July 31, 2007 The standard aircraft design with which we have all become so familiar throughout the 20th century is headed for the scrap heap. Despite its ubiquitous nature, the traditional shape is set to be superseded in the push towards cleaner, greener aircraft that can transport people around the globe using less and less fuel. We wrote recently about Boeing’s Blended-Wing Body (BWB) aircraft, currently in testing – and now a new research group at a Netherlands university has been formed with the explicit goal of consigning the current shape of passenger airliners to the history books. The CleanEra project will investigate BWB, high-tech propeller engines and even UFO-style body shapes in their efforts to produce a light, efficient airliner model that produces less noise and cuts carbon dioxide emissions by at least 50% over current designs.

With air traffic around the globe growing at a huge rate each year, CO2 emissions from airplanes are set to jump from 2% of global emissions to a possible figure of around 5% by 2050 according to some scientists. Clearly, the passenger airplane needs to be overhauled as part of any emissions-control regime and this is the key point that has driven Etnel Straatsma to set up the CleanEra project at the Delft University of Technology in the Netherlands.

The current body shape is still not optimized for efficiency and emissions control – but Straatsma’s Delft colleague Alexander De Haan believes that if all current proposed improvements were made to the design of such aircraft, the best that could be hoped for is a 10 to 15 per cent efficiency gain. “These ideas cannot keep up with the 5 per cent growth that the industry continues to have year after year,” said de Haan.

Airline industry groups are beginning to agree that a fundamental body shape change is becoming necessary. "Ever since the Boeing 707 first flew in 1957, airliners have changed very little in their basic appearance," said Andreas Hardeman of the International Air Transport Association. "However, because future improvements to the basic design are getting harder to make, economic and environmental pressures mean that the case for radical change is getting stronger" added Hardeman.

Straatsma’s group plans to investigate several models and modifications in pursuit of their goals. A regression to propeller-driven planes might be one idea – they’re more efficient than jet engines. They’re also much slower though, and specially designed propellers that can reach passenger-jet speeds are typically extremely noisy. However both of these issues conflict with one of CleanEra’s stated goals – the maintenance of passenger comfort.

Another idea is to replace metal with much lighter plastic composite materials – which is already happening on Boeing’s 50% plastic 787 Dreamliner – but de Haan believes that by “thinking in composites” instead of simply swapping the materials into a design that was originally based on steels, further efficiencies could be gained.

Different fuels including biofuels and hydrogen fuel cells are being investigated, but each have their own difficulties – biofuel, for instance, has a tendency to freeze at altitude, and there is still difficulty in compressing hydrogen to a small enough tank space to make it viable. Fuel cells are also an energy-inefficient storage medium.

Blended-wing body aircraft like the shapes Boeing is experimenting with could boost aerodynamic efficiency as well as increase a plane’s carrying capacity up to 800 or more passengers – but 800 seats could be difficult to fill on many routes, and the cargo/passenger layout of a BWB plane moves passengers away from the central tilting axis of the plane, meaning that as the plane rolls slightly to turn, passengers at the outside experience much more vertical movement. BWB airliners would likely require an extra stash of sickbags – which runs the design up against the passenger comfort goal once again.

Still, if efficiency and emissions reduction are serious goals of the aviation industry, the current airliner shape has to be radically revised, and the CleanEra group aims to play a central role in that project.