formation flight, extended formation flight, compressibility, transonic, high-speed, drag savings, aircraft, CFD, Euler
Aircraft flown in formation can realize significant reductions in induced drag by flying in regions of wake upwash. However, most transports fly at transonic speeds where the impact of compressibility on formation flight is not well understood. This study utilizes an Euler solver to analyze the inviscid aerodynamic forces and moments of transonic wing/body configurations flying in a two-aircraft formation. Formations with large streamwise separation distances (10-50 wingspans) are considered.
This work indicates that compressibility-related drag penalties in formation flight may be eliminated by slowing 2-3% below the nominal out-of-formation cruise Mach number (either at fixed lift coefficient or fixed altitude). The latter option has the additional benefit that the aerodynamic performance of the formation improves slightly at higher lift coefficients. While optimal in-formation lift coefficients are not as high as those estimated by incompressible analyses, modest increases in altitude can yield further improvements in aerodynamic efficiency. Increasing the lateral separation of the aircraft allows for slightly higher cruise speeds in exchange for higher induced drag. For the configurations examined here, a 1-2% reduction in Mach number combined with a lateral spacing increase of 5% span achieves a total formation drag savings of about 10%.
Original Publication Citation
Ning, A., Kroo, I., Aftosmis, M. J., Nemec, M., and Kless, J. E., “Extended Formation Flight at Transonic Speeds,” Journal of Aircraft, Vol. 51, No. 5, Sep. 2014, pp. 1501–1510. doi:10.2514/1.C032385
BYU ScholarsArchive Citation
Ning, Andrew; Kroo, Ilan; Aftosmis, Michael; Nemec, Marian; and Kless, James, "Extended Formation Flight at Transonic Speeds" (2014). Faculty Publications. 1674.
Ira A. Fulton College of Engineering and Technology
Copyright © 2013 by S. Andrew Ning. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
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