Abstract:
Various embodiments of the present disclosure provide a helicopter-mediated system and method for launching and retrieving an aircraft capable of long-distance efficient cruising flight from a small space without the use of a long runway.

Description:
PRIORITY CLAIM 
       [0001]    This patent application is a continuation of, and claims priority to and the benefit of, U.S. patent application Ser. No. 14/597,933, which was filed on Jan. 15, 2015, which is a continuation-in-part of, and claims priority to and the benefit of, U.S. patent application Ser. No. 14/230,454, which was filed on Mar. 31, 2014, which claims priority to and the benefit of U.S. Provisional Patent Application No. 61/808,392, which was filed on Apr. 4, 2013, and is now expired, and U.S. Provisional Patent Application No. 61/807,508, which was filed on Apr. 2, 2013, and is now expired, the entire contents of each of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    It is well known in the aeronautical sciences that an aircraft capable of hover and/or of slow flight is typically not well-suited to long-distance efficient cruising flight. One drawback of aircraft capable of long-distance efficient cruising flight is that such aircraft typically require long runways to be utilized for take-off and landing. This becomes problematic when there is not sufficient space for the requisite runway, meaning that such aircraft may not be used. 
         [0003]    Certain known or proposed aircraft launch, retrieval, or launch and retrieval systems and methods have attempted to solve these problems, but are each flawed in multiple manners. A first known or proposed aircraft launch and retrieval method employs a rotary wing aircraft to facilitate launch and retrieval of a fixed wing aircraft. To launch the fixed wing aircraft in the first known or proposed aircraft launch and retrieval method, the rotary wing aircraft is stiffly mated to the fixed wing aircraft via insertion of a plurality of balls mounted to the fixed wing aircraft into corresponding socket structures of the rotary wing aircraft. After mating, the rotary wing aircraft hoists the fixed wing aircraft, accelerates to a desired airspeed, and releases the fixed wing aircraft. To retrieve the fixed wing aircraft in the first known or proposed aircraft launch and retrieval method, this process is reversed—the rotary wing aircraft matches the airspeed of the fixed wing aircraft, stiffly mates with the fixed wing aircraft in midair, decelerates, and carries the fixed wing aircraft to a desired landing area. 
         [0004]    This first known or proposed aircraft launch and retrieval method has numerous disadvantages. One disadvantage is that retrieving the fixed wing aircraft by stiffly mating the rotary wing aircraft to the fixed wing aircraft in midair is impractical in that it requires extreme precision and is unforgiving. Specifically, retrieval involves the rotary wing aircraft matching the fixed wing aircraft&#39;s airspeed, aligning each socket structure above its corresponding ball, and decreasing its altitude such that each socket structure receives and secures its corresponding ball. Even partial improper performance of one of these steps could result in retrieval failure, or worse: damage to either aircraft. Retrieval becomes even more complex in adverse weather conditions, such as rain or high winds, when aircraft movement becomes even more imprecise and unpredictable. Another disadvantage with this first known or proposed aircraft launch and retrieval method is that retrieving the fixed wing aircraft by stiffly mating the rotary wing aircraft to the fixed wing aircraft in midair is (relatively) high fuel costs—the operator must ensure that the rotary wing aircraft has enough fuel to chase the fixed wing aircraft to mate therewith. Launch using the first known or proposed aircraft launch and retrieval method is also problematic since imperfectly-synchronized release of the multiple connections can lead to destruction of both the rotary wing aircraft and the fixed wing aircraft. 
         [0005]    A second known or proposed aircraft retrieval method employs a helicopter to facilitate retrieval of a fixed wing aircraft. To retrieve the fixed wing aircraft from wing-borne flight in the second known or proposed aircraft retrieval method, the helicopter hovers at a designated altitude while supporting a complex capture apparatus. In one proposed embodiment, this capture apparatus includes a horizontal beam from which a plurality of capture lines freely dangle (i.e., have one end connected to the horizontal beam and one free end). The helicopter is attached to a fixture, such as a vehicle, via an attachment line. The fixed wing aircraft is flown such that the fixed wing aircraft avoids the attachment line and contacts and captures one of the dangling capture lines. 
         [0006]    This second known or proposed aircraft retrieval method has numerous disadvantages. One disadvantage due to the freely dangling capture lines is that the likelihood of capture is lower if the fixed wing aircraft contacts a capture line near its free end. For instance, if the fixed wing aircraft contacts a capture line near its free end, the capture line may simply bounce off of the fixed wing aircraft and upward, making capture impossible at this point. This minimizes the window within which the fixed wing aircraft may approach the helicopter for capture, increasing the difficulty of capture. Another disadvantage due to the freely dangling capture lines is that, after the fixed wing aircraft captures a capture line, the momentum of the fixed wing aircraft may cause the fixed wing aircraft to wrap-around the horizontal beam and contact the helicopter, with disastrous results. Another disadvantage is that the fixed wing aircraft must approach the helicopter in a direction that is substantially perpendicular to the horizontal beam. In other words, the fixed wing aircraft must approach the helicopter in one of only two directions—toward the front of the helicopter substantially perpendicularly to the beam or toward the rear of the helicopter substantially perpendicularly to the beam. Otherwise, the fixed wing aircraft would contact the attachment line during capture. Another disadvantage is that the fixed wing aircraft must avoid the attachment line while aiming for the capture lines, adding complexity to controlling the fixed wing aircraft during retrieval. Another disadvantage is that continued movement of the fixed wing aircraft after capture will violently jerk the helicopter a certain distance while the fixed wing aircraft is decelerating, which could damage the helicopter or the capture apparatus. 
         [0007]    A third known or proposed aircraft retrieval method employs a kite, a balloon, or a crane and a tether to facilitate retrieval of a fixed wing aircraft. To retrieve the fixed wing aircraft from wing-borne flight in the third known or proposed aircraft retrieval method, the kite, balloon, or crane is used to suspend the tether between the kite, balloon, or crane and a fixture on the ground or a vehicle. The fixed wing aircraft is flown such that the fixed wing aircraft contacts and captures the tether. 
         [0008]    This third known or proposed aircraft retrieval method has numerous disadvantages. One disadvantage when the third known or proposed aircraft retrieval method employs a kite or a balloon is that the kite or balloon cannot be maneuvered by the operator. The kite or balloon is thus vulnerable to poor weather conditions that could wreak havoc on the stability of the tether. For instance, high winds could cause location and/or altitude of the kite or balloon—and the location, altitude, and orientation of the tether suspended therefrom—to vary wildly, making it difficult to capture the tether with the fixed wing aircraft. One disadvantage when the third known or proposed aircraft retrieval method employs a kite is that, in most instances, the kite must be anchored to a moving vehicle (such as a boat at sea) to ensure that the kite remains airborne during retrieval. This makes land-based retrieval using the kite impractical at best and impossible at worst. One disadvantage when the third known or proposed aircraft retrieval method employs a crane that is expensive, heavy, and limits the flexibility of the third known or proposed aircraft retrieval method—it is difficult, time-consuming, and expensive to move a crane from one location to another to conduct retrievals in different places and also difficult to compactly stow a crane. 
         [0009]    A fourth known or proposed aircraft retrieval method employs a helicopter to facilitate retrieval of a fixed wing aircraft. To retrieve the fixed wing aircraft from wing-borne flight in the fourth known or proposed aircraft launch and retrieval method, one end of a line is connected to a helicopter and a free end of the line dangles below the helicopter. The fixed wing aircraft is flown such that the fixed wing aircraft contacts and captures the line. 
         [0010]    This fourth known or proposed aircraft retrieval method has numerous disadvantages. One disadvantage due to the freely dangling line is that the likelihood of capture is lower if the fixed wing aircraft contacts the line near its free end. For instance, if the fixed wing aircraft contacts the line near its free end, the line may simply bounce off of the fixed wing aircraft and upward, making capture impossible at this point. This minimizes the window within which the fixed wing aircraft may approach the helicopter for capture, increasing the difficulty of capture. Another disadvantage due to the freely dangling line is that, after the fixed wing aircraft captures the line, the momentum of the fixed wing aircraft may cause the fixed wing aircraft to wrap-around and contact the helicopter, with disastrous results. Another disadvantage is that continued movement of the fixed wing aircraft after capture will violently jerk the helicopter a certain distance while the fixed wing aircraft is decelerating, which could damage the helicopter. 
         [0011]    There is a need for new systems and methods by which aircraft that otherwise require a long runway may be launched and retrieved from small spaces that solve these problems. 
       SUMMARY 
       [0012]    The present disclosure solves the above-described problems by providing a helicopter-mediated system and method for launching and retrieving an aircraft capable of long-distance efficient cruising flight from a small space without the use of a long runway (sometimes referred to herein as the “aircraft launch and retrieval system” for brevity). 
         [0013]    Generally, in various embodiments, to launch an aircraft using the aircraft launch and retrieval system of the present disclosure, a helicopter is stiffly mechanically connected to the aircraft, hoists the aircraft to a desired altitude and accelerates to a desired airspeed, and then releases the aircraft into wing-borne flight. 
         [0014]    Generally, in various embodiments, to retrieve the aircraft from wing-borne flight using the aircraft launch and retrieval system of the present disclosure, a tether is connected to the helicopter and an anchor assembly, the helicopter is flown above and station-keeps above the anchor assembly to extend the tether therebetween, and the aircraft is flown such that the aircraft contacts and captures a part of the tether extending between the tether and the anchor assembly. The continued movement of the aircraft following capture of the tether causes the anchor assembly to pay out tether and impose a resistive force opposing movement of the aircraft to decelerate the aircraft. 
         [0015]    More specifically, in one embodiment, the aircraft launch and retrieval system includes a helicopter, a tether, and an anchor assembly. To launch an aircraft using this embodiment of the aircraft launch and retrieval system, a first connector attached to the underside of the helicopter is stiffly and releasably connected to a second connector attached to the aircraft, such as a hook attached to the top surface of the aircraft&#39;s fuselage. After the helicopter and the aircraft are connected to one another, the helicopter hoists the aircraft to a desired altitude, and accelerates to bring the aircraft to a suitable airspeed. Once the desired altitude and airspeed are reached, the first and second connectors are disconnected from each other, whereby the aircraft is released into wing-borne flight. 
         [0016]    In this embodiment, in preparation for retrieval of the aircraft from wing-borne flight, the tether is connected to the helicopter and to the anchor assembly, and the helicopter is flown to a designated height above the anchor assembly such that a first portion of the tether extends between the helicopter and the anchor assembly and a second portion of the tether is maintained within or otherwise near the anchor assembly. Here, the designated height above the anchor assembly is determined such that, once the helicopter reaches that designated height, the tension in the portion of the tether extending between the helicopter and the anchor assembly is substantially equal to a designated tension. Once the helicopter reaches the designated height above the anchor assembly, the helicopter hovers substantially at that designated height and station-keeps (either automatically or via manual operator control) along a substantially horizontal plane such that, during retrieval of the aircraft, the helicopter remains substantially aligned above the point at which the tether is connected to the anchor assembly. 
         [0017]    Once the helicopter is hovering above the anchor assembly at the designated height above the anchor assembly, the aircraft is flown toward, contacts, and captures part of the portion of the tether extending between the helicopter and the anchor assembly via a tether capture device near the end of one of the aircraft&#39;s wings. The motor of the aircraft is then shut down. After the aircraft captures the part of the portion of the tether extending between the helicopter and the anchor assembly, continued movement of the aircraft and the captured part of the tether relative to the anchor assembly imposes a pulling force on the portion of the tether extending between the helicopter and the anchor assembly in the direction away from the anchor assembly. The anchor assembly is configured such that this pulling force causes the anchor assembly to begin paying out the tether. While the anchor assembly is paying out the tether, the anchor assembly imposes a resistive force on the portion of the tether extending between the helicopter and the anchor assembly. This resistive force causes the imposition of a force on the aircraft that counteracts the continued movement of the aircraft, thereby causing the aircraft to decelerate and come to a stop hanging below the helicopter. Thereafter, the helicopter lowers the aircraft into a docking fixture. 
         [0018]    The aircraft launch and retrieval system of the present disclosure solves the above-identified problems with previously-known or proposed aircraft launch, retrieval, or launch and retrieval systems and methods. 
         [0019]    Turning to the first known or proposed aircraft retrieval method described above, unlike the first known or proposed aircraft retrieval method, the aircraft retrieval system and method of the present disclosure is forgiving, does not require extreme precision to retrieve the aircraft, and has a smaller risk of damaging either the helicopter or the aircraft. 
         [0020]    Turning to the second known or proposed aircraft retrieval method described above, unlike the dangling capture lines of the second known or proposed aircraft retrieval method, the tether of the aircraft retrieval system and method of the present disclosure does not dangle freely during retrieval, and is instead attached to both the helicopter and the anchor assembly. This enables the aircraft to easily capture the tether nearly anywhere along the length of the tether, and prevents the aircraft from wrapping around and contacting the helicopter after capture. Further, unlike the second known or proposed aircraft retrieval method, the aircraft may approach the tether of the aircraft retrieval system and method of the present disclosure from any angle without substantially affecting its ability to capture the tether. In other words, the aircraft is not required to approach the tether in one of a only limited number of viable directions. Also, unlike the second known or proposed aircraft retrieval method, the aircraft retrieval system and method of the present disclosure eliminates complexity by including a single tether for the aircraft to capture; if the aircraft misses this single line, then in continues in undisturbed flight without running the risk of improperly contacting another capture line. Additionally, unlike the second known or proposed aircraft retrieval method, the combination of the anchor assembly of the aircraft retrieval system and method of the present disclosure paying out tether after capture and imposing a resistive force to slow the aircraft ensures that the helicopter will not be violently jerked after the aircraft captures the tether. 
         [0021]    Turning to the third known or proposed aircraft retrieval method described above, unlike the kite or balloon of the third known or proposed aircraft retrieval method, the helicopter of the aircraft retrieval system and method of the present disclosure is highly maneuverable and can be used in non-ideal weather conditions. Further, unlike the kite of the third known or proposed aircraft retrieval method, the helicopter of the aircraft retrieval system and method of the present disclosure can be readily used for land-based retrieval. Also, unlike the crane of the third known or proposed aircraft retrieval method, the helicopter of the aircraft retrieval system and method of the present disclosure is (relatively) low-weight and thus inexpensively portable. 
         [0022]    Turning to the fourth known or proposed aircraft launch and retrieval method described above, unlike the line of the fourth known or proposed aircraft retrieval method, the tether of the aircraft retrieval system and method of the present disclosure does not dangle freely during retrieval, and is instead attached to both the helicopter and the anchor assembly. This enables the aircraft to easily capture the tether nearly anywhere along the length of the tether and prevents the aircraft from wrapping around and contacting the helicopter after capture. Also, unlike the fourth known or proposed aircraft retrieval method, the combination of the anchor assembly of the aircraft retrieval system and method of the present disclosure paying out tether after capture and imposing a resistive force to slow the aircraft ensures that the helicopter will not be violently jerked after the aircraft captures the tether. 
         [0023]    Additional features and advantages of the present disclosure are described in, and will be apparent from, the following Detailed Description and the Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0024]      FIG. 1  is a side view of example devices of the present disclosure that facilitate helicopter-mediated launch and retrieval of an aircraft. 
           [0025]      FIG. 2  is a side view of other example devices of the present disclosure that facilitate helicopter-mediated launch and retrieval of an aircraft. 
           [0026]      FIG. 3  is a side view of an unmanned multi-rotor helicopter carrying an unmanned aircraft before releasing the aircraft into wing-borne flight. 
           [0027]      FIG. 4  is a side view of an aircraft retrieval system of the present disclosure including the helicopter of  FIG. 3 , a tether, and an anchor assembly before retrieval of the aircraft of  FIG. 3 . 
           [0028]      FIG. 5  is a side view of the aircraft retrieval system of  FIG. 4  after the aircraft has captured the tether. 
           [0029]      FIG. 6  is a side view of the aircraft retrieval system of  FIGS. 4 and 5  after the aircraft retrieval system has stopped the aircraft from moving. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Launch of an Aircraft into Wing-Borne Flight Using a Helicopter 
         [0031]    Referring now to the drawings, in one example embodiment illustrated in  FIG. 1 , a helicopter  100  (which may be manned or unmanned and include any suitable quantity of rotors) includes a first connector  120  connected to and extending from the helicopter  100 , and an aircraft  200  (such as a fixed-wing aircraft capable of long-distance efficient cruising flight or any other suitable aircraft) includes a second connector  220  connected to and extending from the aircraft  200 . In one embodiment, at least a portion of the first connector is flexible and the second connector is rigid. In another embodiment, both the first connector and the second connector are rigid. In another embodiment, the first connector is rigid and at least a portion of the second connector is flexible. In another embodiment, at least a portion of the first connector is flexible and at least a portion of the second connector is flexible. 
         [0032]    The first connector  120  includes a first gripper or mating device  170  at a bottom end (with respect to the orientation shown in  FIG. 1 ), and the second connector  220  includes a second gripper or mating device  270  (such as a hook mounted to the fuselage of the aircraft  200 ) at a top end (with respect to the orientation shown in  FIG. 1 ). The first and second mating devices  170  and  270  are configured to mate with one another and releasably connect to one another (such as by latching together or otherwise mechanically securely coupling together) to link the helicopter  100  with the aircraft  200  and facilitate launch of the aircraft  200  (as described below). In certain embodiments, at least one of the first and second connectors includes a locking mechanism configured to connect and lock the first and second mating devices together and to disconnect and release the first and second mating devices from one another. It should be appreciated that, once mated and connected to one another, the mating devices  170  and  270  only disconnect from each other when it is desired to separate the linkage between the helicopter  100  and the aircraft  200 . 
         [0033]    The first connector  120  is configured to enable the first mating device  170  to rendezvous with, mate with, and connect to the second mating device  270  of the second connector  220  when linkage between the helicopter  100  and the aircraft  200  is desired when the helicopter  100  is airborne and the aircraft  200  is substantially stationary (such as when the aircraft  200  is on the ground and not moving relative to the ground). It should be appreciated that the first connector is stabilized and tip-guided to facilitate such procedures while the helicopter  100  is in forward flight. 
         [0034]    The second connector  220  is configured to create a rendezvous target with sufficient physical separation from sensitive components of the aircraft  200  such that any impact between such sensitive components and the first connector  120  during mating and connecting of first and second mating devices  170  and  270  is unlikely. Additionally, the second connector  220  is configured to minimize weight and to minimize drag, particularly when the aircraft  200  is in wing-borne flight, whether the second connector  220  is in a deployed configuration, as shown in  FIG. 1 , or in a stowed configuration (not shown). 
         [0035]    It should be appreciated that the first and second connectors are configured to stably support the aircraft when the aircraft is linked with the helicopter. 
         [0036]    In this example embodiment, the aircraft  200  includes one or more retractable lay lines  290  deployable from, and retractable into (when not in use), any suitable portion of the aircraft  200  (such as the wings of the aircraft  200 ). In this example embodiment, as described below, the lay lines  290  are deployed during retrieval to enable a ground crew and/or ground equipment to guide the aircraft  200  safely into the landing area  50 . In other embodiments the aircraft does not include any such lay lines. 
         [0037]    To launch the aircraft  200  when the aircraft  200  is initially stationary (such as when the aircraft  200  is on the ground and not moving relative to the ground), in one example, the first mating device  170  of the first connector  120  is stiffly mated with and connected to the second mating device  270  of the second connector  220  of the aircraft  200  (such as via the locking mechanism) to link the helicopter  100  with the aircraft  200 . In one example embodiment, this is accomplished by maneuvering the helicopter  100  relative to the aircraft  200  such that the first mating device  170  of the first connector  120  of the helicopter  100  mates with and connects to the second mating device  270  of the second connector  220  of the aircraft  200  to link the helicopter  100  with the aircraft  200 . After the helicopter  100  is linked with the aircraft  200 , the helicopter  100  hoists the aircraft  200  to a desired altitude and accelerates to bring the aircraft  200  to a suitable airspeed. Once the desired altitude and airspeed are reached, the first and second mating devices  170  and  270  are disconnected from each other. Once the first and second mating devices  170  and  270  are disconnected from one another, the aircraft  200  is released into wing-borne flight, gains speed in a dive, and continues normal flight. 
         [0038]    In various embodiments, to facilitate releasing the aircraft  200  into wing-borne flight, the linked, airborne helicopter  100  and aircraft  200  are operated such that the loads on the connected first and second mating devices  170  and  270  of the first and second connectors  120  and  220  are minimized just before the first and second mating devices  170  and  270  are disconnected from one another. Once such loads are minimized, the first and second mating device  170  and  270  are disconnected from one another, such as by: (a) the first mating device  170  initiating the disconnection from the second mating device  270 , (b) the second mating device  270  initiating the disconnection from the first mating device  170 , (c) the first mating device  170  and the second mating device  270  initiating the disconnection from the other mating device, or (d) a device separate from the first and second mating devices  170  and  270  initiating the disconnection of the first and second mating devices  170  and  270 . 
         [0039]    In various example embodiments, to minimize the loads on the connected first and second mating devices  170  and  270  of the first and second connectors  120  and  220  to facilitate the disconnection of the first and second mating devices  170  and  270  (and, therefore, the disconnection of the helicopter  100  and the aircraft  200  and the release of the aircraft  200  into wing-borne flight): (a) the helicopter  100  descends relative to the aircraft  200 , (b) the helicopter  100  descends relative to the aircraft  200  and reduces its speed relative to the speed of the aircraft  200 , (c) the aircraft  200  ascends relative to the helicopter  100 , (d) the aircraft  200  ascends relative to the helicopter  100  and increases its speed relative to the speed of the helicopter  100 , or (e) any suitable combination thereof. 
         [0040]    In the above-described example embodiment, the aircraft is stationary prior to being hoisted by the helicopter. In another embodiment, the aircraft is mobile prior to being hoisted by the helicopter. For example, a short runway may be utilized to slowly move the aircraft prior to the helicopter hoisting the aircraft. 
         [0041]    Turning to  FIG. 2 , in another example embodiment, a helicopter  1100  includes an aircraft capturer  1120  connected to and extending from the helicopter  1100 . In this example, the aircraft capturer  1120  includes a flexible tether  1122  (though in other embodiments the tether is rigid or at least partially rigid) connected to and extending from the helicopter  1100  and a capture device  1124  connected to an end of the tether  1122  opposite the end of the tether  1122  connected to the helicopter  1100 . The capture device  1124  includes a mating device  1126  configured to mate with and releasably connect to (such as by latching to or otherwise mechanically coupling to) a portion of the aircraft  1200 . Thus, the mating device  1126  is configured to releasably connect the capture device  1124  (and, therefore, the aircraft capturer  1120 ) to the portion of an aircraft  1200 . This connection links the helicopter  1100  with the aircraft  1200  and facilitates launch and retrieval of the aircraft  1200  (as described below). In certain embodiments, at least one of the mating device and the aircraft includes a locking mechanism configured to connect and lock the mating device together with the aircraft and to disconnect and release the mating device and the aircraft from one another. It should be appreciated that, once the mating device  1126  connects to the aircraft  1200 , the mating device  1126  only disconnects from the aircraft  1200  when it is desired to separate the linkage between the helicopter  1100  and the aircraft  1200 . 
         [0042]    The aircraft capturer is configured to fly stably when trailed below a cruising helicopter while being guided into appropriate contact with an aircraft. For instance, in this example embodiment, the aircraft capturer  1120  includes a stabilizer  1128  configured to stabilize the aircraft capturer  1120  during flight. The aircraft capturer also includes features that enable stable behavior of the linked helicopter and aircraft in all phases of flight, including hover, forward flight, acceleration, and deceleration. Further, the aircraft capturer is configured to stably support the aircraft when it is linked with the helicopter. 
         [0043]    In this example, the aircraft  1200  include one or more lay lines  1290  and the mating device  1126  includes one or more lay lines  1295 , which are described above. In this example, the lay lines are retractable, while in other embodiments the lay lines are not retractable. In other embodiments, only one of the aircraft and the mating device includes one or more lay lines. In further embodiments, the aircraft capturer includes one or more lay lines that are stowable somewhere other than the mating device. In other embodiments the aircraft does not include any such lay lines. 
         [0044]    To launch the aircraft  1200  when the aircraft  1200  is initially stationary, in one example, the helicopter  1100  is maneuvered such that the mating device  1126  mates with and connects to a portion of the aircraft  1200  to link the helicopter  1100  with the aircraft  1200 . After the helicopter  1100  is linked to the aircraft  1200 , the helicopter  1100  hoists the aircraft  1200  to a desired altitude and accelerates to bring the aircraft  1200  to a suitable airspeed. Once the desired altitude and airspeed are reached, the mating device  1126  is disconnected from the aircraft  1200 , breaking the linkage between the helicopter  1100  and the aircraft  1200  and releasing the aircraft  1200  into wing-borne flight. 
         [0045]    In certain embodiments, one or both of the first and second mating devices are configured such that the pitch angle of the aircraft is variable by the operator. Put differently, in these embodiments, the operator may manipulate one or both of the first and second mating devices to control the pitch rate of the aircraft upon release. One such embodiment is depicted in  FIG. 3 , which depicts an unmanned multi-rotor helicopter  10  hoisting an unmanned winged aircraft  20  using fixtures on both the helicopter and the aircraft. These fixtures are configured such that the aircraft pitch, roll, and yaw attitude is suitable for release into stable wing-borne flight, even as the helicopter  10  is pitched into a nose-down attitude for forward flight. When flight conditions are reached suitable for subsequent wing-borne flight of the aircraft  20 , the aircraft  20  is released to fly conventionally. 
         [0046]    Retrieval of an Aircraft from Wing-Borne Flight Via Capture of a Tether Suspended Between the Helicopter and an Anchor Assembly 
         [0047]    As best shown in  FIGS. 4 to 6 , in certain embodiments, an aircraft retrieval system including the helicopter  10 , a tether  30 , and an anchor assembly  40  is used to retrieve the aircraft  20  from wing-borne flight. This system is particularly applicable to relatively small aircraft that are sufficiently tough to enable dangling from a hook on either wing, said hook engaging a tether as described below. Such aircraft are typically unmanned. In various embodiments, the helicopter  10  is the same helicopter used to launch the aircraft  20  into wing-borne flight in one of the above-described manners. In such embodiments, the helicopter with its aircraft mating device for hoisting the aircraft, the tether, the anchor assembly, and the hooks on the aircraft together comprise an aircraft launch and retrieval system. 
         [0048]    In this illustrated embodiment and as best shown in  FIG. 4 , in preparation for retrieval of the aircraft  20 : (1) a portion of the tether  30  is connected to the helicopter  10  at a point at or near the center-of-lift of the helicopter  10 , (2) another portion of the tether  30  is connected to the anchor assembly  40 , and (3) the helicopter  10  is flown to a designated height (or within a designated range of heights) above the anchor assembly  40 . When the helicopter  10  reaches the designated height above the anchor assembly  40 , a first portion of the tether  30  extends between the helicopter  10  and the anchor assembly  40  and a second portion (not shown) of the tether  30  is maintained within or otherwise near the anchor assembly  40  (i.e., does not (yet) extend between the helicopter  10  and the anchor assembly  40 ). In certain embodiments, the designated height is determined such that, when the helicopter  10  reaches the designated height above the anchor assembly  40 , the tension in the first portion of the tether is substantially equal to a designated tension. 
         [0049]    Once the helicopter  10  reaches the designated height above the anchor assembly  40 , the helicopter  10  station-keeps (either automatically or via manual operator control) along a substantially horizontal plane such that, during retrieval of the aircraft  20 , the center-of-lift of the helicopter  10  remains substantially aligned above the point at which the tether  30  is connected to the anchor assembly  40 . The helicopter  10  does so regardless of whether the anchor assembly  40  is stationary (e.g., located on the ground) or moving (e.g., located on a vehicle, such as the deck of a ship at sea). 
         [0050]    As shown in  FIG. 4 , once the helicopter  10  is hovering above the anchor assembly  40  at the designated height, the aircraft  20  is flown toward, contacts, and captures part of the portion of the tether  30  extending between the helicopter  10  and the anchor assembly  40  in a manner similar to that described in U.S. Pat. No. 6,264,140, the entire contents of which are incorporated herein by reference. Specifically, the aircraft  20  is flown toward the portion of the tether  30  extending between the helicopter  10  and the anchor assembly  40  such that the leading edge of one of the wings of the aircraft  20  contacts the tether  30 . After the leading edge of one of the wings of the aircraft  20  contacts the tether  30 , continued movement of the aircraft  20  relative to the tether  30  causes the tether  30  to slide away from the fuselage of the aircraft  20  along the leading edge of the wing toward the end of the wing until a tether capture device (not shown) near the end of the wing captures part of the tether  30 . Once the tether capture device of the aircraft  20  captures the part of the tether  30 , the tether capture device holds that part of the tether  30  such that the aircraft  20  does not substantially move relative to the tether  30 . It should thus be appreciated that the aircraft captures the same tether that connects the helicopter and the anchor assembly. At this point, the motor of the aircraft  20  is shut down. 
         [0051]    After the tether capture device of the aircraft  20  captures the part of the tether  30 , continued movement of the aircraft  20  and the captured part of the tether  30  relative to the anchor assembly  40  imposes a pulling force on the portion of the tether  30  extending between the helicopter  10  and the anchor assembly  40  in the direction away from the anchor assembly  40 . This pulling force causes the anchor assembly  40  to begin paying out the tether  30  (as indicated by the arrow near the anchor assembly  40  in  FIG. 5 ). While the anchor assembly  40  is paying out the tether  30 , the anchor assembly  40  also imposes a resistive force on the portion of the tether  30  extending between the helicopter  10  and the anchor assembly  40 . This resistive force causes the imposition of a force on the aircraft  20  that counteracts the continued movement of the aircraft  20 , thereby causing the aircraft  20  to decelerate and come to a stop hanging below the helicopter  10 , as best shown in  FIG. 6 . 
         [0052]    After the aircraft  20  is hanging below the helicopter  10 , the helicopter  10  lowers the aircraft  20  into a docking fixture (not shown). The helicopter  10  may then depart to land or to execute other tasks. 
         [0053]    In certain embodiments, a portion of the tether near the portion connected to the helicopter is elastic. In these embodiments, the elasticity of this elastic portion of the tether aids in maintaining tether tension without demanding excessive maneuvers of the helicopter. 
         [0054]    In one embodiment, the tether includes a tension sensor that is configured to measure and transmit, to a helicopter control system, the tension at the upper end of the tether. This measured tension is used to aid in retrieval of the aircraft. For instance, in one embodiment, the position of the helicopter relative to the anchor assembly is regulated using this measured tension by (either automatically or via manual operator control) maneuvering the helicopter relative to the anchor assembly to maintain the designated tension in the tether during aircraft retrieval. In a related embodiment, the helicopter then descends and lowers the aircraft towards the docking fixture when the tether is pulled downward. In one embodiment, the helicopter control system is attached to the helicopter, while in another embodiment the helicopter control system is remote from the helicopter. 
         [0055]    In certain embodiments, the aircraft retrieval system includes a navigation device configured to communicate to the helicopter control system the geographical location of the anchor assembly, which enables the helicopter to maintain its position above the anchor assembly. Specifically, in these embodiments, the geographical location of the anchor assembly is used to cause the helicopter to station-keep (either automatically or via manual operator control) along a substantially horizontal plane such that, during retrieval, the center-of-lift of the helicopter remains substantially aligned with the point at which the tether is connected to the anchor assembly. This device may employ a satellite-enabled Global Positioning System (GPS) or any other suitable system. 
         [0056]    In certain embodiments, the helicopter carries a device configured to determine its position relative to the anchor assembly for purposes of enabling the helicopter to station-keep above the anchor assembly. Many options are known for this device, including methods based upon non-contacting optical, radio-frequency, magnetic, and thermal sensors. Mechanical sensors detecting the tether may also be used. 
         [0057]    In certain embodiments, the anchor assembly is configured not to pay out the tether until the aircraft captures the tether. In various embodiments, the anchor assembly does so by including a breakaway link that is configured to: (1) prevent the anchor assembly from paying out the tether as long as the breakaway link remains unbroken; and (2) break when the tension in the lower portion of the tether at the anchor assembly exceeds a designated breaking tension. Thus, in these embodiments, the breakaway link prevents the anchor assembly from paying out the tether until the tension in the portion of the tether extending between the helicopter and the anchor assembly exceeds the designated breaking tension, at which point the breakaway link breaks and the anchor assembly can pay out the tether. In one such embodiment, the designated breaking tension is greater than a designated pre-retrieval tension in the portion of the tether extending between the helicopter and the anchor assembly prior to retrieval of the aircraft. 
         [0058]    In certain embodiments, the anchor assembly includes a retracting device to which the tether is operably attached. The retracting device is configured to impose a designated retracting force on the portion of the tether extending between the helicopter and the anchor assembly. In these embodiments, the designated retracting force is less than or equal to the resistive force that the anchor assembly imposes upon payout of the portion of the tether extending between the helicopter and the anchor assembly. In these embodiments: (1) when a pulling force that exceeds the designated retracting force is imposed on the portion of the tether extending between the helicopter and the anchor assembly in a direction opposite that of the designated retracting force, the anchor assembly pays out the tether; and (2) when the pulling force is less than the designated retracting force, the retracting device retracts the tether. By this method, energy is dissipated from the swinging motion of the aircraft below the helicopter. 
         [0000]    Retrieval of an Aircraft from Wing-Borne Flight Via Rendezvous with the Helicopter 
         [0059]    Returning to  FIG. 1 , in other embodiments, to retrieve the aircraft  200  from wing-borne flight, the helicopter  100  rendezvous with the aircraft  200  in flight and maneuvers such that the first mating device  170  of the first connector  120  of the helicopter  100  mates with and connects to the second mating device  270  of the second connector  220  of the aircraft  200  to link the helicopter  100  with the aircraft  200 . The linked helicopter  100  and aircraft  200  then slow (such as by independently decreasing the speed of both the helicopter and the aircraft), and as the linked helicopter  100  and aircraft  200  gradually slow, the helicopter  100  gradually accepts the weight of the aircraft  200 . The helicopter  100  then lowers the aircraft  200  to the landing area  50 , which is not of sufficient size to enable the aircraft  200  to utilize the landing area  50  for take-off or landing (though it should be appreciated that the landing area may, in other embodiments, be of sufficient size to enable the aircraft to utilize the landing area for take-off or landing). 
         [0060]    As the helicopter  100  lowers the aircraft  200  to the landing area, the lay lines  290  may be deployed. As the aircraft  200  nears the landing area  50 , if the lay lines  290  are deployed, the ground crew and/or ground equipment may use the lay lines  290  to guide the aircraft  200  over and onto the landing area  50 . The first and second mating devices  170  and  270  are then disconnected from each other (such as in any of the manners described above), breaking the linkage between the helicopter  100  and the aircraft  200  and enabling the helicopter to perform other activities. 
         [0061]    In further embodiments, returning to  FIG. 2 , to retrieve the aircraft  1200  from wing-borne flight, the helicopter  1100  rendezvous with the aircraft  1200  in flight and maneuvers such that the mating device  1126  of the capture device  1124  mates with and connects to the portion of the aircraft  1200  to link the helicopter  1100  with the aircraft  1200 . The linked helicopter  1100  and aircraft  1200  then slow (such as by independently decreasing the speed of both the helicopter and the aircraft), and as the linked helicopter  1100  and aircraft  1200  gradually slow, the helicopter  1100  gradually accepts the weight of the aircraft  1200 . The helicopter  100  then lowers the aircraft  1200  to the landing area (not shown), which is not of sufficient size to enable the aircraft  1200  to utilize the landing area for take-off or landing (though it should be appreciated that the landing area may, in other embodiments, be of sufficient size to enable the aircraft to utilize the landing area for take-off or landing). 
         [0062]    As the helicopter  1100  lowers the aircraft  1200  to the landing area, the lay lines  1290  and/or  1295  may be deployed. As the aircraft  1200  nears the landing area, if the lay lines  1290  and/or  1295  are deployed, the ground crew and/or ground equipment may use the lay lines  1290  and/or  1295  to guide the aircraft  1200  over and onto the landing area. The mating device  1126  is then disconnected from the aircraft  1200 , breaking the linkage between the helicopter  1100  and the aircraft  1200  and enabling the helicopter  1120  to perform other activities. 
         [0063]    Various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.