This paper provides a high-level review of the potential failure modes and hazards to which electrified aircraft propulsion (EAP) systems are susceptible, along with potential gas turbine control-based strategies to assist in the mitigation of those failures. To introduce the types of failures that an EAP system may experience, a generic EAP system is considered, consisting of gas turbine engines, mechanical drives, electric machines, power electronics and distribution systems, energy storage devices, and motor driven propulsors. The functionality provided by each of these EAP subsystems is discussed, along with their potential failure modes, and possible strategies for mitigating those failures. To further illustrate the role of gas turbine controls in mitigating EAP failure modes, an example based on a simulated EAP concept aircraft proposed by NASA is given. The effects of failures are discussed, along with turbomachinery control strategies, including reversionary control modes, and control limit logic.

Following the successful development of aircraft jet engines during World War II (WWII), the United States Navy began exploring the advantages of gas turbine engines for ship and boat propulsion. Early development soon focused on aircraft derivative (aero derivative) gas turbines for use in the United States Navy (USN) Fleet rather than engines developed specifically for marine and industrial applications due to poor results from a few of the early marine and industrial developments. Some of the new commercial jet engine powered aircraft that had emerged at the time were the Boeing 707 and the Douglas DC-8. It was from these early aircraft engine successes (both commercial and military) that engine cores such as the JT4-FT4 and others became available for USN ship and boat programs. The task of adapting the jet engine to the marine environment turned out to be a substantial task because USN ships were operated in a completely different environment than that of aircraft which caused different forms of turbine corrosion than that seen in aircraft jet engines. Furthermore, shipboard engines were expected to perform tens of thousands of hours before overhaul compared with a few thousand hours mean time between overhaul usually experienced in aircraft applications. To address the concerns of shipboard applications, standards were created for marine gas turbine shipboard qualification and installation. One of those standards was the development of a USN Standard Day for gas turbines. This paper addresses the topic of a Navy Standard Day as it relates to the introduction of marine gas turbines into the United States Navy Fleet and why it differs from other rating approaches. Lastly, this paper will address examples of issues encountered with early requirements and whether current requirements for the Navy Standard Day should be changed. Concerning other rating approaches, the paper will also address the issue of using an International Organization for Standardization, that is, an International Standard Day. It is important to address an ISO STD DAY because many original equipment manufacturers and commercial operators prefer to rate their aero derivative gas turbines based on an ISO STD DAY with no losses. The argument is that the ISO approach fully utilizes the power capability of the engine. This paper will discuss the advantages and disadvantages of the ISO STD DAY approach and how the USN STD DAY approach has benefitted the USN. For the future, with the advance of engine controllers and electronics, utilizing some of the features of an ISO STD DAY approach may be possible while maintaining the advantages of the USN STD DAY.

Active magnetic bearings (AMBs) have the well-documented advantage of reduced operational power losses when compared to conventional fluid-film bearings; however, they have yet to be widely adopted in industry due to the high initial costs of manufacturing and supporting power electronics. As AMBs look to become more cost competitive in more widely based applications, permanent magnet biased designs seek to reduce both the operating electrical power losses and the power electronic hardware costs while maintaining normal load and maximum load capacities. In these new designs, permanent magnet components are used to provide the necessary bias magnetic flux in the bearing usually provided by an electrical bias current in traditional all electromagnetic AMB designs. By eliminating electrical bias currents, operating electrical power losses can be significantly reduced while allowing for smaller, cheaper electronic components. This paper provides a comparison of the performance of permanent magnet biased thrust and radial bearing designs with conventional, all electromagnetic bearing designs. The thrust bearings are designed with nominal and maximum load capacities of 1,333 N and 4,000 N, while the radial bearings are designed with nominal and maximum load capacities of 1,000 N and 3,000 N. The shaft diameter is considered to be 70 mm for all bearings. Finite element modeling is used to calculate load capacities and operating electrical power requirements. Power requirements for a number of loads ranging from nominal to maximum capacity are presented for the permanent magnet biased and all electromagnetic bearing designs. A significant reduction in electrical power requirements under maximum load conditions is shown in the permanent magnet biased designs. This reduction is further magnified under nominal load conditions. Additionally, the number of pole wire turns and maximum wire currents are adjusted to realize even greater electrical power losses. The required bias magnetic flux can be generated with reduced wire currents by increasing the number of wire turns. While reducing wire currents also reduces electrical power requirements, the increase in wire turns increases the circuit induction. This increase in induction decreases the bearing slew rate and, in turn, the bandwidth. This study looks at a number of wire turns and current combinations. Tradeoffs between reduced electrical power losses and bearing bandwidth are presented and discussed. The permanent magnet biased AMB designs are shown to significantly reduce electrical power losses having the potential to improve overall machine efficiency. Implications of adopting this technology to both operating and manufacturing costs are discussed. The use of permanent magnets in AMBs is shown to make the costs of these systems more competitive with oil lubricated bearings when compared to conventional AMB designs.

The More Electric Aircraft (MEA) is a system architecture concept for the aircraft that reduces fuel consumption and environmental load while improving safety, reliability, and maintainability. MEA architecture replaces some of the conventional hydraulic and/or mechanical control system with electric motor-driven system, integrates system power management into the aircraft/engine controls, and optimizes the aircraft geometry by flexibly arranging the accessory devices. The primary challenge to realize the MEA concept is how to manage the heat from these additional power electronic devices. The authors’ group proposed novel cooling system, the Autonomous Air-Cooling System (AACS) which cools the power electronics of the motor devices distributed in the aircraft. In AACS, each power electronic device (e.g. motor controller) is air-cooled by heat sinks connected to compact blowers. This system is very simple and efficient since it re-uses the cabin air and needs no additional coolant. One of the key technologies which realize AACS is an efficient heat sink. In this study, at first the performance evaluation targeting a single-aisle 180-seater aircraft was performed. In the analysis, a plate-fin heat sink was adopted, and the pressure loss and heat transfer was estimated by using empirical correlations. In the analysis, the value of heat generation was assumed from power demand for each operation condition, and the required mass flow rate of cooling air was calculated so as for the enclosure temperature of the power electronics to be 80°C which was the allowable maximum temperature of the motor controller. The effect of the fin geometry on the cooling performance was also examined by varying the geometric parameters (fin height, thickness, and spacing). In order to further enhance the cooling performance without increasing the pressure loss, the water-mist injection to the cooling air flow was adopted and its effect was analytically confirmed. In addition, the effectiveness of the water-mist injection on the cooling performance was verified by performing experiments for a plate-fin heat sink manufactured by a wire electric discharge method.

Following three decades of research in short duration facilities, Purdue University has developed an alternative turbine facility in view of the modern technology in computational fluid mechanics, structural analysis, manufacturing, heating, control and electronics. The proposed turbine facility can perform both short transients and long duration tests, suited for precise heat flux, efficiency and optical measurement techniques to advance turbine aero-thermo-structural engineering. The facility has two different test sections, linear and annular, to service both fundamental and applied research. The linear test section is completely transparent for visible spectra, aimed at TRL 1 and 2. The annular test section was designed with optical access to perform proof of concepts as well as validation of turbine components at the relevant non-dimensional parameters in small engine cores, TRL 3 to 4. The large mass flow (28 kg/s) combined with a minimum hub radius to tip radius of 0.85 allows high spatial resolution. The Reynolds (Re) number extends from 60,000 to 3,000,000, based on the vane outlet flow with an axial chord of 0.06 m and a turning angle of 72 deg. The pressure ratio can be independently adjusted, allowing for testing from low subsonic to Mach 3.2. To ensure that the thermal boundary layer is fully developed the test duration can range from milliseconds to minutes. The manuscript provides a detailed description of the sequential design methodology from zero-dimensional to three-dimensional unsteady analysis as well as of the measurement techniques available in this turbine facility.

The growing environmental impacts and dwindling supply of conventional fuels have led to the development of more efficient and clean energy systems. Micro gas turbines (mGT) have emerged as energy conversion technology, which offer promising features like high fuel flexibility, low emissions level, and efficient cogeneration of heat and power (CHP). Numerical simulation is a vital tool to predict the off-design performance of mGT cycles, and it also helps in cycle optimization. Starting from a model available at Ansaldo Energia, for steady state simulation of mGT T100 cycles based on user requirements, within the cooperation between University of Genova (Unige) and Ansaldo Energia, a new more comprehensive simulation tool has been developed through the incorporation of additional components, features, and involving a more detailed mathematical approach. The most important upgrades involved a number of different air path flows and the power electronics, which takes into account the power consumption from auxiliary components as well as the generator and inverter efficiencies. Once the model has been verified against the existing tools, it was used in real operating conditions at the Ansaldo Energia test rig. The mGT performance has been assessed for different power levels, starting from 100 kW (nominal power) to 60 kW and then back to 100 kW, with 10 kW steps. The two tests at 100 kW operating conditions have been carried out with two different ambient temperatures: 20°C and 25°C, respectively. Data have been acquired under stable operating conditions, considering the recuperator cold outlet temperature as the stability indicator. Finally the new model AE-T100 has been used also for diagnosis of the whole mGT cycle. The model has been successfully applied to a special mGT equipped with an on-purpose damaged recuperator, identifying the causes of performance degradation.

The control and limiting of gas turbine speed and temperature is most readily achieved with an electronic fuel control system. The control system to be described is practical hardware for vehicular applications. The same basic electronics used with a suitable choice of fuel metering valve and choice of actuator for whatever means of torque transfer is employed, provide proper control for a turbine of any horsepower rating using liquid or gaseous fuels. Minor modification in the electronics can adapt the control for generator sets and other industrial applications.

A low-drag, low-power magnetic bearing and a permanent magnet brushless d-c motor-generator have been developed for a satellite flywheel. These will be combined with a terrestrial flywheel and control electronics to make up a flywheel energy storage and conversion system for use in a stand-alone solar photovoltaic residence. Technical and economic performance analyses indicate that, contrary to general thought, a flywheel system will be competitive if not superior to more conventional systems utilizing either present-day or advanced batteries. This derives from the ability of the flywheel to perform the functions of d-c to a-c inversion and optimal impedance matching between the PV arrays and the load in addition to providing energy storage. The motor-generator design will also be discussed. This paper describes the structural topology, performance data, design parameters, and test measurements of the magnetic bearing and motor-generator as well as a description of the flywheel and control electronics to be used. A preliminary discussion of the economic aspects is also included.

Flow data taken directly from turbomachine rotors are valuable, but the instrumentation problems are difficult. Information must be transferred from high-speed rotors, and the measurements require miniature transducers that can operate in high-acceleration environments. Recent advances in electronics, particularly in integrated circuitry, have permitted the design of miniature radio-telemetry systems for the transmission of data from rotors to stationary measurement equipment. Measurements are obtained without physical contact with the rotor, eliminating a principal problem. The present paper describes the design of a six-channel telemetry system for on-rotor research in turbomachinery.

Electronic controls are being used on more gas turbine engines today than ever before. Part of this has been due to the proven capability of electronics, and part has been due to the increasingly complex tasks that controls have been required to perform. Unfortunately, for industrial gas turbines, there has been little coordination between the various aspects of the total system: control, sequencing, monitoring, and annunciation. This paper describes a control system which has integrated all those functions into a hierarchical system that is both powerful and reliable. The key elements of the system are a microprocessor controlled programmable sequencer and a proven modular analog control system. A gas pipeline application will be explored in detail.

In the U.K. full-authority digital controls are now being successfully demonstrated on military aero-engines following some years of practical research into suitable configurations for this class of power plant. For the case of Civil aero-engines the appropriate configuration of systems that will enter service from the mid-1980’s has been the subject of much debate between engine/airframe manufacturers and the principal accessory suppliers. This paper discusses the major features that will be embodied in these new systems, particular reference being made to: System tasks and performance requirements; configuration; life cycle costing; electronics design and system interfacing; and reliability and integrity.

This paper discusses the Ultra Electronic Controls Fault Identification Moduel (F.I.M.) as used in the Electronic Engine Control Unit (E.C.U.) for the Olympus 593 engines of the Concorde Supersonic Transport Aircraft. This is based on a C.M.O.S. Microprocessor for low power consumption and enables the Module to be applied to existing units without redesign of power supplies. The Module examines the outputs of existing fault monitoring circuits and compares these with software defined reference levels. It then determines from this and other signals taken from the E.C.U. safety consolidation circuits, the Engine Control Sub-System which is at fault. This Module has been in service with British Airways and Air France for close to one year now and the impact on rapid and accurate fault diagnosis, elimination of premature E.C.U. removals and thus reduction of cost ownership of the E.C.U. is discussed.

The advent of large scale integration techniques into electronics has had a dramatic effect on the technology of engine control systems and accompanying this change has been the wider use of digital computational techniques to replace functions previously performed in analogue electronic technology and even by mechanical means. The industry has thereby benefited by smaller and more powerful electronic control systems but at the same time had to deal with costly and potentially difficult to manage technologies associated with the generation of software appropriate for these controllers.

Many exciting opportunities to enhance aircraft performance, cost and reliability/availability are rapidly becoming available to the propulsion system designer, with use of digital electronics, information/sensor sharing between airframe systems, and integrated functional designs for propulsion and aircraft flight controls. The propulsion engineer must become an active participant in this area to take full advantage of the advanced technology. In this endeavor, he is faced with the task, which seems to occur all so frequently in a rapidly advancing technology age, of developing new working tools and approaches not normally part of the propulsion engineers experience. A discussion is presented of some key technologies available to the propulsion designer, such as digital electronics, serial data buses, analytical redundancy and avionics standards. Analytical tools in computational fluid flow analysis and modern control theories are reviewed. These tools can be utilized to provide the analytical understanding of the flow characteristics of the propulsion system and to develop the optimal control laws for multivariable, integrated control systems. A design methodology for integrating the propulsion control system with the aircraft controls and avionics systems is presented. The required simulation facilities necessary for the development and checkout of integrated systems are described with examples of their use in advanced research projects.

The new series of turbofan engines use advanced technology features which enhance their attractiveness through reductions in the cost of ownership, noise, and pollution. Improvements in aerodynamics, mechanics, electronics, and materials technology reduce the cost of ownership via such factors as cost, reliability, durability, and operability. Primarily, advanced technology addresses fuel consumption, a parameter with a very large effect on direct operating cost. In addition, these advances do not trade convenience of operation for environmental acceptability. The advanced technology concepts used in the new commercial aircraft turbine engines offer both economic and environmental benefits.

In the field of today’s military aircraft engines, the engine control system consists in most cases of hydromechanical controls, as such, with an electronic supervisory system. This type of control makes the integration of engine and aircraft systems rather difficult. Even with the Tornado engine which features a full authority electronic engine controller, only initial steps in systems integration are realized. With the introduction of digital electronics into both the engine control and the aircraft systems, together with the availability of data highway systems, large scale systems integration can be envisaged on future fighter aircraft, with the resultant improvement in overall weapon system performance. This paper puts forward a proposal for a control concept for a reheated fighter engine, and outlines possibilities for integration with aircraft systems.

The Garrett GTCP36-300 Series Auxiliary Power Unit is being developed for use on advanced technology transport aircraft in the 150-passenger size class. The first application will be the Airbus Industries A320 Aircraft. The APU uses a 6:1 pressure ratio, single-stage compressor and turbine, driving a single-stage load compressor and accessory gearbox. The 480 horsepower APU delivers compressed air to the aircraft pneumatic system and drives a customer furnished 90 kva, 24,000 rpm electrical generator. State-of-the-art aerodynamics, materials, and digital electronics are used to give the user-airlines an APU delivering maximum performance with minimum envelope, weight, and cost of ownership.

Rotating component measurements in a combustion turbine continues to be a most difficult instrumentation problem. Measurements in the turbine high temperature environment makes the problem even more challenging. This paper presents an approach in overcoming the difficulties of acquiring accurate stress data from turbine blades during full load operation. Through the application of existing electronics, which were adapted for these special hostile conditions, a reliable telemetry technique for obtaining dynamic strain gage data of combustion turbine blading is demonstrated.

This paper describes the development of a portable data acquisition system for use in a plant-wide, predictive maintenance program for rotating machinery. Designed to replace hand-logging and other clipboard surveillance methods, the portable instrument stores the measured parameters in digital memory for transfer to a desktop host computer for processing and analysis. Developments in electronics and computer technology as well as preventive/predictive maintenance procedures have made this instrument system possible. These developments are outlined, along with a discussion of the operation and use of the system.

The use of coal and coal-derived fuels in combustion gas turbines is being aggressively pursued. Contaminants in these fuels can lead to various detrimental effects to the turbine including increased pressure drops, altered gas flow patterns, and the potential for surging. An instrument has been developed to provide a real-time measure of the loading of particles entrained in the products of combustion of these fuels. The unit is a self-compensating, two color transmissometer which measures the obscuration of a laser beam due to the scattering of light by particles along the path of the beam. The transmissometer consists of, a HeNe laser (632.8 nm) and a HeCd laser (441.6 nm), detectors, and data acquisition/control electronics. Utilizing windows appropriately placed in the products of combustion stream, the transmissometer has a time resolution of about 1 second and a sensitivity of about 0.1 percent.