In-Flight-Simulator EC 135 FHS

Fig 1: EC 135 helicopter
Flying Helicopter Simulator (FHS)

EC 135 (FHS), Flying Helicopter Simulator, is a unique, advanced airborne testbed which is under development. The aim of the development project, which is commonly funded by the German Ministry of Defense, DLR, and industry, is to validate key technologies for the future generation military and civil helicopters for extending the flight operation in direction of 24h and all- weather conditions. EC 135 (FHS) is designed to allow the in-flight evaluation of new control technologies, cockpit designs, and man-machine interfaces in a real environment and with the pilot in the loop.
It is based on an EC 135 helicopter, Fig. 1, that is refitted with fly-by-light technology, smart actuators, high speed processors, state-of-the-art sensors, and advanced, programmable display systems.

The Institute is well experienced in developing and operating a helicopter in-flight simulator. As the precursor of FHS, DLR has utilized the Bo 105 ATTHeS In-Flight Simulator until 1995. ATTHeS was successfully used in many national and international cooperation programs. In 1993, the needs for an upgraded testbed were formulated by industry and the Institute in a Memorandum of Agreement. The development of EC 135 HESTOR was initiated in 1995 with a one-year project definition study, which included the definition of the system concept and the application spectrum. Additionally, the host helicopter was selected and the structure of the development project including sharing of cost and work was proposed. The development started mid 1995.

Fig 2: System architecture
System Architecture

HESTOR has to cover a broad spectrum of applications including the demonstration of the operational benefits of integrated technologies and the more research oriented flight evaluation of systems and software with a not yet proven standard. Accordingly, the system is structured with a hierarchical architecture and consists of two associated on-board units, a core system, developed by industry, and an experimental system, developed by the Institute, Fig. 2.
The core system, which is a four times redundant direct link (1:1) fly-by-light control system, is designed with a 10-9 failure probability in accordance with the operational certification requirements. The experimental system is designed as a simplex system and fulfills the demands of a modular multi-role system. The prospects for future system modifications and an extension of system redundancy are considered. The ground based facilities (system simulator, telemetry ground station, and engineers test station) are part of the overall HESTOR system concept.




Fig 3: Crew stations
Crew Stations Concept

For the use as in-flight simulator, HESTOR is being designed with three crew stations, a safety pilot on the left hand seat, an evaluation pilot on the right hand seat, and a flight test engineer on the mid back seat. The engineer's station is prepared to be converted to a second evaluation pilot´s station, if necessary. This comprehensive and modular station concept will allow the use of HESTOR for the evaluation of the critical pilot vehicle interface early in the development of new technologies in a real operational environment without compromising flight safety.
The safety pilot´s station provides all the equipment which is standard for EC 135. The safety pilot is in the final command and flies with the primary control system which is the 1:1 fly-by-light control system. The evaluation pilot can select and switch between the 1:1 control system and the experimental system. When the evaluation pilot is flying the testbed, the actuator inputs are mechanically fed back to the safety pilot's controls. The evaluation pilot's station is equipped with a programmable display, which replaces the standard instruments, and with the standard control. The installation of side arm controllers is optional. For the pilots, the control and display units (CDU) for the core and experimental systems are integrated in the center console. The test engineer can use a multi-function display and the CDU for the experimental system, which are installed in the engineers panel. In addition, he can use quick look and experimental system management capabilities, Fig. 3.



Fig 4: Actuator unit
Core System

The core system is the redundant direct link fly-by-light system, which is the primary control system for both pilots without any restrictions in the flight envelope. The main structure is composed of the quadruplex pilot input position sensors, the four-lane control signal processing computer (CSPC), and "smart" actuators for the four axes, each supplied with a four-lane actuator electronics box, which is an integral part of the actuator block and performs internally the closed loop actuator control, Fig. 4.
The CSPC is the central processing unit of the core system, where the functions for switching, fading, and blending between the modes, the signal monitoring, and the signal filtering are implemented. The CSPC is the only interface to the experimental system. In the experimental mode, the evaluation pilot's control inputs are transferred via CSPC to the experimental flight control computer and the rotor control commands are sent to the actuators.

Experimental System

The modular experimental system is realized as a simplex system and is designed as a fail-safe system. The system consists of the flight control computer, the data management computer, two multi-function displays with the graphics processors, various sensors, interfaces to the basic helicopter equipment, and the data acquisition and telemetry system. Standard type interfaces are provided to allow integration of additional components. The modularity provides the capability to easily replace or add individual components and to modify or extend the system.

System Simulator

For the training of the crew and especially the evaluation pilot, a system simulator is adapted to the HESTOR demands. The simulation is based on a comprehensive model of the EC 135 host helicopter and the core system. The components of the experimental system are duplicated with the objective to enable the testing of the system and software configuration in a hardware/ software-in-the-loop scenario before going into flight. 

Development Schedule and Utilization Plans

The first flight of EC 135 HESTOR (ACT/FHS) is scheduled for 2000. The delivery is planned for the middle of 2001. The airborne simulator will be operated by DLR and will serve as a technology testbed until about 2020.

The plans of utilization for the first few years will include:

  • Development and evaluation of mission and cost oriented flight control systems,
  • Sidestick integration and evaluation of side stick modes including envelope protection,
  • Helmet/head mounted display integration and evaluation of sensor based approach and low level flight techniques including obstacle detection and avoidance systems and techniques,
  • Development and evaluation of pilot assistant systems and redundancy concepts,
  • Generation of handling qualities databases,
  • Support of the certification of new technologies, and
  • Support in helicopter and technology development projects.

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