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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.

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.

Electrical and mechanical failures (such as bearing, winding and rotating-diode failures) combine to cause premature failures of the generators, which become a flight safety issue forcing the crew to land as soon as practical. Currently, diagnostic / prognostic technologies are not implemented for aircraft generators where repairs are time-consuming and costly. This paper presents the development of feature extraction and diagnostic algorithms to 1) differentiate between these failure modes and normal aircraft operational modes; and 2) determine the degree of damage of a generator. Electrical signature analysis (ESA) based time-domain features were developed to distinguish between healthy and degraded generators while taking into account their operating conditions. Frequency-domain based ESA techniques are used to identify the degraded components within the generators.

The H-1 Upgrades Program is an Acquisition Category 1D Program executing an Engineering and Manufacturing Development contract with Bell Helicopter Textron Inc. The Upgrades Program will take the existing UH-1N and AH-1W helicopter airframes and provide a common 4-bladed rotor and drive system, a new main transmission, 4-bladed tail rotor, and many changes designed to bring the two airframes into as identical a configuration as possible. The aircraft will also receive integrated cockpits as a part of the modification. The program recently passed its Preliminary Design Review. This paper will discuss some of the program rationale and background information and focus on the advantages of the IPT process in general, and specifically as it relates to system safety.

An onboard Acoustic Wiring Diagnostic System to monitor the health of aircraft wiring is under development by Innovative Dynamics Inc. The AWDS incorporates passive acoustic sensors to monitor wire chafing. The system operates continuously in-flight so that intermittent wiring fault conditions can be detected as they happen. Trend analysis data can be logged to enable pro-active maintenance prior to catastrophic failure. A key advantage of the in-situ system is to perform the inspection without removing or disconnecting the wiring. Acoustic signatures of representative aircraft wiring have been characterized under simulated damage conditions. Flight ready hardware and software have been developed and flight testing is underway on an H-53 helicopter. This paper will present the wire diagnostic approach, the AWDS flight instrumentation, and some representative lab test results.

More electric aircraft (MEA) architectures have increased in complexity leading to a demand for evaluating the dynamic stability of their advanced electrical power systems (EPS). The system interactions found therein are amplified due to the increasingly integrated subsystems and on-demand power requirements of the EPS. Specifically, dynamic electrical loads with high peak-to-average power ratings as well as regenerative power capabilities have created a major challenge in design, control, and integration of the EPS and its components. Therefore, there exists a need to develop a theoretical framework that is feasible and useful for the specification and analysis of the stability of complex, multi-source, multi-load, reconfigurable EPS applicable to modern architectures. This paper will review linear and nonlinear system stability analysis approaches applicable to a scalable representative EPS architecture with a focus on system stability evaluation during large-displacement events.

In the continuing effort to save Fleet Operations and Maintenance (O&M) costs, a united effort was launched to propose the replacement of the Nickel-Cadmium battery on the F-5 aircraft with a valve-regulated, sealed lead-acid battery. The Aging Aircraft IPT (AAIPT) at Naval Air Systems Command, Patuxent River (PAX River), Maryland presented the concept to the Value Engineering group at Defense Supply Center Richmond, Virginia and successfully obtained funding for this and other Aging Aircraft efforts. The AAIPT then approached the Propulsion and Power Division of Naval Air Systems Command (AIR-4.4.4.1) as the cognizant engineering activity over batteries. AIR-4.4.4.1 then requested the assistance of Crane Division of Naval Surface Warfare Center (NSWC Crane) to develop a test plan and a Memorandum of Agreement and to obtain flight test authority as well as conduct the flight test.

Future more electric aircraft (MEA) architectures that improve electrical power system's (EPS's) source and load utilization will require advance stability analysis capabilities. Systems are becoming more complex with bidirectional flows from power regeneration, multiple sources per channel and higher peak to average power ratios. Unknown load profiles with large transients complicate common stability analysis techniques. Advancements in analysis are critical for providing useful feedback to the system integrator and designers of multi-source, multi-load power systems. Overall, a framework for evaluating stability with large displacement events has been developed. Within this framework, voltage transient bounds are obtained by identifying the worst case load profile. The results can be used by system designers or integrators to provide specifications or limits to suppliers. Subsystem suppliers can test and evaluate their design prior to integration and hardware development.