Book excerpt: The lift interference was calculated for a porous wall wind tunnel by a modified method of block cyclic reduction. This efficient, numerical method has indicated its accuracy by comparison with other available analytical and approximate solutions. A scheme is introduced to search for optimum wall configurations. The lift interference computed for an NACA 64-series finite airfoil in some optimum configurations has demonstrated the achievement of minimization of interference. The effect of test section length is also examined. (Author).