A liquid fuel sheet injected into the combustor of gas turbine engines is deformed and atomized by the complex interactions between the liquid sheet and air flows. Aiming at improving the control technology of a fuel spray, the oscillation phenomenon and the primary break-up process of a planar liquid sheet with air flows have been studied for many years. Based on the previous studies, we propose a new correlation on the longitudinal wavelength lambda(Lon) given by lambda(Lon)/D-Lip = C/root MRLip and that on the oscillation frequency f(Lon) of a liquid sheet given by f(Lon) = c'V-c/root rho L/rho C root DLDLip, where MRLip is the lip momentum ratio defined in this study. In addition to previous visualization experiments of a planar liquid sheet and parallel air flows with various densities of gas and liquid, gas and liquid velocities, liquid sheet thicknesses and lip thicknesses, we carry out an additional experiment with various gas velocities and liquid viscosities to cover all the effects of fluid properties, injector geometries including gas and liquid boundary layers on the deformation and the atomization characteristics of the oscillating liquid sheet. Image analysis is conducted to obtain f(Lon). As a result, we confirm that liquid viscosity does not affect f(Lon) and lambda(Lon) of the liquid sheet in a wide range of liquid Reynolds number. Finally, we verify the validity of the correlations of lambda(Lon) whose constant c is 14.3 and f(Lon) whose constant c' is 0.095. (C) 2018 Elsevier Ltd. All rights reserved.