Airliners have not changed much outwardly in 60 years, but that may soon change:
Earlier improvements went mostly unnoticed because they focused on building better and quieter turbine engines with higher performance and improved fuel consumption. There have also been huge strides in computer controls and fly-by-wire systems, which make a big difference to the pilot, but not to the passengers. And in recent years, the biggest development has been the use of strong, but lightweight plastics and composite materials rather than metals, reducing the weight of planes and the amount of fuel they need to burn. This has also allowed the development of “radical” new planes like the giant Airbus A380 and the Boeing Dreamliner.
A team from MIT in Cambridge, Massachusetts, for example, put forward the D8 for consideration by Nasa. This “double-bubble” aircraft design, features a double-wide fuselage composed of two standard body cylinders melded together side-by-side, as well as low-swept wings that cut drag and weight. The idea of the wider body shape is to increase lift generated by the fuselage, rather than it being mostly dead weight slung between two wings. The extra lift and reduced drag cuts back on the quantity of fuel that the engines must burn. If the jet were built today from standard aluminum alloys it could provide a 50% reduction in fuel use, according to the MIT designers; a low-mass polymer-composite version could give 70% efficiency gains. In addition, because the D8’s turbine engines sit on top of the fuselage in a box-shaped tail, they would cut the amount of engine noise broadcast to the ground.
The D8’s idea for generating greater lift is taken to an extreme in another design called the N3-X hybrid wing-body airplane, which Nasa developed in-house. At first glance, the N3-X looks a lot like a so-called flying wing design, used by planes such as the US Air Force’s B-2 stealth bomber. These comprise a single, thick triangular wing that enclose all of the plane’s contents – cockpit, stores, engines, fuel tanks and flight surfaces. But, unlike the B-2 flying wing, the N3-X hybrid wing-body also features two thin, rather conventional wings attached to the sides of its ultra-wide fuselage.
The primary advantage of the hybrid, or blended, wing-body design is better fuel efficiency, Del Rosario says. Like a flying wing, the hybrid aircraft produces lift with its entire aerodynamic airframe, thus ridding itself of the drag associated with the cylindrical fuselage and the tail surfaces of a conventional plane. As with the D8, the more lift that can be produced overall, the less effort is needed from the engines, which in turn means less fuel must be burned. Fuel efficiency could be raised further by building the airframe from lightweight polymer composite materials instead of metals, Del Rosario says.
Nasa’s N3-X is also designed around a completely new engine concept, called turboelectric distributed propulsion. It splits the main functions of a standard turbine engine in two — generating power by burning fuel and creating thrust by blowing air rearward with a large fan.
The idea is to use two large turbine engines to drive electric generators that would produce electricity to power 15 electric motor-driven, thrust-producing fans that would be embedded across the top rear of the broad fuselage. Such a configuration could be very efficient, Del Rosario says. The array of small electric propulsion fans at the stern of N3-X enables the designers to cut drag significantly by accelerating the flow of drag-causing air moving over the upper surface of the fuselage, keeping efficiency-sapping air friction at a minimum. Like the D8, the top-mounted propulsor fans would also effectively lower noise emissions because the body would come between them and the ground below.
(Hat tip to Jonathan Jeckell.)