Single-wing passenger jet

The Cambridge-MIT Institute this week unveiled plans for an innovative ‘single-wing’ aircraft, which it said could herald a much quieter, more energy-efficient generation of passenger jets.

The SAX-40 is designed to reduce noise for people living near airports, but also promises to cut fuel consumption by about 25 per cent compared with current aircraft.

In their quest for quieter flying, researchers at Cambridge University and MIT did not just look at engine design. Half the noise from some planes is caused by the way their airframes are structured. The decision to design an aircraft in the shape of a single wing enables the main body to provide additional lift, enabling a slower approach, which reduces noise. The shape also improves fuel efficiency in cruise.

Other improvements include the elimination of flaps and slats, which are a major source of airframe noise during landing. Additionally, the SAX-40 has a simplified undercarriage with improved aerodynamics, and the engines are mounted on top of the aircraft so less noises reaches the ground.

Another advance is that the design calls for ultra-high bypass engines, which have variable-size jet nozzles to allow slower jet propulsion during take-off and climb for low noise, while allowing optimisation for greater efficiency during cruise, which requires higher jet speeds.

Colin Smith, Rolls-Royce director of engineering and technology, said, ‘The Silent Aircraft Initiative has been a great success in bringing many stakeholders together to study what an aircraft of the future might look like if very low noise was the primary requirement. The study has confirmed that the solution for extremely low noise must be a highly integrated combination of engine and aircraft design and operation.’

The Silent Aircraft Initiative began in 2003, funded by the Cambridge-MIT Institute (CMI), which has backed a wide range of research and educational collaborations between the two universities.

The project received a CMI grant of £2.3m and was led by professor Ann Dowling of Cambridge University Engineering Department, and Professor Ed Greitzer of the Aeronautics and Astronautics Department at MIT. The researchers formed a Knowledge Integration Community (KIC), including staff and students from both institutions and collaborators from a wide range of organisations in the aerospace industry.

Dowling emphasised the value of collaboration between academia and the private sector. ‘This project has brought stakeholders together around a grand challenge that has captured the enthusiasm and imagination of all partners,’ she said. ‘There has been effective collaboration, knowledge exchange, and development of a real team approach.’

Greitzer of MIT agreed: ‘The Silent Aircraft Initiative has been very much an enterprise in which the whole is greater than the sum of the separate parts.’

The organisations involved in the project included British Airways, BAA, Boeing, Brüel & Kjær, the Civil Aviation Authority, Marshall of Cambridge Aerospace, National Air Traffic Services, the Royal Aeronautical Society and Rolls-Royce.