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50KJ and up...

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: mobile chernobyl » Thu Nov 10, 2011 2:20 am

Here is a very simple first concept for how a HVLP monster would be constructed, undoubtedly inspired by VERA

Image

The chamber is 50" of sch80 8" steel, for a total volume of just about 10 gallons. The total width could grow a little depending on the trailer design.

The barrel is 15 feet of sch40 4" steel.

As you can see its not only capable of 100KJ, but 100Ft-lbs - no doubt in part to the larger surface area that a 4" barrel can provide for it's projectile vs. a 3".

Surprisingly all parts included in just the gun portion are well under $1K - looking at about $600. This doesn't include a trailer yet and that will be very necessary. I could either design and construct a trailer myself, or use an existing one.
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Unread postAuthor: MrCrowley » Thu Nov 10, 2011 2:24 am

Any reason your burst disk failure pressure is so low? Should be able to burst at closer to 1000PSI without problem.

Design and HGDT results look promising though. Seems more plausible than I first expected.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 10, 2011 2:27 am

... and if it doesn't work, you can hold it by the barrel and hammer your target to a pulp!

Much more deserving of the "Mjölnir" moniker :)
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Unread postAuthor: mobile chernobyl » Thu Nov 10, 2011 2:31 am

MrCrowley wrote:Any reason your burst disk failure pressure is so low? Should be able to burst at closer to 1000PSI without problem.

Design and HGDT results look promising though. Seems more plausible than I first expected.


The inertia of the projectile itself does more to aid in building up chamber pressure than the burst disc does.

However I went and plugged in all values from 600-1000 and I'm only seeing an increase of 2K ft-lb @ 1000psi bursting pressure.

So yea, inertia takes the cake, and when your talking about a 3lb projectile that can be expected. With a lighter projectile and a shorter barrel, the burst disc would be handy get get that extra "oomph"

Also - the "contoured" selection is certainly not correct I would think lol. with a blunt profile, 750psi bursting disc is needed to maintain >100K ft-lb performance.

JSR - It does kind of look like a hammer lol. I had named the concept "T-Bar".
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Unread postAuthor: MrCrowley » Thu Nov 10, 2011 2:35 am

Right you are. I still haven't gotten over my jealousy with your recent hybrid, if you build this I may never recover :shock:

:wink:
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Unread postAuthor: paaiyan » Thu Nov 10, 2011 8:28 am

I agree with JSR. Name it Mjölnir.
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Unread postAuthor: saefroch » Thu Nov 10, 2011 11:24 am

jackssmirkingrevenge wrote:... and if it doesn't work, you can hold it by the barrel and hammer your target to a pulp!

Much more deserving of the "Mjölnir" moniker :)
Honestly when I first looked at that I thought he was suggesting that we should abandon high muzzle energy experiments and just use sledgehammers to bash our targets instead.
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Unread postAuthor: D_Hall » Thu Nov 10, 2011 11:54 am

mobile chernobyl wrote:The inertia of the projectile itself does more to aid in building up chamber pressure than the burst disc does.

Another effect that I discovered with VERA that is not accounted for in HGDT... Increased turbulence once the gases start to move. Burst disk in place with no projectile at all. Projectile in... The pressure ramp looked the same. The decay looked very different, of course... But the ramp? Virtually identical. Once that disk goes and the gases start to move the turbulence goes nuts and the burn rate follows. Seriously, on the shots where I had no projectile at all, once the disk blew (visible due to accelerometers) the pressure rise took a step function INCREASE. Seriously. I had an 18" diameter hole in my chamber but the pressure was increasing faster than before the hole appeared!

In summary: Based on my experience, whether you have an optimized disk or not makes even less difference than HGDT indicates.

Also - the "contoured" selection is certainly not correct I would think lol. with a blunt profile, 750psi bursting disc is needed to maintain >100K ft-lb performance.


You can get your system to perform as if it's contoured using a trick... I don't know if it's the correct name (probably not), but at the office we refer to it as using a "dork."

So what is a dork?

OK, see that small length of pipe you have welded to your chamber that provides the breech flange? Yeah, that pipe. When you're building your chamber, extend that pipe into the main portion of the chamber maybe 2 or 3 diameters. Now, for the length of pipe that is inside the chamber, drill a bunch of holes in the pipe.

That's it. That's a dork.

Thought experiment to explain function: If you don't have the holes drilled, the pipe will act very much like it did before. You'll have a choke point at the entry of the pipe that will neck the flow down. OK, fine. But past that choke point the pressure will be lower than it was at the mouth of the pipe. If this were not so, there would be no flow. OK, now imagine the holes... You have a pressure differential between the main chamber and the main flow area of the pipe. And a hole between the two. More air is going to flow in via the drilled hole. Voila, an increased flow coefficient.

Done perfectly it will give you flow that matches a perfectly contoured entrance. Of course, you won't be doing it perfectly, but the point is that significant improvements in flow are available with a bit more work with no increase in build complexity.
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Unread postAuthor: MrCrowley » Thu Nov 10, 2011 2:59 pm

paaiyan wrote:I agree with JSR. Name it Mjölnir.

I already named my piston hybrid Mjölnir, JSR was rightly saying this design would be much more deserving of the name than my cannon, which doesn't look much like a hammer :wink:
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Unread postAuthor: paaiyan » Thu Nov 10, 2011 3:14 pm

How about naming it MC then?
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Unread postAuthor: MisterDoctor » Thu Nov 10, 2011 3:47 pm

Holy Jenova, that's quite the war hammer you've got there. When do you plan on acquiring thy materials?
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Unread postAuthor: mobile chernobyl » Thu Nov 10, 2011 6:11 pm

A little while after its fully designed and I've priced it out, to make sure I won't pour a summer's paid internship earnings into it lol. I don't want to spend more than $1500 up front on it, and preferable right around the $1K mark.

I'm not even sure I'll keep the hammer design, but it was more of a concept to get an image into peoples heads and something to talk about, rather than just ideas.

But there are benefits to my hastily designed "hammer".
-First off it looks like a big ass hammer, so that means its very manly.
-That out of the way, the chamber can provide a pivoting location for the gun, in the off chance I will be shooting at any other inclination than horizontal lol.
-The hammer design allows appx 40" to come off the overall length - which means less of a trailer to make or buy.
-The hammer design is easily constructed with NO pipe fittings, just flanges - which are affordable and easily acquired.
-Both sides of the chamber can be removed for easy access and adjustments inside of it.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 10, 2011 9:01 pm

mobile chernobyl wrote:That out of the way, the chamber can provide a pivoting location for the gun, in the off chance I will be shooting at any other inclination than horizontal lol.


A bit like theDormoy-Chateau ;)
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Unread postAuthor: mobile chernobyl » Thu Nov 10, 2011 11:41 pm

Here is a more conventional concept... Same internal dimensions - 8" X 50" chamber, 4" x 15ft barrel.

This one would cost roughly 6-700 before the cradle portion gets added. Tis will be a costly endeavor if I choose to pursue it properly.

Image

Image

The barrel moves on this concept, to open the breach and keep everything aligned so a human can close the breach - not a machine lol. At close the barrel is biased toward the breach - it opens about 18" and then the COG is right at the last support - so it never has excess weighting off the end of the cradle.

The barrel clamps are over sized in Dia appx 1/8" in so that the barrel can slide.

The chamber has supports that will be welded to the ibeam then the chamber (once its set in place for the last time) This should provide a solid fixture for the force to be transferred through

D_Hall - another question your way - How does your design cope with the [expectedly] massive recoil it generates? Is it all carefully dissipated through the trailer and into rearward movement? I don't think you had mentioned any type of damping but you never know lol. I feel with a proper pivot calculation given the sheer stresses present at a maximum load this guy could easily operate as a solid unit, transferring all recoil though the rearward movement of it.

This project will probably cost all of my budget, but I have a feeling it would be worth it in the end though... :D
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 11, 2011 12:49 am

Your design is already mounted on a rail, have that rail slide in a channel and fit some sort of damper - could be anything from bungee chord to an automotive gas strut.

A muzzle brake would also go some way to cutting down on the recoil, as well as looking badass.
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