Abstract:
An apparatus for the recovery of an aircraft includes a capture device and first and second pole pairs. The first pole pair includes first top and bottom poles respectively placed near first top and bottom portions of the capture device. The first pole pair is configured to move from a first position, in which the pole pair holds the capture device in an open position to capture the aircraft, to a second position, in which the pole pair holds the capture device in a closed position to contain the captured aircraft after impact of the aircraft on the capture device. The second pole pair includes second top and bottom poles respectively placed near second top and bottom portions of the capture device. The second pole pair is also configured to move from the first position to the second position. Further, energy elements are coupled on one end to a respective top or bottom portion of the capture device and on another end to a respective top or bottom pole. The energy elements are disposed to absorb the force of the impact of the aircraft.

Description:
BACKGROUND 
     Embodiments of the present invention relate generally to new and useful improvements in mobile aircraft recovery, and more particularly to an apparatus and method for the capture of aircraft, including unmanned aerial vehicles (UAVs), drones, and other flight devices or projectiles. 
     The recovery of aircraft without the use of a runway is generally known in the art. See, for example, the “skyhook” approach, as disclosed in U.S. Pat. Nos. 7,090,166, 7,104,495, 7,114,680 and Pre-Grant Publication Nos. 2005/0151009 and 2005/0178894, where a boom from a ship or other vehicle is extendable to deploy a recovery line to capture the aircraft in flight. The skyhook approach requires that the leading edge of the aircraft wing be strong enough to survive the wire impact on the recovery line. Thus, the aircraft structure is heavy, resulting in a negative impact on aircraft payload capacity and endurance. Other approaches, such as the arresting hook in U.S. Pat. No. 7,143,976 to Snediker et al., or the deployable lifting device in U.S. Pat. No. 4,753,400 to Reuter et al., share similar problems. 
     In short, there exists a need in the art for a mobile aircraft recovery system that is able to limit damage to the aircraft during recovery using a lighter aircraft and, thus, minimizing, the impact on aircraft endurance. A further need exists for a mobile aircraft recovery system that is itself small and lightweight so as to be mobile, versatile on land and sea, and transportable. Additionally, a need exists for a mobile aircraft recovery system having a strong wind tolerance, including tolerance of wind variation, direction and speed. 
     SUMMARY 
     In an embodiment, an apparatus for the recovery of an aircraft includes a capture device and a first and second pole pair. The first pole pair includes first top and bottom poles respectively placed near first top and bottom portions of the capture device. The first pole pair is configured to move from a first position, in which the pole pair holds the capture device in an open position to capture the aircraft, to a second position, in which the pole pair holds the capture device in a closed position to contain the captured aircraft after impact of the aircraft on the capture device. The second pole pair includes second top and bottom poles respectively placed near second top and bottom portions of the capture device. The second pole pair is also configured to move from the first position to the second position. The apparatus further includes energy elements each coupled on one end to a respective top or bottom portion of the capture device and on another end to a respective top or bottom pole. The energy elements are disposed to absorb the force of the impact. 
     According to one exemplary embodiment, the first pole pair comprising first top and bottom poles may be coupled at first ends to a first support beam, the top and bottom poles extending to first top and bottom portions of the capture device. Similarly, the second pole pair comprising second top and bottom poles may be coupled at first ends to a second support beam, the top and bottom poles extending to second top and bottom portions of the capture device. Further, a pivot beam may be coupled to each of the first and second support beams, wherein the pivot beam is disposed to pivot each of the first and second support beams forward in the direction of the impact of the aircraft. 
     In another embodiment, a method for the recovery of an aircraft includes coupling a first pole pair comprising first top and bottom poles respectively to first top and bottom positions of a capture device and coupling a second pole pair comprising second top and bottom poles respectively to second top and bottom positions of the capture device. The method further includes moving each pole pair from a first position, in which the pole pairs hold the capture device in an open position to capture the aircraft, to a second position, in which the pole pairs hold the capture device in a closed position to contain the captured aircraft. The method includes absorbing he force of the impact using energy elements, each coupled on one end to a respective top or bottom position of the capture device and on another end to a respective top or bottom pole. 
     According to a further embodiment, the method includes pivoting the first and second pole pairs forward in the direction of the impact. 
     This summary is provided merely to introduce certain concepts and not to identify any key or essential features of the claimed subject matter. Further features and advantages of embodiments of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of embodiments of the invention will be apparent from the following, more particular description of embodiments of the invention, as illustrated in the accompanying drawings wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. Unless otherwise indicated, the accompanying drawing figures are not to scale. 
         FIG. 1  depicts a perspective view of the mobile aircraft recovery system according to an embodiment of the present invention; 
         FIG. 1A  depicts a rear detailed view of the shock absorption device of the mobile aircraft recovery system, as shown in  FIG. 1   
         FIGS. 2A and 2B  depict a detailed view of the tear straps of the mobile aircraft recovery system as shown in  FIG. 1 ; 
         FIG. 3A  depicts a side view of the mobile aircraft recovery system prior to impact of the aircraft, according to an embodiment of the present invention; 
         FIG. 3B  depicts a side view of the mobile aircraft recovery system during impact of the aircraft, according to an embodiment of the present invention; 
         FIG. 3C  depicts a side view of the mobile aircraft recovery system after impact of the aircraft, according to an embodiment of the present invention; 
         FIG. 4  depicts a side view of the mobile aircraft recovery system during impact of the aircraft, according to an alternative embodiment of the present invention 
         FIGS. 5 and 6  depict an exploded view of the mobile recovery unit in a stowed position, according to an embodiment of the present invention; and 
         FIG. 7  depicts a front view of a control unit of the mobile aircraft recovery system, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the invention are discussed herein. While specific embodiments are discussed, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected and it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations can be used without parting from the spirit and scope of the invention. Each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
     Referring now to the drawings, there is shown in  FIG. 1  a perspective view of the mobile aircraft recovery system  100  according to an embodiment of the present invention. A capture device  102 , for example, a net, sits in an open vertical position above the ground prior to the capture of an aircraft. The vertical position of the net  102  may be referred to as a “ready to capture position.” The net  102  is shaped to focus the deceleration loads on the aircraft wing closest to the fuselage, thus avoiding wing tip bending. For example, according to one embodiment, the net  102  may be a ribbon net or other net which forms a basket shape, expanding outward to cradle the aircraft during capture. The use of a basket-shaped net retains the aircraft after impact and prevents the aircraft from falling out of the net or springing backwards off the net  102  and incurring damage. 
     The net  102  is supported, for example, by two pole pairs  104 . The pole pairs  104  of the mobile aircraft recovery system  100  are used to absorb the momentum of the aircraft during capture. Each pole pair  104  may include an upper net pole  104 ′ coupled to an upper portion of the net  102  and a lower net pole  104 ″ coupled to a bottom portion of the net  102 . In the embodiment shown, the poles  104 ′,  104 ″ are coupled to corners of the net  102 . Each net pole  104 ′,  104 ″ may rotate about a pivot point located at an opposite end of the respective net pole  104 ′,  104 ″ from the net  102 . Further, the upper and lower net poles  104 ′,  104 ″ of each pole pair  104  may move in synchronization relative to one another. 
     The initial impact of the aircraft on the net  102  engages the pivoting movement of the pole pairs  104 . A timing or kinematic mechanism may be coupled to each pole pair  104  to help synchronize the movement of the top and bottom net poles  104 ′,  104 ″ together. Such synchronization allows the net  102  and pole pairs  104  capture an aircraft  300  (see  FIG. 3A ) by folding around the primary aircraft wing to decelerate the aircraft while engulfing the aircraft for post deceleration retention. 
     According to one embodiment, the net  102  and pole pairs  104  may be coupled using energy elements  106 , i.e. tear straps. The tear straps  106  may be positioned on the corners, or other positions, of the net  102  to improve capture geometry and to reduce the initial structural shock impulse, i.e. to attenuate the initial peal load. As seen in  FIG. 2A , the tear straps  106  may be positioned between ropes or lanyards  108  holding the corners of the net  102  and the ends of each net pole  104 ′,  104 ″. Prior to capture, the tear straps  106  are embodied in a retracted position  106 ′ and, for example, may comprise Nylon, or other material, doubled-over straps sewn together down the center of the strap with a thin sewing thread. In the retracted position  106 ′, the tear straps  106  may provide additional slack to the net  102  to attenuate the impact force as the aircraft wings initially hit the net  102 . 
     Following the impact of the aircraft  300  on the net  102 , the tear straps  106  may shift from the retracted position  106 ′ into a released position  106 ″, as shown in  FIG. 2B . This may occur, for example, when the sewing thread of the tear strap  106  registers a certain force, for example, a force of approximately 50 lbs, that is associated with the impact of the aircraft on the net  102 , and breaks; ripping the seam holding the tear strap  106  in the retracted position  106 ′. Thus, the breaking of the sewing thread allows the force of the impact to pull the tear strap  106  in retracted position  106 ′ fully or partially straight into the released position  106 ″, as seen in  FIG. 2B . This causes the tear straps  106  to change the angle of the net to improve capture of the aircraft. As the straps tear they smoothly accelerate the pivot arms thus avoiding a rapid acceleration similar to an impact that would occur without these devices. Alternatively, other energy elements may be used, such as, for example, slip devices, Velcro® or shock absorbers. After use, the energy elements may either be reused or replaced. 
     According to the embodiment shown in  FIG. 1 , the pole pairs  104  are held in place by two hydraulically erectable arm assemblies  110  joined to a central shaft, called the recovery pivot beam  112 . Each arm assembly  110  includes a vertical beam  114 , a corner beam  116  and a diagonal beam  118 . On one end of the arm assembly  110 , the vertical beam  114  is coupled to the pole pair  104 . On the other end of the arm assembly  110 , the diagonal beam  118  is connected to the recovery pivot beam  112 . The corner beam  116  serves to connect the vertical beam  114  to the diagonal beam  118 . 
     According to one embodiment, the mobile aircraft recovery system  100  may include one or more shear devices  120 , such as a shear pins, nylon ties, or the like, which hold the net in the ready to capture position prior to recovery. Specifically, the shear devices  120  maintain an open net  102  by holding the lower net pole  104 ″ in a certain position relative to the arm assembly  110 . This prevents the pole pairs  104  from prematurely pivoting, for example, due to wind or other external forces. When a certain force that is associated with the impact of the aircraft on the net  102  is registered by the shear device  120 , the shear devices  120  release allowing the pole pairs  104  to gain their initial momentum forward. The shear devices  120  may be replaced after each recovery. 
     According to another embodiment, the mobile aircraft recovery system  100  may include one or more shock absorption devices  122  positioned to absorb energy upon impact of the aircraft  300 . As shown in  FIG. 1 , the shock absorption devices  122  may be coupled to the top of vertical beam  114 . The shock absorption devices  122  may also be coupled to the pole pairs  104  and may provide the pivot point for each pole pair  104 . The shock absorption devices  122  may be, for example, friction dampers or brakes, rotary shock absorbers or dampers, or linear dampers. Such shock absorption devices  122  may help slow the aircraft and bring the aircraft to rest in the net. The pivot of the whole structure of the mobile aircraft recovery system  100  helps keep the aircraft from swinging. 
       FIG. 1A  depicts a rear detailed view of a shock absorption device  122 , as shown in  FIG. 1 . According to one embodiment, the shock absorption device  122  includes a vertical bar  125  which may be coupled to the vertical beam  114  of the arm assembly  110 . A sliding mechanism  127  may be coupled to the vertical bar  125  to control the pivoting movement of the pole pair  104 . Coupled to the sliding mechanism  127  are two dampers  123  to absorb the shock of the impact of the aircraft in the net  102 . As described above, the dampers  123  may be friction, rotary or linear dampers. Pole levers  124  may be further coupled to each end of the sliding mechanism  127  and are able to attach to the ends of the top and bottom net poles  104 ′,  104 ″. 
     According to a further embodiment, each shock absorption device  122  may include the timing or kinematic mechanism which, as previously discussed, facilitates the synchronous movement of the top and bottom net poles  104 ′,  104 ″. The timing mechanism enables the pole levers  124  of the top and bottom net poles  104 ′,  104 ″ to move at the same time. The synchronous movement of the pole pairs  104 , when combined with the energy elements  106 , forms the net  102  into a basket configuration which cradles the aircraft upon impact. Non-synchronous movement of the pole pairs  104  may cause the net  102  to remain in the flat ready to capture position, causing the aircraft to fall or bounce out of the net  102 . 
     According to a further embodiment, the mobile aircraft recovery system  100  includes a hydraulic activation system  126 , including the recovery pivot beam  112 , a recovery actuator  128  and a recovery base  130 , for raising and lowering the arm assemblies  110  and net  102 . The hydraulic activation system  126  may also include a hydraulic cushion (not shown). For example, the hydraulic cushion may include hydraulic valves and gas accumulators that are separate from the raising and lowering actuation function that permits the actuator to move passively in the direction of recovery. The motion is permitted because the valves cause oil holding the actuator in the upright position to flow into the gas accumulator. 
     According to one embodiment, the recovery pivot beam  112  of the hydraulic activation system  126  allows the diagonal beams  118  of the arm assemblies  110  to fall or pivot forward during the capture of the aircraft to further help dissipate the momentum of the aircraft. This is shown in  FIG. 4 , which depicts a side view of the mobile aircraft recovery system during impact of the aircraft. Angle α shows the change in position of the diagonal beam  118  forward from a starting position along axis A (see  FIG. 3A ), that is perpendicular to the ground. 
       FIG. 3A  depicts a side view of the mobile aircraft recovery system  100  prior to impact of the aircraft  300 , according to an embodiment of the present invention. The vertical beam  114  of the arm assembly  110  is positioned along a perpendicular axis A relative to the ground. Prior to impact of the aircraft  300 , the top net poles  104 ′ are positioned at a pre-determined angle θ 1  relative to axis A and the bottom net poles  104 ″ are positioned at a predetermined angle θ 11  relative to axis A. The predetermined angles θ 1  and θ 11  of the net poles  104 ′,  104 ″ are selected to ensure that the net  102  remains in the ready to capture position prior to impact. According to one embodiment, angle θ 1  is approximately equal to angle θ 11 . According to another embodiment, angles θ 1  and θ 11  of the net poles  104 ′,  104 ″ are both less than 45 degrees. Further, the tear strips  106  remain in their initial retracted position  106 ′, which aids in pulling the net  102  close to each of the top and bottom net poles  104 ′,  104 ″ and in ready to capture position. 
     As discussed above, shear devices  120  may be used maintain the angles θ 11  between the bottom net poles  104 ″ and the vertical beam  114  prior to impact. Because each bottom net pole  104 ″ moves in synchronization with its respective top net pole  104 ′, maintaining the angle θ 11  of the bottom net pole  104 ″ using a shear device  120  simultaneously maintains the angle θ 1  of the top net pole  104 ′. The shear devices  120  prevent wind or any other external force from inadvertently interfering with the recovery of the aircraft  300 . 
       FIG. 3B  depicts a side view of the mobile aircraft recovery system  100  during impact of the aircraft  300 , according to an embodiment of the present invention. As the aircraft  300  strikes the net  102 , the force of impact releases the shear device  120  and causes the pole pairs  104  to each pivot about their pivot points forward in the direction of impact D. The pivoting momentum of the pole pairs  104 , allows the net  102  to form a basket-like configuration to envelop and capture the aircraft  300 . The energy absorbing devices  122 , i.e. the dampers, attached to the pole pairs  104  help bring the aircraft  300  to rest in the net  102 . 
     As the pole pairs  104  pivot forward the angles θ 1  and θ 11  of the top and bottom net poles  104 ′,  104 ″, respectively, increase to angles θ 2  and θ 22  relative to the perpendicular axis A defined by the vertical beam  114  of the arm assembly  110 . According to one embodiment, the angle θ 2  of the top net pole  104 ′ increases more than the angle θ 22  of the bottom net pole  104 ″ during capture. 
     Furthermore, the impact of the aircraft  300  on the net  102 , as well as the pivoting motion of the pole pairs  104 , causes the tear straps  106  to pull from the retracted position  106 ′ into the released position  106 ″. The release of the tear straps  106 , i.e. the straightening out of the retracted position  106 ′, may occur in the direction N of the net  102  (See  FIG. 2B ). The release of the tear straps  106  may also transform the net  102  from the ready to capture position, as depicted in  FIG. 3A , into the basket-like configuration, as depicted in  FIG. 3B . 
     According to one embodiment, the top net poles  104 ′ are loaded similarly to the bottom net poles  104 ″, however the tear straps  106  are rated lower and are longer on the top than on the bottom. This ensures to improve the basket-like configuration of the net  102 . The top tear straps  106  may tear all the way and, since they are longer, they compensate for the top poles being higher. 
     After recovery, the pole pairs  104  and net  102  are lowered using the hydraulic actuator  128  and the aircraft  300  may be manually removed from the net by a ground crew. 
       FIG. 3C  depicts a side view of the mobile aircraft recovery system  100  after impact of the aircraft  300 , according to an embodiment of the present invention. In this embodiment, the aircraft  300  has been captured and has come to rest in the net  102 . The top and bottom net poles  104 ′,  104 ″ have similarly come to rest at angles θ 3  and θ 33 , respectively, relative to the vertical beam  114 . 
       FIG. 4  depicts a side view of the mobile aircraft recovery system  100  during impact of the aircraft  300 , according to an alternative embodiment of the present invention. In addition to that described in  FIG. 3B , in this alternative embodiment, as the aircraft  300  first strikes the net  102 , this initial impact force causes each arm assembly  110  to pivot forward on the recovery pivot beam  112  (see  FIG. 1 ). As seen in  FIG. 4 , the arm assembly  110  has pivoted away from the perpendicular axis A in the direction of impact D by an angle α. This additional movement of the arm assemblies  100  helps further dissipate the momentum of the aircraft  300  during capture. 
       FIGS. 5 and 6  depict an exploded view of the mobile aircraft recovery unit  100  in a stowed position, according to an embodiment of the present invention. As shown, the mobile aircraft recovery unit  100  comprises a modular design to permit disassembly for compact storage when not in use. Specifically, the recovery base  130  may house the disassembled net poles  104 ′,  104 ″, the recovery pilot beam  112 , the vertical beams  114 , the corner beams  116 , the diagonal beams  118  and the recovery actuator  128 . The recovery base  130  may fit into a mobile unit  500 , for example a trailer assembly. According to one embodiment, a launcher assembly  502  may be coupled to the recovery base  130  of the mobile unit  500  to launch the aircraft  300 . 
     Additionally, the net  102 , tear straps  106 , hand control unit (see control unit  700  below), electrical cables and other equipment may be transported within the mobile unit  500  in transit cases (not shown). 
       FIG. 7  depicts a front view of a control unit  700  of the mobile aircraft recovery system  100 , according to an exemplary embodiment of the present invention. According to one embodiment, the control unit  700  may control both the mobile aircraft recovery system  100 , as well as the launch system. The control unit  700  may include a mode switch  702  to switch between “off,” “standby,” “launch,” and “net” modes. The control unit  700  may include a net position switch  704  for lifting or lowering the position of the net  102  using the hydraulic activation system  126 . Further, the control unit  700  may include a net cushion switch  706  for adjusting the pre-determined angle α of the arm assembly  110  relative to the perpendicular axis A to ensure that the net  102  remains in the ready to capture position prior to impact of the aircraft  300  on the net  102 . 
     The control unit  700  may include one or more indicators  708  to indicate, for example, that the mobile aircraft recovery system  100  or launch assembly  502  is safe to operate, that the hydraulic activation system  126  of the mobile aircraft recovery system  100  is ready to pressurize, or that the launch assembly  502  is ready to launch the aircraft  300 . The control unit  700  may further include, for example, a hydraulic power unit (HPU) switch  710  to activate the hydraulic activation system  126  for either recovery operation or launch, a pressurize switch  712  to pressurize the hydraulic activation system  126  and/or a launch switch  714  to launch the aircraft using the launch assembly  502 . 
     Alternatively, the mobile aircraft recovery system  100  may be embodied as a passive capture system, where no electronics or computers are required. For example, switch logic may be used without the use of computers or software. 
     Embodiments of the mobile aircraft recovery system  100  enjoy several advantages over other systems known in the art. The mobile aircraft recovery system  100  can be mobilized on land or on a ship deck with a single trailer and does not require the use of separate supporting structures or anchors. One exception is the use of the mobile aircraft recovery system  100  on a ship deck during a high sea state, where tie-downs are required for all deck equipment. The small footprint of the mobile aircraft recovery system  100  allows for easy ship integration, including minimal modification and interference with current operations, also known as normal operations on the flight deck or “OPS.” Because the mobile aircraft recovery system  100  may be added to an existing ship, it is important that the system does not interfere with existing operational procedure and business. The mobile aircraft recovery system  100  is further able to withstand ship motion having pitch, heave and roll tolerance, as well as navigation sensitivity. 
     The mobile aircraft recovery system  100  is quick and easy to both assemble and disassemble. The mobile aircraft recovery system  100  does not require a unique configuration of the aircraft  300  due to the basket-like configuration of the net  102  which supports a soft impact on the aircraft wings. For example, the aircraft  300  does not require the use of strengthening devices in the aircraft&#39;s wings to support the capture, as is known in the prior art. Similarly the soft landing enabled by the mobile aircraft recovery system  100  has a minimal impact on the aircraft  300  weight since flight loads are the driving consideration for structural sizing. Only minor wing leading edge enhancement may be required with minimal weigh impact on the aircraft. 
     The mobile aircraft recovery system  100  may be sized to work accurately with existing aircraft navigation systems and may be combined with a launcher assembly  502 , as described above. The mobile aircraft recovery system  100  is both compact and transportable, as well as reliable and durable during use. The mobile aircraft recovery system  100  is cost efficient in both the development and production stages. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and that the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.