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Unread postAuthor: Jolly Roger » Sun Jun 26, 2011 11:42 pm

MrCrowley wrote:Oh yeah wow, I didn't notice how much the chamber pressure increased with the extra 9 ignition points. Jumps up to around 20,000PSI, for an increase of about 10ms.

Is there a problem with sticking a longer barrel on it? Hybrids aren't very portable to begin with, especially one like this.


No I think that's what I'll do, put a longer barrel on it. This is really just a concept design so I shouldn't be too concerned with those sorta things anyway.

[quote="ramses"]All right, I got 799 m/s. But for a real design IT WILL NEVER WORK. suffice to say that the aspect ratio of the chamber is... well... *em*

HGDT reports the maximum chamber pressure as 221ksi, but the graph only shows a peak at around 16ksi. It is also extremely inconsistent in that the velocity varies 200m/s between runs with identical parameters./quote]

I've noticed that as well. After running the sim I change an input, run the sim, then change it back and run it again, different results... But for now I think it is still the best way to optimise the gun.

Once I get Solidworks down pat I'll upload the design for you all to have a look over
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Unread postAuthor: MrCrowley » Mon Jun 27, 2011 12:37 am

After running the sim I change an input, run the sim, then change it back and run it again, different results...

I thought I was going crazy. Noticed that in the past as well, never mentioned it though.
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Unread postAuthor: Jolly Roger » Mon Jun 27, 2011 2:16 am

David did say when things quieten down again for him that he'll be combining GGDT and HGDT together, and will hopefully solve some of these errors. Someday
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Unread postAuthor: Ragnarok » Mon Jun 27, 2011 12:24 pm

I can't get more than about 615 m/s within those limits and a practically achievable real world design - and that's using some of the dirtiest cheats I can think of.

ramses wrote:HGDT reports the maximum chamber pressure as 221ksi, but the graph only shows a peak at around 16ksi.

Bear in mind that the graph does not show all data points, just every 25th one (I think). It's perfectly possible to have a peak between those that doesn't show on the graph.
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Unread postAuthor: ramses » Mon Jun 27, 2011 6:04 pm

Ragnarok wrote:I can't get more than about 615 m/s within those limits and a practically achievable real world design - and that's using some of the dirtiest cheats I can think of.

ramses wrote:HGDT reports the maximum chamber pressure as 221ksi, but the graph only shows a peak at around 16ksi.

Bear in mind that the graph does not show all data points, just every 25th one (I think). It's perfectly possible to have a peak between those that doesn't show on the graph.


I realized that shortly after I typed most of the post, but I still wanted to get the meme in there. Also, I misspoke (mistyped) when I said the chamber pressure exceeded 221ksi. That was actually the peak barrel pressure. A 0.25cm chamber opening into a 2.1cm barrel would not produce such peak pressures.
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Unread postAuthor: Jolly Roger » Wed Jun 29, 2011 1:25 am

ramses wrote:
Ragnarok wrote:I can't get more than about 615 m/s within those limits and a practically achievable real world design - and that's using some of the dirtiest cheats I can think of.

ramses wrote:HGDT reports the maximum chamber pressure as 221ksi, but the graph only shows a peak at around 16ksi.

Bear in mind that the graph does not show all data points, just every 25th one (I think). It's perfectly possible to have a peak between those that doesn't show on the graph.


I realized that shortly after I typed most of the post, but I still wanted to get the meme in there. Also, I misspoke (mistyped) when I said the chamber pressure exceeded 221ksi. That was actually the peak barrel pressure. A 0.25cm chamber opening into a 2.1cm barrel would not produce such peak pressures.


Technically it may be able to but if the chamber diameter is smaller than the barrel, I dont see how the barrel pressure would be higher than the chamber.
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Unread postAuthor: ramses » Wed Jun 29, 2011 7:19 pm

Jolly Roger wrote:
ramses wrote:...
I realized that shortly after I typed most of the post, but I still wanted to get the meme in there. Also, I misspoke (mistyped) when I said the chamber pressure exceeded 221ksi. That was actually the peak barrel pressure. A 0.25cm chamber opening into a 2.1cm barrel would not produce such peak pressures.


Technically it may be able to but if the chamber diameter is smaller than the barrel, I dont see how the barrel pressure would be higher than the chamber.


I know :D
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