Application of the Multiple Swashplate System for Individual Blade Control of a 5-bladed Model Rotor in the DNW-LLF Wind Tunnel

After a successful wind tunnel test in the DNW in late 2015, where for the first time DLR’s patented multiple swashplate system (META) was used to demonstrate its full IBC capabilities on a Mach-scaled, 4-bladed model rotor, the META system as well as DLR’s rotor test rig were modified and upgraded extensively to allow IBC operation on a 5-bladed rotor system. After these system upgrades, a second wind tunnel test was performed in late 2016. The goal of this test was to reduce vibration, noise and required rotor power in different flight conditions on a 5-bladed model rotor using proven individual blade control (IBC) as well as localized pitch control (LPC) strategies. In the test the 5/rev hub vibration levels were reduced significantly both through the application of 3/rev higher harmonic control (HHC) and a vibration controller using a 4-6/rev multi-harmonic control signal. The highest reduction was achieved for the vertical 5/rev force, nearly eliminating this most prominent component of rotor hub vibrations. Additional highlights of the test were 2/rev HHC sweeps and the test of different LPC schedules for the reduction of noise and required rotor power. In descent flight condition, significant blade vortex interaction (BVI) noise reductions relative to the baseline case were achieved on both sides of the rotor disk through the application of 2/rev HHC as well as LPC. In simulated high-speed flight, the required rotor power was successfully reduced using 2/rev HHC.