Guns convergence and harmonization

[Yo-Yo]

This is very interesting material from one of our user, or, I should say unofficial tester with great engineering experience.
 

Just in case, to start interest I asked Chat GPT to translate the material here, diagrams for them one can see in the original place.

 

The reasons here are obvious - the aircraft's armament has changed.

In general, adjusting the machine guns on an aircraft is a rather interesting topic. But not in terms of the armament itself - that part is clear. It's a perfect example of how the internet influences the process of destroying human knowledge. In the past, in order to acquire reliable knowledge on a particular subject (or at least what was considered reliable at the time), one had to go to the library. Books (especially technical ones) were the result of human intellectual effort, and everything presented in them had been extensively tested, reviewed, and approved by specialists. The likelihood of obtaining unreliable knowledge was extremely low.

Currently, books are no longer a source of knowledge. The source of knowledge nowadays is a line in any search engine, providing links to countless rambling articles written by people who have no understanding of the subject matter they write about, engaging in senseless information copying from one internet page to another, often with their own interpretation of well-known facts at a level accessible to their understanding.

The paradox of the situation is that now it is easier than ever to obtain the necessary book on a particular subject. Not only can anyone sign up for scientific and technical libraries and the Russian State Library (formerly known as the Lenin Library), but also a multitude of books have been digitized and are freely accessible. However, no one reads them.

I speak from personal experience - about ten years ago, I digitized and published excerpts from a book on aerial marksmanship theory on the internet. Among other things, it provided a detailed analysis of the principles of weapon alignment, and on various forums, I would say, "Look, this is how it is, and this is how it should be read and studied." What do we have now? We open the internet and observe a variety of nonsense about how the alignment distance of weapons depends on the individual characteristics of the pilot and should be adjusted independently.

The mechanism of spreading this "knowledge" is evident - people take the path of least resistance. To understand a certain issue, one needs to exert certain (and sometimes quite significant) efforts. To follow "common sense logic," no effort is needed. From the perspective of "common sense logic," everything is extremely simple and understandable - bullets fly in an arc, and wing-mounted machine guns are also at a certain distance from each other, so in order to hit an aerial target, the trajectories of bullets and the aiming line must intersect; such intersection is only possible at a certain distance, so you should shoot at that distance, otherwise, you will miss. And since this distance depends on the individual style of aerial combat - it should be adjusted individually. Many go even further and talk about how important it is to accurately determine the distance to the target during aerial combat - it's all so logical that only a fool would object. At one point, they even bothered veterans with questions like, "At what distance were the machine guns aligned in your regiment?"

Interestingly, "common sense logic" explains the world around us not just "a little bit wrong," but completely opposite! According to common sense logic, the sun revolves around the earth - in the real world, it's the opposite. According to common sense logic, a synchronizer interrupter of a machine gun delays the shot when the propeller blade passes the barrel - in the real world, it's the opposite. According to common sense logic, an airborne gunner with zero dispersion machine guns (they even came up with a special term: "laser guns") would hit a squirrel in the eye from a kilometer away - in the real world, it's the opposite: the probability of hitting the target would be zero. The same applies to the alignment of machine guns. Machine gun alignment is not done
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We can see that zeroing the wing machine guns at a distance of 400 meters provides continuous engagement space in the range of 85 to 520 meters from the aircraft. In other words, by aiming the sights at the center of the target and without making any adjustments for trajectory drop, the shooter will reliably hit a target located at any distance from the aircraft within the range of 85 to 520 meters. This applies, of course, to shooting head-on or in pursuit. Shooting at crossing courses requires the use of a circular sight, which is a topic for a separate discussion.

It should be noted that these are the bullet flight trajectories for ground conditions. In the air, the bullet's initial velocity will increase due to the aircraft's own speed, and the air density will decrease. As a result, the bullet will fly higher and farther, and the point where its trajectory intersects the aiming line will shift forward by about a hundred meters. Therefore, zeroing at "400 meters" will become zeroing at "500 meters". It is interesting to consider whether proponents of "adjusting the sighting to individual combat style" take this into account.

Furthermore, in the illustration shown above, we can observe another interesting feature: the vertical zeroing of the wing machine guns on the I-16 (the distance from the gun to the sight is 1 meter, slightly more for the I-16: 1070 cm, but this difference can be neglected) at 400 meters is identical to zeroing at 200 meters; it's just that at 200 meters, the bullet's trajectory intersects with the aiming line in its ascending part, while at 400 meters, it intersects in the descending part.

What will happen if the machine guns are zeroed at 600 meters?

• Nothing good: in the engagement space at medium distances, there will be a "gap" where bullets will fly above the upper dimension of the target, resulting in a guaranteed miss.
  *******************

  eroing at 100 meters?

• Not any better. And that's on the ground! In the air, the bullet trajectory will be higher, and the upper machine guns at medium distances will also shoot past the target. Additionally, in the illustration, the upper machine guns are positioned 0.5 meters below the sight, and in the case of the modeled I-16 Type 24 in this simulator, they are positioned 0.2 meters below the sight, which means the trajectory is even higher.
  *******************
  From all of this, we can conclude that the zeroing of the machine guns on the ground should be such that the bullet trajectory at its highest point is slightly below the upper limit of the target (0.5 meters above the sight line). Therefore, for the I-16 with its "two-tier" armament arrangement, the optimal option is 200 meters (in the illustration, the upper machine guns are positioned 0.5 meters below the sight, and in the case of the I-16 Type 24, they are positioned 0.2 meters below the sight: the trajectory will be slightly higher, but there is a margin).
   
•  

 

We can relax the criterion for target engagement in the horizontal plane and consider the critical zone to be 1.5 meters wide instead of 1 meter (as aircraft are generally wider horizontally than vertically). In that case, for the I-16 Type 5, the horizontal engagement area would start at 200 meters and end at 600 meters.

The overall engagement area is the intersection of the vertical and horizontal engagement areas. Additionally, I would like to remind you that all the diagrams mentioned above are for ground shooting. In the air, the trajectories will be higher and farther, and the exact calculations would depend on the changes in air density and aircraft speed for each specific case. Therefore, we can conclude that the zeroing of the I-16 Type 5 aircraft (as described in 1937) ensured target engagement at relatively long distances: 200-600 meters. Shooting at "rivets" would be pointless. The two wing-mounted machine guns, spaced a significant distance apart, provided sufficient depth of engagement only at longer distances. Zeroing the wing-mounted machine guns at 300 meters would reduce the vertical engagement area.

Zeroing the wing-mounted machine guns at 200 meters for the vertical plane is equivalent to zeroing at 400 meters, but in the horizontal plane, it would significantly reduce the engagement area to a range of 100-300 meters. Therefore, the choice of a 400-meter zeroing distance is evident for the I-16 Type 5. The need to enhance the armament by adding synchronized machine guns was also evident, and it was implemented later.

What changed after adding two synchronized machine guns to the I-16?

In the vertical plane:

• Zeroing the high-mounted synchronized machine guns (with a slight offset of 0.2 meters between the gun and the sight) at 400 meters is not desirable. Even on the ground and at medium distances, the bullet will pass close to the upper profile of the target. In the air, the bullet's speed will increase by the aircraft's own speed. The influence of the aircraft's speed of 150 m/s (540 km/h) is as follows:
•  

I have come across statements on the internet like "The sight is calibrated for a specific distance," and from there, people often draw the conclusion, using common logic, that in order to hit the target accurately, one must approach the enemy at that particular distance.

In this regard, I would like to clarify the following:

Ring sights are not designed for shooting at a specific distance! They are intended for shooting at any distance in effective aerial combat.

The notion that "the sight is calibrated for a specific distance" obviously arises in people's minds after reading a phrase from the sight description, such as "the large ring of the sight is calibrated for a target speed of 300 km/h and a distance of 400 m at a 4/4 aspect angle."

Indeed, the ring is calibrated for a distance of 400 m, but the sight itself is not! When aiming at the ring calibrated for 400 meters, the sight allows for guaranteed hits on targets at any distance from 0 to 600 meters!

This can be explained as follows:

If we take the extreme case and assume that the target is flying perpendicular to the shooter's course and accurately calculate the lead necessary to hit the target at various distances, we obtain a curve (dashed line in the diagram). The ballistics of Soviet ammunition were such that this curved line can be approximated by a straight line passing through the point calculated for a distance of 400 meters (hence the significance of these "sacred" 400 meters!). As a result, the bullet deviation at any distance from 0 to 600 meters does not exceed the dimensions of the same critical area of a hypothetical target measuring 1m x 1m, and the target will be hit.

Indeed, the most important (and practically the only) thing a pilot needs to know about a ring sight is not "400 meters" but the speed for which the ring is calibrated!

This greatly simplifies the shooter's task. It is sufficient to estimate the speed and aspect angle of the target and mentally adjust the size of the ring proportionally to the speed and aspect angle. As long as the distance to the target does not exceed 600 meters, it will be hit (assuming the estimation is done correctly, which can be challenging). The pilot doesn't need to worry about the exact distance to the target (as long as it is within 600 meters). That's the essence of aiming with ring sights.

 

There was a topic and research conducted on this matter. In brief, the essence of these findings is as follows:

Zero dispersion for aerial shooting means zero probability of hitting the target. This statement may seem strange to many, but it is important to understand that aerial shooting is fundamentally different from shooting, for example, with a sniper rifle. For a sniper, who takes a single shot, low dispersion is desirable, ideally aiming for zero dispersion. However, in aerial shooting, both the target and the shooter are in continuous motion. Therefore, aerial shooting is more akin to shooting at ducks with a shotgun, where the pellets are not fired simultaneously but sequentially.

If we imagine hypothetically that an aerial shooter is using a weapon with zero dispersion and the target is not extremely close, where missing is impossible, the shooter will never hit the target with the first burst. This is because there will always be some error in aiming, and the burst will pass by without the shooter knowing which way to correct since without tracers, it is not visible, and even with tracers, it is not straightforward because they show the ascending branch of the bullet's trajectory, which does not coincide with the direction of the potential hit point. If the targeted aircraft, assuming it's not foolish, notices that it is being fired upon, it will start maneuvering, making it even more challenging to hit.

Likewise, the probability of hitting the target with a weapon with significant dispersion is also zero. It is evident that if the bullets fly in all directions, hitting the target becomes impossible.

From these observations, a logical conclusion was drawn: there exists an optimal dispersion level between zero and infinity, where the probability of hitting the target is maximized. Practical shooting tests were conducted, and the results helped determine the approximate boundaries of this optimal dispersion, which turned out to be several times greater than the inherent dispersion of the aviation machine guns and cannons available at the time.

Another logical inference was made: it would be beneficial to vary the dispersion during shooting!

Corresponding mechanized mounts were developed, tested, and their results obtained. However, at that moment, the weapon designers quickly reconsidered their approach.

This was because it did not make much sense to install devices in an aircraft that artificially increased dispersion when the pilot could easily control dispersion by himself!

Indeed, with a burst, the pilot can simply adjust the dispersion by slightly pressing the pedal, and there you have it – dispersion is achieved!

Additionally, any defensive burst can be seen as a burst with dispersion. Instead of considering it as a flock of bullets flying one after another towards an approaching aircraft, it can be viewed as a stationary aircraft in the sky with a series of trajectories converging towards it at some interval – that's dispersion!

Moreover, increasing the number of wing-mounted machine guns for the British and American pilots allowed for a decent dispersion without any mechanisms. Many have likely seen images like the one provided. Here, the area of engagement is expanded by adjusting the sighting distances for different groups of machine guns. It's not a panacea, but still quite effective.

Knowing the width and height of the total dispersion, it is easy to obtain its probable deviation in the lateral and vertical directions (in the case of circular distribution, they will be the same) – it is 1/8 of the total dispersion value. In this case, the probable deviation will be 1 mil.

This is a very small value. For example, in the Soviet Union, the probable linear deviation of technical dispersion (in meters) was considered to be 1.5t, where t is the bullet flight time.

For ShKAS (referring to the I-16 Type 24 sighting table), the bullet flight time at a distance of 300 meters and an altitude of 4,000 is 0.35 seconds.

Consequently, the linear value of technical dispersion for ballistic calculations at this distance is 1.5 * 0.35 = 0.525 meters.

In angular terms, this is 0.525 / 300 * 1,000 = 1.2 mils.

From this, it can be concluded that the influence of wing vibration on the dispersion of weapons installed in the wing, at least for the Americans, was not particularly significant – it was not even considered in the calculations. The "multi-level" sighting played a much larger role.

In this regard, it is interesting to see how the Germans approached this issue.

Looking at the Focke-Wulf sighting card, it immediately catches the eye that they consider the critical zone target size not as 1 meter or 1.5 meters, but as 1.2 meters! That's what German precision means!

Another interesting point is that in their sighting calculations, they use data on the technical dispersion of the weapon, and they determine the depth of the hit zone not based on the intersection of the "ideal" bullet trajectory with the target size, but based on the intersection of the inner edge of the dispersion ellipse with the target size (vertical dotted lines on the diagram) – the calculated hit zone is thus enlarged.

And they conduct sighting not at 400 meters or 200 meters, but at 300 meters – well, they decided that it would work better with their ballistics.

So, what about the probable deviation of technical dispersion for them?

• It is specific to each weapon model (figures on the right side of the diagram in percentages). "Waffenstreuung" is the width of the band in the dispersion ellipse that contains 50% of the best hits. The probable deviation is half the width of this band.

For MG 17 and MG 151: 0.25%. Therefore, the lateral probable deviation is 1,000 * 0.25 / 100 / 2 = 1.25 mils. Practically the same as in the USSR.

It is also worth noting the significantly smaller technical dispersion of the wing-mounted MG FF: 0.125% – not even a hint of considering any consequences of vibration!

[Ala13_ManOWar]

Wow, I wish I could read the original just for fun. What a read, permanent link to any guy posting, again, anything about "convergence" and why we can't have that option. Terrific explanation, the understanding and knowledge of the OP can be clearly felt in there.

Thank you so much for translating and posting Yo-yo. Loved to read that, and it's definitely knowledge to bear in mind next time we're in the air with a warbird.

Edited June 29, 2023 by Ala13_ManOWar

[Cool-Hand]

Great post! Definitely should be stickied up top somewhere in the forums for when the setting of infinite numbers of custom gun convergences inevitably comes back up again.

[Hobel]

 there are squadrons who were not satisfied with the factory settings and some of them made their own harmonization

Basically, the pilots have found out from experience the best Harmonizing for their aircraft, which was then partly adopted by other squadrons.
How is this to be evaluated?

 

http://beyourfinest.com/sticking-to-your-guns/

[Ala13_ManOWar]

7 hours ago, Hobel said:

How is this to be evaluated?

Very well known to exhaustion story. But you're getting it wrong, it's the other way around. We aren't at the BoB in 1940 with wrong assumptions because it was all a new thing with fast highly weaponized aircraft, we're flying 1944 aircraft with well studied, very well studied, scientifically studied, harmonization patterns from factory because of stories and experiences like that one, and many more. No pattern of yours or anybody else will be better than the factory studied pattern, it won't never, ever, be better than the perfectly scientifically studied factory pattern. Period .

[Screamadelica]

What would be nice to know is what range the various gunsights convergences have been set to by ED.

Is the setting at start up the correct one?

I think I remember people testing the Spitfire's convergence to determine the range and coming up with results of 250 yards, which may have matched the RAF settings at some point.

The question has been asked before but never had an official reply. Why the mystery? 

We just need to know so the gunsight can be set correctly, or is it correct already?

Then again, " Just get closer" never fails....

[Skewgear]

The Spitfire gun harmonisation pattern was set at 250yds by the time the LF IX entered service. The DCS harmonisation pattern looks very similar to reality but I suspect it may be slightly different in terms of where the cannon are aimed.

The convergence zone in game is more of an elongated box than a point but from my unscientific visual testing with tracer, it stretches between 260yds and 280yds.

Bear in mind that no machine gun or autocannon produces a steady stream of shots through the same hole. Instead you have a beaten zone of a given size. For a specific application (aircraft gun, indirect fire ground machine gun, etc) there is a permissible variation in the mean point of impact and the intended correct zero position, where the CZP is the point where shots from all of the guns have the greatest probability of hitting the target even if the pilot has made mistakes in range estimation or deflection. Provided the as-zeroed MPI sits somewhere within that PV area, you could end up with significant (but permissible) differences in actual MPI between one airframe and another.

The relationship between gunsight, airframe and gun mountings is also critical. An error of a few thousandths of an inch in the sight mounting may lead to all guns being skewed in one direction or another. I don't have time for the maths as I write this but that could be in the order of feet at the intended harmonisation distance.

Remember also the concept of operations for these aircraft. Unlike the Il-2 game that all online flight sim pilots refer to on this topic, real pilots were expected to jump in any of their squadron's fighters on command and be able to shoot effectively. There was simply no question of messing about with individual aeroplanes'  harmonisation unless the airframe was personally allocated to a wing leader.

Guns therefore had to be zeroed to a common standard across the whole command. Gunnery was taught at rear echelon units and tested by number of hits scored on towed drogue targets. You cannot effectively teach these techniques unless all guns in all aircraft of the same type that the pilot will encounter are zeroed in the same way.

I spoke to a researcher who's part way through writing up the history of the Spitfire gun harmonisation settings and he sent me some draft web pages and graphics he's prepared. Unfortunately he asked me not to share them as he intends publishing them, but they're very clear and logical and a good contribution to the historical record of how these aircraft were used in combat. They also explain how the British thinking on armaments, tactics and lethality changed over time. I have encouraged him to publish them soon so I can link them here.

Incidentally, "just get closer" doesn't work unless you aim off. At 100yds you'll be hitting mid-wing or further out on a 109 if you aim for the fuselage. I'm not sure if it's a video game perspective thing but the RAF seemed to engage at very long ranges by DCS standards.

[probad]

i think is not worthwhile to attack this subject from the realism angle but rather from a sociological angle. i have come to terms with the fact that most enthusiasts adopt a hobby for its aesthetics. for them, the airplane is a fashion statement of their taste and values. that's why its important for them to be able to adjust the minutiae, because a "personal gun convergence" is a personal expression.

what reality and history say is immaterial whenever they fail to serve this objective of personal expression.

Edited October 13, 2023 by probad

[Ala13_ManOWar]

On 10/13/2023 at 10:01 AM, Screamadelica said:

…

The question has been asked before but never had an official reply. Why the mystery?

…

Yep, many times it's been asked, many times answered. The harmonization (not convergence) from American stuff is 1000ft, 300 yards, with a very well studied pattern that will pepper the target either if you fire at 600 yards or 150. It's done like that on purpose, obviously. The RAF harmonization pattern is 250 yards. The German one is 600m as per historical references, but it works well either at 300 or even more than 600 (well known some pilots fired at that distance to bombers even before gunners had a firing opportunity), but that's because most German stuff had nose mounted weapons. The tricky part is Bf109E in 1940 also had 600m harmonization, even in the wings' cannons, and so Fw190A-8 has even in the outer wing cannons. But Dora and 109 with nose mounted weapons are perfect as they are. Just, and I know ""just"", fire at range and it works really well.

 

Yes, the gunsight setting is up to you . Obviously you should set your sight to the wingspan and speed of your target, so it can't be set in beforehand and in an absolute way to always work. But if you care to set the sight every flight it works quite well.

 

[Screamadelica]

Guess I should do more research on this forum. Always learning. 

Some great information in this thread, thanks to all.

Nice to have it confirmed at 250 yards.

S!

[grafspee]

Now i wonder why in P-51 manual you can find this ?

According to this manual in P-51 with K-14 gun sight guns converge at 450-466 yards, for N-9 gun sight it was indeed 250 or 300 yards.

So if DCS P-51 has 300 yards converge, it is wrong and needs to be changed.

Edited October 15, 2023 by grafspee

[Ala13_ManOWar]

2 hours ago, grafspee said:

So if DCS P-51 has 300 yards converge, it is wrong and needs to be changed.

 

Funny you post a pattern which shows exactly 1000 feet harmonization/convergence while you say it's wrong…

[grafspee]

19 hours ago, Ala13_ManOWar said:

Funny you post a pattern which shows exactly 1000 feet harmonization/convergence while you say it's wrong…

Where do you see 1000ft harmonization on this pattern, pls point me where is it? I don't know how you came out with 1000ft converge from this diagram? It is obvious that converge point is somewhere around 1500ft. Exact point would be 1350-1400 ft which is 450-466 yards and not 300 yards. And 1000ft is 333yards not 300.

So i have no idea from which planet you took that 1000ft convergence. 

And on top of that you are laughing tears out of my recent post.

Not to mention that i took time to provide meaningful evidence to discussion and you only talking about things which you think should  be.

You didn't even take time to convert 1000ft to yards because you are saying over and over that 1000ft is 300 yards.

Normally i don't care if someone talk fairy-tails, but when you laugh at me when i post manual pages contradicting your imaginary view on this topic, i won't let it go.

Edited October 16, 2023 by grafspee