About WW2 fighter aircraft firing power

[Rob Philips]

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