Divergence of shells and rounds

[HagarTheHorrible]

I haven't noticed any recoil effects implimented yet, I was wondering is anyone had had a look at the trajectories of the bullets and cannon shells ?

 

I assume that with the cannon shells, being bigger and slower, they would tend to fall away quicker than the machine gun bullets and that this effect would be far more pronounced if the firer was pulling back on the stick in any way, the more "G's" the greater the divergence ?

[Finkeren]

Recoil is one thing, ballistic trajectories another matter.

 

As for recoil, it's hard to determine if it's implemented because the effect on the aircraft would be minimal, even for the fast firing ShVAK. A fighter aircraft outweighs the bullets it fires by quite a few orders of magnitude and would not decellerate noticeably due to recoil. With the firepower concentrated in the nose, I very much doubt, that there would be much noticeable traversing effect (such as would be felt in a plane with wing mounted guns, where some guns on one side were inoperable or firing out of synch) For heavier calibers the effect might be noticeable, the 30mm GAU on the A-10 Warthog has a recoil force more than half the maximum thrust of its engines, but that gun fires shells more than 4 times as heavy as a standard WW2 20mm shell, at a 25% higher muzzle velocity and at a rate of more than 4000 rpm, more than 5 times that of the (unusually fast firing) ShVAK.

 

As for the bullet drop, it's definately there, though we tend to open fire at ranges, where it's largely irrelevant. Contrary to what you seem to think, the muzzle velocities of the MG 151 and ShVAK weren't significantly lower than for the machine guns used alongside with them, and some of the Soviet heavy cannon, like the 23mm and 37mm ones we're getting now, actually had higher muzzle velocities than either the MG 151 or the ShVAK. The weight of the projectile is completely irrelevant in relation to bullet drop as we have known since the time of Gallilei. The thing that really matters is the aerodynamic properties of the projectile, but in that case, there isn't a whole lot of difference between machine gun bullets and cannon shells either. Therefore, there shouldn't really be a great difference in bullet drop.

[HagarTheHorrible]

Recoil is one thing, ballistic trajectories another matter.

 

As for recoil, it's hard to determine if it's implemented because the effect on the aircraft would be minimal, even for the fast firing ShVAK. A fighter aircraft outweighs the bullets it fires by quite a few orders of magnitude and would not decellerate noticeably due to recoil. With the firepower concentrated in the nose, I very much doubt, that there would be much noticeable traversing effect (such as would be felt in a plane with wing mounted guns, where some guns on one side were inoperable or firing out of synch) For heavier calibers the effect might be noticeable, the 30mm GAU on the A-10 Warthog has a recoil force more than half the maximum thrust of its engines, but that gun fires shells more than 4 times as heavy as a standard WW2 20mm shell, at a 25% higher muzzle velocity and at a rate of more than 4000 rpm, more than 5 times that of the (unusually fast firing) ShVAK.

 

As for the bullet drop, it's definately there, though we tend to open fire at ranges, where it's largely irrelevant. Contrary to what you seem to think, the muzzle velocities of the MG 151 and ShVAK weren't significantly lower than for the machine guns used alongside with them, and some of the Soviet heavy cannon, like the 23mm and 37mm ones we're getting now, actually had higher muzzle velocities than either the MG 151 or the ShVAK. The weight of the projectile is completely irrelevant in relation to bullet drop as we have known since the time of Gallilei. The thing that really matters is the aerodynamic properties of the projectile, but in that case, there isn't a whole lot of difference between machine gun bullets and cannon shells either. Therefore, there shouldn't really be a great difference in bullet drop.

 

One of the things that stood out for me, from the original IL2, was when you fired the forward firing guns on the ground the aircraft would move backwards from the recoil.

 

I would have thought weight would have been very relevent, especially if trying to fire while pulling back on the stick.  That added weight would be affected by "G's" more than smaller lighter rounds not to mention that they would run out of steam quicker, unless, as you say, the aerodynamic properties were much better.

[Finkeren]

One of the things that stood out for me, from the original IL2, was when you fired the forward firing guns on the ground the aircraft would move backwards from the recoil.

Hmmm, I thought I tried that in BoS as well, and that it actually was posible but I'm not 100% convinced I really tested it. The thing is, that it takes a lot more energy to get a wheeled vehicle rolling, than to simply accelerate it from an already moving state (well, up to a certain point anyway, before wind resistance and later relativity starts to kick in) This is something that's modeled well in BoS, but is more or less absent in the old IL2, which BTW also grossly overmodeled the effect of recoil and the muzzle flash of guns.

 

I would have thought weight would have been very relevent, especially if trying to fire while pulling back on the stick.  That added weight would be affected by "G's" more than smaller lighter rounds not to mention that they would run out of steam quicker, unless, as you say, the aerodynamic properties were much better.

The weight of the projectile is not totally irrelevant, when the aircraft is pulling Gs while firing, but remember that a projectile accelerating down the barrel is experiencing an acceleration of several hundred Gs (sometimes thousands), so 2 - 3 Gs in another direction isn't really gonna make than much difference.

 

As for "running out of steam quicker", that's not really how it works. When a projectile leaves the barrel it pretty much stops accelerating instantly having achieved a maximum speed known as "muzzle velocity". The projectile at that point is at its maximum kinetic energy. As it moves through the air the resulting drag bleeds off the kinetic energy, slowing the projectile down, the rate at which it slows down depends on the kinetic energy it starts with and the amount of drag, which again depends on the shape of the projectile as well as air density. A heavy projectile takes more energy to accelerate up to muzzle velocity, but once it leaves the barrel it often slows down at a lower rate than a similar lighter projectile going at the same velocity.

 

Bullet drop is an entirely different thing as well. It is caused by gravity and accelerates the projectile towards the ground at the rate of around 9.82m/s² completely independent of what speed the projectile is going (if the projectile is fired directly upwards, the gravitational pull still accelerates it downwards, but since the projectile starts out with a much larger acceleration in the opposite direction, it simply decellerates the projectile up until the point, where all its kinetic energy is spent and then accellerates it downwards again)

 

Since the gravitational pull is independent of the speed of the projectile, a projectile fired completely horizontally (as from an aircraft flying level) will always hit the ground after the same amount of time, regardless of what its muzzle velocity is, indeed if you fire a bullet horizontally and at the same time drop a similar bullet from your hand at the same height, they will hit the ground at almost exactly the same time. The difference in "bullet drop" is not how fast the projectile is falling, it always falls at the same rate, but how far it can go in that time. 

[Finkeren]

Regarding recoil force, I just did some calculations and it appears, that a single ShVAK cannon will produce around 1000N of recoil force (a fraction of which is spent on cycling the mechanism - but we'll leave that out for now) This is actually quite a bit more than I expected, but in the grand scheme of things it still doesn't add up to much.

 

If we take the example, where the recoil would be most noticeable: The aircraft sitting on the tarmac, engine off and brakes disengaged. Also we're completely ignoring any kind of drag or friction as well as the fact that the vector of the recoil force is not pointing directly backwards but slightly downwards. Even in that best case scenario of a completely frictionless world, a solid 3 second burst from the ShVAK would only accellerate our 3 ton LaGG up to a slow walking speed of around 1m/s.

 

In the real world, firing the entire ammo supply for the ShVAK  while sitting on the runway with engine and brakes off, might actually get the LaGG moving backwards very slowly, but it's not something that would be very noticeable when firing short bursts while going 400 km/h, the acceleration is less than what you experience when you start walking slowly from a standstill.

[BigPickle]

 the more "G's" the greater the divergence ?

 

G force wouldnt affect the divergence and G force bearly effects trajectory too.

 

Not more G's would appear to equal a greater trajectory but in reality when the bullet is fired the trajectory would ramain the same as as the G force is not being sustained on the bullet only the regular force of gravity.

To the pilot in the aircraft however if still under still under sustained G force it would appear the trajectory has increased but in reality its just the angle of the aircrafts movement ie like in a turing fight, meaning more lead would have to be applied to the shot.

Edited December 28, 2013 by BigPickle

[HagarTheHorrible]

Thanks for that. I was just wondering because it was one of the things I picked up, or at least I think I did, from Mig Alley (they had some great doc's to go with the game, those were the days). In it it said something about the Mig 15 being armed with cannon which fired slower than the F86's armament and therefore needed more lead to get a shot in giving, in theory, a slight advantage to the Sabre as they had a similar turn but the Mig had to turn slightly more in order to get a good shot.

[Finkeren]

What you're saying about the Korean War fighters does make some sense, but it has nothing to do with the weight of the projectiles.

 

The Browning M3 .50 cal of the Sabre has both a higher rate of fire and a higher muzzle velocity than the 23mm NR-23, both of which is an asset in a fast dogfight.

 

The higher muzzle velocity will give less "bullet drop", not because the lighter projectile falls slower or bleeds less energy but because it takes a shorter time to reach it's target.

 

It worth noting, however, that history has more or less vindicated the Soviet/German approach to aircraft armament, that of fast firing, heavy caliber autocannon with high muzzle velocity in a central single or pair configuration.

Edited December 28, 2013 by Finkeren

[Skoshi_Tiger]

The higher muzzle velocity will give less "bullet drop", not because the lighter projectile falls slower or bleeds less energy but because it takes a shorter time to reach it's target.

 

Not sure about the term "Bullet Drop",  but because of the higher muzzle velocity the round would have a flatter trajectory.