It's a pipe dream....


Postby D_Hall » Wed Nov 08, 2006 10:37 pm

Without the ability to tip the barrel to load the gun you now need to roll the barrel several feet forward (rather than the few inches currently required). This now takes the CG of the barrel beyond the trailer bed meaning that I'll still have to build some sort of extra support structure or rely upon the pipe/wheel interface to not deform under the cantelever.
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Postby spudkilla » Sat Nov 11, 2006 8:26 am

I have a good name for this beast THE 2ND AMENDMENT
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Postby SpudMonster » Sun Nov 12, 2006 12:46 am

Already been used on a pumpkin chunker.
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Postby spudkilla » Sun Nov 12, 2006 9:03 am

Thats where i got the name from...:(
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Postby Navigator7 » Sun Nov 12, 2006 10:04 am

The of the greatest joys in my life is to go out and do something nobody else is doing....and either succeed or fail with equal enthusiasm.
It is always the guys out doing something that receive all the criticism.
How can anybody be critical of you is you are all balled up infront of a puter and never take any risks?
With that in mind I offer the following:

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by D_Hall
...The barrel rolls forward about 10 inches on the whole carriage and then tips upwards to align itself with the loading ramp.

...You then drop the barrel back to level, slide the barrel back, and you're ready to go...
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Now hold it!
I'm seeing what...a 300 # flange holding the barrel to the chamber.
Being as I have bolted too many 150# and 300# flanges together in my lifetime....I guarantee the process will take all the fun out of using the cannon....after the first shot.

Tell me you are using another method???

I do have the solution.

Would you be open to constructive criticism from the peanut gallery??
This big cannon stuff is up my ally. Are you and DR consorting?
DR....should we try again?
I have a commercial application for this.
Winter is a coming.....and my big projectile juices may get flowing again.
Should we all talk?
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Postby D_Hall » Mon Nov 13, 2006 12:42 am

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Navigator7
Now hold it!
I'm seeing what...a 300 # flange holding the barrel to the chamber.
Being as I have bolted too many 150# and 300# flanges together in my lifetime....I guarantee the process will take all the fun out of using the cannon....after the first shot.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

I guarentee we routinely do much worse (hint: The forward end of a Trident first stage has a 3000# flange held on by *120* screws that all must be precisely torqued.). By comparison, a mere 300# flange with 24 bolts that don't need to be torqued to any specific value (ie, air tools are fair game)? Doesn't sound like any big deal to me.

And as an aside, this gun ain't about fun.

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Tell me you are using another method???<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Well, I plan on tack welding the bolts to the backside. Having the bolts in place will aid in alignment when the barrel slides back. Thus all one is left with is 24 nuts to be zipped down with an air wrench (we've BIG air wrenches). Should take less than 10 minutes.

THAT said...
<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Would you be open to constructive criticism from the peanut gallery??
This big cannon stuff is up my ally.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Sure. I'm absolutely open to ideas.
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Postby BewareOfDog » Mon Nov 13, 2006 1:21 am

D_Hall, I would be very interested to hear your thoughts on this theory:

A "Hybrid" that has a burst-disc that will rupture not much higher than the maximum intended pre-ignition pressure, will only need HALF the chamber volume of a standard combustion... for a 2x/2atm mix?

If iginiting a <b>3x/3atm mix</b>, then the chamber volume only need be 1/3 of a standard combustion, and so on...? Otherwise, you just get a huge bang because of all the wasted fuel.

However, the peak pressure of (for instance) a 2x/2atm mix is around 204psi (plus 15psi added for the compressed air). At 219 psi, if the burst-disc were designed to rupture at approximately 100psi, then would you have the benefit of that 100psi, instead of an average 40psi for a standard combustion? (Using just a 1:1 chamber/barrel ratio)

Or, with a 3x/3atm mix : 102 + 102 + 102 + 32 = 339psi
With the disc designed to rupture at approximately 200+ psi, then you would have the benefit of that 200+psi dumping all at once, instead of (again) just 40psi?

I hope you're following me on this!:? - What I'm getting at is:
Otherwise, the only benefit of a "hybrid" is to be able to use a much smalller chamber volume than the barrel volume. - So you either make the cannon a 1:1 that dumps a shitload of pressure, or a much smaller chamber than barrel launcher that STILL has enough fuel/air volume to push a projectile down a long barrel.
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Postby D_Hall » Mon Nov 13, 2006 1:59 am

Couple points....

1) Although not documented in the thread as the thread had largely died out by the time I got this far, I've got the burst diaphrams priced. Suffice to say that I can have a custom diaphram built to burst at 175 psi for about $200/each in quantity. For hobby purposes that is, of course, prohibitively expensive. This is not a hobby gun, however. $200 is in the noise compared to the other costs associated with the kind of test I have in mind.

2) Not quite true, DR. The big advantage from my perspective in going with a hybrid is having the gases heated. At similar pressures, the mass/energy flow through an oriface of HOT gases as compared to cold gases is higher. 'Tis that hot gas flow through the oriface that I need. I've not kept the notes, but going from memory my back of the envelope (read: using GGDT) calculations indicated that with ambient temperature air at 210 psi the gun would be limited to about 750 fps. That's an interesting speed but right on the ragged edge of usable for me (ie, any slower and there's no point). By contrast, using post combustion gases I get 1000 fps out of the gun. THAT is a very interesting speed to me that's right in the heart of the velocity regimes people care about. So... While your comments about hybrid vs. cold gas and how that effects chamber size are true, that's not what's pushing me in the hybrid direction. 'Tis the massflow increase associated with hot gas flow that's doing the pushing.
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Postby spudkilla » Sat Feb 24, 2007 4:11 pm

I know that this is a dead thread.....but.....have you made any progress?If so post some pictures of this beast!
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Postby D_Hall » Sun Feb 25, 2007 2:46 pm

Sadly, no progress.

Shortly after this thread started I got a new job (I think I commented on it in the thread somewhere). The downside of the new job is that I am INSANELY busy these days. Since I'm the gun's only advocate, not much has happened.

I haven't given up on it, mind you.

The good news is that I have just about everything I need to build the gun in "my domain". So if things ever slow down at the office I can throw my welder on it. The bad news is that while history tells us that things DO slow down around here, such slow downs can be years between.

So I continue to make small refinements to the design in my head, but in the meantime... :(
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