Abstract:
A fixed wing flight vehicle has wing, a center-mounted propulsion unit and a pod that is moveable between a center of the wing and a displaced position at or near one end of the wing. When the pod is at or near the center of the wing, that is, having a center of mass at or near a thrust vector of the propulsion unit, the flight vehicle flies with the characteristics of a regular fixed wing aircraft. However, when the pod is translated to the position at or near an end of the wing, an overall center of mass of the flight vehicle is substantially offset from the thrust vector of the propulsion unit. This causes the flight vehicle to spin like a samara, e.g., a maple seed, so that the flight vehicle can take off or land in a very limited space, much like a helicopter.

Description:
FIELD 
     This disclosure relates to a flight vehicle adapted to dual modes of flight. 
     BACKGROUND 
     Fixed wing flight vehicles enjoy good stability and control, efficient fuel economy, and good payload carrying capability. However, these vehicles require long take-off and landing areas. Conversely, vertical flight vehicles, such as helicopters, can take off and land vertically in very tight areas but are slower and have reduced endurance compared to a fixed wing vehicles of comparable mass and payload. 
     SUMMARY 
     In an aspect of the disclosure, an aerial vehicle may include a wing, a propulsion unit coupled to the wing, and a pod moveably coupled to the wing. The aerial vehicle may also include a translation mechanism that selectively moves the pod between a first position substantially at a lateral centerline of the wing and a second position substantially at an outboard end of the wing. By moving the pod between positions, a center of mass of the aerial vehicle is altered allowing transition between a straight flight mode of a fixed wing aircraft and a rotational mode capable of vertical takeoff and landing. 
     In another aspect of the disclosure, a method of operating an aerial vehicle having a fixed wing includes providing, in a first flight mode, for a center of mass of the aerial vehicle to be substantially along a lateral centerline of the fixed wing so that in the first flight mode, thrust is substantially in line with the center of mass of the aerial vehicle. In a second flight mode, the center of mass of the aerial vehicle may be altered to be offset from the lateral centerline of the fixed wing so that the thrust is offset from the center of mass of the aerial vehicle which causes the aerial vehicle to rotate about a rotational axis. 
     In yet another aspect of the disclosure, a method of operating an aerial vehicle having a pod moveably attached to a fixed wing of the aerial vehicle includes setting the pod proximate to a centerline of the fixed wing for use in a first flight mode and launching the aerial vehicle in the first flight mode using a propulsion unit that provides a thrust vector generally aligned with a center of mass of the aerial vehicle. In the first flight mode, the aerial vehicle may be operated as a fixed wing aerial vehicle. The method may also include moving the pod distal to the centerline of the fixed wing for operation of the aerial vehicle in a second flight mode so that a center of mass of the aerial vehicle is offset from a lateral centerline of the fixed wing of the aerial vehicle. In the second flight mode, the method may include recovering the aerial vehicle using a vertical descent caused by rotation of the aerial vehicle about a rotational axis. 
     The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiment illustrated in greater detail on the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of an embodiment of an aerial vehicle; 
         FIG. 2  is a top view of an embodiment of an aerial vehicle; 
         FIG. 3  is a top view of the aerial vehicle of  FIG. 3  to in a different configuration; 
         FIG. 4  is an illustration of an exemplary pod; 
         FIG. 5  is an illustration of another exemplary pod; and 
         FIG. 6  is a flowchart of a method of operating an aerial vehicle. 
     
    
    
     It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein. 
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of an aerial vehicle  100  having a wing  102  and control surfaces  104 ,  106 . The aerial vehicle  100  may also have a propulsion unit  108 , which in the exemplary embodiment shown uses a propeller  110 . In other embodiments, another kind of propulsion unit  108  may be used. The propulsion unit  108  provides thrust to the aerial vehicle. In various flight modes, discussed below, the thrust is used for straight flight or the thrust may cause rotation of the aerial vehicle  100 . When configured as shown in  FIG. 1 , the aerial vehicle  100  can be piloted like any fixed wing, forward thrust aircraft. 
     Aerial vehicle  100  also has a pod  112  which may be movable along a track  114 . As will be discussed in more detail below, when the pod  112  is positioned along a centerline of the wing  102 , a center of mass of the aerial vehicle  100  is generally aligned along both the centerline of the wing and of a thrust vector of the propulsion unit  108 . When the pod  112  is moved to an opposite end of the track  114 , the center of mass of the aerial vehicle  100  is moved off of the centerline of the wing  102  and also off of the thrust vector of the propulsion unit  108 . The effect of this movement of the pod  112  is to change the center of mass of the aerial vehicle  100  in order to cause the aerial vehicle  100  to spin, allowing more or less vertical flight, similar to a samara (seed) of a maple tree. Unlike the maple samara, however, the propulsion unit  108  is able to add power to the aerial vehicle  100  and the control surfaces  104 ,  106  are able to effect changes in attitude of the wing  102 . Thus, the aerial vehicle  100  may be piloted through a controlled vertical descent or even a controlled vertical ascent. 
     The aerial vehicle  100  may achieve both the benefits of the stability, ease of flight, and payload capability of a fixed wing aircraft and the vertical takeoff and landing capability of a rotary aircraft. 
       FIG. 2  is a top view of another embodiment of an aerial vehicle  120 . The aerial vehicle  120  may include a wing  122 , a plurality of control surfaces  124 - 130 , a propulsion unit  132 , a pod  134 , a track  136 , and a drive mechanism  138 . A thrust vector  140  of the propulsion unit  132  is coincident with both a lateral centerline of the wing  122  (that is, a line equidistant between wingtips) and a lateral center of mass of the aerial vehicle  120 . For ease of illustration, any small change in the lateral center of mass due to the track  136  and/or drive mechanism  138  are ignored. 
     In this configuration, or first flight mode, the aerial vehicle  120  performs similarly to any other “flying wing” aircraft. The aerial vehicle  120  exhibits the control stability, fuel economy, and payload capability of such aircraft. Takeoff and landing may be accomplished via a runway in a known fashion, a catapult, or if the aerial vehicle  120  is small enough, it may be hand launched. 
       FIG. 3  is a top view of the aerial vehicle  120  of  FIG. 2  shown in another configuration. In this configuration, or second flight mode, the pod  134  is displaced from the thrust vector  140 /centerline of the wing  122 . The lateral center of mass  142  of the aerial vehicle  120  has shifted off-center. The offset between the thrust vector  140  and the lateral center of mass  142  causes the aerial vehicle  120  to rotate about a rotational axis  144 . 
     The exact location of the lateral center of mass  142  may vary based on factors such as a mass of the pod  134 , the mass of the wing  122 , and the mass of other components of the aerial vehicle  120  such as the propulsion unit  132 . Similarly, the rotational axis  144  may vary based on the mass of the various components and the magnitude of the thrust vector  140  of the propulsion unit  132 . In some embodiments, the rotational axis  144  may be farther from the aerial vehicle  120  or may actually be inside the furthest extent of the wing  122 . 
     The rotation of the aerial vehicle  120  provides enough apparent wind speed at an end of the wing  122  opposite the pod  134  to provide both lift and responsiveness to controls, particularly control surfaces  127 ,  128 , and  130 . 
       FIG. 4  is a simplified illustration of an exemplary pod  134  showing various contents of the pod  134 . A payload section  150  may carry activity-specific materials such as a camera, medical supplies, or other items in keeping with an overall weight capacity of the aerial vehicle  120 . A navigation and flight control electronics section  152  may include a GPS receiver, a controller to manage adjustments to the propulsion unit  132  and control surfaces  124 - 130 , radio communications equipment, navigation lighting, gyroscopes, etc. An energy source  156 , for example, containing a fuel tank, a fuel cell, a battery, or another source of energy, either separately or in combination, may be used to power the propulsion unit  132  via either a fuel line or electrical wiring umbilical cord that connects the pod  134  with the propulsion unit  132  and the control surfaces  124 - 130 . A pod drive mechanism  154  may, in one embodiment, include a motor  158  and a transmission  160  that couples to the drive mechanism  138 . In an exemplary embodiment, the transmission  160  may include a worm gear and the drive mechanism  138  may be a threaded rod. In other embodiments, the transmission  160  may include a wheel or a gear that engages the drive mechanism  138  in the form of a track or strip with perforations that mesh with the teeth of the gear. This arrangement of the elements in the pod  134  is merely for an exemplary embodiment. More or less equipment and components or a different arrangement of equipment and components may be used based the needs of the actual aerial vehicle and its field of operation. The function of the motor  158  and/or transmission  160  is to move the pod  134  from a centerline position to an outboard position. In some embodiments, the motor  158  may only drive the pod  134  in one direction, while in other embodiments, the motor  158  may drive the pod  134  in both directions. 
       FIG. 5  illustrates another embodiment of a pod  170 . The pod  170  is similar to the pod  134  in that it has a payload section  172 , a navigation and flight control electronics section  174 , and a fuel or battery section  178 . In the embodiment of  FIG. 5  the pod drive unit  176  may include a spring mechanism  180  such as a clock spring that may be unrolled to place the pod  170  in one position, for example, in the center of the wing  122 . When the spring mechanism  180  is released, tension in the spring mechanism  180  may cause the pod  170  to move to the opposite position. In this embodiment, the mass of the unrolled spring is spread over the length of the track  136  when operating in a straight flight flight mode. When operating in a rotational flight mode with the pod  170  off-center, the entire mass of the spring mechanism  180  is rolled into the pod  170  and is located at the outboard position. This additional mass further contributes to the offset between the thrust vector  140  and center of mass  142 . 
     Unlike the motor  158 , the use of the spring mechanism  180  may allow only a single transition between flight modes, that is, between straight flight mode and rotational mode or between rotational mode and straight flight mode. Alternatively, the single the transition may be from rotational mode to straight flight mode, depending on the nature of the environment in which the aerial vehicle  120  is deployed. In another embodiment, the spring mechanism  180  may simply be a shock cord or elastic band. 
       FIG. 6  is a flowchart of a method  200  of operating an aerial vehicle  120 . At a block  202 , the aerial vehicle  120  may be configured for a first flight mode as a conventional fixed wing aircraft. A pod  134  may be located at a lateral centerline of the wing  122  of the aerial vehicle  120 . The pod  134  may contain, for example, a payload section  150 , an energy source  156 , control electronics and navigation equipment section  152 , and a pod drive mechanism  154 . With the pod  134  located at the lateral centerline of the wing  122 , a center of mass  142  of the aerial vehicle  120  may be proximate to both a thrust vector  140  of a propulsion unit  132  and the lateral centerline of the wing  122 . 
     At block  204 , the propulsion unit  132  may provide thrust that is substantially in line with the center of mass of the aerial vehicle. In this first flight mode the aerial vehicle  120  may be launched using a runway, catapult, or by hand, depending on size and weight of the aerial vehicle  120 . 
     At a block  206 , the center of mass of the aerial vehicle  120  may be offset from the lateral centerline of the wing  122 . In an embodiment, the pod  134  may be moved along a track  136  to a position distal to the centerline at or near one wingtip of the wing  122  so that an overall center of mass is moved away from the lateral centerline of the wing  122 . Movement of the pod  134  may be accomplished while the aerial vehicle  120  is in flight so that the flight mode of the aerial vehicle  120  can be changed while in the air. 
     At block  208 , in the second flight mode the thrust from the propulsion unit  132  may be offset from the center of mass of the aerial vehicle  120  because by moving the pod  134  the center of mass has been changed while the thrust vector  140  from the fixed propulsion unit  132  remains in the same position. In an alternate embodiment, the pod  134  may be maintained along a centerline of the wing  122  and the propulsion unit  132  may be moved outward toward a wingtip. In yet another embodiment, both the pod  134  and the propulsion unit  132  may be moved to opposite ends of the wing  122 . In still another embodiment, an alternate propulsion unit (not depicted) may be permanently located at an outward position for use only when the pod  134  is positioned at its outward location. By moving the propulsion unit  132  or providing for an alternate propulsion unit at the wingtip the rotational axis  144  of the aerial vehicle  120  in the second flight mode may be moved inward and/or the rotation speed may be increased, which may provide additional control while in the vertical flight mode of operation. 
     In operation, with the pod  134  set along the centerline of the wing  122 , the aerial vehicle may operate as a standard fixed wing aircraft. When the pod  134  is offset to one end of the wing  122 , the aerial vehicle may assume a vertical flight capability allowing launch and/or recovery in confined areas where a runway or similar clear access may not be available. When descending in the vertical flight mode, the propulsion unit  132  may or may not be engaged depending upon an amount of control required, a freefall rate of descent, and safety issues for recovery personnel if the propulsion unit  132  is operating. 
     In other embodiments, partial movement of the pod  134  between endpoints of the track  136  may create a natural spiral effect which could in theory be implemented simply by using the flight control surfaces  124 - 130  but that may in practice be simpler to execute with the aid of the offset of the mass of the pod  134 . 
     Flight Mode Descriptions 
     As discussed above, an aerial vehicle, such as aerial vehicle  120  may operate in two basic modes, a straight flight mode and a rotational flight mode. In the straight flight mode, the aerial vehicle  120  may operate as a typical fixed wing aircraft. Launching may be accomplished in several different ways. The aerial vehicle  120  may taxi using fixed or retractable wheels (not depicted) on a runway or other surface, or waterway if floats are used, and build up speed until sufficient lift is generated for flight. In various embodiments depending on the size of the aerial vehicle  120  and the launch area, a catapult or sling may be used to shorten the distance needed to achieve rotation speed (speed at which the aerial vehicle can lift off) or the aerial vehicle  120  can be hand launched. The aerial vehicle  120  may climb out at a standard rate for a given control surface setting and airspeed. Once at altitude, the aerial vehicle may fly straight and level, turn, ascend and descend using standard controls and propulsion unit settings. The range of the aerial vehicle may be set by the efficiency of the propulsion unit  132  and the amount of energy available from the energy source  156  in the form of electricity from a battery or fuel cell, or combustible fuel, for example. 
     To recover the aerial vehicle  120  in straight flight mode, the aerial vehicle may be aligned with a runway, grass strip, waterway, etc. and guided to a landing by descending using a combination of power settings and control surface adjustments in a known manner. One or more of the control surfaces  124 - 130  may be or include retractable flaps to allow control of the aerial vehicle  120  at lower airspeeds. The aerial vehicle  120  may land on wheels or floats, if provided, or may enter a low-speed stall and land in a low-altitude controlled crash. In some embodiments, the aerial vehicle may be hand recovered during low-speed flight. 
     In the rotary flight mode, with the pod  134  offset, a rotary launch may be accomplished using a launcher or pivoting wheel (not depicted) that allows the aerial vehicle  120  to gain angular velocity about a rotational axis. When the aerial vehicle  120  has enough angular velocity and a corresponding wind speed over enough of the wing surface to create lift, the aerial vehicle  120  may begin to rise. Control surfaces farthest from the rotational axis, such as control surfaces  128  and  130  may have the most influence on flight because they experience the highest virtual airspeed. As above, some of the control surfaces  124 - 130 , particularly again, control surfaces  128  and  130  may be or include retractable flaps to provide more lift surface during takeoff and recovery. In some embodiments, retractable flaps may be used at all times during rotary flight mode. After the aerial vehicle has risen to a flight altitude, the rotary flight mode may be maintained using the control surfaces  124 - 130  to maintain a location or to steer in a desired direction. Power adjustments to the propulsion unit  132  may be used to adjust altitude. Increased power may increase altitude and decreased power may cause the aerial vehicle  120  to descend. 
     To recovery the aerial vehicle  120  in rotary flight mode the aerial vehicle may be piloted to a recovery location and power decreased so that the angular velocity of the aerial vehicle  120  may be reduced, correspondingly reducing the lift provided by the wing  122 . As the lift is decreased, the aerial vehicle may descend. In an embodiment, depending on the total mass and distribution of mass, the aerial vehicle  120  may accomplish an acceptable landing in rotary flight mode with no power applied by the propulsion unit, that is, entirely in a passive mode. In either flight mode, an acceptable landing may range from a damage-free landing, to a easily repaired amount of damage, to a substantial amount of damage as long as the payload is protected or recoverable. 
     As in the straight flight mode, fixed or retractable wheels may allow the aerial vehicle to land or the aerial vehicle  120  may land in a low-altitude controlled crash. 
     Transition between flight modes may be accomplished anytime the aerial vehicle  120  has sufficient altitude and maneuvering space. To transition from straight flight mode to rotary flight mode, the pod  134  may be translated from an axial centerline of the aerial vehicle (along thrust centerline  140 ) to an offset position. During the transition, the aerial vehicle may begin a broad spiral that becomes tighter as the pod  134  reaches its final offset location. In some embodiments, such as when using a spring or shock cord to move the pod  134 , the movement of the pod  134  may be abrupt and the transition from linear velocity to angular velocity may be fairly quick with minimal loss of altitude. Changes to the control surfaces, such as deployment of flaps, if used, may be synchronized with the transition of the pod  134 . In an embodiment, the propulsion unit may be depowered i.e. turned off or variable pitch propellers set to neutral during the translation of the pod. In such an embodiment, the aerial vehicle may experience some loss of altitude which must be accounted for when determining a minimum safe altitude for the transition. 
     Transition from rotary flight mode to straight flight mode is essentially the reverse of the straight flight mode to rotary flight mode transition. The aerial vehicle  120 , after reaching an appropriate altitude may transition the pod  134  from an outboard position to a centerline position. During the transition the angular velocity of the aerial vehicle will decrease as the linear velocity increases and lift is developed across the entire surface of the wing  122 . Any asymmetrical components used in the rotary flight mode, such as flaps on the distal end of the wing  122  (the end of the wing with control surface  130 ) from the pod  134  may be balanced on both ends of the wing by adding flaps to the pod-end or retracting the flaps on the distal end. 
     INDUSTRIAL APPLICABILITY 
     The ability of an aerial vehicle  120  to change flight modes between straight-line flight and vertical takeoff and recovery provides a significant advantage over either fixed wing aircraft such as drones or vertical takeoff and landing vehicles such as quadcopters or helicopters. For example, firefighters or military personnel in a forested area may be able to launch an aerial vehicle  120  configured for surveillance from a confined area while receiving the benefits of the endurance, speed, wide range and stable flight characteristics of a fixed wing aircraft. Similarly, an aerial vehicle  120  may be launched at a conventional air field and recovered at the end of a run in a vertical flight mode that does not require a runway or a highly skilled remote pilot and the attendant radio communication links. 
     While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims. 
     In summary, various aspects of the disclosed embodiments include: 
     1. An aerial vehicle comprising: 
     a wing; 
     a propulsion unit coupled to the wing; 
     a pod moveably coupled to the wing; and 
     a translation mechanism that selectively moves the pod laterally along the wing. 
     2. An additional aspect of aspect 1, wherein the propulsion unit is oriented to provide thrust substantially along a lateral centerline of the wing. 
     3. An additional aspect of any of aspects 1-2, wherein when the pod is at a first position substantially at a lateral centerline of the wing, a center of mass of the aerial vehicle is substantially aligned with the lateral centerline of the wing. 
     4. An additional aspect of any of aspects 1-3, wherein when the pod is at a second position substantially at an outboard end of the wing, a center of mass of the aerial vehicle is offset from a lateral centerline of the wing. 
     5. An additional aspect of any of aspects 1-4, wherein the translation mechanism provides, in flight, one-time movement of the pod laterally along the wing. 
     6. An additional aspect of any of aspects 1-5, wherein the translation mechanism is a spring. 
     7. An additional aspect of any of aspects 1-6, wherein the translation mechanism provides, in flight, two-way movement laterally along the wing. 
     8. An additional aspect of any of aspects 1-7, wherein the translation mechanism is a motor. 
     9. An additional aspect of any of aspects 1-8, wherein the pod contains flight controls, a payload, and an energy source used to power the propulsion unit. 
     10. An additional aspect of any of aspects 1-9, wherein the pod further contains the translation mechanism. 
     11. A method of enhancing operation of an aerial vehicle having a fixed wing, the method comprising: 
     providing, in a first flight mode, for a center of mass of the aerial vehicle to be substantially along a lateral centerline of the fixed wing; 
     providing, in the first flight mode, thrust substantially in line with the center of mass of the aerial vehicle; 
     altering, in a second flight mode, the center of mass of the aerial vehicle to be offset from the lateral centerline of the fixed wing; and 
     providing, in the second flight mode, thrust offset from the center of mass of the aerial vehicle that causes the aerial vehicle to rotate about a rotational axis. 
     12. An additional aspect of aspect 11, wherein altering the center of mass of the aerial vehicle comprises moving a pod between a first position generally aligned with the lateral centerline of the fixed wing and a second position away from the lateral centerline of the fixed wing. 
     13. An additional aspect of any of aspects 11-12, wherein the pod contains an energy source and a payload of the aerial vehicle. 
     14. An additional aspect of any of aspects 11-13, wherein moving the pod comprises operating a motor in the pod to drive the pod along a track coupled to the fixed wing. 
     15. An additional aspect of any of aspects 11-14, further comprising operating the motor to move the pod from one of the first position or the second position to an opposite position. 
     16. An additional aspect of any of aspects 11-15, wherein moving the pod comprises activating a spring to drive the pod along a track coupled to the fixed wing. 
     17. A method of method of enhancing operation of an aerial vehicle having a pod moveably attached to a fixed wing of the aerial vehicle, the method comprising: 
     setting the pod proximate to a centerline of the fixed wing for use in a first flight mode; 
     launching the aerial vehicle in the first flight mode using a propulsion unit that provides a thrust vector generally aligned with a center of mass of the aerial vehicle; 
     operating the aerial vehicle in the first flight mode as a fixed wing aerial vehicle; 
     moving the pod distal to the centerline of the fixed wing for operation of the aerial vehicle in a second flight mode wherein the center of mass of the aerial vehicle is offset from a lateral centerline of the fixed wing of the aerial vehicle; 
     recovering the aerial vehicle in the second flight mode using a vertical descent caused by rotation of the aerial vehicle about a rotational axis. 
     18. An additional aspect of aspect 17, wherein recovering the aerial vehicle comprises recovering the aerial vehicle with the propulsion unit disabled. 
     19. An additional aspect of any of aspects 17-18, further comprising: launching the aerial vehicle in the second flight mode in a vertical ascent using the rotation of the aerial vehicle powered by the propulsion unit. 
     20. An additional aspect of any of aspects 17-19, wherein the pod contains a payload and an energy source used to power the propulsion unit.