Airfoil Selection for Mars Rotor Applications

This short white paper is aimed at providing an overview of design considerations for airfoil choices for rotor applications in the Martian atmosphere, at very low chord-based Reynolds number flows, around Rec = O (103 -104). The low Reynolds number typical of rotorcraft operation in the Martian atmosphere reduces the rotor lifting force and efficiency, which is only partially compensated for by a lower gravity on Mars. Additionally, the low temperature and largely CO2 based atmosphere of Mars compound the overall aerodynamic problem by resulting in a lower speed of sound, further constraining rotor operation in the Martian atmosphere by limiting the maximum rotor tip speed possible so as not to exceed an acceptable tip Mach number. In light of the expected reduced rotor efficiency, evaluating airfoils for compressible, low-Reynolds number Mars rotor applications is key. Prior research on airfoil optimization and performance evaluation at low Reynolds numbers, especially in the compressible regime, is scarce and deserves further understanding. Specifically, the proposed goal stemming from this overview is to develop airfoils tailored to the unique demands of the second generation of Mars rotorcraft, i.e. the Mars Science Helicopter (MSH). This research focuses on the airfoil performance at low Reynolds numbers and hopes to add to the work performed by, amongst others, Kroo et al., Kunz and Kroo, Oyama and Fujii, Anyoji et al.