Conventional transport aircraft wing design is driven mainly by cruise efficiency, i.e., adequate lift is generated at high speed for level flight with minimal drag. Conventional high-lift systems (leading edge slats and trailing edge flaps) were designed to augment lift and stall characteristics at the low speeds encountered during landing.
Noise produced by unsteady flow around aircraft structures, termed airframe noise, is an important source of aircraft noise during landing approach. Conventional leading-edge slat devices for high lift are a prominent source of airframe noise. Notional concepts for a slatcove filler (SCF) have been proposed to fill the cavity behind the slat and reduce the unsteadiness of the flow in the deployed configuration. The invention disclosed here is a unique approach to realizing a deployable SCF. The structural concept is simple and will enable autonomous achievement of the desired deployed shape while enabling a clean cruise configuration with minimal weight addition.
It is desirable for the multi-element airfoil to revert to a smooth, single-element profile during the cruise phase of flight to reduce the drag of the wing. In current practice, the multiple airfoil elements are nested together with the leading edge of each element after the foremost fitting into a cove in the aft lower surface of the preceding element. These coves present a cavity to the flow when the elements are deployed, and the flow forms a vortical recirculation region within each cavity. While this vortical recirculation disrupts the lift-producing capability of the airfoil by only a minor amount, a high-velocity gradient or shear, which is found to be highly unsteady, is generated at the boundary of such a recirculating region. This unsteadiness generates considerable noise that radiates outward from the wing and may be heard by an observer on the ground. A SCF approach to slat noise reduction has the advantage of preserving the gap between the slat and main wing element for aerodynamic benefit. A SCF can also be a very effective treatment for airframe noise reduction if designed properly, but it cannot eliminate the noise because some noise generation mechanisms remain.
The approach adopted in this work is that of a deformable SCF structure that stows in the cavity between the slat and main wing element under the authority of the slat actuators, and deploys automatically with deployment of the slat. The SCF concept has been shown, both computationally and experimentally, to provide significant broadband noise reduction. The design can be retrofitted to existing aircraft structures, and can be easily incorporated into existing or forthcoming designs for aircraft wing structures. The concept involves very few components, requires no additional mechanical support from pneumatic or hydraulic systems, and makes use of existing slat actuation systems for retraction. Hence, the design is completely autonomous, extremely simple, and constitutes a low-weight addition. The concept is failsafe in that lift would not be diminished in the event that the SCF failed to deploy.
This work was done by Travis L. Turner, David P. Lockard, Mehdi R. Khorrami, and Craig L. Streett of Langley Research Center; and Reggie T. Kidd and Douglas L. Webber of ATK Space Division. NASA is actively seeking licensees to commercialize this technology. Please contact LaRC-PatentLicensing@ mail.nasa.gov to initiate licensing discussions. Follow this link for more information: http://technology.nasa.gov/patent/LARTOPS-87 . LAR-17877-1