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ePaper created 2014-08-08, 11:09:35 | version 1.32.01
The chevron nozzle, as shown in the photo- graph [Ú 03], considerably reduces pressure fluctuations and, consequently, the jet noise emitted by the engines. The sawtooth concept is applied also to the outer trailing edge. There, too, it reduces noise emissions. In 2001, Lufthansa and the German Aerospace Center together used overfly measurements to demonstrate that chevrons on the exhaust nozzle reduce the exhaust noise of an Airbus A319 engine by about 1 dB(A). In addition to the A320neo short- and medium-haul aircraft ordered in 2011 and 2013, 59 state-of-the-art aircraft—34 Boeing 777-9X and 25 Airbus A350-900—will join the Lufthansa Group’s long-haul fleet in the future [Ú 01]. Delivery of the A350-900 will begin as early as 2016. By 2025 they will have replaced the older Boeing 747-400 and Airbus A340-300 aircraft. The new models will have a considerably smaller noise foot- print than today’s aircraft [Ú 02]. ß www.lufthansagroup.com/fleet_development Ú 01/ Investments in the most advanced aircraft Ideally, active noise abatement would either prevent noise from occurring in the first place or substantially reduce it by using the most advanced technologies. We therefore invest continually in state-of-the-art aircraft. By 2025 the Lufthansa Group will take delivery of 261 aircraft of the latest generation at a list value of EUR 32 billion. It is clear from the example of the new Boeing 747-8—the leg- endary jumbo jet—that modern commercial aircraft are becoming quieter all the time. As compared to its predecessor model the Boeing 747-400, the noise footprint of the Boeing 747-8 is 30% smaller [Ú 02]. On May 1, 2014 the Lufthansa Group received the 13th of the 19 Boeing 747-8 aircraft it has on order. This aircraft is powered by thor- oughly redesigned, considerably quieter, and highly fuel-efficient engines. The most striking of the numerous technological innovations is the chevron, a sawtooth pattern on the trailing edge of the engine’s exhaust nozzle. This results in a better mixing of the turbulent shear layer, the stratum of air between the hot, fast exhaust jet from the engine’s turbine and the cold bypass stream that flows around or envelops the engine’s core. The noise footprint of a Boeing 747-8 on takeoff is, despite its 10% higher maximum takeoff weight, about 30% smaller than that of the Boeing 747-400. The Boeing 777-9X ordered by Lufthansa will have a noise footprint that is about 40% smaller than that of the Boeing 747-400, according to the manufacturer’s specifications. The chart shows the 85 dB maximum level contours for a takeoff according to standard Lufthansa takeoff procedures (modATA) and with the takeoff weights as shown. New long-haul aircraft (A350-900 and Boeing 777-9X) [Ú 01] Airbus A350-900 Boeing 777-9X More quietly into the future: The new long-haul aircraft will be powered by exceptionally quiet and fuel-efficient engines: the Airbus A350-900 by Rolls Royce Trent XWB 84 engines and the Boeing 777-9X by the GE-9X engines manufactured by General Electric. The noise footprint of both models will be considerably smaller than that of today’s aircraft. Boeing 747-8 442 t 2012 – 40% – 30% Start 2 km 4 km 6 km 8 km 10 km Boeing 747-400 395 t 1989 MTOW First flight Noise contours compared (B 747-400 vs. B 747-8 and B 777-9X) [Ú 02] For each of the contours shown, the intensity of sound at takeoff is 85 decibels. ß Boeing 777-9X 351 t ~ 2020 14 // More quietly into the future