Stability Augmentation of Ultralight Helicopters

Der Hubschrauber CoAX2D mit Stabilisierungssystem wird zu Testzwecken zunächst in diesem Stahlgestell geflogen

Photo: edm aerotec GmbH

Since the end of 2016, Germany has officially had the Ultralight (UL) helicopter class.
This allows UL helicopters to be approved as aerial sports equipment.
The acquisition of a pilot's license for this is associated with a lower expenditure of time and money than with a normal private pilot's license.
Due to the lower entry hurdle and the cost-effective operation of these helicopters, it can be assumed that the number of UL helicopter pilots will increase in the coming years.
Since a helicopter involves cross couplings between the axes of motion and typically exhibits an unstable flight behavior, mastering a helicopter is a challenging task for a pilot. Apart from the rotor speed, ultralight helicopters typically lack any sort of pilot assistance systems. To change that, the iFR cooperates with the edm aerotec GmbH, the initiator of the ultralight helicopter class in Germany and also the manufacturer of the first helicopter to receive a type certificate in the German ultralight helicopter class.

At the Institute of Flight Mechanics and Flight Control, a stabilization system was developed that supports pilots and can relieve them on tiring missions.
The aim was to make the system as simple as possible without sacrificing function. Since UL helicopters generally do not use hydraulic amplification of pilot forces in the control train, electromechanical actuators were installed directly in the control linkage. These actuators can lengthen the control linkage again in addition to the pilot. The main objective of the research project is to find out whether the pilot is more disturbed than relieved by the force feedback of the actuators to himself when flying. The stabilization system was installed in a UL helicopter of the type "CoAX 2D" from edm aerotec GmbH in Geisleden in Thuringia. First flight tests show a significant stabilization of the helicopter in hovering flight, while the pilot classified the disturbance as low.

Since September 2020, the project has been continued under the name EASY (Electromechanically Controlled Stability Augmentation System) in the course of LuFo VI-1, funded by the German Federal Ministry for Economic Affairs and Energy (BMWi). The financial support is gratefully acknowledged. The goals of EASY are further research in concepts for pilot assistance systems and transferring the results to the free flying helicopter. The research at the iFR also includes modern governor systems for ultralight helicopters. A constant rotor speed is essential for the safe operation of a helicopter. This requires constant corrections of the motor power depending on the flight condition. Most helicopters feature a governor that controls the rotor speed automatically so that the pilot can concentrate on flying. In cooperation with edm aerotec, a governor for the CoAX 600, a version of the CoAX with a maximum take-off mass of 600 kg, is currently developed.

The goals of the research activities regarding pilot assistance at the iFR are

The development and testing of modern governor systems for ultralight helicopters.
The research regarding and testing of methods and systems to assist helicopter pilots and enhance stability.

The research goals regarding pilot assistance systems in the primary control train include

integrating all components into the helicopter within the limits regarding mass, energy consumption and overall complexity.
Proving that the pilot workload can be reduced by an assistance system that includes actuators in the control train. This includes proving that the actuator forces do not disturb the pilot.
Proving that safe flight is still possible if a system failure occurs.

[1] Richter, T., Rothaupt, B., Steinwandel, A., Fichter, W., & Grebing, B. (2020). Stability Augmentation System for Coaxial Ultralight Helicopters. Proceedings of the VFS International 76th Annual Forum.

[2] Richter, T., Rothaupt, B., Fichter, W., & Grebing, B. (2020). System Identification of a Coaxial Ultralight Helicopter. Proceedings of the VFS International 76th Annual Forum.