Chamber Pressure for Static Test

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harishrajan96

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Hello,
I want to find the chamber pressure for a model pvc based rocket in static firing.
Can anyone please give me any ideas on how to measure the chamber pressure :wink:
 

Incongruent

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Hello,
I want to find the chamber pressure for a model pvc based rocket in static firing.
Can anyone please give me any ideas on how to measure the chamber pressure :wink:
The chamber pressure will be 1 atmosphere if the PVC blows and sends sharp shrapnel everywhere. Do you have access to paper tubes? They're much safer in case something goes wrong, and since (I'm assuming) you're making your own rocket motors, the chances of that are much higher,

You should be able to calculate the chamber pressure if you have measurements of the thrust and nozzle diameter, but I'll let one of the Experimental Rocketry people chime in on that. Alternatively, there are programs for making motors (such as BurnSim) that probably calculate the chamber pressure (theoretically).
 

harishrajan96

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Yes theoretical calculations are done, as this is a project for my university it would be nice to include actual chamber pressures too.
 

Incongruent

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ttabbal

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If you want actual pressure, you need to install a pressure transducer in the motor and measure it. If it's a BATES grain or otherwise has a path the length of the motor case, you can drill/tap the forward closure and install one there. The only issue I see is that I'm not convinced the threads will hold in PVC.

The next best would be to measure thrust and calculate pressure using the nozzle data.

Please take precautions for the possibility of the motor failing. PVC doesn't show on xray images, making it more difficult for the doctors trying to remove it. That is the primary reason that the organizations for Rocketry ban PVC motors at events. It needs to be fully enclosed in some sort of bunker and monitored electronically. If you can see it, it can bite you.
 

ksaves2

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I don't know of any methods to measure chamber pressure directly, however, as thrust is defined by an equation, you should be able to find the chamber pressure if you know the other variables.
https://www.grc.nasa.gov/WWW/k-12/airplane/rockth.html
Um, there are means with a test motor that has a pressure tap on the forward closure but I believe discussion would have to be moved to the Research forum to be certain the moderators won't intervene. If the OP is from India, would be hard to do.
A simple search leads to this on Amazon: https://www.amazon.com/dp/160402352X/?tag=skimlinks_replacement-20 Am with incongruent on this. If using too aggressive a propellant, PVC leaves nasty radiolucent shards to pull out of a wound. Kurt
 
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rocket_troy

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If you want actual pressure, you need to install a pressure transducer in the motor and measure it. If it's a BATES grain or otherwise has a path the length of the motor case, you can drill/tap the forward closure and install one there. The only issue I see is that I'm not convinced the threads will hold in PVC.

The next best would be to measure thrust and calculate pressure using the nozzle data.

Please take precautions for the possibility of the motor failing. PVC doesn't show on xray images, making it more difficult for the doctors trying to remove it. That is the primary reason that the organizations for Rocketry ban PVC motors at events. It needs to be fully enclosed in some sort of bunker and monitored electronically. If you can see it, it can bite you.
I second these points. Use a pressure transducer tapped into the forward closure if you also want to measure thrust as well. You'll need to take some measures to thermally protect the transducer which can be achieved utilising various methods - longer entry small diameter tube (non filled) or shorter entry tube filled with grease. Shouldn't be a problem holding the thread so long as it's a small diameter thread (say 1/4 or 1/8 pipe thread) and you have at least say 5 threads of engagement.
If you weren't measuring thrust, you can utilise a characteristic nozzle ie. no entry taper or exit cone - just a straight hole throat of minimum length. You'll probably need graphite for that to maintain some level of throat area consistency, but this allows you to directly measure pressure from a load cell Chamber Pressure = Thrust/Throat Area.

Troy
 
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