View Single Post
  #1  
Old 7th September 2008, 22:16
Rob Philips Rob Philips is offline
Member
 
Join Date: Jul 2008
Location: The Netherlands
Posts: 53
Rob Philips is on a distinguished road
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

Last edited by Rob Philips; 8th September 2008 at 00:50.
Reply With Quote