Preeti, Catherine E. Jones, Graeme M. Burt, Patrick J. Norman
Department of Electronic and Electrical Engineering
Decarbonisation is a route to reduce the negative environmental impact of air travel [1]. According to European Union, emissions from aviation accounted for 3.8% of total CO2 emissions in 2017 [2]. Prior to the Covid-19 pandemic, air travel was increased by over 18% in last 5 years (2015-2019) [3]. Hence, approaches to reduce emissions from aircraft to date have been unable to keep pace with the increased rise in air travel. Therefore, new and innovative approaches to improving aircraft performance and reducing fuel burn are required [4]. Alongside this, the UK aviation industry is the third-largest in the world, directly contributing £22 billion to the UK economy every year [5]. It connects the world. Thus, the growth of aviation is important both economically and socially, as it provides connectivity. However, this growth needs to proceed in a sustainable manner and address the negative environmental impacts of air travel [6].
Two routes to reducing the fuel burn of aircraft, and hence emissions, are reducing the weight of the aircraft structure and the electrification of power systems on the aircraft. Carbon fibre reinforced polymer (CFRP) structures are lighter and offer better mechanical performance compared to traditional, metallic structural materials [7]. For example, more than 50% of the structure of a Boeing 787 aircraft is made from CFRP, and this provides an average of 20% weight savings compared to an equivalent size aluminium aircraft [8]. However, due to the poor electrical conductivity of CFRP, the composite structure and electrical power system (EPS) of aircraft must be kept physically separate by using cable harnesses and raceways which are bulky and heavy and increase maintenance time [8,9]. The closer integration of the EPS with the CFRP structure offers an opportunity to form an embedded system enabling a more light-weight, compact solution, which in turn improves overall aircraft efficiency and therefore supports the achievement of the relevant UN SDGs [9].
Electrical power systems on aircraft are operating in an extreme environment: extreme temperatures, low air pressure, and significant vibration. Hence an integrated electrical –CFRP system must be resilient. If an electrical fault occurs within the integrated system, there is a possibility that electrical current may flow to electrical earth through the CFRP structure. The poor electrical conductivity of the CFRP under certain circumstances will significantly limit the amount of current flowing from the fault to electrical earth. This level of current may not be high enough to cause damage to the electrical power system but will cause thermal degradation of the CFRP structure due to localised Joule heating. As a result, conventional fault detection methods cannot be relied upon to detect the fault in a timely manner [10]. Therefore, new fault detection and electrical protection solutions are required for effective integration of innovative electrical power systems within aerospace structures.
To date, in this research project, a systematic literature review was employed to investigate challenges posed by integrating EPS with CFRP by reviewing existing solutions for state-of-the-art aircraft and analysing fault protection techniques in different systems: aerospace, marine, automotive, and land-based grid. This has been combined with existing, published knowledge on the electrical properties of composite materials. Looking forwards, the second stage of this research is to explore fully the interdependencies between fault diagnostics, architecture design, and the CFRP electrical properties, and to map out the key design trades. Secondly, this stage will identify gaps in knowledge around electrical properties of CFRP, and areas for further experimental testing to develop electrical models of CFRP at an appropriate level of modelling fidelity. For example, different layups of CFRP, different methods of electrical bonding of CFRP to the electrical earth, and different physical sizes of CFRP panels. Third is the development of appropriate electrical models, to investigate the fault response of the system. Routes to validate the fault response require further investigation but may include experimental methods. Combined these strands of research will all support an analytical framework which identifies viable fault detection and location methods.
This research presented provides a direction for the future to find optimum solutions to enable integration of electrical power systems with composites structures on aircraft and thereafter, appropriate fault protection and management system can be developed.
References
1. B. D. Hirst, “Aviation, decarbonisation, and climate change,” House of Commons Library, 2020.
2. "Reducing emissions from aviation," European Emissions, 2021.
3. “Number of passengers arriving and departing at airport terminals in the United Kingdom (UK) from 1992 to 2019”. Statista. 2019
4. “Sustainable Aviation: ATI Framework”, Aerospace Technology Institute, Insight_16, 2020.
5. “Aviation 2050 - The future of UK aviation”, HM Government, 2018.
6. “UK Aviation Industry Socio-Economic Report”, Sustainable Aviation UK, 2016.
7. “Use of Composite materials in Aerospace”, Composites UK, 2021.
8. J. Hale, "787 From The Ground Up", Aero Magazine, vol. 4, 09/01 2006.
9. C. Lochot and D. Slomianowski, “A350 XWB Electrical Structure Network”, Airbus Technical Magazine, No. 53, 2014.
10. C. E. Jones et al., “Electrical and Thermal Effects of Fault Currents in Aircraft Electrical Power Systems with Composite Aerostructures”, IEEE, 2018.
