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injector question

Unread postPosted: Sun Jun 22, 2008 7:18 pm
Author: rp181
Wasn't sure if this should be here or non-spudgun releated, but here it is:

I was wondering if i would get any significant increse in speed if i did the following:
Original design was a 1/2in x 1/2in square bore, 1ft long. The air tank would be as a 3:1 chamber barrel ratio, the valve being a triggered burst disc.

Would i get any noticable increse if i made the bore 2ft. long and made the chamber larger to fit the 3:1 ratio? Off course it will help some, but by how much? I plan on using it at 60-100PSI (unregged co2 if i get the chance)

Unread postPosted: Sun Jun 22, 2008 7:25 pm
Author: SpudFarm
should be twice as much.. (don't take my word on it)

Unread postPosted: Sun Jun 22, 2008 7:27 pm
Author: rp181
O.o that would be nice.

Unread postPosted: Sun Jun 22, 2008 7:30 pm
Author: TwitchTheAussie
Some pictures would be nice. But Im guessing at an almost double output.

Unread postPosted: Sun Jun 22, 2008 7:31 pm
Author: rp181
i didnt make anything yet, still planning.

Unread postPosted: Sun Jun 22, 2008 7:31 pm
Author: SpudFarm
why have pics? he gave us all details.

Unread postPosted: Sun Jun 22, 2008 7:47 pm
Author: Lentamentalisk
the faster your projectile gets going the less of an increase you will get from an overall size increase

Unread postPosted: Sun Jun 22, 2008 7:55 pm
Author: DYI
I'm hoping that when you said CO2, you really meant helium or hydrogen, because the SOS in CO<sub>2</sub> is horribly low, and you're just wasting your time using it in something like a railgun injector.

My (very) limited knowledge of railguns tells me that efficiency increases as injection speed increases. You'll be making much better use of your hard-earned capacitors if the injector does 3000fps than if it does 800 (as fast as you're going to get with CO<sub>2</sub>.

Unread postPosted: Sun Jun 22, 2008 9:30 pm
Author: rp181
capacitors arn't all that hard earned, *a company* is donating :wink:
As for helium or hydrogen, where can i get some? how much pressure is in those party balloon tanks? Hydrogen doesn't seem like a good idea, with plasma everywhere =) helium will help quench arcs though.

How about nitrogen?

Unread postPosted: Mon Jun 23, 2008 6:07 am
Author: Ragnarok
spudfarm wrote:should be twice as much.. (don't take my word on it)

Decent attempt, but not quite.
Assuming all else is equal, energy will double - speed will increase by slightly over 40%.

However, all else is not equal. CO2 is not good for high velocities, because it's very dense with a low speed of sound.
There will be a significant struggle to surpass 800 fps with CO2, and even then 800 will be hard.

Of course, if you really want to be super mad, you could use an electrothermal cannon as an injector, which essentially removes such velocity limits with thermal brute force - and you could actually completely bypass rail damage if you were clever enough about it.

Would need more capacitors though. :twisted:

Unread postPosted: Mon Jun 23, 2008 9:15 am
Author: rp181
Rag:

Thats not a bad idea :P . Ile see if *the company* will give additional smaller caps to make an ETG injector.

Unread postPosted: Mon Jun 23, 2008 2:00 pm
Author: rp181
I was thinking, for ETG, if i did that, i would use about 1KJ, no chamber, the back of the railgun is blocked by 1/2in alu plate, with a sparkplug, fuel would at the bottom.

My worry is the plastic around it, the bore, would melt. What plastic should i line it with? i was thinking high density polyethylene, or 1/16in carbon fiber.