A team of U.S. and British researchers has unveiled the conceptual design for a near-silent, environmentally friendly passenger plane. The SAX-40, which has been developed by the Cambridge-MIT Institute, is a radically different shape of aircraft. The design is the result of three years' work and includes both new and existing technologies. Here, the BBC News website has details some of the design's key features:

1. Airframe 2. Engines 3. Exhausts 4. Undercarriage 5. Trailing edge 6. Leading edge
The shape of the plane is what is known as a "blended wing" design. This hybrid design uses the wings of a conventional plane smoothly blended into a wide tailless body. As turbulent airflow, generated by irregular surfaces, causes noise, the designers tried to make the airframe as smooth as possible. The aerofoil shape of the body means that it also contributes to the aircraft's lift, meaning it can make a slower approach on landing, again reducing noise. The improved lift also means that the plane can do away with flaps on the wings, which are a major source of airframe noise on conventional aircraft. Because the design does not need a tail, used to provide additional lift and stability on conventional craft, it also cuts down on turbulent airflow and noise from the back of the plane. The design, made of lightweight composites, also improves the fuel efficiency of the craft whilst cruising.

The engines of the SAX-40 are embedded within the blended wing design with the air intakes on top. This means that the upper surface of the aircraft shields people on the ground from engine noise. The engines are also mounted deep within the intake ducts, lined with mufflers, to maximise the noise absorption. By embedding the three engines in the aircraft frame, it also reduces drag and therefore noise. The "ultra-high bypass ratio turbofans", as they are known, are also arranged in a novel way to minimise noise output. Instead of having one large fan, they have three arranged side-by-side. The smaller fans means the noise from each one is easier to absorb with surrounding "acoustic liners", or muffling materials.