Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
2002-11-22
2004-09-14
Barefoot, Galen (Department: 3644)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S200000, C244S216000, C244S130000
Reexamination Certificate
active
06789769
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 101 57 849.0, filed on Nov. 24, 2001, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to an arrangement for reducing the aerodynamic noise generated by a leading edge slat of a main wing of a commercial passenger transport aircraft.
BACKGROUND INFORMATION
Modern commercial passenger transport aircraft are equipped with high-lift auxiliary devices that are typically deployed during take-off and/or landing phases of a flight in order to increase the lift generated during relatively low flight speeds. These high-lift auxiliary devices include leading edge slats and landing flaps, which are respectively movably connected to the leading edge area and the trailing edge area of a main wing, so as to be selectively extendible from or retractable to the main wing. In the extended or deployed positions, these high-lift auxiliary devices, in addition to the extended landing gear, represent the major generators of aerodynamic flow noise of commercial transport aircraft. For example, typical leading edge slats used on modern commercial transport aircraft are of the Handley Page slat type, which forms an air gap or slot between the slat and the forward nose of the main wing. The air flowing through this gap or slot achieves the desired increase of the generated lift, but simultaneously also leads to an increased noise generation. This aerodynamically generated slat gap noise can actually reach or exceed the noise level magnitude of the jet engines, when the engines are sharply throttled back during a landing approach.
In view of the above, it has long been a serious problem and the subject of substantial research in the field of aircraft design, to reduce the aerodynamically generated noise of the air flowing over various aircraft structures, and especially the extended high-lift auxiliary devices, and particularly the extended leading edge slats. For example, results of a flight research program of the Federal Republic of Germany have shown that the leading edge slat contributes a higher proportion of the total noise, in comparison to the noise generated by the landing flap. Detailed studies have identified a well-developed entrapped eddy vortex in the airflow on the concavely curved rear surface or inner surface of the leading edge slat facing the forward nose surface of the main wing. This entrapped eddy vortex is a significant potential noise source.
The noise generation of this entrapped eddy vortex is understood as follows. A flow separation of the gap airflow constantly occurs between the slat and the main wing along the above mentioned concavely curved inner surface of the extended slat, and thus generates the entrapped eddy vortex. This vortex is continuously supplied with energy by the accelerated gap airflow bordering along the slat. Also, small turbulence cells are continuously formed along the boundary or flow separation line between the vortex flow area and the continuous gap airflow flowing through the gap. These turbulence cells continuously become entrained in the accelerated gap flow, whereby the major noise is generated, especially due to the further flow of these turbulence cells past the upper rear or trailing edge of the slat and then over the upper surface of the main wing.
A study by Dr. Werner Dobrzynski, Mr. Burkhard Gehlhar, and others, entitled “Airframe Noise Studies on Wings with Deployed High-Lift Devices”, Deutsches Zentrum fuer Lift- und Raumfahrt e.V. (DLR), Institut fuer Entwurfsaerodynamik, Abteilung Technische Akustik, Forschungszentrum Braunschweig, Germany, published in the American Institute of Aeronautics and Astronautics, 4
th
AIAA/CEAS Aeroacoustics Conference, Jun. 2-4, 1998, Toulouse France, is also directed to the reduction of aerodynamic noise on an extended leading edge slat of an aircraft. Among other things, this study investigates a possible solution to the noise problem, which involves an airflow guide plate that is hingedly secured to the leading edge slat in the area of the inner or rearward profile area thereof and extends in a direction toward the main wing in the airflow direction. This airflow guide plate is hinged and can thus be pivoted inwardly relative to the leading edge slat. This solution aims to reduce the noise level during take-off and landing of an aircraft with extended slats. When the slat is retracted for cruise flight, the guide plate is then pivoted inwardly against the slats.
Although the above described arrangement of a hinged airflow guide plate may have achieved noise reductions in wind tunnel tests, this solution is not expected to find substantial use in real world applications, in view of practical considerations and difficulties in the actual practice thereof. For example, in the retracted condition of the leading edge slat, e.g. the cruise configuration, the guide plate must be pivoted or tilted against the rearward profile surface of the leading edge slat, and must then have a contour or configuration that is sufficiently matched to the rear curvature of the slat. However, that is not the proper curvature contour of the guide plate for its operation. Furthermore, the retracted position of the slat does not provide sufficient space to allow such a rigidly configured guide plate to be stored between the retracted slat and the nose area of the main wing. On the other hand, if the guide plate is to be flexible, to adapt itself to the curvature of the available space in the retracted and stowed condition of the slat, then such a flexible guide plate would not have sufficient strength and stiffness to durably withstand the significant aerodynamic forces that arise from the airflow through the slat gap in the extended condition of the slat. As a result, the guide plate will tend to flutter, with the end result of radiating noise, which is directly contrary to the intended noise reduction effect.
Furthermore, a pivotally connected or hinged guide plate requires additional mechanically movable parts, which disadvantageously lead to an increase of the manufacturing, installation, maintenance and repair costs, as well as an increase of the total installed weight in the aircraft. Another problem is that the transition from the lower surface of the slat to the hinge of the guide plate or separation surface must be free from contour discontinuities or jumps as well as open slots, which therefore requires very high fabrication and installation accuracy with low tolerances.
Another problem is that the metal guide plate or separation surface is subjected to considerable alternating forces that are initiated by the airflow. Since this guide plate or separation surface is connected only to the bottom edge of the slat via the hinge joint, and no further supports or stiffening arrangements are provided, there is a significant danger that the guide plate or separation surface will be stimulated to oscillate or vibrate back and forth. That would cause significant airflow disruption, drag, and additional noise. Furthermore, since the contour of the rear surface of the slat, as well as the geometry of the air gap, varies over the span of the wing, the various elements of this guide plate or airflow separation surface must be formed with a taper or angled inclination over the span, which leads to additional complication of the retraction mechanism. The situation of any fault or failure becomes especially critical, for example if the mechanism becomes blocked, because then the slat can no longer be retracted.
The above cited publication gives no suggestions or motivations toward overcoming or avoiding these disadvantages, or toward any other device or arrangement that might achieve a better overall result without suffering such disadvantages.
The German Patent Publication DE 199 25 560 A1 aims to reduce the above discussed aerodynamic noise by installing a massive separating member forming a separation surface that is movable relative to the slat, for e
Dobrzynski Werner
Mau Knut
Airbus Deutschland GmbH
Barefoot Galen
Fasse W. F.
Fasse W. G.
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