Steady lift with angle of attack and unsteady lift in heaving oscillation for some wings of low aspect ratio are studied theoretically and experimentally Measurements are compared with the numerical calculations by a lifting surface theory in which the velocity potential is expressed by doublet distribution over the wing and the wake. Steady and unsteady lifts generally show good agreement with theory m the extent of the present experiments, but some nonlinear effects appeared in added-mass coefficients at low reduced frequency Three-dimensional effects on the unsteady lift due to aspect ratio of the wing are also presented graphically.
The theory of the wing was developed in aeronautical science and engineering, and there are many papers relating to the aerodynamic characteristics of oscillating wings [1,2,3,4] Wings are an element equally as important and use full in a ship or underwater vehicle as the rudder or propeller The lifting line and lifting surface theories have been applied with great success to the problems of ship propellers, but studies on unsteady hydrodynamics of oscillating wings of low aspect ratio remain inadequate  The dynamic effects of oscillating wings are important as they influence motion problems of winged remotely operated vehicles (ROVs), because the reduced frequency often takes a certain value where these dynamic effects are severe, This is a fundamental study on hydrodynamic characteristics of a towed vehicle developed by our institute for ocean measurements. [6,7] Steady lift with angle of attack and unsteady lift in heaving oscillation for wings of low aspect ratio are studied experimentally and compared with numerical results derived by a lifting surface theory.
We assume that the wing is so thin that we can deal with the problem by the linearized thin wing theory.