Reinhard Reichel

Enabling FlexRay for avionic data buses

The aeronautic industry and its suppliers show increasing interest in utilizing the automotive FlexRay protocol for their applications, more than ever since an opening of the standard for all industries and field of applications becomes apparent. With its combination of deterministic and flexible c o m m u n ication and data rates up to 10 Mbit/s on a single twisted wire pair, FlexRay is a promising candidate for future system developments and the modernization of CAN based systems. Currently, the performance of the protocol is rather unknown i n a n aeronautic environment, in particular with respect to its physical layer. This paper analyzes the signal decoding process of FlexRay and derives dedicated signal integrity criteria for the protocol. An efficient method based on the transmission and evaluation of worst-case bit patterns is developed for the assessment of signal integrity on demanding topologies with significant attenuation and resulting inter-symbol interferences. RS485 is discussed as a possible alternative physical layer for the FlexRay protocol to improve the communication performance. Finally, a use-case topology with a harness length of 90 m is presented to evaluate the achievable performance when utilizing the FlexRay protocol. Signal integrity is demonstrated and validated on the topology at a data rate of 10 Mbit/s to prove the suitability of FlexRay for aeronautic applications.

Flexible platform approach for fly-by-wire systems

The development of highly fault tolerant fly-by-wire systems for FAR25/CS25 aircraft is an extensive and inherently complex task. This paper presents the Flexible Platform approach which aims on reducing the development effort of fly-by-wire systems and hence allowing more cost-effective realizations - with a potential even for FAR23/CS23 aircraft. The main features of the Flexible Platform approach are: 1) The software architecture provides a clear separation of system management (i.e. platform management) and applications (e.g. flight control laws). 2) With respect to the applications, the platform management provides transparency of distribution, redundancy and fault tolerance for the complete system, i.e. including sensors and actuators 3) The platform management is composed of a generic middleware and model-based upper management layers, both offering a high degree of specialization capability. As a consequence, the management functionality of any fly-by-wire system can be developed essentially by specialization of the platform management. 4) With respect to quantity and complexity, specialization of the platform management is a challenging task and requires tool-based support. Based on manually defined input data at system level (i.e. without explicit reference to the software), a tool-suite uses modeled system- and software-domain knowledge to generate the major part of the specialization data in an automatic three step refinement process. The paper presents the Flexible Platform in general, but with emphasis on the specialization topic and the specialization tool-suite.

An adaptive middleware approach for fault-tolerant avionic systems

The distributed nature of avionic systems is hidden by the system architecture, containing a middleware which abstracts the communication and the system management. To introduce scalability and modifiability in future fault-tolerant avionic systems, adaptive mechanisms have to replace the still common manual configuration and parameterization of the middleware. This requires a fundamentally new middleware approach, which is presented in this paper. Adaptivity refers to the autonomous adaption during the initial middleware configuration and has to take domain specific requirements into account, e.g. deterministic communication paths. This is why known concepts from congeneric domains cannot be transferred directly, e.g. PnP from computer science. The publish/subscribe communication paradigm (pub/sub paradigm), with its inherent loose-coupling property serves the ability to interconnect an arbitrary unconfigured system autonomously. The concept of the pub/sub paradigm is applied to the adaptive communication middleware. Alongside the conceptual consideration, the concept is validated on a laboratory demonstrator. The results are promising and the adaptive middleware approach aims to push future avionic systems further towards adaptivity. Further validations should iteratively close the gap towards authorized avionics hardware and for aerospace certified protocols.

Approaching the Limits of FlexRay

The aeronautic industry is strongly interested in utilizing the automotive FlexRay protocol. Economic benefits to be derived from the automotive mass market, and technological benefits arising from to the deterministic communication behavior are projected. The physical layer of the protocol is customized to suit automotive applications. The topology of aeronautic systems is more critical in terms of greater cable lengths and protection circuits. This paper therefore analyzes the suitability of topology implementations exceeding the recommendations defined in the FlexRay specification. This paper derives worst case signal integrity criteria for FlexRay and applies them to an exemplary aeronautic topology with six nodes and an overall length of 90 m. The paper highlights the fact that reliable communication is conditionally possible on the topology at data rates up to 5 Mbit/s.

Automated generation of certification relevant documentation for a distributed avionics platform approach

The development of distributed and fault tolerant avionics systems from the first drafts to the finalization of the certification process is complex, resource intensive (financial and man power) and involves high risks. Therefore, implementations like fly-by-wire systems are usually limited to the FAR25 (CS25) domain. Previous research at the Institute of Aircraft Systems at University of Stuttgart was focused on the development of an avionics platform and a tool suite for a cost-efficient development process for class 23 and class 25 aircraft. Now, the aim is to extend the platform idea towards certification. In doing so, the generation of the specification documentation and testing activities shall be automated while avoiding tool qualification where feasible. This paper presents an approach for the documentation generation and provides an outline to interface with the testing activities.

Automatic safety computation for IMA systems

During the last years, the integrated modular avionics (IMA) design philosophy became widely established at aircraft manufacturers, giving rise to a series of new design challenges, most notably the allocation of avionics functions to the various IMA components and the placement of this equipment in the aircraft. This paper presents a modelling approach for avionics that allows for automatic computation of the safety of large and heavily interdependent systems, and shall help to quickly evaluate candidate system configurations during early and intermediate design. It is part of a project striving to automatise some steps of the design process by applying an optimisation algorithm which searches for system configurations that fulfil the safety requirements and have low costs.

A utility aircraft for remote sensing missions with a high-precision automatic flight control system

Light civil utility aircraft are well suited for remote sensing missions and to serve as an airborne platform for efficient reconnaissance, surveillance, exploration, and measurement tasks in a growing market. Missions where the pilot has to operate a payload require an automatic flight control system (AFCS) to support the pilot. In missions that are extremely difficult, long or dangerous, the AFCS may even replace the pilot. Such an AFCS has to follow precisely predefined trajectories and should compensate disturbances due to atmospheric turbulence. For un-manned aircraft operations it has to have full authority, it has to be highly reliable, and it must be able to take off and land automatically. The development and certification of such an AFCS at competitive cost is a major challenge. This paper gives an overview on the STEMME S15 utility aircraft, for which an AFCS has been developed. It describes the design objectives, the selected flight control architecture, the system, and the flight test equipment as well as flight test results that demonstrate the high precision of flight path control.

X-by-Wire Plattform — Konzept und Auslegung

Zusammenfassung Dargestellt wird eine X-by-Wire Plattform zur gesamtheitlichen Umsetzung des Global Chassis-Control. Die Plattform basiert auf FlexRay-Technologie. Sie vermag eine Vielzahl aktiver Fahrerassistenzfunktionen unterschiedlicher Sicherheitsintegrität auszuführen — ohne mechanische Rückfallebene. Die X-by-Wire Plattform wurde im Rahmen des Forschungsprojektes SPARC entwickelt, als Prototyp in drei Fahrzeuge integriert und auf einer Teststrecke getestet. Einen Weg zu zeigen, wie eine komplexe Plattform unter Berücksichtigung der Sicherheitsintegrität ausgelegt werden kann, ist Kern dieses Beitrags. Abstract Content of this paper is a x-by-wire platform for a comprehensive implementation of Global Chassis-Control. The platform is based on FlexRay technology. It allows the implementation of multiple active driver-assistance-systems function of different Safety Integrity Levels — without any mechanical backup. The x-by-wire platform was developed within the EU research project SPARC, implemented onto three vehicles and tested on a test track. Focus of this paper is to show how to design systematically a complex safety critical x-by-wire platform in compliance with given Safety Integrity Levels.

Automated test artifact generation for a distributed avionics platform utilizing abstract state machines

The development of complex and highly safety-critical avionics systems, such as fly-by-wire, is typicaUy linked with high efforts, risks and thus costs. Especially with regard to certification the testing activities during verification are playing a major role. This paper introduces the automatization complex of the testing artifact generation by use of Abstract State Machines (ASM), which allows a unified approach for system and software testing. The baseline is the Flexible Platform technology (a platform based development approach) currently under development by the Institute of Aircraft Systems (ILS) of the University of Stuttgart. The remaining automatization complex is the automated generation of certification relevant documentation, i.e. the requirements. These three complexes establish the AAA-Process which lays the foundation for an effective total system capability for complex avionics systems while simultaneously mitigating risks and costs. The actual test artifact generation is strictly aligned to development standards used in the aviation industry. Requirements exist as classes in a textual representation as well as in a specification model, represented by ASMs. The functional behavior, as described by the models, serves as a test oracle for test case generation. For this the model is translated into a graph system, instrumented by selectable testing methods and executed. The resulting trace data is used to automatically derive test procedures under consideration of the corresponding test environment as scripts, which are directly executable within our testing infrastructure consisting of a HiL simulation. Furthermore this includes the automatic generation of the associated traceability data and test specification documentation. An initial framework has been defined to support exchangeabiUty of individual tasks in the generation toolchain. The feasibility of the approach has been demonstrated by testing the complete heterogeneous signal communication of an exemplary avionics system, resp. platform instance, at system level as well as at software high-level.

Autonomous peripherals integration for an adaptive avionics platform

Integrated avionics platforms (IMA) provide cost and weight savings compared to federated systems. Drawback of the integrated architecture is an increased configuration demand. Current systems face this demand with individually created and distributed configuration files, causing an enormous configuration effort. This effort should be significantly reduced by introducing adaptivity. Adaptivity refers to the autonomous adaption of the platform resources and autonomous integration of systems, including peripheral devices. The proposed adaptive avionics platform approach comprises an open software architecture and autonomous mechanisms for discovering and adapting the generic platform components. It provides computing, communication and i/o resources for integrating avionic systems, including peripheral devices. Whereby the platforms complexity is transparent for integrated system functions. Peripheral devices that comply to a specific PnP-protocol are integrated fully autonomously. Peripheral devices that do not comply to the PnP-protocol are considered using an adaption tool. This requires minimal human interaction but obviates individual configuration files. The substitution of manually prepared configuration files by an autonomous adaption mechanism reduces the configuration effort significantly. The feasibility of the adaptive avionics platform approach is demonstrated with a laboratory validation system.