Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 57 users online :: 4 registered, 0 hidden and 53 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

dead space

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.
Sponsored 
  • Author
    Message

dead space

Unread postAuthor: PVC Arsenal 17 » Thu Jul 09, 2009 7:37 pm

I've run into a flaw in my most recent pneumatic nerf gun configuration.

There will be, no matter much I move stuff around, 3" of dead space between the outlet of the valve and the dart. The diameter of the space is 0.572", making for a dead volume of about .771 in^3.

Since I can't get GGDT to run on my computer for whatever reason (like I'd be able to figure it out anyway...) I'm going to post as many facts about the parts used and if at all possible, someone please work out the numbers for me and tell me if my design will suffer any significant decrease in performance compared to if there was no dead space. It would be very much appreciated.

Known valve specs:
Exhaust Time: 100 cubic inches in 2 seconds
Flow Rate: 20.2 scfm at 125 psi
QE11-M-44

Barrel specs:
12" x 0.528" (length can be reduced if necessary)

Operation pressure:
100 psi

I will try to find out the weight of the nerf dart, but I do know that it's 2" long. Unfortunately this is all I know.

All help is very much appreciated.[/url]
  • 0


PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Unread postAuthor: btrettel » Thu Jul 09, 2009 8:15 pm

Without running any numbers I'll tell you it's not likely to decrease performance significantly. In fact, I'm willing to bet it's around the optimal amount. Sorry if I had confused you with our correspondence. I think as a rule don't have too much but don't worry if it's not a particularly large amount (like 3 cubic inches in a Nerf gun). I was not originally aware of the precise amount of dead space so I assumed it was too much without thinking.

1.1 grams is a good guestimate for a Nerf dart... my darts weigh around that much. I intend to manipulate their weight once I figure out the drag coefficient as to minimize requisite kinetic energy to get a certain range.

[shamelessplug]You might want to try my simulation BAGS if you can't use GGDT, especially if you want to learn a bit more about the inner workings of a basic pneumatic. As I intend to use BAGS primarily with Nerf it should be adequate for you.[/shamelessplug]
  • 0

All spud gun related projects are currently on hold.

btrettel
Major
Major
 
Posts: 380
Joined: Sun Feb 03, 2008 4:40 pm
Location: Maryland
Reputation: 0

Re: dead space

Unread postAuthor: Technician1002 » Fri Jul 10, 2009 1:04 am

PVC Arsenal 17 wrote:I've run into a flaw in my most recent pneumatic nerf gun configuration.

There will be, no matter much I move stuff around, 3" of dead space between the outlet of the valve and the dart. The diameter of the space is 0.572", making for a dead volume of about .771 in^3.

Since I can't get GGDT to run on my computer for whatever reason (like I'd be able to figure it out anyway...) I'm going to post as many facts about the parts used and if at all possible, someone please work out the numbers for me and tell me if my design will suffer any significant decrease in performance compared to if there was no dead space. It would be very much appreciated.

Known valve specs:
Exhaust Time: 100 cubic inches in 2 seconds
Flow Rate: 20.2 scfm at 125 psi
QE11-M-44

Barrel specs:
12" x 0.528" (length can be reduced if necessary)

Operation pressure:
100 psi

I will try to find out the weight of the nerf dart, but I do know that it's 2" long. Unfortunately this is all I know.

All help is very much appreciated.[/url]


With a 12 inch long barrel and 2 seconds to discharge 100 cu in of air, that thing is severely restricted someplace. Do you mean 2 ms? 100 cu in of air is roughly twice the volume of my marshmallow cannon. It dumps fast enough to toss rolled up t shirts 200 feet from a 36 inch long tube.
  • 0

Attachments
Hissboom.jpg
Small air cannon sound. Total time of trace is 0.2 seconds. Recording is the Mouse Musket, a 1 inch coaxial about 30 inches long.
stadium1.jpg
Range of 54 cubic inch launcher with t shirts as predicted for the cure MJ benefit concert Aug 8 at the Hillsboro stadium.
Last edited by Technician1002 on Fri Jul 10, 2009 12:00 pm, edited 1 time in total.
User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: PVC Arsenal 17 » Fri Jul 10, 2009 11:41 am

The actual chamber volume is not 100 cu in. I just copied that off the valve's specification sheet. My guess, and I have not worked it out yet, but the chamber volume shouldn't be less than 2 cu in.

@btrettel- Thanks for the info. I will try out BAGS right away.
  • 0


PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Unread postAuthor: Technician1002 » Fri Jul 10, 2009 12:02 pm

PVC Arsenal 17 wrote:The actual chamber volume is not 100 cu in. I just copied that off the valve's specification sheet. My guess, and I have not worked it out yet, but the chamber volume shouldn't be less than 2 cu in.

@btrettel- Thanks for the info. I will try out BAGS right away.


I just saw the 2 seconds to vent 100 cu in, at 100 PSI and thought, slower than a tire valve.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: jackssmirkingrevenge » Fri Jul 10, 2009 1:34 pm

Some limited testing I had done here.

jackssmirkingrevenge wrote:The 16 inch barrel is made up with a ten inch barrel and a 6 inch extension, so I took the opportunity to measure shots for 10 inch effective barrel length, starting from zero and 6 inches away from the piston respectively. I got 225, 227 and 221 fps for a normal 10 inch barrel, and 198, 190 and 196 fps for the 16 inch barrel with the projectile 10 inches away from the muzzle.

An almost 13% decrease in velocity for the extra dead space, meaning 26% less muzzle energy. A very limited test, granted, but food for thought nonetheless ;)
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: PVC Arsenal 17 » Fri Jul 10, 2009 2:57 pm

Technician1002 wrote:
PVC Arsenal 17 wrote:The actual chamber volume is not 100 cu in. I just copied that off the valve's specification sheet. My guess, and I have not worked it out yet, but the chamber volume shouldn't be less than 2 cu in.

@btrettel- Thanks for the info. I will try out BAGS right away.


I just saw the 2 seconds to vent 100 cu in, at 100 PSI and thought, slower than a tire valve.


Yeah the valve I'm using is a super small 1/8" QEV.
  • 0


PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Sponsored

Sponsor
 


Unread postAuthor: POLAND_SPUD » Fri Jul 10, 2009 4:52 pm

a super small 1/8" QEV


it's not a full ported valve, is it ?
1/8" is still quite big... if it's not fully ported then it might be a 5mm version
  • 0

Children are the future

unless we stop them now
User avatar
POLAND_SPUD
Chief of Staff
Chief of Staff
 
Posts: 5405
Joined: Sat Oct 13, 2007 4:43 pm
Country: Israel (il)
Reputation: 10

Unread postAuthor: PVC Arsenal 17 » Fri Jul 10, 2009 5:26 pm

It is a Pneumadyne QE11-M-44. I will be replacing it with a Clippard JEV-F2F2 eventually anyway.
  • 0


PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'