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The Combustion Machine Gun

A place to ask general spud cannon related questions.
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Unread postAuthor: john bunsenburner » Wed Aug 12, 2009 4:30 am

ey i spent 3/4 of first grade in the corner right of the door, don't make fun of it!
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Unread postAuthor: smiley_666 » Wed Aug 12, 2009 4:41 am

dont worry, ive spent more than my fair share of my time involintarily sitting in corners :roll: :)
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Unread postAuthor: Moonbogg » Wed Aug 12, 2009 5:34 am

I actually think its about as hopeless of an idea that any mind could possibly bring to the table. Thats why I wanted to see if he could pull it off thus shocking us all.
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Unread postAuthor: NinjaFish » Wed Aug 12, 2009 10:17 am

It could be a pretty intresting adventure and even if i do fail i will have learnt alot.

Does the magazine have to keep up with the engine cant it just pop a projectile in when it feels like it.

Overall there are many problems with the idea but nothing that cant be adressed i think the pulse jet engines that glow white are normally powered by propane which burns hot anyway. I plan to use a liquid fuel so that shouldnt be as large of a problem.

Oh and finnally if anything bad happened .. god forbid. The NHS will make it all better :P im from England.
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Unread postAuthor: POLAND_SPUD » Wed Aug 12, 2009 12:03 pm

be warned that even the simplest semi-auto/ auto designs can be very discouraging and depressing...

your idea doesn't really seem doable and even if you manage to get it to work it might not be very powerful nor practical... I am not trying to discourage you because your idea rocks and I am jealous or something

IMO it would be better if you try something that at least seem doable...
like a HP bbmg with a detent..
..or first an advanced combustion to gather some experience and then a fully working semi auto combustion

they are quite demanding and cool projects
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Unread postAuthor: jimmy101 » Wed Aug 12, 2009 1:43 pm

Yep, very difficult and may well be impossible. So what. Try a few simple things and see what happens.

Probably need a double pipe pulse jet. That way even when a round is in one pipe you still have the other to suck fresh air in through. So it's a bit more complex than the "mason jar" engines.

Reed valves on the second pipe would be great.

50 Hz is a big challenge but well within the range of a cloud BBMG. Other mechanical feeds are probably out. We can of course fantasize about a "gattling pulse jet gun". 8)

As a test setup... run a hose from the outlet pipe into a bucket of water. See if you can just get spurts of water up out'a the bucket as the engine runs.
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Unread postAuthor: smiley_666 » Wed Aug 12, 2009 7:19 pm

its reasonably difficult t get a pulse jet running on its own, let alone running with a projectile blocking the exhaust half the time.
on the other hand, it might be an idea to start thinking about a 'combustion machine gun' using the basic principles of a valved pulse jet, only not really pulsing. IE just use the pulse jet valves and base a cannon around that
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Unread postAuthor: GalFisk » Thu Aug 13, 2009 4:00 am

Smiley_666: that is indeed an interesting idea. Experimentation is needed to see if/how enough air can be drawn in through reed valves in the rear of the combustion chamber to support another combustion. If not enough air is being drawn in, the cycle will peter out. C:B ratio will make a major difference in how the gasses move around, maybe some projectile speed even needs to be sacrificed to draw in enough air.
If the finished cannon can double as a pulse jet when run without a projectile and with a continuous fuel feed, all the better :D
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Unread postAuthor: inonickname » Thu Aug 13, 2009 4:19 am

cant it just pop a projectile in when it feels like it.

No.

Overall there are many problems with the idea but nothing that cant be adressed i think the pulse jet engines that glow white are normally powered by propane which burns hot anyway. I plan to use a liquid fuel so that shouldnt be as large of a problem.

Are you joking? Pulsejets are hugely inefficient. A lot of the energy, no matter what fuel you use goes to wasted heat.

Did you know that the peak flame temp. of propane is a mere 20 degrees fahrenheit higher than gasoline. You haven't mentioned what fuel you want to use, but I'd assume it's hardly been researched. You will also need to vaporize the fuel and use a pump.

Please stop trying to tell yourself it will work, because it won't. It's nothing to do with any construction awesomeness you may or may not have, it just won't work.

The only way you'll power a gun with a pulse jet is use it to heat a chamber (eg. boil steam)
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Unread postAuthor: smiley_666 » Thu Aug 13, 2009 6:16 am

i think he is planning on using alcohol of some sort, as this is the stuff used in the "jam jars" in the first post...
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Unread postAuthor: inonickname » Thu Aug 13, 2009 6:31 am

Ok, if he's happy to hold his flame constantly to a methanol flame then I'll believe him that it won't be a problem.

It's not a working concept. There is not a way to directly use the exhaust fumes of a pulsejet to power a spudgun at all. End of. It's not even "a chance of working if done perfectly", it just will not work. The cycle rate is too fast, and you'll block essential functions of the jet.

The only way I can see a pulsejet powering a spudgun is by heating water in a closed chamber to form steam (and thus pressure).

Also, in case you didn't realize methanol is very toxic. The utmost care would have to be taken to ensure there isn't a single leak. Not as dangerous as spilling half a liter of HF, but still a big consideration.
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Unread postAuthor: Technician1002 » Thu Aug 13, 2009 11:42 am

inonickname wrote:Ok, if he's happy to hold his flame constantly to a methanol flame then I'll believe him that it won't be a problem.

It's not a working concept. There is not a way to directly use the exhaust fumes of a pulsejet to power a spudgun at all. End of. It's not even "a chance of working if done perfectly", it just will not work. The cycle rate is too fast, and you'll block essential functions of the jet.

The only way I can see a pulsejet powering a spudgun is by heating water in a closed chamber to form steam (and thus pressure).

Also, in case you didn't realize methanol is very toxic. The utmost care would have to be taken to ensure there isn't a single leak. Not as dangerous as spilling half a liter of HF, but still a big consideration.



For more valid information look up the MSDS for any chemicals you intend to use. (MSDS Material Safety Data Sheet)

Limit your exposure to the fumes. Avoid skin and eye contact. Drinking the stuff is a no no. Methanol received the poison rating of 3 on a scale of 0-4.

http://www.jtbaker.com/msds/englishhtml/M2015.htm
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Unread postAuthor: jimmy101 » Thu Aug 13, 2009 1:22 pm

inonickname wrote:Also, in case you didn't realize methanol is very toxic. The utmost care would have to be taken to ensure there isn't a single leak. Not as dangerous as spilling half a liter of HF, but still a big consideration.

No, MeOH is not "extemely" toxic. It is only midly toxic. If you don't drink it then the toxicity is fairly low. It is much more hazardous for it's flammability, and the fact that it's flame is nearly invisible, than it is for it's toxicity.

Ya know, a 2 stroke engine is darn near what this thread is talking about. An autocycling combustion with a projectile. Since 2 stroke engines work just fine ...

Edit: ENgrish
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Unread postAuthor: dudeman508 » Fri Aug 14, 2009 5:33 pm

after reading your post for the first time i made one out of a jam jar, and i didn't create and force at all. you would have to use super light ammo and a huge pulse jet, plus they are soooo impractical and hard to start i don't think it is worth trying, but if you do make one it would be really cool.
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Unread postAuthor: inonickname » Fri Aug 14, 2009 7:14 pm

jimmy101 wrote:
inonickname wrote:Also, in case you didn't realize methanol is very toxic. The utmost care would have to be taken to ensure there isn't a single leak. Not as dangerous as spilling half a liter of HF, but still a big consideration.

No, MeOH is not "extemely" toxic. It is only midly toxic. If you don't drink it then the toxicity is fairly low. It is much more hazardous for it's flammability, and the fact that it's flame is nearly invisible, than it is for it's toxicity.

Ya know, a 2 stroke engine is darn near what this thread is talking about. An autocycling combustion with a projectile. Since 2 stroke engines work just fine ...

Edit: ENgrish

I did not say "extremely", I said "very". It can cause blindness through skin contact and ingestion. If you want that, then good for you. I was just highlighting another issue with this non-working idea.

Actually nah, you don't know. There are big differences between a 2-stroke and a pulsejet.
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