Techno-economic, environment and risk analysis of an aircraft concept with turbo-electric distributed propulsion

The commercial aviation industry has always been driven by the need to grow and increase profitability. This has led to the evolution of aircraft from the early jets capable of carrying tens of passengers to current large airliners capable of carrying hundreds of passengers across the globe. Whilst these aircraft look superficially similar to their predecessors, they are significantly more efficient, thanks to the continuous evolution of technology. However, new aircraft are bound to increasingly stricter targets that aim to develop an environmentally sustainable industry for the future. Previous technological development has largely focused on reducing fuel consumption through iterative improvements. However, new emissions and noise targets have been set that necessitate dramatic leaps in technology. To achieve these goals, revolutionary technologies are the subject of research in the aerospace sector. Research focus predominantly focuses on proving the technological viability of these novel concepts. The aim is generally to ensure that concepts are feasible and capable of meeting performance targets. However, commercial aviation is a profit-oriented industry. It is therefore vital to ensure that concepts are economically as well as environmentally sustainable. This form of study is more rarely seen but is vital in ensuring that aviation remains both environmentally and economically sustainable. This research presents the development of a techno-economic and environmental risk assessment (TERA) framework that combines the performance and economic aspects of an aircraft in order to inform a conclusion as to the aircraft’s viability. The methodology addresses two key questions. How can an operator differentiate competing concepts when they are designed for similar performance targets? How can the economic viability of a novel aircraft concept be predicted when there is no historical data on which cost estimates can be based? The research focuses on a case study of NASA’s N3-X, a blended wing body aircraft concept with a turbo-electric distributed propulsion system and boundary layer ingestion. In order to quantify economic viablity, it was first necessary to identify the performance benefits offered by the novel aircraft configuration. Modelling methodologies were therefore developed to simulate novel propulsion systems that utilise boundary layer ingestion and distributed propulsion. In particular, a methodology was developed to address a gap in literature with respect to simulating the off-design performance of such propulsion systems. Performance simulation demonstrates that the aircraft is able to meet the 60% fuel saving target versus the baseline aircraft for the design mission. The high fuel saving of the N3-X in comparison to the baseline aircraft has the potential to provide direct operating cost saving of up to 21% versus the baseline aircraft. This enables the manufacturer to offer the aircraft at a higher acquisition price, whilst retaining an attractive product for customers. Economic viability of the aircraft is more limited for short haul mission ranges, as fuel is a less dominant factor for the aircraft’s direct operating cost. Acquisition cost estimation suggests that the aircraft could achieve the cost target for an economically viable aircraft. This cost estimate is associated with a reasonable number of aircraft sales that could feasibly be supported by the future aircraft market for large widebodies. However, viability is closely tied to the economic environment, especially factors such as the current fuel price or environmental taxation levels. In particular, low fuel price reduces the financial value of high efficiency technology, and hence the maximumeconomical viable price of the aircraft is lower. The research also performs a design space exploration for the case study aircraft. This included the assessment of liquid hydrogen as an alternative to conventional kerosene and the exploration of alternative configurations for the propulsion system. As the final stage of the TERA analysis of the aircraft, a risk assessment was also performed to identify those technologies and factors that may have the greatest influence over the aircraft’s viability. The methods developed in this research open up a wide range of activities for further work in both the performance and techno-economic aspects of the research. Further design space exploration is possible, particularly with respect to the propulsion system design. In addition, the TERA framework may be used to assess alternative novel aircraft concepts to identify aircraft and technology combinations that may benefit most from further investment

Installed performance assessment of a boundary layer ingesting distributed propulsion system at design point

Boundary layer ingesting systems have been proposed as a concept with great potential for reducing the fuel consumption of conventional propulsion systems and the overall drag of an aircraft. These studies have indicated that if the aerodynamic and efficiency losses were minimised, the propulsion system demonstrated substantial power consumption benefits in comparison to equivalent propulsion systems operating in free stream flow. Previously assessed analytical methods for BLI simulation have been from an uninstalled perspective. This research will present the formulation of an rapid analytical method for preliminary design studies which evaluates the installed performance of a boundary layer ingesting system. The method uses boundary layer theory and one dimensional gas dynamics to assess the performance of an integrated system. The method was applied to a case study of the distributed propulsor array of a blended wing body aircraft. There was particular focus on assessment how local flow characteristics influence the performance of individual propulsors and the propulsion system as a whole. The application of the model show that the spanwise flow variation has a significant impact on the performance of the array as a whole. A clear optimum design point is identified which minimises the power consumption for an array with a fixed configuration and net propulsive force requirement. In addition, the sensitivity of the system to distortion related losses is determined and a point is identi ed where a conventional free-stream propulsor is the lower power option. Power saving coefficient for the configurations considered is estimated to lie in the region of 15%

Installed performance assessment of an array of distributed propulsors ingesting boundary layer flow

Conventional propulsion systems are typically represented as uninstalled system to suit the simple separation between airframe and engine in a podded configuration. However, boundary layer ingesting systems are inherently integrated, and require a different perspective for performance analysis. Simulations of boundary layer ingesting propulsions systems must represent the change in inlet flow characteristics which result from different local flow conditions. In addition, a suitable accounting system is required to split the airframe forces from the propulsion system forces. The research assesses the performance of a conceptual vehicle which applies a boundary layer ingesting propulsion system - NASA's N3-X blended wing body aircraft - as a case study. The performance of the aircraft's distributed propulsor array is assessed using a performance method which accounts for installation terms resulting from the boundary layer ingesting nature of the system. A `thrust split' option is considered which splits the source of thrust between the aircraft's main turbojet engines and the distributed propulsor array. An optimum thrust split for a specific fuel consumption at design point is found to occur for a thrust split value of 94.1%. In comparison, the optimum thrust split with respect to fuel consumption for the design 7500 nmi mission is found to be 93.6%, leading to a 1.5% fuel saving for the configuration considered

Performance assessment of a boundary layer ingesting distributed propulsion system at off-design

As research on boundary layer ingesting aircraft concepts progresses, it becomes important to develop methods that may be used to model such propulsion systems not only at design point, but also over the full ight envelope. This research presents a methodology and framework for simulating the performance of boundary layer ingesting propulsion systems at o -design conditions. The method is intended for use as a preliminary design tool that may be used to explore the design space and identify design challenges or potential optimum con gurations. The method presented in this research enables the rapid analysis of novel BLI con gurations at a preliminary design stage. The method was applied to a case study of NASA's N3-X aircraft, a blended wing body concept with a distributed propulsor array ingesting the airframe boundary layer. The performance of two propulsor in the array was compare, one at the airframe centreline and one at the extreme edge of the array. Due to di erence in ow conditions, the centreline propulsor was shown to be more e cient at o -design than the end propulsor. However, this di erence in e ciency disappeared at sea level static where the boundary layer thickness is negligible and mass ow ratio is high. Di erence in thrust produce by the two propulsors was instead due their di erent sizes. Performance of the propulsor array as a whole was also presented both independently and including a link to a pair of turbogenerators to provide power. At o design, it was found that there was a discrepancy between the maximum power available from the turbogenerators at o -design operating points and that demanded by the propulsor array operating at 100% fan rotational speed. This discrepancy means that the propulsor array's performance is limited by the turbogenerators at o -design, particularly for low speed, low altitude operation

Method for simulating the performance of a boundary layer ingesting propulsion system at design and off-design

Boundary layer ingestion has emerged as a potential propulsion concept on novel aircraft configurations for the future. As these concepts progress, preliminary design tools are required that enable the simulation of these aircraft and the rapid analysis of multiple configurations. Simulation tools for boundary layer ingesting propulsion systems tend to focus on proving performance benefits at design point. However, the simulation of aircraft configurations that utilise boundary layer ingestion requires a method to simulate the propulsion system at a range of flight conditions other than design point. A tool is therefore required to enable simulations at off-design. This research presents a work flow to simulate a boundary layer ingesting propulsion system at design and off-design. The process is intended as a tool for design space exploration and the rapid analysis of concepts at the conceptualisation phase. Boundary layer calculations have been combined with conventional 1-D gas turbine performance methods to predict performance of a propulsion system at design point. This method is then extended to enable simulations at off-design conditions for a range of flight conditions or propulsion system power settings. The formulation provides a thrust-drag representation that supports conventional aircraft simulation tools. A case study of an aircraft configuration which utilises an array of boundary layer ingesting propulsors is used to demonstrate the process. The performance of individual propulsors in the array is compared at off-design. Simulations found that, although each propulsor was sized for the same propulsive force at design point, off-design performance diverged depending on operating conditions. In addition, the performance of the propulsor array as a whole was predicted as a function of altitude and Mach number. The case study is used to draw general conclusions on the performance characteristics of a boundary layer ingesting propulsor

Assessment of an energy-efficient aircraft concept from a techno-economic perspective

An increase in environmental awareness in both the aviation industry and the wider global setting has led to large bodies of research dedicated to developing more sustainable technology with a lower environmental impact and lower energy usage. The goal of reducing environmental impact has necessitated research into revolutionary new technologies that have the potential to be significantly more energy efficient than their predecessors. However, for innovative technologies in any industry, there is a risk that adoption will be prohibitively expensive for commercial application. It is therefore important to model the economic factors of the new technology or policy at an early stage of development. This research demonstrates the application of a Techno-economic Environmental Risk Assessment framework that may be used to identify the economic impact of an energy-efficient aircraft concept and the impact that environmental policy would have on the viability of the concept. The framework has been applied to a case study aircraft designed to achieve an energy saving of 60% in comparison to a baseline 2005 entry-into-service aircraft. The model compares the green aircraft concept to a baseline conventional aircraft using a sensitivity analysis of the aircraft direct operating cost to changes in acquisition and maintenance cost. The research illustrates an economically viable region for the technology. Cost margins are identified where the increase in operating cost due to expensive novel technology is counterbalanced by the reduction in cost resulting from low energy consumption. Viability was found to be closely linked to fuel price, with a low fuel price limiting the viability of energy-efficient aviation technology. In contrast, a change in environmental taxation policy was found to be beneficial, with the introduction of carbon taxation incentivising the use of an environmentally optimised aircraft

Economic viability assessment of NASA's blended wing body N3-X aircraft

Numerous novel aircraft concepts are under development that aim to achieve dramatic increases in efficiency and reductions in emissions in comparison to current aircraft. Research into these concepts typically focuses on performance aspects to establish whether the aircraft will be capable of meeting developmental goals. However, the final goal of such concepts is to progress to viable commercial products. Economic viability assessments are therefore an integral part of the development process to ensure a sustainable industry. The key question to address is whether a high efficiency aircraft concept can translate into an attractive product from an economic perspective. This research performed an economic viability assessment of NASA's N3-X aircraft, a blended wing body aircraft with a distributed boundary layer ingesting propulsion system. The sensitivity of the aircraft's direct operating cost to changes in acquisition price and maintenance cost was predicted to establish maximum cost margins for the aircraft. In a May 2017 fuel price scenario, the N3-X could be no more than 25% more expensive than the baseline aircraft to remain economically viable. Introducing a carbon tax or fuel price jump widens the margin for increased costs. Aircraft cost estimates for the aircraft predict an acquisition cost from 11{37% more expensive than the baseline. In combination with the direct operating cost sensitivity analysis, the N3-X is predicted to need to capture 30% of the aircraft market up to 2035