"AeroStruct" is a joint project of DLR, industry (Airbus, CASSIDIA, Rolls-Royce Deutschland) and universities (TU Berlin, TU Braunschweig, Uni Trier, Uni München and HAW Hamburg). A major goal of the project is the development of a multidisciplinary simulation environment for the analysis and optimization of aircraft based on higher-order methods.
The control of modern commercial aircraft is largely influenced by the flight control system and the flight control functions it contains. On Airbus aircraft, the pilot commands aircraft movement parameters (load multiplier and roll rate specification) via the side-stick. The required rudder deflections are generated by the flight controller and automatically adjusted to the flight condition to provide consistent flight behavior for the pilot over the entire flight envelope. Today's flight controllers include a large number of functions that actively improve flight characteristics (e.g., damper functions) on the one hand and ensure safe flight operation (e.g., flight range limit control) on the other. Additional load alleviation systems allow atmospheric disturbances to be corrected, or they reduce the structural load during highly dynamic maneuvers by means of additional control deflections (e.g. Manoeuvre Load Alleviation on A340). The control surface deflections of modern commercial aircraft are thus influenced by a large number of different controller functions, which often exhibit non-linear behavior. As part of the "AeroStruct" project, the German Aerospace Center is developing a multidisciplinary analysis and optimization platform based on high-quality simulation methods for the integrated preliminary and detailed design of future aircraft generations. This includes, among other things, the investigation of aeroelastic phenomena and the calculation of structural loads using CFD methods. A modern configuration with a forward swept wing (ForSWing) serves as one application example. At the current stage, the simulation models used include only the passive wing. The influence of flight controls on the control surface deflections, and thus on the load distribution over the wing during maneuvers or gust disturbances, is not considered. However, it is crucial to generate realistic simulation results.
In this project, the Department of Flight Mechanics, Flight Control and Aeroelasticity is developing generic flight controller modules in order to extend the multidisciplinary simulation tools for load analysis being developed in the network to include the area of flight control. The controller modules are based on control concepts of modern commercial aircrafts. Only those controller functions are considered which are relevant for dynamic simulations of aeroelastic and structural dynamic problems (e.g. 3DoF position controller, damper functions). It is planned to integrate simple controller functions for load reduction to enable a comparison to the "basic control" within higher-order CFD simulation models. For example, influences of dead times in the control loop can also be investigated under consideration of unsteady aerodynamics. Another goal of the project is to introduce load-relevant scenarios and maneuvers into the analysis process with CFD simulations of the partners. This can be done, for example, with data from simulator tests, which provide realistic courses of rudder deflections.
|AP1||Specification and model analysis||The subject area provides contributions to the definition of the reference case from the point of view of flight mechanics and flight control. For this purpose, a first qualitative analysis of the flight dynamic characteristics and the handling qualities of the reference aircraft without flight controller is performed. Subsequently, the department, in cooperation with DLR, will specify the desired design goals from a flight control point of view.|
|AP2||Controller design||In consideration of the requirements, the general controller structure as well as the individual controller functions for longitudinal and lateral motion are developed. This also includes the modeling of sensor components for the feedback of control variables (e.g. rotation rates p, q, r or load multipliers). A design procedure is set up for the controller parameters, which can be integrated into the multidisciplinary design process. It allows an iterative optimization of the controller parameters to react to changes in the design.|
|AP3||Multidisciplinary optimization process||The integration of the controller modules into the high-quality CFD simulations is carried out by DLR. The department provides supporting work for the integration of the flight controller modules and the parameter design process into the multidisciplinary optimization process.|
|AP4||Verification of the flight controller modules||The functionality of the developed controller modules is verified based on the models of the reference aircraft provided by DLR. For this purpose, test maneuvers are specified which are repeated in the same way in the high-quality CFD simulations. The department uses simulation results provided by DLR to verify the functionality of the controller modules.|
Deutsches Zentrum für Luft- und Raumfahrt, Institut für Aeroelastik