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Possible large burst disk hybrid build(Update with video)

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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Re: Possible large burst disk hybrid build

Unread postAuthor: wdr0 » Mon Oct 06, 2014 9:38 pm

Well I have everything done except for having the pressure transducers set up with the readouts. Here are some pictures
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Spark strip hooked to HV supply
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7"x12' chamber
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4"x20 barrel
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HV feed through for ignition

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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: wdr0 » Mon Oct 13, 2014 5:08 pm

Here is the first test.

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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: DYI » Mon Oct 13, 2014 7:56 pm

I've been quietly following this thread for a while, and I'd like to congratulate you for pursuing the project this far. There aren't many hybrids this big around, and they don't tend to get fired very often, so it's a rare treat to see one in action. What were the parameters for this shot? Specifically, I'm interested in the fuel mix, disk rupture pressure, and projectile, if any, as well as why the gun appeared to accelerate forward violently after the initial recoil.

Was there any damage to the welds or the flange from the gun bouncing around during the shot? You may have been better served by having it resting directly on the ground.

Finally, and I know this is a little belated, but your spark strip wins absolutely everything :lol:
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: wdr0 » Mon Oct 13, 2014 8:24 pm

I had suspected and hopped people were lurking and awaiting the completion. I actually did not plan on building one this big. I was planning on a 2" bore(at some point I may still do this one, but with maybe sch80 and a 20x or higher mix). It came about because my freind and I were looking around for stuff to shoot with the air cannon. We came across the pipe in the process and jokingly thought that would be a big cannon, and then wait this could actually happen. At that point I was not optimistic since I was expecting the weld fittings to cost a lot. I called the plumbing supply and found them quite affordable so then construction began.. And thanks for the compliments.

As for this shot projectile was a coffe can that we filled with melted down aluminum wire scrap. Guestimate of 5lbs. Burst disk was 3/64" aluminum, I think around 22k psi tensile strength. don't recall, but I know the thickness and type of alluminum was selected to give around 850 psi rupture pressure. Fuel mix was what I got off here. 6.44 psi propane, and then raised to 138.7 with air. I used two different transducers to fuel it. I was expecting it to not ignite as I calibrated them just off the gauge on my air compressor(hope to get them calibrated more accurately).

The cannon was placed up off the ground in an ill conceived attempt to retrieve the projectile. It had to be up like that to clear a small rise with the idea that the projectiles would be captured in a small dirt embankment. Somehow durring meticulously aiming at said dirt embankment including the use of a laser transit we failed to remember that we were shooting entirely non aerodynamic aluminum lumps from a slightly bent steel pipe(apfsds rounds are in the works). Anyway it was on wood cribing and cinder blocks. The forward movement is from our technically engineered recoil system consisting of chains around trees looped through tires to absorb the shock. I was actually suspecting the welds could fail as I have welding experience, but have never welded pipe, or even anything open root for that matter. There will be many more tests, it just might be a it before the videos get on here as I have no experience uploading them and it seems to take awhile.
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: wdr0 » Mon Oct 13, 2014 8:33 pm

And yes I am somewhat proud of the spark strip. It took me and a freind atleast four hours to complete. It does need some refinement. The stick itself works great and remains undamaged, however the support structuree was severley damaged after the first shout and needs revission. It is probably entirely destroyed after firing the second shot. Another issue is the 10k psi quick connect leaked after the first shot. I was allitle annoyed since the cannon is theroetically producing only about a tenth of that. But there happened to be a large ball valve laying arround so that issue is fixed. The next imediate plans are to devise a more elegant support scenario, and solve the spark strip trying to exit the barrel issue.
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Ignition control with key interlock
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Dart for the apfsds round, 1" round bar 2ft long with 6" x 1-1/2" x 1/8" flat bar fins.

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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: DYI » Mon Oct 13, 2014 9:37 pm

Thanks for the information. I'm guessing that you didn't actually end up catching the projectile this time around?

What's your projectile situation with this cannon anyway? Do you have a lathe you can use for making projectiles from bar stock? You should be able to get at least 5 pounds up to 400m/s, and that could make for some impressive damage with the right projectiles. Nice as APFSDS would be, even a simple drag stabilized plastic slug carrying a piece of 1.5" or 2" steel round bar would be quite impressive, not to mention much cheaper and quicker to build.

The 10kpsi quick connect probably had some high surface area to mass ratio sealing face that got cooked, similar to what happened to your spark strip's support structure. The long term solution for a fuel system shutoff valve is a hard seat needle valve, readily available up to 10kpsi pressure ratings (and less readily available up to 100kpsi). These have no low melting point components to be damaged, and their sealing action is very robust. Me and Larda have both used them on hybrids running over 100X with no discernible damage at all.
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: MrCrowley » Mon Oct 13, 2014 9:42 pm

Mother of god, that is one helluva muzzle blast. Amazing stuff, looking forward to more test shots!
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Re: Possible large burst disk hybrid build(Update with video

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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: wdr0 » Mon Oct 13, 2014 10:19 pm

As much as I'd like to have a lathe, I don't although I am always on the look out for one and hope to have one eventually. Currently we have made one cast aluminum one, and one concrete one which was fired through a washing machine. The washing machine got tossed about twenty feet with a rather hilarious dispersal of gears and other parts I never knew existed inside a washing machine all around(will get that video up sometime). Neither of the rounds were recovered. The concrete likely fragmented. My freind did find strike marks on some trees after I left though, so next time I go out there we will do a more thurough investigation. It tossed the washing machine about 20ft. The next test will be with an apfsds round, although I think it may not even need a sabot as it is an almost perfect fit with the fins keeping it pretty well centered. I am thinking I just need a wading/puck of some sort behind it. I am concerned if I used wood it would just fire it out around the fine. But my freind has a large amount of translucent 1/2" thick plastic sheet which I believe is polycarbonate. I think that will do nicely. And I planned to use a needle valve, but then needed quick connects anyway and these were cheap so figured Id try it. I did know in the back of my mind they may not work. Just for reference they were McMaster # 53455K36 along with the mating socket. I think they may actually have a metal to metal seal, my suspicion is the ball got marred against the seat from the blast and than bounced to a different position forming a leak path.

And to MrCrowely, I am sorry to say that the muzzle blast was is likely all the crud getting blasted off the inside of the pipe in the first shot. The pipe was pretty dirty. Its certainly exciting still, just not all from the propane though.

Eventaully in theory it will get painted after the technical issues are worked out. It's not the prettiest currently.
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: DYI » Thu Oct 16, 2014 1:09 pm

I wouldn't try launching the dart in your picture without a sabot or some other support further up along its length. You risk destroying the dart in the barrel, and possibly tearing such a large groove along the barrel as to make it unusable. Take a gander at the HyGaC20 thread to see how this looks. High performance launch of finned darts is notorious around here for being a lot harder to get right than you might think, and there have been many more failures than successes.

Also, a lot of that muzzle blast was dirt and dust getting picked up from the ground near the muzzle. I've seen similar before. Incidentally, if you use a heavily fuel rich oxy/fuel mix in this thing (something like 25:75 to 30:70 oxygen/propylene) you could get a *very* impressive muzzle blast (easily visible in daylight), and probably a slight performance increase for the same maximum pressure.
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: Technician1002 » Thu Oct 16, 2014 6:02 pm

I was expecting it to not ignite as I calibrated them just off the gauge on my air compressor(hope to get them calibrated more accurately).


When working at elevated pressure, the combustability range expands.
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: wdr0 » Thu Oct 16, 2014 10:48 pm

Sabot advice noted. I already have a plan for one, just was thinking maybe I could save time and forgo it. But the concern you mentioned was the exact I had. I will definitely look into the richer fuel mix. Although I don't have any propylene available, I may be able to borrow an oxygen tank though.

And thanks for the info about the flammability range.
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: wdr0 » Mon Oct 20, 2014 10:27 am

I have not had a chance for more shots, however my freind located the impact points of the first two. We have not located either projectile in part, or in whole at this point. The next shots will be with the apfsds rounds. We plan to fire one at a steel plate, and one at a large log.
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Hard to see, the splintered area is where the aluminum projectile struck this tree. It hit just to the left of the center passing all the way through. The tree was 8-10". If it had hit an inch to the right it likely would have severed the trunk.
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This is where the concrete projectile struck an oak tree. This is 200+ft down range after going through the washing machine. This tree is 18-20"
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Here is the exit side of the washer. Old one so thick steel drum, it also hit the spindle in the middle tearing it out. The projectile entered sideways.

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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: mobile chernobyl » Tue Oct 21, 2014 10:34 am

This is so cool dude.

I wanted to build something on this scale for so long!

Plan on trailer mounting it if you haven't already!
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: wdr0 » Tue Oct 21, 2014 12:34 pm

Yes a trailer mount of some sort is planned. I am not sure when it will get done as my freind and I seem to only both be around about one day a week. I think we may fire some more shots this weekend though.
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Re: Possible large burst disk hybrid build(Update with video

Unread postAuthor: wdr0 » Mon Nov 10, 2014 10:01 am

Planning to do another firing of the cannon. Did a lost foam casting of aluminum Saturday and got two decent spheres. I will get video and photos and update after the test.
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