Blade Design Parameters Which Affect Helicopter Vibrations

Designing the main rotor blades for minimum airframe vibration has been impeded by lack of understanding of vibration producing mechanisms. The experiences gained during two flight test programs namely Higher Harmonic Controls (HHC) and Composite Main Rotor Blade (CMRB) are described in this paper. These investigations provide insight into the role of aerodynamics in producing vibrations. Testing of CMRB on the Army's Advanced Attack Helicopter produced an airframe vibration problem which prompted a flight test program described herein. The vibration problem was subsequently solved by modifying the flight set of blades. The HHC produced major reductions in airframe vibration.