H infinity control design for generalized second order systems based on acceleration sensitivity function

This article presents an Hinfinty control design method based on the Acceleration Sensitivity (AS) function. This approach can be applied to any fully actuated generalized second order system. In this framework, classical modal specifications(pulsations / damping ratios) are expressed in terms of Hinfinty templates allowing other frequency domain specifications to betaken into account. Finally, a comparison between AS with a more classical Hinfinty approach and with the Cross Standard Form(CSF) is presented. A 2 degrees of freedom spring-damper-mass academic example is used to illustrate the properties of the AS,though this method was developed and is used for atmospheric reentry control design

Lidar-based Gust Load Alleviation - Results Obtained on a Generic Long Range Aircraft Configuration

In this paper a lidar-based preview gust load alleviation controller is synthesised via modern robust control methods in discrete time and optimised for an industrial long-range aircraft configuration. The synthesis and load analysis is performed using a set of 54 linear-time-invariant state-space models corresponding to a wide range of mass distributions and flight conditions. The controller performance is tested in a realistic hybrid and multi-rate simulation environment in which, in addition to the aeroelastic aircraft model (continuous time) and the various control functions in discrete time, the lidar measurement chain (sensor, wind estimation) as well as speed and position-limited actuators are simulated. The load alleviation performance is evaluated for a wide range of mass distributions, altitudes, airspeeds and gust lengths, leading to results based on over 4000 analysed gust load cases. The paper concludes with a discussion of the impact of the GLA control function on the structural loads, the load hierarchy and the general aircraft behaviour. The gust load alleviation controller achieves a reduction in peak bending moment between 17 % and 18 % at the important wing root, about 20 % in the middle of the wing and still over 10 % near the wing tip. It barely reaches the rate and position limits even on the extreme gusts defined in the certification specifications for large aeroplanes and only moderate increases of peak gust loads are observed on other load types or stations. Directly outside of the engine position a few percent increase in torsional moment is found. The controller yields an increase of about 50 % of the HTP gust loads, which is not critical as the HTP is usually, by far, not sized by gust loads but rather by manoeuvre loads. If needed, this figure could drastically be reduced by reducing the aggressiveness of the pitching behaviour and tolerating slight higher loads on the wing

A multi-channel H-infinity preview control approach to load alleviation design for flexible aircraft

Gust load alleviation functions are mainly designed for two objectives: first, alleviating the structural loads resulting from turbulence or gust encounter, and hence reducing the structural fatigue and/or weight; and second, enhancing the ride qualities, and hence the passengers' comfort. Whilst load alleviation functions can improve both aspects, the designer will still need to make design trade-offs between these two objectives and also between various types and locations of the structural loads. The possible emergence of affordable and reliable remote wind sensor techniques (e.g., Doppler LIDAR) in the future leads to considering new types of load alleviation functions as these sensors would permit anticipating the near future gusts and other types of turbulence. In this paper, we propose a preview control design methodology for the design of a load alleviation function with such anticipation capabilities, based on recent advancements on discrete-time reduced-order multi-channel H-infinity techniques. The methodology is illustrated on the DLR Discus-2c flexible sailplane model

Method for designing multi-input system identification signals using a compact time-frequency representation

A flight test campaign for system identification is a costly and time-consuming task. Models derived from wind tunnel experiments and CFD calculations must be validated and/or updated with flight data to match the real aircraft stability and control characteristics. Classical maneuvers for system identification are mostly one-surface-at-a-time inputs and need to be performed several times at each flight condition. Various methods for defining very rich multi-axis maneuvers, for instance based on multisine/sum of sines signals, already exist. A new design method based on the wavelet transform allowing the definition of multi-axis inputs in the time-frequency domain has been developed. The compact representation chosen allows the user to define fairly complex maneuvers with very few parameters. This method is demonstrated using simulated flight test data from a high-quality Airbus A320 dynamic model. System identification is then performed with this data, and the results show that aerodynamic parameters can still be accurately estimated from these fairly simple multi-axis maneuvers

COAST - A Simulation and Control Framework to Support Multidisciplinary Optimization and Aircraft Design with CPACS

This paper describes COAST (CPACS-oriented aircraft simulation tool), a fixed-wing aircraft simulation framework tailored to an XML-based open source common exchange format for multidisciplinary aircraft design, called CPACS (Common Parametric Aircraft Configuration Schema). COAST enables designers to utilize flight simulation on desktop computers or even on full motion simulators in early stages of aircraft design, which facilitates the assessment of flight characteristics and handling qualities as well as early flight control design. The core model of COAST is presented along with its interface to the data exchange format CPACS, which is implemented via import functions based on XML parsers. Due to the necessity of generically working autopilot functionalities, a nonlinear flight control concept based on the idea of the nonlinear model following control (NMFC) methodology is proposed. In order to handle novel aircraft configurations with a redundant set of control effectors, an optimization-based control allocation module is integrated. The process of integrating the model into the German Aerospace Center's full motion flight simulator AVES (Air Vehicle Simulator) in Braunschweig is discussed

Parameter Analysis of a Doppler Lidar Sensor For Gust Detection and Load Alleviation

This paper analyzes the performance of Doppler lidar sensors for gust detection and load alleviation purposes w.r.t. selected parameters of the lidar system and the wind reconstruction algorithm. The presented sensitivity studies are the first part of a larger investigation focused on identifying ideal lidar sensor configurations for gust load alleviation. This first study consists of two parts: in the first part, the effect of the measurement geometry is investigated by varying the scan angle, the number of measurements per laser pulse, and the rotational speed of the sensor's line of sight. In the second part, the effect of wind reconstruction parameters is investigated by varying the power aperture product of the lidar and the smoothing parameters of the wind reconstruction process

An Aeroelastic Flight Dynamics Model for Gust Load Alleviation of Energy-Efficient Passenger Airplanes

Gust load alleviation (GLA) can reduce the maximum loads encountered by airplanes, allowing the structure to be designed lighter, thus saving fuel. Active GLA therefore represents an important subarea in the research of energy-efficient passenger airplanes. However, from a flight dynamics perspective, there are no publicly available simulation environments that allow for an efficient and modular investigation of different technologies like novel GLA controllers or novel flow actuators. Therefore, this paper presents such a simulation environment. The presented aeroelastic flight dynamics model is based on indicial functions combined with a dynamic stall model to predict the unsteady aerodynamics similar to a strip theory approach, while the downwash is considered using a nonlinear steady lifting line method. The structural dynamics are based on the mode displacement method and coupled with the aerodynamics model using constant transformation matrices as well as nonlinear transformations for the inflow. A comparison of the presented model with unsteady Reynolds-Averaged Navier--Stokes simulations shows good agreement for a selected gust case. The presented simulation model is parameterized as an energy-efficient passenger airplane with a light-weight wing sizing by reducing the limit loads from 2.5\,g to 2.0\,g for equivalent pull-up maneuvers. Open-loop gust load envelopes are presented and discussed for the energy-efficient airplane with different model settings, e.g. with and without dynamic stall model. The source code of the simulation modules is available at: https://github.com/iff-gsc/se2a_aviation_2023. A video of the flight simulation is available at: https://youtu.be/cO5q06Qkkg