FORMATION FLIGHT AS AN ENERGY-SAVING MECHANISM

Formation flight is widely used by migrating birds. Each wing flies in an upwash field generated by ail other wings in the formation, and th is leads to a reduction in flight power demand for each wing as well a s for the whole formation. The benefits of aerodynamic interference ca n be determined from aerodynamic theory, and comparisons with flight t ests on formations of two airplanes show excellent agreement. For maxi mum power reduction, the rear wing has to be located as close as possi ble aside the wake of the front wing. For formations in a horizontal p lane, the total power reduction of the whole formation depends strongl y 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 in volved individuals. The local flight power reduction is highest in the inner parts of the formation and decreases towards the apex and the s ide edges. Small and light individuals experience larger benefits than larger and heavier birds. The considerable benefit of saving energy b y aerodynamic interference is thought to be the most important reason for the occurrence of formation flight of large birds.