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The Story Behind: Quieter Jet Engines
Bigger, faster, quieter
Since the airplane made its first sustained flight in 1903, inventors have been hard at work improving the product, focusing on creating faster, bigger, more reliable and more economical passenger aircraft. This was eventually achieved in the form of the jet engine, an invention that has given the world airplanes that are fast, reliable and relatively fuel-efficient. Despite improvements to the jet engine itself, until the current day, there hasn't been much energy devoted to inventing an aircraft that that produces minimal environmental pollution.
Pressure from environmentalists, improved knowledge of the dangers of noise pollution and resultant flight restrictions at major airports are starting to change that. The jet engine, that amazing contraption that allows us to travel faster than the speed of sound, is about to get quieter
The jet engine
A jet engine is an engine that produces forward motion as a result of the rearward discharge of a jet of heated air and exhaust gases. The earliest attempts at jet engines were hybrid designs in which an external power source first compressed air, which was then mixed with fuel and burned for jet thrust. These were unsuccessful, and some were actually slower than engines already in use. Then, engineers turned to an engine that was originally patented in 1791: The gas turbine.
In 1903, Norwegian engineer Ægidius Elling built the first self-sustaining gas turbine engine. By 1917, patents for jet propulsion were issued, but manufacture was prevented by problems of safety, reliability, weight and sustained operation. In Germany, Hans von Ohain patented his version of a jet engine in the mid-1930s and began development. Working with Ernst Heinkel, an important aircraft industrialist, and Max Hahn, a master machinist, Ohain found success. His gasoline-fuelled HeS 3 jet engine was fitted to Heinkel's He 178 airframe and the resulting He 178 jet plane - the first ever - made its maiden flight on 27 August 1939.
The development of the jet engine meant that airplanes could go further, faster. But it had its drawbacks. Although the jet engine ultimately prevailed, the earliest types (known as turbojets) were noisy, fuel-inefficient and problematic. Modern jet aircraft usually use high-bypass turbofan engines, which are reliable, high-speed, and more fuel-efficient than many other forms of long-distance transportation.
Still, engine noise was until recently just as significant a problem as it was in the 1930s - perhaps even more so as environmental groups have drawn new attention to the negative environmental and human effects of noise pollution.
Noise pollution
Jet engines are encased in a nacelle, which is insulated to protect against the extreme heat of jet propulsion and to dampen some of the noise they create. Previously, the nacelle was no match for the extreme noise generated during take-off and landing.
Surplus airplanes and unemployed pilots led to significant growth of commercial airlines in the years after the Second World War. Today, there are 2.5 million flights each month across the world. Thanks to urban sprawl in the post-war decades, airports are today frequently built right up against homes and businesses. Little wonder that they have imposed significant flight restrictions and fines to pacify their neighbours.
Until recently, noise generated outside the cabin was overlooked. As recently as the 1970s, governments generally considered noise pollution to be a "nuisance," not an environmental problem. Research, however, has shown that noise pollution has serious health effects on all animals, including humans. More than an annoyance, noise pollution leads to aggression, hearing loss, tinnitus, hypertension and high stress levels, among other issues. Especially at take-off and landing, the noise from a jet engine can be overpowering.
The zero-splice inlet, patented in 1999, changed that.
The solution
Researchers found the gaps in nacelle linings are a significant source of the tremendous noise jet engines generate. Before the zero-splice inlet, nacelle linings consisted of two to three sections that were fitted together, which left gaps between the individual lining sections. The vibration and noise of the engine escape through these tiny gaps and create acoustic scattering, basically deflecting noise in all directions.
To address the problem, Alain Porte of Airbus pioneered a new material for nacelle linings that could cover the entire inside in just one piece. This was achieved through a perforated, heat-resistant fabric that is flexible enough to line the nacelle, but highly sound-absorbent. The innovative material is strong enough to withstand everything from pressure during flight, the weight of people on some portions to the aerodynamic and inertial forces of the entry of air into the motor housing.
Better yet, zero-splice inlet engines are not only much quieter than their conventional counterparts, but also lighter and more fuel efficient. This uniquely high level of acoustic performance has made it possible for the world's largest passenger plane to also be the world's quietest passenger plane, giving it a significant commercial advantage in an environmentally aware marketplace: The Airbus 380, armed with the zero-splice engine housing, generates 50 percent less noise than any other passenger plane in the world.
Read more about the inventors: Alain Porte, André Robert, Hervé Batard (France)