Unimorph active rigidity joints, constructed from Shape Memory Alloy and Shape Memory
Polymer and capable of bending actuation, are reported in this work. An embedded aluminum
shim was added to each joint as a structural element to facilitate actuation. Joints were actuated
using ohmic Tri-Phase and pulse heating processes with different results. It appeared that openloop
position control could be achieved using pulse heating. Actuator improvements and future
experiments are proposed.
The morphing of wings from three different bat species is studied using an extension of the Weissinger method.
To understand how camber affects performance factors such as lift and lift to drag ratio, XFOIL is used to study thin
(3% thickness to chord ratio) airfoils at a low Reynolds number of 100,000. The maximum camber of 9% yielded the
largest lift coefficient, and a mid-range camber of 7% yielded the largest lift to drag ratio. Correlations between bat
wing morphology and flight characteristics are covered, and the three bat wing planforms chosen represent various
combinations of morphological components and different flight modes. The wings are studied using the extended
Weissinger method in an "unmorphed" configuration using a thin, symmetric airfoil across the span of the wing through
angles of attack of 0°-15°. The wings are then run in the Weissinger method at angles of attack of -2° to 12° in a
"morphed" configuration modeled after bat wings seen in flight, where the camber of the airfoils comprising the wings is
varied along the span and a twist distribution along the span is introduced. The morphed wing configurations increase
the lift coefficient over 1000% from the unmorphed configuration and increase the lift to drag ratio over 175%. The
results of the three different species correlate well with their flight in nature.
A new actuator system is being developed at the Cornell Laboratory of Intelligent Material Systems to address the
problems of dynamic self-actuated shape change. This low profile actuator, known as the 'smart joint', is capable of
maintaining rigidity in its nominal configuration, but can be actively strained to induce rotation at flexure joints. The
joint is energetically efficient, only requiring power consumption during active morphing maneuvers used to move
between shapes. The composite beam mechanism uses shape memory alloy (SMA) for strain actuation, with shape
memory polymer (SMP) providing actively tailored rigidity due to its thermally varying properties. The first phase of
the actuator development was modeling of the generic composite structure, proving analytically and computationally that
the joint can produce useful work. The next phase focuses on optimization of this joint structure and usage, including
ideal layering configurations and thicknesses in order to maximize various metrics specific to particular applications.
Heuristic optimization using the simulated annealing algorithm is employed to best determine the structure of the joint at
various scaling ratios, layering structures, and with varying external loading taken into account. The results are briefly
compared to finite element models.
Recent interest in morphing vehicles with multiple, optimized configurations has led to renewed research on biological
flight. The flying vertebrates - birds, bats, and pterosaurs - all made or make use of various morphing devices to
achieve lift to suit rapidly changing flight demands, including maneuvers as complex as perching and hovering. The first
part of this paper will discuss these devices, with a focus on the morphing elements and structural strong suits of each
creature. Modern flight correlations to these devices will be discussed and analyzed as valid adaptations of these
The second part of the paper will focus on the use of active joint structures for use in morphing aircraft devices. Initial
work on smart actuator devices focused on NASA Langley's Hyper-Elliptical Cambered Span (HECS) wing platform,
which led to development of a discretized spanwise curvature effector. This mechanism uses shape memory alloy
(SMA) as the sole morphing actuator, allowing fast rotation with lightweight components at the expense of energy
inefficiency. Phase two of morphing actuator development will add an element of active rigidity to the morphing
structure, in the form of shape memory polymer (SMP). Employing a composite structure of polymer and alloy, this
joint will function as part of a biomimetic morphing actuator system in a more energetically efficient manner. The joint
is thermally actuated to allow compliance on demand and rigidity in the nominal configuration. Analytical and
experimental joint models are presented, and potential applications on a bat-wing aircraft structure are outlined.
As more alternative, lightweight actuators have become available, the conventional fixed-wing configuration seen on modern aircraft is under investigation for efficiency on a broad scale. If an aircraft could be designed with multiple functional equilibria of drastically varying aerodynamic parameters, one craft capable of 'morphing' its shape could be used to replace two or three designed with particular intentions. One proposed shape for large-scale (geometry change on the same order of magnitude as wingspan) morphing is the Hyper-Elliptical Cambered Span (HECS) wing, designed at NASA Langley to be implemented on an unmanned aerial vehicle (UAV). Proposed mechanisms to accomplish the spanwise curvature (in the y-z plane of the craft) that allow near-continuous bending of the wing are narrowed to a tendon-based DC motor actuated system, and a shape memory alloy-based (SMA) mechanism. At Cornell, simulations and wind tunnel experiments assess the validity of the HECS wing as a potential shape for a blended-wing body craft with the potential to effectively serve the needs of two conventional UAVs, and analyze the energetics of actuation associated with a morphing maneuver accomplished with both a DC motor and SMA wire.
Morphing aircraft design - the design of aircraft capable of macroscale shape change for drastic in-flight performance variation - is an extremely broad and underdefined field. Two primary means of developing new concepts in morphing exist at Cornell University: design of broad test platforms with generalized motions that can provide future insight into targeted ideas, and specifically adapted aircraft and shape change mechanisms attempting to accomplish a particular task, or hybridize two existing aircraft platforms. Working with both schools of thought, Cornell research has developed a number of useful concepts that are currently under independent analysis and experimentation, including three devices capable of drastically modifying wing structure on a testbed aircraft. Additional concerns that have arisen include the desire to implement ornithological concepts such as perching and wingtip control, as well as the necessity for a compliant aerodynamic skin for producing flight-worthy structural mechanisms.