Abstract:
A system and method for a reconfigurable aircraft having a fuselage with one or more propellers, at least one tail assembly, a processor, and a memory having instructions stored thereon that, when executed by the processor, cause the system to: determine a safety clearance for the at least one tail assembly; and selectively move the at least one tail assembly upon a determination that the safety clearance is achieved.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional patent application Ser. No. 62/000,826, filed May 20, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The subject matter disclosed herein relates generally to the field of rotorcraft, and to a vertical take-off and landing aircraft with a reconfigurable tails or empennage that reduces its overall dimensions during flight. 
       DESCRIPTION OF RELATED ART 
       [0003]    Typically, a vertical take-off and landing (VTOL) aircraft, e.g., a helicopter, tiltrotor, tiltwing, or a tail-sitter aircraft, can be airborne from a relatively confined space. Some tail-sitter aircraft can include a tail section (rear portion of the fuselage) to add flight stability during horizontal flight. However, this tail is not utilized while in the rotor-borne flight state. A tail-sitter aircraft has a fuselage that is vertically disposed during take-off and hover and must transition from a vertical flight state (i.e., rotor borne) to a horizontal flight-state (i.e., wing borne). However, in designing aircraft, such as a tail-sitter aircraft, occasional problems arise by using a tail for flight stability. For example, operational and practical dimensional constraints of the takeoff and landing environment limits where aircraft with a tail can be used. Such environments, such as an urban area or on a flight deck of a ship limit applicability of such aircraft due to the additional height requirements that a tail adds to the aircraft. This causes the resulting aircraft design to be less optimal because it must be able to take off and land in these confined environments. A VTOL aircraft that can operate in confined environments while having a tail for horizontal flight stability would be well received in the art. 
       BRIEF SUMMARY 
       [0004]    According to an aspect of the invention, a method for controlling a reconfigurable aircraft includes receiving, with a processor, one or more signals indicative of position of the aircraft with the ground; determining, with the processor, information indicative of a safety clearance for at least one tail assembly; and selectively moving the at least one tail assembly upon a determination that the safety clearance is achieved. 
         [0005]    In addition to one or more of the features described above, or as an alternative, further embodiments could include receiving sensor information indicative of weight of the vehicle on a plurality of landing gears. 
         [0006]    In addition to one or more of the features described above, or as an alternative, further embodiments could include receiving sensor information for a strut and linkages coupled to the at least one tail assembly. 
         [0007]    In addition to one or more of the features described above, or as an alternative, further embodiments could include providing the at least one tail assembly with a first portion that is coupled to a second portion. 
         [0008]    In addition to one or more of the features described above, or as an alternative, further embodiments could include selectively moving the second portion from a retracted position to an extended position. 
         [0009]    In addition to one or more of the features described above, or as an alternative, further embodiments could include attaching the second portion to the first portion in the extended position. 
         [0010]    In addition to one or more of the features described above, or as an alternative, further embodiments could include retracting the second portion from the first portion to be substantially orthogonal with the first portion. 
         [0011]    In addition to one or more of the features described above, or as an alternative, further embodiments could include coupling the at least one tail assemble to a wing portion of the aircraft. 
         [0012]    According to another aspect of the invention, a system for a reconfigurable aircraft having a fuselage having one or more propellers; at least one tail assembly; a processor; and memory having instructions stored thereon that, when executed by the processor, cause the system to: determine a safety clearance for the at least one tail assembly; and selectively move the at least one tail assembly upon a determination that the safety clearance is achieved. 
         [0013]    In addition to one or more of the features described above, or as an alternative, further embodiments could include at least one tail assembly with a first portion that is coupled to a second portion. 
         [0014]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to selectively move the second portion from a retracted position to an extended position. 
         [0015]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a second portion that is attached to the first portion in the extended position. 
         [0016]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a second portion that is substantially orthogonal to the first portion in a retracted position. 
         [0017]    In addition to one or more of the features described above, or as an alternative, further embodiments could include respective strut and linkages coupled to the at least one tail assembly. 
         [0018]    In addition to one or more of the features described above, or as an alternative, further embodiments could include at least one tail assembly that is coupled to a wing portion of the aircraft. 
         [0019]    Technical effects of a VTOL aircraft with reconfigurable tail assemblies includes operation in confined areas on land or on water, e.g., on a storage area of a flight deck of a ship or an urban landing zone. The VTOL aircraft of the present invention provides a reconfigurable tail assembly that can be selectively extended or retracted in flight and provides for a VTOL aircraft that can operate in confined areas of ships or urban environments. 
         [0020]    Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0021]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which like elements are numbered alike in the several FIGURES: 
           [0022]      FIG. 1A  is a perspective view of an exemplary aircraft with retracted tail assemblies during flight according to an embodiment of the invention; 
           [0023]      FIG. 1B  is a perspective view of the aircraft of  FIG. 1  but is shown during horizontal flight according to an embodiment of the invention; 
           [0024]      FIG. 2  is a schematic view of an exemplary computing system according to an embodiment of the invention; 
           [0025]      FIG. 3A  is a perspective view an aircraft that is shown in transition to a rotor-borne state during landing according to an embodiment of the invention; 
           [0026]      FIG. 3B  is a perspective view an aircraft that is shown in transition to a rotor-borne state during landing according to an embodiment of the invention; and 
           [0027]      FIG. 3C  is a perspective view an aircraft that is shown in a stored configuration according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Referring now to the drawings,  FIGS. 1A and 1B  illustrate a perspective of an exemplary VTOL vehicle in the form of a tail-sitter aircraft  100  for implementing a transition algorithm according to embodiments of the invention. As illustrated, tail-sitter aircraft  100  includes a fuselage  102 , an elongated wing structure  104 , and a plurality of tail assemblies  106  and  108 . Although a particular configuration of a tail-sitter aircraft  100  is illustrated and described in the disclosed embodiments, it will be appreciated that other VTOL configurations of aircraft having a single or a plurality of stabilizing tails that can operate in confined areas on land or on water including fixed-wing aircraft, tiltrotor aircraft, rotary-wing aircraft, and tail-sitting VTOL aircraft including micro air- or organic air-vehicles may also benefit from embodiments disclosed. 
         [0029]    As illustrated in  FIG. 1A , an exemplary tail-sitter aircraft  100  is shown in hover during take-off and landing (i.e., rotor-borne flight state  101 ) whereby longitudinal axis A of fuselage  102  is oriented in a vertical direction with respect to the ground plane. Fuselage  102  is generally located in the middle of wing structure  104 , which is generally orthogonal to longitudinal axis A of fuselage  102  and substantially parallel to the ground plane. Wing structure  104  is configured to provide lift when tail-sitter aircraft  100  is in horizontal flight state  103  (i.e., wing-borne flight) as shown in  FIG. 1B . A plurality of propellers  110 ,  112  are mounted to wing structure  104  along respective axes B, C. Axes B, C are generally parallel to axis A. Propellers  110 ,  112  include substantially similar propeller blades  114  that provide thrust during hover and horizontal flight. Tail-sitter aircraft  100  includes a plurality of reconfigurable tail assemblies  106 ,  108  that can be selectively extended or retracted during flight. 
         [0030]      FIG. 1A  depicts tail-sitter aircraft  100  with retracted tail assemblies  106 ,  108  and  FIG. 1B  depicts tail-sitter aircraft  100  with extended tail-assemblies  106 ,  108  during a horizontal flight state  103  (i.e., wing-borne flight). In its extended state or orientation, tail assemblies  106 ,  108  are substantially aligned with respective longitudinal axes B and C. As shown in  FIG. 1A , Tail assembly  106  includes a first portion  118 , a hinged second portion  120 , and a stabilizer fin  122  coupled to a distal end of second portion  120 . An actuating device and linkages (not shown) are provided to enable the folding of second portion  120 . Operation of the strut and linkages cause second portion  120  to pivot away from or towards first portion  118  at the hinge connecting the portions  118 ,  120 . The actuating device and linkages functions to selectively retract and extend first portion  118  with respect second portion  120  during flight. The first portion  118  of tail assembly  106  also provides a landing gear  123  while tail-sitter aircraft  100  is on the ground. Additionally, landing wheels  119 ,  121  are coupled to respective vertical stabilizers  116 ,  117  to provide stability on the ground. Similarly, Tail assembly  108  includes a first portion  124 , a hinged second portion  126 , and a stabilizer fin  128  coupled to a distal end of second portion  126 . An actuating device and linkages (not shown) are provided to enable the folding of second portion  126 . Operation of the strut and linkages cause second portion  126  to pivot away from or towards first portion  124  at the hinge connecting the portions  124 ,  126 . The actuating device and linkages function to selectively retract and extend first portion  124  with respect second portion  126  during flight. The first portion  124  of tail assembly  108  also provides a landing gear  127  while tail-sitter aircraft  100  is on the ground. Vertical stabilizers  116 ,  117  and stabilizer fins  122 ,  128  provide stability to tail-sitter aircraft  100  during horizontal flight. 
         [0031]      FIG. 2  illustrates a schematic block diagram of a system  200  on board tail-sitter aircraft  100  according to an exemplary embodiment. As illustrated, the system  200  includes aircraft computer  202  that executes instructions for implementing a flight transition algorithm  204  for selectively retracting and extending tail assemblies  106 ,  108  ( FIG. 1A-1B ) during flight. Aircraft computer  202  may receive real-time information acquired from sensors  206 , e.g., accelerometers, Light Detection And Ranging (LIDAR), weight-on-wheels, or an obstacle perception system that may be used to acquire data related to aircraft&#39;s  100  location to the ground in order to deploy or extend tail-assemblies  106 ,  108  ( FIG. 1A-1B ). Computer  202  includes a memory  208  that communicates with a processor  210 . Memory  208  may store flight transition algorithm  204  as executable instructions that are executed by processor  210 . The instructions may be stored or organized in any manner and at any level of abstraction, such as in connection with the execution of the flight transition algorithm  204 . The processor  210  may be any type of processor (such as a central processing unit (CPU) or a graphics processing unit (GPU)), including a general purpose processor, a digital signal processor, a microcontroller, an application specific integrated circuit, a field programmable gate array, or the like. Also, in embodiments, memory  208  may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored the mixing algorithm described below. 
         [0032]    The system  200  may include a database  212 . The database  212  may be used to store information on which the tail-sitter aircraft  100  operates. The tail-sitter aircraft  100  may also operate on real time data acquired by sensors  206  or other terrain and obstacle perception sensors. Also, sensor data acquired by sensors  206  may be stored in database  212 . The data stored in the database  212  may be based on one or more other algorithms or processes for implementing flight transition algorithm  204 . For example, in some embodiments data stored in the database  212  may be a result of processor  210  having subjected data received from sensors  206  to one or more filtration processes. Database  212  may be used for any number of reasons. For example, database  212  may be used to temporarily or permanently store data, to provide a record or log of the data stored therein for subsequent examination or analysis, etc. In some embodiments, database  212  may store a relationship between data, such as one or more links between data or sets of data acquired on board tail-sitter aircraft  100 . 
         [0033]    System  100  may provide one or more controls, such as vehicle controls  214 . Vehicle controls  214  may provide directives based on, e.g., flight configurations. Directives provided by vehicle controls  214  may include navigating tail-sitter aircraft  100  including extending or retracting tail assemblies  106 ,  108  ( FIG. 1A-1B ). The directives may be presented on one or more input/output (I/O) devices  216 . I/O devices  216  may include a display device or screen, audio speakers, a graphical user interface (GUI), etc. In some embodiments, I/O devices  216  may be used to enter or adjust a linking between data or sets of data. It is to be appreciated that the system  200  is illustrative. In some embodiments, additional components or entities not shown in  FIG. 2  may be included. In some embodiments, one or more of the components or entities may be optional. In some embodiments, the components or entities of system  200  may be arranged or configured differently from what is shown in  FIG. 2 . For example, in some embodiments I/O device(s)  216  may be commanded by vehicle controls  214 , as opposed to being commanded by processor  214  as shown in  FIG. 2 . 
         [0034]      FIGS. 1B and 3A-3C  illustrate views of configurations for tail-sitter aircraft  100  for transitioning from a horizontal flight state  103  to a rotor-borne flight state  101  for landing or take-off according to exemplary embodiments of the invention. In  FIG. 1B , tail-sitter aircraft  100  is shown in a horizontal flight state  103  (i.e., wing-borne flight) whereby propellers  110 ,  112  provide thrust and lift while tail-assemblies  106 ,  108  provide stability. In the horizontal flight state  103 , tail assemblies  106 ,  108  are fully extended and propellers  110 ,  112  are adjusted to provide propulsive thrust. In order to transition to a rotor-borne flight state  101  ( FIG. 3A ) such as, for example, during landing, propellers  110 , 112  and wing structure  104  are adjusted to pitch up and/or yaw and cause tail-sitter aircraft  100  to be generally vertically oriented. In this state, fuselage  102  is oriented along longitudinal axis A which is substantially orthogonal to the ground plane. Tail-sitter aircraft  100  continues transitioning and maintains a safety clearance between tail assemblies  106 ,  108  and a ground or other surface or obstacle. During this transition, portions  120 ,  126  of respective tail assemblies  106 ,  108  are rotated inwards in direction of arrows  302 ,  304  towards longitudinal axis A.  FIG. 3B  is shown with fully retracted tail assemblies  106 ,  108 . 
         [0035]    In  FIG. 3B , once tail-sitter aircraft  100  has completed its transition whereby—tail-assemblies  106 ,  108  are fully retracted, tail-sitter aircraft  100  may descend vertically downwards for landing until it transitions to a ground configuration  306 . In embodiments, as shown in  FIG. 3C , tail-sitter aircraft  100  can be stored by transition from ground configuration  306  to a stored configuration  301  and may include selectively foldable wing portions  310  of wing structure  104  and propeller blades  114  that are selectively foldable which further reduce the profile of tail-sitter aircraft  100  for during storage. In order to transition from a take-off configuration  306  to a rotor-borne flight state  101  ( FIG. 1A ), the above process depicted in  FIGS. 1A and 3A-3C  is reversed. For example, wing portions  310  can be selectively extended to a ground configuration  306  ( FIG. 3B ). In this configuration, propellers  110 ,  112  are operated so as to provide lift. During launch, propellers  110 ,  112  function as rotors to provide lift to tail-sitter aircraft  100 . Once a predetermined height, e.g., a safety clearance for portions  120 ,  126  and a stall speed or above is achieved, tail-sitter aircraft  100  can selectively extend portions  120 ,  126  to transition to a rotor-borne flight state  101  ( FIG. 3A ). In this state, tail-sitter aircraft is in an intermediate flight state. As tail-sitter aircraft  100  continues transitioning, the angle of attack of wing structure  104 , and throttle of propellers  106 ,  108  may be adjusted to cause the fuselage  102  to pitch down and yaw. As the tail-sitter aircraft  100  continues to pitch and roll, it completes the transition to a horizontal flight state  103  ( FIG. 1B ) whereby the fuselage  102  is substantially horizontal and propellers  106 ,  108  provide thrust to propel tail-sitter aircraft  10   
         [0036]    Benefits of the exemplary tail-sitter aircraft  100  include operation in confined areas on land or on water such as, a storage area of a flight deck of a ship where such operation would not be feasible without the embodiments disclosed herein. Prior art tail-sitter aircraft have foldable fuselages which add complexity to extend and retract such aircraft while not substantially providing reduced profile for operation in these confined areas. The tail-sitter aircraft  100  of the present invention provides a selectively extendable tail assembly that provides stability during flight as well as a landing gear during landing for a tail-sitter aircraft to operate in confined areas of ships or urban environments. 
         [0037]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while the various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.