ACT/FHS Fly­ing He­li­copter Sim­u­la­tor

The ACT/FHS 'Flying Helicopter Simulator' of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is based on a standard Eurocopter EC 135 type helicopter, which has been extensively modified for use as a research and test aircraft. The mechanical controls, for example, have been replaced by a fly-by-wire/fly-by-light (FBW/FBL) flight control system. Now the control commands are transferred by electric cables and fibre optic cables instead of control rods.

The application portfolio of the FHS covers pilot training, trials of new open and closed-loop control systems, up to simulation of the flight characteristics of other helicopters under real environmental conditions. The FHS is equipped with two engines, a bearingless main rotor and a Fenestron tail rotor as standard; its key features are notably quiet operation and high manoeuvrability and safety.

The fly-by-light control system is a groundbreaking new system where, in contrast with fly-by-wire, the control signals between the controls, the flight management computer and the actuators for rotor blade control are transferred optically via fibre optic cables instead of electrically.

The advantages compared with electrical data transfer are the high transmission bandwidth, high reliability and low weight. The fly-by-light flight control system consists of a quadruple redundant computer and is designed such that the stringent safety criteria of the European aviation authorities are met in full.

FHS is the first helicopter in the world with this flight control system. The cockpit layout provides seats for a safety pilot, the test pilot and the flight test engineer. A comprehensive equipment line-up with sensors and systems for onboard data recording and processing is used to record the data from the flight tests. This data is available to users and engineers for analysis both on board and - via telemetry - on the ground.


The following modifications differentiate FHS from the standard Eurocopter EC 135 helicopter:

  • Optical and electronic FBW/FBL flight control system.
  • On-board computer system that enables simulation of the flight characteristics of other - real (existing) or virtual - aircraft. In this way, it provides important information for the operational assessment of a helicopter at an early stage of its development. These capabilities are also used in basic research into flight characteristics.
  • Modular experimental system: The system consists of flight-control computers, data measurement and pre-processing systems, displays and additional equipment and controls in the cockpit. The system also includes a data analysis station and a simulator for test preparation.

Conversion of the ACT/FHS was planned and implemented with the close cooperation of Eurocopter Deutschland (ECD), Liebherr Aerospace Lindenberg (LLI), the German Federal Office of Defense Technology and Procurement (Bundesamt für Wehrtechnik und Beschaffung; BWB) and DLR.

Missions - research focus

The powerful ACT/FHS helicopter is used for the following research trials and applications:

Development of flight control software that significantly reduces the pilot's workload in difficult flying situations and, at the same time, maintains intuitive control of the helicopter. In particular, the focus is on flight, take-off and landing under adverse conditions, such as launch and landing sites with obstructions and restricted visibility. The test pilot controls the helicopter via the DLR-developed experimental system, while the safety pilot oversees the manoeuvres.

The experimental system is a modular, multi-purpose system, whose safety concept is structured so that new, even not fully tested, technologies can be checked and evaluated, before their development is completed.

Other fields of application are:

  • Implementation and testing of active control units (sidesticks)
  • Testing pilot-assist systems
  • Integration and testing of sensors and vision systems
  • Measurement of flight characteristics
  • Training of test pilots and flight trials engineers

Technical data

Eurocopter EC 135 ACT/FHS

Fuselage length:

12.20 metres

Length, rotors turning:

12.20 metres


3.51 metres

Rotor diameter:

10.20 metres




2835 kilogrammes max.


up to 740 kilogrammes


two Turbomeca Arrius 2B1 engines, each rated at 415 kW

Flight altitude:

up to 6000 metres

Range (at sea level):

up to 440 kilometres


254 kilometres per hour max.


up to 2h30mins

Fuel quantity:

615 litres

Original use:

Use for national and state duties such as: civil defence, air rescue flights, police, armed forces

DLR flight facility:

Braunschweig (Brunswick)

Related links


Martin Gestwa

Head of Flight Facility Braunschweig
German Aerospace Center (DLR)
Flight Experiments
Lilienthalplatz 7, 38108 Braunschweig