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| drex |
 Posted: 05/07/2008 18:14 PM Post subject: DDT, has it ever happend in a hybird? |
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Sergeant
Joined: 21 Apr 2008
Posts: 86
118.16 Spud Bux
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i hear all about DDT, but i have yet to find an instance where it has actually accrued in a cannon. has it ever happend?
[Clarification]
im not doubting that it is very real and dangerious.
[/Clarification] |
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| DYI |
| Posted: 05/07/2008 18:29 PM Post subject: |
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Major General
Joined: 07 Jul 2007
Posts: 2025
6846.48 Spud Bux
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I don't believe it has happened accidentally, but noname (who isn't active here anymore, but used to be a highly valued member) caused it by design in a 1/2" x 5' chamber at 6x. The chamber was 1/2" SCH 40 steel, and there was a noticeable bulge and cracks at the area where the DDT had ocurred.
I want to do DDT testing at some point, but right now I'm just working on avoiding it, and I'm in pretty deep in several other projects. |
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| drex |
| Posted: 05/07/2008 18:32 PM Post subject: |
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Sergeant
Joined: 21 Apr 2008
Posts: 86
118.16 Spud Bux
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| thanks, you would'nt happen to have a photo of his test would you? |
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| Sticky_Tape |
| Posted: 05/07/2008 18:35 PM Post subject: |
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Colonel
Joined: 31 Jan 2008
Posts: 549
651.98 Spud Bux
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| I would like to see this bulge too.(No dirty jokes) |
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| clide |
| Posted: 05/07/2008 18:51 PM Post subject: |
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Donating Member
Joined: 06 Mar 2005
Posts: 649
1872.80 Spud Bux
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There is no way to confirm it, but many have suspected that this failure may have been DDT
http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=13&t=6095
Failure at a fairly low mixture and still the most powerful shot that the gun had.
Of course he could have just had a hairline crack in the chamber and not been getting the mixture right for previous shots. |
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| DYI |
| Posted: 05/07/2008 19:01 PM Post subject: |
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Major General
Joined: 07 Jul 2007
Posts: 2025
6846.48 Spud Bux
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On any large diameter, low length PVC hybrid chamber, I'm inclined to suspect fatiguing and microfractures from repeated shock loads over DDT. PVC has very low impact resistance, and even the ABS barrel on my prototype hybrid failed at only 4x (oxy/propane though). If it can rip 12" of highly shock resistant ABS pipe almost clean in half, it shouldn't have any problem with SCH 80 PVC, especially if given a few goes at it.
You're going to have to ask noname about the pictures though, if you can get a hold of him somehow. |
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| drex |
| Posted: 05/07/2008 20:29 PM Post subject: |
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Sergeant
Joined: 21 Apr 2008
Posts: 86
118.16 Spud Bux
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| over the summer i might try and see if i cant make DDT happen. do you think that DDT wold happen in a 10 foot .25 inch thick copper chamber at 8X with one spark gap at the end of the chamber? |
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| bigbob12345 |
| Posted: 05/07/2008 20:32 PM Post subject: |
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Experienced n00b
Joined: 01 Dec 2007
Posts: 1514
362.74 Spud Bux
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Yes it will most definately happen
but DDT is no joke, stand well back
and if you want to make absolutely sure there will be a DDT then use
oxy propane instead of air propane. |
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| psycix |
| Posted: 05/08/2008 7:53 AM Post subject: |
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Major General
Joined: 25 Jun 2007
Posts: 1347
190.10 Spud Bux
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| bigbob12345 wrote: | Yes it will most definately happen
but DDT is no joke, stand well back
and if you want to make absolutely sure there will be a DDT then use
oxy propane instead of air propane. |
Or even hydrogen/oxy 
It is indeed no joke to do this. This is not a cannon chamber, but its more like a pipe bomb. Get yourself a nuclear-proof bunker if you want to survive this. |
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| paaiyan |
| Posted: 05/08/2008 8:02 AM Post subject: |
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Major General
Joined: 27 Dec 2006
Posts: 1996
155.37 Spud Bux
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| Well, technically I'm not sure if DDT can happen with oxy/hydrogen actually. It's not actually burning, it's a combination reaction. |
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| SpudFarm |
| Posted: 05/08/2008 8:34 AM Post subject: |
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Hybrid Guy
Joined: 04 Nov 2006
Posts: 1464
174.52 Spud Bux
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well paaiyan pulse detonation engines uses hydrogen/oxy..
mabe the spudtech hybrid was weakened by the extreme recoil stresses to the chamber? if i am going to build a large scale PVC hybrid i will make a stand that allows it to be hold up by the barrel |
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| paaiyan |
| Posted: 05/08/2008 8:37 AM Post subject: |
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Major General
Joined: 27 Dec 2006
Posts: 1996
155.37 Spud Bux
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After reading over some material on the subject, I concede my previous point. I had never heard of this type of engine.
Carry on. |
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| _Fnord |
| Posted: 05/08/2008 8:45 AM Post subject: |
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reenigne
Joined: 13 Feb 2007
Posts: 1168
1612.75 Spud Bux
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| Quote: | | It is indeed no joke to do this. This is not a cannon chamber, but its more like a pipe bomb. Get yourself a nuclear-proof bunker if you want to survive this. |
Gun powder has thousands of times the energy density of typical propane mixes. I wouldn't want to be standing by it when it happens, but it's not likely to be as spectacular and destructive as everyone has made it out to be.
I mean, when ddt happens in a car engine, it will weaken it and eventually ruin the engine unless you fix the problem, but it's not like your engine block explodes. |
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| paaiyan |
| Posted: 05/08/2008 8:47 AM Post subject: |
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Major General
Joined: 27 Dec 2006
Posts: 1996
155.37 Spud Bux
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| _Fnord wrote: | | Quote: | | It is indeed no joke to do this. This is not a cannon chamber, but its more like a pipe bomb. Get yourself a nuclear-proof bunker if you want to survive this. |
Gun powder has thousands of times the energy density of typical propane mixes. I wouldn't want to be standing by it when it happens, but it's not likely to be as spectacular and destructive as everyone has made it out to be.
I mean, when ddt happens in a car engine, it will weaken it and eventually ruin the engine unless you fix the problem, but it's not like your engine block explodes. |
And just for the record, how thick is an engine block? |
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| _Fnord |
| Posted: 05/08/2008 8:56 AM Post subject: |
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reenigne
Joined: 13 Feb 2007
Posts: 1168
1612.75 Spud Bux
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Depends on the engine block. Yes, it should be stronger than a typical hybrid chamber, but it has to stand up to thousands of explosions every minute at high temperatures.
The pressure spike in a ddt is so short that it just causes fatigue, bulges or cracks, not total annihilation. Noname's results may have demonstrated this.
(Edit: that is, IF you are using a chamber that is not brittle. Otherwise you can expect fragmentation.)
I really need to do some testing this summer...
Last edited by _Fnord on 05/08/2008 9:01 AM; edited 1 time in total |
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