Aeromechanical Loads on a Mars Coaxial Rotor

A detailed aeromechanical understanding of a coaxial rotor flying on Mars is presented using a combination of vacuum chamber tests and free-wake based comprehensive analysis. The objectives are to understand the limits of performance, structural loads, control loads (pitch link), wake interaction, and blade strike for hingeless and articulated coaxial rotors. Because of the uniqueness of Martian conditions and the impossibility of testing a rotor at such conditions on Earth on ground a variety of unit tests and a progressively refined set of analysis are used to build up the problem. The unit tests include: construction of composite blades, structural testing, development of a vacuum chamber rotor rig, inclusion of full swashplate controls and hover testing of an isolated rotor. The analysis suite include: 3D FEA, 2D CFD, and a coaxial comprehensive analysis with flexible blades and free-wake. The key conclusions of the research are: (1) the hingeless rotor has high blade root loads and hub loads as expected but the articulated rotor experiences much greater pitch link loads across all the rotor cases explored due to C.G. offsets dictated by an ideal low Re sharp leading edge airfoil (2) the hingeless and articulated rotors both have similar blade tip separation for rotor spacing of 20% R or lower (3) the blade tip separation in fact increases with advance ratio–not decreases–because of the cyclic phasing of the blade passing locations, and (4) tip separation is determined not by blade dynamics but cyclic inputs on relatively wide chord blades.