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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.

The combination of increasing performance demands, increasing system complexity, and the need for reduced program development schedule and budget costs in the aerospace industry is driving engineers to increasingly rely upon modeling, simulation, and analysis (MS&A) in the platform development cycle. One approach to ensuring that such integrated system simulations remain computationally tractable is co-simulation utilizing technology found in commercially available packages, such as PC Krause and Associates, Inc.'s (PCKA's) Distributed Heterogeneous Simulation (DHS) / FastSim software. In such co-simulation environments, dynamic models are executed in independent model spaces, with coupling between subsystems achieved by exchanging a minimal set of required data typically found at subsystem boundaries.

Mn and/or rare earth-doped xCaTiO₃ - (1-x)CaMeO₃ dielectrics, where Me=Hf or Zr and x=0.7, 0.8, and 0.9 were developed to yield materials with room temperature relative permittivities of Εr ~ 150-170, thermal coefficients of capacitance (TCC) of ± 15.8% to ± 16.4% from -50 to 150°C, and band gaps of ~ 3.3-3.6 eV as determined by UV-Vis spectroscopy. Un-doped single layer capacitors exhibited room temperature energy densities as large as 9.0 J/cm₃, but showed a drastic decrease in energy density above 100°C. When doped with 0.5 mol% Mn, the temperature dependence of the breakdown strength was minimized, and energy densities similar to room temperature values (9.5 J/cm₃) were observed up to 200°C. At 300°C, energy densities as large as 6.5 J/cm₃ were measured. These observations suggest that with further reductions in grain size and dielectric layer thickness, the xCaTiO₃ - (1-x)CaMeO₃ system is a strong candidate for integration into future power electronics applications.

The desire of the US Department of Defense (DoD) to field new directed energy systems for a variety of applications increases daily. This desire stems from recent advances in energy storage and solid-state switch technologies, which enable researchers to make systems more compact and energy dense than ever before. While some systems can draw power from the mobile platform on which they are mounted, other systems need to operate independent of a platform and must be completely self-sufficient. The transient and repetitive operation of these directed energy systems requires that the prime energy source provide high power to intermediate energy storage devices. The ability of electrochemical energy storage devices, such as lithium-ion batteries, to source high power quickly has previously been limited. However, battery manufacturers have recently produced cells that are more power dense then previously available.

Aircraft utilize electrical power for many functions ranging from simple devices such as resistive heaters to highly advanced and complex systems responsible for communications, situational awareness, electronic warfare and fly-by-wire flight controls. The operational states of these electronic systems affect safety, mission success and the overall economic expense of operation and maintenance. These electronic systems rely on electrical power within established limits of power quality. In recent years, electrical power quality is becoming excessively degraded due to increased usage of nonlinear and dynamic loads coupled to aircraft power systems that were neither designed nor tested for these loads. Legacy power generation systems were designed for electrical loads with resistive and inductive properties, which previously represented the majority of actual aircraft electrical loads.

Turboelectric propulsion is a technology that can potentially reduce aircraft noise, increase fuel efficiency, and decrease harmful emissions. In a turbo-electric system, the propulsor (fans) is no longer connected to the turbine through a mechanical connection. Instead, a superconducting generator connected to a gas turbine produces electrical power which is delivered to distributed fans. This configuration can potentially decrease fuel burn by 10% [1]. One of the primary challenges in implementing turboelectric electric propulsion is designing the power distribution system to transmit power from the generator to the fans. The power distribution system is required to transmit 40 MW of power from the generator to the electrical loads on the aircraft. A conventional aircraft distribution cannot efficiently or reliably transmit this large amount of power; therefore, new power distribution technologies must be considered.

This paper introduces a novel method for an electric power generation system (EPGS) employing a lead-unity-lag (LUL) permanent-magnet (PM) generator operation for a direct current (DC) power distribution bus. In addition, background information of the prior art for a leading power factor EPGS is discussed. The concept of the new approach is defined and a comparative analysis between the new and old state-of-the-art solutions are documented. The performance features and technical details of the system parameters with respect to power generation system requirements are presented and discussed. Analysis and testing results are included. Finally, the advantages of this system, a conclusion, and recommendations for future work are provided. Test results from a system having elements of this novel approach are included. With this method for an LUL EPGS, the capability of the high-performance electric power generation systems is improved substantially.

The utilization of converter interfaces has the potential to significantly alter the protection system design requirements in future aircraft platforms. However, the impact these converters will have can vary widely, depending on the topology of converter, its filter requirements and its control strategy. This means that the precise impact on the network fault response is often difficult to quantify. Through the analysis of example converter topologies and literature on the protection of DC networks, this paper tackles this problem by identifying key design characteristics of converters which influence their fault response. Using this information, the converters are classified based on their general fault characteristics, enabling potential protection issues and solutions to be readily identified. Finally, the paper discusses the potential for system level design benefits through the optimisation of converter topology and protection system design.

A number of promising technologies to perform ground movements without main engines are currently being researched. Notably, onboard ground propulsion systems have been proposed featuring electric motors in the landing gear. While such on-board systems will help save fuel and avoid emissions while on ground, they add significant weight to the aircraft, which has an impact on the performances in flight. A tool to assess the global benefits in terms of fuel consumption and emissions is presented in this work. A concept of an aircraft-integrated ground propulsion system is firstly considered and its performances and weights are determined, assuming the Auxiliary Power Unit or a zero-emission device like a fuel-cell as power source for the system. Afterwards, a model of the propulsion system integrated into an object-oriented, mid-sized aircraft model is generated, capable of precisely simulating a whole aircraft mission.

The benefits of lithium battery systems lie within their high energy density (Wh/L) and high specific energy (Wh/kg). Manganese dioxide (MnO2) is an attractive active cathode material because of its high energy density and low material cost. Manganese dioxide is an intercalating compound for lithium that functions by solvating and desolvating lithium cations from the electrolyte in solid state. The lithium cations are deposited into the vacancies of the MnO2 cathode crystal structure. The objective of this effort focuses on the limited cycle life of rechargeable lithium manganese-based electrochemical systems, most importantly capacity fading of the cathode. These two characteristics are considered the major technology hurdles in rechargeable lithium battery technology.1, 2, 3, 4

The demands for high-performance power electronics systems are rapidly surpassing the power density, efficiency, and reliability limitations defined by the intrinsic properties of silicon (Si)-based semiconductors. The advantages of silicon carbide (SiC) are well known, including high temperature operation, high voltage blocking capability, high speed switching, and high energy efficiency. These advantages, however, are severely limited by conventional power packages, particularly at temperatures higher than 175°C and ≻100 kHz switching speeds. Here, APEI, Inc., presents the design process and testing data of its newly developed high performance HT-2000 SiC power module for extreme environment systems and applications.

Automated Fault Isolation of Intermittent Wiring/Conductive Path Systems Inside Weapons Replaceable Assemblies Wiring/conductive path faults inside Weapon Replaceable Assemblies (WRAs) that result in No Fault Found (NFF) or intermittent diagnosis are estimated to cost the DoD over $2B annually. To date there is no logistically supportable, standardized capability to reduce this annual cost. This report covers the development of this capability and its subsequent testing and fielding as a means to reduce this component repair costs. This new capability is called the Automated Wiring Test Set (AWTS) intermittent testing capability. To test the new capability, the F/A-18 APG-73 Radar Receiver (RR) chassis was selected due to its high repair cost and its #1 ranking as an avionics mission degrader for this type aircraft.

Aviation battery maintenance is continuing to evolve. Much recent effort has been devoted to battery redesign to totally maintenance free or non-maintainable batteries. These batteries are placed into service and replaced at predetermined intervals. Still, some batteries are failing before their scheduled replacement period. For this reason attention is being focused on methods to transition batteries to an on-condition maintenance status. Nickel-Cadmium (NiCd) and Valve Regulated Lead-Acid (VRLA) are used to start engines, provide emergency back-up power, and assure ground power capability for maintenance and pre-flight checkout. Various Lithium-based battery chemistries are also now being developed and considered for use in these applications. As these functions are mission essential, State of Health (SoH) recognition is critical. SoH includes information regarding battery energy, power and residual cycle life.