Stability and Control Characteristics of the Winglet Configured KC-135A

Abstract : Using the Boeing FLEXSTAB digital computer system, rigid and elastic models of the winglet configured KC-135A are made. With a rigid analysis, the winglets reduce total drag from 2 to almost 8% with improvements both laterally and longitudinally in static stability. Dynamically, the rigid winglet model is more stable laterally but slightly more oscillatory longitudinally. The lateral dutch roll mode damping ratio increased with winglets from 3 to 12% with only a 3% increase in frequency. Elastic static stability is still improved both laterally and longitudinally with winglets; and dynamically, the winglets improve lateral stability with very little effect longitudinally. With aeroelastic effects, the overall benefit derived from winglet application to the model is less. However, no significant detrimental effects due to winglets are found.