The use of wing tip sails to reduce vortex drag

With the increasing need for fuel economy all possible areas of drag reduction need investigating. One form which offers considerable promise is lift-dependent drag which for most transport aircraft is approximately 30% of the total drag in the cruise and more at lower speeds. A reduction in lift-dependent drag at a given flight speed would directly reduce the operating costs of existing aircraft. Even greater savings might be obtained for twin-engined airliners where the wing loading is fixed by the high lift-dependent drag at climb-out from the airfield. A method of increasing the effective aspect ratio of a wing would allow new aircraft of this type to have lower wing areas and weights in addition to higher cruise lift-drag ratios.