Catapults date back at least 2,400 years, when Greek soldiers used them to hurl flaming arrows at enemies on the field of battle. More recently, the U.S. Navy has catapulted jets into the air from aircraft carriers. In January 2011, Mexican drug dealers unsuccessfully tried to use a catapult to hurl 4-pound bales of marijuana over a border fence into Arizona. Today, modelling companies offer kits for building your own working catapult, good for tossing rocks or other small objects. Throughout this long and varied history, techniques for aiming catapults, particularly the traditional counterweight trebuchets, have remained largely unchanged.
Fire a test shot at your target. Catapults almost never hit the target on the first try, so you will need to bracket the target. You will adjust based on whether the projectile lands long or falls short, or whether it drifts to one side or the other due to wind or other factors.
Release the projectile early for a higher, shorter trajectory. Release it later for a flatter, longer trajectory.
Adjust your projectile's weight. Heavier objects loft higher and fly shorter distances. Lighter objects fly flatter, faster trajectories.
Observe carefully where each projectile lands. Continue to adjust your release time or projectile weight until you have zeroed in upon your target.
A catapult quickly releases a great deal of energy in a relatively small space, so stand clear when one is working. Stay out of the way of moving objects. Check before you fire, so people and valuable property remain safe.