Keywords

extended formation flight, aircraft formation flight, formation aerodynamics, aircraft wake development, formation induced drag savings

Abstract

Close formation flight is of limited practicality for commercial aviation. Our concept of extended formation flight takes advantage of the persistence of cruise wakes by extending the streamwise spacing between aircraft in a formation. This allows the aircraft to fly at safe separation distances from each other, while still benefiting from the upwash of the upstream wake(s). In this paper we are interested in estimating the performance of these extended formations, and estimating some of the effects that limit the longitudinal extent of the formation. We consider the effects of wake rollup, vortex decay, vortex instabilities, vortex motion, and atmospheric turbulence and stratification in an incompressible analysis. Formations consisting of two and three aircraft are examined. For each we evaluate the mean formation induced drag savings and associated uncertainties. At separation distances less than 20 spans, a two aircraft formation saves 26-31% in induced drag, while a three aircraft formation saves 38-45% in induced drag. Aircraft tracking error, and vortex motion due to turbulent gusts are the greatest contributors to the variation in drag savings. Extended formations are likely only practical in low to moderately low turbulence levels and for streamwise spacings less than about 50 spans.

Original Publication Citation

Ning, A., Flanzer, T., and Kroo, I., “Aerodynamic Performance of Extended Formation Flight,” Journal of Aircraft, Vol. 48, No. 3, May 2011, pp. 855–865. doi:10.2514/1.C031046