New Jet Engine Brake Muffles Airplane Landings

An engineering firm has used its computer-aided prowess to create a solution to airplane noise—putting a new kind of "air brake" on the back of a jet engine.

Airplanes are amazing machines that revolutionized how the world gets around. They're also loud. Much time and investment has gone into fine-tuning planes so that humans can live in harmony with their wondrous flying contraptions, and now one company has a clever new idea to make takeoff and landing even quieter.

ATA Engineering was commissioned by NASA to design a drag-management device that would allow aircraft to make quiet approaches and landings to airports with sensitive noise requirements. These days, most of the noise that large aircraft generate on approach comes from airframe noise sources such as flaps, slats, and landing gear sticking out in the wind. So ATA has demonstrated a quiet engine air brake (EAB)—a device that generates similar drag without using flaps or slats on the wing. 

The device uses a deployable swirl vane mechanism to create a vortex of air from the outflow of the turbofan jet engine exhaust nozzle. Because it stows during flight to be aerodynamically neutral, the EAB does not affect the normal operation of the exhaust nozzle while the plane cruises.

The idea is an evolution on a concept originally conceived by researchers at MIT. They used turning vanes inside an engine cowling to disrupt the flow of ram-air as it passed through. That constant flow of swirling air creates a steady and relatively quiet vortex that results in additional drag. Using powerful computers and complicated software, ATA was able to calculate how much drag could be generated and the noise reduction potential when applied to a turbofan engine exhaust.

Back in October of 2010, ATA tested a number of prototypes inside NASA Glenn's Aero Acoustic Jet Propulsion Laboratory (AAPL). The AAPL dome is sixty-five feet high and 130 feet in diameter, providing an echo-free testing environment for engine component research and development. These tests measured the relationship between swirl, drag, flow, and noise. Along with flyover simulations using NASA's Aircraft Noise Prediction Program, the tests suggest a steeper approach path from a 3.2-degree glideslope up to 4.4-degree for a 737-800-class aircraft could result in a perceived noise level reduction of up to 3.1 dB.


The full-scale prototype was successfully tested on a Williams International's FJ44-4 mixed-flow turbofan engine at the Williams Outdoor Test Facility. This type of engine is commonly found on medium sized business jets like the Cessna CJ4, Hawker 400XPR, and Pilatus PC-24. The live test was a soaring success. Not only did the plane meet its goals for drag, flow capacity, and noise, but also the device was deployed and rapidly stowed, and saw a noticeable reduction in fuel burn at full deployment.

Once further ground testing proves the technology is reliable and durable, flight tests will commence. Someday soon, ATA hopes, not only will new airplanes come standard with this quiet drag technology, but also it will be possible to retrofit older aircraft engines with this system so they can meet more stringent noise reduction rules.


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