Three-Dimensional Aeromechanical Analysis of Lift Offset Coaxial Rotors: A Helios Test Case

Three-dimensional (3-D) solid finite element analysis (FEA) is used to model and study coaxial helicopter rotors. The 3-D 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 rotorcraft), and the other is the coaxial rotor built from articulated UH-60A-like rotors. The former is the main focus of this work and is developed as an example case for the U.S. Army/DoD rotorcraft simulation software CREATE™–AV Helios, while the latter is merely for a regression test. The analysis is performed on a low-speed transition flight for which qualitative data are available for the Sikorsky S-97 Raider aircraft for comparison. Predictions of performance, airloads, vibratory loads, and 3-D stresses are discussed. In the absence of available geometry or property data of the S-97, this study is primarily meant to serve as a capability demonstration of 3-D rotor structural dynamic modeling for such rotors.