Helicopter Vibration Suppression Using Simple Pendulum Absorbers on the Rotor Blade

A design analysis for the installation of simple pendulums on the blades of a helicopter rotor to suppress the root reactions is presented. This analysis consists of a frequency response study for a hingeless rotor blade excited by a harmonic variation of spanwise airload distribution, during forward flight, as well as a concentrated load at the tip. A single blade with hingeless hub restraint undergoing coupled flapwise bending, chordwise bending, and torsional vibrations is considered with both uniform and nonuniform properties. Simple flap and lead‐lag pendulums are treated individually. On the basis of a rational ordering scheme the general nonlinear equations of motion are linearized. A quasi‐steady aerodynamic representation is utilized in the formation of the airloads. The solution of the system equations is based on their representation as a transfer matrix. The results include the effect of pendulum tuning on the minimization of hub reactions. The pendulum mass effectiveness is also investigated. The results for the concentrated load and the distributed air loads are compared.