Decambering

Abstract: A novel scheme is presented for an iterative decambering approach to predict the post-stall characteristics of wings using known section data as inputs. The new scheme differs from earlier ones in the details of how the residual is computed. With this scheme, multiple solutions at high angles of attack are brought to light right during the computation of the residual for the Newton iteration. As with earlier schemes, multiple solutions are obtained for wings at high angles of attack and the resulting converged solution depends on the initial conditions used for the iteration. In general, the new scheme is found to be more robust at achieving convergence. Results are presented for a rectangular wing with two different airfoil lift curves and for a wing-tail configuration.

Abstract: This paper presents an innovative wing profile featuring an internal truss-like structure of chiral topology. The chiral design is selected because of its unique deformation characteristics, which produce a theoretical, in-plane Poisson's ratio of -1. Such a Poisson's ratio yields a very high shear modulus, which in principle does not require the wing profile to be defined by a closed section or stressed-skin configuration. In addition, the peculiar deformation mechanism of the chiral configuration allows large decambering deflections to occur, with all the members of assembly behaving within the linear range of the material. Hence the proposed design combines large chordwise compliance and large in-plane shear stiffness. Such conflicting mechanical properties can be achieved through the proper selection of a limited number of geometric parameters defining the core configuration. The objective of the paper is to investigate the compliance characteristics of the airfoil. Two-dimensional profiles, designed according to results from previous investigations, are manufactured and tested to assess compliance and evaluate decambering deflection limits. The experimental analysis is guided by numerical models that account for deviations from the ideal configuration due to manufacturing limitations. Numerical and experimental results demonstrate the influence of core geometry on the compliance and confirm the ability of chiral-core airfoils to sustain large deflections while not exceeding yield strain limits.

Abstract: An iterative decambering approach for the post stall prediction of wings using known section data as inputs is presented. The method can currently be used for incompressible .ow and can be extended to compressible subsonic .ow using Mach number correction schemes. A detailed discussion of past work on this topic is presented first. Next, an overview of the decambering approach is presented and is illustrated by applying the approach to the prediction of the two-dimensional C(sub l) and C(sub m) curves for an airfoil. The implementation of the approach for iterative decambering of wing sections is then discussed. A novel feature of the current e.ort is the use of a multidimensional Newton iteration for taking into consideration the coupling between the di.erent sections of the wing. The approach lends itself to implementation in a variety of finite-wing analysis methods such as lifting-line theory, discrete-vortex Weissinger's method, and vortex lattice codes. Results are presented for a rectangular wing for a from 0 to 25 deg. The results are compared for both increasing and decreasing directions of a, and they show that a hysteresis loop can be predicted for post-stall angles of attack.

Abstract: SUMMARY Nonlinear aerodynamics of wings may be evaluated using an iterative decambering approach. In this approach, the effect of flow separation due to stall at any wing section is modeled as an effective reduction in section camber. The approach uses a wing analysis method for potential-flow calculations and viscous airfoil lift curves for the sections as input. The calculation procedure is implemented using a Newton–Raphson iteration to simultaneously satisfy the boundary condition, which comes from potential-flow wing theory, and drive the sectional operating points toward their respective viscous lift curves, as required for convergence. Of particular interest in this research is the calculation of the residuals during the Newton iteration. Unlike a typical implementation of the Newton iteration, the residual calculation is not performed via a straightforward function evaluation, but rather by estimating the target operating points on the input viscous lift curves. Estimation of these target operating points depends on the assumptions made in the cross-coupling of the decambering at the different sections. This paper presents four residual calculation schemes for the decambering approach. The residual calculation schemes are compared against each other to assess computational speed and robustness. Decambering results are also compared with higher-order computational fluid dynamics (CFD) solutions for rectangular and swept wings. Results from the best scheme compare well with the CFD solutions for the rectangular wing, motivating further development of the method. Poor predictions for the swept wings are traced to spanwise propagation of separated flow at stall, highlighting the limitations of the current approach. Copyright © 2014 John Wiley & Sons, Ltd.

Abstract: Apparatus and method for squaring and decambering at the assembly plant, and shimming at the job site, a thin metal door frame wherein the frame becomes an integral part of its own setting jig until installation, after which the semi-permanent setting jig is removed. Temporary jigs are used in the method to set the minimum door width tolerance and to square the frame elements.