Abstract:
A variable sweep winglet with a negative dihedral angle is provided for a ground effect vehicle. The winglet is positionable at a sweep angle to control the winglet tip clearance from ground. Variable winglet tip clearance reduces the risk of damage or instability due to collision with the ground or water, thereby permitting more efficient flight at lower altitude with an equivalent safety. The winglet is generally positioned by an actuator. The actuator is controlled by a flight control system, or by other manual or automatic systems. A sensor may also be included for determining whether an object lies in the path of the winglet. The sensor communicates with the flight control system in order to vary the sweep of the winglet to increase clearance from the ground or water, thus avoiding impact with the object.

Description:
FIELD OF THE INVENTION 
     The present invention relates to winglets, and, more particularly, to a wing of a ground effect vehicle having a winglet with negative dihedral angle and variable sweep. 
     BACKGROUND OF THE INVENTION 
     Ground effect vehicles have been developed in both fields of aeronautics and marine craft. Ground effect vehicles are those vehicles which receive reduced drag due to the reduction of wing-tip vortices while traveling at low altitudes near ground, and more typically, near water. The closer the wing tip is to the ground or water, the lower the drag. 
     Ground effect vehicles generally comprise marine craft and aircraft. The two are typically distinguished by those that can sustain extended flight without the aid of ground effect (aircraft) and those that cannot (marine craft). The International Civil Aviation Organization (ICAO) and International Maritime Organization (IMO), both organizations of the United Nations, jointly exercise jurisdiction over these vehicles. The ICAO and IMO have also united to develop uniform navigation and safety rules for these types of vehicles, expected to be published by the year 2004. 
     The marine engineering arts have developed ground effect craft that either induce ground effect, such as hovercraft, or utilize some benefits of ground effect in combination with hydrodynamic hull and fin arrangements, such as catamarans and hydrofoils. Other maritime ground effect aircraft are being developed, and typically include ground effect wings to provide greater stability and lift. They cannot, however, sustain flight without maintaining close distance to the ground. 
     The aeronautical engineering arts have also advanced ground effect vehicles beginning with the Russian Ekranoplan KM, also known as the Caspian Sea Monster, which was developed in the 1960s for cargo transport and missile delivery applications. The KM uses extended wings with negative dihedral winglets on each end in order to promote the ground effect. The negative dihedral winglets are generally allowed to touch water if the KM is unintentionally flown too low. However, allowing the winglets to touch the water substantially increases drag, and may damage the wing or winglets. As such, the structural weight of the wing must be increased to account for water loads. If too much of the winglets contact water, the airplane may also experience stability problems. 
     It is typical for ground effect vehicles to travel within a few feet of the sea. In general, drag is reduced when the distance between the wingtip and the ground or water is reduced. in high wave conditions, altitude must be increased to avoid a collision between the wings or winglets and the water. Positive dihedral winglets on ground effect vehicles are effective in reducing drag, but not as effective as winglets that allow for decreased height between the lowest point on the wingtip to the water or ground. Additionally, ground effect vehicles with negative dihedral winglets may face the problem of winglet contact with the ground or water during landing and takeoff. As such, there exists a need in the art for ground effect vehicles with negative dihedral angles that can temporarily increase ground clearance or water clearance on the winglets, thus avoiding impact with the ground or water. 
     BRIEF SUMMARY OF THE INVENTION 
     To meet these and other needs, a ground effect vehicle and ground effect wing with a negative dihedral winglet are therefore provided. The ground effect wing includes a fixed wing capable of being attached to a ground effect vehicle fuselage. At the outward extension of the wing, a winglet is attached with a negative dihedral angle. The winglet is attached about a hinge or other mechanism so that it may rotate about a pivot axis. The pivot axis is generally defined at an angle that is roughly perpendicular to the direction of flight. This angle is also roughly normal to the plane of the winglet. The plane of the winglet is here defined by a flat surface between the leading and trailing edge of the winglet. In one such embodiment, the pivot axis is substantially perpendicular to the chord of the fixed wing. As such, the rotation of the winglet about the pivot axis results in variation of the winglet ground clearance through a range of sweep angles. 
     In several advantageous embodiments, an actuator is connected to the winglet in order to position the winglet through the range of sweep angles. Such actuators may include hydraulic actuators, springed actuators, rotating ballscrew actuators or other such actuators known to those skilled in the art. One advantageous embodiment includes an actuator with stored energy that may be activated in order to actuate the winglet through rotation about the pivot axis toward an aft sweep angle. A locking mechanism is included to lock the winglet in place against the stored energy actuator such that as the locking mechanism is unlocked the stored energy actuator automatically actuates the winglet through aft rotation. One embodiment of the locking mechanism includes a ratcheting mechanism. The ratcheting mechanism also permits rotation of the winglet about the pivot axis in order to change the sweep angle to avoid impact with an object such as the ground or water. Other embodiments for actuating the winglet through aft rotation include an aerodynamic device, such as a control surface or movable flap. The aerodynamic device is controlled to increase drag on the winglet such that the drag translates to rotational force about the pivot axis. Thus, the rotational force induces the winglet to position an aft sweep angle. In one embodiment, the rotational force caused by the drag is controlled by a locking mechanism. Thus, the winglet will increase sweep aft, thereby increasing clearance between the ground or water. As such, the winglet avoids contact with ground or water, consequently avoiding the stability problems or structural problems that would otherwise be caused from the impact. 
     Another advantageous embodiment of the present invention includes a ground effect vehicle comprising a fuselage and at least one ground effect wing. The ground effect wing is typically a wing with one end attached to the fuselage between the forward and aft portions of the fuselage and a winglet attached to the outer periphery of the second end of the fixed wing. The winglet is attached so as to form a negative dihedral angle and to be positionable through a range of sweep angles about a pivot axis, the pivot axis being defined at an angle with respect to the plane of the winglet. According to one embodiment, the pivot axis will be substantially perpendicular to the plane of the winglet. One embodiment of the ground effect vehicle includes actuators for actuating the winglet through the range of aft sweep angles. Such actuators may include hydraulic assisted actuators, spring assisted actuators or other actuating mechanisms known to those skilled in the art. Such actuators are generally controlled by flight control systems adapted to control the actuator and vary the sweep of the winglet to a desired position. 
     Several embodiments of the ground effect vehicle include sensors to determine whether an object lies in the path of the winglet. As such, the sensors are in communication with the flight control system to provide advance warning to the flight control system of an impending impact. Accordingly, the flight control system is adapted to vary the sweep of the winglet in order to increase the clearance from the ground or water to avoid impact. In certain embodiments, these sensors include forward looking sensors such as radar, laser, infrared, acoustic and imaging sensors. Another embodiment of the ground effect vehicle comprises physical sensors including an elongate member with a first end attached to the ground effect wing and second end extending downwardly therefrom. Such physical sensors are commonly known to those skilled in the art and referred to as “feelers.” In either embodiment, a physical sensor or an electromagnetic sensor provides signals either to the flight control system or directly to the actuators on the winglet in order to immediately vary the sweep of the winglet in order to avoid impact with the sensed object. 
     Therefore, a ground effect vehicle with a ground effect wing having a variable sweep winglet advantageously permits increasing clearance of the winglet tip from ground or water by actuating the winglet to a further aft sweep. As such, control of the winglet can be maintained in order to avoid contact of the winglet with ground or water, thereby avoiding structural or stability problems. Consequently, the ground effect vehicle may advantageously maintain flight altitude for most efficient travel in ground effect. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
     Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
     FIG. 1 is a perspective view of a ground effect vehicle with a variable sweep winglet according to one embodiment of the present invention; 
     FIG. 2 is a front elevation view of a variable sweep winglet with a negative dihedral angle according to one embodiment of the present invention; 
     FIG. 3 is side elevation view illustrating three sweep positions of a variable sweep winglet according to one embodiment of the present invention; 
     FIG. 4 is a perspective sectional view of a variable sweep winglet with an actuator according to one embodiment of the present invention; 
     FIG. 5 is a flow diagram of a system for controlling a variable sweep winglet according to one embodiment of the present invention; 
     FIG. 6 is a perspective view of a variable sweep winglet with an electromagnetic sensor according to one embodiment of the present invention; 
     FIGS. 7 and 8 are front elevation views of a variable sweep winglet with a feeler according to one embodiment of the present invention; and 
     FIG. 9 is a perspective view of a variable sweep winglet with a movable flap according to one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     FIG. 1 illustrates one embodiment of a ground effect vehicle  10  with a ground effect wing  12  having a variable sweep winglet  14 . Ground effect vehicles generally comprise marine craft and aircraft. An inexact division between the two is made among those that can sustain extended flight without the aid of ground effect (aircraft) and those that cannot (marine craft). For purposes of illustration, the present invention is described in conjunction with a ground effect vehicle  10  generally regarded as an aircraft and illustrated in FIG.  1 . Marine craft engineers, however, are continuing development of marine craft incorporating ground effect wings and winglets. Such marine craft may also benefit from utilization of the variable sweep winglet described herein. In particular, the ability to temporarily increase ground clearance between the winglet and the ground may improve performance in both types of vehicles. Therefore, the variable sweep winglet  14  can be employed in conjunction with other ground effect vehicles without departing from the spirit or scope of the present invention. 
     Therefore, FIGS. 1 through 3 illustrate one exemplary embodiment of a variable sweep winglet  14  for a ground effect vehicle  10 . A fixed ground effect wing  12  is attached to a fuselage  11 , as commonly found on ground effect vehicles. At the outermost extremity of the fixed wing  12  is a winglet  14 . The winglet  14  has a negative dihedral angle  13  in order to reduce drag during ground effect flight. As described herein, dihedral angle refers to the inclination of the winglet  14  with respect to a horizontal plane, and a negative dihedral angle is a downward inclination. In general, winglets are designed to achieve certain aerodynamic properties according to design parameters, such as camber, chord length, span, etc., and such design criteria are well known to those skilled in the art. More particularly, design criteria vary according to specific parameters of the fixed wing  12 , fuselage  11 , and control surfaces of various ground effect vehicles to which the variable sweep winglet  14  may be applied. As a result of such variability, specific winglet design parameters are not discussed herein, however, the variable sweep winglet  14  of the present invention is capable of implementation with many different designs, as will be appreciated by one skilled in the art. 
     The winglet  14  is rotatably attached to the wing by way of a pivoting device, such as a hinge  28 . The pivot axis  15  of the pivoting device is oriented at an angle of intersection, ψ, FIG. 2, to the plane of the winglet such that rotation of the winglet changes the distance of the tip of the winglet from the ground. The pivot axis is also oriented at an angle, θ, FIG. 4, to the chord of the wing. Accordingly, the winglet  14  is rotatable about the pivot axis  15  such that the sweep angle of the winglet  14  varies corresponding to rotation. As used herein, sweep angle refers to the fore and aft angle that the winglet  14  rotates about the pivot axis  15 . Zero degrees sweep, no sweep, and nominal position all refer to the typical flying position of the winglet  14 . According to one embodiment of the variable sweep winglet  14 , the angles ψ and θ may advantageously be substantially perpendicular angles, which is within at least a range of angles about and including a perpendicular angle. 
     The winglet sweep angle is varied through rotation about a pivot axis  15 . As the winglet  14  rotates to a sweep angle further aft, it is a characteristic of the negative dihedral winglet  14  to move further away from the ground. The furthermost position of the winglet tip  16  from the ground, as depicted at  19  in FIG. 2, occurs at a full aft sweep angle. In the nominal position, which is the position most conducive to ground effect, the winglet tip  16  is nearest the ground and the winglet sweep angle is least. As such, the variation of sweep advantageously provides increased ground clearance to the winglet tip  16  for a constant altitude of the fuselage  11 . FIG. 2 illustrates the maximum possible change in clearance  19  from the ground between nominal position and the full aft position, which would place the leading edge of the winglet substantially even with the lowest edge of the fixed wing  12 . By selectively controlling the sweep angle, the ground effect vehicle  10  may conserve altitude while avoiding winglet  14  contact with the ground, thereby maintaining efficiency of flight. 
     FIG. 4 is a cross-sectional schematic of one advantageous embodiment of the variable sweep winglet  14  referencing the direction of flight  23 . FIG. 4 illustrates one configuration of an actuator  18 , in this case a hydraulic actuator, for rotating the winglet  14  about the pivot axis  15 . The actuator  18  is attached to the fixed wing  12  and pivotably attached to the winglet  14  by way of a hinge  28 . In this embodiment, the actuator  18  comprises a hydraulic housing  26  and an extendable rod  24 , the extendable rod  24  being pivotably attached to the winglet  14  by means of a rotating joint  20  and lever  21  via the hinge  28 . The housing  26  typically contains the operation controls for extending the rod  24  and position for providing feedback to a controller. Numerous actuators of a similar nature operate using a variety of controls including hydraulic movement, electric motor movement, springed motors, transfer of motion by ballscrew, etc. and may be substituted accordingly. Generally, these will be generally custom produced according to specifications and requirements for loading, torque, moment, extension, etc. As will become apparent to one skilled in the art, many other configurations of actuators may be employed with the variable sweep winglet described herein. 
     The extendable rod  24  connects by way of a rotating joint  20 , lever  21 , and hinge  28  to the winglet  14  to allow rotational motion about the rotating joint  20  in order to transfer lateral motion of the extendable rod  24  to rotational motion of the winglet  14  about the hinge  28 , the longitudinal axis of the hinge  28  corresponding to the pivot axis  15 . Therefore, as the actuator  18  varies the winglet  14  to a further aft sweep the winglet tip  16  necessarily increases its clearance from the ground or water. The actuator  18  is typically controlled by a flight control computer or other manual or automatic control systems generally known to those skilled in the art. Accordingly, the actuator  18  is adapted to be responsive to the flight control computer to selectively position the winglet  14  to a desired sweep angle and ground clearance. 
     Additional embodiments of the actuator  18  include a stored energy actuator. Such stored energy actuators include springed energy storage, hydraulic stored energy, and other stored mechanical energy sources capable of immediately releasing stored mechanical energy to actuate the wing. In one particular embodiment, it is desirable use the stored energy actuator to position the winglet  14  to an aft position thus increasing winglet tip  16  clearance from the ground. Such stored energy actuators are advantageous when rapid response is required to elevate the winglet  14  out of way of impact with the ground or water. In this embodiment, the actuator may be actuated upon command from the flight control system, another control system of the ground effect vehicle  10 , or manually via a control system. 
     Another advantageous embodiment of the variable sweep winglet includes a system for sensing objects, such as ground or water, that lie within the path of the variable sweep winglet  14  and position the winglet  14  in order to increase winglet tip  16  clearance from the ground or water. FIG. 5 illustrates a block diagram of a sensor  30  in communication with a flight control system  32 , which controls the actuator  18  to vary the sweep of the winglet  14 . The flight control system  32  generally comprises a flight control computer and related equipment, however, control systems are well known to those skilled in the art and may be substituted accordingly. By way of example, as the ground effect vehicle  10  travels above waves on a sea, large waves have the potential to strike the winglet  14 . These waves are sensed by the sensor  30 , and indication is therefore provided to the flight control system  32 . The flight control system  32  determines whether the wave lies in the path of the winglet  14 , and accordingly controls the actuator  18  to position the winglet  14  to a further aft sweep angle in order to increase the clearance of the winglet tip  16  from the wave and avoid impact with the wave. Therefore, the altitude of the fuselage  11  does not require change to avoid winglet tip  16  impact with the wave. Similarly, one embodiment permits the sensor  30  and flight control system to determine whether the path of the winglet is clear. Accordingly, winglet  14  may be returned to the nominal sweep angle once the control system repositions the winglet  14  to the nominal position. 
     FIG. 6 depicts one embodiment of the sensor  30 , a forward looking sensor  30   a  positioned on the fixed wing  12 . Forward looking sensors are well known to those skilled in the art and generally include active and passive sensors such as laser, infrared, radar, acoustic, and imaging sensors, among others. For example, an active forward looking sensor  30  includes a signal transmitter for producing a forward looking signals, such as an electromagnetic signal or acoustic signal, to be reflected from the object that lies within the path of the winglet  14 , such as water  25 . The sensor  30  also includes a receiver for receiving the reflected signal and providing an indication to the flight control system  32 . Generally, the object&#39;s range and azimuth from the winglet are available from the sensor or may be calculated by the flight control system  32  using algorithms known to those skilled in the art, such as doppler, beam steering, arraying techniques, etc. Alternatively, a passive forward looking sensor may also be used. For example, an imaging device may receive naturally reflected light and use ray optic and image analysis techniques to determine range. Active and passive sensors such as these are known to those skilled in the art and commercially available examples include altimeters, range finders, motion detectors, etc. 
     From the detection provided by the sensor, the flight control system  32  determines whether the ground or water  25  lies in the path of the winglet  14 . If so, the flight control system  32  selectively controls the actuator  18  to vary the variable sweep winglet  14  to a sweep angle sufficient to increase the clearance of the winglet tip  16  from the ground or water  25  and thus avoid, or at least reduce or minimize, impact. The embodiment illustrated in FIG. 8 depicts the electromagnetic sensor  30   a  located on the fixed wing  12  nearest the winglet  14 , however, the forward looking sensor  30   a  may be positioned anywhere that it is capable of sensing whether ground, water, or another object lies in the path of the winglet. These locations include the winglet  14  itself, the fuselage  11 , or other outer surfaces of the ground effect vehicle  10 . 
     Referring now to FIGS. 7 and 8, another embodiment of the sensor  30  includes a mechanical sensor  30   b , such as a feeler, to detect impending contact with the ground or water  25 . As such, the mechanical sensor  30   b  extends downwardly from the winglet  14 , or alternatively from another portion of the wing  12  or fuselage  11 , and provides mechanical indication that the winglet  14  may strike ground or water  25 . Upon contact with the water, the mechanical sensor  30   b  produces a corresponding mechanical distortion. For example, the mechanical sensor  30   b  may be attached to a strain gauge or similar mechanical distortion measuring devices known to those skilled in the art. The mechanical indication is then converted to an electrical signal and provided to the flight control system  32 . Mechanical to electrical converters are well known to those skilled in the art and include resistive strain gauges, magnetic displacement devices, capacitive displacement devices, etc. Upon receiving indication of impact from the mechanical sensor  30   b , the flight control system  32  actuates the winglet  14  to a further aft sweep angle to increase the clearance from ground of the winglet tip  16  and thus avoiding impact of the winglet  14  with the ground or water  25 . Furthermore, the mechanical sensor  30   b  may be employed in conjunction with any of the other embodiments described herein. 
     In another embodiment, the mechanical sensor  30   b  mechanically communicates with the actuator  18 , such as an embodiment of the stored energy actuator described above. As such, the mechanical sensor may be linked to a trigger for releasing stored energy to actuate the winglet  14  to an aft sweep angle. Additionally, a locking mechanism, such as a ratchet pawl and gear, locks the winglet  14  in position about the pivot axis  15 . The stored energy actuator  18  is adapted to provide actuation of the winglet  14  about the pivot axis  15  toward an aft sweep angle upon the locking device becoming unlocked. As such, the sensor provides an indication of impending impact and mechanically triggers the locking mechanism to allow the winglet  14  to achieve a further aft sweep angle thus increasing winglet tip  16  clearance from the ground or water. 
     Another advantageous embodiment of the variable sweep winglet  14  includes an aerodynamic device, such as a movable flap  34  illustrated in FIG. 9, attached to the winglet  14 . As such, the movable flap  34  may be positioned to increase the drag forces on the winglet  14 , and the drag force translates to rotational moment about the pivot axis  15 . In one advantageous embodiment, a locking mechanism, such as a ratchet pawl and gear or the like, provides pivotal resistance to the aerodynamic rotational forces, if any, and locks the winglet at the nominal sweep angle. The locking mechanism includes an unlocking set point, which is a predetermined rotational force required to unlock and actuate the stored energy actuator to rotate the winglet aft. As the flap  34  is repositioned, the drag forces, and thus rotational forces increase. The locking mechanism unlocks and the increased drag rotates the winglet  14  aft about the pivot axis  15 . The locking mechanism then locks the winglet  14  to the new sweep angle. As illustrated in FIG. 8, the movable flap  34  may advantageously be provided on a trailing edge of the winglet  14 . The flap  34  may be controlled by the flight control system, such as the flight control computer or the like. Furthermore, movable flap  34  may be employed in conjunction with any of the other embodiments described herein as a supplemental system to vary the sweep of the winglet  14 . 
     In yet another embodiment, the winglet  14  is constructed to withstand momentary impact with the ground or water and then translate the force of momentary impact to rotational force about the pivot axis  15 . This momentary impact force may come from an impact on the winglet or feeler  30   b . As such, a locking mechanism, such as a ratchet pawl and gear, locks the winglet  14  into the nominal sweep angle. The locking mechanism includes an unlocking set point, which is a predetermined rotational force required to unlock and actuate the stored energy actuator to rotate the winglet  14  aft. As the winglet  14  positions to an aft sweep position, the winglet tip  16  increases clearance from the ground or water. Therefore, the winglet  14  or feeler  30   b  only sustains a temporary impact with the ground or water and limits the instability and structural damage caused by the impact. 
     Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.