Researchers Unveil Quieter, More Fuel-Efficient Aircraft Concept

6 November 2006

Four views of the SAX-40. Click to enlarge.

Researchers from Cambridge University and the Massachusetts Institute of Technology (MIT) have unveiled their revolutionary concept for a “silent aircraft”: the SAX-40 (Silent Aircraft eXperimental).

Originally conceived in 2003 to make a huge reduction in the noise experienced by people in the vicinity of airports, the design of the SAX-40 also offers improvements of around 25% in the fuel consumed in a typical flight compared to current aircraft.

The designers currently predict the SAX-40 will deliver:

• 149 passenger-miles per UK gallon of fuel (124 passenger miles per US gallon) compared with about 201 for the best current aircraft in this range and size). This is equivalent to the Toyota Prius Hybrid car carrying two passengers.

• A noise of 63 dBA outside airport perimeter. This is some 25dB quieter than current aircraft.

The design is intended for the generation after next of aircraft for entry into service in 2030. The design looked at improving the airframe as well as the engines as half of the noise from a landing plane comes from the airframe. Some of the key design features employed are:

• The overall shape of the aircraft which is a single flying wing. This shape allows the body to provide lift as well as the wings allowing a slower approach, thereby reducing noise. The shape also improves fuel efficiency in cruise.

• Flaps and slats have been eliminated. These are a major source of airframe noise when a plane is landing.

• The undercarriage has been simplified and its aerodynamics improved.

• The engines are mounted on the top of the aircraft which screens much of the noise from the ground.

• Novel ultra-high bypass engines, which have variable-size jet nozzles to allow slower jet propulsion during takeoff and climb for low noise, and optimization for maximum efficiency during cruise which requires higher jet speeds.

The Silent Aircraft Initiative was funded by the Cambridge-MIT Institute (CMI) in 2003 as a collaboration led by Prof Ann Dowling at Cambridge University Engineering Department and Prof Ed Greitzer, Aeronautics and Astronautics at MIT. The project, with a grant from CMI of £2.3 million, brings together teams involved in different aspects of aircraft design for a multidisciplinary approach. The Initiative has involved 40 researchers from the University of Cambridge and the Massachusetts Institute of Technology (MIT).

The project has had significant collaborations from all parts of the civil aerospace/aviation industry including: British Airways, BAA, Boeing, Brüel & Kjær, the Civil Aviation Authority, Cranfield University, DHL, easyJet, Eurocontrol, HACAN Clearskies, Lochard, London Luton Airport, Marshall of Cambridge Aerospace, National Air Traffic Services (NATS), Nottingham East Midlands Airport, the Royal Aeronautical Society and Rolls-Royce.

My first reaction on hearing of the Silent Aircraft Initiative was profound scepticism. Three years on, I have to concede that the SAI has surpassed my expectations by quite a margin. The team has produced a high-risk but credible design that is predicted to meet the original target. In retrospect, I ought to have expected a team from Cambridge and MIT, supported by Rolls-Royce and Boeing, to achieve something special. A radical approach to the challenges of the future comes more naturally from Academia than Industry, but the outcome will carry credibility only if the team is sufficiently strong and if it has the support of Industry and access to modern design methods. The SAI team has shown how this can be done.

—Dr John Green, Chairman of the Science and Technology Sub-group of Greener by Design

Resources:

• The Silent Aircraft Initiative