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Noise annoys: Making jets ever quieter is compromising improvements elsewhere
Stringent noise regulations at airports are holding back engineers from developing more environmentally friendly aircraft, the head of engineering for Airbus has said.
Charles Champion told the aircraft-maker’s annual “Innovation Days” at its Toulouse HQ that 90% of the firm’s engineering effort went towards improving environmental performance but increasingly tougher noise regulations meant design concessions were being made that reduced fuel efficiency.
Champion said: “Compared to the jets of 50 years ago we have reduced fuel consumption by 80%. Whatever we do in terms of aerodynamics, laminar flow, new materials, we are always trying to transport more passengers for less fuel. What’s changed is that we are now more constrained by noise.
“Today, you can hardly hear the A350 and you are shocked when an A320 or a 737 takes off. At the time those aircraft were perceived as being not noisy but today they are the noisy aircraft. We have the same trend for the A320neo. Our design parameters have changed towards less noise, whereas previously they were only focused on fuel consumption.”
The International Civil Aviation Organization (ICAO) oversees the standards for aircraft noise emissions and has been making the standards, or “chapters”, progressively stricter since the 1960s. Chapter 4 aircraft, such as the A380 or soon-to-be-delivered A350, have to be 10dBa quieter than previous Chapter 3 aircraft such as the A320 or Boeing 737. From 2017 large aircraft will have to be 7dB quieter than Chapter 4 aircraft.
Champion added: “The A380 was the first aircraft where we de-optimised the performance towards noise. We introduced larger fans to reduce noise at takeoff against what would have provided the best performance in cruise. People said we had made a mistake, that we were not making it as competitive as we should. In the meantime the focus on noise in densely populated areas has become even stronger.”
But Bill Hemmings, programme manager for aviation and shipping at European campaign group Transport and Environment said: “We see noise regulations and the push for high bypass turbofan engines as mutually reinforcing. Noise regulations have forced the development of high bypass turbofan engines.”
He said that engine configuration on the A380 was a design choice by Airbus related to aircraft size.
“The A380 wings are shorter than they should be for the size of the fuselage because of ICAO regulations that states runways have to be separated by at least 80m. Changing the wing aspect ratio to not exceed the 80m box is a penalty in terms of lift, which makes it a quieter aircraft at the cost of performance.
“Things have improved compared to 50 years ago but jet aircraft represented a penalty over piston engines in the first place. Engineers optimise for the lowest operating cost; fuel efficiency is just one parameter. If they optimised just for fuel efficiency the aircraft would be very different,” he said.
“It’s not that they’re not improving but to go beyond what the marketplace is demanding would take moderate regulatory pressure. We are involved in discussions with ICAO along those lines.”