Calculating recoil

[hyldgaard]

Hello.
Does anyone here know about any kind of program, spreadsheet or whatever to calculate recoil for at spudgun? Now that i have higher pressure available and planning a larger launcher, i thought that recoil energies was something to keep in mind. I saw Ragnaroks calculations on the forums, but im not quite sure i understand how to adapt them to my launcher
Thanks in advance.

Casper

[biggsauce]

Can you use ggdt and find the projectile acceleration and go from there? If you have the acceleration and its mass, you got force. the force of motion of your projectile should be equal to the force exerted on your gun. I think.

Is that what youre looking for?

[hyldgaard]

Can you use ggdt and find the projectile acceleration and go from there? If you have the acceleration and its mass, you got force. the force of motion of your projectile should be equal to the force exerted on your gun. I think.

Is that what youre looking for?

Yea thats what im looking for but i can see that you know about as much about this as i do i roughly know what its about, i just dont know the specifics on how to do it

[jackssmirkingrevenge]

mass x velocity of your projectile should equal the mass x velocity of your recoiling launcher.

Therefore your launcher will move back at a velocity of (mass x velocity of projectile / weight of launcher).

[Ragnarok]

@Jack: Although simple, that doesn't include propellant gas momentum, which is a very significant part in many situations, especially high pressure ones.
Strictly, that equation is only really accurate for crossbows, catapults, and coilguns - or other similar things without a propellant gas (but not railguns, even uninjected ones).

@ hyldgaard: Now, I do have a recoil spreadsheet, but it's a little complicated to operate at the moment.
If you can post a GGDT(s) of your launcher, along with the mass of your launcher, I can do an estimate of it for you.

I don't imagine it will be a problem, even with the heaviest of projectiles, but it won't hurt to be wary.

[THUNDERLORD]

I have been looking for a formula that will be exact myself.

It's tricky because for one thing the calculated lb.s per square foot of projectile striking energy are of the projectile striking and coming to a complete stop (the total energy)

But when you think about it the projectile is in the barrel for a set amount of time.

The weight(mass) of the launcher should reduce the recoil figure somehow because obviously heavier launchers have less reoil.

Then also there is the "jet" effect that the exhaust gas propeling the projectile have on the launcher which seems to really complicate things (but luckily doesn't add too much).

Also the configuration of barrels and stock or stand and length of the barrel can really effect the actual "felt recoil"

I am basically moving towards a little math and brute trial and error at this point or a small model and multiplying the size from there.
Sorry I don't have a better method now.

BTW mythbusters did a show segment on bullet knock-down power and the way they described recoil in that segment made me start to doubt their scientific merit.

[hyldgaard]

@Jack: Although simple, that doesn't include propellant gas momentum, which is a very significant part in many situations, especially high pressure ones.
Strictly, that equation is only really accurate for crossbows, catapults, and coilguns - or other similar things without a propellant gas (but not railguns, even uninjected ones).

@ hyldgaard: Now, I do have a recoil spreadsheet, but it's a little complicated to operate at the moment.
If you can post a GGDT(s) of your launcher, along with the mass of your launcher, I can do an estimate of it for you.

I don't imagine it will be a problem, even with the heaviest of projectiles, but it won't hurt to be wary.

For now, its not for a particular gun as im just fooling around with some ideas. My main idea however, is a 2" (1½" porting) pistonvalve, so i tried to throw something together real quick in GGDT. Admitted, im not the hardcore user of GGDT, so flow coeff. is probably way off.
Looking forward to see what your calculations will say
thanks in advance

Edit1: forgot picture

Edit2: just realised that my projectile diameter was left unchanged from another calculation by mistake, but im on my way out so i dont have time to change it right now

Edit3: corrected most spelling mistakes(hopefully) -i really have to go now

[Ragnarok]

There is a slight problem - I still need to know the mass of the launcher (or at least an estimate, and as I don't even know what materials it will be made from, that's rather hard), as it's integral to knowing how much recoil there will be.

[POLAND_SPUD]

I assume he is going to build it from galvanized fittings and pipes....
judging from the pic it would weight about 8-12 kg

he can always make it heavier to reduce recoil - that's just my suggestion

EDIT
on the second thought it would probably be about 15kg bc the chamber he is planning to use is huge

[jackssmirkingrevenge]

@Jack: Although simple, that doesn't include propellant gas momentum, which is a very significant part in many situations, especially high pressure ones.

Granted, though in the case of spudguns the recoil of the air alone is going to be negligible compared to what would happen if you had a projectile in the barrel.

[SpudFarm]

hey your projectile is twice as big as your bore...

[rcman50166]

I imagine that the recoil is probably equivalent to the force accelerating the projectile. (Newton's laws?) There are a lot of ways it can be calculated. The method you use depends on what you do and don't know about the gun.

[THUNDERLORD]

@Ragnarok, I must have been typing and missed your first reply when I submitted mine.
I hope you get your formula posted on SF.

To clarify my reply, mythbusters sounded like if the projectile has say 1000 ft./lb.s striking energy the rifle or pistol would have that much. Which I found rediculous.

Ft./lbs of energy at the muzzle should factor in the math though.
Either way it's one of Newton's laws (which I like) about for every action there's an equal reaction.

Based on that there has to be a formula that will be accurate,
It's just a matter of figuring that into the other considerations(weight of launcher, muzzleblast effect and others.

Personally, I like the one that goes, "a force in motion will remain in motion unless acted upon by an equal or greater opposite force"
I had a book I was working on and that was on the opening page.

BTW a coil gun has recoil just not rearward if it works by pulling the projectile in. As I'm sure you know magnetism is a form of mass(plasma).

[Brian the brain]

You don;t need to know the velocity of your cannon moving backwards, it's the force you need to worry about.

A really heavy cannon moving fairly slow still packs a punch.

[hyldgaard]

hey your projectile is twice as big as your bore...

Ya, i realised that right after i posted the pic.. im sorry about that last post, i was in a rush not to be late for an appointment. I edited the picture now.

There is a slight problem - I still need to know the mass of the launcher (or at least an estimate, and as I don't even know what materials it will be made from, that's rather hard), as it's integral to knowing how much recoil there will be.

Ofcourse.. as said earlier, i was in a rush I will estimate that particular launcher to be around 12kg.


On a sidenote, can anyone tell me how i figure out my valve flow coeff.?