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Taternator II SUPERSONIC

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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Taternator II SUPERSONIC

Unread postAuthor: Dumbascii » Thu May 17, 2007 9:31 am

...but unfortunately not with a potato. With a wax slug, I reached 1263 FPS before suffering minor ignition damage. This was a 3X air/MAPP mix with the 8 foot barrel. With a potato, I've never gone past 779 FPS because the slug instantly vaporizes. I used a remote trigger so I could safely stand behind a huge wood pile. Nothing ruptured on the gun, but I don't entirely trust it. The noise is unbelievable. It is not possible to see the path of the flying slug, just the point of impact.

The wax slugs are 1.5" diameter, 3" long and weigh 80 grams. I machined several pieces of barrel material to make the molds. The wax is ordinary candle / canning wax, melted on the stove and poured in. I stand up the molds on my cast iron table saw which sinks the heat very quickly, preventing leaking from the bottom of the molds. After the wax is completely cooled, the slugs can be pushed out easily because the wax shrinks a tiny bit. Click for large.

Image Image

I also made heavy 115 gram slugs from automotive body filler. I slicked the molds with a film of motor oil first. The body filler gets ferociously hot while curing, then shrinks a tiny bit for a perfect fit. I did not test the speed of these since I only had 2 and wanted to destroy things with them, meaning the chrony had to be out of schrapnel range. The only things I had on hand to shoot at were hard drives which needed sanitizing. The drives were utterly destroyed, with fragments flying 300 feet from the point of impact. The platters stayed on the spindle, but were deeply cup shaped. Photos soon . . .

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http://www2.taconic.net/fkennedy/
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Unread postAuthor: Arborman » Thu May 17, 2007 10:04 am

I want to see some pics of that gun. Unless youve alrdy posted the gun and i'm just being a stupid nube.


btw...

AWESOME!!!
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Unread postAuthor: jackssmirkingrevenge » Thu May 17, 2007 10:09 am

Arborman wrote:I want to see some pics of that gun. Unless youve alrdy posted the gun and i'm just being a stupid nube.


yes, you are :wink: :P
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Unread postAuthor: rna_duelers » Thu May 17, 2007 9:18 pm

Thats great news,another super sonic spudgun.

Any chance of some videos of some supersonic wax projectiles?Or rather there unseen path before impact?
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Unread postAuthor: Arborman » Thu May 17, 2007 10:05 pm

jackssmirkingrevenge wrote:
Arborman wrote:I want to see some pics of that gun. Unless youve alrdy posted the gun and i'm just being a stupid nube.


yes, you are :wink: :P


Of course. I knew that was coming :joker:

Any way.....

holy crap, that is a sweet gun. The speed of those slugs are amazing.
keep up the good work! 8)
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Unread postAuthor: dongfang » Fri May 18, 2007 3:32 am

Hi,

Great stuff! 385 m/s, that is sligtly faster than my sonic combistion. But your slug is about 10* heavier.

I wonder if you can reach mach 2 with a lightweight (drilled hollow) slug.

Regards
Soren
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Unread postAuthor: jackssmirkingrevenge » Fri May 18, 2007 3:54 am

As air drag increases exponentially with velocity and you're going so fast, I doubt blunt cylindrical slugs are doing you any favours. Why not try something like the profile below? It shouldn't be too hard to turn a wooden mould for the nose section, and the rear hollow can be a simple dowel mandrel.
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Unread postAuthor: jrrdw » Fri May 18, 2007 7:39 am

I made a 1" bondo slug for my cannon, shot it at 40 psi, it went aprox. 50 yards and split into 3 pieces. Remember that shot was only 40 psi, no where near supersonic. Plus i had sanded a nice point to cut through the air, it flew straight without tumbling, but couldn't handle the stress of flight!
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Unread postAuthor: ShowNoMercy » Fri May 18, 2007 7:41 am

Why not just machine some nice aluminum rounds?
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Unread postAuthor: BC Pneumatics » Fri May 18, 2007 8:27 am

I must say, your work is unparalleled and you are an asset to this forum.
Keep up the good work, and hopefully you stick around!

Edit::
Accuracy +/- 12" @ 100'

Perhaps you should spend some time in this area, it seems to be the only aspect of spudguning that this thing doesn't already dominate. (Well, that and simplicity, but screw simplicity.) :wink: 8)

Edit 2::
I think that using jackssmirkingrevenge's round would provide more advantages than he mentioned. Only only will it reduce air drag and increase speed, it will be more accurate. Also, if it was constructed from wax, the gases in the rear cavity may exert enough force to push the walls of the slug firmly against the barrel's wall, (The heat of combustion would probably make this all the more likely.) and thus create a better seal. This would obviously lead to better efficiency, provided it isn't canceled or even countered by the increased drag, but (hot) wax isn't exactly a high drag projectile.
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Unread postAuthor: Dumbascii » Fri May 18, 2007 10:36 am

rna_duelers wrote:. . . Any chance of some videos of some supersonic wax projectiles?Or rather there unseen path before impact?

I was so excited to test it, and there are so many effing parts to pack, I completely forgot to bring a camcorder. All we had on hand was a camera phone whose owner has not sent me the (crappy) photos yet.

dongfang wrote:. . . I wonder if you can reach mach 2 with a lightweight (drilled hollow) slug.

Not likely. The chamber would have to be much larger, running on hydrogen, and the barrel much longer.

jackssmirkingrevenge wrote:As air drag increases exponentially with velocity and you're going so fast, I doubt blunt cylindrical slugs are doing you any favours. Why not try something like the profile below? It shouldn't be too hard to turn a wooden mould for the nose section, and the rear hollow can be a simple dowel mandrel.

Your dowel design is excellent and easy to make - I'll try it. Keeping the weight up front should reduce tumbling.

jrrdw wrote:I made a 1" bondo slug for my cannon, shot it at 40 psi, it went aprox. 50 yards and split into 3 pieces. . .

Something was wrong with your bondo or some contamination left weak crevices. The bondo slugs I made are hard as a rock. Even the wax slugs do not break apart, as I saw two of them bounce off the ground far downrange. Try again - the bondo really packs a punch.

ShowNoMercy wrote:Why not just machine some nice aluminum rounds?

Because the material is $1.40 per inch, and aluminum-on-aluminum creates tearing friction.

BC Pneumatics wrote:Accuracy +/- 12" @ 100' Perhaps you should spend some time in this area, it seems to be the only aspect of spudguning that this thing doesn't already dominate. (Well, that and simplicity, but screw simplicity.) :wink: 8)

That spec is understated. Accuracy is more like +- 6" if you try to pick spuds of the same weight and try to keep the forward surface of the spud as flat as possible when loading into the breech. I think the turned wood slugs will help a lot. I have not measured the accuracy of wax, but I suspect it will be drastically improved because of the predictable and even flat ends. I also have not tested accuracy of the 8 foot barrel, though it is probably not much different.

I've been trying to find someone to rifle the aluminum barrel (maybe just the short 4 footer) with no luck. The air acting on uneven spud shapes steers them all over the place once the initial speed is reduced by drag. The next major factor is the weight of the slug. Lighter slugs go faster and fly straighter initially, heavier slugs fly slower, drop faster, but are less deflected by the air.

The most detrimental factor for accuracy is the combustion pressure. If I run air/MAPP or oxygen/MAPP at one atmosphere, the results are very predictable. Hybrid mixes are all over the place. It is difficult to get exactly the same mix every time - even with the finely graded pressure guage I have on it.

I also have not tested total distance with wax or bondo at 3X mix with the 8' barrel. Since I test distance at a lake, it should be easy to canoe out and recover intact floating wax slugs and see what shape they are in. By time they hit the water, they are merely falling at terminal velocity - water impact is not likely to bruise them.
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Unread postAuthor: dongfang » Fri May 18, 2007 11:14 am

Hi,

To jackssmirkingrevenge and BC Pneumatics:

Nice idea with the profile.

But how about keeping it together? The mass per cross section area unit is small in the center, but large at the edge (at any point of the cross section it it proportional to the front to back thickness of the projectile at the point, along the axis).

I guess than with ~10-20 bar on the breech side, the suggested profile will simply shed its tail. It's only a guess though, but really, wax breaks easily under "pull" stresses.

But maybe something like

...-----------
../******/
/ *****/
\ *****\
..\******\
...-----------

(disregard the dots)

would work.
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Unread postAuthor: jackssmirkingrevenge » Fri May 18, 2007 11:26 am

It's a possibility, which could be mitigated by adding some sort of disc wad behind the projectile, or filling the hollow with expanding foam.
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Unread postAuthor: BC Pneumatics » Fri May 18, 2007 4:08 pm

You could also build a 'frame' out of hardware cloth for added strength, but we may be going just a little too far for a projectile by then. (Even if this cannon does warrant it.)
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Unread postAuthor: dongfang » Sat May 19, 2007 3:58 pm

Hi,

. . . I wonder if you can reach Mach 2 with a lightweight (drilled hollow) slug.


I´d be optimistic - even though all else equal, it would require a 4 * bigger bang than Mach 1... Not all else needs be equal. There are 3 variables to tune:

- Barrel length

- Projectile mass

- Size o´ bang

and you have not pushed the envelope of either very hard yet..

If only I were at HOME and if that kind of stuff was LEGAL there (or here), and if I had a machine SHOP and knew how to WELD, I wouldn´t be able to sleep until I had tried, haha.

Regards
Soren
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Last edited by dongfang on Mon May 21, 2007 4:50 pm, edited 1 time in total.
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