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.

General theory of thin wing sections

Abstract: This report contains a new, simple method of calculating the air forces to which thin wings are subjected at small angles of attack, if their curvature is not too great. Two simple integrals are the result. They contain only the coordinates of the wing section. The first integral gives the angle of attack at which the lift of the wing is zero, the second integral gives the moment experienced by the wing when its angle is zero. The two constants thus obtained are sufficient to determine the lift and moment for any other angle of attack. This with the theory of the aerodynamical induction, and with our empirical knowledge of the drag due to friction, the results are valuable for actual wings also. A particular result obtained is the calculation of the elevator effect. (author)

Wake Integration for Three-Dimensional Flowfield Computations: Applications

Abstract: A momentum balance approach is used to extract lift and drag from flowfield computations for wings and wing/bodies in subsonic/transonic flight. The drag is decomposed into vorticity, entropy, and enthalpy components that can be related to the established engineering concepts of induced drag, wave and profile drag, and engine power and efficiency. This decomposition of the drag is useful in formulating techniques for accurately evaluating drag using computational fluid dynamics calculations or experimental data. A formulation for reducing the size of the region of the crossflow plane required for calculating the forces is developed using cutoff parameters for viscosity and entropy. This improves the accuracy of the calculations and decreases the computation time required to obtain the results. The improved method is applied to a variety of configuration s, including an elliptic wing, the M6 wing, the W4 wing - body, the M165 wing-body-foreplane, and the Lockheed Wing A. The accuracy of the force calculations is related to various aspects, including the axial position of the downstream crossflow plane, grid type (structured or unstructured), grid density, flow regime (subsonic or transonic), and boundary conditions.

Experimental Investigation of Lift, Drag, and Pitching Moment of Five Annular Airfoils

Abstract: From Summary: "An investigation was carried out in the Langley stability tunnel to determine the lift, drag, and pitching-moment characteristics of a family of annular airfoils. The five annular airfoils had equal projected areas but had varying chords and diameters which covered aspect ratios of 1/3, 2/3, 1.0, 1.5, and 3.0. The results showed that the effects of aspect ratio on the aerodynamic-center location were similar for annular and unswept airfoils and that annular airfoils had larger maximum lift-drag ratios below an aspect ratio of 2.4 than did plane rectangular airfoils with faired tips."

A Computational and Experimental Study of Nonlinear Aspects of Induced Drag

Abstract: Despite the 80-year history of classical wing theory, considerable research has recently been directed toward planform and wake effects on induced drag. Nonlinear interactions between the trailing wake and the wing offer the possibility of reducing drag. The nonlinear effect of compressibility on induced drag characteristics may also influence wing design. This thesis deals with the prediction of these nonlinear aspects of induced drag and ways to exploit them. A potential benefit of only a few percent of the drag represents a large fuel savings for the world's commercial transport fleet. Computational methods must be applied carefully to obtain accurate induced drag predictions. Trefftz-plane drag integration is far more reliable than surface pressure integration, but is very sensitive to the accuracy of the force-free wake model. The practical use of Trefftz plane drag integration was extended to transonic flow with the Tranair full-potential code. The induced drag characteristics of a typical transport wing were studied with Tranair, a full-potential method, and A502, a high-order linear panel method to investigate changes in lift distribution and span efficiency due to compressibility. Modeling the force-free wake is a nonlinear problem, even when the flow governing equation is linear. A novel method was developed for computing the force-free wake shape. This hybrid wake-relaxation scheme couples the well-behaved nature of the discrete vortex wake with viscous-core modeling and the high-accuracy velocity prediction of the high-order panel method. The hybrid scheme produced converged wake shapes that allowed accurate Trefftz-plane integration. An unusual split-tip wing concept was studied for exploiting nonlinear wake interaction to reduced induced drag. This design exhibits significant nonlinear interactions between the wing and wake that produced a 12% reduction in induced drag compared to an equivalent elliptical wing at a lift coefficient of 0.7. The performance of the split-tip wing was also investigated by wing tunnel experiments. Induced drag was determined from force measurements by subtracting the estimated viscous drag, and from an analytical drag-decomposition method using a wake survey. The experimental results confirm the computational prediction.

Applications of a Counterflow Drag Reduction Technique in High-Speed Systems

Abstract: Potential applications of a counterflow drag-reduction technique were investigated to assess performance improvements on aerospace vehicles. The motivation for this study was the 30-50% drag reduction achieved by counterflow blowing experiments on hemispherical cylinders at Mach 4 and higher. Exploratory studies indicate that drag improvements by counterflow drag reduction on hemispherical bodies cannot match those of aerodynamically shaped sharp-nosed bodies. Hence, the approach taken in the present study is that for hypersonic Mach numbers: if the nose shape is required to be blunt for considerations other than drag, counterflow blowing can be effective in improving the performance of the system. Although for generic body shapes counterflow blowing is most effective for blunt-nosed bodies, when applied to actual systems, many other factors need to be considered, such as available internal volume and extreme compressed carriage requirements. Depending on the vehicle speed and nose shape, estimated drag reductions of 15-30% were applied to predict the overall performance gains on Space Operations Vehicle, Gun-Launched Rocket, and Pegasus XL configurations. Potential savings in propellant and improvements in burnout velocity and range are reported. For launch systems with high fuel fraction, the payoff with counterflow drag reduction is marginal as the overall effects of aerodynamic drag on performance are small in the upper atmosphere. For the lower fuel fraction vehicle, the Gun Launched Rocket, a range improvement of 7% was achieved for a drag reduction of 30% with 0.3 blunting of nose flying above Mach 3; with greater blunting, however, the volume of fuel cannot compensate for the increase in drag.