For the greatest performance benefits, it is necessary to move away from conventional technol-ogy towards revolutionary concepts. The associated risk for revolutionary technoltechnol-ogy is high, as performance is based on projections. In addition, the economic risk is high as costs for novel technologies are almost entirely unknown. This leads to a corresponding risk that the technolo-gies will not be commercial viable and hence will not be adopted by the industry. The necessity for economical aircraft in combination with the high risk of novel technology lead towards the final pillar of the research: proving or predicting the economic benefits of novel concepts.
As a commercial product, economic considerations are a crucial component of the aircraft design process. Fuel cost contributes a significant amount to the operating cost of an aircraft and has been a key driver in aircraft development. However, there are other costs to consider, as fuel is only a percentage of overall costs. In addition, the concept should be viable for both the operator and the manufacturer. Naturally, the cost of both developing and manufacturing the aircraft technology will be key factors in a concept’s final economic viability as a commercial product. Costs should ideally be factored into the decision making process at a reasonably early stage. The general expectation is that 70-80% of program costs are committed at the early concept phase [69]. For example, fundamental decisions such as the size and capacity of an aircraft will fix a certain cost level for manufacture. A long-haul airliner will never cost the same as a light aircraft, if only because of the costs of material for an aircraft that is significantly larger. Once the preliminary design phase is complete, it can be more difficult to reverse design decisions that are later found to result in high costs of development or manufacture. In addition,
2. Literature Review
costs incurred by a manufacturer are relatively low in the preliminary phase. The best scope for mitigating or avoiding high costs in a new design is therefore at the preliminary concept phase.
Design optimisation can be used during the development of a new concept to ensure costs are kept low. However, there are generally conflicting goals for a commercial aircraft. An air-craft optimised for fuel consumption will be very different from an airair-craft optimised for flight time, noise, emissions, or life cycle costs [70]. Optimisation must therefore account for a num-ber of variables, meaning there is no perfect solution but there may instead be a selection of options that attempt to address conflicting design drivers and that weight each variable differ-ently [71]. It is important to highlight that viability is not only influenced by internal project costs, but also by external factors. An individual concept may therefore be optimised, but neverthe-less not be an attractive investment. Section 2.1 identified that fuel price has a dominant role in determining whether a concept will be attractive to potential customers. Competing options, both internally (i.e. a number of proposed concepts) and externally (from other manufacturers) will also influence viability. Other factors such as governmental policy and environmental tax-ation will play a role, in addition to factors such as airport infrastructure or whether there is a market that may be served by the new aircraft. These factors may lead to a concept that is less attractive to customers, regardless of its state of completion.
Goel and Rich [72] studied the incentives that drive the adoption of new innovations, using a sample set of US airlines. The main conclusion from the study was that more competition in the market led to a higher likelihood for new innovations to be adopted. The study highlighted the point that a significant operating cost difference between existing and new technology was an incentive for adoption. The greater the magnitude of difference, the higher the likelihood of adoption. The study highlights the importance of comparative frameworks in assessing the viability of the aircraft. A dominant factor in the adoption of new technology is whether the benefits offered outweigh the cost versus current technology.
Given all these factors, it is vital to have a framework for assessing the economic aspects of a design at the preliminary phase. This combines both technological aspects, in terms of the ability to meet performance targets such as fuel burn, emissions, or noise levels, and the economic viability, in terms of manufacturer and operator costs. This techno-economic perspective is then used to inform design decisions or determine viability.
A techno-economic and environmental risk assessment (TERA) framework has been used in numerous bodies of research at Cranfield University to assess concepts and policies includ-ing performance (aircraft and/or engine), economics, environmental impact, noise, emissions and cost in a modular framework [73]. This framework has been used on a number of research projects, including ULTIMATE (Ultra Low emission Technology Innovations for Mid-century Air-craft Turbine Engines) [74], LEMCOTEC (Low Emissions Core-Engine Technologies) [75], and DREAM (valiDation of Radical Engine Architecture systeMs) [76].
Rolt and Kyprianidis [77] performed a design space exploration of new engine core tech-nologies to rank and compare the specific fuel consumption and direct operating cost changes for each option. This was then used to identify the most promising technologies. The frame-work was also applied to the previously described propfan case by Nalianda et al. [78]. Two key unknown costs were identified for a novel technology: maintenance cost and acquisition price, and the sensitivity of operating cost to these unknowns was predicted. Fuel was identified as a key factor in determining viability, reinforcing the historical case of the propfan.
The TOSCA study (Technology Opportunities and Strategies towards Climate friendly trAns-port) presented a techno-economic analysis of various options for reducing CO2 emissions in Europe for two aircraft types [79]. The goal was to assess the technical, economic and societal issues of the technology, rather than performance aspects alone. The study identified both technologies and changes to operation that would achieve the best reductions in CO2
emis-sions and the oil price for which these options would be economically feasible.
Techno-economic perspectives can be used to assist in the decision-making process and when identifying the best combination of design variables and technologies. Mavris et al. pro-duced a number of studies that assess the impact of various technology options on an aircraft concept in order to determine economic viability [80]. Probability curves are included that ac-count for uncertainty in the design and are used to determine feasibility and the likelihood of a design reaching target design goals. Each technology infusion is presented as a ‘technology metric’, with a corresponding impact on performance and cost, amongst other factors. More recently, Burgaud et al. considers the different divisions in a manufacturer and their influence on an aircraft development program [81]. The study proposes a number of tools that can be used to compare and select different technology options for the ‘ideal solution’. The study focuses on the fact that the different divisions of a manufacturer should be able to make risk-aware decisions in an multi-objective environment with a high level of risk and uncertainty.
Techno-economics can also be used to help determine aviation policies that will encourage investment in an aviation concept. Dray et al. [82] used the Aviation Integrated Model (AIM) to perform a study on the CO2taxation level required to encourage operators to retire aircraft over 20 years old and to invest in new, more efficient aircraft. The study also included wider perspec-tive of the aviation industry by accounting for the influence of taxation on demand, fares, and fleet composition. The study highlights the interdependencies of different factors, as a change in policy or the introduction of new technology may have a wider ranging effect. The wider effect of technology infusion was also assessed in the study on the silent aircraft by Tam et al. [83].
The study predicted regional economic influence of the introduction of a low noise aircraft for both the aviation sector and the wider effects on the economy. In particular, a low noise aircraft was found to boost the local economy, suggesting there may be larger benefits to the introduc-tion of revoluintroduc-tionary aircraft technology. The study also assessed the costs for which the silent aircraft concept may be economically attractive to operator. In particular, the trade-off between purchase price and maintenance cost was identified. This perspective was used to identify where their novel aircraft was more or less attractive than alternative technologies. The study highlighted that policy decisions will influence profitability and that there is a wider context that may need to be considered in the course of developing a revolutionary aircraft. In particular, policy makers must consider the need to maintain a profitable and sustainable industry when setting taxation levels. The TERA study by Nalianda et al. [78] was also used to identify the taxation scenario that could be used to incentivise investment in a technology such as the prop-fan. In general, emissions taxation incentivises investment in more efficient technology where an operating cost benefit alone is not sufficient. However, the necessary taxation level may be high, which may unreasonably penalise the industry.
The studies presented here cover a range of perspectives on the aspects that are required for a techno-economic analysis and a viability assessment. Some focus on how design deci-sions influence a concept’s direct operating cost. Other studies use a techno-economic frame-work to identify the policy or economic environment that is most favourable for a concept’s viability. Others take a wider perspective and assess how an aircraft may influence the wider in-dustry or aircraft market. Whilst the approaches to techno-economics are different, each study consistently highlights the importance of cost and economics in aircraft design. In addition to assessing whether a concept is able to meet performance targets, it is necessary to assess the economic risk that a concept will not be viable. A techno-economic and environmental risk assessment therefore provides a view of risk from an investment rather than performance perspective.
2. Literature Review
Figure 2.9: Main market groupings for the commercial passenger aircraft market with future concepts marked [84]