Abstract:
An apparatus to modify a wing to provide increased lift over drag ratios compared to similar wings with straight leading edges. For wings extending in a lateral direction, and defining a longitudinal upstream direction, the apparatus forms a laterally extending leading edge facing in the upstream direction. The apparatus forms a plurality of protrusions spaced laterally along the leading edge, the protrusions creating a smoothly varying, alternately forward-and-aft sweep along the leading edge relative to the upstream flow direction along the leading edge.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to a streamlined body (e.g., a wing having an airfoil cross-section) and, more particularly, to a streamlined body having a leading edge configured to maximize the body&#39;s lift while minimizing the body&#39;s drag. 
     Designing the lift over drag ratio of a wing (or other streamlined body) for the efficient production of lift, while producing a minimal level of drag, is a normal aspiration for a wing designer. The efficiency of a wing directly correlates to the overall fuel required for a flight, which can significantly impact the overall cost of operating an aircraft. Therefore, it is highly desirable to have an apparatus for improving the efficiency of a wing. 
     Numerous types of apparatus have been designed to affect the aerodynamics of wings. Many of these apparatus can be divided into three categories: slats; strakes and vortex generators. Slats are deployable leading edge devices that enlarge the wing area to increase lift. Typically a slat will extend the leading edge of the wing in a forward and downward direction to increase both the chord and the effective thickness or camber of the wing. The extension and/or retraction of a slat can be driven either by an actuator or by aerodynamic forces. Slats are found on most commercial aircraft and are used primarily during landing. While slats do increase lift, they also appreciably increase drag. Furthermore, slats are active devices, adding significantly to the cost of manufacturing and maintaining the wing. 
     Strakes are a category of typically passive fin-type devices that generally extend from the leading edge of a wing or other aerodynamic structure. Strakes are used for any of a variety of reasons relating to controlling the flow of air over a wing. Depending on the manner in which they are used, strakes can be used to modify airflow so as to either increase the wing&#39;s lift or decrease the wing&#39;s drag. However, the use of strakes is primarily limited to aerodynamic structures that have airflow occurring in undesirable patterns along the surface of the structure. 
     Vortex generators are typically small protrusions across the airflow that are generally placed on the low pressure side of an airfoil. As indicated by their name, the vortex generators typically have discontinuities that create vortices. Typically these vortices help maintain a boundary layer of flowing air attached to the wing. When the air separates, it causes wing stall, loss of vehicle control, and catastrophic crashes. Vortex generators cause additional parasitic drag. 
     Accordingly, there has existed a definite need for an apparatus for improving the efficiency of a streamlined body, and to related methods. The present invention satisfies these and other needs, and provides further related advantages. 
     SUMMARY OF THE INVENTION 
     The present invention provides apparatus and methods for improving the efficiency of a streamlined body, such as a wing. The invention typically provides for increased lift over drag ratios compared to similar streamlined bodies with straight leading edges. 
     Wings are bodies that extend in a (generally) lateral direction, and define a longitudinal upstream direction. They have a laterally extending leading edge facing (generally) in the upstream direction. Other streamlined bodies can similarly be said to extend laterally, defining a leading edge facing (generally) in an longitudinally upstream direction. The invention features a plurality of protrusions spaced laterally along the leading edge, the protrusions creating a smoothly varying, alternately forward and rearward sweep (or greater and lesser sweep) along the leading edge (relative to the upstream flow direction along the leading edge). An advantage of this feature, in the inventors&#39; belief, is that it creates lateral air flow along the leading edge of the streamlined body, thereby limiting the creation of high static pressure stagnation points along the leading edge. Furthermore, it introduces streamwise vortices near the leading edge, and lowers tip vortex strength and the related induced drag by compartmentalizing low pressure regions. 
     Another feature of the invention is that the protrusions are preferably separable from the remainder of the laterally extending wing and/or streamlined body. This feature advantageously allows the protrusions to be manufactured separately from, and even significantly after, the manufacture of the remainder of the streamlined body. It also potentially allows the protrusions to be lightweight structures that can be structurally supported by the streamlined body. Preferably, it is inexpensive, non-load bearing, and held in place by fluid-dynamic forces. 
     Other features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is an exploded perspective view of a wing section under a first embodiment of the invention, 
     FIG. 1B is a perspective view of the wing section depicted in FIG.  1 . 
     FIG. 2 is a plan view of the wing section depicted in FIG. 1 
     FIG. 3A is a cross-sectional side view of the wing section depicted in FIG. 1, taken along line A—A of FIG.  2 . 
     FIG. 3B is a cross-sectional side view of the wing section depicted in FIG. 1, taken along line B—B of FIG.  1 . 
     FIG. 4 is a plan view of an aircraft under a second embodiment of the invention, having a swept wing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A section of a wing  10  according to one embodiment of the present invention is shown in FIGS. 1A and 1B. The wing is a laterally extending body having a laterally extending primary portion  12  and a laterally extending leading portion  14 . The primary portion forms an unswept wing characterized by a constant chord and cross-sectional airfoil shape, and by a straight, laterally extending leading edge  16 . The leading portion of the body is disposed along the leading edge of the primary portion, and is scalloped, i.e., it forms protrusions  18  that extend forward significantly from the leading edge. 
     The wing  10  can be configured for a broad array of functions. Many typical vehicles, such as aircraft, watercraft (both surface and submersible), and land vehicles, use horizontal, vertical and/or canted wings for creating lift, stabilizing airflow, maneuvering, and/or creating other aero- and/or hydrodynamic forces. Similarly, various apparatus that handle fluids (i.e., liquids or gasses), and particularly ones that handle large quantities of fluids, employ wing structures to direct the flow of the fluids, stabilize the fluids, measure the flow rate of the fluids, and other such functions. 
     With reference to FIGS.  1 A— 3 B, the primary portion  12  of the wing  10  is constructed using conventional techniques for the type of wing that is being designed. For example, if the wing is being designed for a typical commercial aircraft, the wing will likely include one or more longitudinally extending spars, with a series of frames at longitudinally spaced locations along the spars, and a skin panel that is attached around the frames to form the exterior shape of the body. If the wing is being designed for a car spoiler, the primary portion will likely be a composite structure that is solid throughout. 
     Preferably, the cross-section of the primary portion  12  (depicted in FIGS. 3A and 3B) is characterized by an airfoil shape, with a rounded leading edge  16 , a sharply pointed trailing edge  22 , and a smoothly varying upper and lower camber  24  and  26 , respectively, in between. The camber reaches its maximum thickness at approximately a quarter-chord or 30% chord location  28  (i.e., the maximum thickness of the primary portion is spaced from the leading edge by approximately 25% or 30% of the distance between the leading and trailing edges). Whether the upper and lower camber are symmetric to the chord line  30  will depend on the function that the wing is being designed for, as is known in the art. 
     As noted above, the leading portion  14  forms a series of protrusions  18  that define a leading edge  32  for the wing as a whole. It can be designed either as a single, unitary structure (as depicted) or as a plurality of parts (not shown). In the latter case, each part can include either a single protrusion or a plurality of protrusions. The leading portion is relatively small in comparison with the primary portion  12 , and will typically be primarily supported by the support structure of the primary portion. Therefore, the leading portion will not be as likely to need spars, supports or exceptionally high strength materials that might well characterize the primary portion. Instead, it can be made to minimize weight and cost. 
     The method of attachment used to affix the leading portion  14  to the primary portion  12  will be selected from among the types of methods typically used for the particular application. On an aircraft wing, for example, the leading portion could be riveted to the primary portion at the longitudinal locations of the frames, with additional attachments at spaced intervals along the wing skin. Alternately, the primary portion and leading portion can be formed as a unitary member. This might be particularly desirable for simpler structures, such as that of a car spoiler. In such a case, there would be no need for an underlying primary structure with a leading edge. Instead, it could be one solid piece, or a wing with spars, frames, and other structures to support the scalloped leading-edge&#39;s shape. 
     As seen in FIGS. 2,  3 A and  3 B, at the longitudinal peak  40  of each protrusion  18  (i.e., the longitudinal location along the wing of the protrusion&#39;s fore-and-aft peak), the protrusion preferably extends back substantially to the points  42  and  44  at which the upper and lower cambers  24  and  26  reach their maximum height. This can occur at a different fore-and-aft position on the upper camber as opposed to the lower camber. Thus, the resulting upper and lower camber of the combined leading and primary portions is preferably an elongated variant of the primary portion&#39;s upper and lower camber. 
     At the bottom  46  of the fore-and-aft trough between each succeeding protrusion (see FIG.  2 ), optionally being laterally equidistant from the peak  40  of each protrusion, the leading portion  14  might add little to no shape to that of the primary portion  12 . Thus, the resulting upper and lower camber of the combined leading and primary portions is preferably substantially the same as the primary portion&#39;s upper and lower camber. However, this might not be true near the root and/or tip of a wing that otherwise fits this description. 
     In between each trough  46  and peak  40 , the wing&#39;s leading edge  32  varies in a fore-and-aft direction in an approximately smooth and oscillatory manner, thus creating an alternating forward and rearward sweep along the leading edge of the wing. The maximum fore-and-aft slope (i.e., change in fore-and-aft direction verses longitudinal location) of the leading edge reaches roughly the same magnitude on each side of each trough, although opposite in sign. 
     The forward extension distance that the leading portion  14  adds to the camber of the primary portion  12  varies smoothly, thus forming a smoothly varying set of forward protrusions on a wing that otherwise has a relatively constant chord and airfoil. However, it is to be understood that the invention can be applied to a wide variety of wings, including wings that already have varying chords, sweeps, and cambers. It is to be understood that application of the invention to a swept wing might lead to a wing with a leading edge having a leading edge sweep that repeatedly varies between smaller and larger values of the same sign. For example, a highly rearward-swept wing with small protrusions that extend forward and outward at an angle normal to the sweep of the wing might not have any forward-swept portion of its leading edge. Also, it should be clear that rearward-swept wings will likely have outboard protrusions located in a more rearward (i.e., downstream) position, and forward-swept wings will likely have outboard protrusions located in a more forward (i.e., upstream) position. 
     The longitudinal spacing and/or amplitudes (i.e., the distance that the fore-and-aft peak extends forward) of the protrusions preferably increases in a portion near a wing root and decrease in a portion near a wing tip (relative to more centrally located protrusions). The wing root and wing tip portions each commonly constitute 20 -30% of the wing, the remaining 40 -60% being a center portion. Wing roots and wingtips can sometimes be defined by changes in a wing&#39;s chord, camber, sweep and/or dihedral, as well as the placement of attached items such as pylons. 
     In the case of wings with decreasing chords (i.e., where the minimum chord between each adjacent pair of protrusions decreases), or with wings having wing sections that have decreasing chords, the protrusions preferably decrease in size corresponding to, and preferably proportional to (or otherwise related to), the decrease in chord, the decrease in maximum height, or some proportional/related combination of the two. Additionally, it is preferable that the distance between each peak and trough proportionately decrease, such that tapered wings have protrusions of increasing frequency and decreasing size. 
     With reference to the aircraft  50  of FIG. 4, if the leading edge  52  of the primary portion  54  is swept back or forward (i.e., it is not zero), the wing forms pairs of adjacent protrusions where, relatively, one is aft  56  and one is forward  58 . The lateral center point  60  of the fore-and-aft trough  62  preferably moves toward the aft protrusion  56 , thus allowing the maximum fore-and-aft slope of the leading edge to reach at least roughly the same value on each side of each trough. 
     In experimentation, the present invention has proven to typically both increase lift and lower drag at relatively modest angles of attack up to 10°. Even when no increase in lift was detected near zero angle of attack, there continued to be no drag penalty. Thus, in experimentation the present invention has proven to consistently have an equal or higher lift over drag ratio, and incurs no penalty in wing performance. Other preferred embodiments are anticipated to likewise have this advantage. 
     It is believed that the present invention will likewise function at higher angles of attack, and that it will delay the onset of stall through these higher angles of attack, thereby extending the useful operating envelope of lifting surfaces and control surfaces. 
     The present invention appears to function by altering the typical aero- or hydrodynamics occurring over an airfoil. In particular, in cross-section a typical airfoil will have a stagnation point on the leading edge, where the fluid particles have zero velocity with respect to the airfoil. In front of the stagnation point is a stagnation region, where the fluid has negligible relative velocity. The reduction of the relative speed to zero creates a significant pressure on the wing, and therefore, a significant amount of drag. On a typical wing, a line of stagnation points are thus present longitudinally along the leading edge of the wing, creating a line of high static pressures along the leading edge of the wing. Airfoil drag in a viscous fluid can be reduced by decreasing the size and strength of high static pressure regions. In other words, lower leading edge static pressures improve airfoil leading edge suction. In the present invention, preferably one stagnation point exists at each peak and trough along the leading edge, while the remainder of the leading edge experiences lower static pressures. 
     From the foregoing description, it will be appreciated that the present invention provides an apparatus for improving the efficiency of a wing, and to related methods. While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Furthermore, it is understood that a wide range of applications exist, such as for aircraft, water craft and land vehicles, including rudder leading edges, submarine dive planes and conning towers, sailboat keels, sailboat masts, spoilers, stators, rotors, fans and various appendages. Thus, although the invention has been described in detail with reference only to the preferred embodiments, those having ordinary skill in the art will appreciate that various modifications can be made without departing from the invention. Accordingly, the invention is not intended to be limited, and is defined with reference to the following claims.