The Investigation of the Maximum Possible Drag Reduction of the Winglet Under the Limitation of Wing Root Bending Moment

摘要

When reducing the drag of the aircraft using winglet, the size of the winglet is limited mainly under the wing root bending moment increment (ΔBM) due to the winglet. The existence of the maximum possible drag reduction (ΔC_D) at certain ΔBM is not touched by the majority of public resources. 24 winglet plans are evaluated in Computation Fluid Dynamic (CFD) to study the impact of 5 major geometric parameters (span, cant angle, incident angle, twist angle, sweptback angle) on the ΔC_D and ΔCm. It is found that for a fixed span, a linear trend line exists between ΔC_D and ΔCm for various winglet plans that the ΔC_D/ΔBM is the highest. This trend line is defined as the maximum ΔC_D achievable at certain ΔBM at a fixed span. With increasing span, the obtainable ΔC_D is higher but the ΔC_D/ΔBM decreases. The concept of the ΔC_D/ΔBM trend line as the drag reduction limit will greatly simplify the optimization process of winglet design.