Rotary wing aeroelasticity_ a historical perspective

This paper provides a historical perspective of the fundamental developments that have played a central role in rotary-wing dynamics and aeroelasticity and have had a major impact on the design of rotary-wing aircraft. The paper describes a historical progression starting with the classical flap-pitch problem that emulated fixed-wing behavior and describes the evolution of the dynamic and aeroelastic problems into those that are unique to rotorcraft, such as the flap-lag problem, the lag-pitch problem, and the coupled flaplag-torsional problem. Subsequently, the coupled rotor\fuselage aeromechanical problems such as ground and air resonance are considered. A description of the evolution of the methodology used in the formulation and solution of these types of problems is also provided, emphasizing the structural and aerodynamic models required for their effective formulation and solution. The mathematical techniques used for solving the rotary-wing aeroelastic problems in hover and forward flight are also described. The primary emphasis of the paper is on aeroelastic stability, and aeroelastic response is only treated briefly. The paper focuses on contributions that have historical value because they represent landmark treatments. Because of the large amount of material available, an all-inclusive treatment of the research done in this field is impractical, and the paper has unavoidable omissions.