'Silent Plane' Could Someday Mean Quiet Skies
Nov. 6, 2006— -- If you live anywhere remotely close ... rrrr ... to the landing area of a major airport ... rrrrrr ... you know that the noise can be ... rrrrRRRRRRrrrrrrrr -- well, deafening.
Airlines, aircraft manufacturers and politicians have struggled with the problem for decades. Now a coalition of engineers from MIT and Cambridge University say it is on the way to some solutions.
Today they showed off the results of the Silent Aircraft Initiative -- a design for a sleek, birdlike plane that could someday make airport noise a thing of the past. If aerospace companies decide to build it, the MIT-Cambridge consortium says it could be flying by 2030.
"Think about the noise of an office conversation," says Zolti Spakovsky, a professor of aeronautics at MIT, during a London news conference. "That's about the noise level the aircraft would have on takeoff and landing."
Lifting Body
The proposed plane -- known for now as the SAX-40 -- will have 215 seats and jet engines but is dramatically different from current airliners.
Instead of having a tubular body with wings, the entire plane is a "lifting body" -- shaped to slip through the air more smoothly.
As a result, it can fly more slowly on takeoff and landing, which helps reduce the vibrations that bother residents of airport neighborhoods.
There are no flaps. If you've ever sat in a window seat near the wings, you've probably seen flaps extend from the wings' leading and trailing edges. That increases lift but creates vibration you can feel.
Landing gear has aerodynamic shielding. Engine nozzles vary in size and are opened fully only when the plane is at high altitude.
Finally, engines do not hang from the wings, as they do on many current planes. Instead, they are built into the airframe.
Work to create the SAX-40 took about three years. It was not just an academic project; work also came from Boeing, Lufthansa Cargo, Britain's Civil Aviation Authority and Rolls-Royce, which is a major manufacturer of jet engines.
Engines on Top
"It's a very different looking aircraft," said Ann Dowling, a Cambridge engineer who was a leader of the project. "The way we have been able to achieve low noise is that the engines are mounted on top of the airframe, and that means the airframe shields the engine noise from listeners on the ground.
"We have embedded the engines in the airframe, and that's given us space to put lots of absorbent materials, so we're absorbing some of the sound energy."
One extra payoff from this redesign, say the engineers, is that the plane would use less fuel per passenger than most jets today.
"It's about 25 percent more efficient than aircraft flying out there," says Spakovsky.
Will the SAX-40 ever come to be? One minor drawback: The designers say that while the plane would be quiet on the outside, noise levels inside the cabin would probably be more than most fliers are used to today.