Definition and Discussion of the Intrinsic Efficiency of Winglets

Abstract

Three simple equations are derived to define the "intrinsic aerodynamic efficiency of winglets" independent of the horizontal extension of the winglet and independent of the winglet’s (relative) height. This "intrinsic aerodynamic efficiency" allows a quick comparison of purely the aerodynamic shape of winglets independent of the selected size chosen for a certain aircraft installation. The intrinsic aerodynamic efficiency is calculated in 3 steps: STEP 1: The relative total drag reduction due to the winglet is converted into an assumed contribution of the winglet only on the span efficiency factor. STEP 2: If the winglet also increases span, its performance is converted into one without the effect of span increase. STEP 3: The winglet’s reduction in induced drag is compared to a horizontal wing extension. If the winglet needs e.g. to be three times longer than the horizontal extension to achieve the same induced drag reduction, its "intrinsic aerodynamic efficiency" is the inverse or 1/3. Winglet metrics as defined are calculated from literature inputs. In order to evaluate winglets further, the mass increase due to winglets is estimated in addition to the reduction of drag on aircraft level and fuel burn.