I was playing an aircraft battle within a tank battle when the gun jammed without much time left, so I tried to ram the enemy aircraft in front of me. It got a kill, but when I looked at the replay my plane mostly just phased through the enemy and only damaged their tail, so I don’t understand how that counts as a kill. Is it just the quality of the replay or is there something wrong with the physics? I have quality on maximum.
More likely server issues. Some sort of desync.
The tail itself qualifies as a kill.
Severe damage to a plane is considered to be: destruction of all engines (or destroying one engine if there is only one left), destruction of all elements of the control system (or the remaining controls left), which makes impossible to control the ailerons, elevators and rudders, separation of more than half of at least one wing, and destruction of all horizontal stabilizers (or the remainder of the horizontal stab).
To destroy a plane you’ll need to hit its pilot or inflict enough damage so that its tail is torn off. For helicopters, the conditions for destruction are similar: knocking out the pilot or inducing a large accumulated amount of damage to the fuselage, which emulates the destruction of the main structure, in aircraft it usually leads to the tail being torn off.