the way out, even if we build a cage with extra safety margin built in .

The guide rail as I have replied to RaZias earlier, I don't think will help much overall in keeping the car straight along the run, but it will help it get out of the cage safely.


> Pass through a frame
I dont think this adds any value to the competition. Its also quite difficult to do, its akin to putting a hoola hoop 20m or so above a vertical rocket and making the rocket pass through it. Im also concerned about the chance of collission and damaging the car, its hard enought to keep the car out of the gutters without putting more obstacles in the way to hit :)


> Using a wooden box
Maybe an option for those wanting to use this method is to mandate several 10mm holes on each panel, this would ensure pressurized gas can escape the box without spliting it open in the case of an explosion.


>Allow metal couplers and nozzles as long as they are covered by the cage
Agree. I also agree no metal pressure vessles.


> Attaching a WR pressure vessel to a RC car that was purchased would not be allowed
Agree, half the fun is building the car yourself anyway :)


>Also remember that a wooden (or other solid material) chassis counts as part of the cage
Agree, the cage would need to be securely attached to the chassis at several points though

>If the coupling is contained inside the cage then I believe that the tethers will not be necessary
Agree :)

>The "opposite direction" was supposed to cover it but I can add that 180 degrees to the text on the draft
Yes I think "opposite" would cover it, I must have missed it ;)

>Should we add a rule that covers sharp edges and pointed edges on the car as part of the safety rules
At the speeds we (HHWRSA) are going a sharp nosecone wouldnt make any difference, but if someone was pushing the limits for a speed record perhaps a pointed nosecone may be an option and shouldn't necessarily be banned. Perhaps a a compromise could be a pointed nosecone could be used as long as it has a builtin crumple zone ie: if its wood or metal with no way to crumple, then its dangerous and not allowed, if its a shaped bottle which will crush on impact then its not as dangerous.

Also the car shoudlnt have any edges that can cut when you run your fingers over the said edge. If Burt Rutan can design SS1 to do Mach3 using composite materials and glue with no sharp edges then we dont need them either :)

-todd-


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Re: Thampson WR-car record

Post by RaZias » Sat Nov 06, 2010 12:26 pm

I was looking in a long term and for a distance record and one day we will need like 500m, so I was thinking that since it´s impossible to find a area like that the only way to allow that record would be to make 5 runs in a 100m road.

That means that at end of each 100m the car should turn to the opposite direction by RC control.

That means that somehow the driver should be at one side of the road seeing the rocket passing by, otherwise in the turns it would see the rocket running towards him :shock:

So the rule of the positioning of the persons during the run should be changed...at least in a near future where we will have a WR able to run 500m.


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Re: Thampson WR-car record

Post by U.S. Water Rockets1 » Sat Nov 06, 2010 10:12 pm

RaZias wrote:I was looking in a long term and for a distance record and one day we will need like 500m, so I was thinking that since it´s impossible to find a area like that the only way to allow that record would be to make 5 runs in a 100m road.

That means that at end of each 100m the car should turn to the opposite direction by RC control.

That means that somehow the driver should be at one side of the road seeing the rocket passing by, otherwise in the turns it would see the rocket running towards him :shock:

So the rule of the positioning of the persons during the run should be changed...at least in a near future where we will have a WR able to run 500m.
Do you think it would really be possible to turn the wrocket car at the end of 100 meters and it would still be thrusting at that point? It also seems like the thrust would make it virtually impossible to steer with any accuracy. There's nothing to stop someone from trying to set a record this way, but it seems like the turns would be a handicap because steering causes extra frictional losses.


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Re: Thampson WR-car record

Post by RaZias » Sun Nov 07, 2010 5:59 am

USWR,

I know that it´s almost impossible to turn the rocket unless you make very open turns...even so it´s very hard to make it, just imagine the speed of it.

But once again, how do past from a 500m record ?

For WR the sky is the limit, but for the WR-cars 500m would be a serious limit.


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Re: Thampson WR-car record

Post by thampson » Sun Nov 07, 2010 6:54 am

> Do you think it would really be possible to turn the wrocket car at the end of 100 meters and it would still be thrusting at that point?

Making a 180 degree turn while the car is still thrusting will just spin the car. IF we put too much steering correction while our car is thrusting it fishtails and can become uncontrollable, so I dont think its realistic to make 180 degree turns during the run.

we have been thinking of longer areas to use and have come up with
- airport runways (unused ones or active ones with permission)
- dragstrips
- salt pans (dried lake beds)

as possible options. We have Western Sydney International Dragway not too far away and Im sure I could convince them to let us run the car there if we only used water and not foam.

-todd-


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Re: Thampson WR-car record

Post by air.command » Sun Nov 07, 2010 6:56 am

RaZias wrote: But once again, how do past from a 500m record ?
Just go around in circles. Say you have a 50m radius, your car cannot drive around the circle closer than the 50m radius. Do as many laps as you need. 50m radius is gentle enough that friction due to turning is minimal. The car stays within your and a ground camera's view as well. As long as you do at least 1 lap then any slope and wind advantages are also negated. You can probably find a parking lot to do this in.

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