Gunsight & convergence ranges

[MD_MarxMD_Marx]

Firstly, congratulations for the quality of BOS/M/K in all areas

 

My 'issue' is the range of selection for 'gun convergence range'.

 

Anyone who has flown  a quick mission against AI targets must have observed at some point, that firing against an opponent who is beyond the gun's effective range allows the player to actually see the shells falling short and dropping prematurely by gravity. It's a bit of a no-brainer, I suppose, but what is concerning me are the possible adjustment to the physics (or not) associated with the trajectory of the projectiles in relation to the gunsight.

Firstly, to remind our audience, the 'Guns convergence range' can be set to up to 1000m. This is clearly nonsense. The effective range of any fixed wing (or engine) mounted weapon is mainly dictated by the ballistic characteristics of the munitions fired from the barrel. The effective range is the early (mainly linear)  part of the

ballistics curve, where the fall of short is not yet dominated by gravity - as can be seen in the latter part of the curve; it is not whether the shell can kill. Now, while there are variations in ballistic characteristic from gun (and munition) to another gun (and munition), the dominating (approximate) 'law' to determine the scale of the effective range of the weapon, is the product of the muzzle velocity and mass of the munition. To exemplify this, I merely need to compare the German MG101 firing the large 30mm minengeschoss with the German MK108 firing similar munitions; the MG101 has a markedly high effective range at something like 350 - 360m while the MK108 has a very poor effective range of about 120m. This is due to the very low muzzle velocity of the MK108. In general terms, a 20mm cannon of the 1940s has an effective range of about 250 - 300m  - at best. Beyond this range, the fall of shot with gravity ensures that the gunsight is useless, because it cannot be adjusted without a computer to predict where the shell will be at that range!

Another way of looking at setting a gunsight (to beyond the gun's capability) is to know beforehand how much the shell will fall at that range and to compensate for it by adjusting the gunsight - such that the pilot has to sight through it by looking through an axis that goes through the propeller spinner (because he will be aiming just like an artilleryman with his howitzer)!!!

I cannot understand the reason why the 'Guns convergence range' can be set to 1000m; it simply does not make any sense, when any weapon of the time simply could not be sighted at that range. So, my question is, if setting the gunsight range affects the gunnery model in the game, why are there not realistic values ONLY for selection? I suspect that the adjustment has no significant effect, as getting within gun range in the game (i.e. about 270m) and getting my flight line close to that of the target's always seems to have the desirable effect of causing damage. Adolf Galland and Sailor Malan were right; get as close as you can, then open fire.

Sorry for the extraneous b**llsh*t, I'm an engineer

 

Marx

[Ghost666]

Ok let me take a shot at this. You are talking about 2 different subjects here. 1)Effective range: the range that an average person can hit a target 50% of the time. 2)convergence: the range that the projectile of the left gun crosses the path of the projectile of the right gun. this is the point that all rounds from both gun will pass. This is the range were you want your target so that it is hit by both guns.

 

So yes you can have a convergence at 1000m, but that would mean that a target any closer my not be hit. the rounds simply passing over it on there way to 1000m.  

[=TBAS=Sshadow14]

WTH..

German 20mm on BF110 are great at 1000m
It let you start shooting arty or aaa from 1,500m in 90* nose dive on ground targets and killing them between 800-1200m
even then i often use 800m and can hit aaa from over 800m if i try

Also same for straffing with 6 x 50cals or Italian 20mm pods on MC 202 work fine upto 800m
Specially firing on steep angle or straight down as there is little to no loss in Velocity of round.

Also if you using HE ammo then velocity means nothing much.

[MD_MarxMD_Marx]

Ok let me take a shot at this. You are talking about 2 different subjects here. 1)Effective range: the range that an average person can hit a target 50% of the time. 2)convergence: the range that the projectile of the left gun crosses the path of the projectile of the right gun. this is the point that all rounds from both gun will pass. This is the range were you want your target so that it is hit by both guns.

 

So yes you can have a convergence at 1000m, but that would mean that a target any closer my not be hit. the rounds simply passing over it on there way to 1000m.

No, effective range is defined in my comment - it is a technical definition, not involving statistics.

My comments are based on fighter gunnery concepts. All shells fired by any gun come to earth eventually because of gravity. When a shell leaves the muzzle, the axial velocity (i.e. in the direction of the barrel) is huge in comparison with the slow acceleration toward terra firma (9.81 m/sec/sec), but the shell certainly is moving away from the axial direction, albeit slowly. The typical path of a shell from  a muzzle, up to the effective range, is more or less a straight line. The trouble is, the greatest drag force on the shell is at the muzzle (it is proportional to the square of the velocity), and during its flight, the shell will decelerate markedly. The 'effective range' is marked where the flight of the shell from the muzzle no longer follows that line, but is on quite a well defined curve. At this point, or just beyond it, the once small gravity effect has now become very significant. Now you have to put yourself in a combat situation where you want to land your shells on a fast moving aircraft. How are you going to do this, say, at 500m range? 1. While your eye can see through the reflector sight in a straight line, unless your shells are exactly at that point, at that distance,

your gunsight is useless. No 20mm cannon of this genre has shells that fly in a linear fashion for that range. The 'bullet drop' is going to be huge at 500m. But you could, of course, re - align your gunsight so that you look 'down' to where the shells will be - if you could do such a thing - which of course you can't unless you're firing from a 'bomb aimers' position with a gunsight that has computer controlled adjustment for the non linarity at that range . 2. So your shells fly in a straight line to 500m and get there instantly? Ha ha. Nope. You are talking of seconds for the shell to arrive, even though you are now 'lobbing' them at the enemy. There is no point in using a weapon like this for fighter combat, is there?

My original comment queries the value of setting the convergence range anywhere near 1000m,.

OK convergence is as you describe, but the guns still have a range issue, don't they - i.e. they are useless to the pilot if the gunsight and gun settings are incompatible - which they certainly are if the gun range is beyond 'effective'.

Another point to note maybe, is that unless your name was 'Galland', I know of no fighter pilot in WW2 who could get his gun and gunsight re-aligned to suit his requirements.

 

But maybe there is a case for specialist long range ground strafing, where the target is ostensibly stationary and your run-up is similarly constant in a shallow, accelerating dive. Here the gunsight might be adjusted for maximum range, since that range will be closing very fast.......but even the German BK 50mm had a limited effective range to about 500m........

 

Food for thought?

[Yogiflight]

The convergence setting for the BK 3.7 mounted to the Bf110 G2 was 800m.

The settings for the 20mm guns and the 7.92mm machineguns was 400m and later 500 or 550m in the Focke Wulf and the Bf 110.

The main problem is, that the balistics are not quite correct in all IL2 games and I suppose other flight simulations as well. In the games you can see the tracers going up to the sightline, touching it in the distance you chose in the convergence setting, and then disapear to the ground. This would only be possible with high velocity projectiles. The projectiles, that were shot by the guns, we have in game, were not flying that straight. For example, the 20mm rounds, fired with the MG151/20, in the 109s, crossed the sightline for the first time in 135m, had the highest point in 250m, about 28cm above sightline, and crossed it the second time in 400m. So between 135 and 400m the tracers were above the sightline and therefore good to see for the pilot. Second advantage was easier shooting in deflction shots, disadvantage, you needed to know the distance more precisely, to hit the target.

[Inkophile]

I agree with Sshadow. You are talking about completely different things.

 

The gun's convergence range simply means that the shots from all armaments on the plane (well, at least all that can be adjusted by ground crew) will intersect at that given range. As it works in the game guns are vertically adjusted too, so that at the given range all weapons will hit at the crosshairs (assuming level flight). Ergo, if you have say... 250m convergence range the vertical adjustment can be pretty small, so the shots are travelling more or less in a straight line until that point.

 

However if you set your convergence range to 1000m that will mean that the guns will have to be elevated quite a bit to make the shots "fall" through the point of aim at that distance.

 

Also, since different guns (and even different ammunition within the same gun) have different ballistic properties that means that the actual trajectory for each gun can be wildly different (good example is the MG 17s and the MG FF/Ms on the Bf 109 E-7 and Bf 110 E-2), so up until the point of aim and past the point of aim it can be so bad that only one type of your guns will hit the target at any one point, and the other gun types will miss.

 

Now this can of course affect the effective firing envelope for the plane. For example that with 1000m convergence you might only be able to hit the same target with all guns at 0-250m, and 850-1100m, just as a wild, made-up example.

 

So, well... Yes, a gun's ballistic properties does dictate the gun's effective range, because it is harder to hit further out the trajectory as it drops more and more, but it does in no way cause the shots to be unable to hit at the point of aim.

 

As for adjusting guns and point of aim... It could be done by nearly everyone. It was up to personal preference. There was of course a "standard" setting described in the manuals, but generally if a pilot felt he wanted a different setting that could of course be done by the ground crew.

[II/JG17_HerrMurf]

Uh, no. That is absolutely incorrect. Individual pilots do not get to customize their convergence and never have. A few of the very top experten probably got to mess around with their convergence but that is an exception to the rule. As a case in point; USN didn't even have individualy assigned aircraft. Mucking about with the convergence wouldn't help you because you probably wouldn't have the same AC on the next hop and the next guy climbing into that bird would wonder why all of his rounds were missing.

[II/JG17_HerrMurf]

And guns don't shoot on a level plane. They have a slight upward cant in relation to the sights (in layman terms). Even a trusty M-16 has both a mechanical offset and a sighting system which has the bullet rising in comparison to the sights. That little 5.56 crosses the sight line twice. First as it rises through the sight picture and later, due to gravity, a second time much further down range as it falls through the sight picture.

 

Ask a sniper about long distance shooting on a significant incline or decline sometime.

Edited May 4, 2017 by II/JG17_HerrMurf

[Ghost666]

I hate to disagree with you Herr Murf, manly be cause I agree with you. But in my 20 years of Airforce service I have personnelly seen dozens of pilots adjusting the aim of there guns. One example would be John Wyne in Flying Tigers. And what about Peal harbor? Not to mention countless other movies I watched, always on duty of coarce.  

[II/JG17_HerrMurf]