Dynamics Of Ultralight Aircraft Motion In Vertical Gusts

Through the use of difference equations and matrix notation a systematic procedure is developed for the calculation of the structural response of an aircraft flying through a gust. The method takes into account wing bending and twisting flexibilities, fuselage flexibility, vertical and pitching motion of the airplane, and some tail forces. Strip theory is used, but approximate three-dimensional and compressibility corrections can be made without difficulty. Either sharp-edge or arbitrary gusts may be treated.

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The effects of spanwise distribution of longitudinal and vertical components of gust velocity and longitudinal distribution of the lateral component on the lateral-directional response of a hovering VTOL aircraft are analyzed. Results show that spanwise effects of the longitudinal and vertical components are negligible, and the longitudinal distribution of the lateral component is significant in computing the power spectral densities of gust-induced side force, yawing moment, rolling moment, and the aircraft sideslip, yaw, and roll root-mean-square response angles. If the gust-induced angles of attack and sideslip angles are in the nonlinear range of lift curve slope, the above conclusions, which are based on linear aerodynamic theory, may not hold and an analysis based on momentum transfer of gust energy to the aircraft is recommended. Flow field interaction effects due to engine intake and exhaust also were not considered. (Author).