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reaching the speed of sound (summer Project)

A place to ask general spud cannon related questions.
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reaching the speed of sound (summer Project)

Unread postAuthor: jerb » Mon Jul 17, 2006 2:10 am

Hello there! Its summer and that means its time for yet another devilishly destructive project to keep me busy. This year it comes in the form of a supersonic golf ball! (Well, at least that’s the plan)

Here’s the premise:
The goal of this project is to have the projectile (golf ball) reach the speed of sound when exiting the barrel

now I live right on the shoreline of CT, long island sound is a stones throw from my house, I plan on setting my cannon up there on a private dock and remotely firing this (If its going to be loud I will let the police know before firing). Proper safety will be exercised at all times

I’m hoping to use Air though I have no problem using propane, helium, or CO2
I have about $200 to put into this project but that amount can go up if absolutely necessary


Onto the body of this post:
Knowing that the speed of sound is 340.29 m / s or 1116.435 F / S
I have a feeling I must use a very low C: B ratio but have a very long barrel (>5 FT)

Here’s what I'm not sure of, at 100 PSI I'm not sure this is even possible using compressed air. I have access to very nice, very fast solenoid valves and can easily parallel 5 or 6 so they won’t impede flow.

If propane is needed (or helium, CO2, etc) I *think* this is what you guys are calling Hybrid cannons. I can’t find much information on these, or where to start with these gases (I've only made pneumatic cannons so far)

I would appreciate any links or places to start off. Your opinions and expertise on this subject matter would be much appreciated as would your input as to the feasibility of this project as a whole.

Best regards,
Jerb
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Unread postAuthor: carlbelcher » Mon Jul 17, 2006 3:17 am

Just so you know a hybrid cannon is a combustion cannon that uses compress air and a burst disc to allow a higher air/fuel ratio, sometimes in multiples up to six times. Hybrid cannons are not for spud gun noobs and even for experts can be dangerous. Breaking the sound barrier with a spud gun is not something that is easy to do, and has only been done couple times, But good luck!
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Unread postAuthor: WOW!! » Mon Jul 17, 2006 4:37 am

Yea, I would suggest a Hybrid too.
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Unread postAuthor: jerb » Mon Jul 17, 2006 6:59 am

other than stepped up saftey precautions is ther anything special needed for a hybrid?

I can weld pipe if need be.


after reading all the material i can find here on spudtech i have only a few more questions:

what kind of PVC are people using? it has a dark grey color to it, I've heard cpvc mentioned but im not sure if this is it.

does this thing count as an explosive or something that i would require a permit for?

I understand the risks involved and that a mistake on my part may result in my death or maiming and am willing to take that responsibility. safty precaustions will be taken to extremes whenever i deal with this project.
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Unread postAuthor: Mihlrad » Mon Jul 17, 2006 8:38 am

For a hybrid you need SCH 80 pvc pipe, yes it is grey colored. sch 40 is not your safest choice due to the fact that the power of a strong mixture in a hybrid, can grenade it which would send high speed shrapnel all over the place possibly being fatal.

You dont seem to really know what a hybrid is so i will explain.

(plz feel free anyone to correct my errors)

A hybrid is a launcher that is essentially a combustion, it uses metered propane, some kind of spark for ignition, and of course, makes a loud bang ^^. But the real reason it is a hybrid is because along with the metered propane, it uses metered air to allow the use of more propane.

-Propane, in order to combust requires a certain amount of oxygen, if you have too much propane and too little oxygen, simply nothing happens. By injecting more air, you gain more oxygen in your chamber, which allows for more propane to be used. The addition of more oxygen can allow for up to 4x more propane. (if you see anyone say something like 1x mix , 2x mix etc, this is what they mean) This is why a hybrid is insanely dangerous for a person who is not a complete expert on all spud guns.

The knowledge required to make one of these amazingly powerful launchers:
-knowing how to make a remote starting system (way too dangerous to launch standing near it)
-Knowing how to wire a stun gun for a spark (u can use other methods, but with a stun gun you will be much much safer because it is surefire.
-How to make a propane metering sytem
-How to make an air metering sytem
-Ballistics and physics knowledge (how to calculate everything to ensure less chance of failure)
-Everything about combustions and how they work
-Everything about pnuematics and how they work
-Knowing how to make a burst disc setup

Theres more but i dont know what to put. Basically if you dont really know what a hybrid is yet, and please do not take offense to this, for your own safety reframe from building one.
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Unread postAuthor: jerb » Mon Jul 17, 2006 9:01 am

as informative as that post was I did know most of that regardless im thankful you guys are so hesitant


I notice your a firefighter, Im a firefighter too :D got my emt-1 aswell :D

external firing boxes are easy as anything to make. I ahve a few setup for lighting off fireworks with NiChrome wire come 4th of july. made a cool one with a PIC to control several bottle rockets along side a fountain and mortars :D

why use a stun gun when i can use a flyback with a solid state driver?

metering systems are easy, two valves to partition off a section of pipe thats been calculated to have a specific area^3 to give optimal mix (I beleive propane will ignite @ 4.6%)

iirc O2 is precent in STP @ ~20% where as nitrogen makes up 70% and misc other gases constituting the remaining 10%

im quite familiar with combustion (firefighter 1) and am no stranger to pnuematics.

I cannot stress how much saftey is involved in this. remote fire will definatly be present (100'?) along with ear and eye protection (I wear these even with the little guns) . the gun itself will be fired on a private dock, beach will be clear 250' in every direction. I am quite aware that PVC will shatter and will almost certainly be deadly in this scenerio.

I admitt I am not familiar with burst disks though, if you still feel that i am underprepared for this project (who knows maybe im too headstrong on this one) then by all means tell me again knowing my background. my basic understanding of burst disks is simply a disk fashioned from a soda bottle or foil placed infront of the chamber sealing it from the barrel. air and propane are metered in and then ignited using a sparksource. the combustion blows the burst disk apart/outof the way so it doesnt limit flow along the full brunt of the explosion to propel the projectile out of the barrel
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Unread postAuthor: mark.f » Mon Jul 17, 2006 9:03 am

I say stick to pneumatic. If you don't know what a hybrid is, then don't fool with them.

The lighter the mass of your gass, (Helium and Hydrogen are the two lightest gases), the better your chances. This is because the local speed of sound inside the launcher is hightened, allowing the projectile to accelerate past the speed of sound OUTSIDE the gun while remaining below the speed of sound INSIDE the gun, allowing it to accelerate without the effects of the sound barrier.

Onto the materials, I would also use a much longer barrel, (more than 5'). This will require some skill to make the barrel extenders to join your 10' sections, (unless you got a 20' section).

I would also make the chamber SCH-80. For these speeds you'll want more than just 100 psi, (but not more than 150 or so).

I would also suggest placing a light burst disk, (bursts at 20 psi and is made from some sort of plastic), at the end of the barrel and then evacuate the barrel using a vaccuum pump. The fit between the golfball and the barrel shouldn't be piston perfect, so air will be able to escape from behind the golfball also.

Good luck! I know we can't talk about it here, but there are a lot of other ways to break the sound barrier besides a spudgun.
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Unread postAuthor: x.X.Cpt.Rollhart.X.x » Mon Jul 17, 2006 9:11 am

And dont think that all gray colored PVC are SCH80 because you can buy grey SCH40 ... And good luck to reach the speed of song with 200$ ...

The hybrid has been designed by DR. For a perfect ignition in a combustion, you need 4.03 % of propane in your chamber. This is for 1 atmosphere (14.7psig). If you put 8.06% of propane in your chamber, you need 2 double the pressure inside than you add an atmosphere (15 psig round ). You keep the air inside the chamber via a burst disk, it may be a lot of stuff (aluminium sheet, plastic ..)the burst disc is inserted in a union or in a camlock. for exemple, in a 2" camlock, 1 layer of aluminium sheet, hold 8 psig than if you make a 3X mix(12.09 % and 30 psig) you need 4 layer of aluminium to hold the pressure before the ignition. And when the ignition is done, the aluminium will burst and the pressure will shoot your projectile. You put the perfect amount of propan via a propane meter, you need to do some calculation to have a good propane meter.
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Unread postAuthor: frogy » Mon Jul 17, 2006 9:52 am

Hybrids must use All Sch 80 PVC Pipe and Fittings if you use PVC (it's normally Grey)...

A metal Hybrid is safer, but a Sch 80 one isn't exactly dangerous, the unions have blown up though (a part by the barrel which the burst disk is placed in)...

Hybrids must be remotely detonated if you are using a 3x + mix (which you would be if you wanted speed of sound)

Hybrids need multi-spark gap stun gun ignitions to work good...

Hybrids also need a fuel meter regulator, an air regulator setup and normally a fan inside of them to mix the fuels....

Just the Fuel Meter, stun gun setup, fan setup, and remote ignition of a Hybrid would probably get you very close to your $200 budget, and then you need to make the actual gun...

I'd reccommend a BIGASS pneumatic with a Pneumatically Actuated Supah-Valve.... Here's the one Joel made that went over the sound barrier...

<img src="http://spudtech.com/images/products/UOkcannonfull.jpg">

And note that a Pneumatically Actuated Supah Valve is going to cost $150+
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Unread postAuthor: x.X.Cpt.Rollhart.X.x » Mon Jul 17, 2006 10:01 am

frogy wrote:Hybrids must use All Sch 80 PVC Pipe and Fittings if you use PVC (it's normally Grey)...

A metal Hybrid is safer, but a Sch 80 one isn't exactly dangerous, the unions have blown up though (a part by the barrel which the burst disk is placed in)...

Hybrids must be remotely detonated if you are using a 3x + mix (which you would be if you wanted speed of sound)

Hybrids need multi-spark gap stun gun ignitions to work good...

Hybrids also need a fuel meter regulator, an air regulator setup and normally a fan inside of them to mix the fuels....
Just the Fuel Meter, stun gun setup, fan setup, and remote ignition of a Hybrid would probably get you very close to your $200 budget, and then you need to make the actual gun...


you dont need a multi spark gap in a hybrid :roll:

And you dont need a fan either. by adding compressed air in your chamber, you will mix the fuel. people add fan to their hybrid to ventilate the chamber after shooting. but if you want, you can only shoot air in your hybrid via the air entry and that will ventilate your gun ...
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Unread postAuthor: jerb » Mon Jul 17, 2006 11:40 am

I have all the parts on hand to make the metering and firing systems (+/- a ball valve or two)

If it can be done with air (such as with Joels cannon) I will use that (safer?) route.

Thanks you all for your patience and understanding toward my stubbornness

*a quick edit* is there any mroe information regarding the cannon you posted the picture of? i looked around on joels forums but couldnt find any information about it
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Unread postAuthor: frogy » Mon Jul 17, 2006 12:45 pm

I don't know, but I believe the chamber is like 5"? 4" maybe and the barrel is at least 10ft of 2"

I know you need a Supah valve or some other great state of the art valve to do it with Compressed air, but it's also possibly with a dinky gun and hydrogen...

A pneumatic isn't really a safer route, it's just easier... Hybrids cant hurt you because you remotely detonate them, and none has actually exploded, the union just blows up someimtes, which is because the union is the weakest part of the gun, even if it is Sch 80...
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Unread postAuthor: x.X.Cpt.Rollhart.X.x » Mon Jul 17, 2006 1:18 pm

Dont use an union, they are weak. Use a camcoupling.
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Unread postAuthor: benstern » Mon Jul 17, 2006 1:27 pm

Speed of sound is not 1116.435 The speed of sound in air is dependent on temperature. http://www.sengpielaudio.com/calculator-speedsound.htm
As far as propellent goes, you best use Hydrogen as it is the ultimate pneumatic launcher propellent.
Also, you would be smart to use a combonation of GGDT and launcher range calc.

Also, use an actuated burst disc in a metal union for the best preformance.
The DOBA cannon I am making can launch a golfball to mach 2.053 at a temperature of 100 degrees Fahrenheit.
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Unread postAuthor: Darkerweb12 » Mon Jul 17, 2006 7:49 pm

I suggest you learn alot more about what you are trying to build. Build a few pneumatic cannons and combustion cannons so you can learn the pros and cons of both. I suggest you wait until next summer to build your big gun, so you can get better at actually building spudguns. If you are trying to build a gun that will break the sound barrier, it NEEDS to be well constructed.

There are many variations on both types of cannon, and I would personally use a pneumatic. They are much more predictable, safer, and quieter.

On a hot day, the air molecules are spread out, so sound moves slower, which means it will be easier for you to break the sound barrier. But seeing as you live right next to the ocean, the extra water in the atmosphere may make it harder for you to break the sound barrier...

In any case, I suggest you wait until next year or until you can reliably make a safe gun.
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