In modern aircrafts like the AIRBUS-series the control
stick is realized by a small side stick mounted beside the
pilot’s seat, where the electrical signals transferred by the
stick’s electronic are used for controlling the rudders - Fly
by Wire. The conventional side stick is only operated by
passive mechanics forcing the stick back to its neutral
position. The main disadvantage is the absence of any
feedback from the rudders.
In order to realize an active control stick an actuator has to
be introduced in the mechanical assembly of the stick.
The actuator on the one hand generates feedback forces
which help the pilot to get a better control on the aircraft
and on the other hand it serves for reproducing a nonlinear
spring characteristic which otherwise is generated by the
passive mechanic of the stick but now can be varied on-
line. Additionally the generation of mechanical warning
signals in form of stick vibrations and the coupling of
pilot’s and copilot’s sticks are possible when using an
The mechanical assemblies of previous realizations by use
of conventional electrical actuators are huge and heavy.
Rotary travelling wave type USMs are more compact as
conventional electrical geared motors and have high driv-
ing torque at low rotational speed. Due to their low noise
in operation and low electromagnetic emission they are
suitable for use in aviation. Thus a USM is used here for
realizing an one axis active control stick. The motor
which is used is the AWM90 (Prototype USM of Daimler-
Chrysler) which at the authors best knowledge is presently
the most powerful piezo drive.
The driving principle of travelling wave type USMs is
based on two orthogonal mechanical vibration modes
which are excited in the stator to their single eigenfre-
quency by a piezo ceramic layer, , . Superimposing
both standing waves by proper amplitudes and temporal
phase shift a travelling bending wave is generated, which
performs elliptic motions of the stator’s surface points.
The rotor, which is pressed aga