Flight dynamics simulation modeling for hingeless and bearingless rotor helicopters

A mathematical model is described for an articulated, hingeless or bearingless rotor helicopter that is suitable for flight dynamics analysis. The mathematical model is formulated to provide a non-linear state-space representation of the helicopter dynamics. The model may be configured to incorporate either a blade element level unsteady aerodynamics analysis, based on a state-space representation of unsteady aerodynamics, or a finite state wake dynamic inflow model. The main rotor model is based on a finite element analysis allowing moderately large elastic deflections for coupled blade flap, lag, torsion and axial deformations. The formulation of the coupled rotor and fuselage equations enables the use of common solution techniques for trim and linearization in arbitrary steady climbing or descending turning flight, as well as free flight response calculations. An innovative trim algorithm is presented which reduces the otherwise prohibitive computational requirements associated with the large increase in total number of states when the state-space unsteady aerodynamics model is included.;The mathematical model for an articulated configuration is validated by comparing model responses against flight test data measured on an articulated rotor aircraft. Comparisons are made for three aerodynamic model configurations. These are quasi-steady airfoil aerodynamics in conjunction with a three state dynamic inflow model, quasi-steady airfoil aerodynamics in conjunction with a 21 state finite state wake model and unsteady airfoil aerodynamics in conjunction with a three state dynamic inflow model. Trim control positions, frequency response and free flight time history response results have been generated in each case. Results are presented for hover and steady level forward flight at 80 kts and 120 kts.;For the bearingless main rotor configuration a comparison is made against results generated by an aeroelastic rotor code. A comparison of frequency response results for a range of retained main rotor mode shapes is made for hover flight condition as well as steady level forward flight at advance ratios of 0.15 and 0.30. An analysis of frequency response for this configuration in turning flight is made together with a comparison of frequency response behaviour for varying flexbeam stiffness.