Experimental investigation on hover performance of a single-rotor system for Mars helicopter
Abstract Mars helicopter, as an aerial auxiliary platform with the abilities of vertical take-off whenever a rover requires and directly landing wherever the destination is determined, is of great significance in the field of planetary exploration. Since a thin atmosphere exists on Mars, the feasibility of helicopter flight on Mars should be validated. In addition, a proper understanding of the flight performance, especially the hover performance, is necessary for the design and optimization of the Mars helicopter's rotor system. In this work, hover performance experiments of a two-bladed untwisted rectangular planform single rotor with NACA 6904 airfoil are conducted in the Martian Atmosphere Simulator (MAS), which is used to simulate the Martian atmospheric density. Based on the experimental results, the collective pitch angle effects and Reynolds number effects on the lift-drag characteristics and efficiency of the single-rotor system are investigated during the hovering process with Reynolds number ranging from 3050 to 6100 (using the chord and speed at 0.75 wingspan) and Mach number ranging from 0.23 to 0.46 (using the speed at blade tip). The results reveal that it is feasible for a 500 g Mars helicopter with 30 ∘ optimum collective pitch angle at 4510 r/min minimum rotational speed to work under the Martian atmospheric density and obtain a maximum figure of merit of 0.40 as well as a hover endurance of 17.0 min. Additionally, increasing the Reynolds number (ranging from 3050 to 24020) at a constant Mach number of the rotor system by increasing the rotor blade solidity can lead to a higher figure of merit, which is important for improving the load capacity of a Mars helicopter.