Projects & Collaborations

ONERA/DCSD - Flight Dynamics and Control Department

In the current development process for auto land systems of civil airliners, high non-recurring costs are involved, because a time-consuming trial-and-error approach is used to design the control laws. This trial-and-error approach should guarantee that the closed-loop system is robust against the large number of parameter variations and model uncertainties that influence the design. Especially when control laws have to be redesigned in a late program stage, this kind of approach becomes very expensive, because for each iteration extensive tests must be performed to validate the controlled system. These tests consist of large batches of stochastic (Monte Carlo) simulations to verify compliance with the design requirements, statistical analysis tests to assess the robustness of the design, and ground-based simulations and flight tests to validate the design under realistic circumstances. Each update also affects the work carried out in related disciplines, such as system loads and structural dynamics analysis, which can cause substantial additional costs. For this reason, it is desirable to achieve a mature design in an early phase of the development program, when iterations are less expensive. This requires a new design procedure, based on advanced robust control techniques, in which model uncertainties and parameter variations are taken into account explicitly. The main goal of the REAL project is to develop this procedure, which is a major scientific and industrial challenge, because until now advanced robust control techniques have hardly ever been applied to solve practical autoland control problems.

Despite many significant advances in the theory of nonlinear control in recent years, the majority of control laws implemented in the European aerospace industry are still designed and analysed using predominantly linear techniques applied to linearised models of the aircraft dynamics. Given the continuous increase in the complexity of aircraft control laws, and the corresponding increase in the demands on their performance and reliability, industrial control law designers are highly motivated to explore the applicability of new and more powerful methods for design and analysis.

The overall objective of the Action Group was to explore new nonlinear design and analysis methods that have the potential to reduce the time and cost involved with control law development for new aerospace vehicles, while simultaneously increasing the performance, reliability and safety of the resulting controller. This objective was to be achieved by investigating the full potential of nonlinear design and analysis methods on demanding benchmarks developed within the project, in order to focus the research effort on the issues of most relevance to industry.

Before an aircraft can be tested in flight, it has to be proven to the authorities that the flight control system is safe and reliable, i.e. it has to go through a certification and qualification process. Currently significant time and money is spent by the aeronautical industry on this task. An important part of the certification and qualification process is the clearance of flight control laws (CFCL). The overall objective of this project is to develop and apply optimisation techniques to CFCL in order to improve efficiency and reliability of the certification and qualification process. The application of an optimisation-based approach relies on clearance criteria derived from the certification and qualification requirements. To evaluate these criteria different types of models of the aircraft are employed, which usually both serve for clearance as well as for control law design purposes. The development of different models and of suitable clearance criteria are therefore also objectives of the project. Bec ause of wider applicability optimisation-based CFCL will open up the possibility to design innovative aircraft that today are out of the application field of classical clearance tools. Optimisation-based CFCL will not only increase safety but it will also simplify the whole certification and qualification process, thus reduce costs. The speedup achieved by using the new optimisation-based approach will also support rapid modelling and prototyping and reduce "time to market". It is therefore believed that the project is addressing the two top-level objectives of the Work Program, i.e. ". To meet society's needs for a more efficient, safer and environmentally friendly air transport. ". To win global leadership for European aeronautics, with a competitive supply chain, including small and medium size enterprises. Specifically the project targets Research Area 1: "Strengthening Competitiveness" and its first objective.

SMAC (Systems Modeling, Analysis and Control) is a Matlab-Simulink based toolbox developed within the Systems Control and Flight Dynamics department of ONERA - The French Aerospace Lab, Toulouse, France.
The aim of this toolbox is to provide both researchers and control engineers with a complete set of tools to handle parameter-varying dynamical systems with uncertainties and hard nonlinearities such as magnitude and rate saturations. The key element of this toolbox is the Linear Fractional Representation (LFR). More specifically, the main features of the SMAC Toolbox are the following:

• Provide LFT modeling tools (a dedicated Matlab-Simulink compatible object)
• Provide LFT-based analysis tools (based on μ or IQC-based analysis)
• Provide LFT-oriented control design routines (robustified nonlinear dynamic inversion techniques, structured H∞ design, anti-windup compensation...)

This collection of tools, extending and unifying previous versions available from Jean-Marc Biannic's homepage will be accompanied by realistic aerospace benchmarks.