Project Description

Current Rotorcraft Developments like under the Future Vertical Lift Program in the US and RACER and NextGENCivil Tiltrotor in Europe deal with High-Speed Rotorcraft or Tiltrotor-/Tiltwing Aircraft which require a variable rotor speed either to adopt the rotor speed to high forward speed or to meet the different requirements of a rotor in Hover and Aircraft Mode of a Tiltrotor-/Tiltwing Aircraft. As the required speed range can not be covered by the turbine TU Munich (Germany), TU Wien (Vienna, Austria) and Zoerkler Gears (Austria) work in the transnational project “VARI-SPEED II” on a rotor system that can change the rotor speed via change of the ratio of the transmission (variable rotor speed with constant turbine speed). The project is based on the results of „VARISPEED“ and the direct follow-up project. The efficiency and the flight envelope of the rotorcraft can be improved by this technology. Furthermore, a method for rotor blade design in a RPM range was invented.

Control Concept

We developed a  two-degree-of-freedom controller that determined the optimal reference trajectory generated by the pilot input. The increased degrees of freedom provide the controller with an energy-optimal-engine speed. Additionally, active damping reduces the vibrations that are cause by the elastic rotor components. Different methods like the robust control method and optimal control theory are explored to effectively compensate torsional vibrations of the rotor.

The combination of the optimal operating point of the variators regarding efficiency and constraints for temperature and speed/torque is calculated offline and stored in maps that are used for the feedforward control. The feedback DOF is assigned the task of torsional vibration suppression, which is solved by an adaptive model predictive controller.

Schema Feedforward Control


VARI-SPEED II will now build up a model of the complete dynamic system from engine to rotor of a helicopter with a variable speed rotor. This model will be used for dynamic simulations of the system. A scaled model of the module that changes the speed will be developed and pilot studied in a simulator are planned to find out the characteristics of such a system.


Bischläger, Mario, Agnes Poks, Michael Weigand, Jonas Koch, and Christopher Gross. "Dynamic Simulation of a Rotor System with Variable Speed, opens an external URL in a new window." In Forum 78 - Fort Worth, TX, May 2022


  • January 2019 - April 2023

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Ao.Univ.Prof. Dipl.-Ing. Dr.techn. Martin Kozek

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