Helicopter Gust Response Characateristics Including Unsteady Aerodynamic Stall Effects

The results of an analytical study t o evaluate the general response characteristics of a helicopter subjected to various types of discrete gust encounters are presented. The analysis employed was a nonlinear coupled, multi-blade rotor-fuselage analysis including the effects of blade flexibility and unsteady aerodynamic stall. Only the controls-fixed response of the basic aircraft without any aircraft stability augmentation was considered. A discussion of the basic differences between gust sensitivity of fixed and rotary wing aircraft is presented. The effects of several rotor configuration and aircraft operating parameters on initial gust-induced load factor and blade vibratory stress and pushrod loads are discussed. The results are used to assess the accuracy of the gust alleviation factor given by MILS-8698. Finally, a brief assessment of the relative importance of possible assumptions in gust response analyses is made and a brief comparison of gust and maneuver load experiences in Southeast A s i a is presented. The results confirm that current gust alleviation factors are too conservative and that the inclusion of unsteady stall effects result in higher initial load factors than predicted using a steady stall aerodynamic analysis.