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Preliminary design - long range golfball cannon

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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Preliminary design - long range golfball cannon

Unread postAuthor: MortarArmy » Wed Sep 26, 2007 3:33 pm

Working out the details on a new cannon and looking for some feedback

Here's what ive got in mind, and im hoping for at least 350yds. My current metered potato gun with much smaller dimensions and no fan is getting 225 yards consistently.

5ft of BC arms golfball barrel
4"x14" Combustion chamber
over/under style gun with 2 90deg bends
Ball valve vent
80mm Vantec Tornado 84cfm case fan....yep it moves 84 cubic feet of air per minute, probably over kill, but i want this thing well mixed and venting as fast as possible.
probably bbq ignition, maybe stungun, not sure yet.
Metered MAPP using adapted parts from a current cannon

Going for basic nitty grity nothing flashy get the job done haul some golfball ass type gun. Anything I can do to improve range/acccuracy would be great.[/list]
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Unread postAuthor: thespeedycicada » Wed Sep 26, 2007 3:35 pm

use more than one spark gap and sdr 21 for the barrel i just think it works a little better.
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Unread postAuthor: MortarArmy » Wed Sep 26, 2007 3:53 pm

thats why i said i was using the bcarms golfball barrel, its 1.5" sdr21 pipe sleaved into a 2" pipe.
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Unread postAuthor: thespeedycicada » Wed Sep 26, 2007 3:57 pm

i thought it was the 2 inch sleved golf ball barrel the kind with the annoying ridge in it.
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current projects: co-axial piston valve.Status DONE!
S.P.E.C.S update mk 1 construction begining in febuary all the maths for it are done plans are drawn up and parts are listed.
NEXT project:auto piston valve.
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Unread postAuthor: dongfang » Wed Sep 26, 2007 4:22 pm

Hi,

Which size of bends do you plan to use?

Regards
Soren
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Unread postAuthor: Hubb » Wed Sep 26, 2007 4:30 pm

thespeedycicada wrote:use more than one spark gap...


Agreed. Make a spark strip and go for at least three good, solid sparks. If you're going through the trouble of making a combustion like this, you might as well use a stungun for ignition. Get the C:B ratio right (it may be but I don't feel like counting right now) then have at it.
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Unread postAuthor: MortarArmy » Wed Sep 26, 2007 7:15 pm

well, i havent seen anything definative on c:b ratios, i see a crap load of numbers floating around on whats best, but no mention to why or what application. My C:B ratio and fuel were "perfect" on my last gun according to one of the calculators i saw, but when i fired it, i got crap range. doubled the barrel length to like a 2:1 ratio and i got 2x the range
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Unread postAuthor: jimmy101 » Thu Sep 27, 2007 10:07 am

MortarArmy: If the gun performed better with a 2:1 CB then there is something odd about the gun.

What were the specs; Chamber and barrel dimensions, spark type, fan, ammo etc?

IIRC, "squirt and screw" (aka "spray and pray") guns often work a bit better at high CB ratios. Add a fan and the optimal CB will drop into the range of 0.6 to 1.0.
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Unread postAuthor: williamfeldmann » Thu Sep 27, 2007 10:40 am

I agree with the spark comments, more is better and you are on the edge of a big chamber. If you are looking for range add some sparks.

Your chamber should be in the vicinity of 1:1 with the barrel, a little lower with a good fan. Most numbers I see are pretty close to .8:1 c:b.

@speedycicada
BC arms has sdr21 sleeved barrels. I have seen the 2 inch in 2 inch before and I don't like them either, besides wouldn't that be more expensive than just getting sdr 21.
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Unread postAuthor: MortarArmy » Thu Sep 27, 2007 5:58 pm

this next gun is going to have a big ass mofo of a fan, thing sounds like a vacuum cleaner when its running.

how does ammo type, fan speed and spark effect c:b ratio? golfball's are a very consistant predictable ammo, high speed fan should mix things very well, although im thinking ill have to turn it off prior to firing or risk blowing out the spark or making it too turbulent. Maybe ill do speed controller on the fan circuit.
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