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H. Amri:
"Variable Rotor Speed Drivetrain Investigation";
Supervisor, Reviewer: M. Weigand, V. Zhuravlev, F. Heitmeir; Institut für Konstruktionswissenschaften, 2018; oral examination: 2018-11-16.

The research presented in this thesis focuses on the development of a transmission ratio
variable transmission system for rotorcraft to enable a variable rotor speed. Di erent drivetrain
technologies were investigated according to their potential for rotor speed variation.
The bene ts of rotor speed variation in the context of missions and under consideration of
di erent drivetrain technologies was calculated for di erent rotorcraft con gurations.
Transmission systems were rated according to the requirements of rotorcraft on the drivetrain
to nd the most suitable transmission technology. A functional failure mode and e ects
analysis was performed for the most suitable transmission system. Furthermore, a kinematic
and a mass analysis of the most suitable transmission system was carried out and the
in
uence of the shifting process on the whole drivetrain was simulated.
The investigation should show if rotorcraft rotor speed variation as performed by transmission
ratio variable transmission systems can improve rotorcraft e ciency and
ight envelope.
Furthermore, a possible design for a transmission-variable gearbox should be de ned.
Four rotor speed variation technologies, rotor, electric, turbine and gearbox technology, were
investigated according to their usability. Only turbine and gearbox technology are applicable
in the near future, the turbine technology for small, about 10%, and the gearbox technology
for large variation range.
The mission analysis showed that high speed rotorcraft con gurations such as tilt rotor need
a large rotor speed variation range of about 50% but only two rotor speeds, one for hover
and one for fast forward
ight. Utility rotorcraft con gurations gain most bene ts from
continuous rotor speed variation. The variation range within one mission is about 20% and
about 36% if more missions are taken into account.
Compound split transmission systems are most suitable for rotor speed variation according
to the requirements analysis. The failure mode and e ects analysis showed that there are
additional risks with this new technology but they can be negated with additional compensation
actions like free wheel clutches. The mass and kinematic analysis showed that
compound split con gurations can be distinguished by their stationary transmission ratio of
the planetary gears and that they have a di erent mass depending on the basic transmission
ratio and the transmission ratio variation.
The simulation of the shifting process showed that in principle a two-speed and a continuousvariable
transmission ratio variation is possible with a compound split. The continuousvariable
transmission ratio variation enables a smooth transition and less load peaks on the
drivetrain. Therefore, this is the preferable variant.
The research in this thesis is the basis for the development of a new variable transmission
ratio drivetrain system for rotorcraft. It enables di erent rotorcraft con gurations to increase
their
ight envelope and e ciency. This could be one corner stone for a more ecologically
e cient rotorcraft aviation.