Turboelectric Distributed Propulsion Research Articles

Feasibility Study on Copper-Clad Lithium Conductors for Cryogenic Applications

The trend towards efficient turbo-electric distributed propulsion aircraft calls for more research concerning lightweight power distribution and power conversion, especially in the context of cryogenic power systems. This paper explores one such avenue in this context – the prospect of manufacturing and using copper-clad lithium (CuCLi) wires at cryogenic conditions for aircraft and high frequency applications – and compares it to Yttrium Barium Copper Oxide (YBCO) coated superconductors. Lithium, a lightweight and inexpensive metal, exhibits superior conductivity per unit weight characteristics compared to copper, aluminum, and other metals at cryogenic temperatures. While the metal always remains in its resistive hence lossy state, it is unlikely to reach the same current densities as superconductors. On the other hand, copper-clad lithium wires are expected to be less expensive, are round, and can be manufactured at long lengths and in large quantities. In this paper, the relevant electric parameters of these wires, such as current carrying capability and power losses, are estimated and compared to those of superconductors. The paper also includes a brief study of the manufacturing method of proposed copper-clad lithium wires.

Design Factors of High-Speed Turbo-Electric Distributed Propulsion System

Turbo-electric Distributed Propulsion (TeDP) is a promising concept to achieve the operational goals of more electric aircraft. The application of TeDP architecture can achieve the desired weight reduction of an aircraft power system. The use of a superconducting machine is expected to provide the workaround for the weight issue, but its current state of technology has not yet been extensively tested for aircraft applications. Another more practical option is to directly couple the aircraft's propeller system to a high-speed permanent magnet (PM) electrical machine, eliminating the gear part that also contributes to the total weight. A critical part of the design for a high-speed PM machine is choosing the optimum magnet configurations. This study used finite element modelling to analyze the impact of scaling the PM’s critical parameters on the weight and machine speed. A prototype testing of a 2-KW high-speed machine, suitable for a Remotely Piloted Aircraft System (RPAS), was developed and tested. The results confirmed the following critical parameters that should be carefully designed to achieve the optimum output, such as the (a) number of winding turns, (b) stack length, (c) sleeve thickness, and (d) terminal voltage.

Sizing of Superconducting Cables for Turbo-ElectricDistributed Propulsion Aircraft Using a Particle Swarm Optimization Approach

Superconducting electrical power systems are proposed to meet high specific power densities required for turbo-electric distributed propulsion aircraft. Superconducting materials have unique thermal and electrical requirements for maintaining the superconducting state, which is critical to their normal operation. Electrical system faults can lead to this state being lost for all network assets in the electrical fault path. The resulting temperature rise can prevent the superconducting state from being immediately resumed following fault clearance, requiring disconnection of nonfaulted equipment. Undersized cables experience a higher temperature rise under faulted conditions and disconnect from the system more readily. Oversized cables are heavier and more costly. Therefore, there is a need to optimize the cable size, preventing disconnection of equipment due to temperature rise following a fault while minimizing the weight and cost penalty. This article proposes a system parameter-driven methodology, using particle swarm optimization, to identify fault-tolerant cable designs, which deliver minimum through-life costs. This facilitates high-value, quantifiable design trade studies incorporating system parameters. Key observations drawn are that the choice between improving fault ride-through capability of a superconducting cable by increasing the amount of either superconducting material or conventional former material strongly depends on acceptable system operating temperature and voltage.

Design of a Brushless Doubly-Fed Machine for Aviation Electric Propulsion

This article discusses a high-speed brushless doubly-fed machine (BDFM) for aviation turboelectric distributed propulsion application. After a brief overview of the machine fundamentals and propulsion architecture, the electromagnetic properties of the newly designed BDFM are analyzed. An innovative rotor mechanical design is introduced, which allows for a significant increase of speed compared to legacy rotor designs. Experiments were conducted to verify the 12 000-r/min high-speed operation. The findings in this article will give prominence to the feasibility of applying BDFMs for aviation applications.

Effect of Endogenous Failure Events on the Survivability of Turboelectric Distributed Propulsion System

Recent advancements in aircraft electrification have led to the introduction of turboelectric distributed propulsion (TeDP). For instance, NASA's N3X airplane aims to curb jet fuel emissions with the aid of TeDP. However, it is crucial to analyze the survivability of the TeDP system during extreme conditions. The endogenous failure events are of specific interest as they were found to cause a significant number of accidents for commercial aircraft. While the distribution reconfiguration is necessary to meet the critical load demands under extreme failure events, it can also create a transient overload condition in the turboshaft engine. The power system survivability is further deteriorated in the presence of constant power loads. In this article, a mathematical analysis of the survivability of the system is presented to make the aircraft power system highly resilient to endogenous failure events. A power system collapse mitigation strategy is proposed by adding an energy storage system. Moreover, the analytical expressions are formulated to size the energy storage unit to prevent the system collapse. Various failure conditions are modeled using PSCAD/EMTDC to study the minimum energy storage required to prevent system collapse.

Key performance indicators for turboelectric distributed propulsion

PurposeRecent advancements in electrified transportation have been necessitated by the need to reduce environmentally harmful emissions. Accordingly, several aviation organisations and governments have introduced stringent emission reduction targets for 2050. One of the most promising technologies proposed for achieving these targets is turboelectric distributed propulsion (TeDP). The objective of this study was to explore and identify key indicators for enhancing the applicability of TeDP in air transportation.Design/methodology/approachAn enhancement valuation method was proposed to overcome the challenges associated with TeDP in terms of technological, economic and environmental impacts. The result indicators (RIs) were determined; the associated performance indicators (PIs) were analysed and the key RIs and PIs for TeDP were identified. Quantitative measurements were acquired from a simulated TeDP case study model to estimate the established key PIs.FindingsIt was determined that real-world TeDP efficiency could be enhanced by up to 8% by optimising the identified key PIs.Originality/valueThis study is the first to identify the key PIs of TeDP and to include a techno-economic environmental risk analysis (TERA) based on the identified key PIs. The findings could guide developers and researchers towards potential focus areas to realise the adoption of TeDP.

Development of a Turbo Electric Distribution System for Remotely Piloted Aircraft Systems

Turboelectric distributed propulsion systems are paving the way for more electric aircraft systems (TeDP). This type of system provides a solution for some of the drawbacks of current low-energy-density batteries, which limit the ability of long-endurance electric aircraft. However, turboelectric propulsion requires the use of advanced turboelectric motors, superconductive materials and cryogenic cooling technologies, which are still under development and may be in production in the near future. This paper investigates a turboelectric propulsion system that can be considered an initial step in the production of TeDP in a remotely piloted aircraft system with the use of existing technology. This is achieved by replacing the gear and the starter motor of a turboprop with a high-speed permanent magnet electric machine to generate electrical power and propelling the aircraft through a distributed electric propulsion system. In this theoretical study, an augmentation to Breguet’s range and endurance equation is developed. This study confirmed that the new system is 31% lighter than the turboprop engine. Then the effect of the weight savings is used in the distributed electric propulsion (DEP) aerodynamic studies and found that there is a drastic increase in the range for a TeDP developed with the high-speed machine.

Single Turboshaft Engine Failure Analysis of an Inner Bus Tie Architecture for Turboelectric Distributed Propulsion System

Single Turboshaft Engine Failure Analysis of an Inner Bus Tie Architecture for Turboelectric Distributed Propulsion System

Economic and environmental viability assessment of NASA’s turboelectric distribution propulsion

The concept of turboelectric-distributed propulsion (TeDP) has become integral to engineering because of its ability to generate electricity. However, social science compels careful evaluations of TeDP’s environmental and economic impacts—out of caution, such elements must be taken up before TeDP is put into practice. Responding to this call, this research investigates TeDP’s economic and environmental viability with a case study of the National Aeronautics and Space Administration’s (NASA) proposal for a TeDP aircraft, N3-X, using technical aspects and real data integration. The economic assessment measures NASA’s N3-X economic added value for aviation manufacturing, operations, and investors as well as net present value, internal rate of return, and payback period. Meanwhile, the environmental assessment looks at carbon monoxide and dioxide and oxides of nitrogen. The economic and environmental evaluation results establish the viability of TeDP.

Voltage-Based Current-Compensation Converter Control for Power Electronic Interfaced Distribution Networks in Future Aircraft

Superconductors have a potential application in future turboelectric distributed propulsion (TeDP) aircraft and present significant new challenges for protection system design. Electrical faults and cooling system failures can lead to temperature rises within a superconducting distribution network, which necessitates a reduction or temporary curtailment of current to loads to prevent thermal runaway occurring within the cables. This scenario is undesirable in TeDP aircraft applications where the loads may be flight-critical propulsion motors. This article proposes a power management and control method that exploits the fast-acting measurement and response capabilities of the power electronic interfaces within the distribution network to maximize current supply to critical loads, reducing the impact of a temperature rise event in the superconducting distribution network. This new algorithm uses the detection of a resistive voltage in combination with a model-based controller that estimates the operating temperature of the affected superconducting cable to adapt the output current limit of the associated power electronic converter. To demonstrate the effectiveness of this method and its impact on wider system stability, the algorithm is applied to a simulated voltage-source converter supplied aircraft dc superconducting distribution network with representative propulsion motor loads.

Assessment of the BWB aircraft for military transport

PurposeThe growth in air mobility, rising fuel prices and ambitious targets in emission reduction are some of the driving factors behind research towards more efficient aircraft. The purpose of this paper is to assess the application of a blended wing body (BWB) aircraft configuration with turbo-electric distributed propulsion in the military sector and to highlight the potential benefits that could be achieved for long-range and heavy payload applications.Design/methodology/approachMission performance has been simulated using a point-mass approach and an engine performance code (TURBOMATCH) for the propulsion system. Payload-range charts were created to compare the performance of a BWB aircraft with various different fuels against the existing Boeing 777-200LR as a baseline.FindingsWhen using kerosene, an increase in payload of 42 per cent was achieved but the use of liquefied natural gas enabled a 50 per cent payload increase over a design range of 7,500 NM. When liquid hydrogen (LH2) is used, the range may be limited to about 3,000 NM by the volume available for this low-density fuel, but the payload at this range could be increased by 137 per cent to 127,000 kg.Originality/valueThe results presented to estimate the extent to which the efficiency of military operations could be improved by making fewer trips to transport high-density and irregular cargo items and indicate how well the proposed alternatives would compare with present military aircraft. There are no existing NATO aircraft with such extended payload and range capacities. This paper, therefore, explores the potential of BWB aircraft with turbo-electric distributed propulsion as effective military transports.

Optimal Sizing and Control of Battery Energy Storage Systems for Hybrid Turboelectric Aircraft

<div class="section abstract"><div class="htmlview paragraph">Hybrid-electric gas turbine generators are considered a promising technology for more efficient and sustainable air transportation. The Ohio State University is leading the NASA University Leadership Initiative (ULI) <i>Electric Propulsion: Challenges and Opportunities</i>, focused on the design and demonstration of advanced components and systems to enable high-efficiency hybrid turboelectric powertrains in regional aircraft to be deployed in 2030. Within this large effort, the team is optimizing the design of the battery energy storage system (ESS) and, concurrently, developing a supervisory energy management strategy for the hybrid system to reduce fuel burn while mitigating the impact on the ESS life. In this paper, an energy-based model was developed to predict the performance of a battery-hybrid turboelectric distributed-propulsion (BHTeDP) regional jet. A study was conducted to elucidate the effects of ESS sizing and cell selection on the optimal power split between the turbogenerators (TGs) and ESS. To this extent, the supervisory energy management strategy is formulated into a discrete time optimal control problem and solved via dynamic programming. The performance of BHTeDP was compared to a turboelectric distributed-propulsion (TeDP) next-gen aircraft that assumes improvements in weight, drag, and engine efficiency consistent with regional jet entering operation in 2035.</div></div>

Aerodynamic Characteristics of Different Airfoils under Varied Turbulence Intensities at Low Reynolds Numbers

A numerical study was conducted on the influence of turbulence intensity and Reynolds number on the mean topology and transition characteristics of flow separation to provide better understanding of the unsteady jet flow of turboelectric distributed propulsion (TeDP) aircraft. By solving unsteady Reynolds averaged Navier-Stokes (URANS) equation based on C-type structural mesh and γ - Re ˜ θ t transition model, the aerodynamic characteristics of the NACA0012 airfoil at different turbulence intensities was calculated and compared with the experimental results, which verifies the reliability of the numerical method. Then, the effects of varied low Reynolds numbers and turbulence intensities on the aerodynamic performance of NACA0012 and SD7037 were investigated. The results show that higher turbulence intensity or Reynolds number leads to more stable airfoil aerodynamic performance, larger stalling angle, and earlier transition with a different mechanism. The generation and evolution of the laminar separation bubble (LSB) are closely related to Reynolds number, and it would change the effective shape of the airfoil, having a big influence on the airfoil’s aerodynamic characteristics. Compared with the symmetrical airfoil, the low-Reynolds-number airfoil can delay the occurrence of flow separation and produce more lift in the same conditions, which provides guidance for further airfoil design under TeDP jet flow.

Systems Evaluation of Subsonic Hybrid-Electric Propulsion Concepts for NASA N+3 Goals and Conceptual Aircraft Sizing

The air-travel demand is anticipated to grow in future and therefore the worldwide airtraffic is forecast to increase significantly. This growth in demand further increases the concerns pertaining to environmental and human health, which results in stringent aviation policies. Emission regulations have been set for the aviation sector to reduce its climate change impacts, and these support the efforts to meet the goals of the UN’s Paris treaty on climate change. The aviation sector is exploring sustainable and improved technologies to become more energy and cost efficient. Along these lines, NASA has developed the concept of ‘N+i’ goals to decrease fuel consumption, noise, and landing and take-off (LTO) oxides of nitrogen (NOx) emissions, and to enhance aircraft performance. The ‘N+3’ represents three technology generations into the future, where ‘N’ represents the current aircraft generation, with a forecasted technology readiness level 4-6, in year 2025 timeframe which will enable year 2035 service-entry. To meet NASA’s N+3 goals, significant improvements must be made in the air transportation system, airframe, mission design, and propulsion systems. A pivotal element to achieve these goals, is the propulsion system. This is because the role of propulsion system can be crucial in reducing emissions, noise, and fuel burn. This work evaluates the N+3 concepts in detail, based on the systems engineering approaches and selects the best of those concepts. A detailed analysis is presented for phase one of such a project using Georgia Institute of Technology’s Integrated Product-Process Development (IPPD) method. This work finds that the NASA N3-X turbo-electric distributed propulsion (TeDP) is the best concept for meeting the NASA N+3 goals, based on the systems engineering approach.

Method to Explore the Design Space of a Turbo-Electric Distributed Propulsion System

AbstractMeeting future goals for aircraft and air traffic system performance will require a fundamental shift in approach to aircraft and engine design. In 2005, the National Aeronautics and Space Administration (NASA) released plans of a next generation commercial airplane for 2030 combining the blended wing body (BWB) and a superconducting distributed propulsion system. The BWB concept adapts NASA’s cruise-efficient short take-off and landing (CESTOL) airframe. The propulsion system employs distributed electric fans, which are embedded on the upper surface of the airframe, driven by superconducting motors with power provided by two wing-tip mounted turboelectric generators. This paper describes a method to design a turboelectric distributed propulsion (TeDP) system on the hybrid wing body airframe, including a way to obtain the propulsor number and its weight, a method to simulate boundary layer ingestion, and a method to calculate electric system performances and its weight. An examination of the syste...

Comparison of Candidate Architectures for Future Distributed Propulsion Aircraft

Turbine-engine-driven distributed electrical aircraft power systems [also referred to as turboelectric distributed propulsion (TeDP)] are proposed for providing thrust for future aircraft with superconducting components operating at 77 K, in order for performance and emission targets to be met. The proposal of such systems presents a radical change from current state-of-the-art aeroelectrical power systems. Central to the development of such power systems are architecture design trades which must consider system functionality and performance, system robustness, and fault ridethrough capability, in addition to the balance between mass and efficiency. This paper presents a quantitative comparison of the three potential candidate architectures for TeDP electrical networks. This analysis provides the foundations for establishing the feasibility of these different architectures subject to design and operational constraints. The findings of this paper conclude that a purely ac synchronous network performs best in terms of mass and efficiency, but similar levels of functionality and controllability to an architecture with electrical decoupling via dc cannot readily be achieved. If power electronic converters with cryocoolers are found to be necessary for functionality and controllability purposes, then studies show that a significant increase in the efficiency of solid-state switching components is necessary to achieve specified aircraft performance targets.

Design point analysis of the turbofan-driven turboelectric distributed propulsion system with boundary layer ingestion

The performance benefits of boundary layer ingestion in the case of air vehicles powered by distributed propulsors have been documented and explored extensively by previous study. However, the increased inlet flow distortion and the system total weight would dramatically reduce the expected benefits. In this paper, a novel turboelectric distributed propulsion module on the N3-X airframe has been developed. It includes two direct-shaft-driven turbofans (each drives a free power turbine) and a propulsors array, and therefore both the direct-shaft-driven turbofan and the propulsors unit produce thrust. Secondly, a parametric and quasi two-dimensional study at component and at system level is carried out so that the effects of these two aerodynamic issues over the system performance can be assessed. The figure of merit in this study is the thrust-specific fuel consumption and the system parameters examined are: the thrust split between propulsors and engines, the capture height and the direct-shaft-driven turbofan parameters. Preliminary results found optimum configurations at around 60–90% thrust split ratio, when installation effects were neglected. The final value depends on the propulsor intake pressure loss and the bypass ratio of the propulsion system.

Propulsion Powertrain Simulator: Future turboelectric distributed-propulsion aircraft

The NASA Glenn Research Center, in collaboration with the aerospace industry and academia, has begun the development of technology for a future hybrid wing-body electric airplane with a turboelectric distributed-propulsion (TeDP) system. It is essential to design a subscale system to emulate the TeDP power grid, which would enable rapid analysis and demonstration of the proof-of-?concept of the TeDP electrical system. This article describes how small electrical machines with their controllers can mimic all the components in a TeDP powertrain.

Implications of distribution voltage configuration on TeDP electrical systems

Purpose – This article is aims to inform aircraft propulsion system designers of the implications which fundamental power distribution design assumptions have on the effectiveness and viability of turboelectric distributed propulsion (TeDP) systems. Improvements and challenges associated with selecting alternating or direct current for normal- and superconducting distribution systems are presented. Additionally, for superconducting systems, the benefits of bi-polar DC distribution are discussed, as well as the implications of operating voltage on the mass and efficiency of TeDP grid components. Design/methodology/approach – The approach to this paper selects several high-level fundamental configuration decisions, which must be made, and it qualitatively discusses potential implications of these decisions. Findings – Near term TeDP architectures which employ conventionally conducting systems may benefit from alternating current (AC) distribution concepts to eliminate the mass and losses associated with pow...

A Method for the Evaluation of the Effectiveness of Turboelectric Distributed Propulsion Power System Architectures

Radical new electrically propelled aircraft are being considered to meet strict future performance goals. One concept design proposed is a Turboelectric Distributed Propulsion (TeDP) aircraft that utilises a number of electrically driven propulsors. Such concepts place a new and significant reliance on an aircraft's electrical system for safe and efficient flight. Accordingly, in addition to providing certainty that supply reliability targets are being met, a contingency analysis, evaluating the probability of component failure within the electrical network and the impact of that failure upon the available thrust must also be undertaken for architecture designs. Solutions that meet specified thrust requirements at a minimum associated weight are desired as these will likely achieve the greatest performance against the proposed emissions targets. This paper presents a Fault Tree Analysis (FTA) based design approach for the electrical system and thrust reliability analysis of TeDP aircraft architectures. This approach extends beyond the single failure rate provided by traditional FTA methods by profiling the reliability and thrust provision of each possible system configuration (i.e. following the failure of one or more components), which combined with a measure of total system weight and volume provides an effective design capability. The paper presents a case study for a TeDP design configuration showing how Thrust - Reliability (TR) dispatch targets may be achieved using a contingency analysis method utilising k-out-of-n probability and concludes by discussing plans to build upon the described work and utilise the method for more complex studies.