New guy here. Chamber design question (venturi design)

[TideJoe]

I'm in the process of gathering info/parts for a 2.5" cannon for tennis balls. I've got a friend that has a cannon that he uses to shoot golf balls. In the past, he had a 4" chamber (roughly 20" long) and got good distance using an aerosol propellant (Tag body spray). Now, he uses a venturi shaped chamber design and gets a lot more distance (around 1800 feet). He uses a lantern spark igniter in the cap of a cleanout.

Have any of you guys tried this chamber design using direct propane injection?

Rough look at the chamber design is attached. I'm estimating that the chamber is 2 feet in total length and the 1.5" sdr 21 barrel is 45" in length.

Thanks for your help.

[ALIHISGREAT]

So this would increase turbulence and therefore there would be more fuel ignited? its the only way i can see it working...

My understanding of the venturi effect was that it increased the speed of a fluid.. but decreases the pressure...

[TideJoe]

So this would increase turbulence and therefore there would be more fuel ignited? its the only way i can see it working...

My understanding of the venturi effect was that it increased the speed of a fluid.. but decreases the pressure...

I guess it's behaving as a fan during combustion (mixing air and fuel). I have witnessed the extra power though. It's guess it's also likely that the decreased volume from using reducing couplers (instead of a straight 4" chamber) also helped increase the pressure?

For the purposes of building my 2.5" gun, if I get my C:B ratio right, there's really no reason to go with the venturi chamber design. I don't plan on using a fan at first, but may add one later.

[Biopyro]

While it would increase the surface area (therefore losing performance to heat loss), the first funnel would create a high(er) speed jet of burning fuel through the gun, as well as igniting the side branches on it's path. This would perhaps eliminate the need for multiple ignition points and a fan.

I don't think you're getting the full benefit of the venturi effect at the barrel in that picture, because you're suddenly blocking the air's passage. Either make the barrel the same size as the chamber, or make it a conical shape leading to the barrel (like a bell reducer).

[TideJoe]

While it would increase the surface area (therefore losing performance to heat loss), the first funnel would create a high(er) speed jet of burning fuel through the gun, as well as igniting the side branches on it's path. This would perhaps eliminate the need for multiple ignition points and a fan.

I don't think you're getting the full benefit of the venturi effect at the barrel in that picture, because you're suddenly blocking the air's passage. Either make the barrel the same size as the chamber, or make it a conical shape leading to the barrel (like a bell reducer).

He actually has a 4" x 2" reducer coupling at the end of the chamber, I just left it out by accident. I want to use propane injection, but don't want to deal with fans and electronic ignition. I might decide to roll with this venturi idea afterall.

[MrCrowley]

and gets a lot more distance (around 1800 feet).

Well for starters, he's definitely not shooting 1800feet.

[TideJoe]

and gets a lot more distance (around 1800 feet).

Well for starters, he's definitely not shooting 1800feet.

He most certainly is..... (well, 1770 measured via GPS). We shot the balls on a grass runway and the longest ball traveled 1770 feet. Most fell in the 1500 foot range, but consistently over 1500.

[rcman50166]

Yes I found that number strangely skeptical. My General can theoretically make a 2500 ft shot with a 500 g projectile at an ideal 45 degrees and that gun is huge.

As far as my input on the actual topic, interesting idea. Its not the first time I've seen it though. Others claim to have "multiple chambers" when its two chambers in series, but not far off from what you're describing. I'll get back to you on that.

[starman]

and gets a lot more distance (around 1800 feet).

Well for starters, he's definitely not shooting 1800feet.

I can easily see a golfball shooting that far, my shots with trip thunder are in the half mile or better zone.

However Tide Joe, this is an interesting concept. You are losing a good bit of chamber space and therefore energy and adding some complication to the chamber body build. I can see this offering some turbulence advantages over a plain straight chamber but not anymore than you get by adding a fan.

Why wait on the fan install?...the best, most effective add-on you can have on your cannon.

Welcome to Spudfiles! Any studies you can do regarding this shape would be highly received.

[Pilgrimman]

I could see 1800 feet happening if there was a strong wind and a light projectile... It sounds like a good design! I wonder how it would do in a hybrid

[MrCrowley]

and gets a lot more distance (around 1800 feet).

Well for starters, he's definitely not shooting 1800feet.

He most certainly is..... (well, 1770 measured via GPS). We shot the balls on a grass runway and the longest ball traveled 1770 feet. Most fell in the 1500 foot range, but consistently over 1500.

I've never heard of a golfball going further then 450m from a cannon so small. Even with a huge cannon, golfballs can struggle to go further though I know a few members have pushed them over the 500m mark, or at least can.

and gets a lot more distance (around 1800 feet).

Well for starters, he's definitely not shooting 1800feet.

I can easily see a golfball shooting that far, my shots with trip thunder are in the half mile or better zone.

Aside from the fact that you're using a burst disk and a better fuel, I still can't see a golfball travelling 800m (half a mile) from anything 1x mix combustion. Maybe this venturi effect can make all the difference but it appears he's using the 'spray and pray' method, with a single spark from the rear and a slightly above average barrel length.

[TideJoe]

Well for starters, he's definitely not shooting 1800feet.

He most certainly is..... (well, 1770 measured via GPS). We shot the balls on a grass runway and the longest ball traveled 1770 feet. Most fell in the 1500 foot range, but consistently over 1500.

I've never heard of a golfball going further then 450m from a cannon so small. Even with a huge cannon, golfballs can struggle to go further though I know a few members have pushed them over the 500m mark, or at least can.

Well for starters, he's definitely not shooting 1800feet.

I can easily see a golfball shooting that far, my shots with trip thunder are in the half mile or better zone.

Aside from the fact that you're using a burst disk and a better fuel, I still can't see a golfball travelling 800m (half a mile) from anything 1x mix combustion. Maybe this venturi effect can make all the difference but it appears he's using the 'spray and pray' method, with a single spark from the rear and a slightly above average barrel length.

I'm the new guy and won't even begin to claim to understand the specifics as well as you veterans. However, this gun can consistently reach 1500 feet and has hit a max of nearly 1800 feet (with a golf ball). If it helps any (in convincing you), we are using 'Tag Body Spray' which seemed to have a lot more power than the hairspray that we used in the past.

[rcman50166]

Ok here I have a kind of simulator. I already know there are some things wrong with it but it's just a visualization. But I designed both kinds of chambers in a side by side comparison. I haven't really made any assumptions off of it but maybe you can find some value.

[youtube][/youtube]

[starman]

Aside from the fact that you're using a burst disk and a better fuel, I still can't see a golfball travelling 800m (half a mile) from anything 1x mix combustion. Maybe this venturi effect can make all the difference but it appears he's using the 'spray and pray' method, with a single spark from the rear and a slightly above average barrel length.

And yet, it does. Potato and tennis balls shots are nothing significantly different than your average spud cannon, but my golf ball shots are something to behold. I gauge my distance based on a known quarter mile marker and 45 degree shots are still rising at that point. However, I have yet to actually find and mark the resulting shot. I've been thinking about a dusk shot with a glo-golf ball to help the process.

@rcman: were you actually modeling propane flame and pressure fronts there or just throwing together a pretty animation?

[TideJoe]

Aside from the fact that you're using a burst disk and a better fuel, I still can't see a golfball travelling 800m (half a mile) from anything 1x mix combustion. Maybe this venturi effect can make all the difference but it appears he's using the 'spray and pray' method, with a single spark from the rear and a slightly above average barrel length.

And yet, it does. Potato and tennis balls shots are nothing significantly different than your average spud cannon, but my golf ball shots are something to behold. I gauge my distance based on a known quarter mile marker and 45 degree shots are still rising at that point. However, I have yet to actually find and mark the resulting shot. I've been thinking about a dusk shot with a glo-golf ball to help the process.

I'm sure this is going to sound extremely stupid, but the way we measured ours was shooting over a grass runway. The first few shots we never found so I decided to ride down the runway in an ATV and communicate with the shooter via cell phone. When he shot, he gave me a basic heading of the ball and I tried to locate the landing (as long as it wasn't heading for me). If it was heading anywhere near me, I got on the ground behind the ATV.