Aeromechanical Analysis of a Next-Generation Mars Hexacopter Rotor

A three-dimensional (3D) aeromechanical analysis is carried out on the rotor blades of a 20 kg conceptual Mars Hexacopter. The objectives are to understand the aeroelastic behavior of its unique ultrathin low-Reynolds-number and high-Mach-number blades and study the interactions of structures, aerodynamics, and control moments in the Martian atmosphere. Beginning with structural analysis in vacuum, comprehensive analysis is carried out in hover and forward flight using 3D Finite Element Method (FEM), three-dimensional (2D) airfoil tables, and free wake. Natural frequencies of the rotor, elastic response of the blade, control moments at the root, airloads of blade sections, and 3D stresses are studied. Two types of designs are considered: a baseline design with pitch axis at the quarter chord and an unconventional design with the pitch axis moved to the midchord. Unusual nose-up elastic twist is observed on the rotor blades that appears to stem from the trapeze effect that counteracts the flattening effect of the propeller moment. By moving the pitch axis to midchord, the control moment is reduced by 30–40% without any noticeable adverse effect on stability due to the low Lock number. Both designs have maximum stresses well below the material limits, but the midchord design has a more uniform distribution of stress in general and lower levels of shear stress in particular. These and many other unconventional phenomena make Martian aeromechanics unique and ripe with possibilities of innovations tailored to its atmosphere.