an individual tab to change its state through serial commands that include the identifier of the tab device.  The second scheme attempts to eliminate the assignment (and/or cataloging) of individual tab actuator  identification codes by incorporating a “daisy-chain” interconnection of the tabs, where the most inboard  tab microcontroller strips off the first command signal (pulse) and sends the rest down the serial databus  to all the other actuators. This scheme allows for identical software to run on all tab actuator  microcontrollers, but interrupts the signal coming from the master unit at each tab station, potentially  impacting robustness. However, this same re-broadcasting technique can also be viewed as boosting the  signal of the transmitted pulse train as the signals propagate spanwise from inboard to outboard actuator  unit.  Printed circuit boards compatible with the dual tab design seen in Figure 11 are shown in Figure 12, along  side the tab assembly and a pen for scale comparison. The board has solder pads that directly accept a  programming header so that software changes may be made in-circuit, if necessary.  Figure 12. Dual  dual power MOSFETS.  Installation of the actuators on CDl’s model aircraft was expedited through the use of an extra control  channel for the model. Since this model lacks a rudder, an additional control channel was available from  the hand controller that had an output on the aircraft receiver, but not servo actuator that would connect to  it. Thus, an auxiliary roll command channel was constructed using the output of the rudder command to  drive a “master” microcontroller that, in turn, sent out serial daisy-chain tab command signals to both the  left and right wing actuators. This model arrangement was flown, and found to exhibit moderate roll  effectiveness, despite the fact that a full span complement of active tabs was in fact not driven from these  serial command sequences. Testing on this configuration continues, along with integration efforts to  support tests on NASA’s APV-3 aircraft.  Other Possible Aerospace Applications  Other aerospace applications suggest themselves for use of this actuation concept. While initially  developed as a trailing edge control component, the fundamental nature of an SMA-actuated over-center  spring like system has a variety of other possible uses. The essential features of this actuation concept  are captured in a simple example. If a structural member, such as a beam or plate, is buckled and placed  between two end constraints (either pinned or cantilevered), the beam (or, actuator “armature”) will  assume one of two possible equilibrium shapes, representing the minimum stress condition that satisfies  the end conditions (Figure 13). By attaching pre-strained, opposing SMA wires on each side of the buckled  member, and heating the most elongated SMA wire, one may induce a moment within the buckled  structure (at the SMA connection points) that forces the base material back toward its other equilibrium  position. As this induced moment is increased, the buckled structure will eventually move to a shape  where the incremental moment required to produce additional motion vanishes, and then rapidly switch, or  “snap” or “pop”, to its other equilibrium position. This behavior is often called “snap-through” or “oil-  canning” in the structural community, and is characterized by linearly elastic material properties but large  (nonlinear) deformations.  383