TABLE OF CONTENTS Modern helicopters often feature rotor designs with larger equivalent hinge offsets and/or reduced moments of inertia to increase the effective flap stiffness for improved maneuverability and agility. The fuselage and rotor responses become fully coupled, and the quasi-steady assumption used in the model structures of Chapter 13 is no longer suitable. The accurate characterization of these configurations requires an extended model structure that includes explicitly the regressive flapping, coupled inflow/coning, and regressive lead-lag states of the rotor.
The hybrid model structure for coupled fuselage/rotor dynamics identification was proposed initially by Tischler and Cauffman15 and is presented in its complete form in this chapter. The formulation is a general template for helicopter system identification, applicable to a wide range of design configurations and flight conditions. Flight-test identification results using this model structure are presented for the SH-2G helicopter (updated from Tischler and Tomashofski139). A series of models spanning the flight envelope was identified using a common model structure.
The key topics covered in this chapter include the following: background and literature on the identification of extended helicopter models, hybrid model structure for coupled rotor/fuselage identification, hybrid model identification of SH-2G helicopter dynamics, and lead-lag dynamics identification of S-92 helicopter.
The rotorcraft identification results of Chapters 13 and 14 were based on quasi-steady model structures, which characterize the aircraft forces and moments solely in terms of the fuselage states. For flight vehicles with symmetric configurations, such as fixed-wing, tilt-rotor, and...
