About WW2 fighter aircraft firing power

[Juha]

Hello Tony
thanks for the correct link. How embarrassing! I googled to Emmanuel’s site by typing “WWII Gun power” and seeing the book covers assumed that it was yours. I even looked vainly for analyze of ammo effectiveness which I remembered to be somewhere in your site but of course didn’t find it. Then I concluded that you have removed it. Really embarrassing.
But you cleared my mistake and so Rob got the info.

Juha

[Harri Pihl]

Originally Posted by Rob Philips

Harri demonstrates to be a close reader. Shall try to match that and state that we also agree that muzzle velocity is a factor when talking about aiming error. I'm not sure how important that factor is. That may change as we proceed.

I've tried to stay on my original point on relation between muzzle velocity and hitting probability. However, aiming error is another issue despite connected to the muzzle velocity due to easier aiming.

Things get very complicated when increasing number of factors are accounted; I have not even touch the factors like rate of fire, lenght of the burst and density of projectiles in the target area (dispersion in other words). I have seen probably similar analysis as mentioned by Peter Verney above; as example RAE did analysis on gun camera films (real combat footage from RAF, USAF and GAF and simulated attacks) and studied many factors like aim wander and error, lenght of the burst etc. were measured and analysed.

I think you have couple possibilities here. The easy way is to stay strictly on easily measurable factors like rate of fire, muzzle velocity and energy content and in the end you have probably very similar results as Tony got. The hard way is to try to understand how these more or less random factors like aim wander and error, dispersion, burst lenght etc. affect on different guns.

[Harri Pihl]

Originally Posted by Tony Williams

It's worth considering the German and Russian experience. The Germans had two versions of the MG 151 from which to choose: the high-velocity 15mm and the medium-velocity 20mm. The 15mm would certainly have had a higher hit probability, but it was almost entirely dropped in favour of the 20mm which was far more destructive. The Russians similarly preferred the 20mm ShVAK over the faster-firing, higher-velocity 12.7mm UB.

Well, on other side, it's worth considering USAF experience; after all the M53 is by far the most succesfull fighter weapon of the WWII.

There is obviously differences how the Air Forces saw the benefits of the guns. The MG 151 is a good example because USAF did seriously consider to use it (15mm version) while the Germans went towards larger calibers.

In the Russia 20mm ShVAK was older weapon and, at least according to Finnish experience, less problematic than the Berezin.

[Rob Philips]

Thanks, Harri. In his analysis Tony Williams included factors such as the benefits of mass production of a single weapon type rather than a multitude, and most of all the fact that the US considered their .50 to be, perhaps not the most efficient gun, but a combat proven and adequate one. Benefits of a different nature than can be expressed with gun & ammo technicalities only.

Regarding the complexities of a hitting capability definition: let's go the hard way, and see where we end. If the matter was easy, and with that most likely well known, then I would not have raised it. I agree that equasions with rate of fire, muzzle velocity and energy content shall lead to conclusions that were already nicely summarized by Tony. I do not agree with his proposed calculation of explosive energies, that rather simplifies the matter, but would agree that a more elaborate calculation would probably lead to the same or similar results in a table with comparative data.

In any case, I'm not finding pattern density, or dispersion, anywhere in these considerations. It strikes me that this could be a flaw, that is not present in the world of hunting shell ballistics. Note that "dispersion" has a negative ring to it, as in "deviation from the perfect line". That would be valid at the target practice range, but it might be a desirable feature in aerial combat.

I once witnessed so-called accidental automatic fire coming out of an AR 15 rifle. Obviously the interruptor was modified to produce automatic fire from this civil version of the M16. Three rounds, and all three in a group of 3 cm diameter at a 100 meter range, and on top of that all within the inner circle of the bullseye of the 100 m target. First class accuracy, that would however be pointless in actual combat, where one of these hits would have been quite enough to incapacitate the opponent. This splendid accuracy does not increase the chances of hitting, it merely wastes ammo at the same point of a basically motionless target. The pattern is too dense to make sense under these conditions.

In aerial combat things would be different, as the target is moving fast, in four dimensions. Multiple hits at the same spot with non-explosive rounds could accumulate the damage done. If not at the same spot, which is very unlikely anyway at regular firing ranges, then multiple hits close together could lead to a greater net effect than can be calculated as the sum of the effects of all hits. A wing spar may not yield after a hole has been shot into it. It may not yield after several holes. But it may yield if several holes are shot close together. This is another way of saying that, if we forget about explosives for the moment, pattern density is a factor that needs to be considered. And surely, as stated by Tony in his post of today, this makes sense only if the individual rounds can do damage at all.

Pattern density is presented here as a factor in damage infliction. It is also a factor in my key interest: hitting capability. Perhaps it would be better to speak of "pattern spread" here. The larger the pattern, the easier it is to score hits on a target of a given size on a given distance. The pattern cannot be enlarged beyond the point where the projectile density becomes too low to score hits, and/or to be effective in inflicting damage. There must be an optimum here. My question is: how can we define that optimum? Leaving out explosive rounds, then this optimum is likely to be a trade-off between number of rounds per second, their damage inflicting properties, and their dispersion in a plane vertical to the line of fire.

Regards,

Rob

[Tony Williams]

Originally Posted by Harri Pihl

Well, on other side, it's worth considering USAF experience; after all the M53 is by far the most succesfull fighter weapon of the WWII.

Better known as the Browning .50 M2...it depends on how you measure success. Certainly US fighters armed with the .50 shot down lots of planes, but there are other factors involved than the quality of the gun: such as the superiority of the aircraft, the superiority of pilot training, superiority in numbers (later) and so on. And of course the fact that few planes carried anything other than the .50 meant it was bound to shoot down a lot of planes. What that doesn't tell you is whether or not they would have been even more successful if armed with a good cannon: personally, I think they would.

I have analysed the US reliance on the .50 here: http://www.quarry.nildram.co.uk/CannonMGs.htm

[Tony Williams]

Originally Posted by Rob Philips

I agree that equasions with rate of fire, muzzle velocity and energy content shall lead to conclusions that were already nicely summarized by Tony. I do not agree with his proposed calculation of explosive energies, that rather simplifies the matter, but would agree that a more elaborate calculation would probably lead to the same or similar results in a table with comparative data.

If you look at the final section of my armament effectiveness article, you will see that Henning Ruch suggested a more scientific calculation for chemical energy and the results are tabulated: but this made very little difference to the relative power scores, except to magnify the effectiveness of high-capacity HE shells.

In any case, I'm not finding pattern density, or dispersion, anywhere in these considerations. It strikes me that this could be a flaw, that is not present in the world of hunting shell ballistics. Note that "dispersion" has a negative ring to it, as in "deviation from the perfect line". That would be valid at the target practice range, but it might be a desirable feature in aerial combat.

Pattern density is partly a function of the harmonisation arrangements, but equally so a function of the combined rates of fire of the armament: which also affects the overall armament effectiveness scores in Table 3 of that article.

The harmonisation arrangements are also affectd by the destructiveness of each hit: the less powerful your ammo, the more important it is to concentrate its fire to achieve acceptable effectiveness. So the RAF had to reduce the harmonisation distance - in other words, tighten the pattern - for its 8x .303 fighters during the BoB, but considered increasing the dispersion of Hispano armament, because only a few hits were needed for a kill.

In aerial combat things would be different, as the target is moving fast, in four dimensions. Multiple hits at the same spot with non-explosive rounds could accumulate the damage done. If not at the same spot, which is very unlikely anyway at regular firing ranges, then multiple hits close together could lead to a greater net effect than can be calculated as the sum of the effects of all hits.

Multiple hits on the same spot are highly improbable, even with a high pattern density. All you have to do is look at camera gun film of ground attack strafing runs, where you can see (especially against naval craft) the shots scattered all around the craft or vehicle, due to the movement and vibration of the plane, aim wander, and the dispersion of each gun. Then add to that the fact the aircraft are moving far more quickly than naval craft or vehicles, and the chances of concentrated hits go down sharply.

There was only one way to ensure a close grouping of hits - and that was to get very, very close before opening fire. And by that I mean 50 metres or less. Not many pilots were capable of that.

[Rob Philips]

Thanks, Tony. I had read the statements from Henning Ruch. I believe that your suppositions made to make the matter manageable, underestimate the power that is delivered by explosives. However, as said, if these, or other, suppositions are applied consistently to all gun/ammo systems in a comparison, then results are likely to be comparable, and perhaps even quite similar. I cannot prove this as I cannot point to objective measurements of explosive force. The cavity size blasted in gelatin would be an objective measurement, if this would be a practicable technique.

"Pattern density is partly a function of the harmonisation arrangements, but equally so a function of the combined rates of fire of the armament."
Exactly. And added to that factors such as gun platform vibration under firing, delivering a dispersion that did not result from design, but that could nevertheless be used in a weapons system design. Density required shall be controlled by the projectiles employed, as in your .303 machine gun vs. 20mm cannon comparison. Now we are heading towards clarity about desirable pattern densities. This cannot be studied by looking at individual guns and/or ammo's. The entire aircraft with multiple gun and/or cannon and ammo needs to be considered as a system. Or ammo's, plural, if more than one type is to be deployed. The last is what you did, calculating for a repetitive 3 HE + 1 AP ammo arrangement in the belt.

Pattern density shall be maximal at the point where projectile trajectories converge. Before and after that the pattern shall be basically conical in the direction of projectile flight. Harmonisation seems to have been done according to this one-point-convergence strategy, that point being about 300 to 200 yards out, as the fashion of the day had it. Are you aware of other arrangements that may have been used? Meaning harmonisation to parallel trajectories, or perhaps to a circular pattern at the envisaged engagement range?

One other point that you raised in the articles. The presence of tracer is mentioned as undesirable, as it reduces space that could otherwise be filled with HE, and as tracer gave away the fact that somebody was shooting at you. On the other hand, wasn't tracer an excellent aid in deflection shooting, as the pilot could see where the rounds were going, enabling him to let the opponent fly into the pattern, or to chase the pattern into the opponent?

Regards,

Rob

[PeterVerney]

ISTR that harmonisation of our Mosquitos in 1952 was two guns at 350 yards and two at 250 yards. Giving an idealised firing range of 300 yards. Of course in practise, firing at drogues and at ground targets, there was only time for a quick squirt at about 350 yards with the range rapidly decreasing. Bear in mind that firing on the target was not permitted at less than 30 degrees angle off for fear of ricochets hitting the tug.
When we switched to the Meteor NF with wing mounted guns I think similar harmonisation applied. Incidentally I do remember an incident when a wing commander, eager to get a better score, closed to a lower angle off and bounced a shell clean into one of the tugs engines. Ball ammo of course, but made a horrible mess of the engine and as we only had one aircraft modded to tow a flag that put an end to the fun.
In any instance scores were not marvellous and it was not unknown for a pilot to score a blank while over 15% on air to air was considered reasonable and over 30 very good.

[Rob Philips]

Thanks, Peter, a most vivid picture of the difficulties encountered in practice. Two point harmonisation added to the list.

Regards,

Rob

[Tony Williams]

Two-point harmonisation was also used by some US fighters. I have a diagram of a P-47's harmonisation which is exactly the same as Peter described - 250 and 350 yards. I have also read that some pilots set each pair of .50s to converge at a different range. This meant that they never had really concentrated fire at any range, but moderate concentration at all ranges.