Lift-induced drag

About: Lift-induced drag is a research topic. Over the lifetime, 2861 publications have been published within this topic receiving 41094 citations.

Effect' of winglets on a first-generation jet transport wing

Abstract: SUMMARY OF RESULTS A wind-tunnel investigation of winglets mounted on the tip of a 0.07-scale KC-135A jet transport model wing has been conducted. Configurations with an upper winglet only and with upper and lower winglets are compared with a simple wing-tip extension which is designed to produce the same increase in bending moment at the wing root (at a lg load factor) as do the winglets. Data are pre- sented at four high subsonic Mach numbers and one low subsonic Mach number, and indicate the following conclusions: 1. Both winglet configurations reduce induced drag by approximately 20 per- cent at design cruise conditions. The tip extension reduces induced drag by about 10 percent at design conditions. 2. At cruise conditions winglets produce improvements in lift-drag ratio of about 9 percent. improvement in lift-drag ratio. At the same conditions the tip extension produces a 4-percent 3. The negative increments in pitching-moment coefficient due to the wing- lets are less than those produced by the tip extension. 4.

The design of winglets for high-performance sailplanes

Abstract: Although theoretical tools for the design of winglets for high-performance sailplanes were initially of limited value, simple methods were used to design winglets that gradually became accepted as benefiting overall sailplane performance. As understanding was gained, improved methods for winglet design were developed. The current approach incorporates a detailed component drag buildup that interpolates airfoil drag and moment data across operational lift-coefficient, Reynolds-numbe{, and flap-deflection ranges. Induced drag is initially predicted using a relatively fast multiple lifting-line method. In the final stages of the design process, a full panel method, including relaxed-wake modeling, is employed. The drag predictions are used to compute speed polars for both level and turning flight. The predicted performance is in good agreement with flight-test results. The straight- and turningflight-speed polars are then used to obtain average crosscountry speeds as they depend on thermal strength, size, and shape, which are used to design the winglets that provide the greatest gain in overall performance. Flight-test measurements and competition results have demonstrated that the design methods produce winglets that provide an important performance advantage over much of the operating range for both span-limited and span-unlimited highperformance sailplanes.

Development of a Twisting Wing Powered by a Shape Memory Alloy Actuator

Abstract: A variably twisting wing has many beneficial qualities that can improve aircraft performance for a variety of flight conditions. Beneficial variable wing twist features include a means to reduce induced drag in cruise conditions, to increase lift performance, and to increase roll control. However, the actuation hardware usually required to twist large scale wings, especially given their structural stiffness, presents a substantial limitation. Through the use of shape memory alloy (SMA) torque tubes and other associated active spars, such structural deformations can be enabled. In this work, we consider the development of a benchtop and wind tunnel testing platform for potentially assessing the response of a variety of SMA-based wing twisting concepts. Using additive manufacturing (3D printing), we have designed, built, and tested a small scale prototype. The SMA actuated twisting wing developed herein consists of a rapid prototype shell that was specifically designed using a finite element approach to maintain stiffness in bending while reducing torsional rigidity. Using LabView and a simple PID controller, we have shown that an SMA torque tube was able to drive and steadily maintain the spanwise linear twist in the wing under both benchtop and wind tunnel conditions. This prototype will allow future assessment of new control schemes, new SMA actuator materials, and new structural configurations toward the development of flight-capable self-twisting wings.

Wake analysis of drag components in gliding flight of a jackdaw (Corvus monedula) during moult

Abstract: To maintain the quality of the feathers, birds regularly undergo moult. It is widely accepted that moult affects flight performance, but the specific aerodynamic consequences have received relatively little attention. Here we measured the components of aerodynamic drag from the wake behind a gliding jackdaw (Corvus monedula) at different stages of its natural wing moult. We found that span efficiency was reduced (lift induced drag increased) and the wing profile drag coefficient was increased. Both effects best correlated with the corresponding reduction in spanwise camber. The negative effects are partially mitigated by adjustments of wing posture to minimize gaps in the wing, and by weight loss to reduce wing loading. By studying the aerodynamic consequences of moult, we can refine our understanding of the emergence of various moulting strategies found among birds.