Gust Load Alleviation on a Large Transport Airplane

Abstract

This study develops an active control technology to reduce the incremental dynamic loads of a large four-engine transport airplane flying through a gust field. The mathematical model of the proposed gust-alleviation system features composite structural motions (for example, rigid-body motions, elastic vibrations, and deflections of control surfaces) and unsteady aerodynamic forces induced by the structural motions and the gusts. A clear outline of the procedure is first provided to determine the aeroservoelastic equation of the system. Then, an adaptive feedforward controller that uses the preview information of the gust sensed by an onboard alpha probe is designed to operate the ailerons symmetrically to alleviate the wing-root bending moment induced by the gust. The rigid-body motions due to travelling gusts are also compensated for using symmetrical deflections of the elevators. To solve the problems of weight drift and weight bias that are commonly encountered in adaptive control, the circular leaky least meansquared algorithm is applied to update the weights of the adaptive controller. The simulation results show that a large transport airplane equipped with the proposed gust-alleviation system experiences a significantly lower wing-root bending moment in both stationary and nonstationary gusty environments.

Prediction of Preliminary Maximum Wing Bending Moments Under Discrete Gust

“…These preliminary parameters are: the aircraft mass, the zero fuel aircraft mass, the quantity of fuel, the true air speed, the Mach number, the altitude, the load factors (NX, NY, NZ), the coordinates of the center of gravity (CGx, CGy, CGz) and the moments of inertia (Ixx, Ixy, Ixz, Iyy, Iyz, Izz), the wavelength (H) of the discrete gust and the flight profile alleviation factor F g . Note that the the time history of the discrete gust has the following form [7,25]…”

Adaptive Feedforward Control for Gust-Induced Aeroelastic Vibrations

“…This decision was made based on the experimental observation that the dynamics of the actuator was fast enough, compared to the characteristic times of the aeroelastic plant, to be neglected [22]. Their inclusion is straightforward [25] and their effect would appear within the transfer function . As this is rarely the case in practice, the transfer functions of the plant are approximated using system identification (SI) methods.…”

A Modified NSGA-II for Solving Control Allocation Optimization Problem in Lateral Flight Control System for Large Aircraft

“…Large transport aircraft are inevitably affected by various turbulence events during the long distance flight. The lateral Flight Control System (FCS) is required to alleviate the adverse effects from these events as much as possible [1], [2]. The lateral FCS consists mainly of two parts: the aileron based roll control channel and the rudder based yaw control channel.…”

“…Since there exists tight aerodynamic couplings between these two channels, study of the control allocation relationship between the two control surfaces, aileron and rudder, is necessary in the lateral FCS design process. Moreover, depending on mission needs and requirements, the aircraft flying qualities are classified into three levels (1)(2)(3). A lateral FCS can only perform well if it can satisfy the corresponding flying quality requirements.…”