Efficiency Estimation of Formation Flight Types

Abstract

Formation flight is usually seen in birds’ migration and military operations, and will be more often in unmanned aircrafts applications in future. It is known that drag reduction and fuel saving can be achieved in formation flight and positional parameters are important to this effect. But few literatures about efficiency of formation flight types on this effect are published. Wake vortexes of the leading aircraft in formation flight are assumed to be a pair of reversed vortexes. Using potential flow techniques, models of the trailing aircraft’s lift and drag coefficients are constructed which are functions of lateral spacing and vertical spacing. An estimation of energy saving is conducted on three formation flight types-V mode, Λ mode and echelon mode. The formation studied consists of three the same aircrafts. The total drag of three aircrafts in a formation is regarded as an index for energy saving efficiency under a precondition that all aircraft’s lift equals to their own weights. Each type is under its best status. Results show that echelon mode has the highest energy saving efficiency, Λ mode is a little low and V mode is markedly lower than the two others. This result accords well with formation flight types used in birds’ migration.