Abstract
This paper interprets the inaccuracies arising from the Mach box evaluation of unsteady aerodynamic forces based on the method of Aerodynamic Influence Coefficients (AIC), and proposes refinements to minimize these inaccuracies. The basic equations of inviscid flow are reviewed and the assumptions and restrictions inherent in present application of the AIC method are discussed. The inaccuracies, which result in large fluctuations of the pressure distribution, stem primarily from distortion of the leading edge which results from a Mach box grid representation of the wing planform. The refinement consists of a subdivision of the grid of pulse-sending boxes while maintaining the original grid of pulse-receivi ng box control points. Numerical examples are included to demonstrate its efficiency. The downwash singularity near a subsonic leading edge is also considered and a numerical procedure for evaluating its effect is shown. Nomenclature A = integrated area and integration constant a = speed of sound aj = amplitude of the y th mode oscillation br = reference length Z>! = chordwise dimension of Mach box ki = reduced frequency based on b^k^ = L = lift force M = Mach number in uniform flow condition TV = subdivision factor P = pressure <2i j = Generalized force for the /th elastic mode and loading for
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