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Lord_Flashheart

Ballistics investigion/inquery

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Let just say outright that I do not know if anything is for sure wrong. This thread is to see what can be done to find out.

 

 

The potential problem: For some time now I have felt that the gunnery in il2 is significantly harder in some respects than other sims. Due to the lack of recoil, gunnery at low deflection is perhaps easier, but deflection shooting seems to be unusually hard. Compared to several other sims including DCS, the ballistic drop under G seems far worse.

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Really hard to test bullet drop under significant g. Almost impossible to get consistent conditions...

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'Ballistic drop under G' isn't a thing. Once a bullet leaves the barrel, it is subject to 1G acceleration, vertically down. No more no less. The bullet neither knows nor cares what acceleration it was subject to before it was fired, and neither does it matter what acceleration the gun is subject to afterwards. Because physics...

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I suppose being charitable to the OP he may be talking about the degree to which the bullets fired, when turning, appear to drop below the nose, although this is actually the nose going "up" rather than the bullets going down, except in their normal earthwards acceleration, of course. From all the tests I have seen or made, BoS is remarkably accurate in it's ballistics modelling for a piece of gaming software, especially with recent tweaks to dispersion. DM and AI shooting is another matter.

 

But as usual, to get any kind of discussion in detail, it is up to the OP to be clear and document the phenomenon that may be bothering him. 

 

 

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2 hours ago, AndyJWest said:

'Ballistic drop under G' isn't a thing. Once a bullet leaves the barrel, it is subject to 1G acceleration, vertically down. No more no less. The bullet neither knows nor cares what acceleration it was subject to before it was fired, and neither does it matter what acceleration the gun is subject to afterwards. Because physics...

I didnt mean to imply that being under G should cause more drop. Only that in game the deflection required to hit targets when pulling more than 1 g appears to be more than in other games. I also dont know that that is the cause, assuming there is a problem at all, only that it is my impression.

 

The only thing I know is this: In every other sim the bullets go roughly where i expect. In il2 they do not. So either il2 is right and everyone else is wrong, the reverse is true, or something else is going on here to produce the sensation that something is off.

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2 hours ago, AndyJWest said:

'Ballistic drop under G' isn't a thing. Once a bullet leaves the barrel, it is subject to 1G acceleration, vertically down. No more no less. The bullet neither knows nor cares what acceleration it was subject to before it was fired, and neither does it matter what acceleration the gun is subject to afterwards. Because physics...

 While I agree with the first two sentences, the rest isn't entirely true.

 If the barrel has a sideways motion while projectile is passing through the projectile is of course also accelerated sideways. Far less then it is accelerated forward but nevertheless. So it will fly in a sideways and downwards curve. After leaving the barrel the same air resistence that slows down it's forward motion will also slow down it's sideways motion so the sideways curve is fading. (So sideways it is decelerated while downwards - as you pointed out - it is accelerated)

 

What I do not know about is if and by how much the G-forces affect muzzle velocity. Does the powder burn at a diffrent speed, when under 4G? Is the friction in the barrel increased under 4G? I have no idea...

 

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22 minutes ago, Eisenfaustus said:

 If the barrel has a sideways motion while projectile is passing through the projectile is of course also accelerated sideways. Far less then it is accelerated forward but nevertheless. So it will fly in a sideways and downwards curve.

 

And what force would make it fly a sideways curve, after it has left the barrel?

After lots of sideways acceleration, do you see the projectile flying a sideways curve after release:

 

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Posted (edited)

@ Eisenfaustus: the OP isn't talking about aerodynamic effects though. At least I assume not. And I'm not sure you are correct about a 'sideways curve', unless again you are looking at it from the perspective of the aircraft. Viewed from the frame of reference of the air mass the bullet is travelling through, the only thing that will make it curve is any aerodynamic force due to the angular difference between the bullet's direction of flight and its long axis. Well that, and the other things that make bullets curve, like spin and Coriolis drift.

 

As for your other questions, no idea, though I'd guess that the chemistry of propellant ignition would be unlikely to be influenced much by a few Gs, given the forces actually involved when it goes off.

 

 

Edited by AndyJWest

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Tacview might be your friend there. 

you can get the g and see bullet trajectory.

Perhaps the reason for op feeling is the perceived g are underestimated because of game sensitivity.

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When the gun/barrel moves the same motion is applied to projectile as long as it hasn't left the barrel yet.

 

If my IFV is moving at 30 km/h and I'm shooting a standing target 1500m away at 3 o'clock and I set my sight to the centre of the target I'll miss.

 

The Projetile will leave the muzzle with 1000 m/s in target direction and 8,3 m/s in the direction my IFV is moving. So ignoring air resistance it could reach the target in 1,5 s but will be 12,6 m left of where I have aimed. So I have to put my sight to a point 12,6m right of where I want to hit.

 

But I think I get the misunderstanding - the curve I meant is not in the direction of the movement but into the opposite direction due to air resistance induced deceleration. Without that it would move in a straight line of course but not to point you put your sight.

 

I'm sorry but English is not my native language and technical English even less ^^

 

What sideways speed the barrel in a fighter has during a 4G turn I have now idea...

 

So I can't tell how big the influence would be - but it will be there :)

 

Hitting a moving target from a moving platform is difficult - there is a reason why historic acces like to get very close ^^

 

 

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29 minutes ago, gabuzomeu said:

Tacview might be your friend there. 

you can get the g and see bullet trajectory.

Perhaps the reason for op feeling is the perceived g are underestimated because of game sensitivity.

 

TAcview is useless for ballistics: as another poster who tried to use it to show that BoX ballistics features neither convergence or gravity effects found out, and as the developer of Tacview himself warned.

 

10 minutes ago, Eisenfaustus said:

When the gun/barrel moves the same motion is applied to projectile as long as it hasn't left the barrel yet.

 

 

 

The effect you are talking about is modeled in BoX. You can see this clearly if you take an He111 side gunner and fire at 90 degrees out while the plane is flying straight and level. The bullets leave the barrel with the forwards motion of the plane added to the sideways motion from the propellant: ie their momentum is conserved. They gradually fall behind the direct 90 degree eye line as sideways wind resistance takes effect.   AI gunners, BTW, cannot take into account this effect: if you set up a mission in which the side gunners are to fire at a ground target, they will always miss well in front of the target - ie in the direction of travel of the plane, because they aim at it, taking into account drop due to gravity, but not their sideways motion.

 

1 hour ago, Fumes said:

The only thing I know is this: In every other sim the bullets go roughly where i expect. In il2 they do not. So either il2 is right and everyone else is wrong, the reverse is true, or something else is going on here to produce the sensation that something is off.

   

As I have not played any other sim for years I can only say that if you want specific feedback you have to give a specific, documented case. This is just too vague to elicit any useful response.  All I can say is that every investigation of BoX ballistics that I have seen shows them to be remarkably realistic for a PC game, with a few quibbles about the expected dispersion of different gun and shell types. 

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9 hours ago, AndyJWest said:

'Ballistic drop under G' isn't a thing. Once a bullet leaves the barrel, it is subject to 1G acceleration, vertically down. No more no less. The bullet neither knows nor cares what acceleration it was subject to before it was fired, and neither does it matter what acceleration the gun is subject to afterwards. Because physics...

This is my thinking as well, but OP is postulating that bullets drop more while in a higher-g turn in this sim than they do in other sims and and in real life. I just think it would be very difficult to prove this is the case. How would you know how much G your are pulling, how would you track the impacts of the bullets, and how would you compare accurately between two sims?

If we are comparing between sims, then its entirely possible that gunnery is more accurately modeled in Il-2 and the others are 'wrong'. 

Honesty I find deflection shooting easier in this sim than I have in others I've played, but I've never played DCS.

Comparing between sims is kind of a red herring anyway if you aren't also including comparisons to real-life data. Its like comparing two paintings and trying to say which one looks like the real guy without having a photo.

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1 minute ago, RedKestrel said:

This is my thinking as well, but OP is postulating that bullets drop more while in a higher-g turn in this sim than they do in other sims and and in real life. I just think it would be very difficult to prove this is the case. How would you know how much G your are pulling, how would you track the impacts of the bullets, and how would you compare accurately between two sims?

If we are comparing between sims, then its entirely possible that gunnery is more accurately modeled in Il-2 and the others are 'wrong'. 

Honesty I find deflection shooting easier in this sim than I have in others I've played, but I've never played DCS.

Comparing between sims is kind of a red herring anyway if you aren't also including comparisons to real-life data. Its like comparing two paintings and trying to say which one looks like the real guy without having a photo.

 

You don't need to know how much G you are pulling, since it will have no effect whatsoever on the ballistics of a bullet once it leaves the gun. All the OP would need to prove was that the bullet experienced something other than the correct vertical 1G due to gravity. I suppose it is just possible that IL-2 GB gets it wrong, though I'd think it rather unlikely given how simple the physics modelling required to implement this is. A ballistics model which added acceleration to a bullet in flight based on the acceleration experienced on it before it left the gun barrel would not only be wrong, but be unnecessarily complicated.

 

But yes, this thread is going nowhere without some sort of evidence.

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5 minutes ago, AndyJWest said:

 

You don't need to know how much G you are pulling, since it will have no effect whatsoever on the ballistics of a bullet once it leaves the gun. All the OP would need to prove was that the bullet experienced something other than the correct vertical 1G due to gravity. I suppose it is just possible that IL-2 GB gets it wrong, though I'd think it rather unlikely given how simple the physics modelling required to implement this is. A ballistics model which added acceleration to a bullet in flight based on the acceleration experienced on it before it left the gun barrel would not only be wrong, but be unnecessarily complicated.

 

But yes, this thread is going nowhere without some sort of evidence.

Agreed on all points. I guess I'm just trying to see how it could ever be tested in a way that was reproducible. My apologies, I'm probably just talking past people at this point.

A very good indication we have that the ballistics model is accurate is Requiem's deflection shooting videos. He takes gunnery manuals from the various WWII air forces and applies the advice on deflection shooting in-game. While its not super scientific, it shows that you get results that closely match real life when deflection shooting in the way it was done during the war. If there was something truly way off about the gunnery, you wouldn't be able to use those gunnery manuals to get the kinds of results he does. 
 

 

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Posted (edited)

Trajectory Shift or velocity jump is very real IRL . Effectively it increases the lead requirement. The biggest variable is AOA. Trajectory shift and the lead required to vary it will vary directly with AOA. Of course it also occurs laterally as well if firing with slip or skid.

 

Trajectory shift = (Angle of Gunfire) x Fighter Velocity/(Fighter Velocity + Muzzle Velocity)

Angle of Gunfire the angle between the bore line and the flight path. So as AOA changes so does the Angle of Gunfire. So changing AOA will result in changing G so in a roundabout way G does affect the lead requirement.

 

Careful choice of Gun bore angle can offset the effects of Trajectory shift but only in the one design point chosen. Whether Trajectory shift is modeled in the sim who knows.

 

Prdiction.jpg

Edited by Bert_Foster

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3 hours ago, Bert_Foster said:

 

Careful choice of Gun bore angle can offset the effects of Trajectory shift but only in the one design point chosen. Whether Trajectory shift is modeled in the sim who knows.

 

 

Yes it is, as I have explained earlier in the case of the He111 side gunners, which is useful as it is so obvious. (That example also shows how bullets are affected by side wind). 

 

This page has a comprehensible discussion, including this diagram. 

ball003.jpg.be3c212b1e6aeb90446f5129931fc848.jpg

 

https://www.aircav.com/cobra/ballistic.html

 

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