British engineering company Rolls-Royce unveiled plans for a new aircraft engine which it said would be up to 6 percent more efficient than its latest model and could be ready by the end of the decade. Rolls, the world's second-largest maker of aircraft engines behind U.S. group General Electric, said the new engine, which it called "Advance," could be a successor to its Trent XWB which is due to enter service later this year. By 2025, Rolls said an even newer model, the "UltraFan", could be ready to be attached to an aircraft. This would be around 10 percent more efficient than the Trent XWB, it said. Demand for aircraft engines, and in particular more fuel-efficient models, is expected to continue to grow strongly. The world will need to double its fleet of aircraft over the next 20 years as cities expand and Asia's increasingly affluent middle class takes to the skies, planemaker Airbus forecast in September. It said airlines, lessors and cargo operators would need a total of 29,226 new passenger and freighter jets worth $4.4 trillion over the next 20 years. Rolls, which describes its Trent XWB as the world's most efficient engine, said it was confident about appetite from Airbus and its U.S. rival Boeing for its new products. "To some degree we've already started these conversations with the air-framers as part of our normal discussions around future requirements," executive vice president of strategy and future technology Simon Carlisle told reporters in a briefing. Soaring demand for more fuel-efficient engines for planes made by Airbus and Boeing has helped Rolls-Royce enjoy strong profits and revenue growth over the last 11 years, driven by its civil aerospace unit, which generates about half of its sales. Bigger fans and lightweight materials will enable the efficiency progression expected from the two new models, with the Ultrafan benefiting from a geared system. Rolls-Royce warned earlier in February that a decade of profit growth would come to an end this year, sending its shares sharply down, and giving it added incentive to refocus investor attention on its longer term growth prospects. (Reuters)