Three-Dimensional Aeromechanical Analysis of Lift Offset Coaxial Rotors

Three-dimensional (3D) solid finite element analysis (FEA) is used to model and study lift offset coaxial helicopter rotors. The 3D FEA is coupled with a lifting line aerodynamic model with free wake to capture rotor-rotor interactions. Two open access models are developed; one is the Metaltail – a hingeless coaxial proprotor, and two is the coaxial rotor built from articulated UH-60A-like rotors. The former is the main focus of this work while the latter is used to resolve qualitative differences found in former’s analysis. The analysis is performed at a low speed transition flight for which qualitative data is available for the Sikorsky S-97 Raider aircraft for comparison. Predictions of performance, airloads, and vibratory hub loads are discussed. Three-dimensional stresses and strains near the blade root are examined in detail. In absence of available geometry or property data of the S-97, this study is only meant to serve as a capability demonstration of 3D rotor structural dynamic modeling for such rotors.