Marco Molica Colella

Prediction of Tiltrotor Vibratory Loads with Inclusion of Wing­-Proprotor Aerodynamic Interaction

A numerical methodology for the prediction of vibratory loads arising in wing―proprotor systems is presented. It is applicable to tiltrotor operating conditions ranging from airplane to helicopter-mode flights. The aeroelastic formulation applied takes into account the aerodynamic interaction effects dominated by the impact between proprotor wake and wing, along with the mutual mechanical influence between elastic wing and proprotor blades. A boundary integral formulation suited for configurations where strong body―vortex interactions occur yields the aerodynamic loads, and beamlike models are used to describe the structural dynamics. A harmonic balance approach is applied to determine the aeroelastic solution. In the numerical investigation, first, the aerodynamic solver is validated by correlation with experimental and numerical results available in the literature, then the vibratory loads transmitted by the wing―proprotor system to the airframe are predicted, focusing the attention on the analysis of the different aerodynamic contributions.

Tiltrotor Wing-Root Vibratory Loads Reduction Through Higher Harmonic Control Actuation

This paper deals with the application of a via-swashplate higher harmonic control for the reduction of vibratory loads transmitted to tiltrotor fuselage by the proprotor-pyion-wing system. The control laws are derived through a quadratic optimal control methodology, based on the predictions given by an aeroelastic simulation tool developed in the past by the authors. It uses nonlinear beam theory to model the structural behavior ofproprotor blades and wing, and a potential aerodynamics boundary-element approach suitable to capture body-vortex interactions effects to evaluate wake inflow. Considering a XV-15-like configuration in airplane-and helicopter-mode flight, the numerical investigation examines different strategies in the identification of the optimal control law, analyzing their effectiveness and robustness in reducing the wing-root vibratory loads.

Helicopter Vibratory Loads Alleviation through Combined Action of Trailing-Edge Flap and Variable-Stiffness Devices

The aim of this paper is the assessment of the capability of controllers based on the combined actuation of flaps and variable-stiffness devices to alleviate helicopter main rotor vibratory hub loads. Trailing-edge flaps are positioned at the rotor blade tip region, whereas variable-stiffness devices are located at the pitch link and at the blade root. Control laws are derived by an optimal control procedure based on the best trade-off between control effectiveness and control effort, under the constraint of satisfaction of the equations governing rotor blade aeroelastic response. The numerical investigation concerns the analysis of performance and robustness of the control techniques developed, through application to a four-bladed helicopter rotor in level flight. The identification of the most efficient control configuration is also attempted.

A Comprehensive Approach for the Optimal Control of Tiltrotor Cabin Noise Through Actively-Driven Piezoelectric Actuators

This paper deals with the abatement of the tonal noise generated by the propulsive system inside the fuselage of a mid-range tiltrotor aircraft. The problem is basically multidisciplinary, involving interactions among exterior noise field, elastic fuselage dynamics, interior acoustics and control system. A stiffened fuselage, with piezoelectric patches embedded into the structure, is supposed to be impinged by the aeroacoustic field generated by propellers and forced by the wing/pylon/proprotor vibratory loads at the wing-fuselage attachment. An optimal LQR cyclic control formulation, coupled with a genetic optimization algorithm (GA), is applied to synthesize the control law driving the smart actuators so as to alleviate cabin noise. The aeroacoustoelastic model considered in the control problem is obtained by combining a modal approach for the description of the acoustic field within the cabin, the elastic displacements of the smart shell and the wing/pylon/proprotor system, with a Boundary Element Method (BEM) for the prediction of exterior pressure disturbances. Numerical results examine the effectiveness and robustness of the proposed active control strategy when synthesized through the proposed LQR/GA algorithms.

A Spectral Formulation for Structural/Aeroelastic Modeling of Curved-Axis Rotor Blades

The aim of this work is the development of a numerical solver for structural and aeroelastic analysis of rotor blades with advanced geometry, like those with tip sweep and anhedral angles. The mathematical formulation presented is based on a beam-like model assumption, suited for numerical integration via modal approach. It is valid for slender, homogeneous, isotropic, twisted blades with curved elastic axis, although the extension to composite material blades is straightforward. For aeroelastic applications, the distributed loads include the presence of the aerodynamic loads predicted by a simple quasi-steady, sectional theory, but more accurate, complex aerodynamic formulations could be coupled with the structural dynamics model outlined. After application of a second order approximation scheme, the final nonlinear equations of motion are able to predict the dynamics of blades subject to moderate displacements. The model is conceived as a sequence of relations that yield the loads to be included directly in the equilibrium equations of sectional moments and allows both response and stability analyses. Comparisons with results from FEM analyses will be shown for validation, along with a parametric analysis on blade tip sweep and anhedral angles influence on aeroelastic stability.