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| sprayandplay08 |
 Posted: 06/11/2008 11:17 AM Post subject: End Of Week Plans |
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Corporal
Joined: 09 Jun 2008
Posts: 63
2.11 Spud Bux
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This weekend i plan on building a over-under cannon using spray as a propellant.
I will be using 24" of 3" pipe with 60" of 1.5" pipe for a barrel and a
BBQ ignitor
What I would like from the community is suggestions or mods i can do to make it better? or any other advice u can give 
i don't even know if it will work |
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| MaxuS the 2nd |
| Posted: 06/11/2008 11:24 AM Post subject: |
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Colonel
Joined: 19 Jan 2008
Posts: 676
859.77 Spud Bux
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| Use fully pressure rated components, I.E, no bell reducers. |
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| sprayandplay08 |
| Posted: 06/11/2008 11:25 AM Post subject: |
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Corporal
Joined: 09 Jun 2008
Posts: 63
2.11 Spud Bux
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| whats the difference?What should i use? |
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| Maniac |
| Posted: 06/11/2008 11:29 AM Post subject: |
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Lieutenant Colonel
Joined: 23 Oct 2007
Posts: 497
588.84 Spud Bux
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| Ahh sprayandplay just check the link in my signature. But DWV fittings(not pressure rated) ie: bellreducers are generally accepted when building combustions, dont worry yourself. |
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| starman |
| Posted: 06/11/2008 11:35 AM Post subject: |
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Big Daddio
Joined: 11 Dec 2007
Posts: 2148
4768.59 Spud Bux
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| Did you get your other one working yet? |
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| sprayandplay08 |
| Posted: 06/11/2008 11:36 AM Post subject: |
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Corporal
Joined: 09 Jun 2008
Posts: 63
2.11 Spud Bux
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OK i will use pressure rated fittings
i'll be on tomorrow i have to leave for work
"Working at Krogers Sucks" |
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| Canuck |
| Posted: 06/11/2008 13:05 PM Post subject: |
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Private First Class
Joined: 28 May 2008
Posts: 30
81.03 Spud Bux
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| Sounds like the one I just built only my cannon has a 16.5" long chamber and is "inline". |
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| MrCrowley |
| Posted: 06/11/2008 13:12 PM Post subject: |
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Blizzard of Ozz
Joined: 23 Jun 2006
Posts: 6368
3773.55 Spud Bux
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| Boom_erang |
| Posted: 06/11/2008 15:49 PM Post subject: |
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Specialist
Joined: 25 Apr 2008
Posts: 41
160.36 Spud Bux
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Looks to me like it would work OK, although you have more chamber than you really need. Your ratio with that chamber is 1.6:1, and thus you might get quite a bang out of it from the muzzle flash. Also, really long chambers aren't as efficient as shorter, fatter ones, IMO.
I'd suggest going with either something like a 12" to 14" x 3" chamber, personally. It will lighten the gun and give you plenty of power - it may even improve the performance a bit, although there are those that would argue with me about this!
For fuel, hairspray sucks, try Static Guard if you haven't already. No sticky gunk, and doesn't stink nearly as much.
-B |
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| SpudFarm |
| Posted: 06/11/2008 15:56 PM Post subject: |
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Hybrid Guy
Joined: 04 Nov 2006
Posts: 2111
1224.57 Spud Bux
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NEVER EVER CUT OF THE CHAMBER TO GET RIGHT RATIO!
make the barrel longer and you get performance in truck loads  |
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| Boom_erang |
| Posted: 06/11/2008 16:25 PM Post subject: |
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Specialist
Joined: 25 Apr 2008
Posts: 41
160.36 Spud Bux
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So he's supposed to have a 95" barrel? I'm not sure how practical that is.
But I'm not convinced at all that reducing the chamber would not improve performance. Based on burntlake's tests, it seems that there is a ratio yielding max performance that stays fairly constant despite different gun sizes. Too long of a barrel for a given chamber reduces performance, and too short of a barrel reduces performance.
I know what you mean that for the max performance of a given chamber, you want the right length barrel. But the flip side of that is for a given barrel, you might get nearly the same performance from a smaller chamber if the ratio is better, and you'll save weight and fuel, because the gun is more efficient.
-B |
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| rcman50166 |
| Posted: 06/11/2008 17:11 PM Post subject: |
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Major
Joined: 19 Jan 2008
Posts: 381
1022.10 Spud Bux
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| This is true. My "Sarge" doesn't have a cut chamber and as a result it has an awkward look. The flame propagation isn't exactly amazing either. But if I had the chance to built another spray and pray, it would have a 6 in diameter chamber that is 18 in long. The barrel would be a 2.5 in dia. bore with a 36 in length. But I'm just dreaming, you build what you want. Just make sure you have a removable barrel so you can change the bore diameter. I forgot to do that on both my spray and prays. |
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| Maniac |
| Posted: 06/11/2008 21:33 PM Post subject: |
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Lieutenant Colonel
Joined: 23 Oct 2007
Posts: 497
588.84 Spud Bux
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| Hey Mr.C If you havent noticed I have put your identifying pressure rated pvc topic in my sig and I refrenced to it in my first post. |
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| starman |
| Posted: 06/11/2008 22:21 PM Post subject: |
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Big Daddio
Joined: 11 Dec 2007
Posts: 2148
4768.59 Spud Bux
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All other things being equal, you will gain some power by going to a larger chamber and thus fuel mix, etc. However, unless you also lengthen the barrel or utilize a burst disk, much of that extra power will be going to waste and rushing out the end of the muzzle long after the projectile has cleared the barrel...and will represent itself as noise...more BOOM... 
Do some HGDT calculations and just change the chamber size...you'll see the effect it has on it. You'll also see that unless you use a burst disk, you're not going to get a significant performance increase, maybe 10-15% is all if you go from a 3" chamber to a 4" chamber of the same length! ...barrel staying the same of course. |
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