Are you trying to stop the venturi effect by choking the air flow? I don't understand. Did you mean what Tim said about running out of air with water left over?
No, I might just want to try to get more water into the pipe, by introducing a slight drop in the pressure of the air there. Then, more water should rush in. But I will try better water flow first, and only if that fails, I will try worse air flow.
OK since I got several designe revealed in detail, I'll do the same.
I am evaluating this one. Looks OK so far. It is simple....
There is a reason for the long exhaust pipe, but let me see first if it works....
Regards
Soren
I tried something a little like this except I use a bottle on top of the booster to hold extra air and the tube runs down the moddle of the booster like yours but gets the pressure from the top bottle.
RaZias wrote:This is an idea for testing my design without needing to build all the rocket.
First it´s necessary to open the tap to release the water.
After the water is flowing freely then it´s injected the air.
See the draw.
Scan10686.JPG
The problem I see with testing this way is that you will not have such a delay on a real rocket. As soon as the launch is triggered all pressures will start to decrease together. It is a good test to determine if foam can be generated by the injection of air into the water stream. You may find that you need something to "help" create bubbles such as putting a fine screen (like steel wool) in the small air injection tubes (a side benefit would be to interfere with the flow of water backwards into the air reservoirs).
Ideally I would like to complete my rig like Antigravity Research made to test their nozzles. They used a balance arm that was counter weighted so the rocket thrust would move it off balance and this moved a needle along a scale and they could read off the amount of thrust by looking at the needle.
My version mounts a potentiometer on the balance arm and uses a data acquisition system to read the pot and plots a thrust curve. I don't have much cash so I'm trying to get a cheap used ADC board from ebay. I keep getting outbid. For now I am using a needle and a scale like they did.
I have made some experiments with the mixer tube I presented here; it actually improved performance for me! Substantially, too. Details later.
What I am looking for now is an idea for a carburettor rocket where the water tank is in the nose section - and not too complicated to build. That would fly more stably, particularly if there is another stage on top of it.
I have made some experiments with the mixer tube I presented here; it actually improved performance for me! Substantially, too. Details later.
What I am looking for now is an idea for a carburettor rocket where the water tank is in the nose section - and not too complicated to build. That would fly more stably, particularly if there is another stage on top of it.
Any ideas?
Regards
Sorenb
What about concentric cylinders? That is my idea for something similar. a pipe within a pipe is how I would do it. It's not exactly the same as your idea. My design would have an inner pipe 1/3 the volume of the outer pipe and would then contain all the water you launch with. The outer tube around the water is filled with air pressure. and holes at the top let the air in to push the water out the bottom which is closed on the outer chamber and open to the nozzle at the inner chamber.
The main idea I had was to make the rocket stable by evenly distributing the weight of the water mass along the whole length.
Maybe it is not necessary to inject air in the nozzle.
Maybe the pressure of the water is enough if we put an obstacle just before the nozzle
The idea is to make bubbles of vacuum instead of air, so we don't loose any pressure...
Yeah I think I can understand what you want to do... but why? I think cavitation is usually avoided where possible.
I believe the water + air mix - and and soap foam trick - work by combining the high mass of water with the high viscosity of air (compromise with advantage).
The mix is also compressible - I think that when I run it through a short length of pipe at the nozzle, it will go in with high pressure and low velocity, and come out with a lower pressure but higher velocity. That's becuase the air bubbles in the water push the water towards the lower pressure (nozzle) as they expand. Vacuum would not do that.
But I don't really have any calculations or data to substantiate this - it's just what I think. I do have some data from 3 test flights with a small rocket with and without an air/water mixer tube. That rocket did make some longer flights with the tube (I can post the figures when I get home), similar to what people have observed when adding foam.
Well, just like you I have no calculations, I'm a complete new hobbyist but...
What I'm trying to do is not exactly bubbles of vacuum... what I expect is that just in the moment that bubbles of vacuum should appear, what really happened is that the low pressure made the water to evaporate (pressure falls below the evaporation point of water).
Jetman wrote:Well, just like you I have no calculations, I'm a complete new hobbyist but...
What I'm trying to do is not exactly bubbles of vacuum... what I expect is that just in the moment that bubbles of vacuum should appear, what really happened is that the low pressure made the water to evaporate (pressure falls below the evaporation point of water).
Anyway, when I have the time I'll try it ;)
If you lower the pressure enough to evaporate water will it boil like it were heated on a stove?
No, It won't, it would create some kind of cold vapor that I think that condense and turn into water once the pressure is over the evaporation point... I suppose that the key for it to work is to achieve that condensation doesn't occur until the gas or water-gas mixture has has been expelled.
On the other hand I don't know if It would be possible to achieve the point of evaporation inside the nozzle due to the hi pressure inside the bottle.
Jetman wrote:No, It won't, it would create some kind of cold vapor that I think that condense and turn into water once the pressure is over the evaporation point... I suppose that the key for it to work is to achieve that condensation doesn't occur until the gas or water-gas mixture has has been expelled.
On the other hand I don't know if It would be possible to achieve the point of evaporation inside the nozzle due to the hi pressure inside the bottle.
It's only an idea (by now ;) )
I would be curious to know if you get any interesting results from this experiment. I think there's a breakthrough in nozzle design just waiting to be discovered. Trying new stuff is the only way we're going to find it.
Just found some old performance test results from an experiment with the "carburetor" / mixer tube rocket, flown last autumn.
2 rockets were used; both where 2 * 1.5 l Coca-Cola, spliced bottom to top. One had a mixer tube of ID 17 mm, with 16 6 mm holes near the lower bottle throat where the tube was glued in. The other had a tube of the same kind, but with no holes.
Pressure was 6 bar. There was no recovery system; times are just from launch to crash down. I measured the water fill to be exactly the same for both rockets in all flights - but I forgot how much it was.
dongfang wrote:
This seems to confirm that the mixer tube worked! The mixer tube rocket was also seen to burn longer and go higher.
I don't suppose you also measured the flight time without the extra weight of the carburettor tube? 15 % extra flight time is good, but is that cancelled out by the additional weight?
