just a question george, why are you filling the pressure chamber all the way with water, isnt it usually just a third filled with water and the rest filled with air?
Excellent question. This is called hydro-static testing. The water helps reduce any effects of an explosion. You can't compress water like you can air, so if the pressure chamber fails it just sprays a bit of water around, but if it was filled with air you would get a much more violent explosion as the air expands. The water just can't store the energy same way compressed gases can. It's similar to squeezing a rock as hard as you can, and when you release it, how much energy does the rock return? Now squeeze a spring, and when you let go, how much energy does it return?
That’s a lot of work but one big positive from both failures is that it seems the hardware doesn’t fail catastrophically (explosion) but rather progressively, making it a slightly safer way to fail. Great job as always guys!
Exactly, it's hard to convey on video how loud that is. The pressure chamber sounds like it is made from glass when fully pressurised and so any noise it makes is extra loud.
Thanks to video's like this we don't have to make the same mistakes, thanks a lot for that George! Found it really scary to hear the fiberglas layer crack, must be even more frightening live!
I love what you're doing, but I have a few questions about your construction. 1) Would it not be better to have the first layer of the cylinder barrel be wound on with filament as opposed to sleeve? Yes, your method is far easier to be consistent, but for the ultimate in strength-to-weight, I'd think you'd want to better orient fibers to their load paths. From there, I'd suppose you'd wrap a length of unidirectional fabric lengthwise to handle the static thrust of the endcaps. 2) Why use fiberglass the way you do? Structurally, it's effectively invisible in tensile strength until the carbon fails from elongation. 3) Have you ever thought of coating the inside surface with lacquer/tool dip/resin/etc. to deal with pinholes? Sure, wrapping everything around a preformed liner would be ideal, but you gotta work with what you have.
All good questions. 1. We definitely don't have the optimum strength to weigh ratio with how we build our pressure chambers. We don't have a winding machine so any wrapping with CF tow would have to wait for that. You can't do it by hand and expect consistent results. You would also get much better results if you could do vacuum forming, or an infusion process. We could also use a better epoxy and post cure it in an oven. But we don't have a vacuum pump, or an oven long enough. The combination of plain-weave cloth and the carefully selected biaxial sleeve gets us closer to ideal fiber orientations in the pressure chamber, that's inexpensive, easy to manufacture and pretty consistent in terms of performance. 2. The fiberglass isn't for structural reinforcement, it's there to provide a much better surface finish that reduces the number of micro pores and makes sanding much easier. 3. That is exactly what we do, we coat the inside of the tubes with a couple coats of the epoxy, it creates a much better seal, again to reduce the chance of any micro pores.
Question: Shouldn't the chamber also be tested vertically? where there would static/dynamic pressure differences between the long air chamber to a surface small area air chamber? (IDK, I just stayed at a Holiday In Express)
The chamber is tested vertically and under dynamic loads at the time of launch. We typically start launching at a lower pressure than the static hydro test, and increase the pressure on successive launches. If it is going to fail, we want it to fail trying to launch it rather than just fail on the test stand. You also can't test the acceleration forces on the pressure chamber on a test stand.
Random question. While operating, or launching, would using water saturated with co2 or ‘sparkling’ water help sustain pressure at higher altitudes? As I’d assume the massive pressure drop would cause the saturated co2 to release more violently?
That's a good question. I think that would help to some extent, but it all depends on how quickly you can liberate that CO2 from solution before the water itself is ejected from the nozzle. With the sustainer for this rocket, the water is ejected in about 0.1 seconds.
Looks ton of work to me.... I think delamination is due to a change in the material at the interface(glass and carbon don't have the same stress-strain curve, which in turn creates a differential in expansion at the interface)e.g. analogy: bimetallic strip used in heating relays etc. it will be great if you can do some cyclic pressurising for fatigue resistance of these chambers...at some point in time.
We are going to cut the pressure chamber open to see what happened on the inside. The top endcap didn't have any issues with delamination. We also hadn't seen delamination on other pressure chambers we've made.
With such a high pressure, is there an elongation of the cylinder during the test? Because the cylinder is in a steel frame, so cannot elongate, can’t it? Otherwise really pleasant to see your project!
Yes the pressure chamber will stretch. The pressure chamber has about 5mm clearance in the frame to allow it to stretch as needed. You can actually see it in the video 2:14 where the nozzle is pushed out under pressure. That's the amount of clearance the pressure chamber has to stretch.
Have you thought about wrapping the carbon fiber in a wrap to simulate a vacuum bag? You can see the process here for making carbon fiber baseball bats. ruclips.net/video/XzSxaY4nOls/видео.html
We have done tests with a wrap over the top, but that doesn't quite have the same effect as vacuum forming. It doesn't really remove the excess epoxy. Wrapping it tightly around the piece then makes it much harder to remove the long tubes from the mandrel. We don't have the large hydraulic presses like shown in the video.
Would a PET or Polyethylene baloon work for that instead of fibreglass. Similar to those reinforced bottle rockets you used to make years ago, but this time carbon fibre reinforced?
For the inside of the pressure chamber? Yes you could do it, but you would get a weight penalty. The strength to weight ratio of fiberglass compared to PET is higher.
@@AirCommandRockets I may be wrong, but the young modulus of fibreglass is like 6 times lower than that of carbon fibre. So in this case the fibreglass is acting purely as a sealant/barrier, right? Cause by the time the fibreglass stretches enough to get to its tensile strength - the carbon fibre will be already torn. So the carbon fibre is taking all the pressure load. So I thought - if you would take a relatively small PET bottle, heat it up, put it inside a matching diameter steel tube, inflate it like a baloon you would end up having a perfect mandrel to put the carbon fibre "sock". I'm very new to the rocketry, my background is the prototyping engineer and sorry if I'm wrong and you have already tried or thought of that idea.
@@makerbeelab5546 I see what you mean. Yes the carbon fiber provides the vast majority of the pressure containment. But if the glass stretches more than the carbon fiber then that should be good because it won't fail before the carbon fiber does. The problem with making the inside out of PET, how do we get it to be 2m long? This test pressure chamber is only a short version of the final booster segment.
@@AirCommandRockets Maybe to try a PET tubing, heat it up and inflate inside a steel or aluminium tube of large diameter? Something like that www. automaticfiresuppressionsystem .com/ product/ product-85-212 .html
Interesting. Is the most common failure mode ripping or delaminating? And would this delamination instead of straight ripping provide a bit of extra safety in terms of pre-warning sounds, if the vessel was filled with air? Or would the leaking air rapidly rip apart the delaminated layers anyway? After all it’s much less viscous.
We don't have a whole lot of experience with failure modes for carbon fiber pressure vessels. We really haven't had these delamination issues previously. (If it indeed was delamination). We will cut it open and have a look. If I ever heard that fiber breaking noise of a pressure vessel I would sure run as quickly as I can. The hydro-static tests don't show the whole picture either because the pressure chamber will heat up when we partially fill it with compressed air. We can't do those tests at home, if we want to stay friendly with the neighbours.
Perhaps you could use a hydraulic pressure increaser?. Instead of having to make the whole rocket high pressure?. Youd have to have a bigger tank but your mean pressure would increase at nozzle only. Hence youd only have to strengthen second chamber. www.hydraulicspneumatics.com/technologies/other-technologies/article/21884328/book-2-chapter-13-pressure-intensifier-circuits
I don't think that would work in this application, because you wouldn't be able to get the flow rate needed. We are pushing out about 3L of water in about 0.2 seconds. There would also be the added weight of the mechanism which would reduce the overall altitude. But an interesting suggestion.
Do you mean PVC pipe sch 40? In order to compare apples to apples this pressure chamber is 3.14" and from what I can see the operating pressure is 158psi and burst pressure of 840psi. sch 80 is 225psi and 1200psi respectively. So both of these are still too low. Our operating pressure is 1000-1100psi with burst pressure above 1600psi. That aside, PVC fractures into dangerous splinters when it lets go, isn't as stiff as the composite so tends to bend during high accelerations, and is heavier.
@@AirCommandRockets Yeah, those are the listed pressures, I'm sure it's much higher in reality with the glue joints being the failure point. I was just more curious if you had considered it when I made the comment and want to emphasis that I think this is a really cool project and you have gotten some great results. Also I was really impressed with the trigger mechanism.
You would think after 30 years you would remember to remove the coathanger before you put your shirt on. Well done on a great video George.
Hi Eric, Great to hear from you. Hope you are doing well. :) I thought that after 30 years it was safe enough to use that gag again!
Woah. I was not expecting the holding pressure to be this high
It will need to hold at least 1200-1300psi as we need a safety margin.
just a question george, why are you filling the pressure chamber all the way with water, isnt it usually just a third filled with water and the rest filled with air?
Excellent question. This is called hydro-static testing. The water helps reduce any effects of an explosion. You can't compress water like you can air, so if the pressure chamber fails it just sprays a bit of water around, but if it was filled with air you would get a much more violent explosion as the air expands. The water just can't store the energy same way compressed gases can. It's similar to squeezing a rock as hard as you can, and when you release it, how much energy does the rock return? Now squeeze a spring, and when you let go, how much energy does it return?
@@AirCommandRockets what an excellent explanation. thanks a lot George :)
@@AirCommandRockets very nice explanation and kudos on the analogy
That’s a lot of work but one big positive from both failures is that it seems the hardware doesn’t fail catastrophically (explosion) but rather progressively, making it a slightly safer way to fail. Great job as always guys!
Thank you Andre. I'm not looking forward to the day when it does fail catastrophically. :)
That sound of tearing fibres. Better on the test stand than the field tho.
Exactly, it's hard to convey on video how loud that is. The pressure chamber sounds like it is made from glass when fully pressurised and so any noise it makes is extra loud.
Lookin good George. Xant wait to see this beast rip
If it work we can use to power aircraft continuously replenish in flight then use motor generator to compress air and make water to continuous flight
actually very cool you're building a DIY COPV
(sort of)
It need spring load to stable high pressure on continuous release and air pressure separate containner
Thank you for posting high-quality content. It is very refreshing in the times that we are living. Good luck with the construction!
Thanks Daniel. :)
Thanks to video's like this we don't have to make the same mistakes, thanks a lot for that George! Found it really scary to hear the fiberglas layer crack, must be even more frightening live!
Thanks Mathieu. The fibers breaking is pretty loud, it sure made us jump. I'd hate to hear it if the whole pressure chamber let go.
Wow, another video already! Thanks for all the updates!
Cheers ARRO :)
How many g/m² has the carbon fibre tissue ?
The inner couple of wraps are 200gsm plain weave carbon fiber cloth. And the outer CF bi-axial sleeve is 244gsm.
@@AirCommandRockets Ok thanks! :)
........INCRÍVEL................ESPETACULAR
I love what you're doing, but I have a few questions about your construction.
1) Would it not be better to have the first layer of the cylinder barrel be wound on with filament as opposed to sleeve? Yes, your method is far easier to be consistent, but for the ultimate in strength-to-weight, I'd think you'd want to better orient fibers to their load paths. From there, I'd suppose you'd wrap a length of unidirectional fabric lengthwise to handle the static thrust of the endcaps.
2) Why use fiberglass the way you do? Structurally, it's effectively invisible in tensile strength until the carbon fails from elongation.
3) Have you ever thought of coating the inside surface with lacquer/tool dip/resin/etc. to deal with pinholes? Sure, wrapping everything around a preformed liner would be ideal, but you gotta work with what you have.
All good questions. 1. We definitely don't have the optimum strength to weigh ratio with how we build our pressure chambers. We don't have a winding machine so any wrapping with CF tow would have to wait for that. You can't do it by hand and expect consistent results. You would also get much better results if you could do vacuum forming, or an infusion process. We could also use a better epoxy and post cure it in an oven. But we don't have a vacuum pump, or an oven long enough. The combination of plain-weave cloth and the carefully selected biaxial sleeve gets us closer to ideal fiber orientations in the pressure chamber, that's inexpensive, easy to manufacture and pretty consistent in terms of performance.
2. The fiberglass isn't for structural reinforcement, it's there to provide a much better surface finish that reduces the number of micro pores and makes sanding much easier.
3. That is exactly what we do, we coat the inside of the tubes with a couple coats of the epoxy, it creates a much better seal, again to reduce the chance of any micro pores.
Question: Shouldn't the chamber also be tested vertically? where there would static/dynamic pressure differences between the long air chamber to a surface small area air chamber? (IDK, I just stayed at a Holiday In Express)
The chamber is tested vertically and under dynamic loads at the time of launch. We typically start launching at a lower pressure than the static hydro test, and increase the pressure on successive launches. If it is going to fail, we want it to fail trying to launch it rather than just fail on the test stand. You also can't test the acceleration forces on the pressure chamber on a test stand.
You guys are really amazing .
Random question. While operating, or launching, would using water saturated with co2 or ‘sparkling’ water help sustain pressure at higher altitudes? As I’d assume the massive pressure drop would cause the saturated co2 to release more violently?
That's a good question. I think that would help to some extent, but it all depends on how quickly you can liberate that CO2 from solution before the water itself is ejected from the nozzle. With the sustainer for this rocket, the water is ejected in about 0.1 seconds.
Looks ton of work to me.... I think delamination is due to a change in the material at the interface(glass and carbon don't have the same stress-strain curve, which in turn creates a differential in expansion at the interface)e.g. analogy: bimetallic strip used in heating relays etc.
it will be great if you can do some cyclic pressurising for fatigue resistance of these chambers...at some point in time.
We are going to cut the pressure chamber open to see what happened on the inside. The top endcap didn't have any issues with delamination. We also hadn't seen delamination on other pressure chambers we've made.
Sweet. Lovely too see a methodical approach and can't wait for a flight ready beast to take to the skies. Good luck and best wishes.
Thanks Jonathan.
Why not make an air cannon/water rocket hybrid. The air cannon should add a lot of boost with no weight penalty. It could be pretty awesome.
A launch tube that goes up through the nozzle has a similar effect. The booster for this rocket will use 3 launch tubes one for each nozzle.
With such a high pressure, is there an elongation of the cylinder during the test? Because the cylinder is in a steel frame, so cannot elongate, can’t it? Otherwise really pleasant to see your project!
Yes the pressure chamber will stretch. The pressure chamber has about 5mm clearance in the frame to allow it to stretch as needed. You can actually see it in the video 2:14 where the nozzle is pushed out under pressure. That's the amount of clearance the pressure chamber has to stretch.
Getting closer!
No blast shield?
Yes blast shield. We are behind a stone wall when we do the tests.
Haha... turkey
Uhh igen izgalmas próba , yes exciting test 😊😊
Have you thought about wrapping the carbon fiber in a wrap to simulate a vacuum bag? You can see the process here for making carbon fiber baseball bats. ruclips.net/video/XzSxaY4nOls/видео.html
We have done tests with a wrap over the top, but that doesn't quite have the same effect as vacuum forming. It doesn't really remove the excess epoxy. Wrapping it tightly around the piece then makes it much harder to remove the long tubes from the mandrel. We don't have the large hydraulic presses like shown in the video.
@@AirCommandRockets ahhhh dang. I was hoping that would be helpful.
Funny!
thank you George... good luck proceeding!!
More fiberglass layers under the CF, perhaps?
Great work 👍
Thanks ✌️
Would a PET or Polyethylene baloon work for that instead of fibreglass.
Similar to those reinforced bottle rockets you used to make years ago, but this time carbon fibre reinforced?
For the inside of the pressure chamber? Yes you could do it, but you would get a weight penalty. The strength to weight ratio of fiberglass compared to PET is higher.
@@AirCommandRockets I may be wrong, but the young modulus of fibreglass is like 6 times lower than that of carbon fibre. So in this case the fibreglass is acting purely as a sealant/barrier, right?
Cause by the time the fibreglass stretches enough to get to its tensile strength - the carbon fibre will be already torn.
So the carbon fibre is taking all the pressure load.
So I thought - if you would take a relatively small PET bottle, heat it up, put it inside a matching diameter steel tube, inflate it like a baloon you would end up having a perfect mandrel to put the carbon fibre "sock". I'm very new to the rocketry, my background is the prototyping engineer and sorry if I'm wrong and you have already tried or thought of that idea.
@@makerbeelab5546 I see what you mean. Yes the carbon fiber provides the vast majority of the pressure containment. But if the glass stretches more than the carbon fiber then that should be good because it won't fail before the carbon fiber does. The problem with making the inside out of PET, how do we get it to be 2m long? This test pressure chamber is only a short version of the final booster segment.
@@AirCommandRockets Maybe to try a PET tubing, heat it up and inflate inside a steel or aluminium tube of large diameter?
Something like that
www. automaticfiresuppressionsystem .com/ product/ product-85-212 .html
👏👏👏👏
Interesting. Is the most common failure mode ripping or delaminating?
And would this delamination instead of straight ripping provide a bit of extra safety in terms of pre-warning sounds, if the vessel was filled with air? Or would the leaking air rapidly rip apart the delaminated layers anyway? After all it’s much less viscous.
We don't have a whole lot of experience with failure modes for carbon fiber pressure vessels. We really haven't had these delamination issues previously. (If it indeed was delamination). We will cut it open and have a look. If I ever heard that fiber breaking noise of a pressure vessel I would sure run as quickly as I can. The hydro-static tests don't show the whole picture either because the pressure chamber will heat up when we partially fill it with compressed air. We can't do those tests at home, if we want to stay friendly with the neighbours.
Second comment!
Perhaps you could use a hydraulic pressure increaser?. Instead of having to make the whole rocket high pressure?. Youd have to have a bigger tank but your mean pressure would increase at nozzle only. Hence youd only have to strengthen second chamber. www.hydraulicspneumatics.com/technologies/other-technologies/article/21884328/book-2-chapter-13-pressure-intensifier-circuits
I don't think that would work in this application, because you wouldn't be able to get the flow rate needed. We are pushing out about 3L of water in about 0.2 seconds. There would also be the added weight of the mechanism which would reduce the overall altitude. But an interesting suggestion.
@@AirCommandRockets only one way to find out 😉
Why not just make sch. 40 pressure chamber? You should be able to get at least 1200 psi with 2 inch, way cheaper and easier.
Do you mean PVC pipe sch 40? In order to compare apples to apples this pressure chamber is 3.14" and from what I can see the operating pressure is 158psi and burst pressure of 840psi. sch 80 is 225psi and 1200psi respectively. So both of these are still too low. Our operating pressure is 1000-1100psi with burst pressure above 1600psi. That aside, PVC fractures into dangerous splinters when it lets go, isn't as stiff as the composite so tends to bend during high accelerations, and is heavier.
@@AirCommandRockets Yeah, those are the listed pressures, I'm sure it's much higher in reality with the glue joints being the failure point. I was just more curious if you had considered it when I made the comment and want to emphasis that I think this is a really cool project and you have gotten some great results. Also I was really impressed with the trigger mechanism.