KEYWORDS: Actuators, Shape memory alloys, Thermoelectric materials, Transmission electron microscopy, Control systems, Temperature metrology, Sensors, System identification, Convection, Control systems design
Development and test results of a rotor blade twist control system that utilizes a thermo-mechanical shape memory alloy
(SMA) are presented. The actuation system controls the blade shape during flight operations allowing the blade to be
configured for greater lift during takeoff and landing. SMA actuators provided an excellent solution because of their
very high torque output to weight ratio and suitability to the dynamic environment of a rotor blade. Several challenges
related to the behavior of the SMA material are overcome by innovative control system design. Thermoelectric
modules (TEM's) are used to actively transfer heat between SMA tubes and other heat conductor and radiator
components. Modeling and system identification techniques and a non-trivial solution to nonlinear and coupled
thermal response equations are used to insure effective use of the TEM's and to improve control during SMA phase
transition.
Wind Tunnel tests of a NiTinol based actuator have been conducted for the reconfigurable rotor blade program. The
purpose of the test was to demonstrate the potential to improve rotorcraft performance by optimizing the configuration of
major structures in flight. The actuator is integrated into the rotor blade as a structural element controlling blade twist.
A three-blade scale rotor was tested in a Boeing wind tunnel. The tests validated actuator design and performance by
demonstrating simultaneous blade twist and control of twist position over the entire test matrix. A description of system
requirements and compromises associated with the actuator and its integration into the rotor blade are provided and
discussed. Test results showed that the RRB actuators were able to successfully twist the blade, control the twist
between one twist state and the other, and simultaneously control three rotor blades to change state within two seconds
of each other despite unanticipated electrical noise in the system.
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