As a sequel to the previous paper (Ref. 1), aerodynamic characteristics are discussed for lifting surfaces in nonuniform streamwise motions in an incompressible inviscid fluid. Two general approaches are presented; the one is an iterative method and the other is based on the solution for simple harmonic out-of-plane motions.
For the two limiting cases opposite each other, slender wings and two-dimensional aerofoils, analytical treatments are possible. An acceleration increases the lift force for slender wings, while decreases at large the lift force on twodimensional airfoils.

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A performance calculation method for multielement airfoil sections with separation is described in this paper. The potential flow analysis is based on a distributed-singularity method which uses linear-vortex and constant-source distributions. The wake is replaced by source flow representing its displacement effect. The strength of souce is given by an experimental relation derived from tangential directions at separation point. The circulation about each airfoil is determined by conditions of upper and lower separation points. The flow inside the separated streamlines is ignored and the base pressure is assumed constant at the separation value.
By combining this potential flow analysis with boundary layer calculations for the attached part of flow, the pressure distribution over airfoil surface, the maximum lift coefficient of multielement airfoil sections and its dependence on REYNOLDS number can be calculated.
Comparisons of the present method with experimental data and other methods are presented for several airfoil sections. The predicted curves of aerodynamic coefficients for the NACA 4412 airfoil section and the NACA 23012 with a slat and a slotted flap are compared with experiments.

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The characteristics of acoustic linings, which employ felt-type material made of polymidefamily fiber, has been studied by the authors. This material is considered to be one of the future candidates which take the place of HELMHOLTS-resonator-type lining which is commonly used today. To accomplish this purpose, measurement of acoustic characteristics including acoustic impedance as well as sound absorptionwas carried out systematically. In conjunction with the measurement, the procedure to calculate those acoustic characteristics of linings of this kind has been developed. Through these studies, it is shown that polymide-family felt has a superior property as acoustic linings. Agreement between measurement and calculation was good. The calculation method is considered to be a useful tool to find lining dimensions which give us desired characteristics.

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The effect of various control laws and wing properties on active flutter suppression for twodimensional wing is analytically studied in the use of oscillating incompressible aerodynamic forces. Four quantities, i. e. rotation and translation of the wing and their velocities, are feedbacked so as to move aileron. Variations of stable region with the feed-back coefficient are disclosed. The influences of the position of center of gravity, the ratio of bending to torsional natural frequencies and the mass ratio on flutter suppression are studied. If the center of gravity is after a certain position, active flutter suppression is almost impossible in the present framework of control laws. A feed-back system proportional to wing rotation is most useful for flutter suppression. The mechanism of flutter suppression is clearly explained by a simple analysis in the use of static aerodynamic forces.

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In this paper the empirical formula to obtain the approximate flutter velocity of the twodimensional wing, which is useful in the initial stage of the wing design, is proposed. The main purpose is to get the approximate prediction of the flutter velocity and to know the effect of the wing-structural factors in advance of the detailed wing design. The analysis is performed by the iteration method of the complex matrix to solve the fundamental equations of the flutter for various structural parameters. From the exact analytical results, the empirical formula is obtained by the least square method. The formula is considered to be available in the range of all recent airplain wing structures and is convenient to compare the flutter velocity with the divergence velocity. It is shown that the accuracy of our empirical formula is better than the empirical expression obtained by THEODORSEN and GARRICK. The empirical formula of the flutter frequency is also obtained as well as that of the flutter velocity.

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