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Systemsimulation ATTAS und FHS

Fig 1: ATTAS simulation cockpit

System simulation is a key element for the development and operation of both airborne simulators, ATTAS and HESTOR (ACT/FHS). System simulation implies a full replication of all functions and systems on the ground with hardware-in-the-loop. This approach provides a means for efficient flight test preparation, crew training for the test flight, and especially testing of hard- and software modifications under real-time conditions. Test aircraft operation requires full testing of experimental software on the ground based simulators before flight test is authorized. This concept – not to change software functions in flight before testing on the ground – minimizes mistakes, reduces costs, and leads to safe and efficient flight testing.
Fig 2: HESTOR (ACT/FHS) simulation cockpit with vision system
The ATTAS system simulator is equipped with an original VFW 614 cockpit, Fig. 1; the HESTOR system simulator has an original Bo 105 cockpit, Fig. 2, that is currently being modified to provide the pilot with an EC 135 pilot interface. Both fixed-base simulators are provided with flight-vehicle-identical inceptors, multi functional displays, mode controls, and an in-house developed vision system. Several graphical user interfaces to operate the simulators and to get quicklook informations are part of the operator stations. The HESTOR simulator cockpit is fitted with an 8-axes digitally controlled load system providing the control forces on cyclic and collective sticks and pedals for both pilots. The force-feel characteristics can be varied to suit experimental needs. That makes full mission crew training possible including switching between the different operating modes, i.e., safety pilot, evaluation pilot, and experimental mode. The inputs from the pilots in the cockpit and from the flight test engineer at the control station are handled in exactly the same way as in the HESTOR test vehicle. For the evaluation pilot, the HESTOR simulator is equipped with a two-channel backprojection vision system providing a field of view of about 30° to the left and 120° to the right and ± 30° in the vertical direction. The ATTAS simulator currently has a rudimentary single-channel direct projection system that is expected to be upgraded in the near future. The vision systems are based on a Silicon Graphics image generator (ONYX Infinite Reality) with software based on Coryphaeus tools.

Fig 3: Structure of ATTAS and HESTOR simulation facility

The structure of the simulation facility is mostly identical for ATTAS and HESTOR, Fig. 3. The 6 degrees-of-freedom aircraft simulation as well as the 9 degrees-of-freedom helicopter simulation with main and tail rotor include engine, actuator, and atmosphere models. They run in real-time on a high performance simulation computer RTS (Real Time Station) that is supported by a powerful commercial software development tool, called SIMsystem, which is hosted by a UNIX workstation. The VME-Bus Interface Computers (Aircraft Interface Computer; AIC; and Helicopter Interface Computer; HIC) are the central data conditioning and distribution multiprocessor systems. The AIC simulates sensor and avionic systems characteristics whereas the HIC performs the tasks of data acquisition and distribution and of the simulation of the functionality of the cockpit interface including the procedures for switching between various operation and trim modes. All data that are available in the on-board systems are provided on the ground simulators in the same data formats (e.g., ARINC 429, MIL-Bus 1553B). In the case of ATTAS, the sensor data interfacing even has airplane-identical connectors so that on-board computers can be connected to the simulator for failure identification purposes. The on-board computer systems are represented as hardware-in-the-loop elements in the ground based simulators. In contrast to the rugged flight-certified on-board systems; for cost reasons, they are based on commercial hardware for the ground simulators. However, they have the same software structure and functionality as their counterparts in the flight vehicles. Software development for the computer systems is accomplished on a Data General mainframe in case of ATTAS and a VME-Bus system in case of HESTOR.