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The flight made the world a smaller place. If you have the money, it is now possible to commute between the coasts for work or to travel the planet on vacation. But this freedom comes at another cost-pollution. Planes emit greenhouse gases, which contribute to climate change (to the point where some universities ask scientists not to fly), and planes are very noisy if you live near an airport. Mehdi Khorrami, an aerospace researcher at NASA's Langley Research Center in Virginia, said, "The number one public complaint received by the Federal Aviation Administration is aircraft noise. He is part of NASA's research team looking for ways to make aircraft quieter.
When you think of noise, you probably think of the sound of a jet engine. And the companies that build these power plants have already managed to reduce the noise of modern engines by using larger, quieter fans and cutting rafters at the back of the nacelles, as on the Boeing 787.
NASA focuses on the cell. That's the body, the wings, the landing gear, the flaps – everything except the engines. He has just completed a series of test flights using Gulfstream III jets at Armstrong's NASA base in California, where he combined several experimental technologies. When it comes to noise, the messy airflow is the enemy, so the key tactic was to smooth all that air. Essentially, NASA is trying to flatten the plane.
The first major change in the jet was the flaps on the back of the wings. The engineers ripped them off and replaced them with a section of flexible metal and plastic. This experience, called the Adaptive Compliant Trailing Edge, is a long-term effort to improve the aerodynamic efficiency of these control surfaces. When the flaps come out, they leave spaces and hard edges in the wing, which makes the air flow discombobulated. The resulting swirls are not only bad for the aerodynamics, they are also noisy. Eliminate flap gaps, cut the noise. At least that was the theory that the researchers wanted to test.
The second change concerned the landing gear – the wheels that folded into the openings below the plane. When they are open, they create a large cavity that also creates a messy airflow and noise. NASA put a series of rafters at the front of the opening to smooth the air, stretched a net through the opening and added sound-absorbing foam to the aircraft. 39, rear
Engineers also designed porous wheel mounts. through a series of small cheese grater-type holes on the front. This helps to reduce the aerodynamic impact when the landing gear is down for take-off or landing, ie when ground people are most likely to have a landing or landing. To hear a plane. The technology has been proven in computer simulations and models in wind tunnels; It was now time for the engineers to put it on a real plan.
To test the changes, the researchers piloted two Gulfstreams – the type Important Business People like to charter – on a network of 250-foot spiral microphones on the dryer. the lake bed at Edwards Air Force Base, north of Los Angeles. A total of 185 microphones, drenched to survive in desert conditions, listened to planes passing over their heads, measuring the sound of each jet, one modified and the other standard.
Good flying conditions in the desert working a few hours unsociable. "The best time we can find here is at sunrise, when there are the calmest winds and the most stable atmosphere," says Kevin Weinert, project manager for the flights of noise reduction at NASA Armstrong. So, on flying days, the team gathered at 4 am, crammed around the portable heaters, sharing breakfast and coffee with a few people brought with them. When the conditions were perfect, the pilots took off, circled and idled the engines to eliminate almost all their noise. Then they flew about 1000 feet above the microphones for three hours.
These experimental flights were unusual in that they combined several technologies at once. Usually, researchers just change one thing at a time, so that they can evaluate it without worrying about other factors that might upset the results. In this case, the team seized the opportunity to combine technologies developed separately (but with the same purpose), and to observe the real world results. Up to now, these results are encouraging: the researchers found a 70% reduction in noise
. "It was wonderful to see the numbers, after all the work and the early hours of the morning," says Weinert. Now that NASA has proven the concept, it is up to commercial aircraft builders to adopt the technologies and understand how they can use them to make other aircraft quieter. These initial flights show that small jets can be smothered, and that the results should reach much larger planes. "The goal is that it can be used on current and future major transport, like the 777," says Weinert. Ultimately, this could make life near airports a little quieter and help reduce at least one of the flight costs.
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