Abstract:
Various embodiments of the present disclosure provide an apparatus configured to automatically retrieve, service, and launch an aircraft. For retrieval, the aircraft drops a weighted cable, and pulls it at low relative speed into a broad aperture of the apparatus. In certain instances, the cable is dragged along guiding surfaces of the apparatus into and through a slot until its free end is captured. The aircraft becomes anchored to the apparatus, and is pulled downward by the cable into a receptacle. Guiding surfaces of the receptacle adjust the position and orientation of a probe on the aircraft, directing the probe to mate with a docking fixture of the apparatus. Once mated, the aircraft is automatically shut down and serviced. When desired, the aircraft is automatically started and tested in preparation for launch, and then released into free flight. A full ground-handling cycle is thus accomplished with a simple, economical apparatus.

Description:
PRIORITY CLAIM 
       [0001]    This application is a continuation of, and claims priority to and the benefit of, U.S. patent application Ser. No. 13/743,069, filed on Jan. 16, 2013, which is a continuation of, and claims priority to and the benefit of, U.S. patent application Ser. No. 12/702,935, filed on Feb. 9, 2010, which claims priority to and the benefit of U.S. Provisional Patent Application No. 61/152,076, filed on Feb. 12, 2009, now expired, the entire contents of each of which are incorporated herein by reference. 
     
    
     CROSS REFERENCE TO RELATED APPLICATIONS 
       [0002]    The present application relates to the following commonly-owned co-pending patent applications: U.S. patent application No. 13/717,147, filed on Dec. 17, 2012, Attorney Docket No. 0251 00-0021; U.S. patent application Ser. No. 13/037,436, filed on Mar. 1, 2011, Attorney Docket No. 025100-0010; U.S. patent application Ser. No. 13/527,177, filed on Jun. 19, 2012, Attorney Docket No. 025100-0016; U.S. patent application Ser. No. 12/702,935, filed on Feb. 9, 2010, Attorney Docket No. 025100-0003; U.S. patent application Ser. No. 13/743,069, filed on Jan. 16, 2013, Attorney Docket No. 025100-0022; and U.S. patent application Ser. No. 13/899,172, filed on May 21, 2013, Attorney Docket No. 025100-0025. 
       BACKGROUND 
       [0003]    1. Field of Invention 
         [0004]    The present invention addresses launch, retrieval, and servicing of a hovering aircraft, especially in turbulent winds or onto an irregularly-moving surface, such as the deck of a ship in a rough sea. Various embodiments of the present invention are especially suited to unmanned aircraft of small size. These embodiments allow for a fully automated operations cycle, whereby the aircraft can be repeatedly launched, retrieved, serviced, and re-launched, without manual intervention at any point, and while requiring only modest accuracy in piloting. 
         [0005]    2. Description of Problem 
         [0006]    Hovering aircraft, be they helicopters, thrust-vectoring jets, “tail-sitters”, or other types, usually and by gently descending in free thrust-borne flight onto a landing surface, coming to rest on an undercarriage of wheels, skids, or legs. This elementary technique can be problematic in certain situations, such as when targeting a small, windswept landing pad on a ship moving in a rough sea. Decades ago, the Beartrap or RAST system was developed to permit retrieval with acceptable safety in such conditions. Retrieval with this system involves securing a line between a helicopter and landing deck, and then winching the helicopter down onto a trolley. The helicopter is fastened to the trolley. After retrieval, the trolley is used to move the helicopter along the deck. The system is effective and widely used, but requires an expensive and substantial plant in the landing area, as well as manual operations coordinated between helicopter and shipboard crew. Furthermore, the helicopter must carry a complete undercarriage in addition to the necessary Beartrap components. 
         [0007]    Desirable improvements relative to the Beartrap system include (a) simplification of the apparatus, and (b) automated rather than manual operation. Ideally not only would retrieval but also subsequent refueling and launch would be automated. This would be particularly desirable for an unmanned aircraft, whose operations cycle could, then be made fully autonomous. Some experimental work toward this objective has been done for a hovering aircraft, as described in the publication by Mullens et al. titled, “Automated Launch, Recovery, and Refueling for Small Unmanned Aerial Vehicles” (2004); however, success has been limited even with light wind and a stationary base. The present invention by contrast provides for fully automated operation in calm or rough conditions, using apparatus which is simple, portable, and suitable for a small vessel or similarly confined base. 
       SUMMARY 
       [0008]    In one embodiment of the method of the present invention, an aircraft would proceed automatically from free thrust-borne flight to retrieval to launch through the following sequence of actions:
       (a) while approaching a base at low relative speed, the aircraft drops a weighted cable;   (b) the aircraft then flies over a retrieval apparatus, which brings the cable into an aperture of cable guides, which in one embodiment forms the shape of a V in the horizontal or substantially horizontal plane;   (c) further translation pulls the cable into and through a slot at the terminus of the cable guides, which captures the cable;   (d) the aircraft is then anchored;   (e) if the cable is not captured, the aircraft can climb away and return for another approach;   (f) the aircraft, recognizing capture of the cable by an increase in tension, winches-in the cable and so draws itself into a docking receptacle, such as, in one embodiment, a funnel-like receptacle at the vertex of the cable guides;   (g) as the aircraft is drawn into the docking receptacle, guiding surfaces align and ultimately mate the aircraft with one or more connectors for docking and servicing;   (h) the cable is released from the retrieval apparatus, and retracted by the aircraft;   (i) the aircraft is shut-down, refueled and otherwise serviced as necessary through one or more suitable connectors;   (j) the aircraft completes launch preparations, and develops sufficient thrust to accelerate away from the retrieval apparatus when released; and   (k) the aircraft is released into thrust-borne free flight.       
 
         [0020]    Since loads can be low during retrieval from hover, the apparatus can be light and portable. Furthermore, easy targeting makes the technique well-suited for both manual control and economical automation. 
         [0021]    It should be appreciated that the apparatus of various embodiments of the present invention include an aircraft docking assembly attached to an aircraft, a base retrieval apparatus attached to a stationary or movable base, and the combination of these configured so as to accomplish the methods of the present invention. 
         [0022]    Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0023]      FIGS. 1A ,  1 B,  1 C and  1 D are a series of diagrammatic rear-quarter perspective views of an embodiment of the present invention for a helicopter, illustrating an aircraft docking assembly attached to the helicopter, a base retrieval apparatus or servicing station, and the helicopter sequentially entering, capturing, docked in, and launching from the base retrieval apparatus or servicing station. 
           [0024]      FIG. 2  is an enlarged partially fragmentary perspective view of a the base retrieval apparatus or servicing station for capturing, docking, servicing, and launching a helicopter. 
           [0025]      FIGS. 3A ,  3 B,  3 C and  3 D are a series of diagrammatic rear-quarter perspective views of an embodiment of the present invention for a hovering “tail-sitter” aircraft, illustrating an aircraft docking assembly attached to the aircraft, a base retrieval apparatus or servicing station, and the aircraft sequentially entering, capturing, docked in, and launching from the base retrieval apparatus or servicing station. 
           [0026]      FIG. 4  is an enlarged perspective view of a representative docking probe mounted in the tail of a “tail-sitter” aircraft of one embodiment of the present invention. 
           [0027]      FIG. 5  is a perspective view of a representative aircraft as in  FIG. 4  being pulled into a docking receptacle of the base retrieval apparatus of one embodiment of the present invention. 
           [0028]      FIGS. 6A ,  6 B,  6 C and  6 D are a series of diagrammatic rear-quarter perspective views of an embodiment of the present invention for a hovering aircraft, illustrating a possible downwind retrieval and launch sequence. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Various embodiments of the present invention are generally directed to apparatus and methods for retrieving a flying object or an aircraft from substantially thrust-borne free flight. In one embodiment, the apparatus includes an aircraft docking assembly for a helicopter and a base retrieval apparatus attachable to a stationary or movable base. In another embodiment, the apparatus includes an aircraft docking assembly for an aircraft configured for efficient wing-borne flight and a base retrieval apparatus attachable to a stationary or movable base. It should be appreciated that the present invention is not limited to the embodiments illustrated in the figures and described below, and that in alternative embodiments, the shape, size, configuration and/or arrangement of one or more of the various components described below may vary. It should also be appreciated that the present invention need not include each and every of the components in the embodiments illustrated in the figures and described below. 
         [0030]    Referring now to  FIGS. 1A ,  1 B,  1 C,  1 D and  2 , one embodiment of the aircraft docking assembly and base retrieval apparatus for a helicopter are generally illustrated. The base retrieval apparatus includes a base station  5  having a base fuel tank  12  and a base member  33  extending upwardly from the base fuel tank  12 . The base station  5  may include an azimuthal pivot  21 , as described below. In the illustrated embodiment, the base station  5  also includes support member  34  connected to the base member  33  for supporting a base docking device, fixture or probe receiver  11 . A guide, funnel, or funnel like docking receptacle  9  is attached to, and extends upwardly from, the base docking device, fixture or probe receiver  11 . The guide, funnel, or funnel like docking receptacle  9  includes guiding surfaces. The guide, funnel, or funnel like docking receptacle  9  has or defines a slot  10  configured to admit a cable  2 , as discussed below. The support member  34  includes outwardly extending arms  4 . The arms  4  extend outwardly defining an angle. A slot  6  is defined or placed near the vertex of the arms  4 . Aerodynamic surfaces or members  22  may be respectively attached to the arms  4 . 
         [0031]    In one of the illustrated embodiments, the aircraft docking assembly is attached to the helicopter and includes a cable  2 , a cable point or fixture such as a cable end fitting  3 , a cable length reducer such as a winch  7 , and an aircraft docking device or fixture such as a probe  8 . The probe includes guiding surfaces and is substantially cylindrically shaped in one embodiment. The probe  8  is attached to the helicopter and extends beyond the skids  26  of the helicopter. At least a portion of the cable  2  is configured to be wound around a drum of the winch  7 . In another embodiment, the winch  7  is attached to the base retrieval apparatus as described below. 
         [0032]    More specifically,  FIGS. 1A ,  1 B,  1 C and  1 D show an illustrative embodiment of the present invention, as used with the helicopter  1  of conventional layout. In preparation for retrieval, the helicopter  1  deploys the lightweight cable  2  weighted by the cable end fitting  3 , and drags it between the arms  4  of the base station  5 . If the helicopter&#39;s path falls within a capture envelope—determined by, primarily, the length la, vertex angle ψa, and droop angle εa of the arms, and the length lc of the cable (and associated height of the servicing apparatus)—then the cable is guided into a cable holder configured to hold the cable  2  (through the slot  6  located at the vertex of the arms  4  as shown in  FIG. 2 ). The helicopter pulls the cable through the slot  6  until further motion is restrained by the cable end fitting  3 . The cable end fitting thus anchors the helicopter. In various embodiments, the cable end fitting, cable, or slot may be made compliant to limit shock loading. If the helicopter&#39;s path is such that the cable misses the arms entirely, or is pulled over an arm before reaching the slot  6 , then the helicopter simply continues in free flight, and can return for another approach. 
         [0033]    Once the helicopter is anchored it can increase thrust, and the cable will tend to stay nearly vertical despite disturbances. The helicopter&#39;s position can also be regulated by appropriate control, for example of rotor thrust and in-plane moments, 
         [0034]    The constraint imposed by the anchored cable can be recognized by the helicopter, and used to trigger the next retrieval step. This involves pulling the helicopter downward toward the base docking device, fixture or probe receiver  11 , for example by activating a winch  7  on the helicopter or on the base station. In one embodiment, this causes the probe  8  on the helicopter to enter, and to be guided to the base of, the guide, funnel, or funnel like docking receptacle  9  on the base station. In one embodiment, the funnel incorporates a cable aperture such as a slot  10  to admit the cable, and thus allow for close placement of the cable and probe on the helicopter. The guide, funnel, or funnel like docking receptacle  9  guides the probe  8  to mate or match firmly with the base docking device, fixture or probe receiver  11 , thus completing the retrieval. Mating or matching can be detected by a suitable sensor in the probe or in the base docking device, fixture or probe receiver  11 . 
         [0035]    Once retrieval is complete, the cable can be released from the capture slot, and optionally retracted into the helicopter. The helicopter&#39;s engine can be stopped. Servicing, such as provision of electrical power, refueling from a base supply, and weighing of the aircraft, can be effected through one or more suitable connectors and sensors in the probe  8  and base docking device, fixture or probe receiver  11 . The helicopter can remain docked until such time as launch is desired. These connectors can be configured to automatically transfer fluids and/or electricity to the aircraft. 
         [0036]    For launch, appropriate self-testing can be completed, and the helicopter then run-up. Release into free flight should be permitted only when thrust is sufficient for positive separation. This condition can be enforced by various ways, such as an appropriately large break-out force in the docking fixture, or a suitable combination of thrust measurement and active triggering of an unlocking device (not shown). The aircraft would extract the cable from the docking fixture through the slot  10  and could then winch it onboard. 
         [0037]    Referring now to  FIGS. 3A ,  3 B,  3 C,  3 D,  4 ,  6 ,  6 A,  6 B,  6 C and  6 D, one embodiment of an docking assembly and base retrieval apparatus for an aircraft configured for efficient wing-borne flight is generally illustrated. The aircraft includes a fixed wing  17 , a propeller  18 , a fuselage  31 , and an empennage  20 . The empennage  20  includes vertical stabilizer  27  and horizontal stabilizers  28 . The aircraft docking assembly includes cable  2 , cable end fitting  3 , aircraft docking device or fixture such as a probe  8 , and winch  7 . In another embodiment, the winch  7  is attached to the base retrieval apparatus as described below. The probe  8  may include fuel and electrical connectors  13  located at an end portion of the probe  8 . A cable guide  32  may be included to guide the cable as it is wound from the drum of the winch  7 . In the illustrated embodiment, such a cable guide  32  is formed in the shape of a funnel. 
         [0038]    The illustrated base retrieval apparatus for an aircraft configured for efficient wing-borne flight includes base station  5  having a base fuel tank  12  and a base member  33  extending upwardly from the base fuel tank  12 . The base station  5  also includes support member  34  connected to the base member  33  for supporting a base docking device, fixture or probe receiver  11 . The guide, funnel, or funnel like docking receptacle  9  is replaced by guide or docking receptacle  19 , having edges  35  that serve to admit and orient the empennage surfaces  27  and  28  of the aircraft as it is pulled into base docking device, fixture or probe receiver  11 , as discussed below. The support member  34  includes arms  4 . The arms  4  extend outwardly defining an angle. A slot  6  is defined or placed near the vertex of the arms  4 . Aerodynamic surfaces or members  22  may be respectively attached to a portion of the arms  4 . In one embodiment, the base station  5  may include an azimuthal pivot  21 , as described below. 
         [0039]      FIG. 3  shows the aircraft  16  having a configuration suited to efficient wing-borne flight. A propeller  18  is installed at its nose, with the propeller&#39;s spin axis aligned with the fuselage  31 . The winch  7  and probe  8 , which are comparable to those in  FIGS. 1A ,  1 B,  1 C and  1 D and  FIG. 2 , are mounted at the rear of the fuselage  31 , as shown in more detail by  FIG. 4  and described above. To prepare for retrieval, the aircraft pitches up from wing-borne flight, with its thrust line near horizontal, into thrust-borne flight, with its thrust line near vertical. Rotor thrust is adjusted to balance aircraft weight. The cable  2  is then deployed, and retrieval proceeds much as was described for the helicopter of  FIGS. 1A ,  1 B,  1 C and  1 D and  FIG. 2 . In this case, however, the guide or docking receptacle  9  of  FIG. 1A ,  1 B,  1 C and  1 D and  FIG. 2  is replaced by a guide or docking receptacle  19  in the form of a set of petals whose edges  35  serve to admit and orient the empennage surfaces  27  and  28  of the aircraft as its probe  8  is pulled into the base docking device, fixture or probe receiver  11 , as illustrated by  FIG. 5 . Thus, the combination of an appropriately long cable  2 , appropriately open arms  4 , and appropriately shaped petals, permits successful retrieval across a wide range of aircraft approach paths and orientations. After retrieval, the aircraft can be serviced and re-launched much as was described for the helicopter of  FIGS. 1A ,  18 ,  1 C and  1 D and  FIG. 2 . 
         [0040]    For automated retrieval, the aircraft and base retrieval apparatus each can be equipped with a suitable device for measuring relative position and velocity in three dimensions, such as satellite-navigation equipment having antennas on the aircraft  14  and on a reference point such as point  15  near the base docking device, fixture or probe receiver  11 . In an embodiment, each of the aircraft and base retrieval apparatus can also have equipment for measurement of orientation, such as magnetic or inertial sensors, as well as appropriate mechanisms for computation, power supply, and communication. 
         [0041]    Communication between the aircraft and base retrieval apparatus can also be used, for example, to trigger the base retrieval apparatus to release the cable in the event of an anomaly, such as an excessive mismatch in position or orientation as the aircraft is pulled toward the base docking device, fixture or probe receiver  11 . In that case, the aircraft would fly clear of the base station and could return for another approach. 
         [0042]    In many cases, the preferred approach direction will vary with wind velocity. This can be accommodated by providing a base retrieval apparatus including a base station mounted on the azimuthal pivot  21  (as shown in  FIG. 2 ). The base support member  34  could then be oriented or rotated by a suitable actuator on the pivot, or by the weathervane action of the suitably placed aerodynamic surfaces or members  22 . 
         [0043]    In light to moderate wind, the preferred approach direction would typically be upwind. However, if the wind speed V W  were to exceed the maximum airspeed V A,max  at which an aircraft such as that shown in  FIGS. 3A ,  38 ,  3 C and  3 D could sustain level thrust-borne flight, then an upwind approach would be possible only while descending. For an approach in level flight, the procedure illustrated in  FIGS. 6A ,  6 B,  6 C and  6 D would be used instead. In this case, the aircraft would fly into the wind at a designated airspeed V A , while drifting downwind toward the base station at speed (V W −V A ). Capture of the cable would proceed as described for  FIG. 1A ,  1 B,  1 C and D and  FIGS. 3A ,  3 B,  3 C and  3 D; however, once anchored, the aircraft would not be able to hover vertically above the base docking receptacle. Instead, the aircraft could hover, and so maintain line tension, only in a downwind kite-like position as shown in  FIG. 6B . 
         [0044]    To accommodate this situation, the base docking device, fixture or probe receiver and the guide or docking receptacle may be mounted on a gimbal  23  so that the axis of the funnel can align with the cable, as shown in  FIG. 6B . The gimbal could be set as desired after the aircraft mated to the base docking device, fixture or probe receiver, typically to thrust-vertical orientation. The torque necessary thus to orient the gimbal can be provided by the aircraft itself, or by an actuator on the base station. Once set at the desired orientation, the gimbal can be locked in place by an appropriate mechanism. 
         [0045]    For launch in a strong wind, a downwind gimbal tilt may likewise be necessary for the aircraft to accelerate out of the base docking device, fixture or probe receiver upon release. In preparation for such a downwind launch, the gimbal can be unlocked and tilted as appropriate. The aircraft can then pull itself out of the base docking device, fixture or probe receiver as shown in  FIG. 6C . Once clear, the aircraft could reorient if desired to reduce the downwind drift rate, as shown in  FIG. 6D . An anemometer  24  on the base station can be used to select the appropriate orientation for launch. 
         [0046]    It should be understood that 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.