Abstract:
An aircraft with four rotors, a fixed wing, and an adjustable v-tail to allow for both vertical take-off and landing and the capability to fly in straight and level flight. The angle of each rotor and engine, with respect to the airfoil surfaces to which they are attached, is adjustable, allowing for thrust to be directed either downwards, allowing the craft to hover, or backwards, allowing the aircraft to travel horizontally while lift is provided and controlled by the wing and v-tail.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application, under 35 U.S.C. §119, claims the benefit of U.S. Provisional Patent Application Ser. No. 62/192,240 filed on Jul. 14, 2015, and entitled “Aircraft Design,” the contents of which are hereby incorporated by reference herein. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    This disclosure relates generally to aircraft design. In particular, this disclosure relates to fixed wing aircraft with adjustable rotors and tail segments. 
       BACKGROUND 
       [0003]    Quad-rotor aircraft are an increasingly common form of aircraft used in a variety of small to mid-size designs of primarily unmanned aircraft. Quad-rotor aircraft are desirable for their ability to take-off and land vertically and the simplicity of their design. Because they are controlled entirely by varying the application of power to the four rotors, quad-rotor craft can use fixed rotors and do not need variable-pitch rotors such as those found in helicopters, greatly reducing both the complexity and cost of the aircraft. 
         [0004]    However, quad-rotor aircraft are unable to cover ground as efficiently, or quickly, as fixed-wing aircraft when travelling over long distances, and are unable to loiter over an area as efficiently as a circling fixed-wing aircraft can at a reduced power-setting. These deficiencies limit the general usefulness of the quad-rotor design. 
         [0005]    Likewise, fixed-wing aircraft are unable to land or take-off in as short a distance as quad-rotor craft, which in turn limits the general usefulness of the fixed-wing design. Thus, a clear trade-off in endurance and versatility exists between the two designs, and an operator must often choose to accept the inherent limitations of either design over the other when choosing the kind of aircraft best suited to the demands of a given operation. Other drawbacks and limitations of existing devices are also present. 
       SUMMARY 
       [0006]    Accordingly, disclosed embodiments address the drawbacks and limitations of existing devices. Other advantages of disclosed embodiments also exist. 
         [0007]    For example, disclosed embodiments address the trade-offs in operational capabilities between fixed-wing and quad-rotor aircraft. Embodiments are designed to be as versatile as single engine and multiengine rotorcraft in take-off, landing, and hovering while preserving the long-distance endurance and efficiencies of fixed-wing aircraft. Disclosed embodiments allow take off in close-quarters and hovering in a vertical-thrust configuration, but are still able to travel long distances and/or loiter over an area at reduced power settings in a horizontal-thrust configuration. 
         [0008]    Disclosed embodiments also include an aircraft whose core structure includes an up-forcing airfoil with control surfaces, or wing, and two smaller down-forcing airfoils, or tail surfaces. In some embodiments, the two tail surfaces are able to fold up and down, so that they may alternate form being at an angle parallel to the wing to forming a ‘V’ shape when viewed from behind (referred to herein as a “v-tail”). Embodiments of the v-tail allow for the same control of both pitch and yaw provided by a traditional “t-tail” through the coordinated use of the control surfaces on each v-tail surface when the aircraft is traveling horizontally in straight and level flight. 
         [0009]    In some embodiments, propulsion is generated by four motor-driven, or engine-driven, sources of thrust which are located on the wing and tail. As used herein, “motor,” “engine,” “motor-driven,” and “engine-driven” are used interchangeably to mean any sort of electric, combustion-based, or other prime mover that turns a rotor, blade, or other propeller to generate a source of thrust. These sources of thrust are able to rotate into a forward position when engaged in horizontal, wing-sustained flight, and rotate upwards when engaged in vertical, thrust-sustained flight. 
         [0010]    In some embodiments, the main wing remains stationary and the tail folds outwards when adjusting to vertical flight in order to lower the rear two sources of thrust so that they are able to rotate upwards and generate downward thrust. Additionally, for embodiments that use screw propellers as the source of thrust, they may be arranged so that the blades rotate in a direction opposite to the adjacent propellers to ensure that the torque generated by each engine would be balanced by the other engines. This configuration allows for steady flight similar to that of “quadcopter” aircraft; lift is controlled by engine power-setting, pitch by increasing the power in the front or rear to engines, roll by increasing power in the right or left two engines, yaw by temporarily changing the balance in torque in the counter-rotating blades, and forward velocity is achieved by tilting the aircraft forward. 
         [0011]    For embodiments in a horizontal-thrust configuration above a sufficiently high airspeed, the aircraft behaves in flight as a typical fixed-wing airplane; pitch and yaw are controlled by the control surfaces on the v-tail, roll by control surfaces on the wing, lift is generated constantly by the stationary wing, and forward velocity is controlled by engine power setting. Additionally, for embodiments that use screw propellers, the counter-rotational formation implemented for vertical flight also ensures that the aircraft has none of the left-turn tendencies of traditional single-engine propeller airplanes. 
         [0012]    Other advantages and features of disclosed embodiments also exist. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is schematic representation of a disclosed embodiment of an aircraft in straight and level flight with the engines facing forward, the wing attached to the fuselage at the front of the fuselage, and the empennage arranged in a v-formation with the airfoils facing upwards. 
           [0014]      FIG. 2  is a schematic representation of a disclosed embodiment of an aircraft when hovering, taking-off, and landing vertically, with all engines facing forwards. 
           [0015]      FIG. 3  is a schematic representation of a disclosed embodiment of an aircraft in straight and level flight with the engines facing forward, the wing attached to the fuselage at the front of the fuselage, and the empennage arranged in a v-formation with the airfoils facing downwards. 
           [0016]      FIG. 4  is a schematic representation of a disclosed embodiment of an aircraft in straight and level flight with the engines facing forward, the wing attached to the fuselage at the rear of the fuselage, and the empennage arranged in a v-formation with the airfoils facing downwards. 
           [0017]      FIG. 5  is a schematic representation of a disclosed embodiment of an aircraft in straight and level flight with the engines facing forward, the wing attached to the fuselage at the rear of the fuselage, and the empennage arranged in a v-formation with the airfoils facing upwards. 
           [0018]      FIG. 6  is a schematic representation of a disclosed embodiment of a source of thrust mounted to the fixed wing as it appears with optional flaps within the airfoil extended to allow for greater thrust from the engine. 
       
    
    
       [0019]    While the disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0020]    The aircraft  2  in  FIGS. 1-6  is composed of a central fuselage  23 , to which a lift-generating airfoil, or wing  21 , and lift-counteracting airfoils, or tail surfaces  22  are attached in various configurations. Embodiments of aircraft  2  may be constructed so that the wing  21  is attached to the fuselage  23  at the front  23   a  of the fuselage  23  and the two tail surfaces  22  are attached to the rear  23   b  of the fuselage  23  as shown for the embodiments in  FIGS. 1-3 . The aircraft  2  can also be constructed so that the wing  21  is attached to the fuselage  23  at the rear  23   b  of the fuselage  23  and the two tail surfaces  22  are attached to the front  23   a  of the fuselage  23  as appears in the embodiments shown in  FIGS. 4-5 . 
         [0021]    Aircraft  2  may also have a variety of other features as is known in the art. For example, aircraft  2  may have control surfaces (e.g., flaps, ailerons, trim tabs, or the like) mounted on the wing  21  and the two tail surfaces  22  in order to allow the operator to control the roll, pitch, and yaw of the aircraft when in horizontal flight with the sources of thrust  10 ,  11  facing forward as shown in  FIGS. 1, and 3-5 . In addition, embodiments of aircraft  2  may also include other features such as, landing gear, a cockpit, a passenger compartment, storage or luggage compartments, windows, doors, and the like. In other embodiments, aircraft  2  may be an unmanned (i.e., drone) aircraft  2 . Other configurations are also possible. 
         [0022]    In some embodiments, aircraft  2  may have foldable wings  21  for the purposes of reducing the aircraft  2  footprint, or the like. For example, wing  21  may fold along the chord length at a point  25  (as indicated schematically on  FIG. 1 ) beyond both sources of thrust  10 . Other configurations are also possible. 
         [0023]    When the aircraft  2  is in a vertical-thrust configuration, as shown in  FIG. 2 , the aircraft  2  may be controlled by varying the application of power to each of the sources of thrust  10 ,  11 . Changing the application of power in each of the sources of thrust  10 ,  11  allows an operator to control, among other things, the roll, pitch, and yaw of the aircraft  2 . 
         [0024]    In some embodiments, the tail surfaces  22  rotate from being generally flat and parallel as shown in  FIG. 2 , to a position at an angle with respect to the wing  21 , either above the plane of the wing (as shown in  FIGS. 1 and 5 ), or below the plane of the wing (as shown in  FIGS. 3 and 4 ). Typically, the angle between both tail surfaces  22  and the wing  21  must be generally equivalent and constant to ensure steady flight. Either configuration (e.g., tail surfaces  22  above the wing  21 , or below the wing  21 ) will allow an operator to control the pitch and yaw of the aircraft  2  when in horizontal flight with the sources of thrust  10 ,  11  facing forward as in  FIGS. 1 and 3-5 . 
         [0025]    Rotation of the tail surfaces  22  may be accomplished in any suitable manner. For example, motors, gearing, pulleys, actuators, hinges, or the like, may enable tail surfaces  22  to rotate about the fuselage  23 . 
         [0026]    The sources of thrust  10  mounted to the wing  21 , illustrated schematically and exemplarily in  FIGS. 1-6  as screw propellers, may be mounted to wing  21  equidistantly from the center of the wing  21  as in  FIGS. 1-5 . While  FIGS. 1-6  exemplarily show sources of thrust  10 ,  11  as screw propellers, the disclosure is not so limited, and other sources of thrust  10 ,  11  may be used, such as jet engines, turbines, other types of propellers, and the like. Sources of thrust  10 ,  11  are able to rotate at least 90 degrees from facing forwards and parallel to the fuselage  23  (e.g., shown in  FIG. 1 ) to rotating upwards and perpendicular to the fuselage  23  (e.g., shown in  FIG. 2 ). When the sources of thrust  10  face forwards thrust is directed to the rear  23   b  of the aircraft  2  as in the configurations shown in  FIGS. 1 and 3-5 . When sources of thrust  10 ,  11  are facing upwards (e.g., shown in  FIG. 2 ), thrust is directed downwards to the ground as in  FIGS. 2 and 6 . 
         [0027]    Rotation of the sources of thrust  10 ,  11  may be accomplished in any suitable manner. For example, motors, gearing, pulleys, actuators, hinges, or the like, may enable sources of thrust  10 ,  11  to rotate about the wing  21  and tail surfaces  22 . 
         [0028]    The sources of thrust  11  mounted to the tail surfaces  22 , may be mounted on or near the end of each tail surface  22  as shown in  FIGS. 1-5 . Sources of thrust  11  are able to rotate at least 90 degrees from facing forwards and parallel to the fuselage  23  (e.g.,  FIG. 1 ) to rotating upwards and perpendicular to the fuselage  23  (e.g., when the tail surfaces are flat as in  FIG. 2 ). When the sources of thrust  11  face forwards thrust is directed to the rear  23 b of the aircraft  2  as in  FIGS. 1 and 3-5 , when facing upwards thrust is directed downwards to the ground as in  FIG. 2 . 
         [0029]    In addition, while  FIGS. 1-5  show two sources of thrust  10 ,  11  on the wing  21  and tail surfaces  22 , other configurations may also be used. For example, more, or less, than two sources of thrust  10 ,  11  may be used on the wing  21  and tail surfaces  22 . 
         [0030]    When the two tail surfaces  22  rotate into their bent or “V” position as illustrated in  FIGS. 1 and 3-5 , the rear sources of thrust  11  rotate forward relatively quickly in order to maximize forward speed, which is necessary to sustain lift in wing-sustained flight. Likewise, when the tail surfaces  22  rotate down into their flat position, the rear sources of thrust  11  must likewise rotate upwards relatively quickly in order to avoid a potential misbalance in lift between the front and rear of the craft. 
         [0031]    The appropriate speed of rotation for the sources of thrust  10 ,  11  and tail surfaces  22  may be accomplished in any suitable manner. For example, appropriate gearing, levers, or actuator speed may be used to rotate at a sufficient rate. Other configurations are also possible. 
         [0032]    Embodiments of aircraft  2  may transition from the vertical-thrust configuration depicted in  FIG. 2  to the horizontal thrust configuration shown in  FIGS. 1 and 3-5  after a sufficient forward airspeed has been reached. Sufficient forward airspeed may be reached in a variety of ways. For example, it may be achieved by pitching the aircraft  2  forward using the sources of thrust  10 ,  11 , or by entering a controlled forward dive to rapidly gain the initial speed required for transition, after which airspeed is maintained by the sources of thrust  10 ,  11  which are rotated into horizontal, forward-facing positions. Likewise, the aircraft  2  may transition from the horizontal thrust configuration to the vertical thrust configuration by rotating all sources of thrust  10 ,  11  upwards and waiting for the aircraft  2  to slow to an eventual hover while a neutral pitch is maintained. 
         [0033]    Embodiments of the aircraft  2  may also include retractable sections  32  of the airfoil directly under the sources of thrust  10  mounted to the wing  21  as shown in  FIG. 6 . This allows more air to flow through the opening  31  formed by the retraction of these sections  32 , and result in more efficient thrust from the sources of thrust  10 . Other configurations are also possible. 
         [0034]    Although various embodiments have been shown and described, the present disclosure is not so limited and will be understood to include all such modifications and variations are would be apparent to one skilled in the art.