Abstract: Meeting NASA's N+3 goals requires a fundamental shift in approach to aircraft and engine design. Material and design improvements allow higher pressure and higher temperature core engines which improve the thermal efficiency. Propulsive efficiency, the other half of the overall efficiency equation, however, is largely determined by the fan pressure ratio (FPR). Lower FPR increases propulsive efficiency, but also dramatically reduces fan shaft speed through the combination of larger diameter fans and reduced fan tip speed limits. The result is that below an FPR of 1.5 the maximum fan shaft speed makes direct drive turbines problematic. However, it is the low pressure ratio fans that allow the improvement in propulsive efficiency which, along with improvements in thermal efficiency in the core, contributes strongly to meeting the N+3 goals for fuel burn reduction. The lower fan exhaust velocities resulting from lower FPRs are also key to meeting the aircraft noise goals. Adding a gear box to the standard turbofan engine allows acceptable turbine speeds to be maintained. However, development of a 50,000+ hp gearbox required by fans in a large twin engine transport aircraft presents an extreme technical challenge, therefore another approach is needed. This paper presents a propulsion system which transmits power from the turbine to the fan electrically rather than mechanically. Recent and anticipated advances in high temperature superconducting generators, motors, and power lines offer the possibility that such devices can be used to transmit turbine power in aircraft without an excessive weight penalty. Moving to such a power transmission system does more than provide better matching between fan and turbine shaft speeds. The relative ease with which electrical power can be distributed throughout the aircraft opens up numerous other possibilities for new aircraft and propulsion configurations and modes of operation. This paper discusses a number of these new possibilities. The Boeing N2 hybrid-wing-body (HWB) is used as a baseline aircraft for this study. The two pylon mounted conventional turbofans are replaced by two wing-tip mounted turboshaft engines, each driving a superconducting generator. Both generators feed a common electrical bus which distributes power to an array of superconducting motor-driven fans in a continuous nacelle centered along the trailing edge of the upper surface of the wing-body. A key finding was that traditional inlet performance methodology has to be modified when most of the air entering the inlet is boundary layer air. A very thorough and detailed propulsion/airframe integration (PAI) analysis is required at the very beginning of the design process since embedded engine inlet performance must be based on conditions at the inlet lip rather than freestream conditions. Examination of a range of fan pressure ratios yielded a minimum Thrust-specific-fuel-consumption (TSFC) at the aerodynamic design point of the vehicle (31,000 ft /Mach 0.8) between 1.3 and 1.35 FPR. We deduced that this was due to the higher pressure losses prior to the fan inlet as well as higher losses in the 2-D inlets and nozzles. This FPR is likely to be higher than the FPR that yields a minimum TSFC in a pylon mounted engine. 1

Abstract: It has been known for some time that some microorganisms can swim faster in high-viscosity gel-forming polymer solutions. These gel-like media come to mimic highly viscous heterogeneous environment that these microorganisms encounter in-vivo. The qualitative explanation of this phenomena first offered by Berg and Turner [Nature (London) 278, 349 (1979)], suggests that propulsion enhancement is a result of flagellum pushing on quasi-rigid loose polymer network formed in some polymer solutions. Inspired by these observations, inertia-less propulsion in a heterogeneous viscous medium composed of sparse array of stationary obstacles embedded into a incompressible Newtonian liquid is considered. It is demonstrated that for prescribed propulsion gaits, including propagating surface distortions and rotating helical filament, the propulsion speed is enhanced when compared to swimming in purely viscous solvent. It is also shown that the locomotion in heterogenous viscous media is characterized by improved hydrodynamic efficiency. The results of the rigorous numerical simulation of the rotating helical filament propelled through a random sparse array of stationary obstructions are in close agreement with predictions of the proposed resistive force theory based on effective media approximation.

Abstract: The propeller model and a model of the electric system, together with various optimization schemes, are used to design optimal propulsion systems for a mini unmanned aerial vehicle for various goals and under various constraints. Important design trends are presented, discussed, and explained. Although the first part of the investigation is based on typical characteristics of the electric system, the second part includes a sensitivity study of the influence of variations of these characteristics on the optimal system design.

Abstract: This paper documents a new integrating product that allows cross-over between simulation of aerodynamics, dynamic stability and control, structures, propulsion, and store separation. The Kestrel software product is an integrating product written in modular form with a Python infrastructure to allow growth to additional capabilities as needed. Computational efficiency will also be improved by targeting the next generation peta-flop architectures envisioned for the 2010+ timeframe. Kestrel is also targeted to the need of simulating multidisciplinary physics, such as fluid-structure interactions, inclusion of propulsion effects, moving control surfaces, and coupled flight control systems. The Kestrel software product is to address these needs for fixed-wing aircraft in flight regimes ranging from subsonic through supersonic flight, including maneuvers, multi-aircraft configurations, and operational conditions. Preliminary results of the F-16C with comparison to experiments are provided. Parallel scalability analysis of the initial version of Kestrel is also presented.

Abstract: Integrated full electric propulsion systems are being introduced across both civil and military marine sectors. Standard power system analysis packages cover electrical and electromagnetic components but have limited models of mechanical subsystems and their controllers. Hence, electromechanical system interactions between the prime movers, power network, and driven loads are poorly understood. This paper reviews available models of the propulsion drive system components: the power converter, motor, propeller, and ship. Due to the wide range of time constants in the system, reduced-order models of the power converter are required. A new model using state-averaged models of the inverter and a hybrid model of the rectifier is developed to give an effective solution combining accuracy with speed of simulation and an appropriate interface to the electrical network model. Simulation results for a typical ship maneuver are presented.

Abstract: This paper presents the analysis of pulse load operation on the health of a simplified electric ship power system. Two scenarios of the pulse load operation, with and without an energy storage system have been addressed. The energy storage used is a flywheel as it has a very fast time response in supplying high power demands. The health of the electric ship power system is monitored by observing key indicators in the components critical to the working such as the generator and propulsion motor. The time-domain simulation of two test cases is carried out in the PSCAD/EMTDC software platform. The results underscore the vital importance of the flywheel energy storage system in maintaining the stability of the ship power system in the event of pulse load operation.

Abstract: A brief review of both near-term and far-term platforms proposed for near-space operations is given. The primary focus of the paper is, however, a review of potential advanced propulsion systems for such long-duration near-space platforms. The basic requirements for near-space propulsion systems are defined. Low Reynolds number propellers, the current workhorse, are used as a baseline for comparison. Two broad classifications are identified as potential sources of force in near space: rarefied gas and electric propulsion. Radiometric force propulsion systems, the only candidate propulsion systems found in the open literature, suffer from both significant uncertainty in their underlying physics and from significant operational difficulties. Thermal transpiration propulsion systems were shown fundamentally incapable of providing the required performance. Air-breathing electric propulsion systems for long-duration near-space missions will be significantly different than their in-space counterparts with specific impulses likely under 100s. Electrohydrodynamics propulsion systems show some promise, but have thus far shown limited thrust efficiency at sea level operation, and the efficiency is only predicted to get lower at higher altitudes. The potential effects of systems based on breakthrough physics are also qualitatively discussed. All of the identified potential advanced propulsion concepts for long-duration near-space operations suffer from major technological challenges with significant advancements required for any of them to be viable.

Abstract: : During the early development stages of Hall thruster technology, plasma research and propulsion advancements centered primarily on 300 V, 1600 s specific impulse operation. Since the first thruster firing on a Soviet satellite in 1972, extensive investigations of the plasmadynamic discharge phenomena and operating characteristics progressed the propulsion concept to a high-level of performance suitable for a wide range of near-earth maneuvers and interplanetary missions. The expanded performance envelope is primarily a function of improvements in thruster lifetime, thermal margin, discharge stability, and power system capability. Advancements in the Hall thruster propulsion system have enabled a wider range of input parameters to the thruster, including the applied anode potential. Operation in the low discharge voltage regime is associated with a decline in total thruster efficiency. This dissertation is intended to investigate low voltage Hall thruster physics, identify dominant performance loss mechanisms, and determine the discharge characteristics that drive efficiency.

Abstract: Contra Rotating Open Rotor (CROR) propulsion systems have come back into focus as a possible economic and environmentally friendly powerplant for future transport aircraft. Having been widely applied to the simulations of single rotation propellers, the DLR CFD code TAU and the aeroacoustic analysis tool APSIM have been employed for the analysis of the complex aerodynamics and aeroacoustics of this type of aircraft propulsion system. In order to demonstrate the codes applicability to these types of simulations as well as to develop an understanding of the impact of configuration variations, a generic 8x8 and 10x8 pusher CROR powerplant are studied here at typical sea-level take-o conditions of M=0.2. The results allow for a detailed analysis of the aerodynamic interactions between the two rotors as well as the noise generation mechanisms, allowing for an improved understanding of interaction tone sources. In addition, the impact of the numerical approach to the aeroacoustic simulations on the results is studied with a focus on determining the importance of the quadrupole contributions.

Abstract: Predictive modelling of turbulent combustion is important for the development of air-breathing engines, internal combustion engines, furnaces and for power generation. Significant advances in modelling non-reactive turbulent flows are now possible with the development of large eddy simulation (LES), in which the large energetic scales of the flow are resolved on the grid while modelling the effects of the small scales. Here, we discuss the use of combustion LES in predictive modelling of propulsion applications such as gas turbine, ramjet and scramjet engines. The LES models used are described in some detail and are validated against laboratory data-of which results from two cases are presented. These validated LES models are then applied to an annular multi-burner gas turbine combustor and a simplified scramjet combustor, for which some additional experimental data are available. For these cases, good agreement with the available reference data is obtained, and the LES predictions are used to elucidate the flow physics in such devices to further enhance our knowledge of these propulsion systems. Particular attention is focused on the influence of the combustion chemistry, turbulence-chemistry interaction, self-ignition, flame holding burner-to-burner interactions and combustion oscillations.

Abstract: An electric sail is capable of guaranteeing the fulfilment of a class of trajectories that would be otherwise unfeasible through conventional propulsion systems. In particular, the aim of this paper is to analyze the electric sail capabilities of generating a class of displaced non-Keplerian orbits, useful for the observation of the Sun’s polar regions. These orbits are characterized through their physical parameters (orbital period and solar distance) and the spacecraft propulsion capabilities. A comparison with a solar sail is made to highlight which of the two systems is more convenient for a given mission scenario. The optimal (minimum time) transfer trajectories towards the displaced orbits are found with an indirect approach.

Abstract: Propeller design is a complex task that involves a variety of disciplines such as: aerodynamics, structural analysis, and acoustics. A new method of designing an optimal propeller which is based on a MDO (Multidisciplinary Design Optimization) approach is presented. By combining various analysis tools with an optimization tool, a powerful and flexible design method is obtained. During the design process three different optimization schemes are used, leading the design to its optimal goal. This new method is applied for the design of a propeller for an Ultralight aircraft. Several optional designs for different design goals are presented. The results of the new method are compared with results of the classical design method, based on Betz's condition, which considers only the aerodynamic performance of the propeller. The importance of addressing the characteristics of the entire air-vehicle, its aerodynamic characteristics and its propulsion system (engine, gear box, etc.), rather than only the isolated propeller, is emphasized.

Abstract: A novel twelve-stator-pole, twenty-two-rotor-pole (12/22) outer-rotor permanent-magnet flux-switching (PMFS) machine for electric propulsion in a lightweight electric vehicle is presented. Analytical equations are derived for the dimensioning of a 3-phase 5kW in-wheel motor. Optimisation techniques are employed to maximise the performance of the machine. The validity of the analytical equations is verified by finite element analysis (FEA). The results show that the PMFS machine combines the key advantages of the PM machines and the switched reluctance machine, and thus demonstrate the viability of the proposed machine as a suitable candidate for in-wheel electric propulsion.

Abstract: The article discusses the usage of electric plasma engines in spacecraft. The engines' application of electric and electromagnetic fields to plasma clouds in order to create thrust is described. The prediction that future electric plasma engines will be able to propel spacecraft to greater speeds for the same amount of propellant as conventional chemical fuel-burning rockets is also noted. INSETS: Chemical vs. Electric Rockets;EARLY HISTORY OF ELECTRIC ROCKETS;The Proven Plasma Propulsion Workhorse;The Latest Plasma Engine Contender

Abstract: The goal of the European project muFly is to build a fully autonomous micro helicopter, which is comparable to a small bird in size and mass. The rigorous size and mass constraints infer various problems related to energy efficiency, flight stability and overall system design. In this research, aerodynamics and flight dynamics are investigated experimentally to gather information for the design of the helicopter's propulsion group and steering system. Several test benches are designed and built for these investigations. A coaxial rotor test bench is used to measure the thrust and drag torque of different rotor blade designs. The effects of cyclic pitching of the swash plate and the passive stabilizer bar are studied on a test bench measuring rotor forces and moments with a 6---axis force sensor. The gathered knowledge is used to design a first prototype of the muFly helicopter. The prototype is described in terms of rotor configuration, structure, actuator and sensor selection according to the project demands, and a first version of the helicopter is shown. As a safety measure for the flight tests and to analyze the helicopter dynamics, a 6DoF vehicle test bench for tethered helicopter flight is used.

Abstract: Energy efficiency of propulsion systems for cars, trucks and construction machineries has become one of the most important topics in today’s mobile system design, mainly because of increased fuel c ...

Abstract: A series hydraulic hybrid concept (SHHV) has been explored as a potential pathway to an ultra-efficient city vehicle. Intended markets would be congested metropolitan areas, particularly in developing countries. The target fuel economy was ~100 mpg or 2.4 l/100km in city driving. Such an ambitious target requires multiple measures, i.e. low mass, favorable aerodynamics and ultra-efficient powertrain. The series hydraulic hybrid powertrain has been designed and analyzed for the selected light and aerodynamic platform with the expectation that (i) series configuration will maximize opportunities for regeneration and optimization of engine operation, (ii) inherent high power density of hydraulic propulsion and storage components will yield small, lowcost components, and (iii) high efficiency and high power limits for accumulator charging/discharging will enable very effective regeneration. The simulation study focused on the SHHV supervisory control development, to address the challenge of the low storage capacity of the accumulator. Two approaches were pursued, i.e. the thermostatic SOC control, and Stochastic Dynamic Programming for horizon optimization. The stochastic dynamic programming was setup using a set of naturalistic driving schedules, recorded in normal traffic. The analysis included additional degree of freedom, as the engine power demand was split into two variables, namely engine torque and speed. The results represent a significant departure from the conventional wisdom of operating the engine near its “sweet spot” and indicate what is preferred from the system stand-point. Predicted fuel economy over the EPA city schedule is ~93 mpg with engine idling, and ~110 mpg with engine shutdowns.

Abstract: Marine propulsion systems have become increasingly electromechanical in recent years. Proposed systems show increasing torque density in an effort to reduce volume and weight. A magnetic gear is proposed to reduce the size of the propulsion motor and achieve similar torque amplification provided by a mechanical gearbox, without the maintenance and breakdown issues. A magnetic gearbox, of the concentric planetary type, will be studied for the high-torque low-speed requirements of a marine propulsion system. Torque ripple is investigated across multiple models to determine acceptable torque transfer performance.

Abstract: Full scale measurements of the propulsion power, ship speed, wind speed and direction, sea and air temperature from four different loading conditions, together with hind cast data of wind and sea properties; and noon report data has been used to train an Artificial Neural Network for prediction of propulsion power. The model was optimized using a double cross validation procedure. The network was able to predict the propulsion power with accuracy between 0.8-1.7% using onboard measurement system data and 7% from manually acquired noon reports.

Abstract: Damaged aircraft have occasionally had to rely solely on thrust to maneuver as a consequence of losing hydraulic power needed to operate flight control surfaces. The lack of successful landings in these cases inspired research into more effective methods of utilizing propulsion-only control. That research demonstrated that one of the major contributors to the difficulty in landing is the slow response of the engines as compared to using traditional flight control. To address this, research is being conducted into ways of making the engine more responsive under emergency conditions. This can be achieved by relaxing controller limits, adjusting schedules, and/or redesigning the regulators to increase bandwidth. Any of these methods can enable faster response at the potential expense of engine life and increased likelihood of stall. However, an example sensitivity analysis revealed a complex interaction of the limits and the difficulty in predicting the way to achieve the fastest response. The sensitivity analysis was performed on a realistic engine model, and demonstrated that significantly faster engine response can be achieved compared to standard Bill of Material control. However, the example indicates the need for an intelligent approach to controller limit adjustment in order for the potential to be fulfilled.

Abstract: A thrust estimation scheme for marine propellers that can operate in the full four-quadrant range of the propeller shaft speed and the vessel speed has been developed. The scheme is formed by a nonlinear observer to estimate the propeller torque and the propeller shaft speed and by a mapping to compute the thrust from the observer estimates. The mapping includes the estimation of the propeller advance ratio. The advance speed is assumed to be unknown, and only measurements of shaft speed and motor torque have been used. The robustness of the scheme is demonstrated by Lyapunov theory. The proposed method is experimentally tested on an electrically driven fixed pitch propeller in open-water conditions, in waves and with a wake screen that scales the local flow down in order to simulate one of the effects of the interaction between the propeller and the vessel hull.

Abstract: We model an electronic differential that will offer the best vehicle stability on a curved road The proposed traction system consists of two permanent magnet synchronous (PMS) machines that ensure the drive of two back-driving wheels The contribution of each wheel to the advance of the vehicle is represented by an element conveying the accumulation of mechanical coupling The proposed control structure is based on the direct torque fuzzy control for each wheel-motor Different simulations have been carried out: vehicle driven ons straight road, vehicle driven on straight road with slope, and vehicle driven over a road curved left and right The simulation results show good vehicle stability on a curved road

Abstract: Dramatic improvements have occurred since the large AC synchronous - wound field - conventionally cooled motors went to sea on Queen Elizabeth 2, podded propulsion motors not even having been discussed. Electric propulsion motors have become smaller, better and more affordable. Electric propulsion motor drives have followed a similar trend. Subsequent improvements, in both naval and commercial ships, are almost certainly going to be implemented using the systems and technologies which offer the best Life-Cycle Cost benefits; thus ocean-going ships, including naval combatants, will continue to most affordably transport either cargo or a military mission capability.

Abstract: Publisher Summary Gas turbines have dominated warship propulsion for many years but their potential remains to be fully realized in the commercial shipping sector. Breakthroughs in container ships, a small gas carrier and the Baltic ferry Finnjet during the 1970s promised a deeper penetration that was then thwarted by the rise in bunker prices and the success of diesel engine designers in raising specific power outputs and enhancing heavy fuel burning capability. A new generation of marine gas turbine—superseding designs with roots in the 1960s—may eventually benefit from the massive investment in aero engine R&D over the past decade, strengthening competitiveness in commercial vessel propulsion, particularly as more stringent emission limits favour the adoption of very low sulfur-content distillate fuels. Optimizing the combination of low-power manoeuvring and high power operation is accomplished in many naval applications by using a combined diesel or gas turbine propulsion system (CODOG). Combined-cycle gas turbine and steam turbine electric (COGES) plants embrace gensets driven by gas and steam turbines. Waste heat recovery boilers exploit the gas turbine exhaust and produce superheated steam (at around 30 bar) for the steam turbine genset. Significant progress has been made in enhancing the thermal efficiency of simple-cycle gas turbines for ship propulsion over the years, R&D seeking to improve part-load economy and reduce the fuel cost penalty compared with diesel engines. Subsequent advances—design refinements, new materials and cooling techniques, and the appropriate matching of higher compressor pressure ratios—have resulted in some large simple-cycle turbines achieving efficiencies of over 40 per cent. Marine gas turbines are available only in specific sizes and ratings, unlike a given diesel engine design which can cover a wide power range with different in-line and V-cylinder configurations. A power rating at particular ambient conditions determines the internal engine temperatures and the resulting expected service life of components exposed to these temperatures. These “hot section” components include the combustor and the HP turbine blades and vanes. The life of the hot section components will determine the interval between major maintenance actions, resulting in an estimated average maintenance cost.

Abstract: Most UAS propulsion systems currently utilize either Internal Combustion Engines (ICE) or Electric Motor (EM) prime movers. ICE are favoured for aircraft use due to the superior energy density of fuel compared to batteries required for EM, however EM have several significant advantages. A major advantage of EM is that they are inherently self starting have predictable response characteristics and well developed electronic control systems. EMs are thus very easy to adapt to automatic control, whereas ICE have more complex control response and an auxiliary starting motor is required for automated starting. This paper presents a technique for determining the performance, feasibility and effectiveness of powerplant hybridisation for small UAS. A Hybrid Powerplant offers the possibility of a radical improvement in the autonomy of the aircraft for various tasks without sacrificing payload range or endurance capability. In this work a prototype Aircraft Hybrid Powerplant (AHP) was designed, constructed and tested. It is shown that an additional 35% continuous thrust power can be supplied from the hybrid system with an overall weight penalty of 5%, for a given UAS. Dynamometer and windtunnel results were obtained to validate theoretical propulsion load curves. Using measured powerplant data and an assumed baseline airframe performance characteristic, theoretical endurance comparisons between hybrid and non-hybrid powerplants were determined. A flight dynamic model for the AHP was developed and validated for the purposes of operational scenario analysis. Through this simulation it is shown that climb rates can be improved by 56% and endurance increased by 13%. The advantages of implementing a hybrid powerplant have been baselined in terms of payload range and endurance. Having satisfied these parameters, a whole new set of operational possibilities arises which cannot be performed by non-self-starting ICE only powered aircraft. A variety of autonomous robotic aircraft tasks enabled by the hybrid powerplant is discussed.