Gunnery and relative motion

[Amon_ITA]

First of all, please excuse me for my English, it's not my native language and the topic at hand is quite complex.

 

I will try to use an example to make my doubt clear.

 

First: I'm following my target, we are on the same course, at the same speed. There is no speed difference. One could say that considering our relative motion we are stopped. Do i have to fire ahead of him to hit, or i should fire at his current position  ? How does the game work in this situation ?

 

This is the most basic situation of course.

[daki]

You could argue that ship vs ship position remains constant due to same speed and direction.

However, once you fire shells, they no longer "move" laterally in the same direction & speed as your ship so you have to lead.

I.e. while relative motions of the ships are the same, the relative motion of shells vs enemy ship is not.

One could maybe simply put it that at the moment of firing it does not really matter if your ships moves or not since the only thing important is the direction and speed of shells.

[OldGrandad]

You have to lead your target. To make it simple to understand, if you were to fire at your target and the shell travel time was 20 seconds your target, depending on speed, will be 20 seconds further ahead of where you initially fired upon. So, what you would do in this case, is to fire 20 seconds (or the distance travelled in 20 seconds) ahead of your target. Hope that simplifies things for you.

[principat121]

Because the real physics would be counter intuitive.

 

When two ships sail parallel with same velocity, you do NOT have to lead your aim (for everyone who doubt this, do the physics!). But this, despite the fact that this is the real physics, is not intuitive for modern computer game players, who are used to lead a moving targed. For this in this game you have to lead the targed in dependence of target motion and distance.

[Amon_ITA]

From the answes it looks like there is no consensus.

 

In real life the motion of your ship influences the motion of your shells too... so i think that if there is no speed and motion differencies between you and your target you should put the crosshair on him. I'm not even sure if this is the correct answer in real life ( but i think it is )

 

Once we're sure about it the next step is considering if this aspect is present in the game or not.

[tsounts]

No matter the equal speed you will have to lead your shots...

[shamelesscreature]

When two ships sail parallel with same velocity, you do NOT have to lead your aim (for everyone who doubt this, do the physics!).

 

Unless you fight in a vacuum, you still have to lead your target, just not by as much as if you were stationary. Your shell will not maintain your ship's velocity because of drag. 

[Siegwald]

Because the real physics would be counter intuitive.

 

When two ships sail parallel with same velocity, you do NOT have to lead your aim (for everyone who doubt this, do the physics!). But this, despite the fact that this is the real physics, is not intuitive for modern computer game players, who are used to lead a moving targed. For this in this game you have to lead the targed in dependence of target motion and distance.

 

Only in vacuum.

 

In atmosphere you have to lead, at least to compensate for lateral drag.

[Gnirf]

First of all, please excuse me for my English, it's not my native language and the topic at hand is quite complex.

 

 

I will try to use an example to make my doubt clear.

 

 

First: I'm following my target, we are on the same course, at the same speed. There is no speed difference. One could say that considering our relative motion we are stopped. Do i have to fire ahead of him to hit, or i should fire at his current position  ? How does the game work in this situation ?

 

 

This is the most basic situation of course.

 

Or as in football if the player runs you must place the ball before him the distance depends on his speed, angle and distance from you. It is the same physics, you aim at the point where the ship are when the shell arrives.

 

Or as in air combat deflection shooting.

[peoplescavalry]

Because the real physics would be counter intuitive.

 

When two ships sail parallel with same velocity, you do NOT have to lead your aim (for everyone who doubt this, do the physics!). But this, despite the fact that this is the real physics, is not intuitive for modern computer game players, who are used to lead a moving targed. For this in this game you have to lead the targed in dependence of target motion and distance.

 

sorry my friend I am no physics expert but I was a gunnery instructor in the  Army for a while and you definitely have to lead even when both are moving in the same direction.Even if in opposite direction you have to aim off, the art is in how much!

[The_Great_SCH]

This is only true if the distance between the two ships is = 0. I will draw it for you : 

 

Your position                        Enemy position

                         (shells)

A                       --------->                 B

and consider the travel time of shells from A to B, the result will be something like this : 

 

(you)                                       (enemy ship)

A                                                     B

 

                                                   --------->  (your shells)    

 

 

     

So by the times your shells get to the target, it has traveled a certain distance, depending of the speed. 

 

[fnord_disc]

Most of the answers in this thread are wrong.

 

Lateral drag against the v_0 that the ship gives the shell is the reason you have to lead. I have a napkin calculation somewhere... wait.

 

[EsaTuunanen]

sorry my friend I am no physics expert but I was a gunnery instructor in the  Army for a while and you definitely have to lead even when both are moving in the same direction.Even if in opposite direction you have to aim off, the art is in how much!

And energy involved in lateral movement would be quite small.

Ship going at 30 knots moves ~15 m/s.

And when you consider how short distance it takes for shell to lose that amount of speed in more aerodynamic forward direction lateral movement of shell doesn't continue for long.

 

Unless there's lateral direction wind!

[Amon_ITA]

you aim at the point where the ship are when the shell arrives.

 

 

 

 

This is clear. The problem, i guess, is that a projectile's trajectory is influenced by the motion of the ship, i think.

 

 

Another example. Two ships moving at the same speed on parallel courses, showing broadside one another. Do i have to lead ? or the projectile is influenced from the forward motion of the ship that shoots it while it travels inside the barrel, resulting in "auto leading" ?

 

 

I'm trying to express myself the best i can, sorry if i'm not that clear.

[VC381]

*ahem* the guns on ships are rifled. While in theory the shell gets a lateral speed same as the ship forward speed as it leaves the barrel (assuming guns at 90 degrees to line of travel), the shell spins, so as soon as it's out that lateral velocity is suddenly up, then back, then down, a few times around, less each time until cancelled. That's the point of rifling, to smooth out random lateral velocities and eventually get rid of them so the shell flies a true course and the gun is more accurate.

 

In answer to OP, you always have to lead. In game, the component of projectile velocity due to ship speed is ignored. In real life, it is probably accounted for by the fire control but the effect is tiny because it's cancelled by the rifling and air resistance.

[Kartoffelmos]

the guns on ships are rifled

 

The rifling doesn't change anything, as the problem is caused by the ship's movement. In other words, the shell, guns and everything else on the ship is moving at the same velocity as the ship. One comparison is that if you jump from a speeding train/car/whatever, you will still retain the velocity of said vehicle (no matter if you are spinning or not).

 

As such, in theory and excluding air resistance, the ships will be part of the same reference system and you will have to aim as if they were standing still (courtesy of the laws of Newton). However, the air will in reality (depending of the distances involved, of course) affect the shell. It was mentioned a velocity of 15 m/s above, which means that you can view the problem as stationary with 15 m/s side wind (or headwind, depending on the positioning). 

 

The game does not take this into account and you will always have to lead your shots.

[fnord_disc]

 *ahem* the guns on ships are rifled. While in theory the shell gets a lateral speed same as the ship forward speed as it leaves the barrel (assuming guns at 90 degrees to line of travel), the shell spins, so as soon as it's out that lateral velocity is suddenly up, then back, then down, a few times around, less each time until cancelled. That's the point of rifling, to smooth out random lateral velocities and eventually get rid of them so the shell flies a true course and the gun is more accurate.

 

No, this is not correct.

 

The rifling is done to impart spin on the projectile and stabilize it during flight. It has absolutely nothing to do with lateral velocities.

 

And it can't. This is a question of basic physics and reference frames. If you fire a shell, that shell has the same reference frame when it leaves the gun and unless an acceleration acts upon the shell, it would keep flying parallel and away.

 

https://en.wikipedia.org/wiki/Superposition_principle

 

I can't stress this enough. Please read what superposition is before we talk about this.

 

If two ships fly parallel in space at the same velocity and shoot at each other, they will never have to lead. Space has no drag and there is no acceleration that changes the reference frame of the projectile.

[fnord_disc]

If you want to test this,

- take your car onto the highway.

- Throw your mate in the seat next to you an apple

(You're throwing it straight at him because the air in your car moves with the car and so does the apple = no sideways drag on the apple)

 

- Throw the apple out the window at another car

(Once the apple leaves the car out the window, the air on the highway slows the car_velocity that the apple had inside the car and you need to lead if you want to hit the other dude's car)

 

I hope this makes it clear.

[red_eye1980]

OK, let's forget real life here. I think that what the OP means, is weather ''relative motion'' is at all accounted for in this game or not. Is it? or No? Even a tiny little bit?

 

Is it the reason we sometimes fail miserably to hit stationary broadside showing ships? because we are moving and they are not? I was always really wondering about this. But I never chose to aim accordingly and test it.

[fnord_disc]

OK, let's forget real life here. I think that what the OP means, is weather ''relative motion'' is at all accounted for in this game or not. Is it? or No? Even a tiny little bit?

 

Is it the reason we sometimes fail miserably to hit stationary broadside showing ships? because we are moving and they are not? I was always really wondering about this. But I never chose to aim accordingly and test it.

 

This question is the more interesting one.

 

As far as I can tell, the game does not give shells correct lateral motion, i.e. all that is written in this thread does not apply to the game. The reason you lead is because the enemy moves, period.

 

This is fairly obvious on ships like Khabarovsk because they visibly outrun their own shells perpendicularly and there is no curving behavior if you look at trajectories from above.

 

So no, I'm quite sure the game does not account for your own ship's velocity when you fire.

[Ferry_25]

AFAIK the the system is considering you stationary when firing. Even if you're not. So you only need to take your targets' speed in account. Not your own. Calculations are as if you're standing still.

[EsaTuunanen]

OK, let's forget real life here. I think that what the OP means, is weather ''relative motion'' is at all accounted for in this game or not. Is it? or No? Even a tiny little bit?

Even in real life inside atmosphere that "lateral movement of firing platform" counts only for really short distances.

At longer ranges winds woud have lot bigger effect.

[mikelight1805]

One could say that considering our relative motion we are stopped. Do i have to fire ahead of him to hit, or i should fire at his current position

 

despite being on the same course and speed, you  only need to take into consideration the travel time of the shot to the target. If the target is far way, you need to lead the target only by the travel time of the shot.

[VC381]

I understand superposition and of course the projectile has a lateral velocity initally. Of course in a complete vacuum two ships flying side by side won't have to lead to shoot each-other because the projectile would have a combined velocity vector made up of its own muzzle velocity and the velocity of the firing platform.

 

But what's wrong with my rifling argument? If an object is spinning and you impart a velocity normal to its axis of rotation, that velocity remains normal to the body not to a fixed reference, no? So even in a complete vacuum, a bullet fired from a rifled weapon that is moving sideways would end up flying in a spiral around the axis of the barrel at the point when it was fired. In air the spiral would decay due to air resistance. I'm happy to be corrected on this BTW, but that's my impression of how the stabilisation effect of rotation works.

[fnord_disc]

 If an object is spinning and you impart a velocity normal to its axis of rotation, that velocity remains normal to the body not to a fixed reference, no? So even in a complete vacuum, a bullet fired from a rifled weapon that is moving sideways would end up flying in a spiral around the axis of the barrel at the point when it was fired.

 

Ahhhh, now I see where the misunderstand was. However, you're wrong: the velocity is to a fixed reference point and not a specific point on the shell. Think of it the other way around: to generate a helical flight path, we need a v_0 that the shell travels along (given by barrel) and an acceleration a(t) which points to the center of the rotation. The only way to accomplish this would be to have a force F=ma(t) act upon the shell perpendicular to the axis of travel. A velocity is not a force, and besides, your v_ship points outwards, not inwards. So this

 

 In air the spiral would decay due to air resistance.

 

is also the wrong conclusion according to your logic. If it actually worked like this, then the spiral would become bigger and bigger over time since the velocity acts outwards and over time keeps increasing the spiral (although drag reduces this increase to almost nothing eventually).