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TBMA-230 Oxy/Propylene Piston Hybrid

Built a hybrid cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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What do you think?

AWESOME!
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51%
Mildly interesting
2
6%
I'm scared
4
11%
I'm a pneub, go away hybrid supremacist
4
11%
Should have made a pengun instead
7
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Total votes : 35
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Unread postAuthor: Crna Legija » Mon Oct 11, 2010 11:59 pm

look really good. The only place iv seen more valves is at a hardware store :lol:
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Unread postAuthor: Lockednloaded » Tue Oct 12, 2010 10:36 pm

The new Ball valves looks great, but does it take longer to vent your chamber through the 1/2" nipple after the 1" BV?

P.S.
Has anyone ever tested the burst pressure of galvanized steel?
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Unread postAuthor: SpudBlaster15 » Tue Oct 12, 2010 10:58 pm

The port in the 1" valve is relatively small, so the 1/2" diameter pipes which follow in the system don't really constrict flow.

To my knowledge, nobody has done proper burst pressure testing of SCH40 galvanized steel pipe. Calculated values for 2" nominal diameter pipe are in the range of 3KPSI, so this system will never approach the pressures required to significantly stress it.
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Unread postAuthor: SpudBlaster15 » Mon Oct 18, 2010 3:08 am

Good news.

The new valves hold up to oxygen enhanced mixes. After firing mixes containing up to 40% oxygen, the Delrin seals are still perfect, and the steel balls show no signs of deformation.

Through all this, the main valve has held up admirably, and even with the forces it's subjected to, the piston has suffered no mechanical failures.

As is often the case in engineering, solving the issues with this launcher ultimately came down to the use of improved materials and metallurgy. With the launcher platform working well, I can now move onward to projectile design. Interesting things should follow soon.
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Unread postAuthor: Lockednloaded » Mon Oct 25, 2010 9:47 pm

I ma have misinterpreted this, but DYI said he was playing around with GasEQ and he saw that oxygen mixes do not outperform air mixes with an equal volume of fuel.
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Unread postAuthor: ramses » Tue Oct 26, 2010 3:28 pm

correct, until you approach the speed of sound in the burning propellant gas.

The air powered version also heats the ~80% of air that is nitrogen, creating more pressure.

with equal volumes of fuel, pre-ignition pressure at 5x is 4 bar an 0 bar respectively. even with 1/4 the temperature increase, you will still get equal pressure.
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Unread postAuthor: SpudBlaster15 » Sun Nov 14, 2010 4:09 pm

Lockednloaded wrote:I ma have misinterpreted this, but DYI said he was playing around with GasEQ and he saw that oxygen mixes do not outperform air mixes with an equal volume of fuel.


For a given volume of fuel, an air/fuel mixture will produce greater peak pressures than an oxygen/fuel mix, simply due to the much greater molar quantity of gas present in the chamber.

However, the advantage of oxygen enhancement comes from the much lower preignition chamber pressure required to achieve the same peak combustion pressure. With the ~60%N<sub>2</sub>/40% O<sub>2</sub>/C<sub>3</sub>H<sub>6</sub> mixture I'm using, the chamber pressure prior to ignition only needs to be ~30PSIG to produce essentially the same barrel pressure VS displacement curve as a 6X (~75PSIG) air/fuel mixture.

Additionally, half of the pressure is supplied by the onboard bottled oxygen, meaning only one additional atmosphere must be supplied manually with an air pump. This greatly reduces the strain on the 12V compressor I use as a field air supply.
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Unread postAuthor: SpudFarm » Mon Nov 15, 2010 6:33 pm

Any updates at this time?
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Unread postAuthor: SpudBlaster15 » Mon Nov 15, 2010 7:03 pm

Yeah, a few updates to the venting system and barrel support have been finished. The vent system no longer uses a ball valve on the end of the chamber, but expels exhaust gases out through the main valve after firing. The operation of this system is based around a coaxial vent tube, which I'll provide a diagram for soon.

In the meantime, this is somewhat less relevant to the topic, but far more interesting:

Image

http://www.roguesci.org/
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Unread postAuthor: ramses » Mon Nov 15, 2010 8:05 pm

:D :D :D :D

Are we allowed to talk about that now?

[/off-topic]
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Unread postAuthor: Lockednloaded » Thu Nov 25, 2010 12:36 am

I haven't been able to ask if there have been any recent changes since the chat has been down, so is it still in the same state as last seen? Also, you've kind of explained it before, but I still don't understand your vent valve.. :?
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Unread postAuthor: SpudBlaster15 » Thu Nov 25, 2010 12:48 am

It's currently disassembled, as the front piston spool suffered some minor damage. Not certain how this damage was caused, but it's unrelated to bumper issues.

Repairs have been put on hold, due to my recently redeveloped interest in tossing nitrate groups onto organic molecules.
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Unread postAuthor: saefroch » Thu Nov 25, 2010 10:58 am

SpudBlaster15 wrote:my recently redeveloped interest in tossing nitrate groups onto organic molecules.
I'd love to hear all about this, but sadly I guess this falls in with the special projectile SWIM's making.
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