On the Modeling of Hydraulic Components in Rotorcraft Systems

A physics based methodology for modeling of hydraulic devices within multibody-based comprehensive models of rotorcraft systems is developed. The proposed models are developed in two stages. At first, models are developed for three basic hydraulic elements: the hydraulic chamber, the hydraulic orifice and the pressure relief valve. These models consist of nonlinear differential equations involving empirical parameters. Next, these basic elements are combined to yield device models for linear hydraulic actuators, simple hydraulic dampers, and hydraulic dampers with pressure relief valves. The proposed hydraulic device models are implemented in a multibody code and calibrated by comparing their predictions with test bench measurements for the UH-60 helicopter lead-lag damper. While predicted peak damping forces are found to be in good agreement with measurements, the model does not predict the entire time history of damper force to the same level of accuracy. The validated model of the UH-60 lead-lag damper model is coupled with a comprehensive model of the vehicle. Measured aerodynamic loads are applied to the blade and predicted damper forces are compared with experimental measurements. A marked improvement in the prediction is observed when using the proposed model rather than a linear approximation of the damper behavior.