Hello Air Command. Very very interesting video. Looking into the Physics behind Water Rocketry is fascinating, as there are so many variables! It really is Rocket Science! I am using Water Rockery for my Extended Project at College and this is very helpful, so thanks for that. Keep up the good work, Jamie B.
+JSB Rocketry Thanks Jamie. Sounds like a fun college project. :) Both of my kids just did water rockets at school so the years of being around water rockets helped.
Have you done a test on water temperature? Water near freezing vs ambient temperature. I have enjoyed your videos and look forward to more in the future.
Commenting before watching the video, the denser the liquid, the heavier it is, so now you have to account for that extra weight. Ensure your thrust to weight ratio is higher with the denser liquid.
Very interesting, well made video and also very interesting write-up , George! It's great to learn something about the science of this wonderful hobby. We're looking forward to more videos of this series and hope you have a happy new year. :)
Actually, I kind of guessed that the lower density would mean better performance. You can accelerate the lower-density liquid to a higher speed for the same amount of energy, which means your engine is more efficient - better specific impulse. Granted, it doesn't mean much over such a short burn, but it apparently means enough to have a minor effect.
Viscosity is definitely something worth testing. We can change the viscosity of water simply by heating it. There is a significant enough of a difference between 20C and 50C. 50C is still below the glass transition temperature of PET bottles. wiki.anton-paar.com/au-en/water/
What software did you use to compile the simulation data into a 3 - variable graph. I'm trying to find the optimal volume of water for my water rocket and I would love to be able to have that 3D graph. I tried using the link in the description, but that simulator only compared altitude at a set volume, not at variable volumes. Thanks a lot!
what about changing the physical properties of the water by adding a surfactant. Just a drop of dish detergent can make a huge change in the surface tension, and surface wetting properties.
I would like to see if optimum density changes with nozzle size. Wouldn't different nozzle sizes be more efficient with different density? I'm thinking larger would need denser.
It would be an interesting comparison. In general a larger nozzle produces more thrust, but with greater thrust you have higher peak velocity. Because drag is proportional to the square of the velocity you will induce more drag. So it would be interesting to see what kind of overall performance difference there would be.
Using no water, just gas, makes the rocket way lighter, and as there is more space for the compressed gas, there is more power on board. This should make it fly much higher! But... as I know and as you know; it doesn't work well at all. Yes; it works great for the first like 1/30 of a second, and then the party is over. Less weight and more power, but it doesn't fly as high. Can you explain why this is?
+Giesbert Nijhuis It's because a higher proportion of the stored energy in the compressed air is lost to kinetic energy in the exhaust rather than to the rocket. As the air in the exhaust has a low density, it has to be accelerated to a much higher speed than the water to get equivalent thrust. Unfortunately whilst thrust scales linearly with exhaust velocity (for a given mass), the kinetic energy in the exhaust goes to the square of the exhaust velocity. Of course a rocket with no liquid can store more energy in the first place (a higher volume of compressed air) and it has less mass (as the air is lower density than the liquid). However, that's not enough to compensate for the other effects. It's all a bit more complex of course, but the issue of thrust being linearly related to velocity change and kinetic energy imparted to the reaction mass going to the square is at the heart of why fixed wing aeroplanes are more energy efficient than helicopters or why turbofan engines are more efficient than turbojets. In essence, it's more energy efficient to accelerate larger masses more slowly than smaller masses to higher velocities for any given level of thrust (or lift). It's more complex with rockets, but that's the main issue.
+Steve Jones - Hello Steve Jones, thanks for your excellent reply. So: accelerating the propellent mass to double the speed, will give double the force, but will cost 4 times the energy. Is that a correct quote? Then accelerating the propellent mass to 4x the speed, will give 4x the force, but will cost 8 times the energy? (and accelerating half the propellent mass to 4x the speed, will give 2x the force, but will cost 4 times the energy) That would indeed explain your real life examples of: accelerating a heavy mass of air a bit is more energy efficient than accelerating a tiny mass of air a lot. Though, I am still puzzled, and I am actually making a video about this subject. Let’s think of an extreme example: as propellent mass we have only 1 water molecule. This molecule is pushed out of the water rocket, and, well, no lift off. Now my point on this: the reason why this gass pressured water rocket gets practical no force from pushing this one molecule, is because it loses touch with it. The molecule has inertia, but it is almost immediately out of reach. Isn’t this the root of light propellent weight inefficiency, or can “force = mass * acceleration” explain it better?
With only gas, the propellant mass fraction of the rocket drops hugely. If you were to use a very dense compressed gas, your result would be much better. E.g., carbon dioxide (molecular weight ~44 vs. air ~29) should provide measurable improvement, even if the carbon dioxide isn't liquefied (which would improve the mass fraction even more). Presumably sulfur hexafluoride (MW 146) would be yet better (though there are good reasons not to do this). [Real rockets sometimes go to a lot of trouble to 'densify' their propellants to improve their mass fraction, e.g., Falcon 9 and its "super-chilled" LOX and RP-1, just so they can get more fuel/oxidizer into the rockets' tanks.] Steam (MW 18), ironically, would decrease it, unless it was compressed enough to liquefy it (presumably it could vaporize as it expanded through the nozzle?)
If you compress the air to higher PSI’s can you increase the relative volume of the water and attain higher flights? I am assuming the 29% ratio has to do with the limitation of 150 psi due to the weakness of the bottle- The smaller the volume of air in relation to water, the more quickly that 150 psi limit of air pressure drops as the water is expelled resulting in a higher mass, with a more rapid fall off in imparted thrust. Right? Essentially, where water rockets differ from other rockets is that the impulse of a water rocket rapidly falls off rather than remaining constant. The much higher air pressure would mean higher initial thrust, to better lift the higher mass of water. So if you figure that with the last of the water leaving the bottle, you want the air in the bottle to still be at 300 psi- you should be able to pressurize your empty horizon rocket with 300 psi of air, and then pump water in against the pressure until that head of air is compressed to 2000 psi. Is this what you are after with the horizon rocket project?
There are many parameters that affect the final altitude of the rocket, not just the water/air ratio and pressure. The best way we use to optimize the amount of water for a particular pressure is to use a simulator. Dean Wheeler's simulator seems to do the best job at taking all the parameters into account. He has done a really good job in creating the mathematical model behind water rockets. www.et.byu.edu/~wheeler/benchtop/pix/thrust_eqns.pdf
The question asked by Oliver can be interpreted differently... "Can I add something to the water to make more thrust to make my water rocket go higher". Adding solutes to change the propellant density is one possibility; an additive to reduce viscosity -- for instance a detergent, or a "slippery water" polymer additive fire departments add to make water easier to pump on fires -- is another. Would these help the rocket thrust by increasing the exhaust velocity / reducing turbulence in the nozzle?
P.S.: This -- www.iafss.org/publications/frn/959/-1/view/frn_959.pdf -- mentions "long chain, high-molecular weight polymers such as polyethylene oxide, polyacrylamide, polyisobutylene and polymethyl methacrylate, guar gum (a natural material), and some soaps". These are typically added in
Yes quite possibly. We do know that when we add detergent to the water and create a dense foam then we do get a performance boost, but I am not sure if that is due to the foam creating a lower density liquid or because the viscosity is reduced. ruclips.net/video/Gqm9xIJp9ms/видео.html Thanks for the link to the paper, I'll have to have a read of that.
Likely it gives the air a chance to expand more as the froth passes through the nozzle, accelerating the mix. You get work from expanding air, and ideally you want to use that expansion -- as much of it as possible -- to accelerate water out the nozzle. Turbulence in the nozzle throat will naturally limit flow and flow velocity severely, and a pure liquid exhaust provides no opportunity to extract extra work from the air's expansion. If you had a uniform foam of about 1/3 liquid + 2/3 air, compressed to about 225 psi, the foam would expand about 10-fold after it passed through the choke point of the nozzle (to extract the maximum possible energy from the air's expansion). Ideally, the post-chokepoint nozzle would transfer as much of this expansion energy as possible into the foam's liquid. (For which you'd need a suitable convergent+divergent nozzle.)
Late to the game, and perhaps a foolish question... But rather than using the same volume of liquid for different densities, why not try using the same mass? If you use a more dense liquid to achieve the same mass as a given amount of water, will that not leave more room for air. Therefore more stored energy expelling the same mass?
Could you please tell me how you created the 3d graphs of pressure/dry mass/altitude? I want to create similar ones for my rocket but i find it difficult to construct them
Helium actually performs worse because of its low molecular weight. During the air-pulse phase of the boost the helium atoms carry less momentum than their air (N2) counter parts. CO2 is actually the better gas to use because it is heavier than air.
Good Afternoon! im doing my extended essay on a water rockets and how the liquid density effects the hight that the rocket will reach. I Would love to ask you some questions regarding this topic
Thank you so much! I find it quite difficult to find enough calculations on this topic to fill up my extended essay. What calculations could i do that would be related to how liquid density impacts the behaviour of the water rocket?
Here is a good write up of the thrust equations relating to a water rocket. You can see how density affects flight. www.et.byu.edu/~wheeler/benchtop/pix/thrust_eqns.pdf
+BlackBeltnate 'e' stands for exit. And the '0' represents free stream (ambient/external). So Ve is the exit velocity and P0 is the free stream pressure.
I was trying to show my daughter that science is fun and with a blistering hot summer, water rockets were the way to go. However, my rockets were really wimpy. :( I tried 2 liter bottles and 500ml bottles with a 4mm dia I got really pathetic heights and incredibly inconsistent flights. Have you got a video I could follow so that I could be the hero - again.
+Paulo De Oliveira Without knowing more about the rockets it's hard to recommend a particular course of action. Did you use about 1/3 water? How much pressure did you use? You want to use at least 80-100psi for good flights. If the nozzle was only 4mm then that's pretty small. I would try 9mm or larger. Was the rocket designed to be stable? Did it fly straight or tumble? Here are a couple of articles that may be of assistance: www.aircommandrockets.com/flying_higher.htm and www.aircommandrockets.com/flying_straight.htm
How about half water and half veggie oil.Seeing how water and oil don't mix..oil stays on top of the water,the rocket pushes out water first then the veggie oil last.This way there's less chance getting the launcher all greasy.
![[Special Clip] ATEEZ(에이티즈) 홍중 'Why Do You Love'](http://i.ytimg.com/vi/I6XYXQKN_pY/mqdefault.jpg)
So mercury wouldn't work very well.
+TAOFLEDERMAUS But it would be fun to see :)
I wouldn't want to clean it up!
+TAOFLEDERMAUS Agreed. Great channel by the way!
AirCommandRockets thank you. I've been watching a lot of your videos. I really like the creativity you put into them.
I mean, it was tried for chemical combustion rockets. (Seriously. The story is in Ignition!, and I highly recommend the book)
Hello Air Command. Very very interesting video. Looking into the Physics behind Water Rocketry is fascinating, as there are so many variables! It really is Rocket Science! I am using Water Rockery for my Extended Project at College and this is very helpful, so thanks for that. Keep up the good work, Jamie B.
+JSB Rocketry Thanks Jamie. Sounds like a fun college project. :) Both of my kids just did water rockets at school so the years of being around water rockets helped.
Have you done a test on water temperature? Water near freezing vs ambient temperature. I have enjoyed your videos and look forward to more in the future.
No we have not, but it would be worth testing.
Commenting before watching the video, the denser the liquid, the heavier it is, so now you have to account for that extra weight. Ensure your thrust to weight ratio is higher with the denser liquid.
+Duane C That's really the point of the video. :)
Very interesting, well made video and also very interesting write-up , George!
It's great to learn something about the science of this wonderful hobby. We're looking forward to more videos of this series and hope you have a happy new year. :)
+RaketfuedRockets Thanks Julian. We have another video in the works from day 170. :)
And the science too, great stuff.
Also viscosity plays a role
Actually, I kind of guessed that the lower density would mean better performance. You can accelerate the lower-density liquid to a higher speed for the same amount of energy, which means your engine is more efficient - better specific impulse. Granted, it doesn't mean much over such a short burn, but it apparently means enough to have a minor effect.
What would happen if you change the viscosity of the liquid? I think that with other viscosity and density at the same time you may get more trust.
Viscosity is definitely something worth testing. We can change the viscosity of water simply by heating it. There is a significant enough of a difference between 20C and 50C. 50C is still below the glass transition temperature of PET bottles. wiki.anton-paar.com/au-en/water/
Well work George
What software did you use to compile the simulation data into a 3 - variable graph. I'm trying to find the optimal volume of water for my water rocket and I would love to be able to have that 3D graph. I tried using the link in the description, but that simulator only compared altitude at a set volume, not at variable volumes. Thanks a lot!
It took a while, but I just ran a bunch of simulations and recorded each run in a spreadsheet. Then just used the spreadsheet to graph the data.
@@AirCommandRockets ok. Thanks!
Hey, I believe the Dean Wheeler website isn't working anymore?
Not sure, you can always try the web archive/wayback machine to access it.
On your website is written you live in australia. Why are some czech books behind you? Does you, or someone from your family speak czech?
Jsme původem z Prahy :)
Can you design the nozzles to have some sort of Venturi effect something like a Dyson fan to push more air with the water?
very interesting
Did you control for the effects of the changes in viscosity of the different liquids?
what about changing the physical properties of the water by adding a surfactant. Just a drop of dish detergent can make a huge change in the surface tension, and surface wetting properties.
+tom adams Good question. Here is what happens when you add a little bit of kids bubble bath to the water. ruclips.net/video/Gqm9xIJp9ms/видео.html
I would like to see if optimum density changes with nozzle size. Wouldn't different nozzle sizes be more efficient with different density? I'm thinking larger would need denser.
It would be an interesting comparison. In general a larger nozzle produces more thrust, but with greater thrust you have higher peak velocity. Because drag is proportional to the square of the velocity you will induce more drag. So it would be interesting to see what kind of overall performance difference there would be.
Using no water, just gas, makes the rocket way lighter, and as there is more space for the compressed gas, there is more power on board. This should make it fly much higher! But... as I know and as you know; it doesn't work well at all. Yes; it works great for the first like 1/30 of a second, and then the party is over. Less weight and more power, but it doesn't fly as high. Can you explain why this is?
+Giesbert Nijhuis It's because a higher proportion of the stored energy in the compressed air is lost to kinetic energy in the exhaust rather than to the rocket. As the air in the exhaust has a low density, it has to be accelerated to a much higher speed than the water to get equivalent thrust. Unfortunately whilst thrust scales linearly with exhaust velocity (for a given mass), the kinetic energy in the exhaust goes to the square of the exhaust velocity.
Of course a rocket with no liquid can store more energy in the first place (a higher volume of compressed air) and it has less mass (as the air is lower density than the liquid). However, that's not enough to compensate for the other effects.
It's all a bit more complex of course, but the issue of thrust being linearly related to velocity change and kinetic energy imparted to the reaction mass going to the square is at the heart of why fixed wing aeroplanes are more energy efficient than helicopters or why turbofan engines are more efficient than turbojets.
In essence, it's more energy efficient to accelerate larger masses more slowly than smaller masses to higher velocities for any given level of thrust (or lift). It's more complex with rockets, but that's the main issue.
+Steve Jones - Hello Steve Jones, thanks for your excellent reply. So: accelerating the propellent mass to double the speed, will give double the force, but will cost 4 times the energy. Is that a correct quote? Then accelerating the propellent mass to 4x the speed, will give 4x the force, but will cost 8 times the energy? (and accelerating half the propellent mass to 4x the speed, will give 2x the force, but will cost 4 times the energy) That would indeed explain your real life examples of: accelerating a heavy mass of air a bit is more energy efficient than accelerating a tiny mass of air a lot. Though, I am still puzzled, and I am actually making a video about this subject. Let’s think of an extreme example: as propellent mass we have only 1 water molecule. This molecule is pushed out of the water rocket, and, well, no lift off. Now my point on this: the reason why this gass pressured water rocket gets practical no force from pushing this one molecule, is because it loses touch with it. The molecule has inertia, but it is almost immediately out of reach. Isn’t this the root of light propellent weight inefficiency, or can “force = mass * acceleration” explain it better?
With only gas, the propellant mass fraction of the rocket drops hugely. If you were to use a very dense compressed gas, your result would be much better. E.g., carbon dioxide (molecular weight ~44 vs. air ~29) should provide measurable improvement, even if the carbon dioxide isn't liquefied (which would improve the mass fraction even more). Presumably sulfur hexafluoride (MW 146) would be yet better (though there are good reasons not to do this).
[Real rockets sometimes go to a lot of trouble to 'densify' their propellants to improve their mass fraction, e.g., Falcon 9 and its "super-chilled" LOX and RP-1, just so they can get more fuel/oxidizer into the rockets' tanks.]
Steam (MW 18), ironically, would decrease it, unless it was compressed enough to liquefy it (presumably it could vaporize as it expanded through the nozzle?)
what if you ignited the gas? the explosion would make an enormous amount of pressure, it would make it a then fuel powered rocket
If you compress the air to higher PSI’s can you increase the relative volume of the water and attain higher flights? I am assuming the 29% ratio has to do with the limitation of 150 psi due to the weakness of the bottle- The smaller the volume of air in relation to water, the more quickly that 150 psi limit of air pressure drops as the water is expelled resulting in a higher mass, with a more rapid fall off in imparted thrust. Right? Essentially, where water rockets differ from other rockets is that the impulse of a water rocket rapidly falls off rather than remaining constant.
The much higher air pressure would mean higher initial thrust, to better lift the higher mass of water. So if you figure that with the last of the water leaving the bottle, you want the air in the bottle to still be at 300 psi- you should be able to pressurize your empty horizon rocket with 300 psi of air, and then pump water in against the pressure until that head of air is compressed to 2000 psi.
Is this what you are after with the horizon rocket project?
There are many parameters that affect the final altitude of the rocket, not just the water/air ratio and pressure. The best way we use to optimize the amount of water for a particular pressure is to use a simulator. Dean Wheeler's simulator seems to do the best job at taking all the parameters into account. He has done a really good job in creating the mathematical model behind water rockets. www.et.byu.edu/~wheeler/benchtop/pix/thrust_eqns.pdf
The question asked by Oliver can be interpreted differently... "Can I add something to the water to make more thrust to make my water rocket go higher". Adding solutes to change the propellant density is one possibility; an additive to reduce viscosity -- for instance a detergent, or a "slippery water" polymer additive fire departments add to make water easier to pump on fires -- is another. Would these help the rocket thrust by increasing the exhaust velocity / reducing turbulence in the nozzle?
P.S.: This -- www.iafss.org/publications/frn/959/-1/view/frn_959.pdf -- mentions "long chain, high-molecular weight polymers such as polyethylene oxide, polyacrylamide, polyisobutylene and polymethyl methacrylate, guar gum (a natural material), and some soaps". These are typically added in
Yes quite possibly. We do know that when we add detergent to the water and create a dense foam then we do get a performance boost, but I am not sure if that is due to the foam creating a lower density liquid or because the viscosity is reduced. ruclips.net/video/Gqm9xIJp9ms/видео.html Thanks for the link to the paper, I'll have to have a read of that.
Likely it gives the air a chance to expand more as the froth passes through the nozzle, accelerating the mix. You get work from expanding air, and ideally you want to use that expansion -- as much of it as possible -- to accelerate water out the nozzle.
Turbulence in the nozzle throat will naturally limit flow and flow velocity severely, and a pure liquid exhaust provides no opportunity to extract extra work from the air's expansion.
If you had a uniform foam of about 1/3 liquid + 2/3 air, compressed to about 225 psi, the foam would expand about 10-fold after it passed through the choke point of the nozzle (to extract the maximum possible energy from the air's expansion). Ideally, the post-chokepoint nozzle would transfer as much of this expansion energy as possible into the foam's liquid. (For which you'd need a suitable convergent+divergent nozzle.)
Late to the game, and perhaps a foolish question... But rather than using the same volume of liquid for different densities, why not try using the same mass? If you use a more dense liquid to achieve the same mass as a given amount of water, will that not leave more room for air. Therefore more stored energy expelling the same mass?
I think that is a reasonable question. Worthwhile running some sims to see.
How to make the nose con
www.aircommandrockets.com/construction_7.htm
where to buy this altimeter?
jollylogic.com/products/altimeterone/
@@AirCommandRockets SORRY I'M ASKING YOU SO MUCH MORE WHICH CAMERA YOU USE ON BOARD IN THE ROCKET?
@@francuadasilvacosta5116 No worries happy to answer questions. We use the 808 key chain cameras V16, and now the Mobius mini V2.
good work, I see what you mean now.
Could you please tell me how you created the 3d graphs of pressure/dry mass/altitude? I want to create similar ones for my rocket but i find it difficult to construct them
We just use the 3D graph feature in Excel.
pls make more
What would happen if you filled the rocket with two or more liquids of different densities that do not mix?
You could probably customize your thrust profile a little more.
thank u
What about helium instead of air? pressures about same but ? lighter loading?
Helium actually performs worse because of its low molecular weight. During the air-pulse phase of the boost the helium atoms carry less momentum than their air (N2) counter parts. CO2 is actually the better gas to use because it is heavier than air.
Good Afternoon! im doing my extended essay on a water rockets and how the liquid density effects the hight that the rocket will reach. I Would love to ask you some questions regarding this topic
Happy to answer any questions I can. You can either ask them here, or send us an email. www.aircommandrockets.com/contact.htm
Thank you so much! I find it quite difficult to find enough calculations on this topic to fill up my extended essay. What calculations could i do that would be related to how liquid density impacts the behaviour of the water rocket?
Here is a good write up of the thrust equations relating to a water rocket. You can see how density affects flight. www.et.byu.edu/~wheeler/benchtop/pix/thrust_eqns.pdf
it's a great write up but sadly after reading it a few times i still dont understand how i can relate those equations to my experiment.
So what is your actual question? Are you looking for a formula that has density as its input and altitude as its output?
What does "e" and "o" mean in the equation?
+BlackBeltnate 'e' stands for exit. And the '0' represents free stream (ambient/external). So Ve is the exit velocity and P0 is the free stream pressure.
I was trying to show my daughter that science is fun and with a blistering hot summer, water rockets were the way to go. However, my rockets were really wimpy. :( I tried 2 liter bottles and 500ml bottles with a 4mm dia I got really pathetic heights and incredibly inconsistent flights. Have you got a video I could follow so that I could be the hero - again.
+Paulo De Oliveira Without knowing more about the rockets it's hard to recommend a particular course of action. Did you use about 1/3 water? How much pressure did you use? You want to use at least 80-100psi for good flights. If the nozzle was only 4mm then that's pretty small. I would try 9mm or larger. Was the rocket designed to be stable? Did it fly straight or tumble? Here are a couple of articles that may be of assistance: www.aircommandrockets.com/flying_higher.htm and www.aircommandrockets.com/flying_straight.htm
Nice hats fellas... :)
Hi George what equation you use？
Equation to calculate what?
Air Command Rockets Rocket Thrust Equation is what？ and how to use it?
The best reference I have come across: www.et.byu.edu/~wheeler/benchtop/pix/thrust_eqns.pdf
How about using gelatin?
Seeing how veggie oil is less dense than water why not try it?
That's a good question The idea of coating the launcher and launch site with vegetable oil isn't very appealing.
How about half water and half veggie oil.Seeing how water and oil don't mix..oil stays on top of the water,the rocket pushes out water first then the veggie oil last.This way there's less chance getting the launcher all greasy.
hey george,whats your email?
www.aircommandrockets.com/contact.htm
Have you tryet using cocacola as your fuel?
+Lord Asteroph Yes, we've tried lemonade (carbonated like coke). It didn't make much difference.