The concept proposed in thei work for chord extension is the use of a bistable arch and thin plate system. There are two foci of this paper: (1) Design of the arch and (2)Model validation via experiment. Results show that bistability and symmetric deformation can be achieved when there are flexible hinges at the boundary and input. In addition, the presented finite element model provides good agreement with experimental results.
Research efforts have shown that helicopter rotor blade morphing is an effective means to improve flight performance.
Previous example of rotor blade morphing include using smart-materials for trailing deflection and rotor blade twist and
tip twist, the development of a comfortable airfoil using compliant mechanisms, the use of a Gurney flap for air-flow
deflection and centrifugal force actuated device to increase the span of the blade. In this paper we explore the use of a
bistable mechanism for rotor morphing, specifically, blade chord extension using a bistable arc. Increasing the chord of
the rotor blade is expected to generate more lift-load and improve helicopter performance. Bistable or "snap through"
mechanisms have multiple stable equilibrium states and are a novel way to achieve large actuation output stroke.
Bistable mechanisms do not require energy input to maintain a stable equilibrium state as both states do not require
locking. In this work, we introduce a methodology for the design of bistable arcs for chord morphing using the finite
element analysis and pseudo-rigid body model, to study the effect of different arc types, applied loads and rigidity on arc
In this paper we explore the use of bistable mechanisms for rotor morphing, specifically, blade tip twist. The optimal
blade twist distributions for hover and high-speed forward flight are very different, and the ability of the rotor to change
effective twist is expected to be advantageous. Bistable or "snap-through" mechanisms have multiple stable equilibrium
states and are a novel way to achieve large actuation output stroke at relatively modest effort for gross rotor morphing
applications. This is because in addition to the large actuation stroke associated with the snap-through (relative to
conventional actuator/ amplification systems) coming at relatively low actuation effort, no locking is required in either
equilibrium state (since they are both stable). In this work, the performance of a bistable twisting device is evaluated
under an aerodynamic lift load. The device is analyzed using finite element analysis to predict the device's load carrying
capability and bistable behavior.
In this paper, the optimal location of a distributed network of actuators within a scissor wing mechanism is investigated. The analysis begins by developing a mechanical understanding of a single cell representation of the mechanism. This cell contains four linkages connected by pin joints, a single actuator, two springs to represent the bidirectional behavior of a flexible skin, and an external load. Equilibrium equations are developed using static analysis and the principle of virtual work equations. An objective function is developed to maximize the efficiency of the unit cell model. It is defined as useful work over input work. There are two constraints imposed on this problem. The first is placed on force transferred from the external source to the actuator. It should be less than the blocked actuator force. The other is to require the ratio of output displacement over input displacement, i.e., geometrical advantage (GA), of the cell to be larger than a prescribed value. Sequential quadratic programming is used to solve the optimization problem. This process suggests a systematic approach to identify an optimum location of an actuator and to avoid the selection of location by trial and error. Preliminary results show that optimum locations of an actuator can be selected out of feasible regions according to the requirements of the problem such as a higher GA, a higher efficiency, or a smaller transferred force from external force. Results include analysis of single and multiple cell wing structures and some experimental comparisons.
Actuators based on smart materials generally exhibit a tradeoff between force and stroke. Researchers have surrounded piezoelectric materials (PZT’s) with complaint structures to magnify either their geometric or mechanical advantage. Most of these designs are literally built around a particular piezoelectric device, so the design space consists of only the compliant mechanism. Materials scientists researchers have demonstrated the ability to pole a PZT in an arbitrary direction, and some engineers have taken advantage of this to build “shear mode” actuators.
The goal of this work is to determine if the performance of compliant mechanisms improves by the inclusion of the piezoelectric polarization as a design variable. The polarization vector is varied via transformation matrixes, and the compliant actuator is modeled using the SIMP (Solid Isotropic Material with Penalization) or “power-law method.” The concept of mutual potential energy is used to form an objective function to measure the piezoelectric actuator’s performance. The optimal topology of the compliant mechanism and orientation of the polarization method are determined using a sequential linear programming algorithm. This paper presents a demonstration problem that shows small changes in the polarization vector have a marginal effect on the optimum topology of the mechanism, but improves actuation.