Twenty-two years ago, adaptive munitions using piezoelectric actuators were conceived. The Barrel-Launched Adaptive Munition (BLAM) program used piezoelectric elements to articulate a 10 deg. half-angle conical section on the nose of a 73 mm caliber supersonic wind tunnel model. The test article was designed to pivot the forward portion of the round about the aerodynamic center (which was collocated with the forward section center of gravity). While effective in trim articulation, the majority of actuator power was expended resisting nose inertia rather than manipulating air loads. Adaptive actuators for guided munitions have progressed greatly since that time. In 2001, major advances canard articulation for guided bullets were achieved. These were followed by the Shipborne Countermeasure Range-Extended Adaptive Munition (SCREAM) program. While the piezoelectric effectors designed for these historic programs would allow for respectable deflections, the invention of post-buckled piezoelectric (PBP) actuation would dramatically boost total deflection levels while maintaining full blocked force capabilities. These PBP actuators would be used in a variety of flight control mechanisms for different classes of UAVs. In addition to these applications, the high bandwidth of piezoelectric actuators are particularly well suited to guided munitions. This paper describes the structural mechanics and dynamics of the PBP-class actuator as integrated in guided munitions. As a critical element in ultra-high bandwidth flight control actuation, PBP actuators have been shown to possess pseudo-corner frequencies in excess of 1 kHz. Additionally, PBP actuators have been integrated into tight packing volumes in guided cannon shells while demonstrating setback acceleration tolerances of tens of thousands of g’s. Previous work illustrates several different actuation configurations as well as integration methods with canards and fins. This study links the structural mechanics of previous authors with aeromechanics to arrive at performance predictions in aerial combat. The paper lays out a guided aerial round based on the PBP concept, then uses circular error probable (CEP) predictions in a standard atmosphere quantify the required deflections for engagement of a variety of targets. The results show one order of magnitude fewer rounds being expended per kill in direct air-to-air engagements with peer aircraft. The paper shows that PBP-class actuators could be used for defensive engagements as well with the engagement of oncoming hostile missiles. The paper concludes with prediction of engagement improvements for modern aircraft like the F-35 with 25 mm rounds as well as aircraft like the F-15 with 20 mm guided ammunition.

Bio-inspired hydrodynamic thrust generation using piezoelectric transduction has recently been explored using Macro-Fiber Composite (MFC) actuators. The MFC technology strikes a balance between the actuation force and structural deformation levels for effective swimming performance, and additionally offers geometric scalability, silent operation, and ease of fabrication. Recently we have shown that mean thrust levels comparable to biological fish of similar size can be achieved using MFC fins. The present work investigates the effect of length-to-width (L/b) aspect ratio on the hydrodynamic thrust generation performance of MFC cantilever fins by accounting for the power consumption level. It is known that the hydrodynamic inertia and drag coefficients are controlled by the aspect ratio especially for L/b<5. The three MFC bimorph fins explored in this work have the aspect ratios of 2.1, 3.9, and 5.4. A nonlinear electrohydroelastic model is employed to extract the inertia and drag coefficients from the vibration response to harmonic actuation for the first bending mode. Experiments are then conducted for various actuation voltage levels to quantify the mean thrust resultant and power consumption levels for different aspect ratios. Variation of the thrust coefficient of the MFC fins with aspect ratio is also modeled and validated.

Flexibility is known to improve the propulsive performance of flapping fins. Flapping fins generate forces oscillatory in nature and this paper reports an investigation on the effect of flexibility and other parameters such as heaving, pitching amplitudes and operating frequency in reducing the center of mass oscillations of bodies attached to flapping fins. A detailed theoretical investigation has been carried out to predict the optimal operating parameters along with the fin stiffness to reduce the COM oscillations for a given self-propelled speed (SPS). Some design guidelines have been proposed which reduce COM oscillations that aid in the development of aerial and underwater robotic vehicles.

Ionic polymer metal composites (IPMC) are a new class of smart materials that have attractive characteristics such as muscle like softness, low voltage and power consumption, and good performance in aqueous environments. Thus, IPMC’s provide promising application for biomimetic fish like propulsion systems. In this paper, we design and analyze IPMC underwater propulsor inspired from swimming of Labriform fishes. Different fish species in nature are source of inspiration for different biomimetic flapping IPMC fin design. Here, three fish species with high performance flapping pectoral fin locomotion is chosen and performance analysis of each fin design is done to discover the better configurations for engineering applications. In order to describe the behavior of an active IPMC fin actuator in water, a complex hydrodynamic function is used and structural model of the IPMC fin is obtained by modifying the classical dynamic equation for a slender beam. A quasi-steady blade element model that accounts for unsteady phenomena such as added mass effects, dynamic stall, and the cumulative Wagner effect is used to estimate the hydrodynamic performance of the flapping rectangular shape fin. Dynamic characteristics of IPMC actuated flapping fins having the same size as the actual fins of three different fish species, Gomphosus varius , Scarus frenatus and Sthethojulis trilineata , are analyzed with numerical simulations. Finally, a comparative study is performed to analyze the performance of three different biomimetic IPMC flapping pectoral fins.

Ionic polymer-metal composite (IPMC) actuators with sectored (patterned) electrodes have been fabricated for realizing bending and twisting motion. Such IPMCs can be used to create next-generation artificial fish-like propulsors that can mimic the undulatory, flapping, and complex motions of real fish fins. Herein, a thorough experimental study is performed on sectored IPMCs to characterize their performance. Specifically, results are presented to show (1) the achievable twisting response; (2) blocking force and torque; (3) power consumption and effectiveness; and (4) propulsion characteristics. The results can be utilized to guide the design of practical marine systems driven by IPMC propulsors. The design of an example underwater robotic system is also described which employs the IPMC actuators, and the performance of the robotic system is reported.

An overview of the development and application of postbuckled precompressed (PBP) piezoelectric actuators is presented. It has been demonstrated that PBP actuators outperform conventional piezoelectric actuators by relying on axial compression to counter the inherent stiffness in the actuator element. In doing so the mechanical work output has been shown to increase three-fold compared to conventional bimorph actuators. Actuator stroke has been demonstrated to increase up to 300% without compromising the blocked force capability. This results in an expansion of the design space of piezoelectric bender elements and makes them excellent candidates for substituting conventional electromechanical flight control actuators. Successful application of PBP elements can be found in unmanned aerospace systems ranging from subscale vertical-take-off-and-landing vehicles to supersonic missile fins. With respect to conventional electromechanical servoactuators it is demonstrated that PBP actuator elements induce a lower systems weight fraction, a substantially higher bandwidth, and an order of magnitude lower power consumptions and part count.