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newbie planning to go all out :-)

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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newbie planning to go all out :-)

Unread postAuthor: natas » Thu Mar 01, 2012 4:01 am

Hi there spudders, first of all i would like to thank this forum for a extremely informal place to be :-)
Im a guy from Norway, that just found interrest in the spudding universe.
Inside this forum i have found almost everything i need to go all out on a mapp cannon build. but there is one thing im not able to find info on, im sure there is a thread about it, but im probably not putting in the right search words.

im not asking this so i can be easally spoon fed, but after a week inside this place i still dont find info regarding this issue.

So my question is this : what is best. a long narrow explotion chamber, or a short wide one ?

my options is a 90mm. or a 110mm pvc. (certified for 16bar) pipe for the main chamber.
im also planning to have 3 spark points and two 40mm fans inside the chamber.


Paul.
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Unread postAuthor: Crna Legija » Thu Mar 01, 2012 4:23 am

short and wide is the best you can do with standard parts the very best would be a sphere. so yeah defiantly go for the 110mm.
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 01, 2012 4:30 am

Welcome to the forum :)

The "ideal" chamber is considered to be spherical with the ignition in the centre, in practice this is relatively difficult to do so a cylindrical chamber that is as long as the diameter is a good compromise.

Have a look here for an idea of how the flame front propagates.
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Unread postAuthor: natas » Thu Mar 01, 2012 5:48 am

thnks alot for the reply, ill try to post some pictures in the process,, :-)
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Unread postAuthor: Technician1002 » Thu Mar 01, 2012 9:46 am

Same physics works well for air cannons too. Provides the least friction inside the chamber for maximum pressure on the projectile.

The "ideal" chamber is considered to be spherical with the ignition in the centre


If you could do it, I'm wondering if a "Shaped charge" type multi-point ignition would work better.

See the bottom one. Barrel would extend to near the center of the chamber for that design.
http://en.wikipedia.org/wiki/Gurney_equations It is not something I would build, but just a theory idea.
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Unread postAuthor: natas » Thu Mar 01, 2012 10:02 am

i have no problem making a sphere in aluminium. but i guess the size is a bit unpractical. i would guess the size is close to a basketball for a 2" barrel
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Unread postAuthor: natas » Fri Mar 02, 2012 7:07 am

http://www.drillspot.com/products/455290/Banjo_200B_Female_Coupler

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Is this a good enough/the common used coupler ?

I cant find anyone in norway selling these couplings, so ill just order some online.


Paul
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Unread postAuthor: Moonbogg » Fri Mar 02, 2012 11:50 am

I wouldn't worry about making a sphere to be honest. You would be really hard pressed to see any real difference in performance over a regular chamber with multiple sparks. Plus, it would look ridiculous with a big round chamber. It would look like a turkey baster, a test tube, or a crack pipe depending on your background.
The camlock you linked is perfect for combustion use.
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Unread postAuthor: natas » Fri Mar 02, 2012 1:35 pm

thnx for informative answer moonbogg. ill order a few different diameters and go from there :-) btw, those hybrids of yours looks awesome !!

how about making two combustion spheres, and have "great balls of fire" ROFL !

ill drop the sphere, and go for a clear 110-160mm. chamber, just for the looks of it, maybe add some led lights inside for fun :-)
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Unread postAuthor: natas » Sun Mar 04, 2012 3:28 am

i was planning to have a 2" barrel on my first cannon, bur after reading alot inside this forum, it seems a 1,5" barrel is more usable.
what do you guys think ? or is it better to just make both barrels and find out my self? :-)
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Unread postAuthor: jackssmirkingrevenge » Sun Mar 04, 2012 3:55 am

What do you mean by "usable"?

It really depends on what you mean to fire out of it ;)
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Unread postAuthor: natas » Sun Mar 04, 2012 4:08 am

usable is probably not the right word. but im looking for a "allround" barrel, and it seems like the 1,5" pipe is good for a occational golf ball, and u dont neen that big potatoes.
But is there alot less fire/hit power in 1,5 vs 2" ??
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Unread postAuthor: jackssmirkingrevenge » Sun Mar 04, 2012 4:31 am

natas wrote:But is there alot less fire/hit power in 1,5 vs 2" ??


A bigger diameter means more surface area (on the base of the projectile) available for the gas to push on, which is directly proportional to the force placed on the projectile (force = pressure x area).

1.5" barrel has 1.78 in<sup>2</sup> area available.

2" barrel has 3.14 in<sup>2</sup> area available - over 75% more than the 1.5"

The downside is it's more difficult to make sabots for sub calibre projectiles.
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Unread postAuthor: natas » Sun Mar 04, 2012 4:49 am

so... if you had to choose between 1.5 or 2.0 barrel... what would you go for ? :-)
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Unread postAuthor: jackssmirkingrevenge » Sun Mar 04, 2012 4:57 am

natas wrote:so... if you had to choose between 1.5 or 2.0 barrel... what would you go for ? :-)


Neither ;)
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