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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

ABSTRACThelicopters because of the limitations imposed by aerodynamic physics, there is hope that tiltrotor topend and The requirements for increased speed and productiv-cruise speeds may increase further with improved engiity for tiltrotors has spawned several investigations asso-i n current limitations on speed for the V-22 tiltrociated with proprotor aeroelastic stability augmentation tor are associated with control loads, control margins, and and aerodynamic performance enhancements. Included power, while the tiltrotor is power limited. The among these investigations is a focus on passive aeroe-aeroelastic stability of tiltrotor systems is also an imporlastic tailoring concepts which exploit the anisotropic ca-tant concern, as the stability margins associated with curpabilities of fiber composite materials. Researchers at rent tiltrotors are not far beyond the speed limitations set Langley Research Center and Helicopte~ have de-by loads and power today. It is anticipated that the u p voted considerable effort to assess the potential for using per velocity limit for future high-speed tiltrotors may be these materials to obtain aeroelastic responses which are set by both loads and aeroelastic stability considerations. beneficial to the important stability and performance con-To achieve higher speeds for tiltrotors, structural tailoring siderations of tiltrotors. Both experimental and analyt-of blades and wings using advanced composite ical studies have been completed to examine aeroelastic has been considered in several past investigations. tailoring concepts for the tiltrotor, applied either to the wing or to the rotor blades. This paper reviews some of the results obtained in these aeroelastic tailoring investigations and discusses the relative merits associated with Researchers at Lagley Research Center and Bell Helithese approaches.copter have devoted considerable effort to assess the potential for using composite materials to obtain aeroelastic responses which are beneficial to the important stability INTRODUCTION and performance considerations of tiltrotors. Both experimental and analytical studies have been completed qytrotor aircraft have advantages over conventional he-which examine aeroelastic tailoring concepts for the tiltrolicopters with respect to speed and range. While a heli-tor, applied either to the wing or to the rotor blades. copter is limited at high speeds by compressibility This paper reviews some of the results obtained in these on the rotor advancing side and stall on the rotor retreat-aer0elaStic tailoring investigations and discusses the reling side, a tiltrotor converts from a helicopter mode to ative merits associated with these approaches. While an airplane mode for high speed flight is less re-the material presented in this report focuses on activi-

A new forced oscillation system has been installed and tested at NASA Langley Research Center's Transonic Dynamics Tunnel. The system is known as the Oscillating Turntable (OTT) and has been designed for the purpose of oscillating, large semispan models in pitch at frequencies up to 40 Hz to acquire high-quality unsteady pressure and loads data. Precisely controlled motions of a wind-tunnel model on the OTT can yield unsteady aerodynamic phenomena associated with utter, limit-cycle oscillations, shock dynamics, and nonlinear aerodynamic effects on many vehicle con gurations. This paper will discuss the general design and components of the OTT and will present data from performance testing and from research tests on two rigid semispan wind-tunnel models. The research tests were designed to challenge the OTT over a wide range of operating conditions while acquiring unsteady pressure data on a small rectangular supercritical wing and a large supersonic transport wing. These results will be presented to illustrate the performance capabilities, consistency of oscillations, and usefulness of the OTT as a research tool. NomenclatureC p =deg = pressure coef cient normalized by oscillation amplitude .C p / Im =deg = imaginary component of pressure coef cient normalized by oscillation amplitude .C p / mean = mean pressure coef cient .C p / Re =deg = real component of pressure coef cient normalized by oscillation amplitude f = frequency, Hz k = reduced frequency M = Mach number Q = dynamic pressure, psf Re = Reynolds number x=c = nondimensional chordwise location N ® = mean angle of attack, deg j®j = angular amplitude, deg 1 P = hydraulic pressure amplitude, psi

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.