Abstract:
A wake vortex alleviator is provided. The wake vortex alleviator produces rapid variations in the position of vortices emanating from aerodynamic surfaces by using an active flap that moves span-wise back and forth along the outboard section of the surface. Rapidly moving the flap back and forth in a slot at an appropriate frequency will cause the vortex to oscillate, resulting in interaction between other vortices and subsequent destruction much earlier than it would occur naturally. The slot is positioned near the aerodynamic surface trailing edge and generally transverse to a chord line of the aerodynamic surface. The flap can be moved using a variety of actuators to position, translate and stow the flap. The oscillation frequency and position are guided by information feedback according variations in lift in the aerodynamic surface, such as wind gusts. The flaps can control yaw, roll and pitch of the aerodynamic surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is cross-referenced to and claims the benefit from U.S. Provisional Patent Application 60/791,787 filed Apr. 13, 2006, which is hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   The invention relates generally to flaps on aircraft. More particularly, the invention relates to an active translating partial span flap to produce rapid variations in the position of vortices for causing early destruction of wake vortices thereby reducing the wake vortex turbulence hazard. 
   BACKGROUND 
   The goal in today&#39;s aviation market is to improve airport capacity. Heavy aircraft produce very strong vortices when flying at low speed during takeoff and landing, thus creating potential hazards for following aircraft. Consequently, the wake vortex hazard has become the limiting factor in airport capacity. 
   Flying aircraft leave a system of vortices trailing behind as a necessary consequence of the generation of lift. For large transport aircraft, these vortices typically coalesce into a pair of counter-rotating vortices. The strength of the vortices is proportional to the weight of the aircraft and inversely proportional to the aircraft speed. Therefore, a heavy aircraft produces very strong vortices when it is flying at low speed during takeoff and landing. Under turbulent atmospheric conditions, trailing vortices are diffused rapidly and pose little hazard. However, when the atmosphere is calm or weakly turbulent the vortices can pose a major hazard. The vortices are strong enough that they can cause loss of control and/or physical damage to following aircraft, where several accidents have been attributed to the wake vortex hazard. Currently, to manage this problem large longitudinal spacing between aircraft and large lateral spacing between parallel runways are required to avoid any chance of a wake vortex being encountered by a trailing aircraft. As a result of these rules, the wake vortex hazard has become the limiting factor in airport capacity. 
   Two counter-rotating vortices eventually interact with one another, causing them to link and destroy one another. This process is caused by instabilities and is well known. The problem is that these instabilities build up slowly, and under natural conditions it takes a long time and distance for the instability to lead to vortex destruction. 
   The concept of causing early wingtip vortex destruction by exciting instabilities is of paramount interest. Investigation of several different “perturbators” that produce disturbances in the vortex core has been documented. A Kármán vortex street occurs naturally whenever flow passes over a bluff body at sufficiently high Reynolds number. The Kármán vortex street is a repeating pattern of swirling vortices caused by the unsteady separation of flow over bluff bodies. A bluff body such as a cylinder or a flat plate will periodically shed alternating sign vortices. When a vortex is shed, an unsymmetrical flow pattern forms around the wing, which therefore changes the pressure distribution. This means that the alternate shedding of vortices can create periodic forces on the wing surface, causing it to vibrate. If the vortex shedding frequency is similar to the natural frequency of a wing, it causes resonance. With aircraft this periodic force is highly undesirable. These vortices are perpendicular to the flow direction, and thus also perpendicular to the wingtip vortex. Passive, fixed-position vortex shedding perturbators mounted near the trailing edge of wings, such as a bluff body or a transverse jet, that are positioned in the flow have been studied to determine if the Kármán vortex street will be embedded in the tip-vortex core to cause periodic perturbations to the tip vortex, thus exciting natural instabilities of the vortex system for early destruction. By choosing the size of the bluff body correctly, the perturbations will be the correct wavelength to excite instability in the tip vortex core to make the vortex core diameter larger. These perturbators attached to wings that have two or more lifting surfaces were determined to have a high parasitic drag when deployed and limited to exploiting instability of only a single vortex core, causing that core to increase in size. Having a bluff body protrude into the flow to induce disturbances will cause two problems. First, it will increase the drag of the wing significantly. This may be of less concern if it is intended to be deployed only during takeoff and landing. However, takeoff requires maximum engine thrust and is hindered by the added drag. Secondly, by its very nature the bluff body perturbator will cause vibrations of the wing and the entire aircraft, which may have similar unwanted resonance consequences as mentioned above. 
   Accordingly, there is a strong need to develop new ways to minimize wake vortex hazards for reducing the large longitudinal spacing between aircraft and large lateral spacing between parallel runways to avoid any chance of wake vortices being encountered by trailing aircraft and thus improve airport capacity 
   What is needed is a way to produce rapid variations in the position of each vortex. Rapid variations will cause the vortex emanating from each wing to oscillate resulting in interaction between the two vortices and subsequent destruction much earlier than it would occur naturally. 
   SUMMARY OF THE INVENTION 
   The present invention provides a wake vortex alleviator on an aerodynamic surface. The invention includes a translating flap integrated to a slot in the aerodynamic surface. The flap is positioned in air moving across the aerodynamic surface using an actuator for translating, positioning and stowing the flap. The slot is generally transverse to a chord line of the aerodynamic surface and positioned near a trailing edge of the aerodynamic surface. The flap translates along the slot to induce early destruction of the wake vortex created by the aerodynamic surface. 
   In one aspect of the invention, the flap may be on the low-pressure side or on the high-pressure side of the aerodynamic surface. 
   In one embodiment of the invention, the flap is a Gurney flap. In one aspect of the invention, the flap has a length that is up to ½ of a wing half span. In a further aspect, the flap has an effective height that varies along the slot, where the effective height may be up to 5-percent of a length of the chord line. 
   In a further aspect of the invention, the slot may be at least two times the length of the flap. 
   In another embodiment of the invention, the flap may have holes, slices or features cut there through. 
   In one aspect, the aerodynamic surface can be one or more lifting surfaces of a wing. The additional lifting surface may be a Fowler flap. 
   In one aspect of the invention, the slot may be a void in the aerodynamic surface. The void may be an open span between the trailing edge and a lifting surface deployed from the trailing edge. In another aspect, the void may be a space of air that is positioned away from the aerodynamic surface, where the actuator and flap are positioned in the aerodynamic surface and out of the air flow when the flap is stowed. 
   In a further aspect of the invention, the translation can be an oscillation along the slot. Additionally, the oscillation may be a response-oscillation actuated according to variations in lift in the aerodynamic surface, where the lift variations may be wind gusts. 
   According to one aspect of the invention, the trailing edge of the aerodynamic surface may be a sharp edge or a blunt edge. 
   In another aspect of the invention, the actuator is selected from a group of actuators that include a linear ball screw, a worm drive, a scotch yoke, a crank arm and a solenoid. 
   In another embodiment, the flap can be a pair of the flaps mounted on the aerodynamic surface located on each side of an aircraft. In one aspect, the flaps are mounted symmetrically on the aerodynamic surfaces located on each side of an aircraft. 
   In another aspect of the invention, the flap stowage includes a pivoting flap that rotates the flap into the slot and out of the airflow. Further, the flap stowage can be a hidden slot in a root of the aerodynamic surface, where the flap moves into the hidden slot and out of the airflow. 
   According to one aspect of the invention, the flap controls a yaw, a roll or a pitch of the aerodynamic surface. 
   In another aspect of the invention, the aerodynamic surface further comprises an extended flutter boundary. 
   Some key advantages of the current invention include minimizing wake vortex hazards and reducing the large longitudinal spacing between aircraft and large lateral spacing between parallel runways currently required to avoid any chance of wake vortices being encountered by following aircraft. This results in an improved airport capacity by the alleviation of wake vortices caused by aircraft wings during takeoff and landing. This invention produces rapid variations in the position of each vortex by using an active flap that moves span-wise back and forth along the outboard section of a wing. Rapidly moving the flap back and forth in a slot at the appropriate frequency will cause the vortex emanating from each wing to oscillate, resulting in interaction between the two vortices and subsequent destruction much earlier than it would occur naturally. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The objectives and advantages of the present invention will be understood by reading the following detailed description in conjunction with the drawing, in which: 
       FIG. 1  shows a perspective view of a fixed-wing aircraft generating wake vortex hazards upon lift off from a runway. 
       FIGS. 2   a - 2   c  show planar views of a prior art blunt Gurney flap vertical actuator at the trailing edge of an aerodynamic surface. 
       FIGS. 3   a - 3   e  show an active translating flap integrated to a slot of an airfoil according to the current invention. 
       FIG. 4  shows a planar view of a translating flap having features cut there through according to the current invention. 
       FIGS. 5   a - 5   c  show planar views of different wake vortex alleviators configured to different aerodynamic surfaces according to the current invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will readily appreciate that many variations and alterations to the following exemplary details are within the scope of the invention. Accordingly, the following preferred embodiment of the invention is set forth without any loss of generality to, and without imposing limitations upon, the claimed invention. 
     FIG. 1  shows a perspective view of a typical fixed-wing aircraft  100  generating a circulation  102  in the air flow in which it travels through as it lifts off from an airport runway  104 . This circulation  102  results in discrete trailing vortices  106  that extend far behind the generating aircraft  100 . For large aircraft  100 , these trailing vortices  106  tend to be strong and persistent, such that they can pose a serious threat to any aircraft  100  that may encounter them. This problem is referred to as the wake vortex hazard, where the trailing vortexes  106  have a rotation pattern  108  with a downwash component and an upwash component, depicted by up and down arrows in the drawing. 
   The Federal Aviation Administration (FAA) has implemented a set of rules designed to prevent wake vortex hazard encounters resulting from the large fixed wing aircraft  100 , such as a jumbo jet. The rules include mandatory spacing between aircraft  100  operating near airports, causing airport capacity to be significantly limited. With the introduction of ever larger passenger aircraft  100 , the problem has become much more urgent. The strength of the vortex hazard is directly related to the weight of the aircraft  100 , where it is linearly proportional to lift, and inversely proportional to aircraft  100  velocity. At take-off, the required lift is particularly large due to the amount of fuel being carried by the aircraft  100  at that time, whereby strengthen the vortex hazard generated and magnify the problem. The trailing vortices  106  created by the aircraft  100  are counter-rotating  108 , thus, in the absence of any other velocity field, they advect each other downward and slightly forward (depending on the angle of ascent). Once they approach the ground, they tend to move apart from each other horizontally. These vortices  106  can be dangerous to other aircraft  100  entering or leaving the airspace, where trailing vortices  106  can be extremely stable and have long life-spans. This is especially true on calm days with low atmospheric turbulence. Further, the rate of climb of most commercial aircraft  100  shortly after take-off tends to be quite high where, after a short amount of time, an aircraft  100  may achieve an altitude so high that its vortices  106  will not have reached the ground before another aircraft  100  takes off on a different flight path that intersects those vortices  106 . Some of the incidents resulted in loss of life, while others caused the pilot to have to make drastic control surface deflections in order to land or take off safely. Further, crosswinds on runways  104  can easily cause a vortex  106  to linger, where the vortex  106  would otherwise roll away from the runway. The current rules at airports stipulate minimum distances between consecutive aircraft  100  taking-off and landing on their runways  104 , where a typical matrix of required spacing is shown in Table 1. The size designations are based on maximum take-off weight, where “small” is less than 41,000 lbs, “large” is between 41,000 and 255,000 lbs, and “heavy” is greater than 255,000 lbs. This table gives the required spacing between aircraft  100  operating on a single runway  104  in instrument flight rules (IFR) conditions. Other factors can make the rules even more prohibitive, for example, an airport in IFR conditions has two parallel runways  104  that are less than 2,500 feet apart laterally, the airport cannot treat those runways independently and is effectively reduced to one runway. 
                                                   TABLE 1                   Spacing matrix given in nautical miles       for IFR conditions on a single runway.                Follower                Leader   Small   Large   Heavy                       Small   3   3   3           Large   4   3   3           B757   5   4   4           Heavy   6   5   4                        
The spacing rules currently in place are based on worst case scenarios. The rules work because they are grossly conservative allowing far more distance than should usually be required, whereby they allow adequate time for the effect from the vortices  106  to dissipate such that if a vortex  106  encounter occurs, the effect on the follower would be mild.
 
   The current invention is a wake vortex alleviator that perturbs the wake vortex in real-time at the origin of the vortex on the wing. The main difficulty in achieving a active wake alleviation strategy is in finding an practical way to perturb the trailing vortices. The strategy must perturb them in real-time at an appropriate frequency without significantly changing the total lift experienced by the wing.  FIGS. 2   a - 2   c  show planar side views of an aircraft Gurney flap  200  at the trailing edge  202  of an aerodynamic surface  204 . An aircraft Gurney flap  200  is a small tab, approximately 1-2% of a wing chord length  206 , placed at the trailing edge  202  of an airfoil  204  oriented perpendicular to the airflow  208 . It has been shown that aircraft Gurney flaps  200  are capable of significantly increasing the section lift coefficient of an airfoil  204  (&gt;10%) without incurring a large increase in drag. They do this by effectively changing the chamber of the airfoil  204 , thereby increasing the circulation about it, as shown in  FIG. 2   c . Since Gurney flaps  200  are small, they accomplish this while remaining inside the airfoil boundary layer. Gurney flaps  200  can run along the entire span (not shown) of an aerodynamic surface  204 , or they can be segmented and placed along only certain span-wise portions. 
   Referring to  FIGS. 3   a - 3   e , the present invention is a wake vortex alleviator  300  integrated to an aerodynamic surface  204  (or wing) of an aircraft  100 . The invention includes a translating flap  302 , for example a translating Gurney flap, integrated to a slot  304  in the aerodynamic surface  204 . The flap  302  is positioned in air (not shown) moving across the aerodynamic surface  204  using an actuator (see  FIG. 3(   d )) for translating, positioning and stowing the flap  302 . The slot  304  is generally transverse to a chord line  206  of the aerodynamic surface  204  and positioned near a trailing edge  202  of the aerodynamic surface  204 . The flap  302  translates along the slot  304  to induce early destruction of the wake vortex  106  created by the aerodynamic surface  204 . In  FIG. 3(   a ), the flap  302  is shown deployed near the tip of the aerodynamic surface  204 ,  FIG. 3(   b ) shows the flap  302  deployed along the span of the aerodynamic surface  204 , and  FIG. 3(   c ) shows the flap positioned into the root  306  of the aerodynamic surface  204 , where in this embodiment, the translating flap  302  is stowed in the root  306  and out of the airflow when not deployed.  FIG. 3(   d ) shows an exploded perspective view of the wake vortex alleviator  300 , where the alleviator  300  has an aerodynamic surface  204  for holding an actuator  310  to translate, position and stow the flap  302 . In on embodiment the actuator  310  and flap  302  can be positioned in a cavity  312  of the aerodynamic surface  204 , with a cavity cover  314  that attaches to the aerodynamic surface  204 , where the cover  314  is sized to create the slot  304  in which the flap  302  translates. 
   Some alternate embodiments or the wake vortex alleviator  300  include one where the flap  302  may be located on the low-pressure side (not shown) or on the high-pressure side of the aerodynamic surface  204 . Further, in another embodiment, the flap may have a length that is up to ½ of a wing half span (not shown), where the slot  304  may be at least two times the length of the flap. Further the flap  304  can have an effective height that varies (not shown) along the slot  304 , where the effective height may be up to 5-percent of a length of the chord line  206 . 
   In one embodiment the flap  302  may have holes, slices or features cut there through as shown in  FIG. 4 . 
   In a further embodiment of the invention, the translation can be an oscillation along the slot  304 . Additionally, the oscillation may be a response-oscillation actuated according to variations in lift in the aerodynamic surface  204 , where the lift variations may be wind gusts. According to another aspect of the invention, the trailing edge  202  of the aerodynamic surface  204  may be a sharp edge or a blunt edge (not shown). 
   Common to many large aircraft  100  is an aerodynamic surface  204  that can have one or more lifting surfaces, such as a Fowler flap  500  shown in  FIG. 5   a , where according to one embodiment of the invention, translating flap  302  of the wake vortex alleviator  300  may be positioned on the additional lifting surface such as the Fowler flap  500 . A Fowler flap  500  slides backwards before hinging downwards, thereby increasing both camber and chord  206 , creating a larger wing surface better tuned for lower speeds. In another embodiment of the invention, the slot  304  may be a void  502  as shown in  FIG. 5   b  in the aerodynamic surface  304 . The void  502  may be an open span between the trailing edge  202  and a lifting surface, such as a Fowler flap  500  deployed from the trailing edge  204 . In another aspect, the void  502  may be a space of air that is positioned away from the aerodynamic surface  204 , where for example, the actuator  310  and flap  302  are stowed into the aerodynamic surface  204  when the flap  302  is not in use. In another embodiment of the invention, the stowage of the flap  302  includes a pivoting flap that rotates into the slot and out of the airflow when not in use, as shown in  FIG. 5   c . Further, as shown in  FIG. 3(   c ), the stowage of the flap  302  can be a hidden slot  304  in the root  306  of the aerodynamic surface  204 , where the flap  302  moves into the hidden slot  304  and out of the airflow. 
   In another aspect of the invention, the actuator  310  is selected from a group of actuators that include a linear ball screw, a worm drive, a scotch yoke, a crank arm and a solenoid (not shown). 
   In another embodiment, the flap  302  can be a pair of the flaps  304  mounted on the aerodynamic surface  204  located on each side of an aircraft  100 . In one aspect, the flaps  302  are mounted symmetrically on the aerodynamic surfaces  204  located on each side of an aircraft  100 . According to one aspect of the invention, the flap  302  controls the yaw, roll or pitch of the aerodynamic surface  204 . In another aspect of the invention, the aerodynamic surface  204  further includes an extended flutter boundary (not shown). 
   The present invention has now been described in accordance with several exemplary embodiments, which are intended to be illustrative in all aspects, rather than restrictive. Thus, the present invention is capable of many variations in detailed implementation, which may be derived from the description contained herein by a person of ordinary skill in the art. One variation includes use of the translating flap on helicopter rotors to manage rotor resonance. Another variation includes using the translating flap on jet engine fan blades to reduce noise or improve performance. Another variation includes using translating flaps on wind turbines for load management. 
   All such variations are considered to be within the scope and spirit of the present invention as defined by the following claims and their legal equivalents.