Flight Path Begins to Curve:

Spin plus forward motion causes uneven lift on the boomerang’s wings. The wing at the top of the cycle has it’s spin motion added to it’s forward motion, producing a higher air speed and more lift than on the other wing. This uneven lift across the plane of rotation produces a tilting force on the spin axis. Because of gyroscopic precession, this force on the axis is twisted at right angles causing the boomerang’s flight to curve into a circular path