Lufthansa retrofitting A320 planes with simple, inexpensive, noise-reducing device to stop the “Airbus whine”
The Airbus 320 series of aircraft, many of which are used by the low cost carriers – easyJet in particular – have been known for many years (by the CAA since 2005) to have a particularly irritating high pitched whine. This is caused by air rushing across the under-surface of the wing, where there are Fuel Over Pressure Protector (FOPP) cavities. This generates noise, in the same way as blowing air over the mouth of a bottle.Every A320 series aircraft emits a signature howling noise while approaching to land. It is heard most when the plane is travelling at around 160 knots, and the frequency is around 500-600Hz, which is close to peak sensitivity of the human ear. There is a relatively simple and inexpensive retrofit, to attach a small aluminium “vortex generator” in front of the cavity. Then can be done at routine aircraft maintenance, though the fuel tanks need to be emptied. Lufthansa is in the process of retrofitting all its A320 series planes. Air France will also do so. EasyJet has been reluctant to do much, as it sees no commercial advantage in doing so.
Lufthansa Retrofitting A320 Family with Noise-Reducing Technology
A tiny device, shown here mounted upstream of a circular opening used to equalise the pressure in wing fuel tanks, reduces the whistling noise produced by the Airbus 320. [Photo courtesy of Lufthansa]
Lufthansa is in the process of modifying its fleet of A320 series aircraft with noise-reducing innovations.
After taking delivery of the first Airbus A320 line fitted with the simple, yet innovative, noise-reducing vortex generators earlier this year, Lufthansa is beginning to retrofit its fleet of more than 150 A320 series aircraft.
Every A320 series aircraft emits a signature howling noise while approaching to land. This noise is generated when air flows over an opening on the lower side of the wing, just like blowing air over the mouth of a bottle.
The opening draws in and expels air through vents attached to the fuel tank. Air is drawn in through the opening to replace fuel consumed in flight, then expelled through the same opening when the aircraft is refueled.
The installation of a small vortex generator just in front of the vent opening fixed the howling noise. The device breaks the flow of air just enough to prevent the noise being created, adding minimal drag and without adversely affect the aerodynamics of the wing. Lufthansa expects to complete the modifications to all 157 of its A320 series aircraft by November 2015.
Previously, the howl was accepted as a necessary evil of aircraft operation, and noise-reduction innovations focused primarily on the main noise generators: the engines and the flaps on the wings. Air France, for example, aimed to reduce engine noise by fitting chevrons into the core exhaust nozzle of their A320 series CFM engines.
…. and it continues …..
Small is beautiful: How a tiny device cuts aircraft noise
The name – vortex generator – sounds more complex than the device itself. Yet the small component developed by German researchers provides a big solution to noise produced by one of the most widely flown passenger aircraft.
Under pressure from airlines and new regulations, aircraft manufacturers are locked in a fierce competition to produce planes that are easier on the ear and the environment. During rollouts of new or revamped models of engines and aircraft at the Farnborough International Airshow this week, manufacturers are touting new or updated commercial products billed as the cleanest and quietest ever.
The vortex generator, however, required no big shift in technology or major manufacturing investment. Developed by the German Aerospace Centre, or DLR, the device diverts wind from vents on the underside of wings on the Airbus 320. It reduces the sound radiating from the aircraft in its clean configuration, just before the landing gear and flaps are deployed for landing.
For Jan Werner Delfs, who heads DLR’s Department of Technical Acoustics, the A320’s noise is like the sound produced by blowing across the opening of a beer bottle, though at many magnitudes of difference. In the airplane’s case, the whistle occurs when air passes over circular openings used to equalise the pressure in fuel tanks mounted inside each wing.
“If you listen to landing aircraft you can always say this is an A320,” Delfs explained in a telephone interview from the northern German town of Braunschweig. “You believe those tones are coming from the engines, but they are really coming from those holes.”
‘Very annoying’ tone
The DLR attached a 5-cm triangular piece of aluminium sheet metal upstream of the two vents on each wing, in order to divert the air flow and stop the whistle. A decade of research went into the vortex generator, which stems from efforts to mask a similar whistle produced when air blows over the gun ports of warplanes.
“You will certainly very much notice the difference,” Delfs said, noting that it knocks about six decibels off the sound contour of the A320. “It’s not only the question of decibels, by the way. It’s also a question of the kind of sounds and tones, (which) are usually perceived as much more annoying than some featureless noise without tones. If you have a rushing by of something, it’s not very annoying, but if you have a distinct tone, it’s very annoying. So it’s not just the decibels, its the way [the noise] is perceived.”
This year, Germany’s Lufthansa began installing the device on more than 150 A320s and its sister models, the A319 and A321, and announced that it was deploying new aircraft with the device pre-installed. The airline – Europe’s second carrier in passenger numbers – said it was part of its overall scheme to make airplanes quieter.
A Lufthansa spokesman told EurActiv that the noise appears to affect only the Airbus line of single-aisle jets. He said the airline was spending “a single-digit million amount” to retrofit its fleet.
An Airbus spokesman at Farnborough said the device is available as a retrofit on its aircraft and is already being installed on new-model A320s. Other Airlines, including Air France, have announced that they are installing the sound-reducing component on the affected Airbus aircraft.
[about how in the past more plane noise was from the engines, rather than the airframe. Now the noise is about half and half. During landing, there is often more noise from the airframe than from the engines, especially when flaps are used – which causes drag. That slows the plane, but generates nose].
New EU regulation
Yet even as planes become quieter, the steady growth of air traffic means noise remains a political bombshell in Europe, which leads the world in noise-based flight restrictions. EU states are obliged to limit noise around airports under a 2002 regulation, and the European Parliament and Council approved on April 16, 2014 new aviation noise rules (Regulation 598). The new regulation, which is due to take effect in 2016, puts the EU in line with the International Civil Aviation Organization’s “balanced approach” to noise reduction through measures such as requiring the use of modern aircraft, quieter ground-control operations and – as a last resort – restrictions on nighttime flying.
Still, it could take years for new technology and policies to pay off. More immediate solutions might be found with relatively simple developments, like the vortex generators.
“This tone problem and the vortex generator is rather exceptional,” said Delfs of DLR’s Department of Technical Acoustics. “It’s an exceptionally simple means to get rid of this noise.”
Other noise-reduction efforts may be far more complex and take longer to develop, he said. “At the moment, we are at a stage where any further decibel reduction takes a lot of effort because today’s aircraft are [already] relatively silent.”
“By fitting these vortex generators to our Airbus short and medium-haul fleet, we are continuing to invest in active noise protection”, Kay Kratky, member of the Lufthansa German Airlines Board, said in a statement announcing the retrofit. “In addition to the extensive modernisation of our fleet over the next few years, this is one of several steps that we are taking to reduce noise. It shows our commitment to working towards a balance between the interests of aviation and local residents, especially at our hubs.”
A CAA briefing on the issues (at http://www2.westsussex.gov.uk/ds/cttee/gat/gat171013keymes2.pdf )
Airframe noise from the A320 aircraft family
ERCD 16 October 2013
Tonal noise from the A320 family
Following concerns raised around Heathrow airport in 2005, the issue
of tonal noise emanating from the A320 family of aircraft on approach
was brought to the attention of Airbus by the CAA
Complaints of a high pitch “whine” which could be heard on the ground
at relatively large distances from the airport (Greenwich)
Similar concerns had also been raised around Paris and Frankfurt
airports at around the same time
Measurements undertaken have confirmed the tonal noise is due
airframe noise not engine noise and is on all present A320 family
variants, i.e. A318/319/320/321, irrespective of engine variant.
NTK [Noise and Track Keeping] noise measurements at Heathrow
Tone is emitted around 500-600Hz, close to peak sensitivity of the
human ear, hence it is very perceptible.
Close to the airport it is masked by noise from landing gear, flaps and
the higher thrust required in the landing configuration.
Very audible during intermediate approach phase 7-15nm from
Tonal noise source
Investigation by Airbus has revealed two tonal noise components,
generated by the Fuel Over Pressure Protector (FOPP) cavities.
The A319/320 series account for over 50% of all air traffic at Gatwick, mostly operated by easyjet. They emit a debilitating high pitched whine caused by air rushing over Fuel Over Pressure Protector (FOPP) cavities in the wings – a bit like blowing over the top of an open glass bottle.
The CAA recently admitted that this severe aural annoyance has been recorded on the Airbus series since 2005. They also confirmed that the “Tone is emitted around 500-600Hz, close to peak sensitivity of the human ear, hence it is very perceptible and very noticeable.”
It is noticeable on the long low flight path to touchdown apparent at least 20 miles from the airport and across a variable corridor 2 to 3 miles wide.
The noise is at its worst when the plane is travelling at around 160 knots, so on landing maybe 10 – 20 miles from touch down.
There is a straight forward fix for the issue in place and intense pressure is being applied to easyjet and others to do so.
Though Lufthansa is in the process of retrofitting all their A320 series planes, in order to cut the noise, there is no pressure on airlines to do so. There is no financial incentive for them to do so.
Air France say they will do the retrofits.
The cost of adding the small vortex generators, close to the Fuel Over Pressure Protector (FOPP) cavities is not high. However, it needs to be done when the aircraft is having routine maintenance, and the fuel tanks need to be completely emptied before the vortex generator can be fitted. This would add a few hours to the maintenance.
Please see below a letter sent to easyjet asking that the company does something to retrofit their planes, in order to reduce their noise nuisance.
While Air France and Lufthansa are fixing the problem, easyjet refuse to countenance doing more than 20% of their fleet by 2017.
Letter to EasyJet
Ms Carolyn McCall
Chief Executive Officer
London Luton Airport
Bedfordshire LU2 9PF
14 November 2013
Dear Ms McCall,
In the towns and villages across West Kent and East Sussex concern is being expressed over the debilitating high pitched whine emanating from the Airbus A318/319/320 etc., series of aircraft. For some time it was thought that this was a fault of the high bypass turbofan engines but this was denied by the manufacturers and in any event Boeings equipped with the same engines do not emit this awful and far reaching noise. It is noticeable on the long low flight path to touchdown apparent at least 20 miles from the airport and across a variable corridor 2 to 3 miles wide.
As your fleet has expanded over the past few years many people’s daily lives have become
intolerable because of this noise nuisance. You can imagine then how they are affected when your wailing sirens fly overhead at night. The World Health Organisation has for many years considered that sleep disturbance can lead to fatigue, hypertension, greater risk of heart and respiratory problems, poor performance at work or in school, greater difficulty in concentrating and thinking clearly, an increased likelihood of accidents, depression, anxiety and drug and alcohol abuse. This is particularly the case if people become annoyed about the impact night flights are having on their health and quality of life. These symptoms can also be found in those people suffering excessive noise disturbance during the day.
Much of the nuisance created by your aircraft from Gatwick Airport is over the High Weald
registered as an Area of Outstanding Natural Beauty. It is on these hills and in the tranquil river valleys and upper reaches of the rivers Rother, Arun, Medway, Eden and Ouse that are used for holidays and weekend recreations of hiking, boating, bird watching, horse riding, golfing and other quiet and peaceful pursuits. All are now disturbed by this deep and penetrating noise, mostly from your airline. Many of those troubled, apart from local people in towns and villages, are day trippers from London and other built- up areas all seeking their own refuge from the intrusive noise of daily urban life. In the green parks of inner cities there is also no respite where you and other low cost carriers operate these aircraft.
This annoyance, we are now told, by the CAA has been recorded on the Airbus series since 2005 yet it was only announced on the 13 October 2013 that the ERCD had discovered that the fault was an airframe noise caused by Fuel Over Pressure Protector (FOPP) cavities in the wings. They also confirmed that the “Tone is emitted around 500-600Hz, close to peak sensitivity of the human ear, hence it is very perceptible and very noticeable.”
Purely from a humanity point of view ‘Do you care? If you do please tell me what you propose doing about rectifying this unfair and intolerable burden across much of our country and abroad. Your decision will make all the difference to so many people’s lives.
Michael Knowles OBE
cc The Rt Hon Sir Michael Fallon MP
– The Rt Hon Greg Clark MP.