DERBY - Rolls-Royce (IW 100/234) on Wednesday unveiled designs for its next generation of fuel-efficient plane engines, aimed at powering civilian aircraft of the future.

Two weeks after announcing a shock profit warning with government cutbacks on defense spending impacting its military engines business, the British group revealed plans to build on its successful Trent XWB engine, which is exclusively powering Airbus A350 long-haul passenger planes.

"A big bulk of the (aircraft cost) efficiency is coming from the engines, so we have an important role to play to support our customers," Eric Schulz, in charge of Rolls' large civilian jet engines unit, said Wednesday in a conference call with reporters attending a media presentation in Derby, central England.

Rolls said that Advance, the development name for one of its future engines, will burn at least 20% less fuel -- with a corresponding drop in CO2 emissions -- compared with the first generation of Trent engines that entered service in 1995. The Advance could be ready by the end of the decade, it added.

An even more fuel-efficient model, UltraFan, could be ready for service from 2025.

"One simply cannot rush new technology along so it is something that has to be held in store," said aerospace analyst Sandy Morris at financial group Jefferies.

"If there is a snag, it is that we may have to wait up to a decade before we can start to picture the new aircraft onto which the latest-technology engines could be fitted.

"Even then, Rolls-Royce will doubtless face stern competition," he told AFP.

Rolls is the sole engine provider for the Airbus A350 XWB, a long-range, wide-body plane that is slated to come into service at the end of the year. It makes engines also for the Airbus A380 super jumbo and Boeing's 787 Dreamliner, competing for business here with U.S. conglomerate General Electric (IW 500/6).

Like the Trent XWB, the future engines will make extensive use of light carbon-based composite materials that significantly reduce fuel consumption and costs for manufacturers and airlines.

"They are designed to deliver... even better fuel efficiency, reliability and environmental performance," said Colin Smith, Rolls-Royce director of engineering and technology.

In Derby, where Rolls assembles jet engines for both European planemaker Airbus and its US rival Boeing, the company added that both new engine designs were the result of research and development investment totaling about £1.0 billion ($1.7 billion, 1.2 billion euros) a year across its aerospace and non-aerospace businesses.