A composite airplane fleet of the future could reduce aviation life-cycle carbon emissions by 15 per cent, finds study
Boeing 787 production line in Everett, WA
Wed 7 Jan 2015 – A study by the universities of Sheffield, Cambridge and University College London (UCL) concludes that by 2050 a global fleet of composite airplanes could reduce aviation carbon emissions by between 14 and 15 per cent. The researchers say they are the first to carry out a comprehensive life-cycle assessment (LCA) of a composite plane, such as the Boeing 787 Dreamliner or Airbus A350, and extrapolate the results to the global fleet. Using publicly available information on the Boeing 787 and from the supply chain – such as the energy usage and the robots that construct the planes – the LCA covers manufacture, use and disposal. Compared to traditional – and heavier – aluminium planes, a composite plane creates up to 20 per cent fewer CO2 emissions. Meanwhile, other researchers at Cambridge, in association with Boeing, have successfully tested a single-seat aircraft with a parallel hybrid engine – the first ever to be able to recharge its batteries in flight.
The LCA study – published in the International Journal of Life Cycle Assessment – found that emissions during the manufacture of composite planes are over double those of aluminium planes but the increase is quickly offset after just a few international flights.
“This study shows that the fuel consumption savings with composites far outweigh the increased environmental impact from their manufacture,” said Alma Hodzic, Professor in Advanced Materials Technologies at the University of Sheffield. “Despite ongoing debates within the industry, the environmental and financial savings from composites mean that these materials offer a much better solution.”
The comparative LCA analysis was conducted on Section 46 of the Boeing 787 fuselage, one of the tube sections supplied by Italian aerospace company Alenia and for which manufacturing data was available, and the 787 airframe was chosen for the high proportion, around 50%, of composite used within its structure.
The LCA data was fed into a wider transport model to gauge the impact on aviation CO2 emissions as composite planes are introduced into the global fleet over the next 25 years, taking into account other factors such as the speed of adoption of the new technology.
However, even by 2050, Andreas Schäfer, Professor in Energy and Transport at UCL, does not expect all the fleet will be of composite construction, hence the study’s forecast that overall emissions saved will be less than the 20% potential. “New planes entering the fleet before 2020 could still be in use by 2050, but the faster the uptake of this technology, the greater the environmental benefits will be,” he said.
Dr Lynette Dray from the University of Cambridge estimates that with the projected four-fold growth of air traffic between now and 2050, changing the materials used could avoid 500 million tonnes of CO2 emissions in 2050.
Added Prof Hodzic: “The industry target is to halve CO2 emissions for all aircraft by 2050 and while composites will contribute to this, it cannot be achieved by the introduction of lighter composite planes alone. However, our findings show that composites – alongside other technology and efficiency measures – should be part of the picture.”
The hybrid-electric propulsion system, where an electric motor and petrol engine work together to drive the propeller, was designed and built by engineers at Cambridge with Boeing funding support, and showed the commercially-available demonstrator aircraft used up to 30% less fuel than a comparable plane with a petrol-only engine.
The aircraft uses a combination of a 4-stroke piston engine and an electric motor/generator, coupled through the same drive pulley to spin the propeller. During take-off and climb, when maximum power is required, the engine and motor work together to power the plane, but once cruising height is reached, the electric motor can be switched into generator mode to recharge the batteries or used in motor assist mode to minimise fuel consumption, the same principle that applies to hybrid cars.
A power electronics module controls the electrical current to and from the batteries – a set of 16 large lithium-polymer cells located in special compartments built into the wings. The petrol engine is optimally sized to provide the cruise power at its most efficient operating point, resulting in an improved fuel efficiency overall.
“Although hybrid cars have been available for more than a decade, what’s been holding back the development of hybrid or fully-electric aircraft until now is battery technology,” said Dr Paul Robertson of Cambridge’s Department of Engineering, who led the project. “Until recently, they have been too heavy and didn’t have enough energy capacity. But with the advent of improved lithium-polymer batteries, similar to what you’d find in a laptop computer, hybrid aircraft – albeit at a small scale – are now starting to become viable.”
While an important step, Robertson and his team accept that a commercial airliner powered entirely by electric motors is decades away and estimate that if all the engines and fuel in a modern jetliner were to be replaced by batteries today, it would have a total flying time of roughly 10 minutes.
However, said Marty Bradley, Boeing’s principal investigator for the programme, there was a mission to find innovative solutions and technologies, as well as continually improve the industry’s environmental performance.
“Hybrid electric is one of several important elements of our research efforts and we are learning more every day about the feasibility of these technologies and how they could be used in the future,” he said.
