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Need help understanding recoil force

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Need help understanding recoil force

Unread postAuthor: Moonbogg » Sun Jan 11, 2009 3:01 pm

This question applies to an under over gun design.
OK, this might be obvious to some of you, and it would be obvious to me also if my gun wasn't curved in the back. When the gun recoils, where exactly is the force being applied to at the back of the gun?
It's confusing to me because I know the pressure is pushing on both the projectile and the gun, but is the force pressing on the circular area of the gun thats right behind the barrel and nowhere else? This should be easy to understand but for some reason it's not.
If I imagine the recoil as thrust from a rocket, and the rocket flame was coming out of the barrel, then the force would be applied directly behind the flame, pushing that area of the gun and the rest of the gun would simply follow,right? Why do I feel retarded. That damn bend confuses me.
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Unread postAuthor: sputnick » Sun Jan 11, 2009 3:12 pm

Well yes, the recoil is on the section of barrel in which the projectile is, and then pivoting on where your had is, it pushes back, but since your hand is say, in the middle of the chamber, it turns around that pivot point, so it moves back, then turns back some
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Unread postAuthor: Moonbogg » Sun Jan 11, 2009 3:24 pm

So it takes off like a rocket, with the pressure pushing on the face exactly opposite the projectile. It doesn't push anywhere else in the gun, because all other internal surfaces of the gun that are under pressure, have an opposite face with equal pressure, so it doesn't move in those directions.
But when the the pressure is un-corked, there is now an internal face of the cannon with pressure on it, and nothing to equal it out, so that face gets pushed, right? I mean, the face is being opposed by the projectile, but they are not connected, so those two circular surface areas are being pushed on, while not being connected, so the force is applied to those two faces only...right?
I understand the pivoting part, and if you tossed the gun in the air and remote fired it, it would twirl about the center of gravity of the gun. Is this idea of recoil correct?
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Unread postAuthor: sputnick » Sun Jan 11, 2009 3:31 pm

No, not on the face opposite the projectile, on the projectile itself, because of the force required to start it moving, which is why heavier ammo makes heavier recoil, and why just air makes zero recoil, so its only on the projectile that causes recoil, so once it has left, there is no more force acting on the gun
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Unread postAuthor: Moonbogg » Sun Jan 11, 2009 3:38 pm

OK that sort of makes sense. But if you held the cannon around the chamber in a clamp, and shot it with a super heavy projectile, which part of the cannon would experience force?
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Unread postAuthor: starman » Sun Jan 11, 2009 3:41 pm

The recoil force will be toward anything that is the exact opposite of the direction of your projectile. In your case, that will be the U assembly in the rear. That's why you want that section reinforced (as you have done).

Your configuration will have a smaller recoil force in the other direction as well. The mass of the hot gases firing from the chamber rearward will cause a slight forward recoil. However, because the mass of your projectile is [usually] much greater than that of the hot gases, the projectile recoil will still dominate.

It's about projectile mass and velocity and direction. Notice the small backward recoil on the gun on firing just as a noise cannon. That was from the exiting mass of air.

[youtube]http://www.youtube.com/watch?v=xWLSiAOFmjc&eurl=http://www.spudfiles.com/forums/triple-thunder-noise-cannons-t15211.html[/youtube]
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Unread postAuthor: Moonbogg » Sun Jan 11, 2009 3:49 pm

starman wrote:The recoil force will be toward anything that is the exact opposite of the direction of your projectile.


So then, if we don't think about the small forward recoil of the expanding gasses slamming into the chamber wall near the fan, then if we were to draw the shape of the area of the gun which experiences the actual force that causes it to move, it would be in the shape of the projectile, right?
Thats why a smaller projectile has less recoil, because the PSI has less surface area to build on, and thus a smaller identical shape in the back of the barrel being pushed on. Sound right?
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Unread postAuthor: clide » Sun Jan 11, 2009 3:54 pm

This thread should be helpful to you
http://www.spudfiles.com/forums/recoil- ... 15935.html
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Unread postAuthor: sputnick » Sun Jan 11, 2009 3:58 pm

there is no recoil of the gasses inside the chamber, if you are between to walls, and you push on both of them, the walls wouldnt have a force moving them back, pressur einside the gun doesnt cause recoil,

Imagine instead that the walls move, when you push on one, you would have to in turn push on the other in some way, I'm not sure what law this is, but it is the one that states that every action has an equal and opposite reaction.
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Unread postAuthor: JohnnyBOOM » Sun Jan 11, 2009 4:13 pm

The recoil is the direct result of the projectile's ACCELERATION. This is one of Netwon's basic laws --> F=MA (Force=Mass X Acceleration). This in combination with Newton's principle --> For every action there is an equal and opposite reaction. Thus, the more pressure you have pushing the projectile, the more acceleration the projectile will have. The entire gun will be pushed the opposite direction of the projectile with a force equal to but opposite the force being exerted on the accelerating projectile. Therefore, the stress on the gun will be in whatever location you are actively resisting the backward force of the gun.
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Unread postAuthor: Moonbogg » Sun Jan 11, 2009 4:36 pm

clide wrote:This thread should be helpful to you
http://www.spudfiles.com/forums/recoil- ... 15935.html


Thanks, that was an excellent thread. I think I got it. Inside a chamber with, say 100PSI, the walls are all being pushed on with 100psi, even behind the barrel. This difference is that the walls equal each other and balance the force between, but since the projectile is not connected to the gun, the surface of the projectile and the surface in the chamber right behind it simple separate from each other. The 100PSI is equal everywhere, but the 2 objects simple move away from each other, and the face behind the projectile is simply the direction the gun will move.
If the gun can withstand the initial pressure to begin with, then the only thing it has to contend with is the acceleration force of that portion of the gun moving.
The universe is an amazingly complex place comprised of simple laws.
EDIT: actually I was sort of wrong, the gun now has to deal with the fact that there is a circular section of chamber wall with no opposite section to equal the pressure out which is connected to the gun. So the gun moves based on that lack of support equalization.
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Unread postAuthor: starman » Sun Jan 11, 2009 5:13 pm

JohnnyBOOM wrote:The recoil is the direct result of the projectile's ACCELERATION. This is one of Netwon's basic laws --> F=MA (Force=Mass X Acceleration).


Yes acceleration. I generalize a bit when I call it velocity..my apologies.
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 11, 2009 11:35 pm

clide wrote:This threadshould be helpful to you


See this oneas well ;)
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Unread postAuthor: Daltonultra » Mon Jan 12, 2009 2:40 am

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