PDA

View Full Version : Convergence questions



Noxx0s
03-14-2010, 12:13 AM
Hey, so I've been using 160m because I found that to be a really good distance to open fire at...close enough so I can't really miss, but still far enough away that I can maneuver a bit to adjust. But I was told recently that setting higher convergence affects how straight the bullets come out.

Does this mean that if I set it at say... 500m the bullets would arc upward? I could see this being helpful in pulling off those awkward deflection shots where the plane is obscured under the sight... since there'd be some "lob", it would allow me to not have to pull up as far. Is this true?

At what distance do nose mounted guns come out "straight"?

At the same time though... a distance of 500m might screw me over on planes with wing mounted guns, and it would be real rough to switch it when I switched planes because then I would never really "memorize" where to lead.

Any ideas here?

skarden
03-14-2010, 12:49 AM
160m is a good distance I reckon(I have mine at 165m)I think planes with center mounted guns will arc the guns up most noticeably,but all will have to at 500mts I imagine.As far as what convergence for a "straight" shot,it'll vary from plane to plane and from ammo type to ammo type.

I started out with 350mts as my convergence and it's slowly crept in to where it is now which seems to suite the way I fly the best,less deflection to worry about as well.I guess the rule of thumb is that cannons can be set out further cause they'll still hit pretty hard a bit further out but machine guns should probably be set closer to keep their destructive power up,that said it is best to try and few different things out and see what works best for you.

na85
03-14-2010, 01:05 AM
Actually I'm pretty sure the farther out you set your convergence, the flatter the trajectory the bullets will take.

There's a pretty straightforward graphic explaining how convergence relates to the arc path of the bullet.

Skoshi Tiger
03-14-2010, 04:45 AM
The trajectory of the bullets would only be 'flatter' if you increased their velocity.

Setting the convergence of the guns is basically changing the angle that the guns are mounted in the aircraft so that the curved path of the rounds will fall through the convegence point at the required distance.

Think of the sights of a rifle as setting the "convergence" for the rifle. If you set the sights for 200 yards the barrel is only pointed slightly up. If you get the sight for 1000 yards the barrel is pointed up at quite an angle.

The angle that the gun is set at will depend on the velocity of the round. A faster projectile will have a shorter flight time an will be set at a shallower angle than a slower round.

For anything other than a centre mounted gun the guns will also have to be angled inwards to some degree so that they will converge at a single point.

Heres not too bad a video
http://www.youtube.com/watch?v=NpnJeM3wjew


As an aside this morning I astounded my kids and the carnie that was manning the air rifle range at the local fair! I actually managed to shoot down the three targets with the bent barreled , skew sighted, cork firing air rifles that they provide. The guy had to look twice before he gave my kids the prize and man did he look P155ed off that someone actually won something.

Cheers.

Tully__
03-14-2010, 05:34 AM
It goes something like this:

http://users.tpg.com.au/davken27/convergence.jpg

M_Gunz
03-14-2010, 12:45 PM
You should also be aware that when shooting either upwards or downwards that gravity on the shots will not
be pulling them as much across the sight line as when shooting while level. For more than a small angle up
or down the guns will "shoot high".

If you are closing fast, it will shorten how long the shots take to reach the target. If you look at the
situation relative to yourself, the target is getting closer and meets the shots at less range from you
than it was when you fired. You actually have a high effect area from inside to outside convergence range
where the shots are within about 2-3 meter wide pattern.

Remember that your burst has length and width as well as incredible speed. It's like an hourglass out
ahead of you that pours its sand from the inside v-shape bubble to the outside in maybe a whole second
with 300m convergence and be good (not best effect but) from 150m to 400 with some high or low adjusting
in guessing where the shots will be. If you fire a one second burst then you will have a moment when
the whole pattern is "filled" from close to far. Use THAT to shoot with and not only some crosshair!

It's easier to have a good idea where out in front of you the shots will go and how long for them to get
there then set things up so the target _appears_ to move towards that high effect region. When he will
take as long to get there as your shots then send a burst out to join him. If you are dead six and both
are flying straight then you don't have to wait except for effective convergence range to try and chew
shots in from the tail to the cockpit through everything along the way... deflection needs less ammo.

Run gunnery practice with arcade=1 in conf.ini and you will see every shot that hits as a white dot.
Run track playbacks of gunnery practice and get used to knowing what hits and how long the shots take
to reach target.

It's the same as coordinating to throw a ball to a moving person and you don't need sights to do that.
You see where they are going and you throw the ball there to meet at the same time.

K_Freddie
03-15-2010, 03:40 PM
125-175m (usually 150m) is what I play with.

The hitting power, and spread/grouping up to 2x 150m is still good at these convergences.

I wouldn't go for anything above 200m as it starts looking like a Globular Cluster beyond this. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

TinyTim
03-15-2010, 05:10 PM
I strongly prefer nose mounted weapons. When that's not an option, 100-120m for anti-fighter missions, 250-300m for anti-bomber/strafing missions.

MikkOwl
03-16-2010, 04:31 PM
What the! Convergence settings alter the vertical (i.e. range) setting of the guns/sights?! I had no idea about this, I thought it was the horizontal convergence only. This is the first I heard of it. Thank YOU guys for bringing this to my attention. At first I thought "what are these people babbling about? Don't they know that 'blabla'". Had to go check for myself, setting convergence between 100m and 1000m repeatedly in different planes at the ground to see for myself. And it was true.

After that, off to fly a bit in different planes trying out some gunnery and I huuugely improved already after finding this out. As in 'holy crap what a difference it makes now when I can figure out how the sights work at longer distances'. Hitting someone flying level and straight away from me at 600m is now doable and almost easy (nose mounted Mg 151/20s and Mk.108s). Before it would have been crazy spray and pray and hope for a hit.

Findings: Convergence set to 1000 meters, speed 300km/h, target matching speed and heading. Cannons (151 and 108) seem to hit them if centered in the sights at about 650-770 meters. If further away, need to aim noticably more above them, and if closer aim a little bit below them. I assume this is the result of the relative wind being stronger already because of the 300km/h aircraft speed, combined with the target having moved forward as well for 1-2 seconds since the time of firing.

The 108 seem to reach the target first. The shells are seen visibly overtaking the 151 shells after a few hundred meters, and also seem to have less drop at that point - but the tracers cannot be seen beyond that point, and the 108's had a higher ballistic path to begin with due to the guns being aimed higher than the 151's. Their higher speed retention at longer ranges is noteworthy. Maybe they weigh so much more? The quad Mg17 in the nose fly extremely fast at first but slow down very quickly and get awful drop. Since they have no explosive qualities, no wonder machine guns are outright dreadful except at close range. Good for quick hits at close range and snapshots at canopy and inline engines - they really are unmatched in initial velocity meaning scoring hits at close range is very easy. Machine guns should definitely be calibrated for short range. Cannons for longer ranges.

EDIT: One of the reasons why I never heard about vertical convergence was because no one ever mentioned it anywhere I went. The only thing people talk about is the issue of having to set 'convergence' for wing mounted weaponry, and how nose mounted aircraft don't need to worry at all about any convergence. So in fact they do need to worry about convergence settings like anyone else, but not the horizontal convergence specifically.

thefruitbat
03-16-2010, 05:15 PM
it has been mentioned here many times before, you just must of not been 'lucky' to see those threads.

its one of the reasons i like nose mounted guns so much, as you can easily hit outside of convergance range with a little nose up to compensate, whereas with wing guns to hit outside of convergance, you have to aim up and to the side, and only one side of your guns will hit.

TinyTim
03-16-2010, 05:33 PM
Originally posted by MikkOwl:
The 108 seem to reach the target first. The shells are seen visibly overtaking the 151 shells after a few hundred meters,...

Maybe you are mixing up Mk103 with Mk108, since Mk108 is a slow muzzle velocity weapon (~550m/s) compared to Mg151/20 (~900m/s from the top of my head). This is clearly visible in the sim where 151 tracers zoom past 108 ones.

Mk103 however is completely another story, although often mixed with 108 due to similar calibre. It has much more powerful cartridge (30x184 as opposed to 30x90 with Mk108), and much higher muzzle velocity of about 900m/s. It's also much heavier and bigger weapon.


Originally posted by MikkOwl:
The only thing people talk about is the issue of having to set 'convergence' for wing mounted weaponry, and how nose mounted aircraft don't need to worry at all about any convergence. So in fact they do need to worry about convergence settings like anyone else, but not the horizontal convergence specifically.

Consider that nose mounted weapons are usually mounted much closer (vertically) to sighting line, which minimizes convergence issues. Convergence for wing mounted weapons is thus still way more important, in (obviously) horizontal and in vertical plane.

MikkOwl
03-16-2010, 06:01 PM
Originally posted by thefruitbat:
it has been mentioned here many times before, you just must of not been 'lucky' to see those threads.

its one of the reasons i like nose mounted guns so much, as you can easily hit outside of convergance range with a little nose up to compensate, whereas with wing guns to hit outside of convergance, you have to aim up and to the side, and only one side of your guns will hit.
I have only been checking in here since late last year. I am sure since Il-2 was released there must have been many mentions if it over those 9 years though http://forums.ubi.com/groupee_common/emoticons/icon_razz.gif I'm glad I found out about it, it made a really huge difference for gunnery at non-close ranges.


Originally posted by TinyTim:
Maybe you are mixing up Mk103 with Mk108, since Mk108 is a slow muzzle velocity weapon (~550m/s) compared to Mg151/20 (~900m/s from the top of my head). This is clearly visible in the sim where 151 tracers zoom past 108 ones.
No, did not mix them up (I have an interest in the various types of cannons and machine guns, as well as firearms since a long time back). http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Mk 108 30mm(HE) shell has a muzzle velocity of even less than you thought - 505 meters per second. It weighs 330 grams and only some of that is tracer chemical (I presume?). This leaves a very heavy shell.

Mg 151/20mm(HE-M) has a much higher muzzle velocity at 800 meters per second. It weighs only 92 grams, with some of that going to laser - I mean, tracer chemicals.

When firing them simultaneously, the 151/20 flies the first shorter distance noticably faster compared to the 108. But it loses velocity quickly. The 108 shells just don't lose as much velocity with distance, and they soon overtake the 151/20's (I would estimate at a few hundred meters distance, maybe 250 - hard to tell when so zoomed out in exterior view). It keeps pulling away and then the tracers go out and one cannot see very long range results.

This makes the 108 harder to hit with at closer ranges purely due to being much slower than other weapons. But at medium/long range it gets there at least as fast or faster, although it is hard to tell about the ballistic curvature versus other weapons, as the tracers stop rendering.

Take a 110 G-2 with mk108s as option, start on the ground. External view, zoom way out, then fire both weapons simultaneously and keep observing the trajectories and their relative positions to each other. I keep seeing the 108's being intitially slower but is more consistant, not slowing down so much compared to the lighter weapons.


Mk103 however is completely another story, although often mixed with 108 due to similar calibre. It has much more powerful cartridge (30x184 as opposed to 30x90 with Mk108), and much higher muzzle velocity of about 900m/s. It's also much heavier and bigger weapon.
The 103 is a complete beast. Super high muzzle velocity, flat trajectory, high mass to keep up the velocity. I will try to compare it side by side with other cannons just out of curiosity. Too bad about the weight and messed up wing mounting positions one usually finds it in. Wish my 110G-2 could mount two in the nose, that would be something http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

TS_Sancho
03-16-2010, 07:11 PM
Originally posted by thefruitbat:
it has been mentioned here many times before, you just must of not been 'lucky' to see those threads.


Originally posted by MikkOwl:
I have only been checking in here since late last year. I am sure since Il-2 was released there must have been many mentions if it over those 9 years though http://forums.ubi.com/groupee_common/emoticons/icon_razz.gif I'm glad I found out about it, it made a really huge difference for gunnery at non-close ranges.


There is nothing wrong with asking, its a good question even if it has been answered before.

Sharing information for IL2 is the point behind maintaining this forum. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

BluesmanSF
03-17-2010, 02:37 AM
Good points there MikkOwl and Sancho. It occurred to me quite late aswell, that there's vertical aspect also in the convergence. Hence I didn't fiddle with the nose mounted guns at all as I've had the conv. set to 180 for years, and therefore, while now being aware of the advantages of setting conv to 500+ with nose mounted guns, I hesitate to set it that way, because over the years I've learned to compensate the bullet-drop for ex. in 109G2 conv180m.. And now I'd have to re-learn it again =D

6S_Blues

Noxx0s
03-20-2010, 03:23 PM
Originally posted by Tully__:
It goes something like this:

http://users.tpg.com.au/davken27/convergence.jpg

So basically having a short convergence of say 150-160 causes the bullets to go up slightly just the same as having set to like 400? At what short range do I get that vertical boost?

deepo_HP
03-20-2010, 05:26 PM
Originally posted by MikkOwl:
When firing them simultaneously, the 151/20 flies the first shorter distance noticably faster compared to the 108. But it loses velocity quickly. The 108 shells just don't lose as much velocity with distance, and they soon overtake the 151/20's (I would estimate at a few hundred meters distance, maybe 250 - hard to tell when so zoomed out in exterior view) i have no ballistical curves for the mg-150/20, but probably one can use available calculators for rough estimation of the times to reach 800m (or whatever distance).

in case of 30mm-shells (330g) in comparative tests between mk-103 (860m/s MZ) and mk-108 (500m/s MZ) the times to reach 800m were 1,14s (571 m/s) for the mk-103, resp. 2,0s (371 m/s) for mk-108.
the mg17-shell (11,55g) with a muzzle-velocity of 785 m/s took 0,4s (400 m/s) to reach 800m.
even with different bores and shapes of the shell, the 20mm MG should not take longer for that distance than a 30mm fired by the slow mk-108. since i am a bad shot and am hardly able to track my tracers, i cannot say how it is represented by the game... but i'd say that there should be no visible overtaking of smaller calibres by 30mm at distances below 1000m.

references (Borsig, from cockpitinstrumente.de):

http://www.dadatainment.info/wb/30mm.jpg

http://www.dadatainment.info/wb/mg17.jpg

deepo_HP
03-20-2010, 06:00 PM
Originally posted by IcyScythe:
At what short range do I get that vertical boost? not entirely sure what you mean, but these are the ballistic curves of FW-190 A8/R2 as adjusted:

http://www.dadatainment.info/wb/fw190.jpg

M_Gunz
03-20-2010, 08:09 PM
Originally posted by deepo_HP:
http://www.dadatainment.info/wb/fw190.jpg

You can get an estimate of time of flight by calculating how far the shells rise plus how far they fall.
But I must warn you that you will not be within a millisecond or even 10 just using that chart, let alone EXACT!

Time to rise to a stop is the same as time to drop the same distance, it is the distance and gravity that count.

S (position) = S0 + V0T + 9.81/2 * T^2

In this case the axis being measured along is vertical, rise and drop. T is time in seconds.
In this case we use relative heights so S0 (position 0) is effectively 0 and V0 (velocity 0) is also 0.
S becomes the height of the rise or drop, each calculated for time and the times then added.

T = sqrt(S * 2/9.81)

However I can't put a scale to my screen and hope to read those lines with even half-decent accuracy.

IF the 108 fires from 100 cm below the sight line and rises to 120 cm above then it rises 2.2m and falls 1.2m.
So .6697 sec on the way up and .4946 sec on the way down, 1.1643 sec to target... but I'd round that to one
or two places at most then say screw it since I only eyeballed the lines on that linked drawing anyway.

I'm not sure I believe it. The length of the curve it would have to travel without much loss of speed due
to drag.. over 500m for sure though not as badly as that non-proportional-scale drawing shows.

The lower arcs of the other guns all tell of higher average speed than that of the 108 IF the drawing is
not some convenient invention to get an idea across where only gun positions and ranges are realistic.

BillSwagger
03-20-2010, 08:23 PM
i've always made the argument that convergence charts like these only tell a partial story to the ballistics it represents. You change the airspeed and it will change the way the arcs behave.

you need to look at ballistic coeficients to get a concept of how airflow would also effect velocity.


Bill

deepo_HP
03-20-2010, 09:14 PM
hi billswagger,

this chart is from the weapon manual for maintenance of fw-190 a7/r2 and a8/r2, not an illustration of inflight calculations (as in bomb-tables, i mean). with a max allowed dispersion between 0.125 and 0.25% the chart reflects the (theoretical) curves after adjusting the plane's weapons. where you are right, that it won't be the actual path - this depends on altitude, wind, speed, pressure. alone the temperature changes muzzle-velocity by quite large amounts.
however, it was meant as reply to icyscythe's question about the cross-points... for example the mg131 (no convergence in horizontal, btw) was adjusted to 400m and crossed the gunsight first time at 28m then. the mk-108 was adkusted to 500m, first crosspoint at 92m - and so on...

interesting here is for example that the horizontal and vertical convergence was not always the same - the reason seemed to be explained in the lower chart, which relates to the target-width in relation to the distances of the related weapons (nose, wingroot and wing).
this lower chart shows in my opinion, that vertical convergence with gunsight was in fact much more of a factor than horizontal, regarding probability of hits with a given dispersion and at the adjusted distances.

deepo_HP
03-20-2010, 09:37 PM
hi m_gunz,

i should probably have posted it all in one better...
as i wrote to billlswagger, the chart is just taken from the manual for the fw-190 r2-versions.
so i thought, it describes the ideal ballistics after successful adjusting on the schiesstand.

the other link about the mk-103/108 comparison is from a report of Borsig, testing both cannons with the same shell. here again (as linked image now):
http://www.dadatainment.info/wb/30mm.jpg

very interesting, your approach on the related times for the points of the arcs...
and the values you found are reflected well enough in the actual speeds from the tests! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

i guess, there are still several factors, like the cannon-tests probably haven't been done with shells used for combat later.
nevertheless, the time-to-target fits nicely! given that the top of arc is somewhere between 330 and 360m, the table lists 0.7-0.8s for it.

M_Gunz
03-20-2010, 10:09 PM
Wow! THANKS FOR THE CHARTS!

The method I used is centuries old AFAIK, even older than the ballistic pendulum.

Add: while ballistics isn't *EXACT* and you'll never create *EXACTLY* identical cartridges
However you check on the consistency of standard .22LR ammunition for example, it is so
tight that the differences are swamped by the shooter, gun and environment. I know that
one is effectively the same as the next.

MikkOwl
03-21-2010, 04:51 AM
Originally posted by deepo_HP:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MikkOwl:
When firing them simultaneously, the 151/20 flies the first shorter distance noticably faster compared to the 108. But it loses velocity quickly. The 108 shells just don't lose as much velocity with distance, and they soon overtake the 151/20's (I would estimate at a few hundred meters distance, maybe 250 - hard to tell when so zoomed out in exterior view) i have no ballistical curves for the mg-150/20, but probably one can use available calculators for rough estimation of the times to reach 800m (or whatever distance).

in case of 30mm-shells (330g) in comparative tests between mk-103 (860m/s MZ) and mk-108 (500m/s MZ) the times to reach 800m were 1,14s (571 m/s) for the mk-103, resp. 2,0s (371 m/s) for mk-108.
the mg17-shell (11,55g) with a muzzle-velocity of 785 m/s took 0,4s (400 m/s) to reach 800m.
even with different bores and shapes of the shell, the 20mm MG should not take longer for that distance than a 30mm fired by the slow mk-108. since i am a bad shot and am hardly able to track my tracers, i cannot say how it is represented by the game... but i'd say that there should be no visible overtaking of smaller calibres by 30mm at distances below 1000m. </div></BLOCKQUOTE>
Surely the Mg 17 cannot reach 800 meters in 0.4 seconds if initial muzzle velocity is 785ms?

I have a chart of the Bf 110 G-2 showing adjustment stuff for the version with 108's and 151/20's. But I don't think it has any data on the ballistics beyond the sight alignment graph. http://deutscheluftwaffe.de/ar...e%202%20MK%20108.pdf (http://deutscheluftwaffe.de/archiv/Dokumente/ABC/m/Messerschmitt/Me%20110/Bf%20110%20G-2%20R3%20Schusswaffenanlage%202%20MK%20108.pdf) - it's near the end somewhere I think.

Did you check the zoomed out view (from the side) when firing both weapons together? Don't need to be a good shot or anything, just zoom way out from the side and fire them simultaneously, and observe the tracers. The 108's really do catch up with and overtake the 151/20's and the MG 17's. On the ground standing still, when nose is angled upwards a bit it is very visible. Not as sure about flight (have problems flying straight when not in cockpit view, but I am going to record a replay and observe it from the external view afterwards.

A question: The charts and data, does it assume a static position or the added speed (and drag) from the gun platform moving forward (aircraft)?

Second question: The angle on the Borsig charts seems to be 0 degrees - and they count the distance in the horizontal plane only I think - firing like that makes the shells have to wrestle gravity less than if angled up a bit for arriving on target at the same altitude the shell was fired from. Are there differences in flight time and velocity in any way between zero angle and upward angle? I imagine the shell would lose more speed over the whole flight duration from being angled upwards, as it must fight gravity a bit more than otherwise.

EDIT:

Performed those in-flight tests with the Bf 110 with Mk 108 nose cannons to see how the shells relate to each other. Using the Bf 110 known length as measurement stick I can see that I grossly underestimated the distances of when the shells overtake each other. At an altitude of 810 meters, indicated airspeed of 370km/h (TAS should be about 390km/h), with distance being measured from the cannons, not the absolute fixed point in space where the shells were fired relative to the ground:

- 151/20's had about 40-50% higher velocity initially, pulling away from the 108's.

- At 110 meters the gap between them was the widest, with the 20mm being ahead of the 30mm by 47 meters. This is also where they traveled at the same velocity. Beyond this point the 30mm shells were reducing the distance between them.

- At 550 meters, the 30mm had reduced the gap to zero, with the 20mm falling behind. Tracers stopped rendering very soon after this point. This was about 1.7-2.0 seconds from the point of firing, making the total distance the 20mm and 300mm shells had traveled about 740 meters.

deepo_HP
03-21-2010, 05:30 PM
Originally posted by MikkOwl:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by deepo_HP:
the mg17-shell (11,55g) with a muzzle-velocity of 785 m/s took 0,4s (400 m/s) to reach 800m.
Surely the Mg 17 cannot reach 800 meters in 0.4 seconds if initial muzzle velocity is 785ms? </div></BLOCKQUOTE>you are right, surely not... silly me has read the wrong end of the scale. the time to reach 800m is noted as 1.5s in that small calibre test.


Originally posted by MikkOwl:
A question: The charts and data, does it assume a static position or the added speed (and drag) from the gun platform moving forward (aircraft)?

Second question: The angle on the Borsig charts seems to be 0 degrees - and they count the distance in the horizontal plane only I think - firing like that makes the shells have to wrestle gravity less than if angled up a bit for arriving on target at the same altitude the shell was fired from. the Borsig tests are purely comparative measurements between mg-17 and a mg-131 reduced in calibre, so they fired the same shells but with much higher energy in the mg-131/8.

the 2nd and 3rd rows describe the 'aufsatz' and 'fallhoehe' - which i assume are upwards angle (in 1/64000, which is 'strich') and top-height of the arc. so this should be similar to the adjusting procedure (well, without adjustment)


Originally posted by MikkOwl:
- At 550 meters, the 30mm had reduced the gap to zero, with the 20mm falling behind. Tracers stopped rendering very soon after this point. This was about 1.7-2.0 seconds from the point of firing, making the total distance the 20mm and 300mm shells had traveled about 740 meters. the mg-17 data were just for a very rough estimation since i didn't find proper comparison of 20mm and 30mm. however, i wouldn't have thought that 20mm will fall behind already below 1000m as you found it in the game.

by the method which was presented by m_gunz, the following travel-times can be concluded by the convergence-charts of the fw-190:
- MG151/20 (mounted 113cm below gunsight, top of ballistic curve at 84cm above): 1.05s/550m
- MG151 (mounted 113cm below gunsight, top at 80cm above): 1.04s/700m
- MK108 (mounted 104cm below gunsight, top at 110cm above): 1.13s/500m
- MG131 (mounted 5cm below gunsight, top at 78cm above): 0.81s/450m

surely there is still not much to be concluded... as already mentioned before, environment, moving platform and pilot and belting probably include an error far bigger than the rounded two spaces.
but since these are the values from adjusting convergence, they should be accurate enough for theoretical considerations.
i am still not sure, if 30mm should pass 20mm already at some 740m, as you found ingame - but i think such distance was considered too far for proper aiming anyway.

the tables show that convergence wasn't set to the same point at all, but differed a lot in horizontal and vertical, even for the same weapon - except the mk-108. this makes probably sense in regard to the relative speeds of attacker and target.
the lower chart shows that horizontal convergence is much less of a concern and in a greater range just by weapon-dispersion. the charts represent the different tactical use of the regarding weapon, and in my opinion concentrate on bringing down bombers entirely... with the 30mm the only one converging on spot. i would think that 500m is considered the desirable target-distance of the FW-190 R2 variants.
interesting to see how different convergence is set for the FW-190 A2. convergence here is generally set much nearer and to mid between first and second gunsight-crossing for all weapons:

http://www.dadatainment.info/wb/190a2.jpg

M_Gunz
03-21-2010, 07:03 PM
- MG151/20 (mounted 113cm below gunsight, top of ballistic curve at 84cm above): 1.05s/550m
- MG151 (mounted 113cm below gunsight, top at 80cm above): 1.04s/700m

Aren't those 151's both the same IRL?

And I wouldn't count on IL2 tracers to show me when or where all the shots go for technical purposes.

deepo_HP
03-21-2010, 07:58 PM
hi m_gunz,

the MG 151 here is the 15.1mm Mauser ('machine-gun'), as used in 109 F2 for example.
on developing the 20mm-Minengeschoss, rounds had been given a shorter case to keep the same length as 15.1mm... so the cannon could easily be converted by changing just the barrel to a slightly shorter one. due to the shorter barrel and case, and the heavier shell the muzzle-velocity lowered from 960m/s to 810m/s.
the smaller calibre version was then also referred as MG 151/15 sometimes. whereas after all had been converted, MG 151 was often used for the MG 151/20. well, at least how i understood all the confusion.

in the charts, the suffix 'E' stands for the version with electrical priming to synch the wing-root installations with the prop. again, later the outer wings got electrical as well.

M_Gunz
03-22-2010, 12:36 AM
I see! Not the same gun. I had thought that they were done with the 151/15 (as I knew it) by then.

They would have to change the barrel and receiver at a minimum to fit 20mm, and bolt if the brass
for the 15mm is not the same diameter which from what you wrote I am guessing they didn't have to.
None of the mountings or space inside the wing though, or ammo storage/feed.

But that does go a long way towards explaining the 151/20 ballistics compared to the Russian and
British 20mms. Funny how this is the first time the fact has been raised when for years there was
huge battles over things like the 151/20 vs 'Russian lazers'. Could have used your knowledge then!

deepo_HP
03-22-2010, 02:10 AM
ha, not much 'knowledge' here... http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif
i am just a collector of documents which cross my path. most times i have no clue if i ever will read or understand them properly, but still i dare to delete them. probably a suppressed neurosis.
and in few cases, they actually show usable... so then i can pretend that all the waste makes sense to keep.
likewise the weapon manual of the FW-190 reminded me much of adjusting tank-cannons. still theoretical ballistics is as mysterious as life on mars to me.


the charts were from the manual of May 1944. the MG 151 E is not mentioned anywhere in the text, only shows in the charts - perhaps it was kept on for rare examples still in storage?

M_Gunz
03-22-2010, 03:00 AM
You could get a membership to a decent rifle range. Mine had 35lb match 22's for use by members,
nice and heavy to not wobble so bad. You'll pick up plenty there. There is more about relaxation,
muscle and breath control than rifles and ballistics; you get practical pretty quick there.

WTE_Galway
03-22-2010, 06:19 PM
Originally posted by MikkOwl:

The 103 is a complete beast. Super high muzzle velocity, flat trajectory, high mass to keep up the velocity. I will try to compare it side by side with other cannons just out of curiosity. Too bad about the weight and messed up wing mounting positions one usually finds it in. Wish my 110G-2 could mount two in the nose, that would be something http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif



haha .. well it WAS meant as an anti tank shell not anti aircraft http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

Nice pic that compares the Mk103 with a few other common rounds form the period ...



http://i4.photobucket.com/albums/y101/clannagh/ammunition.jpg?t=1269303389

M_Gunz
03-23-2010, 05:59 PM
So are the 8th and 9th from the left Mk103 the 151/15 ammo?
They look like necked-down 10th, 11th and 12ths (with the 50 cal next in line).
Same height, same diameter brass.

Wow, MG 151 should have more of a following just for fast-flat trajectory!
It makes the 131 look sick!


complete IL2 guns and ammo table below:

MG 151
// HET - AP - HE - AP

HE/HET
mass = 0.057
speed = 960.0
power = 0.0019

AP
mass = 0.072
speed = 859.0
power = 0

MG 151/20
// APIT - HE - HE - MG - MG
APIT
mass = 0.115
speed = 710.0
power = 0.0036

HE
mass = 0.115
speed = 705.0
power = 0.0044

MG
mass = 0.092
speed = 775.0
power = 0.0186




check the date: 08/14/02


Author:
Oleg_Maddox
Rank:
Creator of IL-2
Sturmovik
Date:
08/14/02 12:56PM



Here is the direct table of shells and bullets from source code of IL-2.
Comments:

power - here is the TNT, that also modelled (as well as pices of shells).

T - Tracer bullet
AP - Armor-Piercing bullet
APT - Armor-Piercing with Tracer
API - Armor-Piercing Incendary
APIT - Armor-Piercing Incendary Tracer
HE - High-Explosive shell
HEI - High-Explosive Incendary shell
HET - High-Explosive with Tracer
HEIT - High-Explosive Incendary Tracer
MG - M-Geschoss, thin-shell High Explosive

such line destinated the sequence of shells/bullets:
// APIT - AP - AP - APIT - API - API


Table itself.
==========================


Browning .303
// APIT - AP - AP - APIT - API - API

API/APIT
mass = 0.010668491403778
speed = 835.0
power = 0.0018

AP
mass = 0.010668491403778
speed = 835.0
power = 0

Browning .50
// APIT - AP - HE - AP

APIT
mass = 0.0485
speed = 870.0
power = 0.002

AP
mass = 0.0485
speed = 870.0
power = 0

HE
mass = 0.0485
speed = 870.0
power = 0.00148

Hispano-Suiza Mk.I
// HET - AP - HE - AP

HE/HET
mass = 0.129
speed = 860.0
power = 0.012

AP
mass = 0.124
speed = 860.0
power = 0

M4
// HET - (APT/HET)

HET
mass = 0.604
speed = 612.0
power = 0.044

MG 131
// HET - AP - HE - AP

HE/HET
mass = 0.035
speed = 710.0
power = 0.00148

AP
mass = 0.034
speed = 750.0
power = 0

MG 15
// AP - AP - APT

AP/APT
mass = 0.0128
speed = 760.0
power = 0

MG 151
// HET - AP - HE - AP

HE/HET
mass = 0.057
speed = 960.0
power = 0.0019

AP
mass = 0.072
speed = 859.0
power = 0

MG 151/20
// APIT - HE - HE - MG - MG
APIT
mass = 0.115
speed = 710.0
power = 0.0036

HE
mass = 0.115
speed = 705.0
power = 0.0044

MG
mass = 0.092
speed = 775.0
power = 0.0186

MG 17
// AP - AP - APT

AP/APT
mass = 0.010
speed = 810.0
power = 0

MG 81
// AP - APT

AP/APT
mass = 0.010
speed = 920.0
power = 0

MG/FF
// APIT - HE - HE - MG

APIT
mass = 0.115
speed = 580.0
power = 0.0036

HE
mass = 0.115
speed = 585.0
power = 0.0044

MG
mass = 0.092
speed = 690.0
power = 0.0186

MK 103
// APT - MG - MG - HE

APT
mass = 0.502
speed = 752.0
power = 0.0

MG
mass = 0.330
speed = 900.0
power = 0.072

HE
mass = 0.455
speed = 800.0
power = 0.024

MK 108
// HEIT - MG

HEIT
mass = 0.455
speed = 500.0
power = 0.024

MG
mass = 0.330
speed = 525.0
power = 0.072

NS-37
// HEIT - APT

HEIT
mass = 0.735
speed = 900.0
power = 0.0406

APT
mass = 0.760
speed = 880.0
power = 0

NS-45
// HEIT - AP

HEIT
mass = 1.065
speed = 780.0
power = 0.052

AP
mass = 1.000
speed = 850.0
power = 0.0

PaK40
// HEIT

HEIT
mass = 6.800
speed = 770.0
power = 0.680

ShKAS
// APIT - API - T - API

APIT
mass = 0.0096
speed = 869.0
power = 0.0005

API
mass = 0.0096
speed = 871.0
power = 0.0005

T
massa = 0.0096
speed = 869.0
power = 0

ShVAK
// APIT - HE

APIT
mass = 0.096
speed = 800.0
power = 0.001

HE
mass = 0.0676
speed = 800.0
power = 0.0068

UBS / UBT
// APIT - AP - HEI

APIT
mass = 0.0448
speed = 850.0
power = 0.001

AP
mass = 0.051
speed = 850.0
power = 0

HEI
mass = 0.0428
speed = 850.0
power = (0.00114+0.00128)

VYa
// SIT - API - API

SIT
mass = 0.195
speed = 890.0
power = 0.0156

API
mass = 0.201
speed = 890.0
power = 0.008

API
mass = 0.201
speed = 890.0
power = 0.008


-------------

If you'll ask why some bullets has TNT, its because they had explosive in warhead.



Oleg Maddox
1C:Maddox Games

deepo_HP
03-23-2010, 09:01 PM
Originally posted by M_Gunz:
So are the 8th and 9th from the left Mk103 the 151/15 ammo?
They look like necked-down 10th, 11th and 12ths (with the 50 cal next in line).
Same height, same diameter brass.

yes, could be the ones...
but i would guess, that the MK 151/20 is the sixth from the left, same as on the far right in belt.
here is another one for size comparison (perhaps better to see than on galway's cupboard http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif)

http://www.dadatainment.info/wb/s1.jpg
http://www.dadatainment.info/wb/s2.jpg

(taken from http://www.quarry.nildram.co.uk/WW2guneffect.htm)

M_Gunz
03-23-2010, 09:49 PM
Hard to tell easily since in the first picture the camera in nearer the right end than middle or left.
The picture you provide is much clearer even without the labels!

MikkOwl
03-25-2010, 11:27 AM
hem.bredband.net/mikko.artist/...Aircraft_Cannons.rar (http://hem.bredband.net/mikko.artist/20mm_Aircraft_Cannons.rar)

I discovered these documents on an obscure French website. Took some time to go through them and give the images the correct(?) names to bring some order to the mess. Phew.. Finally done. It shows 20mm ballistic data for the 151/20 and the MG FFM for various types of ammunition.

When compared to the Mk 108 data charts posted here earlier, it shows that the data corresponds pretty well with my in-game findings. The Mk 108 shells are, despite their larger cross section, less affected by air resistance than the smaller, lighter 151/20 shells. If adding the aircraft speed into the equation (I don't think it is accounted for in the charts) IL-2 seems to be completely according to reality. I.e. Mk 108 shells overtake the 151/20 shells beyond 700+ meters in the air when fired from a forward moving aircraft.

What I wonder is then that, would not the 108 be one of the best long range cannons (after the massive bordkanone series and the Mk 103), with the advantage increasing the faster one (and the target) is flying? More speed = more air resistance. Larger shell = retains mega explosive power at distance. Vertical drop certainly an issue, but so with the 151/20 as well as it quickly loses speed. Certainly one must hit the target, and one cannot carry as much 30mm ammo as 20mm either. Still, the choice of 20mm for longer range shooting is not obvious.

M_Gunz
03-25-2010, 11:43 AM
Frontal area increases with the square of the diameter, volume increases with the cube of the diameter
and between shells some are shorter or longer as a factor as well. That's why big ones tend to travel
further.
8" cannon are used to take out 6" cannon from beyond the 6" cannons' range, for example.