Patent Application
20090084904
The present disclosure is directed generally to wingtip feathers, including paired, fixed feathers, and associated systems and methods for designing and operating such systems.
A significant amount of design and manufacturing effort goes into selecting the shape and configuration of the wings used for commercial transport aircraft. The wings must meet a myriad of design goals, including producing high lift with low drag, and providing sufficient structure to carry a payload, without contributing unnecessarily to aircraft weight. To meet these often contradictory design requirements, designers have developed a number of techniques for distributing the load over the span of the wing in a manner that produces sufficient lift without requiring unnecessary structure. For example, the “ideal” load distribution for a flat wing is generally elliptical. However, conventional aircraft wings are typically not designed for elliptical span loads. Instead, they are designed with compromised “triangular” span loads that reduce structural bending loads at the root of the wing. Such designs trade a slight increase in induced drag for a reduction in airframe weight. The degree of compromise varies considerably from one aircraft to another.
Despite the success of designers in developing highly efficient swept wing configurations for transonic commercial transport aircraft, aircraft manufacturers are under continual pressure to improve the efficiency of such wings so as to reduce aircraft fuel consumption and increase aircraft payload. One approach to improving wing performance has been to add wingtip devices. For example, several existing commercial transport aircraft include winglets extending vertically or generally vertically upwardly and/or downwardly from the tips of the wings. Another approach to enhancing lift at the wingtips is to include wingtip feathers. These feathers are typically movable in some fashion relative to the tip of the wing, and typically include a multitude of spaced-apart feather elements. While such designs have proved suitable in some installations, there is a continued need to develop low-cost, low-weight, high-efficiency designs that are suitable for commercial transport aircraft.
Aspects of the present disclosure are directed to methods associated with wings and wingtip feathers. One method for designing an aircraft wing includes providing a geometry for a wing having an upper surface, a lower surface, and an aft-swept wing leading edge. The method further includes selecting a geometry and location for a first feather and a second feather based at least in part on a predicted effect of the feathers on a location of a shock on the upper surface of the wing at transonic flight conditions, with the first and second feathers being positioned at an outboard tip of the wing, and with the second feather being positioned aft of the first feather.
In a particular embodiment, the geometry of the wing, or the first feather, or both, can be altered to change the location of the shock. In another particular embodiment, the location of the shock can be shifted aft by shifting the trailing edge of the first feather aft. In yet further embodiments, the feathers can be selected to have particular geometric characteristics. For example, the first and second feathers can be fixed relative to the wing. In another example, the outboard portion of the wing can have a wingtip with a tip chord length, and the first feather can be selected to have a first chord length that is at least 50% of the tip chord length. The first feather can also be swept aft by a first sweep angle that is equal to or greater than the wing sweep angle, and can be canted upwardly relative to the horizontal by an angle of about 45 degrees. The second feather can have a second leading edge that is swept aft by a second sweep angle greater than the first sweep angle, and is canted downwardly relative to the horizontal by an angle of about 45 degrees.
Further particular embodiments are directed to methods for operating an aircraft. One such method in accordance with a particular embodiment includes flying a swept wing commercial transport aircraft at a transonic Mach number, and forming a shock at an upper surface of the wing. The method can further include controlling a location of the shock via a first feather fixed relative to the wing at an outboard tip of the wing, and a second feather fixed at the outboard tip of the wing and positioned aft of the first feather.
The following description is directed generally to wingtip feathers for aircraft, including tip feathers that are paired and fixed relative to the aircraft, and associated systems and methods including methods for designing and operating such systems. Several of the details describing structures and/or processes that are well-known and often associated with aspects of the systems and methods are not set forth in the following description for purposes of brevity. Moreover, although the following disclosure sets forth several representative embodiments, several other embodiments can have configurations and/or components different than those described in this disclosure. For example, other embodiments may have additional elements, and/or may delete several of the elements described below with reference to
Each of the wings 120 can include a feather system 140. The feather system 140 can in turn include a first, e.g., forward feather 141 and a second, e.g., aft feather 142, both of which can be fixed relative to the wing 120. The fixed positions of the first and second feathers 141, 142, and the presence of only two feathers at each wing 120 can simplify the design, installation and operation of the feather system 140. Further aspects of the feather system 140 that improve overall aircraft performance are described further below with reference to
In a particular embodiment, both the first and second tip feathers 141, 142 can be flat and can accordingly define a plane having a fixed angular value relative to the horizontal H. In other embodiments, the tip feathers 141, 142 can have other shapes that are expected to improve the aerodynamic performance of these surfaces. For example, the first feather 141 can be twisted in a spanwise direction S1, as indicated by arrow T1. In addition to or in lieu of twisting the first feather 141, the first feather 141 can be rolled toward its outboard tip, as indicated by arrow R1. The second feather 142 can also be twisted in a manner that changes along its span, as indicated by arrow S2, and/or can also be rolled toward its outboard tip. It is expected that these arrangements will improve the aerodynamic performance of both the first and second tip feathers 141, 142. For example, the twist provided to both the tip feathers 141, 142 can allow the feathers to operate a higher angles of attack without stalling, as compared with feathers that are untwisted.
Each of the first and second feathers 141, 142 can have a chord length that is selected to improve aerodynamic performance, not only of the feathers but also of the wing 120 from which the feathers depend. For example, the wingtip 123 can have a wingtip chord length 126, and the first feather 141 can have a first feather chord length 145a that is at least 50% of the wingtip chord length 126. Accordingly, the juncture between the first feather trailing edge 144a and the wing tip 123 can be at or aft of a midchord point 127 of the wingtip 123. It is expected that this arrangement will control the location of a shock 125 (shown schematically) that forms on the upper surface of the wing 120 at transonic Mach numbers. In particular, it is expected that by placing the first feather trailing edge 144a aft of the midchord point 127, the shock 125 will tend to “follow” the first feather trailing edge 144a over at least a spanwise portion of the wing 120. Accordingly, it is expected that the shock 125 will be aft of a location it would otherwise be were the first feather 141 to have a chord length 145a less than 50% of the wingtip chord length 126. An expected advantage of this arrangement is that it can keep the shock 125 at an aft location over the outboard portion 122 of the wing 120. Because the pressure of air passing through the shock 125 increases, moving the position at which this increase occurs in an aft direction reduces the amount of wing area subjected to the elevated pressure and therefore can reduce the expected impact on wing lift created by the presence of the shock 125.
In a particular embodiment, the second feather 142 can have a second feather chord length 145b that complements the first feather chord length 145a, e.g., the first and second feather chord lengths 145a, 145b can add up to the wingtip chord length 126. As a result, the second feather trailing edge 144b can be aligned with the wing trailing edge 128. In other embodiments, the trailing edge of the second feather 142 need not be coincident with the trailing edge 128 of the wing 120. However, it is expected that in at least some embodiments, coincident trailing edges will reduce the likelihood for the formation of vortices or other flow disturbances at the trailing edge region.
One feature of at least some of the foregoing embodiments described above with reference to
Another feature of at least some of the foregoing embodiments is that both the first and second feathers 141, 142 are fixed relative to the wing 120, and neither the first feather 141 nor the second feather 142 includes movable high lift devices (e.g., trailing edge flaps, leading edge slats, movable sub-winglets, or other such features). An expected advantage of this arrangement is that it can simplify both the installation and maintenance of the feather system 140. Another expected advantage is that the feathers can be designed to have a particular orientation relative to the wing 120, and that orientation can remain fixed over the entire operating envelope of the aircraft, thereby reducing the likelihood for the feathers to be placed in a less than optimum position.
Methods in accordance with particular embodiments of the disclosure include designing the location and position of the wing 120 and the first and second feathers 141, 142 in conjunction with each other and possibly in an iterative fashion. For example, with a given wing geometry, the size, shape and location of the first and second feathers can be selected in an iterative manner to provide the desired shock location. In another embodiment, the first and second feathers can have a fixed geometry and the outboard portion of the wing can be tailored to produce the desired shock location. In still a further embodiment, the size, shape, and location of the first and second feathers 141, 142, as well as portions of the wing 120 (e.g., the outboard portion) can be changed in an iterative manner until the desired position of the upper surface wing shock is achieved.
After process portions 502-506 have been completed, the wing with the first and second feathers can be analyzed. For example, process portion 508 can include estimating the location of a shock on the wing upper surface based upon the foregoing geometry. The aerodynamic characteristics associated with the shock location can be compared with target values in process portion 510. The desired aerodynamic characteristics can include lift/drag characteristics, vortex formation characteristics, and/or other parameters. If the shock location produces the desired aerodynamic characteristics (as determined in process portion 510), then the design of the wing and wing tip feathers can be completed in process portion 512. If the desired aerodynamic characteristics are not met in process portion 510, the process can return to process portion 502, process portion 504 or process portion 506. For example, if the wing geometry is to remain fixed, the geometry and/or location of the first feather and/or the second feather can be updated in process portions 504 and 506 respectively. If the wing geometry is variable, it can be changed in process portion 502. The geometry and/or location of any combination of the wing, the first feather, and the second feather can be varied in an iterative manner until the expected shock location produces the desired aerodynamic characteristics.
In still a further particular embodiment, aspects of the process 500 can be automated. For example, one or more of the parameters described above (e.g., feather chord length, twist angle, roll-up characteristics, and/or other features) can be parametrically varied using a computer simulation. For example, the chord length of the first feather and the associated location of the first feather trailing edge is expected to have a significant effect on the location of the shock on the upper surface. Accordingly, a computer simulation can include parametrically varying the chord length and trailing edge location and automatically selecting the chord length and trailing edge location that produces the desired shock location. Similar techniques can be used to optimize other characteristics and features of the wing tip feathers and/or the wing (in particular the outboard portion of the wing) to which the feathers are attached.
Suitable analysis tools for conducting the foregoing methods include AGPS, a computer-aided-design geometry generation tool available from The Boeing Company of Chicago, Ill. The TRANAIR code, available from Calmer Research Corp. of Cato, N.Y., can be used to perform flow analysis. The NPSOL code, available from Stanford Business Software, Inc. of Palo Alto, Calif. and/or TRANAIR can be used to optimize the geometry based on flow results. Other suitable tools can be used in other embodiments.
From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from these embodiments. For example, the tip feathers can have different shapes and/or orientations than are not specifically shown in the Figures, while still being arranged in pairs that are fixed relative to the wing and/or that control the wing upper surface shock generally in the manner described above. In still further embodiments, the tip feathers may in some cases be movable relative to the wing from which they depend, while still providing the shock-positioning features described above. Certain aspects of the foregoing embodiments described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, a particular embodiment may include a first feather that is not swept by an angle greater than the wing sweep angle, but that still has a chord length that extends beyond the mid-chord point of the wingtip, so as to provide control over the wing upper surface shock. Further, while advantages associated with certain embodiments have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages. Accordingly, the disclosure can include other embodiments not shown or described above.
