Maximizing a Water-Propelled Bottle Rocket Launch

In summary: Yes! Lots of people have done water rocket projects before, so there are a lot of resources available online if you need them.
  • #1
Heat5444
6
1
I'm going to make a water propelled pop bottle rocket for a competition. The bottle holds 1.5 liters and we are going to fill some amount of it with water and pressurize it to 75 psi. When triggered, water will come out of the hole in the cap and propel the rocket. The rocket is perfectly aligned and will only go directly upwards.
What is the most effective water-air ratio and cap diameter for going as high as possible?
Rocket weight without water: 151 gr
 
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  • #2
Heat5444 said:
I'm going to make a water propelled pop bottle rocket for a competition. The bottle holds 1.5 liters and we are going to fill some amount of it with water and pressurize it to 75 psi. When triggered, water will come out of the hole in the cap and propel the rocket. The rocket is perfectly aligned and will only go directly upwards.
What is the most effective water-air ratio and cap diameter for going as high as possible?
Rocket weight without water: 151 gr
Welcome to the PF.

What reading have you done so far for this project? What do you think the tradeoffs are for the amount of water and air in the rocket?

Also, how did you pick 75PSI? Are you pretty sure the bottle will hold that pressure? What type of fitting will you use to fill the rocket with the compressed air? What kind of exit nozzle design are you considering?
 
  • #3
I have gathered some materials like pop bottles and made a crude rocket that can go in a straight line.It weighs about 151 grams It's not that stable or aerodynamic but making it more stable and aerodynamic will not effect the mass of the rocket too much.

If it has too much water, it will be too massive to accelerate in the first place and it will lower the center of mass which will make it less stable; if it's too low, it will run out of water too fast. I don't think this is too important as log as it does not interfere with the center of mass.

75 psi is coming from contest rules so 1,5-liter pop bottles are probably fine handling it.

When we stick the rocket to the trigger mechanism, it's going to fill it with an electric pump from the exit nozzle.

I think exit nozzle is going to be the most important part because it determines the upwards force but we haven't decided on a particular design right now.
 
  • #4
I have found that water rockets work very well when you start with an empty bottle and fill with pressurized water. The energy and reaction mass run out at the same time. The water will not expand so a nozzle should not either
What do the rules say about hot water ?
 
  • #5
Andy SV said:
I have found that water rockets work very well when you start with an empty bottle and fill with pressurized water. The energy and reaction mass run out at the same time. The water will not expand so a nozzle should not either
What do the rules say about hot water ?
What's pressurized water?
 
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  • #6
:rolleyes: really? ... Go turn on the sink and look at it
 
  • #7
Andy SV said:
:rolleyes: really? ... Go turn on the sink and look at it
Whelp, I'm going to take the calm high road here, and ask a couple of technical questions...

What is the volume of 1 liter of water at 1atm?

What is the volume of 1 liter of water at 1000atm?

How much does the volume of pressurized water at 1000atm expand as it transitions to 1atm?
 
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  • #8
Ok look ... just because water can not be compressed does not mean it can not be under pressure.
Something that in under pressure is pressurized pressure-ized
Experiencing pressure
http://www.dictionary.com/browse/-ize
 
  • #9
Heat5444 said:
I have gathered some materials like pop bottles and made a crude rocket that can go in a straight line.It weighs about 151 grams It's not that stable or aerodynamic but making it more stable and aerodynamic will not effect the mass of the rocket too much.

If it has too much water, it will be too massive to accelerate in the first place and it will lower the center of mass which will make it less stable; if it's too low, it will run out of water too fast. I don't think this is too important as log as it does not interfere with the center of mass.

75 psi is coming from contest rules so 1,5-liter pop bottles are probably fine handling it.

When we stick the rocket to the trigger mechanism, it's going to fill it with an electric pump from the exit nozzle.

I think exit nozzle is going to be the most important part because it determines the upwards force but we haven't decided on a particular design right now.
So a simple Google Images search yields lots of great information about previous work on this type of project. Have you tried that?

https://images.search.yahoo.com/sea...ket+directions&fr2=piv-web&fr=yset_chr_syc_hp
 
  • #10
Ok so concerning this pressurized water bit. Take several approaches to filling a water rocket with a volume of water and compressed air. The question is what percentage of the bottle volume should be water. If we dump in 2 percent volume of water and the rest air compressed to 75 PSI it should not be difficult to see that the water will be expelled long before the pressure drops very far. In other words, there is still enough energy in the bottle as there is plenty of compressed air left with no water left. Take the opposite approach and fill the bottle to 99 percent water and the remaining 1 percent with compressed air and we will run out of compressed air (energy) before we run out of water. The idea is to run out of both at about the same time. This is accomplished by simply hooking the empty bottle at atmospheric pressure to a water spigot with 75 PSI of pressure and let it fill. It is a starting point. Experiment from there with the ratio of total volume/water volume at a constant PSI of 75.
 
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  • #11
After a PM conversation, it turns out that I misunderstood what @Andy SV was trying to say in his post. He meant the same thing that @Averagesupernova said in his later post. Sorry that I misunderstood your meaning, Andy.
Andy SV said:
I have found that water rockets work very well when you start with an empty bottle and fill with pressurized water. The energy and reaction mass run out at the same time. The water will not expand so a nozzle should not either
What do the rules say about hot water ?
Averagesupernova said:
The idea is to run out of both at about the same time. This is accomplished by simply hooking the empty bottle at atmospheric pressure to a water spigot with 75 PSI of pressure and let it fill. It is a starting point.
 
  • #12
@berkeman I wanted to bust your chops on this lol. But I thought I would attempt to post something a bit more neutral and stay somewhat constructive.
 
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  • #13
Averagesupernova said:
@berkeman I wanted to bust your chops on this lol. But I thought I would attempt to post something a bit more neutral and stay somewhat constructive.
Thanks. Yeah, I thought he was displacing all the air -- my misunderstanding. o0)
 
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  • #14
Averagesupernova said:
Ok so concerning this pressurized water bit. Take several approaches to filling a water rocket with a volume of water and compressed air. The question is what percentage of the bottle volume should be water. If we dump in 2 percent volume of water and the rest air compressed to 75 PSI it should not be difficult to see that the water will be expelled long before the pressure drops very far. In other words, there is still enough energy in the bottle as there is plenty of compressed air left with no water left. Take the opposite approach and fill the bottle to 99 percent water and the remaining 1 percent with compressed air and we will run out of compressed air (energy) before we run out of water. The idea is to run out of both at about the same time. This is accomplished by simply hooking the empty bottle at atmospheric pressure to a water spigot with 75 PSI of pressure and let it fill. It is a starting point. Experiment from there with the ratio of total volume/water volume at a constant PSI of 75.
I think I can do few dozens of experiments and find the perfect ratio but I came to PF for math. I know there is a way to calculate the perfect ratio because we know all the variables involved like pressure, size and water loss rate etc. I just don't know how.
So, can someone show me how to calculate this without experiments?
 
  • #15
Heat5444 said:
I think I can do few dozens of experiments and find the perfect ratio but I came to PF for math. I know there is a way to calculate the perfect ratio because we know all the variables involved like pressure, size and water loss rate etc. I just don't know how.
So, can someone show me how to calculate this without experiments?
After posting this, I realized water loss rate is connected to thrust and thrust is connected to mass(wich goes back to water-air ratio again), and speed of the water coming from the nozzle which is connected to the diameter of the nozzle(I think?).
Can there be a formula that we plug in the weight, volume, pressure and it gives us the diameter of the nozzle and water-air ratio for the most time that thrust is greater than gravity?
 
  • #16
Andy SV said:
I have found that water rockets work very well when you start with an empty bottle and fill with pressurized water. The energy and reaction mass run out at the same time. The water will not expand so a nozzle should not either
What do the rules say about hot water?
Rules do not state anything about hot water.
 
  • #17
I searched for a formula the first day you posted this and came up with nothing. The consensus is that there are too many variables to come up with a simple formula. Think of it this way: If it were reduced to a simple formula it would not be much of a contest because everyone would Taylor their rockets about the same.
 
  • #18
If you want to get to the heart of the OP, there are books written by Robert Truax who designed Evel Knievel's rocket powered motorcycle used in his attempt to jump the Snake River. Also he made attempts at speed records at Bonneville.
https://en.wikipedia.org/wiki/Skycycle_X-2

http://newatlas.com/214-mph-in-25-sec-water-powered-record-stands-the-test-of-time/11622/

I could not copy and paste "Robert Truax" from the wiki page ?? anyway as I understand the key is in how much heat energy is held in water with relation to air volume as pressure declines, Robert published books that explained all this, I'm not sure how easy they are to find.
 
  • #19
Averagesupernova said:
I searched for a formula the first day you posted this and came up with nothing. The consensus is that there are too many variables to come up with a simple formula. Think of it this way: If it were reduced to a simple formula it would not be much of a contest because everyone would Taylor their rockets about the same.
You are right, there is no formula for this. But can't we construct one? I mean there's not that many variables. I tried to make one but I don't know enough about the relationship between the speed of ejected water and nozzle size.
If we make the formula it would be great. Because the contest is not about the highest or best, it's about using science to make the rocket. So that kind of formula would guarantee country finals for me.
 
  • #20
Since this experiment involves fluid dynamics, I would like to suggest reading about fluid dynamics and Bernoulli equations to possibly generate the equations you are seeking.
 

1. How can I make my water-propelled bottle rocket go higher?

In order to maximize the launch of a water-propelled bottle rocket, there are a few key factors to consider. First, make sure you have a secure and airtight seal on your bottle. This will allow for maximum pressure to build up inside the bottle. Next, try using a larger amount of water and a smaller amount of air in the bottle. This will increase the force of the water as it is expelled from the bottle. Finally, consider adding fins to your rocket to help stabilize its flight and reduce drag.

2. What type of water should I use in my bottle rocket?

It is recommended to use plain tap water in your bottle rocket. Distilled or purified water does not usually provide any significant advantages and may be more expensive. However, make sure the water is free from any debris or particles that could clog the opening of the bottle or interfere with the rocket's flight.

3. How do I determine the ideal amount of water to use in my bottle rocket?

The amount of water used in a bottle rocket can greatly affect its launch height. To determine the ideal amount of water, you can conduct a series of test launches with different amounts of water and record the height reached. Then, use the amount of water that resulted in the highest launch as the ideal amount for your rocket.

4. What is the best angle to launch a water-propelled bottle rocket?

The ideal angle for launching a water-propelled bottle rocket is between 45-60 degrees. This angle allows for the most efficient use of the rocket's thrust while also providing enough height for the rocket to reach its maximum potential. Launching at a lower angle may result in a shorter flight, while launching at a higher angle may cause the rocket to lose stability and tumble.

5. How can I improve the stability of my bottle rocket during flight?

The stability of a bottle rocket can greatly affect its launch height and overall performance. To improve stability, consider adding fins to the rocket. Fins help to keep the rocket pointed in the right direction and reduce drag. Also, make sure the weight distribution of your rocket is balanced and that the fins are securely attached. You can also try launching your rocket from a stable platform or using a launcher to ensure a straight launch.

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