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Electrical power generation is an important component in the Electrical Power System of an Aircraft (EPS). In this paper we present a model based diagnostic framework for early generator degradation detection and tracking within an Aircraft Generator. The nominal health state is modeled empirically using an Auto-associative Kernel Regression (AAKR) technique using signals extracted from a healthy generator. Later the health state is estimated by comparing sensor observations with the model predictions. Finally, a Sequential Probability Ratio Test (SPRT) is used to detect and track degradation. This model based framework showed excellent degradation tracking performance when it was tested on a unit that was run to failure.

Aviation battery maintenance is trending toward on-condition maintenance. Nickel-Cadmium (NiCd), Valve Regulated Lead-Acid (VRLA), or prospective Li-ion batteries are used to start engines, provide emergency back-up power, and assure ground power capability for maintenance and pre-flight checkout. As these functions are mission essential, State of Health (SoH) recognition is critical. SoH includes information regarding battery energy, power and residual cycle life. This paper describes an SoH recognition technique for on-board aviation batteries and presents a passive diagnostic device (PDD). The PDD monitors on-board system battery current, voltage and ambient temperature and utilizes no active signals to the battery which can be restricted or even prohibited in order to avoid any interference with the vehicle electrical system.

The Cessna Citation CJ4, certified on March 12, 2010, is believed to be the first civil aircraft with a Lithium Ion main battery. The 26.4VDC, 44Ah Lithium Ion main battery weighs 54 lbs, a 35% weight saving over a Nickel-Cadmium battery. Using phosphate-based Lithium Ion cells, which have no positive feedback thermal runaway failure mode, system integration of the battery and aircraft architecture design is simpler. Electronics and software are needed to optimize life only, not to ensure safety. Emergency discharge with failed electronics is enabled with the selection of a less volatile chemistry, the use of an analog Module Management System for cell balancing and protection, and the use of a microcontroller-based digital Central Monitoring System that reports health. System safety failure hazard assessment is considered Major, and the battery software is certified to the requirements of RTCA DO-178B, Design Assurance Level C.

The focus of this research is to perform a detailed investigation of the tradeoffs between mass, efficiency, service factor (SF), power factor (PF), and cost of commercially available induction machines (IMs). To support this effort, data from a large number of IMs is used to establish Pareto-optimal fronts between these competing objectives. From the Pareto-optimal fronts, relatively straightforward models are formulated for the mass versus loss, cost versus loss, SF versus mass, PF versus cost. Parameters of the models are obtained using a genetic algorithm (GA).

This paper describes a framework for developing an Integrated Electrical Power System (EPS) Health Management System. The framework is based on the perspective that health management, unlike other capabilities, is not a self-contained, stand-alone system, but is rather an integral part of every aircraft subsystem, system, and the entire platform. Ultimately, the objective is to improve the entire maintenance, logistics and fleet operations support processes. This perspective requires a new mindset when applying systems engineering design principles. The paper provides an overview description of the framework, the potential benefits of the approach and some critical design and implementation issues based on current development efforts.

MIL-STD-704 defines power quality in terms of transient, steady-state, and frequency-domain metrics that are applicable throughout a military aircraft electric power system. Maintaining power quality in more electric aircraft power systems has become more challenging in recent years due to the increase in load dynamics and power levels in addition to stricter requirements of power system characteristics during a variety of operating conditions. Further, power quality is often difficult to assess directly during experiments and aircraft operation or during data post-processing for the integrated electric power system (including sources, distribution, and loads). While MIL-STD-704 provides guidelines for compliance testing of electric load equipment, it does not provide any instruction on how to assess the power quality of power sources or the integrated power system itself, except the fact that power quality must be satisfied throughout all considered operating conditions.

High-temperature, high-power capacitors are integral components being developed for high-temperature electronics to be used in aerospace, automotive, and other applications. Presently, a wide range of materials and capacitor technologies are being actively developed to address the needs of high temperature applications. Literature and experimental survey of existing materials and technologies focusing on commercially viable technologies has been made. Key parameters for characterizing and assessing capacitors have been compiled. Of the key competing capacitor technologies, including electrolytic, ceramic, polymer thin-film, and supercapacitors, none were found to be clearly superior to the others, thus requiring trade-offs between available choices. The review of these capacitors will be presented with respect to specific energy density, temperature capability, cost, ripple current capability, and failure tolerance.

This paper describes a novel time-varying prognostic modeling framework for computing condition-based residual life distributions of partially degraded aircraft electrical power system (EPS) components. This advanced methodology is suitable for modeling the evolution of degradation signals acquired from aircraft electrical power system components through condition monitoring techniques. The evolution of the degradation signals is modeled as a stochastic process, with fixed and random parameters, and takes into consideration environmental covariates that capture the time-varying nature of the equipment's operating condition. The modeling methodology correlates the degradation signals with the underlying physical transitions that occur prior to component failures to estimate and update the residual life distribution of the system.

Three-dimensional conjugate heat transfer models are built to predict the steady-state performance of microscale pin-fin and cross-flow heat exchangers with hydraulic diameters on the order of 100 μm. Modeling, meshing, and segmentation techniques are presented to allow for macroscale simulation of the microstructured devices. The effect of variation in geometric and flow parameters is investigated. Hydraulic and thermal predictions are compared to published experimental and extended beyond the limited range of test data to provide performance within a wide parametric range. A discussion of the dominating and relevant thermal transport mechanisms in both fluids and solid clarifies the routes to optimizing heat transfer in these small scale heat exchangers.

This paper presents the concept of a dual latent heat sink for thermal management of pulse heat generating electronic systems. The focus of this work is to verify the effectiveness of the concept during charging through experimentation. Accordingly, custom components were built and a prototype version of the heat sink was fabricated. Experiments were performed to investigate the implementation feasibility and heat transfer performance. It is shown that this heat sink is practicable and helps in arresting the system temperature rise during charging (period of pulse heat load).

An overview of aircraft DC power quality specifications reveals that only minor changes have occurred in recent years within industry standards. Current and future advanced electronic aircraft are requiring significant power quality improvements due to increased use of digital and COTS (commercial off the shelf) systems. Certain electronic systems do not function properly due to various types of electrical disturbances. Some systems shutdown, fault or exhibit operational delays due to power interruptions or “blackout” conditions. Undervoltage or “brownout” conditions also cause this effect. Some electronic systems exhibit critical faults that can affect safety or mission success due to overvoltage conditions. Additional effects of high voltage spikes or overvoltage transients are known to reduce the life of utilization equipment [1], which is directly related to the health of the aircraft's electronic system and creates an economic burden.

The thick oxide layer of silicon-on-insulator (SOI) devices significantly reduces the junction leakage current at elevated temperatures compared to similar Si devices, resulting in an elevated maximum operating temperature. The maximum operating temperature, specified by manufacturers, of commercial SOI devices/circuits with conventional packaging is usually 225°C. It is important to understand the performance and de-ratings of these SOI circuits at temperatures above 225°C without the temperature limit imposed by commercial packaging technology. This work tested a low frequency square-wave oscillator based on an SOI 555 Timer with a special high temperature ceramic packaging technology from room temperature to 375°C. The timer die was attached to a 96% aluminum oxide substrate with high temperature durable gold (Au) thick-film metallization, and interconnected with Au wires.

The remarkable evolution of the gas turbine engine has made the world much smaller and provided power for worldwide use. I often think of growing up in a farm environment, being fascinated with machinery and then having the opportunity to take part in the design and development of the world's most complex product. I worked with brilliant engineers and experienced the transition from slide rules and “hand calculation” methods to computers and more precise finite element modeling. Perhaps this story will present insight for current and future design engineers who create the manufactured products used by mankind.

This paper outlines power system architecture trades performed on the N3-X hybrid wing body aircraft concept under NASA's Research and Technology for Aerospace Propulsion (RTAPS) study effort. The purpose of the study to enumerate, characterize, and evaluate the critical dynamic and safety issues for the propulsion electric grid of a superconducting Turboelectric Distributed Propulsion (TeDP) system pursuant to NASA N+3 Goals (TRL 4-6: 2025, EIS: 2030-2035). Architecture recommendations focus on solutions which promote electrical stability, electric grid safety, and aircraft safety. Candidate architectures were developed and sized by balancing redundancy and interconnectivity to provide fail safe and reliable, flight critical thrust capability. This paper outlines a process for formal contingency analysis used to identify these off-nominal requirements. Advantageous architecture configurations enabled a reduction in the NASA's assumed sizing requirements for the propulsors.

Uncontrolled rectifiers are featured heavily in aircraft electrical power systems performing a number of the power conversion and conditioning functions. Detailed modeling and simulation of these and other converters as part of a wider aircraft power system, whilst accurate, can be very computationally intensive, resulting in impractically slow simulation speed. One potential solution to this issue is the use of average-value converter models, which offer a much lower computational requirement and can utilize larger time steps. Of the average-value diode rectifier modeling methods presented in the research literature the parametric method is particularly well suited to system-level simulation because it can be readily derived to represent all modes of rectifier operation. To date however, published results utilizing this methodology have been limited to simpler power system architectures.

Fuel Cells provide an attractive alternative to battery powered Unmanned Aircraft Systems (UAS) as they maintain the simplicity of an all-electric vehicle architecture while taking advantage of highly energy-dense fuels. Unfortunately, the overall energy and power density of the power and energy (P&E) system cannot be determined from the fuel and fuel cell technology without also including the context of the associated aircraft and mission. These outside requirements play a particularly important role in the design of Small UAS (SUAS) P&E systems where the fixed weight of the fuel cell plant may approach or exceed the weight of the fuel utilized. Over the past seven years Protonex has developed fuel cell power systems for a number of different SUAS, creating an empirical database and methodology suitable for future SUAS design efforts.

Efforts are underway to develop technologies to create a more Energy Optimized Aircraft (EOA). The question becomes how should one define an Energy Optimized Aircraft and how should energy optimization be measured to determine what is optimal? This paper provides a top level point of view for the goal of an Energy Optimized Aircraft. It outlines how one should approach the design of such an aircraft, the relevant vehicle systems technologies to enable energy optimization for fighter aircraft, and potential aircraft level measurands for determining degrees of goodness associated with incorporating different technologies. The top-to-bottom approach is provided for traceability of technologies being developed to aircraft and mission level goals.

The diverse and complex requirements of next-generation energy optimized aircraft (EOA) demand detailed transient and dynamic model-based design (MBD) to ensure the proper operation of numerous interconnected and interacting subsystems. In support of the U.S. Air Force's Integrated Vehicle Energy Technology (INVENT) program, several software tools have been developed and are in use that aid in the efficient MBD of next-generation EOA. Among these are subsystem model libraries, automated subsystem model verification test scripts, a distributed co-simulation application, and tools for system configuration, EOA mission building, data logging, plotting, post-processing, and visualization, and energy flow analysis. Herein, each of these tools is described. A detailed discussion of each tool's functionality and its benefits with respect to the goal of achieving successful integrated system simulations in support of MBD of EOA is given.

Variable cycle engines offer the potential to operate a turbine engine more like a high-bypass turbofan during subsonic cruise and more like a turbojet or low-bypass turbofan for high-performance maneuvers or when supercruising. Variable geometry within the engine enables flow holding, allowing it to ingest the maximum amount of air that the inlet can capture even at reduced throttle settings. This approach reduces spillage drag compared to the conventional approach which cuts back engine airflow by reducing fan speed. To achieve the desired thrust, airflow is modulated between the core, inner bypass, and outer bypass. The air in the outer bypass duct, known as the 3rd stream, has been proposed as a heat sink for various engine and aircraft heat loads since it is at a comparatively low temperature, having only passed through the fan portion of the engine's compression system.

NASA's N3-X aircraft design under the Research and Technology for Aerospace Propulsion Systems (RTAPS) study is being designed to meet the N+3 goals, one of which is the reduction of aircraft fuel burn by 70% or better. To achieve this goal, NASA has analyzed a hybrid body wing aircraft with a turboelectric distributed propulsion system. The propulsion system must be designed to operate at the highest possible efficiency in order to meet the reduced fuel burn goal. To achieve maximum efficiency, NASA has proposed to use a superconducting and cryogenic electrical system to connect the electrical output of the generators to the motors. In addition to being more efficient, superconducting electrical system components have higher power density (kW/kg) and torque density (Nm/kg) than components that operate at normal temperature. High density components are required to minimize the weight of the electric propulsion system while meeting the high power demand.