Zoe Brain
04-29-2013, 10:03
http://users.skynet.be/Emmanuel.Gustin/fgun/fgun-ar.html
We can now have a look at the armament of some WWII fighters. For convenience, I sorted them by hitting power, in terms of fired weight per second. There is also a chart of the evolution of fired weight per second, which requires Java, or a plot in static gif format.
Fired weight per second is at best a rough approximation of destructive power. It is a reasonable approximation if the destruction is to be caused by the high-explosive or incendiary chemicals contained in the ammunition. The amount of explosive or incendiary material is of course related to the weight of the projectile, but it is not a linear relationship: Rounds of smaller calibre have proportionally thicker walls, and a smaller fraction of their weight is available for chemical loads. Therefore the fired weight per second is usually more relevant for larger calibre guns.
As a second measure of the destructive power, the muzzle power is given, in kilowatt. This is the rate of production of kinetic energy. AP or "ball" rounds that contain no chemical load only have this kinetic energy to cause damage to the target. More is not always better; a round with a too high kinetic energy might pass clean through the target without doing more damage than two neat, round holes. The optimal velocity to do maximal damage a metal plate is just below that required to penetrate it. Of course projectiles lose a lot of the muzzle energy before they hit the target, because of drag. In general larger calibre projectiles retain their kinetic energy longer.
A disadvantage of AP rounds is that they cause damage in a more limited area than incendiary or explosive rounds. Therefore semi-armour-piercing explosive or incendiary rounds were used more often. These require kinetic energy to penetrate the armour, and have chemical energy to cause destruction afterwards.
A third number given is the number of projectiles fired. If the target is not armoured, the same weight of non-explosive projectiles does more damage when distributed over numerous small projectiles than in a single large one, and the number of projectiles is the most important. But if the target carries armour the smaller projectiles are more likely to be stopped, and that reduces the effectiveness, especially of the rifle-calibre weapons. On the other hand, a larger number of projectiles means that the probability of a single hit increases.
To summarize: Fired weight per second is given as an approximation of the chemical energy that can be transferred to the target, muzzle power as a measure of the kinetic energy, and the number of rounds fired indicates the spreading of this transfer over a number of hits. All three are factors that must be considered in a consideration of the firepower installed in an aircraft. A "firepower formula" that would allow us to actually calculate a single number as a measure of the firepower, would be a nice thing to have. However, too many factors are involved, and the effectiveness of ammunition depends very much on the nature of the target.
http://www.quarry.nildram.co.uk/WW2guneffect.htm
The comparative effectiveness of fighter guns in the Second World War is a subject of perennial fascination (and a great deal of argument) among technical military historians. This is an attempt to take a fresh and objective look at the evidence in order to draw up comparative tables of cartridge destructiveness, gun power and gun efficiency. The effectiveness of typical day fighter armament fits is also considered.
We can now have a look at the armament of some WWII fighters. For convenience, I sorted them by hitting power, in terms of fired weight per second. There is also a chart of the evolution of fired weight per second, which requires Java, or a plot in static gif format.
Fired weight per second is at best a rough approximation of destructive power. It is a reasonable approximation if the destruction is to be caused by the high-explosive or incendiary chemicals contained in the ammunition. The amount of explosive or incendiary material is of course related to the weight of the projectile, but it is not a linear relationship: Rounds of smaller calibre have proportionally thicker walls, and a smaller fraction of their weight is available for chemical loads. Therefore the fired weight per second is usually more relevant for larger calibre guns.
As a second measure of the destructive power, the muzzle power is given, in kilowatt. This is the rate of production of kinetic energy. AP or "ball" rounds that contain no chemical load only have this kinetic energy to cause damage to the target. More is not always better; a round with a too high kinetic energy might pass clean through the target without doing more damage than two neat, round holes. The optimal velocity to do maximal damage a metal plate is just below that required to penetrate it. Of course projectiles lose a lot of the muzzle energy before they hit the target, because of drag. In general larger calibre projectiles retain their kinetic energy longer.
A disadvantage of AP rounds is that they cause damage in a more limited area than incendiary or explosive rounds. Therefore semi-armour-piercing explosive or incendiary rounds were used more often. These require kinetic energy to penetrate the armour, and have chemical energy to cause destruction afterwards.
A third number given is the number of projectiles fired. If the target is not armoured, the same weight of non-explosive projectiles does more damage when distributed over numerous small projectiles than in a single large one, and the number of projectiles is the most important. But if the target carries armour the smaller projectiles are more likely to be stopped, and that reduces the effectiveness, especially of the rifle-calibre weapons. On the other hand, a larger number of projectiles means that the probability of a single hit increases.
To summarize: Fired weight per second is given as an approximation of the chemical energy that can be transferred to the target, muzzle power as a measure of the kinetic energy, and the number of rounds fired indicates the spreading of this transfer over a number of hits. All three are factors that must be considered in a consideration of the firepower installed in an aircraft. A "firepower formula" that would allow us to actually calculate a single number as a measure of the firepower, would be a nice thing to have. However, too many factors are involved, and the effectiveness of ammunition depends very much on the nature of the target.
http://www.quarry.nildram.co.uk/WW2guneffect.htm
The comparative effectiveness of fighter guns in the Second World War is a subject of perennial fascination (and a great deal of argument) among technical military historians. This is an attempt to take a fresh and objective look at the evidence in order to draw up comparative tables of cartridge destructiveness, gun power and gun efficiency. The effectiveness of typical day fighter armament fits is also considered.