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About WW2 fighter aircraft firing power
About WW2 fighter aircraft firing power What exactly is the firing power of a WW2 fighter aircraft? This is a subject that has seen debate and confusion. In this thread the subject is summarized, and expanded, as I believe that it may be possible to improve upon common opinion. Definitions Caliber is the bore diameter of the barrel, expressed in millimeters or inches. Firing rate is the number of rounds fired per minute. Fighter aircraft armament in WW2 is usually of the machine gun or automatic cannon type, meaning automatic projection of projectiles as long as the trigger is squeezed. The division between machine guns and cannon is usually made at a caliber of 15 or 20 mm. Vo is the muzzle velocity, expressed in meters per second, the speed at which the projectile leaves the muzzle. This velocity declines with range, faster with light projectiles and slower with heavier ones. Projectile weight is expressed in grams or grains. Kinetic energy is the product of velocity and weight. A high kinetic energy, resulting from high muzzle velocity and/or high projectile weight, means a high capability to do damage to a target. Opinions 1. Firing power is sometimes seen only in terms of gun caliber. 9mm is bigger and therefore better than 7,5mm. This is not enough. A high speed 7,5mm projectile can have more kinetic energy than a 9mm projectile, meaning that it shall be able to do more damage. 2. Firing power is sometimes seen as the sum of machine guns available. The Dutch Fokker G1 fighter aircraft had an at that time unprecedented eight machine guns, looking most impressive indeed. However, it can be demonstrated that the kinetic energy delivered at targets was a mere 50% of the kinetic energy delivered by two machine guns and one cannon in an Me.109, that would soon become its opponent. 3. Firing power is more commonly seen as the product of projectile weight and firing rate. A hundred 7,62mm, 7,92mm or .303" rounds of 15 grams each, if projected in a second, deliver a mass of 100 x 15 = 1.500 grams per second on the target. Twenty 20mm rounds of say 100 grams each, if projected in a second, deliver a mass of 20 x 100 = 2.000 grams per second on the target. 2.000 is more than 1.500, so that 20mm cannon has a higher firepower than that 7,62 to 7,92mm machine gun. I wonder if this notion of firepower can stand the test of scrutiny. The theory assumes that the target is indeed hit, and that was one of the problems in WW2 fighter combat. We shall not consider the following improvements of WW2 fighter armament. These improvements were highly relevant, but they are difficult to quantify: - introduction of explosive and incendiary substances to the projectiles - introduction and improvements of aiming aids - introduction of rocket munitions After WW2, these improvements were superseded by self-aiming rocket projectiles, leading to a one shot - one kill situation that was unheard of during WW2. Furthermore, cyclic firing rates were vastly improved with new implementations of the old Gatling multi-barrel machine gun or cannon system. 4. Pattern density added to opinion 3 In order to hit a target in WW2 aerial combat, you need to have a high fire power as defined above, meaning a lot of kinetic energy on target, but also a firing pattern that increases the chance of scoring hits. If a fighter would carry a 90mm gun, then surely one hit would be enough to destroy the opposing fighter aircraft. But 90mm guns could not be made to fire at 900 rounds per minute. 20 rounds per minute was the achievement of such guns at the end of the war. And if they could, the aircraft could not carry the weight of ammunition needed for a few seconds of firepower. On the other end of the scale, WW2 fighters would be able to carry a multitude of the number of projectiles, if scaled down in caliber, such as in hunting shells, but these munitions would not have the kinetic energy and the range required to do the job. The practical solutions were in fact trade-offs between technological possibilities of the day. The excursion into the ammunition range from 2mm hunting pellets to 90mm shells shows the missing factor in the firing power definition given above: projectile spread. Or better: kinetic energy delivered per square meter of space. Assuming sufficient pattern density to achieve effective damage at all, then the aircraft with the largest shot pattern had the better chance to achieve hits in the lightning fast aerial combat of WW2 fighter aircraft. Projectile spread from a multi-gun platform results from three factors: 1. Adjustment, also called synchronisation, of the individual guns. 2. Differences between individual rounds of ammunition. 3. Barrel, and especially muzzle, wear. A worn barrel leads to less accuracy, which may not be a bad thing in this case. The adjustment of the guns is by far the most important factor here. Unfortunately for this proposed theory, there is hardly any data about WW2 fighter aircraft gun synchronisation. Some services, or some Squadrons, or even some individual pilots, had the guns synchronised to hit at say 150 meters, others at other distances. But this figure does not tell us a lot about the spread. Were the guns adjusted to catch the size of the opponents silhouette at that distance, or did the projectiles meet at one point at that distance, or was the pattern adjusted to something wider than this? I would be interested to hear from anybody who has real knowledge about this. It seems that the best scoring pilots were the ones who engaged from the closest distances. That did away with most of the considerations above: kinetic energy would be maximal, gun synchronisation would have much less influence, and pattern density would be as high as available. Regards, Rob |
Re: About WW2 fighter aircraft firing power
Just short note- smaller caliber have larger rate of fire and larger calliber have smaller. In other way energy input was different and better for large calliber. There was varius way to find compromise. One of them was mixed armament with machine guns and cannons.
I like your post :) |
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Thanks, Srecko. Usually, but not always, rate of fire is higher in smaller caliber automatic weapons, as a result of less weight of cartridge and breech block metal that needs to be moved. One of the WW2 developments was to increase the rate of fire for aircraft armaments, all calibers, for instance by reducing the weight of the breech block, by increasing the recoil spring force, by different lock mechanisms, and any combination of these. Machine guns for fighter aircraft would evolve in the direction of 1.200 rpm, whilst the army versions of these guns had 800 rpm.
After the war, a .22LR Gatling gun driven by an electric motor was made, that sported a much higher firing power than any of the WW2 aircraft machine guns, as a result of the >20.000 rpm (rounds per minute) firing rate. I believe that this gun was never used operationally, but it serves to demonstrate the technical point. I agree that mixing calibers was one way to achieve compromises, the way in which the Germans led the field. Regards, Rob |
Re: About WW2 fighter aircraft firing power
Hello
Tony Williams' pages are a good introduction to this matter. See:http://www.geocities.com/CapeCanaver...n/fgun-in.html Juha |
Re: About WW2 fighter aircraft firing power
Thanks, Juha. Very well researched article, which is what we expect if Tony Williams is the source. Curiously, fire power or firing power is not defined in this article, and not expressed in the tables given. However, when discussed, the type 3 in my post, projectile weight times firing rate, is intended. Two other expressions are mentioned, the Q and the M factor. Both consider the weight of the weapon as well, and therefore express the efficiency of the weapon. My proposal to include kinetic energy and pattern density cannot be found in these pages. I believe that this article represents the visions of gun manufacturers, whilst I am looking for user visions too. Users mounted multiple guns in flying gun platforms. The difference is between firing range data, and aerial combat data, technological data versus tactical data.
There is one remark in these pages, that points into the direction that I would like to go. It is a remark made by Adolf Galland, stating that the Me.109 armament of two machine guns and one cannon was not good enough for the average pilot. Why? Not because the projected weight was insufficient, but because the pattern was not dense enough. A denser pattern would have led to more results achieved by aviators with average marksman skills. Regards, Rob |
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One important point is the effectiveness of different ammo types, for ex. German Minen HE, API etc. Tony analyses this in his WWII Guns book.
Other is how the guns were sighted, at what distance their bullets/shells converged. Juha |
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IMHO the ability to hit the moving target is a key factor on firing power, therefore the aspects which affect the hitting probability have large influence on firing power. The best known example of this is the velocity of the projectiles; 50% increase in muzzle velocity increase hitting probability by five times according to some sources.
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Re: About WW2 fighter aircraft firing power
Thanks, gentlemen. I excluded HE & I ammunitions from the discussion as it is very difficult to quantify their effects. It is clear that adding explosives to a round increases its effectiveness by a large margin. Have checked what Tony Williams has to say about this, on the site mentioned by Juha. Explosive power is mentioned, of course, but not quantified. Perhaps we can include into the equasion the kinetic energy of an exploding round. But first comes the ability to hit the target at all.
I introduced "sighting" of the guns, as expressed by Juha, as "pattern density" into the equasion. Harri hits the mark I'm trying to make, with "the ability to hit a moving target". Projectile velocity is less of a factor here than you might believe. Projectile velocities are about 800 to 900 meters per second at the muzzle, reducing to say 700 after 150 meters. 700 meters per second translates to 2.520 km/h, about four times faster than the top speeds of the aircraft involved. Max. muzzle velocity of conventional projectiles coming out of rifled barrels is limited; this cannot be increased easily. If a Vo could be raised to say 1.000 m/s, or 3.600 km/h, reducing to say 850 m/s after 150 meters, or 3.060 km/h, then that would be about 5 times faster than the fastest aircraft, lessening the projectile flight time to target by a factor 5/4 = 1,25 only. This would translate to a smaller leading angle in the deflection shooting required in aerial combat, but that would be all. I would be interested to hear how, as Harri said, some sources calculate an increase of hitting probability by a factor 5, if muzzle velocity is increased by 50% - if that would be possible. I would also be interested in a definition of "hitting probability", as that would indeed be the key notion in this matter. Have once done experiments to determine the max Vo that can be obtained from a rifled barrel. Using custom made plastic projectiles, used for their light weight, with .223 cartridges fired from an AR 15 rifle, cartridges loaded to the brim to obtain max. propelling force, a max. Vo of about 1.500 m/s was achieved. This was found to be a limit, that could not be exceeded with these means. Vo's of WW2 aircraft machine guns are all below 900 m/s. Regards, Rob |
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Rob, there are books which explains the effects of different HE, API etc rounds and those effects are very significant, that’s why ball rounds were not very common late war years even if they many times had better kinetic energy than HE rounds.
On hitting, you leave away very important factor, gravity drop. Higher muzzle velocity means flatter flight path and made hitting easier. And some WWII aircraft guns had muzzle velocities as low as appr 520m/s. Juha |
Re: About WW2 fighter aircraft firing power
Rob,
Check your PM. |
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Thanks, Juha. Surely you are correct in stating that gravity drop is a relevant factor. It increases with low muzzle velocities, long firing ranges and low projectile weights. It complicates the difficulties of deflection shooting. This would ideally be taken into account by the gun sight. Hitting probability is not yet well defined, but I am talking about the situation that a target is indeed in the sight, but nevertheless not hit, or not hit effectively.
To obtain some idea about the differences in effectiveness of explosive and non-explosive rounds of aircraft ammunition, I can offer the following: The example is the Hispano Suiza 20mm cannon, widely used in fighter aircraft in WW2. The cartridge is 110mm long, rimless. A HE (High Explosive) projectile weighs 130 grams, and carries 6 grams of TNT. A solid non-explosive projectile weighs 150 grams. Both are fired at a muzzle velocity of 850 m/s. TNT has a detonation speed of 7.000 m/s. Kinetic energy (Joules) = 0,5 x projectile weight (kg) x the square of the muzzle velocity (m/s) The muzzle energy of the non-explosive round is calculated as follows: 0,5 x 0,150 x 850 x 850 = 54.188 Joules, or 54 kiloJoules The muzzle energy of an exploding round is calculated as follows: 0,5 x 0,124 x 7.000 x 7.000 = 3.038 kJ To this should be added the kinetic energy of the round directly prior to explosion: 0,5 x 0,130 x 850 x 850 = 47 kJ Total = 3.085 kJ Meaning that the explosive round has 3.085/54 = 57 times the energy of the non-explosive round. Regards, Rob |
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Thanks, Harri, most interesting. Your material describes the Janecek invention, presented to the BSA company, who presented it to the Ministry of Aircraft Productions in Febr. 1941. The invention is a variation of the squeeze bore principle, designed to obtain higher muzzle velocities.
The basics are as follows. To drive a projectile to a very high speed, you need a lot of propellant. Using that, you also need a long barrel, so that the propellant can be burnt completely into propelling gases. Long barrels can become impractical, and this is where the invention kicks in. If you restrain a projectile, by narrowing the bore towards the muzzle, you create more time for the propellant to burn. This requires two things: 1. a tapered barrel, which is difficult to produce, and 2. squeezable projectiles, which are not too difficult to make. The Janecek invention deals with the first requirement in a simple way: use a normal barrel, and add a choke to the muzzle. A relatively simple accessory, with which standard gun barrels can be transformed into high velocity ones. Or so the claim goes. Quite comparable to the choke applied to the muzzle of 12 gauge hunting guns. Then the document continues, trying to sell the idea. For this a calculation of "hit probability" is introduced, and, as could be expected, this calculation demonstrates that hit probability is proportional to muzzle velocity. That's where the statement appears, that a 50% higher muzzle velocity leads to a hit probability that is five times higher. Elsewhere in the document the calculation leads to a factor eight. I believe that the exercize is executed quite well, but we must realize that this is a marketing exercize. The entire calculation is based on an assumed capability of the target to perform lateral movements, of deviating from a straight line of flight so as to avoid being hit. The outcome of the calculation shall depend on what is agreed about such lateral movement capabilities. In any case, the British did not buy it. Neither the invention, nor its sales talk. I assume that the choke idea could not as easily be implemented to existing guns as was believed. We know that the squeeze bore principle was made operational and succesful by the Germans. They had to surmount the difficulties of producing a tapered bore to get the idea to work. They did so to obtain very high muzzle velocities, meaning very high kinetic energies, which were desirable for armour piercing applications. As far as I know, the Germans did not implement that technology in fighter aircraft armament, let alone that an increased hit probability would have been a reason for doing so. Nevertheless, a most interesting find. Regards, Rob |
Re: About WW2 fighter aircraft firing power
Rob,
The point here is the relation between muzzle velocity and hitting probability regardless the Janacek's invention being bought or not. We do know that allies stayed on relatively high velocity weapons, say HS 404 and M53, because their air targets were generally small and agile fast moving fighters while the axis went towards higher caliber low velocity weapons, say MK 108 and rockets, because the main threat was the slow and large bombers. |
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And regarding a "marketing exercize"; there is no question if Janacek was selling his invention. However, he atleast tried to take account a key factor which is not accounted in some other comparisons at all.
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This is a very, very complex subject. In fact the variables are too great to have been properly computed in WWII conditions. Having done many hours of cine gun assesments, listened to lectures, and sat beside or behind pilots on practice or live firing sorties, I used to take a great deal of interest in this.
Mixed armament is a no no to start with because of the differing ballistics of the rounds Then there is the pilot skill in flying the aircraft correctly when squeezing the tit. If the old turn and bank indicator is not correct, i.e. if there is slip or skid, then the gunsite is not correctly aligned. After that comes variation in the ammo itself, and I could be here all day. |
Re: About WW2 fighter aircraft firing power
Hello Rob
WWII era reflector sight gives only right solution if the range was estimated correctly (that happened seldom, usually range was underestimated many time grossly) and wings were level, any kind of bank bought a need for sideway correction. And as Peter noted any kind of skid ruined the solution. 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. On the effects of explosive component of a shell. It is no use to try to invent wheel again. And I doubt that we have ability to do that. In any case it was over 30 years ago when I last time made rough calculations on effects of certain amount of certain explosive to certain bridge and the amounts were tens or hundreds kilos, so entirely different ball game. And anyway I have only vague recollections on some general principles used in those calculations. So much better solution is that you try to find out some formula made by experts and use it. Juha |
Re: About WW2 fighter aircraft firing power
Thanks, Juha. I agree that a flatter trajectory decreases the effects of errors, and therefore increases the chance of a hit. I did not agree with the quantification of that statement, in that a 50% higher Vo would give a 5 times higher probability of a hit. That would depend upon a definition of "hit probability", and we do not yet have a good one.
About reverting to the experts: if you could point me to a work on the subject, I'd be interested. We are not talking about civil explosive demolition here, where charges can be calculated to do a certain job under known conditions. In military explosive manuals, you'll find much less theory, and much more empirical data, based on substances and applications as they become available. In military applications, the bigger blast is usually seen as the better one. In civil explosive demolition the opposite is the way to go. Ammo parameters in our case are given. Energies can be calculated, based on these parameters. The explosive can be seen as a propellant, that projects the fragmented shell bits initially (Vo of explosion) with the speed of the explosion. Therefore, I felt safe to use the energy formula that is used for non-explosive projectiles: E = 0,5xWeightxVsquare. I'm not claiming absolute accuracy here, I offered a comparison of the energy delivered at the target of a solid and an explosive round with the parameters as stated. This data is not found in the ammo manuals, and that's the reason to give it a try. If there is an error in my reasoning, I would like to know which. In any case, hit probability is not effected by the presence or absense of explosives in a projectile, so it really is a sideline here. Hit effectiveness however is greatly effected by the use of explosive rounds. To Peter: mixing calibers in aircraft armament is a way to achieve compromises, and surely this way introduces new issues resulting from differences in exterior ballistics. That the matter is highly complicated is fully understood. I'm inclined to decide whether it is too complicated only after having given it a try. 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. Regards, Rob |
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Hello Rob
Tony sometimes post here and anyway his site has also discussion board. Maybe a couple years ago we had conversation here on effects of different fillings of HE and Minen shells and Tomislav had better recollections on explosives than me. If you can suck him into this thread he might give some tips. Juha |
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Thanks, Juha. I know how to reach Tony, and shall ask him what he knows about "hit probability".
Regards, Rob |
Re: About WW2 fighter aircraft firing power
Hello Rob
checked the thread, it's here http://forum.12oclockhigh.net/showthread.php?t=5142 Fairly interesting and also gives some indication how complicated the subject is. Juha |
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Re: About WW2 fighter aircraft firing power
Hello Harri
Yes, of course, but Rob acknowledged that already in his message #8. Juha |
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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. |
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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. |
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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. |
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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. |
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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 |
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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 |
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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. |
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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 |
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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. |
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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. |
Re: About WW2 fighter aircraft firing power
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 |
Re: About WW2 fighter aircraft firing power
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I have analysed the US reliance on the .50 here: http://www.quarry.nildram.co.uk/CannonMGs.htm |
Re: About WW2 fighter aircraft firing power
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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. Quote:
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. |
Re: About WW2 fighter aircraft firing power
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 |
Re: About WW2 fighter aircraft firing power
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. |
Re: About WW2 fighter aircraft firing power
Thanks, Peter, a most vivid picture of the difficulties encountered in practice. Two point harmonisation added to the list.
Regards, Rob |
Re: About WW2 fighter aircraft firing power
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.
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