A Generalized Algorithm for Inverse Simulation Applied to Helicopter Maneuvering Flight

Numerical characterization of helicopter noise hemispheres

“…In the second step, the time history of flight data associated to the prescribed trajectory are determined through application of an inverse simulation algorithm [21,22,23]. The inverse flight dynamics tool is implemented for a low order helicopter model.…”

“…Tail rotor is modeled using momentum theory, with a uniform inflow. Given the expected variation of airspeed, and climb, heading and sideslip angles as a function of time, this model allows to efficiently compute pilot control commands (namely, main rotor collective and cyclic pitch, and tail rotor collective pitch) necessary for tracking the prescribed flight path (a nominal problem is solved, with a number of specified variables equal to available controls [21]). Further, it yields additional flight data that characterize the unsteady flight, like helicopter attitude angles, main rotor disc orientation with respect to relative wind, and low-frequency main rotor loads transmitted to the fuselage, that are conveniently used for the next aeroacoustic analysis.…”

“…An inverse simulation (IS) algorithm allows the determination of the control law that realizes a prescribed trajectory for fixed-and rotary-wing aircraft [21]. A model predictive control (MPC) scheme [23] is used for solving the IS problem.…”

“…From this study, it will be possible to identify those flight parameters that need to be matched in order to assure, at a satisfactory level of accuracy, the (instantaneous) noiseemitted equivalence between a maneuver and a steady-state, rectilinear flight. In order to perform the proposed analysis, an unsteady approach maneuver is defined first, and an inverse flight dynamics simulation tool is then applied for determining the time-histories of corresponding pilot commands, hub loads and helicopter attitude variables [21,22,23]. Next, three different criteria are applied to correlate steady-state, rectilinear flights with the local specific unsteady flight conditions at the selected trajectory points.…”

Optimization-Based Inverse Simulation of a Helicopter Slalom Maneuver

“…The same basic technique has been used by Whalley [5], in an interesting study that included a validation of the inverse simulation results through a series of piloted simulation experiments. Hess et al [6,7] have proposed an alternate technique, in which the required trajectory is divided into small steps; for a given step, the controls at the beginning of the step are known, and the equations of motion are integrated with guesses of the controls at the end of the step. The errors between the actual and the desired trajectories are calculated, and the controls at the end of the step are adjusted using a Newton-Raphson technique to reduce the errors to zero.…”