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| noname |
 Posted: 06/11/2007 20:19 PM Post subject: |
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Mr Vortex
Joined: 10 Apr 2006
Posts: 2520
2730.79 Spud Bux
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"what length would my barrel be to get .3 to 1? "
Really frickin' long!!!
Good job on it, wish I could find fire extinguishers to use for stuff.... |
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| spudthug |
| Posted: 06/11/2007 20:25 PM Post subject: |
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Gangster Kitten
Joined: 26 Feb 2007
Posts: 974
609.33 Spud Bux
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| Quote: | | Really frickin' long!!! |
hehe...how long exactly?
thanks! there is like 3 comments on here and the rest are questions and suggestions and what not.. dont get me wrong i always want to improve but i like comments also!!
i have like 5 fire extinguishers laying around.. another huge one and a few little ones...my freind works for the highway and finds fire extinguishers in garbage places and washes em up for me.. |
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| Velocity |
| Posted: 06/11/2007 20:51 PM Post subject: |
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Brigadier General
Joined: 07 Feb 2006
Posts: 1009
80.14 Spud Bux
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mmm... you would need a 3103" barrel for a 0.3:1 chamber to barrel ratio... so yeah, its doable  |
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| VH_man |
| Posted: 06/11/2007 21:03 PM Post subject: |
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Swimmaman
Joined: 09 Dec 2006
Posts: 1497
82.56 Spud Bux
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just get a coupler and make a REALLY long barrel for the thing...........
make sure to bevel the rear ends of the barrels so that your projectile doesnt get caught on the ridges.....
catostrpohic hybrid failure is NOT an option |
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| origin unknown |
| Posted: 06/11/2007 21:48 PM Post subject: |
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Colonel
Joined: 14 Apr 2007
Posts: 532
894.45 Spud Bux
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He he, I like the foot in one of the pictures. Read up on Jack Armstrong A.K.A "Spudkiller"; he has some good info on C/B rations and barrel lengths.
BTW Cool lookin hybrid!
| noname wrote: | | Good job on it, wish I could find fire extinguishers to use for stuff.... |
I saw some small fire extinguishers at Lowes for about $15 and some larger ones for about $20. |
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| spudthug |
| Posted: 06/12/2007 7:34 AM Post subject: |
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Gangster Kitten
Joined: 26 Feb 2007
Posts: 974
609.33 Spud Bux
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yea i dont think im going to get a barrel over 200 feet long any time soon 
i will buy a 10' section of 1 inch and use that for a barrel...i cant go much longer than that.
thanks for the complements guys!
EDIT.
tell me if i did this right but evbec live 1. 5 or whatever said i would geet super sonic at 3x (it said 1195fps) and more at 4x
here is 4x
Chamber length 19 in
Chamber diameter 7 in
Barrel length 72 in
Barrel diameter 1 in
Projectile mass .36 oz (10 grams)
Atmospheric pressure 14.7 PSIA
Chamber pressure 45 PSIG
Fuel-propane
Chamber fan-None
Chamber volume 731.21 in3
Barrel volume 56.55 in3
C:B ratio 12.931:1
Muzzle velocity 1332.4 fps
Muzzle energy 1141.6 ft-lbs
but the wierd thing is....it says i get 200 more fps with a chamber fan...is that correct? why would that matter... |
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| boilingleadbath |
| Posted: 06/12/2007 13:07 PM Post subject: |
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Moderator
Joined: 12 Mar 2005
Posts: 1647
5491.22 Spud Bux
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Burnt latke did a test with and without a chamber fan, and found that it improved performance in their launcher. I assumed that such results are typical of spudguns, and thus programmed EVBEC to subtract a certain percentage of velocity from your spudgun if you don't have a chamber fan.
Now, this is a pretty poor way to predict it, but I don't have any other numbers to go by. There's a reason the tool-tip describes the feature with the wording it does.
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Note that chamber fans improve performance by doing 3 things:
1) Venting the chamber, ensuring better combustion
2) Mixing the fuel-air mixture
3) Turbulating the flame-front, and thus speeding combustion
#1 is really only a problem with lazy people, and #2 is probably covered pretty well by the injection of air into a hybrid's chamber.
This leaves #3 as a source of improved performance - certainly only part of the reason they help velocity.
Now, what this means as far as you are concerned, I don't know... however, my expectation is that the turbulence increases performance mostly because it makes the combustion occur faster... an effect that a burstdisk mimics: they allow more of the fuel to burn before the projectile starts to move.
In short, in hybrids, I'd believe the "with chamber fan" values more than the "without chamber fan" numbers.
But that's just a guess. |
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| SpudBlaster15 |
| Posted: 06/12/2007 23:31 PM Post subject: |
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Human blast shield
Joined: 18 Oct 2006
Posts: 1554
52.84 Spud Bux
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Looks great! My only suggestion would have been to place the spark plugs near the center of the chamber, as this would allow the fuel to burn faster.
I noticed that your meter pipe and air inlet both utilize the same pipe. If you use a spreadsheet or other program to calculate the required fuel meter pressure, remember to add the volume of the meter pipe to the volume of the chamber when inputing the chamber volume, because when you have the 2nd ball valve open to allow air to pressurize the chamber, fuel mixture will occupy that space as well as the main chamber.
Also, after you vent the chamber after a shot to achieve one atmosphere (14.7PSIA) of atmospheric air, remember that you will also have 1 atmosphere of air in the fuel meter, and you will have to add 14.7PSI to whatever number the spreadsheet/program gives you when adding propane to compensate. (Regular combustion guns have one atmosphere of propane in the meter at all times, and thus this compensation is unnecessary for them.) |
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