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Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: Rob748 » Wed Mar 18, 2009 6:30 pm

Thanks guys for all the Information, it is very helpful to read this and get a even better understandment of these wonderful guns.
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Unread postAuthor: Rob748 » Wed Mar 18, 2009 6:35 pm

Well I know something a multiple burst disk setup could work for, Ok lets say you have a union with a 50 psi burst disk on it, 3-4in after that another union with the same or less or more rated burst disk, In the space between the two you could load your projectile !, and it would never fall out of the barrel ! Its kind of like breech loading.
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Unread postAuthor: psycix » Thu Mar 19, 2009 11:58 am

That would make your reloading time very long.
I dont think its worth it.

Also, I dont think its worth it to post two times in 5 minutes.
Please edit your last post if you have anything else to say instead of double posting.
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Unread postAuthor: starman » Thu Mar 19, 2009 1:10 pm

SpudBlaster15 wrote:[Oh, and see these tests, which showed that a burst disk reduces the performance of an optimized (.8:1) launcher.


I'm familiar with those tests although it's been a few years since I have reviewed them. One thought I have is that the projectiles, because they are shot straight up are also fighting the effects of gravity on their way out of the barrel. How that may or may not effect results, with or without a burst disk is unclear to me. Also, spud ammo is a very poor actor for a test like this. However, some trends do seem to appear.

You are really seeing a repeat of Latke's efficiency tests here, not an indictment of burst disk usage. It's perfectly fine to trade long barreled efficiency for shorter barreled practicality and a burst disk helps better capture the energy available in the chamber for real world barrel lengths...making c:b ratios almost irrelevant. Therefore, keeping your barrel sizes constant and adjusting the size of your chamber based on the energy needed is possible. Again, HGDT properly predicts all of this.

Also, regarding burst disk breakage point. I have found that there isn't much to be gained by having the highest possible break pressure for projectiles...about 1/2 of the theoretical peak seems about right for golf balls...projectile size and mass also play into these calculations.

However, the higher break pressure the better for noise generation.... :wink:
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Unread postAuthor: jimmy101 » Thu Mar 19, 2009 1:58 pm

SpudBlaster15 wrote:[Oh, and see these tests, which showed that a burst disk reduces the performance of an optimized (.8:1) launcher.

I don't think you can trust that data. It was a great attempt at a study but since he used hang time as the measure of performance the results are somewhat suspect. Indeed, looking at the numbers there is no statistically significant difference between the no disk versus 1, 2, or 3 disks for the 0.8 CB gun. So, to say the burst disks hurt performance is untrue. The burst disk had no affect on the hang time. The burst disks did reduce the variability of the hang time.

It can be said that the bursk disks didn't appear to significantly improve hang time. For which you might conclude the disks didn't significantly improve the muzzle velocity.
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Unread postAuthor: psycix » Thu Mar 19, 2009 3:04 pm

Spuds are too variable to make a valid test.
For a real test, a chronometer is necessary, along with a constant type of ammo, like golfballs, all of the same brand.
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Unread postAuthor: jimmy101 » Fri Mar 20, 2009 11:44 am

psycix wrote:Spuds are too variable to make a valid test.
For a real test, a chronometer is necessary, along with a constant type of ammo, like golfballs, all of the same brand.

Spud can be used for a valid test. Just need a chrono and the mass of each spud. The mass of the spuds is easy to get, weigh, load, weigh the shavings, subtract. Only variable left is the spud to spud difference in static and dynamic friction. That could be measured as well, though the accuracy may be a bit suspect. Overall, not all that difficult to do but you do have to make the effort to do the study correctly.
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Unread postAuthor: psycix » Fri Mar 20, 2009 1:00 pm

But that would require to calculate stuff and make adjustments on the recorded data, which is just unnecessary and will never make it more accurate.
Just keep the factors which can be constant as constant as possible and focus on the experiment itself.
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Unread postAuthor: jimmy101 » Fri Mar 20, 2009 1:17 pm

Yes, it will make it more accurate. It will be as accurate as the rest of the variables are. Firing the same shell repeatedly is only accurate to about +/-5% (take a look at latke's data for example). So, you just have to get your masses etc. accurate to that level.

The advantage is that you are measuring the results with the ammo that you are actually interested in. Just because performance for something like a gasketed wood slug is such and such, doesn't meant that is the performance with some other ammo. The only way to measure the performance of a gun meant to fire spuds is to actually measure it's performance with spuds.

If you can't be bothered with weighing your ammo and then converting muzzle velocites into KE's then you really aren't up to any type of quantitative study. Just stick with "I think it worked better".
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