Electrified aircraft propulsion (EAP) systems hold potential for the reduction of aircraft fuel burn, emissions, and noise. Currently, NASA and other organizations are actively working to identify and mature technologies necessary to bring EAP designs to reality. This paper specifically focuses on the envisioned control technology challenges associated with EAP designs that include gas turbine technology. Topics discussed include analytical tools for the dynamic modeling and analysis of EAP systems, and control design strategies at the propulsion and component levels. This includes integrated supervisory control facilitating the coordinated operation of turbine and electrical components, control strategies that seek to minimize fuel consumption and lessen the challenges associated with thermal management, and dynamic control to ensure engine operability during system transients. These dynamic control strategies include innovative control approaches that either extract or supply power to engine shafts dependent upon operating phase, which may improve performance and reduced gas turbine engine weight. Finally, a discussion of control architecture design considerations to help alleviate the propulsion/aircraft integration and certification challenges associated with EAP systems is provided.

Propulsion diagnostic method evaluation strategy (ProDiMES) offers an aircraft engine diagnostic benchmark problem where the performance of candidate diagnostic methods is evaluated while a fair comparison can be established. In the present paper, the performance evaluation of a number of gas turbine diagnostic methods using the ProDiMES software is presented. All diagnostic methods presented here were developed at the Laboratory of Thermal Turbomachinery of the National Technical University of Athens (LTT/NTUA). Component, sensor, and actuator fault scenarios that occur in a fleet of deteriorated twin-spool turbofan engines are considered. The performance of each diagnostic method is presented through the evaluation metrics introduced in the ProDiMES software. Remarks about each methods performance as well as the detectability and classification rates of each fault scenario are made.

A purposeful approach has been taken to match teaching pedagogies (techniques), learning experiences, and assessment methods to various types of students learning in undergraduate aerospace propulsion courses at the junior-level at the United States Air Force Academy (USAFA) and senior-level at Oklahoma State University (OSU), Stillwater, OK. Prior studies in the scholarship of teaching and learning have shown the benefits of matching assessment methods, as well as teaching pedagogies and learning experiences, to the types of students learning associated with desired educational outcomes. Literature suggests the best method for teaching and assessing student’ cognitive learning is through explanation and presentation. Oral assessments have been implemented at the Air Force Academy and Oklahoma State University to evaluate students' cognitive learning in undergraduate aerospace propulsion and power courses. An oral midterm exam was performed to assess students' acquisition knowledge and understanding of fundamental concepts, the type of learning occurring early in course lesson sequences. End-of-semester design project poster sessions and presentations served as summative oral assessments of students' creative thinking, decision making, and professional judgment. Conversely, two written midterm exams and a final exam primarily focused on assessing students' problem solving skills and less on comprehensive knowledge. Oral assessments also served as reflective thinking experiences that reinforced student learning. Student feedback on oral assessment methods was collected through surveys conducted after each assessment. Survey results not only revealed the effectiveness of using oral assessments but also on how to improve their design and implementation, including the use of information technology (IT) and broader curricular employment.

A general, dynamical approach developed a high-fidelity, finite element model of a pulse detonation engine (PDE). The approach deconvolved the structural response due to cyclic acceleration that would be measured by a load cell, thereby obtaining the actual thrust that is produced. The model was excited with pressure pulses that simulated actual detonation pressure characteristics at different frequencies. A two-step process was developed. In the first step, the system dynamics was established and validated by deconvolving from a known input in the form of pressure pulses from which the reconstructed thrust output was obtained. The second step required that the deconvolved thrust be compensated for system acceleration. This step required the effective mass and induced acceleration to be determined which then yielded an inertial load that has to be removed from the reconstructed thrust to obtain the actual thrust. The compensated thrust values were expressed in the form of specific impulse for the PDE which compared well with a priori pulsed thrust loading.

This paper aims to present an integrated rotorcraft (RC) multidisciplinary simulation framework, deployed for the comprehensive assessment of combined RC–powerplant systems at mission level. The proposed methodology comprises a wide-range of individual modeling theories applicable to RC performance and flight dynamics, as well as the gas turbine engine performance. The overall methodology has been deployed to conduct a preliminary tradeoff study for a reference simple cycle (SC) and conceptual regenerative twin-engine-light (TEL) and twin-engine-medium (TEM) RC configurations, modeled after the Airbus Helicopters Bo105 and Aérospatiale SA330 models, simulated under the representative mission scenarios. The installed engines corresponding to both reference RC are notionally modified by incorporating a heat exchanger (HE), enabling heat transfer between the exhaust gas and the compressor delivery air to the combustion chamber. This process of preheating the compressor delivery air prior to combustion chamber leads to a lower fuel input requirements compared to the reference SC engine. The benefits arising from the adoption of the on-board HE are first presented by conducting part-load performance analysis against the reference SC engine. The acquired results suggest substantial reduction in specific fuel consumption (SFC) for a major part of the operating power range with respect to both RC configurations. The study is further extended to quantify mission fuel burn (MFB) saving limit by conducting an extensive HE tradeoff analyses at mission level. The optimum fuel burn saving limit resulting from the incorporation of on-board HEs is identified within realistically defined missions, corresponding to modern RC operations. The acquired results from the mission analyses tradeoff study suggest that the suboptimum regenerated RC configurations are capable of achieving significant reduction in MFB, while simultaneously maintaining the respective airworthiness requirements in terms of one-engine-inoperative. The proposed methodology can effectively be regarded as an enabling technology for the comprehensive assessment of conventional and conceptual RC–powerplant systems at mission level.

Recent technology reviews have identified the need for objective assessments of aircraft engine health management (EHM) technologies. To help address this issue, a gas path diagnostic benchmark problem has been created and made publicly available. This software tool, referred to as the Propulsion Diagnostic Method Evaluation Strategy (ProDiMES), has been constructed based on feedback provided by the aircraft EHM community. It provides a standard benchmark problem enabling users to develop, evaluate, and compare diagnostic methods. This paper will present an overview of ProDiMES along with a description of four gas path diagnostic methods developed and applied to the problem. These methods, which include analytical and empirical diagnostic techniques, will be described and associated blind-test-case metric results will be presented and compared. Lessons learned along with recommendations for improving the public benchmarking processes will also be presented and discussed.

Progress in the development of electrical storage and conversion technology progressively attains focus in aerospace motive power research. Novel propulsion system concepts based on hybrid or even entirely electrical energy sources are seriously considered for aircraft design. To this point, unified figures of merit are required in order to allow for consistent comparative investigations of existing combustion engines and future electrically-based propulsion systems. Firstly, this paper identifies the shortcomings of conventional performance metrics used for nonthermal electrical conversion processes and then approaches exergy-based loss methods as means of metrics extensions. Subsequently, energy source-independent figures of merit based on exergy analysis are derived and embedded into the well-known performance definitions. Finally, the unified metrics are demonstrated through application to a conventional turbofan, a parallel-hybrid turbofan, a novel integrated-hybrid turbofan concept, and an entirely electrical fan concept.

Air/gas foil bearings (AFB) have shown a promise in high-speed micro to mid-sized turbomachinery. Compared to rolling element bearings, AFBs do not require oil lubrication circuits and seals, allowing the system to be less complicated and more environment-friendly. Due to the smaller number of parts required to support the rotor and no lubrication/seal system, AFBs provide compact solution to oil-free turbomachinery development.While foil bearing technology is mature in small industrial machines and power generation turbines, its application to aero-propulsion systems has been prohibited due to the reliability issues relevant to unique aero-propulsion environments such as severe rubbing due to the very slow acceleration of typically heavy rotors. This paper presents a hybrid air foil bearing (a combination of hydrostatic and hydrodynamic) with 102 mm in diameter designed for aero-propulsion applications, and preliminary test results on start-stop friction characteristics and thermal behavior at low speeds below 10,000 rpm are presented. The bearing could withstand 1000 start/stop cycles with 6 rev/s2 acceleration under a static load of 356 N (43.4 kPa).

This paper presents the results of a fundamental, comprehensive, and rigorous analytical and computational examination of the performance of the Brayton propulsion and power cycle employing real air as the working fluid. This approach capitalizes on the benefits inherent in closed cycle thermodynamic reasoning and the behavior of the thermally perfect gas to facilitate analysis. The analysis uses a high fidelity correlation to represent the specific heat at constant pressure of air as a function of temperature and the polytropic efficiency to evaluate the overall efficiency of the adiabatic compression and expansion processes. The analytical results are algebraic, transparent, and easily manipulated, and the computational results present a useful guidance for designers and users. The operating range of design parameters considered covers any current and foreseeable application. The results include some important comparisons with more simplified conventional analyses.

A hardware-in-the-loop simulation of a three-shaft gas turbine engine for ship propulsion was established. This system is composed of computers, actual hardware, measuring instruments, interfaces between actual hardware and computers, and a network for communication, as well as the relevant software, including mathematical models of the gas turbine engine. “Hardware-in-the-loop” and “volume inertia effects” are the two innovative features of this simulation system. In comparison to traditional methods for gas turbine simulation, the new simulation platform can be implemented in real time and also can test the physical hardware’s performance through their integration with the mathematical simulation model. A fuel control strategy for a three-shaft gas turbine engine, which can meet the requirement to the acceleration time and not exceeding surge line, was developed using this platform.

This paper describes a test program designed to assess the suitability of a TF40-based gas turbine generator set (genset) for use in the Advanced Hull Form Inshore Demonstrator (AHFID). An overall description of the test program and its objectives is given. Test results are presented. The relevance of the test to the greater program goal of demonstrating the viability of rim-driven propulsion technology is discussed. The genset demonstration test was successfully completed in 2003. The package performed as designed and met all test objectives.

From an operational availability stand point, the U.S. Navy is interested in the short term reliability of its ship based LM2500 gas turbine engines. That is the likelihood that an engine will operate successfully through a six-month deployment (usually 1500 to 2000 operational hours). From a maintenance and cost of ownership standpoint both the short-term and long-term reliability are of concern. Long-term reliability is a measure in time (in operating hours) between engine removals. To address these requirements U.S. Navy Fleet support maintenance activities employ a system of tests and evaluations to determine the likelihood that an LM2500 will meet its short and long-term goals. The lowest level inspection is the predeployment inspection, which attempts to identify primarily mechanical faults with the engine. Gas Turbine Bulletin inspections are used to determine if predefined wear out modes exists. Performance evaluations can be performed which determine the ability of the LM2500 and its control system to meet expected power requirements. Lube oil system data can be analyzed to determine if excessive leakage or excessive scavenge temperatures exist. Engine vibration characteristics can be reviewed to identify the source of both synchronous and nonsynchronous vibration and determine if corrective measures need to be taken. This paper will discuss how the lowest level inspections feed the more sophisticated analysis and how these inspections and evaluations work to provide a systematic method of insuring both short and long-term LM2500 reliability.

The Royal Navy (RN) has in-service experience of both marinized industrial and aero derivative propulsion gas turbines since the late 1940s. Operating through a Memorandum of Understanding (MOU) between the British, Dutch, French, and Belgian Navies the current in-service propulsion engines are marinized versions of the Rolls Royce Tyne, Olympus, and Spey aero engines. Future gas turbine engines, for the Royal Navy, are expected to be the WR21 (24.5 MW), a 5 to 8 MW engine and a 1 to 2 MW engine in support of the All Electric Ship Project. This paper will detail why the Royal Navy chose gas turbines as prime movers for warships and how Original Equipment Manufacturers (OEM) guidance has been evaluated and developed in order to extend engine life. It will examine how the fleet of engines has historically been provisioned for and how a modular engine concept has allowed less support provisioning. The paper will detail the planned utilization of advanced cycle gas turbines with their inherent higher thermal efficiency and environmental compliance and the case for all electric propulsion utilizing high speed gas turbine alternators. It will examine the need for greater reliability/availability allowing single generator operation at sea and how by using a family of 3 engines a nearly flat Specific Fuel Consumption (SFC) down to harbour loads can be achieved. [S0742-4795(00)01203-5]

This paper addresses the motivations for using a distributed control system architecture, technical challenges, typical functions which are off-loaded to remote terminals, sensor/effector interface issues, data bus selection, technology insertion issues, lessons learned, and objectives for future distributed control implementations. Typical design requirements, constraints, environmental conditions, and operational challenges will be described. Examples of various distributed control system implementations will be discussed, including both propulsion control and flight control examples.

Technology assessments during the 1980s projected the development of advanced military fighter aircraft that would require propulsion systems that could accommodate multimission capability with super maneuverability. These propulsion systems would be required to provide significantly improved thrust to weight, reduced thrust specific fuel consumption, and up and away thrust vectoring capabilities. Digital electronic control systems with significantly expanded capabilities would be required to handle these multifunction control actuation systems, to integrate them with flight control systems, and to provide fail-operational capability. This paper will discuss the challenges that were presented to propulsion system control designers, the innovation of technology to address these challenges, and the transition of that technology to production readiness. Technology advancements will be discussed in the area of digital electronic control capability and packaging, advanced fuel management systems, high pressure fuel hydraulic actuation systems for multifunction nozzles, integrated flight propulsion controls, and higher-order language software development tools. Each of these areas provided unique opportunities where technology development programs and flight prototyping carried concepts to reality.

Storable hydrocarbon fuels that undergo endothermic reaction provide an attractive heat sink for future high-speed aircraft. An investigation was conducted to explore the endothermic potential of practical fuels, with inexpensive and readily available catalysts, under operating conditions simulative of high-speed flight applications. High heat sink capacities and desirable reaction products have been demonstrated for n -heptane and Norpar 12 fuels using zeolite catalysts in coated-tube reactor configurations. The effects of fuel composition and operating condition on extent of fuel conversion, product composition, and the corresponding endotherm have been examined. The results obtained in this study provide a basis for catalytic-reactor/heat-exchanger design and analysis.

Fast vessels are being built and operated for a large range of passenger-carrying applications. Fast cargo-carrying vessels are being considered in a variety of sizes as well. A major decision in design and construction of these vessels is the propulsion system; this decision has major impacts on the operation economics as well as the operational capabilities of the vessels. Factors involved in consideration of propulsion alternatives for fast vessels are examined, with emphasis upon the total life cycle operating implications of these factors. A methodology for considering the factors is suggested, and an example is presented with results of the consideration tradeoffs.

The TF40B Gas Turbine Test Facility is the only dedicated Landing Craft, Air Cushion main propulsion engine test complex available to the U.S. Navy. This facility, located at the Naval Surface Warfare Center, Carderock Division (NSWCCD) in Philadelphia, PA, began operation in August, 1992. Since then, the test engine has logged approximately 230 starts and 350 operating hours. This paper will present the installation, testing, and lessons learned of the TF40B test facility. The installation section will discuss the modifications made to the existing test facility to accept the TF40B engine. The test section will include the Foreign Object Damage (FOD) screen evaluation, both on-line and crank wash detergent fluid evaluations, cold weather fuel testing, engine vent line testing and Aerojet 5 oil evaluation. The lessons learned section will include problems related to the electric starter, waterbrake, inlet and exhaust systems, data acquisition system, instrumentation control panel, and the test cell equipment arrangement.

The U.S. Navy is developing an Intercooled Recuperated (ICR) marine gas turbine, designated the WR-21, for propulsion of future surface ships. The objectives of this development program and the key technical requirements are summarized. The design of the WR-21 is described in considerable detail. Meeting all the design requirements for performance, space, weight, reliability, maintainability, and life has been challenging. Numerous design tradeoffs and iterations have been performed to optimize the design within the constraints imposed in the ICR technical specification. Integration of the WR-21 engine into the DDG51 Flight IIA ship, which is the U.S. Navy’s first application, has influenced the WR-21 design. This paper discusses the aspects of the DDG-51 application that were factored into the design of the ICR engine in order to reduce installation costs.