SpudFiles

Okay so I am currently in the process of making my third cannon. My first was the basic potato cannon with hairspray and a piezio bbq igniter, then I made a small pneumatic, and now I am making another combustion.

I have a few questions.

1) Will a propane torch work well as a spray and pray type fuel? I think it will because it has a little hole where it premixes with air.

2) What kind of chamber pressure could I reach with propane as fuel? Also thinking of MAPP, as I have a few bottles laying around (compatible with same torch).

3) Will a regular BBQ igniter ignite the propane/air mix reliably? It did not do so well with hairspray, although I believe propane will yield better results.

4) What chamber size should I use if I go with a 1/2" barrel? Will 2" wide and 6" long do it?

5) How loud will a setup like this be?

Propane and mapp gas tend to work better if you use a chamber fan. Your bbq ignitor should have worked fine, so you either had a bad one or did something wrong, it should be fine, if not a lantern sparker will work. In my opinion the chamber you listed is way too small, try at least 4 inch wide by 12 inch long. Yes the torch will work, and so you know, a main ingredient in hair spray is propane, which is why hair spray works so well!! Welcome to the forum!!!!

frozenveinz wrote: 1) Will a propane torch work well as a spray and pray type fuel? I think it will because it has a little hole where it premixes with air.

Consider syringe metering for a much more reliable, consistent and powerful setup, especially since you're using a relatively small bore and chamber.

2) What kind of chamber pressure could I reach with propane as fuel? Also thinking of MAPP, as I have a few bottles laying around (compatible with same torch).

Not more than 100 psi or so

3) Will a regular BBQ igniter ignite the propane/air mix reliably? It did not do so well with hairspray, although I believe propane will yield better results.

An accurately metered mix should ignite every time.

4) What chamber size should I use if I go with a 1/2" barrel? Will 2" wide and 6" long do it?

Depends, how long is your barrel?

5) How loud will a setup like this be?

Again, depends on barrel length - shorter barrels tend to be louder.

Barrel will be 36" long. And I'll try doing syringe metering.

Like mattyzip77 said to get a consistent shot you need to use a chamber fan. This means you can fire at all angles as the gas doesn't sink to the back or front when you tilt it and provides the gun with a much more equal blast.

How do you install a chamber fan? Just glue it inside or what?

frozenveinz wrote:Barrel will be 36" long.

For ideal performance using 2" diameter tubing for your chamber, 2 inches chamber length will be more than enough for optimum performance.

And I'll try doing syringe metering.

Some more advice from Jimmy's page here: http://www.inpharmix.com/jps/Fuel%20Met ... ghter.html

Like mattyzip77 said to get a consistent shot you need to use a chamber fan. This means you can fire at all angles as the gas doesn't sink to the back or front when you tilt it and provides the gun with a much more equal blast.

A chamber fan definitely aids consistency, especially with larger chambers (not the case here) but no amount of mixing will help if your fuel:air ratio is off, that's the fundamental parameter that should be seen to first.

frozenveinz wrote:Okay so I am currently in the process of making my third cannon. My first was the basic potato cannon with hairspray and a piezio bbq igniter, then I made a small pneumatic, and now I am making another combustion.

I have a few questions.

1) Will a propane torch work well as a spray and pray type fuel? I think it will because it has a little hole where it premixes with air.

2) What kind of chamber pressure could I reach with propane as fuel? Also thinking of MAPP, as I have a few bottles laying around (compatible with same torch).

3) Will a regular BBQ igniter ignite the propane/air mix reliably? It did not do so well with hairspray, although I believe propane will yield better results.

4) What chamber size should I use if I go with a 1/2" barrel? Will 2" wide and 6" long do it?

5) How loud will a setup like this be?

Well as for the chamber:Barrel ratio, I like to stay within 6:1 and 2:1. Longer cannons typically require a larger chamber. With 2 inch chamber, I reccomend that the chamber be about 1 foot long and the barrel can be up to 3 feet long (if 1/2 inch barrel is used). Gas combustion guns can be this long but should have a chamber fan and rear ignition. Either gas will work, but the tank may look too big, so butane would be better in my opinion if you could meter it well. Well metered gases are easy to ignite with any piezo igniter, but electric igniters last much longer. The design i outlined should be relatively quiet, and more of a "poomf" sound if you use a simple supressor.

Bias_P11 wrote:Well as for the chamber:Barrel ratio, I like to stay within 6:1 and 2:1

Anything above 1:1 is going to be bad for performance, for a combustion you want the chamber to be between 0.9 and 0.5 times the barrel volume.

With pneumatics, bigger chamber = more performance, although to a certain degree, but combustion cannons on the other hand do have an optimal chamber size for a given barrel length.

jackssmirkingrevenge wrote:

Bias_P11 wrote:Well as for the chamber:Barrel ratio, I like to stay within 6:1 and 2:1

Anything above 1:1 is going to be bad for performance, for a combustion you want the chamber to be between 0.9 and 0.5 times the barrel volume.

With pneumatics, bigger chamber = more performance, although to a certain degree, but combustion cannons on the other hand do have an optimal chamber size for a given barrel length.

Ive thought about that but to my experiences, it is possible to get a larger chamber if the chamber is longer, and is more forgiving to less than optimal fuel mixtures.

jackssmirkingrevenge wrote:Anything above 1:1 is going to be bad for performance, for a combustion you want the chamber to be between 0.9 and 0.5 times the barrel volume.

With pneumatics, bigger chamber = more performance, although to a certain degree, but combustion cannons on the other hand do have an optimal chamber size for a given barrel length.

I would rather say that there is a optimal barrel length for a given chamber volume.
The 0.8:1 was found to have the highest performance from a test with variable barrel lengths.

It could be that a larger chamber would have performed the same or better with the same barrel as the small chamber. Or am I wrong?

Labtecpower wrote:I would rather say that there is a optimal barrel length for a given chamber volume.

That's just a different way of saying the same thing.

It depends what your governing parameter is.

According to HGDT muzzle velocity increases when the chamber gets larger with fixed barrel length.







With such high C:B ratio's the efficiency suffers however, so I would stick to the 0.8:1 ratio

Labtecpower wrote:According to HGDT muzzle velocity increases when the chamber gets larger with fixed barrel length.

... by 6 m/s, given the limitations of HGDT I don't think that's *quite* so significant

jackssmirkingrevenge wrote:... by 6 m/s, given the limitations of HGDT I don't think that's *quite* so significant

And that's entirely true, so I will stop blabbering