Why a thrown boomerang returns

Settled in 1968 by Felix Hess.

Returning boomerangs are an ancient Aboriginal Australian technology developed through practical trial and error long before any aerodynamic theory existed to explain them. The physics - how a spinning, curved airfoil precesses gyroscopically due to unequal lift on its advancing versus retreating arm, curving the whole flight path back to the thrower - was not rigorously worked out until physicist Felix Hess combined wind-tunnel-informed computer modeling with field experiments in his 1968 Scientific American article, later expanded in his PhD thesis and book. Hess's analysis quantitatively matched observed flight paths and remains the standard reference on boomerang aerodynamics.

A curved stick thrown by hand traces a graceful loop and comes back, powered by exactly the same gyroscopic precession that keeps a spinning bicycle wheel pointed in a slowly rotating direction.

Explanations that circulated

• A common oversimplification says the boomerang returns because it curves like a thrown curveball due to spin alone; the real mechanism is gyroscopic precession combined with differential lift between the advancing and retreating arm during each rotation, which precesses the spin axis and curves the flight path into a loop.
• Some popular accounts claim any spinning flat object thrown correctly will return; the airfoil cross-section of each arm and correctly angled arms are essential, not spin alone.

References

• The Aerodynamics of Boomerangs, Felix Hess, Scientific American, 1968