PLS HT look into Breda MG modelling!

[gripen]

HoHun,
Well, I think that I have admited several times benefits of the center line armamaments and problems with wing guns (ie aiming and convergence problems) but for one reason or another seems that you still can't admit that 2x firepower from the wing guns is better for an average pilot  than 1x firepower from the  centerline because they tended to shoot normally within optimal range of the wing guns.

Within the normal shooting range (say 100-200m) there is not much differences in the pattern size but bullet density is doubled if wing guns offer double firepower. So in the most cases 2x  armament in the wings offer about double chance of hit and therefore much better possibilities to destroy target.

At shorter range advantages of the center line weapons are real as noted several times here.

At longer range shooting was more or less random ie possibilities for correct aim were were about same as for any point within large area around target. It is easy to use standard Gaussian distribution model assuming that average aim point was correct, but in the most cases the average aim point was not in the target (ie systematical errors) and even if it was near it then the variance was probably bigger than in the standard Gaussian (ie probably much less than about 68% of the aims were within about 33% of the whole range of the aims). Before gyroscopic gunsights pilots did not have much possibilities to estimate right deflection therefore aiming was more or less random.

Here is a translation, but you can probably find same from the original language version (actually I believe that you have read this several times but you just can't admit it).

Adolf Galland: Ensimmäiset ja viimeiset. WSOY 1956. German to Finnish translation by T. J. Kivilahti.
Chapter 24 p. 236-237 ("quick, poor and free" finnish to english translation by gripen, couple errors corrected)

"There was a question about armament. When there was just one 20mm cannon and two rifle caliber mgs in the Me 109F, they where not rated as sufficient for against four engines bombers. Also this armament meaned difficult to understand worsening in the Me 109F if compared to the E-series which went out of production previous year, which had two 20mm cannons and two rifle caliber mgs. The cannon of the new F-series was indeed more modern, faster firing, had better ballistic characters and most important it was arranged to shoot through propeller hub. Despite this there were discussion if this armament was a improvement or worsening. Mölders and Udet liked that one center line cannon was better than two in the wings. My opinion was that one cannon was not enough, specially when I had thought long time that mgs were outdated and meaningless "fireworks stuff". They had not much effect against  enemy fighters and even less against four engined bombers. Of course I was aware about benefits of the center line armament, but if it contained just a cannon, then it looked to me - specially when schooling level of the pilots decreased when war continued - that it was still better to use two cannons even if dispersed to the wings. Not all pilots were "rifle shooters" like Udet or Mölders. Flying game animals are most commonly shooted with shot."

gripen

[MANDOBLE]

A question for you, Mg/gun experts, we actualy have two kinds of wing mounted guns/Mgs: root mounted (synchronized) and wing mounted (unsynchronized). I haven't done any test with japanese guns, but in the case of 50", hispanos and Mg151/20 the result is clearly that 50" and hispanos (unsynchronized wing mouted) has less dispersion at convergence than root mounted Mg151/20. All of us know the trajectory and ROF advantages of hispanos and 50" over 151/20, but at short ranges the difference should be minimal. So, lets talk only about short distances (convergence up to 350 yards) where dispersion due ballistic differences is minimized. At these ranges, IMO, the main differences in dispersion will come from gun shake. IMO, these hi-ROF, hi-KEnergy weapons should have a clear disadvantage in dispersion compared to lo-ROF wing root mounted guns. They are (due ROF) almost doubling the recoil effect and they are mounted in a more flexible place. Is that statement correct?

[gripen]

I don't know about German installations of the MG 151/20 but the Russians tended make their armament installations so that there were some built in dispersion in the gun mounting (not poor engineering but purpose built).

gripen

[HoHun]

Hi Gripen,

>Well, I think that I have admited several times benefits of the center line armamaments and problems with wing guns (ie aiming and convergence problems)

Don't forget these disadvantages actually mean something: Poorer firepower.

>Within the normal shooting range (say 100-200m) there is not much differences in the pattern size but bullet density is doubled if wing guns offer double firepower.

Bullet density is doubled at convergence range. Out of convergence range, bullet density decreases and soon reaches a lower value with concentrations off the boresight.

That's why Mölders, Riemensnider and Tuck thought centreline armament to be better than wing guns.

>It is easy to use standard Gaussian distribution model assuming that average aim point was correct, but in the most cases the average aim point was not in the target (ie systematical errors)

I'd like to see any facts to prove that point as I do in fact believe the opposite of what you state. I have to admit I can't prove it. My line of reasoning is that at long range, dispersion is much greater than bullet drop anyhow so that the systematic error due to this factor can be neglected. I also believe that long range shots are only sensible against non-manoeuvring targets from a stern aspect, eliminating most other opportunities for meaningful systematic errors.

>(actually I believe that you have read this several times but you just can't admit it).

Let me assure you that I only read "The First and the Last" once, maybe five years ago, and that it's not even on my bookshelf :-) Of course, there are several other books echoing Galland's thoughts, which might explain why you think I had the passage you quoted in front of me, but I didn't.

Anyway, there's a key remark in the quote: "not rated as sufficient for against four engines bombers"

Galland did not just leave it at that remark: He pressured for heavier armament, flew the F-2/U conversion that set the mold for the Gustav aramement,  lobbied for the RLM's Me 109F-6 armed with wing guns, and actually set out to prove his point by making his personal F-6/U with 20 mm cannon in the wings. He personally told Hitler that he wanted a three-cannon Messerschmitt, and when he got Hitler's support, he finally managed to get fighters equipped with gondola cannons. Galland was quite disappointed when the gondola cannon turned out to make the Me 109 inferior in fighter-to-fighter combat, but he actually saw them as a means of providing the necessary firepower for bomber interception.

I think you'll probably see the key passage as:

"but if it contained just a cannon, then it looked to me - specially when schooling level of the pilots decreased when war continued - that it was still better to use two cannons even if dispersed to the wings."

However, in the light of Galland's campaign for powerful interceptors, I'm convinced this comment was at least partly aimed at bomber interception, too. His unit, JG26, was dealing with the very first Short Stirling the Luftwaffe shot down, and if I remember it correctly, the attacking Messerschmitt expert first silenced the defensive gun position, and then flew repeated attacks at the bomber until it went down.

Clearly, the hastily trained pilot he had in mind couldn't have done that, and more firepower, even as wing guns, would have been highly beneficial for him. However, I think this is an entirely different affair from fighter-to-fighter combat, which the Luftwaffe's Messerschmitt pilots continued to fight with a single cannon for the rest of the war.

Regards,

Henning (HoHun)

[Tony Williams]

Originally posted by MANDOBLE
A question for you, Mg/gun experts, we actualy have two kinds of wing mounted guns/Mgs: root mounted (synchronized) and wing mounted (unsynchronized). I haven't done any test with japanese guns, but in the case of 50", hispanos and Mg151/20 the result is clearly that 50" and hispanos (unsynchronized wing mouted) has less dispersion at convergence than root mounted Mg151/20. All of us know the trajectory and ROF advantages of hispanos and 50" over 151/20, but at short ranges the difference should be minimal. So, lets talk only about short distances (convergence up to 350 yards) where dispersion due ballistic differences is minimized. At these ranges, IMO, the main differences in dispersion will come from gun shake. IMO, these hi-ROF, hi-KEnergy weapons should have a clear disadvantage in dispersion compared to lo-ROF wing root mounted guns. They are (due ROF) almost doubling the recoil effect and they are mounted in a more flexible place. Is that statement correct?

Basically, yes, in that outer wing mountings will be more flexible than inner root ones, so other things being equal outer guns will suffer more dispersion. However, other sources of gun accuracy were not necessarily related to power or RoF but to the quality of the mounting and the basic characteristics of the gun. For example, the Browning was rated less accurate than the Hispano.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://website.lineone.net/~a_g_williams/index.htm
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages

[HoHun]

Hi Mandoble,

>IMO, these hi-ROF, hi-KEnergy weapons should have a clear disadvantage in dispersion compared to lo-ROF wing root mounted guns. They are (due ROF) almost doubling the recoil effect and they are mounted in a more flexible place. Is that statement correct?

I think the rate-of-fire difference actually isn't that decisive. However, the forward spar of the Fw 190 near the wing root is probably the most rigid structure ever designed for a WW2 fighter :-)

The wing is much more flexible outwards at the wing cannon, and accordingly one should expect firing to induce more violent oscillations. In the case of unsynchronized machine gun batteries, it'll be a factor that they fire at random timing shaking the mounts badly. The Focke-Wulf's wing root cannon by contrast fired each round in the same instant, producing only a rearward-directed recoil and no lateral forces or moments.

It's important to realize that the dispersion was almost entirely mounting-induced. For example, when jacked up on the firing range, the MG151/20-armed Ju 87D-5 produced a 70 cm x 70 cm pattern at a distance of about 100 - 200 m when firing bursts. I think that's about the accuracy you should expect from a smoothbore musket, not from a modern 20 mm rifle ;-) Accuracy was better in the air than jacked up, but it still was far worse than the precision the barrel would have yielded in a truly rigid mounting.

In short, I think it would be safe to assume that the dispersion of wing-root or nose-mounted guns like featured by the Fw 190, Me 109 or P-38 should be appreciably lower than that of wing-mounted weapons.

The Me 109E's MG FF/M seem to be an especially interesting case - from what I know (most of it from Tony's book :-) it should enjoy a comparatively low recoil, which I speculate might give it a lower dispersion and accordingly better long range capabilities than one would assume from looking at its low muzzle velocity alone.

Regards,

Henning (HoHun)

[gripen]

HoHun,
Once again: I have admited several times advantages of the center line armament  but for one reason or another it seems that you can't admit that 2x wing armamment was better than 1x in the fuselage for an average pilot.

And once again: The problem with your Gaussian based probably theory is  that there were no way before gyroscopic gunsights to get accurate deflection for shooting at long range so shooting was more or less random (ie variance in the "aims set" is huge and there is no clear concentration around correct aim). Also most pilots used too little deflection ie average target point was behind and under real target. This means that the average of the "aims set" is not correct aim (as you try to present )  but something else. Your theory is valid only  in head-on and directly behind cases, in all other cases bigger dispersion is better because it gives better possibilities to hit. Anyway, at normal shooting ranges 2x wing armament is superior as noted several times.

And  once Again:  Galland rated  two wing cannons better than one in the fuselage for an average pilot  and he also thinked that armament worsened in the F-model if compared to the E.  Also Galland and Oesau presented their critics long before four engined bombers arrived. Right from the beginning of this endless debate I have just pointed out that there were manykind of thoughts about armaments in the Luftwaffe.

gripen

[HoHun]

Hi Gripen,

>Once again: I have admited several times advantages of the center line armament but for one reason or another it seems that you can't admit that 2x wing armamment was better than 1x in the fuselage for an average pilot.

Ah, the good old times when there were records, and they had scratches ;-)

Well, the undisputed advantages of centreline armament are large enough to make them superior for an average pilot - the RAF in 1941 had no shortage of the latter, and yet RAF leaders like Stanford-Tuck considered the Messerschmitt's armament superior to the Spitfire's.

>And once again: The problem with your Gaussian based probably theory is that there were no way before gyroscopic gunsights to get accurate deflection for shooting at long range so shooting was more or less random

"Random" behaviour is a requirement for a Gaussian distribution. Note that you're talking about long range deflection shots, though, which have so low overall chances of killing the target that I consider them operationally insignificant anyway.

>Anyway, at normal shooting ranges 2x wing armament is superior as noted several times.

Wing armament is superior at convergence range. It's inferior short of and beyond convergence range, and as Riemensnider pointed out, getting the burst in at precisely the correct range is a problem by itself.

>And once Again: Galland rated two wing cannons better than one in the fuselage for an average pilot and he also thinked that armament worsened in the F-model if compared to the E. Also Galland and Oesau presented their critics long before four engined bombers arrived. Right from the beginning of this endless debate I have just pointed out that there were manykind of thoughts about armaments in the Luftwaffe.

Oesau compared his twin 20 mm Emil to the new 15 mm Friedrich. The 15 mm cannon was much less powerful than the 20 mm cannon were, so you're comparing apples and oranges here.

Galland was writing in retrospect and formulates his points as if the Friedrich was armed with 20 mm right when it came out - which it wasn't. You'll note that he criticizes MG armement for its low effectiveness against anything, but single-cannon armement only for its lack of effectiveness against bombers.

Regards,

Henning (HoHun)

[MANDOBLE]

HoHun, if you are right (and I think so) about the wing root mounted 151/20s producing only a rearward-directed recoil and no lateral forces or moments, perhaps HiTech should take a look about the actual lateral displacements (small yaw displacements) produced by these guns inducting a clearly noticeable dispersion at short ranges.

Tony, can you confirm 151/20 HoHun point?

[gripen]

HoHun,
As noted several times here, only good shooters and experienced pilots could really benefit from centerline armament, for all others 2x wing armament was certainly better than 1x center armament because much better firepower and better possibilities get hits within normal shooting range of the average pilots.

About Gaussian distribution it should be noted that you used it in it's standard form ie about 68% of all points of the set should be inside about 33% of the measured range and you also presented that the average of the set is same as correct aim. Both assumptions are wrong because without better gunsights there were no possibilities for accurate aim (except in the case where both planes are in the same flight path) and pilots tended to repeat their errors.

Yeah, I know that I have been talking about long range shots and please see my previous posts; I have stated several times that in the case of the long range shooting it was pretty much same where the guns were located, it was very unaccurate anyway but with better firepower there were more possibilities to get random hits. So are you changing your opinions...

And it is not "just" convergence range where the 2x armament in the wings is superior, it is the whole range where this combination has more concentrated firepower against target. And in the case of the average pilots, it is practically whole normal shooting range ie say 100-300m. Experienced pilots could benefit from centerline armament because they tended to shoot from short range. Anyway, you finaly admited that at convergence range 2x armament in the wing is superior, earlier you argued that: "centreline armement is better for inexperienced pilots at any range". So a little movement here too...

About Galland and Oesau: Well, in fact you are writing in retrospect and you try to bend their sayings and doings to fit on your own theories. What they did and wrote is pretty clear.

gripen

[Tony Williams]

Originally posted by MANDOBLE
HoHun, if you are right (and I think so) about the wing root mounted 151/20s producing only a rearward-directed recoil and no lateral forces or moments, perhaps HiTech should take a look about the actual lateral displacements (small yaw displacements) produced by these guns inducting a clearly noticeable dispersion at short ranges.

Tony, can you confirm 151/20 HoHun point?

I don't know about the firing arrangements for the synchronised guns so I can't comment.

I'm also not sure about the yaw effect of wing mounted guns; it depends on how many, their rate of fire and their power. For example, I would not expect any such reaction with eight .303 because each recoil kick was small, and there were so many of them that the effect would even out. Clearly, as guns become larger and slower firing, and there are fewer of them, each recoil impulse becomes more significant and is more likely to have small effects on aiming. I have no data on the likely extent of this with different armaments, though.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://website.lineone.net/~a_g_williams
Gun and ammunition discussions at:
http://forums.delphiforums.com/autogun/messages

[HoHun]

Hi Gripen,

since you seem to think we're caught in some kind of vicious circle, let me attempt to break out by concentrating on a single  point :-) This doesn't mean you aren't wrong about the rest, too, but maybe we can solve them one by one ;-)

>About Gaussian distribution it should be noted that you used it in it's standard form ie about 68% of all points of the set should be inside about 33% of the measured range and you also presented that the average of the set is same as correct aim. Both assumptions are wrong because without better gunsights there were no possibilities for accurate aim (except in the case where both planes are in the same flight path) and pilots tended to repeat their errors.

Please suggest a dispersion example similar to the one I posted to demonstrate wing guns can indeed be better at long range.

I think you're going to find that any function that makes wing guns look better will include an element of avoidance of the correct aiming point, which implies knowledge of the correct aiming point, which you state is an impossiblity. You'd contradict yourself that way :-) I could be wrong, of course, but I'd really like to see some math now.

Good luck!

Henning (HoHun)

[gripen]

HoHun,
I wonder what are you trying to say? You presented a theory without data so actually it's your problem to bring in some kind of data. Anyway, if we have a large random set of aim points and we assume that correct aim point is within set but not necessarily near average of the set, then it is more probable  get hits with the armament which put out  2x more hits within set. Despite the area of the 2x hits set is a bit larger,  there is more density inside the set.

Thanks, but I don't need luck for this.

gripen

[funkedup]

It's pretty easy to see what Gripen is describing if you try it in Aces High.  There is a feature that lets you fire at a white target, and you can select the range of the target.  You can see the pattern of shells at any range.

With a single nose gun you get one area of hits that grows with range.

With wing guns you get two areas of hits at close range.  But as you get near convergence they become one large area of hits.  But as range increases beyond the convergence distance,  the dispersion of each gun becomes so large that the effect of the gun spacing is minimized.  The two patterns are centered maybe 15 feet apart but their diameter is so large that they overlap for the most part.

Remember that dispersion is helpful for long range gunnery.  It is unlikely that you will have the enemy perfectly centered in your dispersion pattern, so the aircraft with the widest pattern can get hits even if the aim is off.  And at long range with low-time pilots and rudimentary WWII aiming devices I'm sure this was the rule.

The M61 Vulcan rotary cannon used in post-war jet fighters and AA units actually had to be modified because it was found that more dispersion increased the probability of a hit unless the pilot/gunner had perfect aim.  They altered the gun so that each barrel was "off center" a little bit, giving a nice fat pattern.

Galland's alleged comment about shotguns will seem pretty accurate if you look at the patterns in AH or the gunnery simulation tool of your choice.  Just use .target xxx where xxx is the range in yards.  Try it for different weapons packages and convergence ranges.  You will see some truth in what Gripen is saying.

[gripen]

Yeah, dispersion is the reason why the Russians did that built in loosenes to their gun installations.

gripen