Analysing the Role of the Propulsive System in the Global Civil Aviation Energy Optimisation Framework

This paper presents a simple explanatory framework to analyse the diverse strategies proposed by the civil aviation sector in attempts to reconcile its growth tendencies with its impact on natural environment. Despite framing the industry as a single entity that has a problem to solve, it is better represented as a diverse set of actors, each responsible for various constituent systems at different phases of their respective life cycles. To elucidate this multi-actor pursuit of higher-level emergent objectives, the paper firstly presents an overview of different development scenarios dedicated to guide the industry towards sustainability. Given that the constituent systems tackled in such strategies strongly depend on each other, the sustainability objective relies on reconciling all the different agendas and contributions in unison, making them collectively compatible with the dynamics of the socio-economic and the natural world. To analyse the problem coherently, a basic description of an arbitrary system as a coarse-grained closed causal network is formulated. A categorisation for the model parameters is proposed to help define the system boundary and interaction with the environment unambiguously, dispensing with the need to know details of the model that represents the system at hand. This formalism was previously derived for preliminary sizing and performance estimation of aeroplane engines; by virtue of recursive nature of the coarse-graining process, the same formalism can be used to describe systems at any arbitrary levels, which enables a small system (in the current paper the system of interest being the propulsive system) to be integrated into a multi-level causal dependence framework. Then, the typical industry evolution scenarios are re-framed on the common ground of the causal network formalism. Subsequently, the framework is extended with a simple quantitative energy-based representation to formulate a qualitative case of how the scenarios could be formulated more coherently to avoid conflicting local optimisation objectives in pursuit of common higher-level goals. Finally, the entirety of the presented elements are brought together in a proposal to conceptualise an industrial system as a life cycle which exchanges matter, energy and information with its large-scale environment. The paper argues that such framing of the problem can pave the way to simplification of the problem of conflicting high-level objectives, by enabling a coherent understanding of the mutual dependence between a system of interest and the much more complex system of systems that is the aeronautical industry.