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I wanna break the sound barrier!

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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I wanna break the sound barrier!

Unread postAuthor: Callipygous » Tue Jul 06, 2010 1:53 am

Ok, maybe that doesn't sound like the smartest title, but it properly expresses my enthusiasm.

My goal is to build a spudgun that is capable of throwing something at the speed of sound. I am curious if someone experienced can tell me roughly what is required to make that happen. That is, can it be done with a purely pneumatic gun, or is combustion/hybrid required to have a reasonable chance? can it be done with air, or would i need to use a higher performing gas? I'm guessing it couldn't be done with plastic, and I would probably have to use something that can withstand higher pressure. Can a basic (if overgrown) piston valve gun pull this off? Is it totally unreasonable, and requires serious amounts of engineering and tens of thousands of dollars? Whats the general outlook on something like this?

I posted this in Pneumatic because my preference is to do it without combustion.
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Re: I wanna break the sound barrier!

Unread postAuthor: velocity3x » Tue Jul 06, 2010 2:26 am

Callipygous wrote:My goal is to build a spudgun that is capable of throwing something at the speed of sound. I am curious if someone experienced can tell me roughly what is required to make that happen.


Welcome to SF, Callipygous

Some work, money, metal parts, much luck and high pressure.
Golf ball @ Mach 1.04 / 700psi Nitrogen.
Not a good idea with off the shelf plastic parts.
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Unread postAuthor: 6T6FR302 » Tue Jul 06, 2010 2:38 am

Shouldn't be too hard with a small bore hybrid. Theres lots of em here that i see. Go 6mm bb's.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 06, 2010 2:46 am

I had come close with compressed air at 400 psi and a burst disk valve, have a look.

There are commercially available pneumatic rifles that exceed the speed of sound using compressed air, such as the Airforce Condor.

You basically need a high chamber:barrel ratio, as long a barrel as you can manage, and as fast a valve as you can manage. The projectile should also be light and as tight fitting/friction free as possible. To greatly increase your chances, you should use a gas that is less dense than air. Nitrogen is marginally less dense, but your best bet is to use Helium.

A well engineered piston valve (optimised - minimum pilot volume, high speed/flow pilot valve) should serve your purposes if coupled with a low density gas at reasonably high pressure.
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Unread postAuthor: Technician1002 » Tue Jul 06, 2010 3:14 am

It is possilbe with a piston cannon, but a very fast high flow valve with a light projectile and light gas at reasonable pressure will do it. A light gas due to comprssion heating or gas selection can work.

An air driven piston into a springer configuration may achieve SOS as well as a burst disk with Helium at about 200 PSI and a lightweight projectile. Neither requires serious amounts of engineering and tens of thousands of dollars.

Is there a reason to try for SOS? Is this for a project for something or just a personal quest?

These guys have clocked some marshmallows at over SOS with a sprinkler valve air cannon. It is possible without huge expense.
http://www.honkernet.net/AHS/departmental/Robotics_engineering/09-intel-blazer_tech-challenge.htm

I have not clocked the marshmallows out of my little launcher, but when they hit a can of soda pop, it splits the can wide open. I still need to clock them.
[youtube]http://www.youtube.com/watch?v=TW3bUP-Fov4[/youtube]
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Unread postAuthor: Stolly32123 » Tue Jul 06, 2010 7:12 am

I know im a noob. but i dont think you could do it. If you did it would cost a lot of money and take a lot of effort.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 06, 2010 7:26 am

Stolly32123 wrote:I know im a noob. but i dont think you could do it. If you did it would cost a lot of money and take a lot of effort.


... yet folks with a bit more experience have amply illustrated that it is indeed a feasible exercise, without excessive effort and financial outlay if the correct parameters are observed ;)
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Unread postAuthor: deathbyDWV » Tue Jul 06, 2010 9:38 am

jackssmirkingrevenge wrote:
Stolly32123 wrote:I know im a noob. but i dont think you could do it. If you did it would cost a lot of money and take a lot of effort.


... yet folks with a bit more experience have amply illustrated that it is indeed a feasible exercise, without excessive effort and financial outlay if the correct parameters are observed ;)


Never try to argue with the amazing power of JSR or Tech...
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Unread postAuthor: Technician1002 » Tue Jul 06, 2010 10:32 am

OK, I'll admit that it will take lots of effort and money, but it can be done for a little less than $10,000. The Arlington team does it for less than $100 not counting the air compressor.

They are claiming this speed on their site.
961 Miles per Hour = 1409.4666666666667 Feet per Second

Is this an orange with a sonic boom? The launcher that launched the orange used less than $100 in parts.

Image

Jet Sonic Boom

Image
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 06, 2010 10:40 am

deathbyDWV wrote:Never try to argue with the amazing power of JSR or Tech...


Au contraire, *do* argue, but at least on some scientific basis ;)

Is this an orange with a sonic boom?


I would argue that it's more likely condensed water vapour coming out of the barrel at a higher velocity than the orange and deflecting outwards...
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Unread postAuthor: Technician1002 » Tue Jul 06, 2010 10:46 am

The chrony the orange is over agrees with you. It's really about 800 FPS.
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Unread postAuthor: urgle the danish cow » Tue Jul 06, 2010 10:59 am

you could increase speed not only by sheer air force with large valves and air chambers but by experimenting with different barrel lengths to find the optimum for you cannon, also you should experiment with different ammuntions such as tighter fitting projectiles, take aerodynamics into account, and different weights as lighter weights will usually increase your speed but the extreme causes inefficiency in your discharge.
just something to think about
cheers good luck.
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Unread postAuthor: saefroch » Tue Jul 06, 2010 10:59 am

And that cloud on the jet isn't a "sonic boom" it's just condensation that's produced by the turbulence across the wings and fuselage at very high speeds. So far as I know, it has little to do with breaking the sound barrier.

Just thought I'd interject that...
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 06, 2010 11:21 am

urgle the danish cow wrote:inefficiency in your discharge


That sounds revolting :)

by experimenting with different barrel lengths to find the optimum for you cannon


Really if you're going for ultimate performance, the barrel should be as long as possible and the chamber as big as possible, so as big as you can make them.

lighter weights will usually increase your speed but the extreme causes inefficiency in your discharge


I think what you mean is that a light projectile gives a good muzzle velocity, but over longer range will lose velocity more quickly than one with a better ballistic coefficient.
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Unread postAuthor: Technician1002 » Tue Jul 06, 2010 11:55 am

Too long of a barrel hurts performance. I have a page on trimming the length of a barrel to peak performance for a pressure, chamber size, and projectile mass. We trimmed a barrel for peak performance with a 3 gallon chamber, 60 PSI, and a rolled up t shirt. A 7 foot barrel out performed the 10 foot barrel. Longer does not always mean better. There really is an optimum barrel for your chamber, valve, pressure, and projectile combination.


As far as projectiles go, I can launch a marshmallow at nearly the speed of sound, but I can't launch it the length of an American football field. I can launch a golf ball several football fields distance only using 1/2 the speed of sound.
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