The hope was to hit the propeller !!
In the first few months of the war most of the pilots, if they didn't wave at their enemy counterparts, simply hurtled insults and rude gestures at them. This progressed to hurtling easily-carried items like bricks, chains, nets, darts and other projectiles, hoping to strike the propeller, wing, or pilot of an enemy machine. Even small bombs and grenades were tried. Fighting in four dimensions left no room for error, which means virtually none of the thrown objects hit their mark.