As part of the NASA Aviation Safety Program at Langley Research Center, a dynamically scaled unmanned aerial vehicle (UAV) and associated ground based control system are being developed to investigate dynamics modeling and control of large transport vehicles in upset conditions. The UAV is a 5.5% (seven foot wingspan), twin turbine, generic transport aircraft with a sophisticated instrumentation and telemetry package. A ground based, real-time control system is located inside an operations vehicle for the research pilot and associated support personnel. The telemetry system supports over 70 channels of data plus video for the downlink and 30 channels for the control uplink. Data rates are in excess of 200 Hz. Dynamic scaling of the UAV, which includes dimensional, weight, inertial, actuation, and control system scaling, is required so that the sub-scale vehicle will realistically simulate the flight characteristics of the full-scale aircraft. This testbed will be utilized to validate modeling methods, flight dynamics characteristics, and control system designs for large transport aircraft, with the end goal being the development of technologies to reduce the fatal accident rate due to loss-of-control.

No abstract

No abstract

No abstract

This article explores piezoelectric ceramics analysis and characterization. The focus is on polycrystalline ceramics; therefore, single crystals, polymeric materials, and organic/inorganic composites are outside the scope of this article. To grasp the behavior of a piezoelectric polycrystalline ceramic thoroughly, a basic understanding of the ceramic itself should not be overlooked. To this end, we have presented a brief introduction of the history of piezoelectricity and a discussion on processing of the ceramic and the development of the constitutive relationships that define the behavior of a piezoelectric material. We have attempted to cover the most common measurement methods and to introduce parameters of interest. Excellent sources for more in‐depth coverage of specific topics can be found in the bibliography. In most cases, we refer to lead zirconate titanate (PZT) to illustrate some of the concepts because it is the most widely used and studied piezoelectric ceramic to date.

This paper assesses the electrical characteristics of piezoelectric wafers for use in aeronautical applications such as active noise control in aircraft. Determination of capacitive behavior and power consumption is necessary to optimize the system configuration and to design efficient driving electronics. Empirical relations are developed from experimental data to predict the capacitance and loss tangent of a PZT5A ceramic as nonlinear functions of both applied peak voltage and driving frequency. Power consumed by the PZT is the rate of energy required to excite the piezoelectric system along with power dissipated due to dielectric loss and mechanical and structural damping. Overall power consumption is thus quantified as a function of peak applied voltage and driving frequency. It was demonstrated that by incorporating the variation of capacitance and power loss with voltage and frequency, satisfactory estimates of power requirements can be obtained. These relations allow general guidelines in selection and application of piezoelectric actuators and driving electronics for active control applications.Key words, piezoelectricity, power requirements, variation of capacitance, empirical relations Subject classification. Physical Sciences: Materials 1. Introduction. The potential of piezoelectric ceramics as actuators and sensors has been widely documented in applications ranging from aerospace to biomedical. One of the areas that incorporates the use of these materials at NASA LaRC is the area of active noise and vibration control [1][2][3]. In this application, the targeted fundamental frequency is between 50-100Hz, with the next higher modes ranging up to 400-600Hz. These are higher frequencies than in structural or aeroelasticity control because of the pressurized or pre-loaded aircraft cabin/fuselage. Practical limitations such as acceptable excitation voltages, mechanical durability, coupling to the control structure and control system complexity and stability are driving research for sensor and actuator improvement. A critical issue that arises when using surface mounted transducers is the piezoelectric power consumption necessary to drive them. Applications are found to depend upon the electrical characteristics of the PZT transducers, namely the capacitive and resistive behavior of the actuator, which in turn affect their power consumption characteristics.A number of researchers have investigated the power consumption characteristics of PZT actuators used to excite a host structure [4][5][6] and found a coupling between the mechanical motion of the structure and the electrical characteristics of the piezoelectric actuator. Research by Brennan and McGowan [7] shows that the power consumption of piezoelectric materials used for active vibration control is independent of the mechanical motion of the host structure when the structure is completely damped. From these findings, they conclude that the power requirements of the piezoelectric actuator are only dependent upon its geometry and material pro...

No abstract

No abstract