About WW2 fighter aircraft firing power

[Harri Pihl]

Originally Posted by Juha

Because flatter flight path of shot/shell lessened the effects of errors, it increased the possibility of hit. Of course lessening the firing distance did the same.

The advantages of high muzzle velocity is not limited to the flat flight path of the projectile and sudden movements of the target (Janacek's point); because the time to reach target is shorter, also the needed lead is shorter and therefore the aiming error will be smaller as well.

[Juha]

Hello Harri
Yes, of course, but Rob acknowledged that already in his message #8.

Juha

[Harri Pihl]

Originally Posted by Rob Philips

To Harri: I understand the point made, and appreciate the effort to come to a quantification of "hit probability". I was not convinced by the result of that effort. The fact that the Germans evolved to low Vo large caliber aircraft armament most likely has to do with bombers being their main targets, as you said, but there may be no direct connection with the achievement of hits here, and more with delivering of the energy levels that could destroy a bomber. That meant shooting with the highest amounts of High Explosive as technology allowed at the time. Not because the bombers were slow, but because more energy on target was needed to bring them down.

I believe that there is fairly direct connection between probability of the hit and muzzle velocity. Janacek's point is just one simple approach based on unknown movement of the target, while we can can disagree on amount of this effect, it is still a valid point. Other advantages being quite clear as well; less room for aiming error.

The Germans had high muzzle velocity weapons, like the MK 103, but these were too bulky for smaller aircraft. And regardless the speed, the bombers were still much larger and less agile targets than fighters so hitting them with low velocity weapons was much easier.

[Harri Pihl]

Originally Posted by Juha

Hello Harri
Yes, of course, but Rob acknowledged that already in his message #8.

I don't see that Rob acknowledged aiming error there, just noted smaller lead. The point is that even if we assume that the relative error in lead is the same for low and high muzzle velocity weapon, the absolute aiming error will be lower for high velocity weapon. In practice also relative error will be lower for a high velocity weapon because smaller lead is easier to quess.

[Kurfürst]

Originally Posted by Harri Pihl

The advantages of high muzzle velocity is not limited to the flat flight path of the projectile and sudden movements of the target (Janacek's point); because the time to reach target is shorter, also the needed lead is shorter and therefore the aiming error will be smaller as well.

... the model remains true if we strictly stay with single-shot weapons.

However, with automatic guns, such as aircraft cannons, a round fired earlier, ie. in case of higher cyclic rate during a given time frame will reach the target earlier, than in a case of a higher velocity round fired at a slower cyclic rate. For practical applications, careful aiming and application of proper lead is less attractive than just let the target 'walked into' a sufficiently dense line of firepower applied - ie. point and shoot. Its a fail-proof method.

There is a reason for using shotguns for hunting small game and birds with a high number of slow pellets instead of .223 bolt action rifles with 1200-1300 m/sec.

[Rob Philips]

Thanks, gents. Lively topic. We agree that high muzzle velocity is good for the capability to score hits. We are unsure about a quantification of this statement. We agree that the Janecek effort regarding "hit probability" is remarkable, and very relevant, even if we cannot (yet?) agree with the presuppositions of that theory.

We do not agree that hitting bombers was easier with low Vo weapons. I believe that a lower Vo was the trade-off in the wish to bring a lot of explosives to the bomber target, as that required a large caliber, meaning a large projectile that could accomodate a lot of TNT, or whatever mixture of the contemporary explosive compounds. Larger calibers meant lower Vo's, or elso the design of weapons that would become prohibitively heavy for use in aircraft.

The earlier thread mentioned by Juha shows that the explosives used by the combattants of WW2 were rather similar. Detonation speeds from 7.000 to 8.750 m/s. Density differences of up to about 35%. Compounds that were either already available during WW1, or were variants of that, with no major developments to this day - if we limit this statement to explosives based on chemical compounds, the so-called conventional explosives. But all that is not relevant to hitting capability, or probability. It is highly relevant to the capability to do damage. But for that, a hit needs to be scored first.

I like to re-adress attention to what I'm after: an understanding of the probability to achieve hits. This is meant in a way that strictly belongs to weapon technology, not to weapon system technology. The latter would include aiming aids, and human factors such as pilot skills. I proposed to leave that out of the discussion, at least for now, so as not to complicate matters too much in round one.

In an effort to direct the thoughts, I would like to use the comparison with hunting ammo once more. If the target is stationary, and/or if it needs a lot of energy to bring it down, you choose ammo with a single high velocity projectile. If the target is a duck in flight, you choose ammo with submunitions, a 12 gauge cartridge loaded with a lot of size 5 to 7 pellets, that deliver a cloud of projectiles at a certain range. This cloud of pellets enables you to hit the duck, flying at about 70 km/h, at all. You would have virtually no chance to hit it with a single .22LR round, even if your marksman skills were exceptionally good. One .22LR round would definitely kill the duck, whilst one size 6 pellet would not. The .22LR round would probably fly through the duck's body, spending only a portion of its energy in that body, but that would be more than enough to bring down the duck. A size 6 pellet, at a shooting range of 40 meters, would penetrate only skin deep, not nearly enough to kill the duck. Three pellets however would bring down the duck, killing it instantly, as his nervous system cannot survive the sensory overload produced by their impact. Three pellets out of perhaps 150 fired with the shot, in a cloud of about 2 meters in diameter, a cloud with sufficient pellet density to score 3 hits at that max. range of 40 meters.

This max. range of 40 meters is the trade-off. The pellets have a very low weight; they go out at about 350 m/s, and they lose their speed very rapidly. If fired at a wooden door from a distance of one meter, the cloud of pellets is small and very dense, blowing a most impressive hole in that door. If fired at the same door from 50 meters, chances are that the pellets shall produce tiny dents in the woodwork, nothing more spectacular than that.

Surely a WW2 fighter aircraft is not comparable to a duck. But the analogy could be useful, to find out which aircraft armament can be considered as the more effective one for the envisaged job of bringing down adversaries, given the non-guided projectiles of that time, the gun sights that were marvels then, but very poor tools to those who are familiar with computers, and the likelyhood that most pilots were common people, meaning average marksmen.

The 12 gauge tool has a game hunting track record of centuries. Apparently it is most effective. It uses a very rudimentary sight only. It enables marksmen of average skills to score on a regular basis. Which WW2 fighter aircraft armament came nearest to a comparable achievement?

Regards,

Rob

P.s.:

1. This was written & send before I had a chance to read the preceding 3 posts. I used many more words to make the same point as Kurfürst did.

2. 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.

[Tony Williams]

My attention has been drawn to this one

The link near the start of the thread was to my co-author Emmanuel Gustin's site, not mine. This is my take on WW2 fighter firepower: http://www.quarry.nildram.co.uk/WW2guneffect.htm

As a result of my analyses, this is my view of the "ideal" WW2 fighter armament: http://www.quarry.nildram.co.uk/ideal.htm

There are also other articles on my site concerning aircraft gun armament.

As with all aspects of this, the question of hit probability is complex. High muzzle velocity is certainly a big help, especially against fighters. But there is no point in hitting with insufficient force to achieve much damage. In the Battle of Britain, Luftwaffe bombers sometimes returned to base with hundreds of .303 holes in them. And planes got tougher and harder to shoot down as the war went on.

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.

[Rob Philips]

Hi Tony,

Thanks for this. I note that "hitting capability" or "hitting probability" is not defined in these articles, as a subject that is said to be too complicated to be dealt with within the scope of these articles, and that pilot skills are the most important factor in any definition of "hitting capability".

I also note your remarkable analysis of the ideal WW2 fighter aircraft armament, based on combinations of features of the best guns & ammo types available then, to which is added an expectation of a possible development of these during that period. Here too, "hitting capability" is not present in the equasions.

Do you consider it possible to design a passable definition of "hitting capability", if we leave pilot skills and aiming aids out of the equasion?

I'm sure that pilot skills are of prime importance here. But it seems passable to leave that out, at least for now, as it would apply to any other measures designed to increase hitting capability.

I believe that a consideration about hitting capability precedes considerations about power of armaments to inflict damage on target. Therefore excursions into the effectiveness of AP versus HE would not be needed at this stage.

If that would strike you as too theoretic, then allow for the use of HE, effectively meaning using 20mm, and then give a go at defining hitting capability.

The relevance of this would be to analyse technological ways that could have helped the average marksman to achieve better results. A historical exercize only, as hardly any of this would apply today.

Regards,

Rob

[Rob Philips]

In correction of earlier statements in this thread, so as to avoid confusion:

Synchronisation/synchronizing is timing the gun firing so that it can fire through the arc of a rotating propellor.

Harmonisation is adjustment of multiple guns in one aircraft, so that the arcs of fire meet at a certain point in space.

Rob

[Tony Williams]

There were three ways to improve the hit probability in WW2 (in no particular order):

1. Minimise the time of flight of the projectiles - achieved by a combination of a high muzzle velocity and a good ballistic coefficient of the projectiles. However, other things being equal, increasing the muzzle velocity involves reducing the rate of fire and increasing the weight of gun and ammo, so you can carry less.

2. Increase the rate at which projectiles are fired by increasing the number of guns or speeding up their rate of fire (N.B. The Luftwaffe preferred to fit 2x low-velocity 30mm MK 108 rather than 1x high-velocity 30mm MK 103 for the same weight, because the MK 108 combo put shells into the air at three times the rate). However, that requires a bigger ammo capacity and more weight again.

You will appeciate that Nos. 1 and 2 are in conflict with each other, within any reasonable weight limit. As with virtually everything else, the best solution is a compromise between conflicting factors.

3. Fit gyro sights - which made a huge difference to the hit probability of the average pilot with no weight penalty - brilliant!

A final comment: the hit probability is not the same as the kill probability. Within any given weight limit, an armament designed to maximise the hit probability is likely to have a reduced kill probability because it will be firing smaller and less destructive projectiles.