Quiet Drag Engine Air Brake
Click here to read about ATA’s recent full-scale Engine Air Brake demonstration!
ATA engineers are currently developing an aircraft engine drag-management device for quiet approach applications. This engine air brake (EAB) has implications for the future of both civilian and military planes. The noise generated by current large aircraft on approach for landing is generally dominated by airframe noise sources such as flaps, slats, and landing gear. This establishes a need for deployable quiet drag devices as technologies enabling operational changes such as steeper, slower, or aeroacoustically cleaner approaches are improved. So-called “quiet” drag could compensate for the loss of drag from the absence of conventional high-drag devices or faired landing gear associated with a cleaner airframe, and enable a steeper and/or slower approach flight path with associated noise benefits.
The Engine Air Brake
The EAB is a novel approach to active and passive control of noise sources for conventional and advanced aircraft configurations. The idea was originally conceived by researchers at MIT as a ram air-driven nacelle with a stationary set of turning vanes that generate a swirling exhaust flow. The research demonstrated that the swirling flow can yield a steady, and thus relatively quiet, streamwise vortex that results in additional drag. This additional drag can steepen the glide slope upon approach, resulting in potential for noise reduction of several dB at ground level below the flight path. ATA is currently extending the technology to produce equivalent drag from swirling flow in a turbofan engine environment. The technical approach includes assessing the impact of various angles of swirl vanes in a turbofan bypass flow, as well as addressing challenges associated with having an engine pylon in the bypass flow path. ATA used a combination of computational fluid dynamics and structural analysis to drive the design of a model-scale prototype to quantify the drag generation and noise reduction potential in a realistic turbofan engine exhaust. Prototypes of different configurations, including swirl vane hardware at different exit flow angles and engine pylon hardware in the bypass flow, were fabricated and tested at NASA Glenn Research Center.
Testing at NASA’s AAPL
In October 2010, ATA completed testing of a variety of EAB configuration 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 anechoic testing environment for engine component research and development. To provide a reflection free acoustic environment, custom-designed 2-foot thick fiberglass wedges are mounted on the dome’s interior walls and floor areas adjacent to the test rigs. The acoustically treated dome walls are also designed specifically to attenuate sound. Together, these elements provide an echo-free testing environment that exceeds the acoustic research testing objectives set forth by NASA and industry. The dome is equipped with near-field and far-field microphone sensor arrays for comprehensive noise measurement.
The test data measured at AAPL quantified the relationship between swirl, drag, flow, and noise for the EAB concept. The measurements also validated the pre-test analysis methods. Application of the measured component noise to system noise fly-over predictions is currently underway. Initial simulations confirm the potential of the EAB to reduce noise on approach.
ATA received funding for this technology through the NASA SBIR (Small Business Innovation and Research) program. The concept has been developed in conjunction with NASA GRC and MIT. ATA has a history of participating in SBIR programs with various agencies. Information on other innovative hardware being developed by ATA can be found here.