Design, fabrication and preliminary testing of an experimental measurement rig for co-axial rotors

A testing rig to provide experimental data related to co-axial rotors has been designed and fabricated. Details of the configuration are provided. The rig is intended for the acquisition of rotor torque for varying flying conditions, including hover, forward flight and during descent flights. In this paper, preliminary data related to descend flight are discussed. The configuration uses two 60.96 cm-diameter, counter-rotating, rotors in a co-axial configuration. Testing was conducted at varying RPMS (2000, 3000 and 4000 RPMs), varying descend velocities (0 m/sec up to 22 m/sec). A second set of tests was conducted at constant total thrust for the varying descend velocities (20 N). Motor power vs. descend velocities are provided for the varying RPMS and for the constant thrust case. Torque vs. descend velocity is also provided for the constant thrust case. For all the results, it is observed that the lower rotor has a sudden decrease in power and torque at approximately 6 m/sec, to then recover afterwards. It is not confirmed that such even is related to vortex ring state conditions, but suggestions to further investigate the phenomenon are provided.