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MPhil in Engineering for Sustainable Development

global challenges, engineering solutions

Studying at Cambridge

 

Emily Schwartz

Environmental Assessment of Silent Aircraft Technologies

Emily Schwartz

Environmental Assessment of Silent Aircraft Technologies

Whilst civil aviation has grown rapidly over the last several decades, so too has concern regarding its environmental impacts. Aviation noise is very costly, contributing to airport delays, reduced airline operations, and lower property values. The trend of decreasing noise exposure has slowed, and in the near future increasing demand for travel is expected to surpass technological progress. Additionally, aircraft engines release greenhouse gases and local pollutants as products of combustion. Control of emissions at the global level is of crucial importance, as aviation is attributed with 3% of total greenhouse gas emissions, a figure which is expected to rise to 6-10% by 2050 without policy intervention. The highly optimized aircraft and engines designed today where improvement in total environmental performance is difficult to achieve, requiring tradeoffs between noise, fuel burn and emissions, cost, and risk. The Silent Aircraft Initiative is a CMI project charged with designing a concept aircraft whose operations are imperceptible outside the airport in a typical urban environment. The design must also be competitive with other 2025 aircraft in terms of operating and acquisition costs. This report examines the environmental impact of the Silent Aircraft design and individual technologies, focusing on the tradeoffs between designing for low noise and low fuel burn. Each of the technologies is assessed in terms of its environmental impact and applicability. This assessment is then used to determine the potential impact of these technologies on the future civil aviation fleet. Power managed takeoff procedure, variable area nozzle, and faired landing gear technology are all identified as technologies capable of low-risk, modest acoustic performance improvement in the near term. Larger benefit in jet noise and potentially fuel burn can be achieved through ultra high bypass ratio engine technology including geared fans at cost to increased engine complexity. To reduce fan noise, acoustic lining must be extending, leading to significant fuel burn and emissions penalties. Increased fuel burn is overcome by novel embedded engine installations in conjunction with unconventional airframes to produce significant noise and fuel burn reductions on the order of 20% in fuel burn and 15dB in noise. Such a design, as proposed by the Silent Aircraft Initiative, would elude the noise-fuel burn tradeoff which has come to characterize modern aircraft and engine design. However, the blended-wing-body airframe, common-core turbofan, and boundary layer ingestion technologies comprising such revolutionary configurations are high risk and would require considerable development before they could be implemented. Whether these technologies are adopted will depend on a number of factors, including the environmental demands which are placed on the aviation industry.