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 71 users online :: 5 registered, 0 hidden and 66 guests


Most users ever online was 218 on Wed Dec 07, 2016 6:58 pm

Registered users: Bing [Bot], Exabot [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

Recoil Energy Calculations

A place to ask general spud cannon related questions.
Sponsored 
  • Author
    Message

Recoil Energy Calculations

Unread postAuthor: saefroch » Fri Jan 28, 2011 9:19 pm

I think I know how one would calculate recoil energy from just the projectile, use conservation of momentum to find the velocity of the cannon based on that of the projectile, then calculate kinetic energy from that, right?

What I'm confused/lost on is how one can calculate recoil based on the expanding gas travelling out the barrel. Normally, I can see how this could be negligible, especially with a high-mass projectile, but with my Trident it's not. There is only slightly more recoil shooting a 11/32" ball bearing than there is with no projectile. So... how does one calculate recoil energy produced by an expanding gas?
  • 0

User avatar
saefroch
Major General
Major General
 
Posts: 1679
Joined: Mon Jun 08, 2009 8:47 am
Location: U.S.A.- See Map
Country: United States (us)
Reputation: 0

Unread postAuthor: inonickname » Fri Jan 28, 2011 9:23 pm

Well, you should be able to calculate the mass of the gas fairly easily... And I suppose use a value roughly that of your projectile speed as the velocity value?
  • 0

PimpAssasinG wrote:no im strong but you are a fat gay mother sucker that gets raped by black man for fun
User avatar
inonickname
Lieutenant General
Lieutenant General
 
Posts: 2606
Joined: Sun Dec 07, 2008 3:27 am
Reputation: 0

Re: Recoil Energy Calculations

Unread postAuthor: Ragnarok » Fri Jan 28, 2011 9:28 pm

saefroch wrote:Normally, I can see how this could be negligible

Less so than you might think, with spudguns. Lots of high density air expanding as far as possible - yeah, that's a lot of momentum.

So... how does one calculate recoil energy produced by an expanding gas?

Calculate mass of gasses (air, or an air/fuel mix will be around 1.2-1.3 grams per litre at atmospheric pressure) then multiply by their speed of sound. This is a close enough approximation to the velocity of the gasses to be sufficient. (And yes, the gasses will be moving faster than the projectile!)

This gives you the momentum of the gases, so then add the momentum of the projectile. Divide by launcher mass to get recoil velocity. Solve kinetic energy equation for launcher mass and recoil velocity. Simples.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: saefroch » Fri Jan 28, 2011 9:32 pm

Dang. I guess it really could be that easy... thanks!

EDIT: I just got a recoil energy of 0.0937 joules. I don't think that's right. :roll: Can somebody check it?
Using:
Mass of cannon: 7lbs
Mass of projectile: 2.75 grams
Velocity of projectile: 912fps
Chamber volume: 5.388in^3
Chamber pressure: 1,000psig

I'm converting all my units correctly... I think.
  • 0

Last edited by saefroch on Fri Jan 28, 2011 9:49 pm, edited 1 time in total.
User avatar
saefroch
Major General
Major General
 
Posts: 1679
Joined: Mon Jun 08, 2009 8:47 am
Location: U.S.A.- See Map
Country: United States (us)
Reputation: 0

Unread postAuthor: linuxexorcist » Fri Jan 28, 2011 9:39 pm

The trident's piston probably has a lot more mass than a .36" BB, and probably contributes to recoil more than said BBs will, that's where I'd look for your recoil, not the moving gas
  • 0

User avatar
linuxexorcist
Corporal
Corporal
 
Posts: 61
Joined: Sun Mar 30, 2008 7:52 pm
Reputation: 0

Unread postAuthor: saefroch » Fri Jan 28, 2011 9:51 pm

Wouldn't the recoil from the piston be in the forwards direction though? We'd be looking at impact force there, which I also have NO IDEA how to calculate. I can mass my piston tomorrow on a friend's kitchen scale, it's too light to mass on my bathroom scale :roll:.
  • 0

User avatar
saefroch
Major General
Major General
 
Posts: 1679
Joined: Mon Jun 08, 2009 8:47 am
Location: U.S.A.- See Map
Country: United States (us)
Reputation: 0

Unread postAuthor: linuxexorcist » Fri Jan 28, 2011 11:05 pm

The piston's recoil would be forward, at first, but when it comes to a stop at after actuating, it works like a little hammer

i know how to calculate the impact energy, but not the force, it's just the kinetic energy of the actuating piston (Ek=mv^2), the majority of that energy will be transferred into the trident and your shoulder, unless there's a bumper to mitigate the force of impact
  • 0

User avatar
linuxexorcist
Corporal
Corporal
 
Posts: 61
Joined: Sun Mar 30, 2008 7:52 pm
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: Ragnarok » Sat Jan 29, 2011 7:23 am

linuxexorcist wrote:The piston's recoil would be forward, at first, but when it comes to a stop at after actuating, it works like a little hammer.

No. Because it is being accelerated, AND being brought to a stop within a contained system, it has no actual recoil. A "kick" maybe, but no recoil - in the same way that a springer air rifle just jolts, rather than actually recoiling.

@saefroch:I get a result of 2 Joules.

0.00275 kg projectile at 278 m/s = 0.76 Ns
88 cc chamber at 68 atmospheres = 0.0078 kg gas. At 340 m/s = 2.65 Ns
0.76 + 2.65 = 3.42 Ns (yes, I know it doesn't add like that, but I'm rounding the numbers here)
3.42 Ns recoil on a 3.2 kg launcher = 1.1 m/s recoil.
1.1m/s <sup>2</sup> * 3.2 kg / 2 = 2 Joules, rounding to the appropriate number of significant figures. (One, as the launcher mass was only given to one.)
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: saefroch » Sat Jan 29, 2011 10:24 am

Okay, thanks for the help. I don't know what I did wrong, but I have a feeling I misplaced a decimal, because I tried it again and got pretty much what you got.

Ragnarok wrote:significant figures
Yeah... I need a better way to weigh things around here. Anyway, thanks for the help!
  • 0

User avatar
saefroch
Major General
Major General
 
Posts: 1679
Joined: Mon Jun 08, 2009 8:47 am
Location: U.S.A.- See Map
Country: United States (us)
Reputation: 0

Return to General Spud Cannon Related

Who is online

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

Reputation System ©'