The Software Development Enviroment of the DLR Research Rotorcraft ACT/FHS

Abstract

To support its applied research on rotorcraft technologies, the German Aerospace Center (DLR) operates the flying testbed ACT/FHS (Active Control Technology/Flying Helicopter Simulator). The ACT/FHS is based on a Eurocopter EC 135, which was heavily modified to suit the needs to efficiently conduct a wide variety of in-flight experiments. This includes a hierarchical fly-by-wire/fly-by-light flight control system and an experimental system, consisting of several computers and a specific system software framework. Due to a thorough safety concept and system design the ACT/FHS is allowed to land while experimental software is engaged and produces control inputs. A distinct software environment was developed to make the implementation process as comfortable and deterministic as possible. This environment is based on the one hand on pure source code files and on the other hand on problem-oriented development tools with automatic program code generation capability. Matlab/Simulink with an extensively modified Real-Time Workshop is used as standard tool. Experimental hardware can be attached to the aircraft using the experimental system as an interface. More than one experimental application can be flight tested in parallel. This is a necessary requirement to perform in-flight research on complete human-machine interface concepts that incorporates different sub-applications. An explicit model based control system was designed and implemented on the ACT/FHS, forming the basis for most of the in-flight research on rotorcraft handling qualities. The developed command models, that explicitly formulate the desired rotorcraft flight mechanics as response-types, as well as the necessary feedforward and feedback controller parts, were designed using Matlab/Simulink. Another software application that uses the experimental software environment is advanced flight path planning for start, en-route flight and landing. Besides terrain, wind condition, rotorcraft procedures and operating limits it takes pilot cognition into account when generating proposals for flight paths. The application proposes flight paths that closely match the individual expectations of the pilots. A combination of hard- and software was implemented for research on active inceptors. Two active sidesticks were implemented in the ACT/FHS. The sticks are controlled via software that is based on Matlab/Simulink code and runs on the experimental computers. Several flight test experiments were conducted to evaluate the basic mechanical characteristics for optimized handling qualities. In-flight research on this topic is ongoing. All applications were successfully implemented on the ACT/FHS experimental system, flight tested and undergo continuous improvement.