SUPPRESSING VIBRATIONS IN THE BA609 TILTROTOR: FLIGHT TESTING AN INNOVATIVE SOLUTION

摘要

The ongoing flight test and development of the Bell-Agusta BA609 presents many interesting engineering challenges. Among these challenges is controlling vibrations within the cabin. In helicopter mode flight, the BA609 demonstrates acceptable vibrations at a frequency of three cycles per rotor revolution (3/rev = 28.5 Hz). As envelope expansion progresses into airplane mode, however, the aircraft experiences significantly higher vibrations (3/rev = 23.9 Hz). In particular, ride quality for the crew is unacceptable for continued envelope expansion and instrument panel vibrations reach limit thresholds. Interestingly, rotor indexing, where reorienting the phasing of blade passage of the side-by-side rotors creates opposing normal rotor shears, proves an effective (if only partial) solution for each of these issues. With the assistance of a proof-of-concept Frahm installation, the BA609 expands its flight envelope to maximum dive airspeed with acceptable cabin vibrations. When applied to a production fuselage finite-element model, reindexed rotors along with Frahm absorbers appear to provide smooth ride qualities to the BA609.