This paper focuses on the development of multibody numerical models to predict the dynamic response, aeroelastic stability, and blade loading of a soft-inplane tiltrotor wind-tunnel model. Comprehensive rotorcraft-based multibody analyses enable modeling of the rotor system to a high level of detail such that complex mechanics and nonlinear effects associated with control system geometry, and joint deadband may be considered. The influence of these and other nonlinear effects on the aeromechanical behavior of the tiltrotor model is examined. To assess the reliability of the multibody approach to rotorcraft analysis, the results obtained using two different rotorcraft-based multibody solvers are analyzed and compared. A parametric study of some design parameters that may influence the aeromechanics of the soft-inplane rotor system is also included in this investigation

The results of a joint NASA/Army/Bell Helicopter Textron wind-tunnel test to assess the potential of Generalized Predictive Control (GPC) for actively controlling the swashplate of tiltrotor aircraft to enhance aeroelastic stability in the airplane mode of flight are presented. GPC is an adaptive time-domain predictive control method that uses a linear difference equation to describe the input-output relationship of the system and to design the controller.The test was conducted in the Langley Transonic Dynamics Tunnel using an unpowered I/5-scale semispan aeroelastic model of the V-22 that was modified to incorporate a GPC-based multi-input multi-output control algorithm to individually control each of the three swashplate actuators. Wing responses were used for feedback. The GPC-based control system was highly effective in increasing the stability of the critical wing mode for all of the conditions tested, without measurable degradation of the damping in the other modes. The algorithm was also robust with respect to its performance in adjusting to rapid changes in both the rotor speed and the tunnel airspeed.

An investigation into the e ects of aerodynamic and aeroelastic scaling parameters on model scale helicopter rotors has been conducted in the NASA Langley Transonic Dynamics Tunnel. The e ect of varying Reynolds number, blade Lock n umber, and structural elasticity on rotor performance has been studied and the performance results are discussed herein for two di erent rotor blade sets at two rotor advance ratios. One set of rotor blades were rigid and the other set of blades were dynamically scaled to be representative of a main rotor design for a utility class helicopter. The investigation was conducted in forward ight at rotor advance ratios of 0.15 and 0.35. Additionally, the rotors were tested over a range of nominal test medium densities from 0.00382 slugs=ft 3 to 0.009 slugs=ft 3 . This range of densities permits the acquisition of data for several Reynolds and Lock n umber combinations. NomenclaturePositive directions for forces, moments, angles, and velocities are shown in Figure 1

The results from a study aimed at improving the aerodynamic characteristics of composite tiltrotor blades through the use of extension-twist elastic coupling are presented. A set of low-twist model-scale helicopter rotor blades was manufactured from existing molds, with a view towards demonstrating the passive blade twist control concept. Hover testing of the set of rotorblades was conducted with the primary goal of measuring the change in blade twist as a function of rotor speed. The blades were spun through the 0-800 rpm range, with a corresponding sweep of collective pitch at 100 rpm intervals to determine the effect on the blade elastic twist obtained.Data

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