16 August 2001 Design of a variable twist tilt-rotor blade using shape memory alloy (SMA) actuators
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This paper presents research aimed at actively altering the twist distribution of a tiltrotor blade between hover and forward flight. Three different concepts-extension-twist coupled composites, bimoment actuation and discrete SMA torque tube actuation - are considered, and the torque tube appears the most feasible. Parametric design of the torque tube and attachment technique is presented with actuation torque, heat transfer and bandwidth issues being considered to arrive at the configuration of the tube. The effect of heat treatment of the SMA in tuning the actuation characteristics is discussed. A dramatic improvement in the actuation cooling time is demonstrated through the use of active cooling using thermodelectric modules. An extension of the one-dimensional formulation of Brinson's model to the torsional case is presented. The model is shown to have good correlation with room temperature characteristics. The criterion for impedance matching between the actuator and the host structure is derived. The torsional actuator is tested both under no load and acting against a restoring spring and shows repeatable actuation characteristics.
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Harsha Prahlad and Inderjit Chopra "Design of a variable twist tilt-rotor blade using shape memory alloy (SMA) actuators", Proc. SPIE 4327, Smart Structures and Materials 2001: Smart Structures and Integrated Systems, (16 August 2001); doi: 10.1117/12.436559; https://doi.org/10.1117/12.436559

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