FORMATION FLIGHT AS AN ENERGY-SAVING MECHANISM

ABSTRACT

Formation flight is widely used by migrating birds. Each wing flies in an upwash field generated by all other wings in the formation, and this leads to a reduction in flight power demand for each wing as well as for the whole formation. The benefits of aerodynamic interference can be determined from aerodynamic theory, and comparisons with flight tests on formations of two airplanes show excellent agreement. For maximum power reduction, the rear wing has to be located as close as possible aside the wake of the front wing. For formations in a horizontal plane, the total power reduction of the whole formation depends strongly on the number and the lateral distance of the wings. A longitudinal displacement of the wings in flight direction has no influence on the total flight power reduction but only on its distribution among the involved individuals. The local flight power reduction is highest in the inner parts of the formation and decreases towards the apex and the side edges. Small and light individuals experience larger benefits than larger and heavier birds. The considerable benefit of saving energy by aerodynamic interference is thought to be the most important reason for the occurrence of formation flight of large birds.