As anyone who lives near airports knows, airliners taking off are very noisy, and for this reason there are laws that require you not to exceed noise limits, expressed in decibels (dB). However, noise pollution does not only affect the outside of airplanes, but also their interiors, and it varies greatly depending on where you are in the cabin. Planes are inevitably noisy, but as Scott McCarteny explains in the Wall Street Journal, the amount of din we hear while flying often depends on the decisions of manufacturers and airlines.
Before moving on, play to make the experience with Post Airlines more realistic
In general, the greater the amount of insulating and sound-absorbing material installed in the fuselage (the part of the aircraft excluding the engines, wings and tail), the less noise coming from outside. The problem is that these materials make airplanes heavier and consequently less fuel efficient.
The main cost for an airline is almost always fuel, so the less it consumes the better for the company's balance sheets. Airplane manufacturers such as Airbus (Europe) and Boeing (United States) know this, and are therefore looking for the right compromise to add as little weight as possible when designing the insulation systems of their airplanes. This way, they can offer customers airplanes that are quiet enough inside and don't consume too much fuel.
Manufacturers' work is facilitated by the fact that there are not many laws or standards that impose limits on the internal noise of airplanes. There are therefore good margins to work on when designing a new aircraft, even if the designers are aware that they cannot go too far in testing the endurance of future passengers.
Anyone who has taken a plane at least a couple of times in their life knows that the noise inside the cabin is not homogeneous. As intuition suggests, the noise is loudest in the vicinity of the engines and behind them, where the exhausts are, while it is lower in the front. Also for this reason, in addition to the practical ones of greater proximity to the main access door, first class and business are placed at the beginning and not in the queue.
Using a decibel meter (a sound level meter), McCartney carried out some tests – very empirical and without too many scientific pretensions – to record the noise of the airplanes on board. He found confirmation that more noise is heard near the engines and in the tail, as well as near the exits, where the hatches make insulation less efficient than the rest of the fuselage.
The loudest moment is of course during take-off, when the engines are pushed to their maximum to get the airplane into the air. On average indoors, the level reaches 84 dB, roughly equivalent to hearing a truck pass one meter away. During the ascent phase, the noise is reduced by a few decibels, up to 78 dB of the classic buzz in the cruising phase. During landing preparation the noise increases again by a couple of dB: in addition to the engines, the opening of the landing gear and the extension of the wings are heard.
The landing is almost as noisy as the take-off, especially when the thrust reversers of the engines are activated to slow the plane on the runway. Measuring a landing on a Boeing 777, McCartney achieved 95 dB.
Once on the runway and en route to the terminal, an airplane produces less noise, although it does not fail to make some distinctive sounds. Among these is the noise of the pumps that are activated to balance the aircraft, moving fuel between the various compartments of the wings.
Apart from the engines, the noisiest things on board during the cruise phase are the call systems for the flight attendants and to fasten / unfasten the seat belts (those that “ping”), and the internal communication system, used by the crew to spread messages and warnings. The system is deliberately set on a high volume: it is good that all the people on board can hear it, since it is through that system that safety warnings and communications in the event of an emergency are spread. The announcements reach 92-95 dB depending on the airplane and the volume at which they are set.
The fans of the air conditioning and air recirculation system also produce a discreet noise, which is added to that of the wind and the motors (and any screaming children).
On a Boeing 777 the noise during the cruise phase in business class is equal to 75 dB, while in the tail it reaches 80 dB. In addition to the engines, the noise is produced by the flow of air passing over the wings and passing through the fuselage. It is estimated that on most airliners, wind and turbulence are responsible for 70 to 80 percent of the noise heard. At one time, on older models, the main source of noise was the engines.
In the case of a couple of hours of flight, the background hum of airplanes does not cause particular problems, but prolonged exposure for several hours – as in the case of transcontinental flights – can have some negative effects on health and mood. . Some struggle to sleep and end their flight dazed and fatigued. Thoughtful airlines offer disposable earplug kits to reduce the problem, but they are often not enough to isolate noise at lower frequencies. Who can use noise canceling / canceling headphones that superimpose a second noise to cancel the first. They are usually effective, but the best models are expensive and tend to only be used by those who take a lot of planes in a year.
In Hamburg, Germany, there is a division of the Center for Applied Aeronautics Research ZAL that is responsible for evaluating the external and internal noise of aircraft. Researchers collaborate with airplane manufacturers and numerous airlines, testing future airplane models in a large wind tunnel. The new generation ones will have larger motors, which consume less, but which produce more noise especially at lower frequencies. It could be a problem for passengers and for this reason new solutions are being studied to better isolate the fuselage, without affecting too much the overall mass of the new aircraft.
