Aeroplanes have essentially adhered to the same design formulas for decades, but this is all about to change with a new generation of aircraft and engines. The demand for energy-efficient air travel has never been greater with the price of jet fuel doubling in the past 12 months. This has been an enormous burden for the airlines, with more than two dozen going under in the past year. As a result, Rolls-Royce, the world's second-biggest manufacturer of jet power systems, is stepping up efforts to meet the needs of a new generation of aircraft expected in the next decade.
"You've got to ask about technology, engine efficiency, service developments and aircraft design. And we see a range of outcomes, from an advanced turbofan at about 15 per cent efficiency gain as early as 2015, through to something like 50 per cent if we are prepared to look at all of the other innovations and, ultimately, alternative fuels as well," said Mark King, the president of civil aerospace at Rolls-Royce.
The company is developing new engines that promise step-changes in efficiency. In the process, the British firm must balance competing forces, as fuel efficiency gains often force alterations to an engine's speed, noise and maintenance requirements. Rolls-Royce is not alone in seeking fuel saving by flirting with radical design changes. Aviation research organisations and the major airframe manufacturers have also joined the quest to design more aerodynamic planes. Boeing and Airbus, the two largest manufacturers, are looking at blended wing-body aircraft, which have the potential to carry more than 1,000 passengers per flight.
Mr King said the company was pursuing different engine strategies that could begin delivering results to airline customers by about 2015. In order to justify the cost of new planes, airlines generally require a 15 per cent improvement in fuel efficiency and a 25 per cent improvement in maintenance costs. "I think you'll get a different opinion from different customers as to what they need and how urgently they need it," he said. "Oil prices have changed quite significantly in the last six months. That means the trade-off between the various parameters differs quite dramatically."
Today, commercial aircraft use turbofans because they are highly efficient and relatively quiet. Rolls-Royce is pursuing two advanced versions of the turbofans using a different number of shafts - the revolving rods that transmit motion or power. But the traditional turbofan may soon lose its decades-old monopoly. Rolls-Royce is one of several engine makers developing open rotor engines. These engines feature several rows of propellers that jut out at different angles like rows of shark's teeth and move in a contra-rotating direction, giving the plane greater lift.
Open rotors require less fuel than turbofans because they have a much higher bypass ratio - the proportion of air bypassing the engine core versus the air passing straight through it. This means the engines are slower running, but more fuel efficient. The open rotor was one of several promising designs selected by the EU's New Aircraft Concepts Research Programme (Nacre) following a three-year study.
The US$47 million (Dh172.5m) programme had sought to identify new ways to reduce the environmental impact of air travel while jointly boosting efficiency and affordability. Nacre's ambitious goals included reducing the amount of fuel burnt per flight by 25 per cent and lowering the noise signature per flight by 10 decibels. Three designs were chosen as the building blocks of the programme, and the preliminary findings were released this month. One design included forward-swept wings and two turbofan engines mounted above a greatly expanded tail section. The design was selected to increase laminar flow, which calls for minimal turbulence so that the boundary layer of air that passes over an aircraft is kept smooth.
Another design Pro-Green 2, centred on a slightly slower aeroplane with high fuel efficiency thanks to an open rotor engine from Rolls-Royce, which was mounted on the back of the plane instead of under the wings. The third design, called the "passenger-friendly" concept, used a blended wing body where the cabin area is integrated into the wings. The two most promising concepts from the work were laminar flow and open rotors, according to Nacre's directors. Boeing has also invested heavily in new aircraft design in the past decade in its strong rivalry with Airbus. In 2001, it unveiled its Sonic Cruiser, an aircraft designed for near-sonic or supersonic flight.
The Sonic Cruiser would have delivered 15 to 20 per cent faster speed than conventional aircraft and could fly at altitudes in excess of 12,000 metres, well above weather systems, with a range of up to 19,000km. But airlines gave the Cruiser a cold reception, instead preferring a slower, more fuel-efficient plane. The research was not in vain, however, as Boeing applied the lessons learnt from this project to its 787 Dreamliner. The Dreamliner has become the fastest selling aircraft in history, with 896 aircraft on order, thanks to its carbon fibre fuselage, lighter and more fuel efficient than the aircraft it will replace.
Part of the appeal of the 787, and also the slightly larger 777 aircraft, is that they are twin-engined, thus burning less fuel than a similarly sized aircraft with four engines. The 777 has significantly outsold the Airbus A340. Now, with airlines projected to lose billions of dollars this year due to record fuel prices, Boeing and Airbus are being pressured to come out with newer versions of their current models, which still rely on heavier aluminium fuselages.
Rolls-Royce was working in tandem with the airframe companies, Mr King said. "The next generation narrow-bodied aircraft could look fundamentally different from today's generation. It could be a twin-aisle. It could be slower, and it could be much shorter-range," he said. "We can do a 15 per cent improvement by the middle of next decade, with an advanced turbofan on an aircraft that looks very similar to the current aeroplanes. If we go for an open rotor, we could have a significantly greater engine efficiency. I would say 2017, 2018 would be the earliest we could see that," he said.
But it can only proceed in step with new design innovations from Boeing and Airbus, and with the final models from the aircraft makers some years off, Rolls-Royce cannot focus on one particular engine design alone. "We are quite deliberately pursuing three different options - two-shaft engines, three-shaft engines and the open rotor. I think we are not sure yet what the market is going to require."