Water rocket highlights from our recent trip to Mullaley, NSWRA's high power launch site. We launched Dark Shadow at its highest pressure to date at 1000psi and also the Nova water rocket at 450psi.
Update 29/5/21: I've managed to fix the altimeter by replacing the LCD screen and hooking up a new battery. I was able to read off the altitude for the Nova rocket that crashed. The altitude was 1,445 feet or 440m. Not bad for a little rocket.
So glad that you turned the camera the right way up at the end! It's been over 50 years since I left Sydney, and I'm still not used to watching British TV the wrong way up! Shame about the lawn dart. But hey, ho; there'll be another day. 🙂🚀
Anyone who is a decent age can probably remember the old water-powered rockets from the 70's and 80's. To this day, that is one of the coolest toys I ever had. It also taught me to understand the mechanical aspects of the machine and how to repair it. Sorry - nostalgia is a powerful emotion when you begin to age.
came here to comment this, this must be correct. I assume the noise level is proportional to the delta p across the inlet, which most definitely is decreasing. btw delta p = pressure difference. delta just means "difference in"
@@AirCommandRockets sir likewise here im your fan. I have a question. How rockets are launched under water like in submarines does it have a different procedure? And can you do it with your rockets while explaining the technicality involved? Thank you.
@@AirCommandRockets impressively beautiful i hope you can post it on you tube. I notice the rocket is already running beneath the water till it lauch. Can you mimic a submarine lauched rocket were the rocket shoots upward then after it reaches above the water the rocket would ignite its engines and fly. Can this be possible?
As always, very entertaining! Particularly the driving joke at the end - gave me a good giggle! Looks like you need a checklist to not forget things like opening the cylinder, etc. Pity about the wind and the offering to the gods! Great to see you guys out there again!
Thanks Willie, yeah about that checklist .... it would help if I remembered to bring the printout! :) I need a checklist for my checklist. The wind on the following day was even worse, and although we put our high power pyro rocket out on the pad, we decided against launching it. I'd say the wind was closer to 35km/h at times. Most other people also decided against launching theirs.
When I was a kid in the 60s we had toy rockets you would fill it a quarter with water and attach it to a hand pump/launcher. Loads of fun, probably don't make them anymore.
Woah this is so impressive, the engineering, the electronics, the maths. This is the first video I've seen of water rockets and this seems awesome! Best thing of all I stumbled across some fellow Australians! Hey from Far West NSW!
4:41 As the pressure gradient between the gas tank and the rocket reservoir gets lower, the gas enters the rocket reservoir at a lower speed and therefore less energy can be converted from the slower moving gas to sound resulting in the noise dropping as filling progresses.
The decrease in volume is likely caused by the increased chamber pressure. Higher pressures prevent the vibration (deformation) of the chamber and thus attenuate the sound.
I believe the decrease in tone recording is because of a decrease in the volume of air being able to pumped in due to resistive pressure. Cheers, Billy in Canada
Also, the natural frequency of the hollow space (compressible void) increases (like how the tone rises when blowing into a filling bottle), allowing for less lower tones to oscilate.
@@fakshen1973: Exactly :) It also has an effect on the container (like how a half filled bottle sounds different when struck on the empty part and when struck on the full part). It's a very complex system of pressure vs volumetrics vs harmonics vs material properties. It's equally amazing that these factors are pre-calculated and accounted for in modern day high tech.
The decrease in sound volume recorded during pressurization is due to the incoming air not compressing or expanding as much when the pressure is higher.
As to timemark 4:30, as the pressure in the rocket increases, the flow rate of gas slows down and thus quieting it. Thanks for your video. Blessings to you.
About 4:30, my hypothesis is as the rocket is filled, the pressure differential between the scuba tank and rocket decreases, resulting in slower, less violent air flow.
Each time the rocket is pressurized there is less of a pressure differential between the rocket and the air cylinder, so the flow velocity into the rocket is likely reduced.
I believe that the sound is more likely lowering in volume because as the tank is pressurized the walls become stiffer and make it harder for sound to travel through it. I think the sound comes from the bubbles of air gluging up through the water so another explanation could have to do with the speed the bubbles rise at different pressures though you can test my first guess by flicking the tube at 100 psi then repeating it as you increase pressure.
@@evilcanofdrpepper I think you're sort of right, the tank wall is like a bell, the increased pressure acts as a brace for the walls of the tank, and dampens it s resonance. that plus the reduced pressure differential I'd say. technically a stiffer wall should let sound 'through' more easily, the way a well pumped bike wheel lets you feel more of the road surface in the ride. then again im not a professional in any sense.
The noise decreases as the pressure builds, as I ponder, because there is more air inside. Each pump represents a smaller percentage of the total air. It also moves slower because it's compressed to a smaller size. Nice footage from the onboard camera.
The decrees in volume that the microphone picks up is due to a reduction in the flow rate of air in to the rocket as the pressure increases. That thing get off the ground in a hurry, nice work!
Regarding the pattern of decreasing amplitude you saw in the sound waves during pressurization pulses-I wonder if it’s because the stiffness of the pressure chamber’s outer wall increases as you add pressure, such that the walls can’t resonate as much with each subsequent pulse?
Thanks Dan. No, the nozzle is just a straight through 7 mm hole. Expansion nozzles are planned for a test campaign probably sometime after we finish our Horizon rocket.
As the air is pressurized inside the tank, this decreases the velocity from the new air coming in. The decrease in velocity means a lower Reynolds number in turn resulting in a more laminar flow for the Fuild(air) resulting in less noise
Good works! Are you sure it has lost battery connection instead of mechanical jammed? In your experience what's the best parachute deployment you ever built?
We don't know the root cause of the failure. I know the circuit had power as I checked the Armed LED before launch, and the part of the servo motor that we recovered with the servo horn, it was still in the locked position, so the servo never moved. The best parachute deployment we use is the one on our regular low pressure water rockets. It has flown hundreds and hundreds of times with only very rare fails.
4:41 I'd guess the reason the sound gets quieter as the pressure rises is due to the changing impedance of the air inside. When sound passes from one medium to another, it experiences attenuation (reduction in amplitude) due to impedance mismatching. Initially, the air inside the rocket is at atmospheric pressure, so the impedance is the same inside and out. As the pressure rises, the impedance will change, resulting in amplitude losses as the sound is transmitted through the rocket.
As the pressure in the rocket increases the infill speed that the air is traveling at from the scuba tank to the rocket drops slower and slower until both the rocket and the air tank are at the same pressure then there is nothing pushing the air either way so the flow would stop completely, that is why it gets quieter as it fills, the speed of the air is slowing down so its not as noisy, I trust this makes sense 😀
I think the volume goes down as pressure is added because it changes the resonance frequency of the model due to internal stresses. Similar to how a piano or guitar string changes in sound as it gets tightened.
4:36 I think the reason the volume decreases, is the energy comes from the difference in pressures between what is in the vessel, and what is coming from the tank. as the pressure gets closer to equivalent, there is less force driving it in?
As pressure inside the rocket rises it comes closer to equalization with the supply tank. As they equalize the rate of flow decreases. You're initially hearing a high rate of transfer, but as the rocket fills the flow rate decreases. If allowed to continue without theoretically exploding - the air flow will decrease and decrease to a zero flow when both tanks are equalized.
The filling noise decreased in subsequent bursts as the delta decreased; the greater resistance of higher pressure inside the reservoir reduced the flow rate. Less flow = less noise.
The pressure difference across every bit of your pressurising system decreases as the rocket pressurises. So the mass flow rate reduces, flow velocities decrease, turbulence reduces, noise reduces.
So nice video again i love to see fly the rockets again , but suddently a spider YaY!! Im arachnofobic !! Poor rocket, but yes sometime can chras happend. And so awesome place you living. Greeting from Hungary Sopron !!
@@AirCommandRockets Probably I would send someone for the rocket ,or just build an other ha ha ha. Im building water rockets too but I make aerodinamic cover from spotwelded aluminium cans shiny side , looks great , but not so far advanced as your work.
@@AirCommandRockets Thanks! I'm building my own rocket with my daughter. I have a cheap go pro clone which is light(ish) but bulky, these look perfect.
I think the noise reduction may have been to a lower flow rate as the potential was decreasing as the pressure was increasing in the rocket. Since the pressures were closer to equal as from the incoming and actual pressure. Less flow, less noise
Great video!! Have you ever experimented with liquids of different viscosities? It would be interesting to see everything from soda pop to maybe a light mineral oil and their affects on flight.
We have not tried different viscosities specifically, but have done different densities. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Fu3rIiPy_18.html Each of the liquids I guess also has a different viscosity.
@@AirCommandRockets for a straight forward thruster H2O is much better than CO2 or N2 since it has 155sec isp But in the study they did not mention what temp was the water or to what psi was it compressed According to your rockets what is the isp you are getting and at what lressure exactl?
@@FirstLast-tx3yj That sounds like a steam rocket. Where the water changes from liquid to a gas. This is a different kind of water rocket. Cold gas acting on a cold liquid.
You need a long nozzle to expand the water into bubbles before it comes out and you can't get work from it anymore. As soon as the pressure is released, a wave of bubbles propagates from the nozzle exit inwards. Within a microsecond your entire water volume becomes a dense foam.... problem is you also already kicked it out during launch.
That is certainly an option, but we would need a drogue chute to slow it down before releasing the main. Drogue-less recovery isn't an option for this rocket design. The chute release and drogue add weight though, so on record attempts that would be a penalty.
Apogee just means the highest point of the flight measured in meters or feet above ground. Arrows behave very similarly to rockets near apogee where they slow down to low speed before accelerating again.
4:34 if the microphone is located on the tip of the rocket and the water is being filled from the bottom it might be that the sound has to travel trough more water that “absorbe” the sound as it fills up. This seems very simple to explain so I doub i got it right :P
Great Test. To get better video of the launch, get further away, and hold the camera in your hands with your arms straight. Follow the rocket accent with your arms straight and camera below your eyes. Keep from moving the camera off the rocket as much as possible. Post process the video putting a red circle around the rocket while in the sky as otherwise it is invisible due to the low resolution of the video image.
did you ask why the burst's sound level drops as the tank is filled? its either because your rocket is being filled from a reservoir tank which has been pressurized appreciably close to equilibrium with your rockets target fill pressure or alternately, if being filled from a source with a near constant flow rate, the chance for cavitation to occur during the turbulence of the fill decreases as the overall pressure rises distantly from vacuum. (source: my pumps quiet down as i raise the net positive suction head)
The pressure is going from 10L 3000psi tank to ~5L volume (air volume) at 1000psi. So yes there is definitely a drop in the flow rate as it gets fuller.
First, at 4:10, what kind of spider is that? I've never seen one like it. Second, suppose you used a propellant denser than water? Would that add to or detract from the altitude achieved? On the one hand, you're pushing more mass out the nozzle, but on the other, you need to lift more mass.
Have no idea what spider that is. There was a huge variety of spiders on the field. Very good question about the density of the water, and good insight why denser liquids don't necessarily translate to higher altitudes. We looked into this a couple of years ago, here is a video where we did some experiments with different densities: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Fu3rIiPy_18.html
It improves performance because it allows us to create foam. Here is some more information on it: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Gqm9xIJp9ms.html
I'm new to the hobby, is there any water additive to encourage laminar flow? In hydraulic fracturing (oil field fracing), we use a "friction reducer" to reduce turbulent flow in the well bore. The friction reducer is a slurry of polymer chains (guar) and surfactants. It will increase the viscosity slightly (5 cp max). I would think this would result in a higher specific impulse, and therefore higher alt. with the same reaction mass and pressure.
This is a really interesting question. We do use a detergent to generate foam inside the rocket that does give a boost in performance. But I have not considered it terms of encouraging laminar flow. It would be interesting to do a comparison between foam and non-foam with just the detergent dissolved in the water.
Why more noise as the pressure builds up?? My grand mother used to say "empty barrels make a lot of noise as full ones stay silent". Density while increasing the speed of sound attenuates it's amplitude.
@@AirCommandRockets The radios normally use an 18650 Li battery, but that gets about a week of operation. For the duration of the flight, anything that puts out about 3.5V would work. I have the ones based on the t -beam v1.1 modules. You wouldn't have to mount the oled display. What is cool about it is that there is a mobile phone app that talks to a nearby module which shows the location of all the others on a map w/ distance (so you could have one on the rocket, plus one next to you). Good luck, I think you have a really cool project here.
Maybe the sound-volume decreases because the pressure stiffens up the tank? I mean: when there is no pressure in the tank, the incoming air flow has an easy time vibrating the tank walls, but as presure builds up the tank walls are becoming ever so stiff, and it is harder to vibrate them.
Would a colored smoke generator make it easier to find the rocket? As the chute deploys the smoke generator comes on? I'm not sure if that's feasible. But considering the propensity for damaged electronics on landing, the smoke canister might be a little more reliable on a hard landing. Also the trail of smoke would be easier to locate as the rocket comes down.
That would certainly make it easier to find, but the weight of the smoke generator could be an issue. I don't have direct experience with smoke generators, but if it is something that is burning, (even internally)? This may be an issue if it was to start a fire on landing.
