Patent Publication Number: US-2022212775-A1

Title: Aircraft and related methods

Description:
RELATED APPLICATION 
     The present application is a non-provisional of and claims priority to U.S. Provisional Patent Application No. 63/133,651, filed on Jan. 4, 2021, entitled “AIRCRAFT AND RELATED METHODS,” the complete disclosure of which is incorporated by reference. 
    
    
     FIELD 
     The present disclosure relates to aircraft. 
     BACKGROUND 
     Rotorcraft (aircraft comprising rotors) utilize spinning rotors to produce thrust. Some rotorcraft tilt their rotors to change thrust direction. For example, vertical take-off and landing (VTOL) rotorcraft may tilt their rotors between horizontal and vertical positions to transition between vertical and horizontal flights, respectively. However, conventional rotors often extend beyond the footprint of the rotorcraft&#39;s airframe (e.g., in front of the wings). As a result, persons on the ground may be more likely to come into contact with these rotors, especially when the rotors are close to the ground (within a few meters off the ground), such as on a small rotorcraft. Thus, rotor configurations that are more contained within the airframe&#39;s footprint are desired. 
     Further, conventional push-pull rotorcraft (aircraft that utilize a forward-mounted puller rotor and a rearward-mounted pusher rotor) often position the rearward-mounted pusher rotor behind the forward-mounted puller rotor. Because of its alignment with the forward-mounted puller rotor, the rearward-mounted pusher rotor operates in the disturbed airflow of the forward-mounted puller rotor, which may reduce the efficiency and thrust output of the rearward-mounted pusher rotor. Thus, rotor configurations that boost the efficiency and thrust output of the rearward-mounted rotor(s) of push-pull aircraft are desired. 
     Further, some cargo aircraft may be difficult to load and/or unload at least because of their size and/or location of their doors. For example, small, unmanned delivery rotorcraft may be difficult to load and/or unload because they may include doors on the sides of the aircraft that are difficult to access when the aircraft is on the ground. Thus, aircraft that are easier and/or faster to load and/or unload are desired. Further, the location of the cargo on such delivery aircraft may vary depending on where the cargo was deposited initially and/or whether the cargo shifted during flight. Changes in cargo location may affect the aircraft&#39;s center of gravity, aerodynamic center, and/or flight characteristics, making it more difficult to maintain stable flight. Thus, aircraft and/or loading/unloading methods are desired that minimize cargo drift in the aircraft. Further, the power sources on some conventional unmanned rotorcraft may be difficult to access and/or replace. Thus, aircraft having more accessible, conveniently located power sources are desired. 
     SUMMARY 
     Aircraft and related methods are disclosed. In one example, an aircraft comprises an airframe comprising one or more wings, one or more pusher rotors supported by the airframe, and one or more puller rotors supported by the airframe, wherein the one or more puller rotors are positioned behind the one or more pusher rotors. In some such examples, one or more pusher rotors extend behind a forward set of wings, and one or more puller rotors extend in front of an aft set of wings. Aircraft optionally include a fuselage comprising a cargo hold configured to store cargo, a cargo door configured to selectively open to receive the cargo through an upper forward portion of the fuselage, and a ramp structure included within the fuselage. When included, the ramp structure is configured to provide a passageway for the cargo to advance between the cargo door and the cargo hold. In some examples, aircraft additionally include a cargo unloading door positioned below the cargo door that is configured to selectively open to unload cargo from a bottom of the fuselage. 
     In another example, a method for loading cargo on to an aircraft comprises loading cargo into a fuselage of the aircraft through an upper forward portion of the fuselage. The method optionally comprises advancing the cargo downwards and rearwards towards and/or into a cargo hold of the aircraft. Additionally or alternatively, the method optionally comprises unloading the cargo through a bottom of the fuselage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a rotorcraft, according to the present disclosure. 
         FIG. 2  is a schematic side view of the rotorcraft of  FIG. 1  illustrating different example positions of the rotors. 
         FIG. 3  is a schematic side view of the rotorcraft of  FIG. 1  illustrating example loading and unloading structures for cargo. 
         FIG. 4  is a perspective view of an example rotorcraft, according to the present disclosure. 
         FIG. 5  is a side view of an example rotorcraft illustrating internal components of the rotorcraft, according to the present disclosure. 
         FIG. 6  is a flowchart schematically representing methods for loading and/or unloading an aircraft. 
         FIG. 7  is a flowchart schematically representing methods for loading and/or unloading cargo. 
     
    
    
     DESCRIPTION 
     Aircraft and related methods are disclosed. Generally, in the figures, elements that are likely to be included in a given example are illustrated in solid lines, while elements that are optional to a given example are illustrated in broken lines. However, elements that are illustrated in solid lines are not essential to all examples of the present disclosure, and an element shown in solid lines may be omitted from a particular example without departing from the scope of the present disclosure. Further, select elements are shown in a different position and/or orientation using dash-dot lines. 
       FIGS. 1-7  illustrate aircraft (e.g., rotorcraft) and related structures and methods for loading and/or unloading the aircraft. In particular,  FIGS. 1-5  illustrate example rotorcraft that include one or more forward rotors and one or more rearward rotors arranged in a push-pull configuration. However, unlike conventional push-pull aircraft where the forward-mounted rotor is a puller rotor and the rearward-mounted rotor is a pusher rotor, the one or more forward-mounted rotors of the rotorcraft of the present disclosure are pusher rotors and the one or more rearward-mounted rotors are puller rotors. Thus, the orientation of the pusher and puller rotors of the present disclosure is reversed as compared to conventional push-pull rotorcraft. In this reversed orientation, the rotors may be set in farther from front and rear ends of the aircraft, closer to a middle of the aircraft. 
     As one example where the rotorcraft comprises forward and rearward sets of wings, the rotors are positioned between the sets of wings. In particular, in some such examples, the one or more pusher rotors are positioned off a trailing edge of a forward set of wings (i.e., behind the forward set of wings) and the one or more puller rotors are positioned off a leading edge of a rearward set of wings (i.e., in front of the rearward set of wings). In this way, the rotors may not stick out as far from the front and rear ends of the airframe and/or may be positioned closer to a middle of the aircraft (farther away from the front and rear ends of the airframe) than conventional rotorcraft. In this way, aircraft of the present disclosure may reduce the chance that the rotors come into contact with a person or object as compared to conventional push-pull rotorcraft. 
       FIG. 3  illustrates loading and/or unloading structures that are optionally included in aircraft (e.g., rotorcraft) of the present disclosure, and  FIGS. 6-7  illustrate methods for loading and/or unloading aircraft of the present disclosure. Unlike conventional aircraft that have front, side, and/or rear doors, in some examples, aircraft of the present disclosure comprise a top cargo door that is configured to selectively open to receive and/or unload cargo through an upper forward portion of the aircraft&#39;s fuselage. Including the cargo door on the top of the fuselage may facilitate and/or expedite the cargo loading and/or unloading process when the cargo is being loaded from, and/or unloaded to, a position above the aircraft. As an example, many smaller, unmanned delivery aircraft may be shorter than the persons, cargo docks, conveyer belts, etc. from which they may receive cargo and/or to which they may deliver cargo. 
     Aircraft of the present disclosure also optionally include a ramp structure that is configured to facilitate the movement of cargo to and/or from a cargo hold of the aircraft that is positioned behind (rearward of) the top cargo door. In some examples, the aircraft include a power source that is configured to occupy at least some of the space above the ramp structure after the cargo has been loaded into the cargo hold. The ramp structure and power source may serve as a physical barrier for the cargo, preventing the cargo from sliding forward during flight. Further, in its position above the above the ramp structure (and directly beneath the top cargo door), the power source may be more accessible to a user and easy to replace. In some examples, the aircraft also include a bottom cargo door positioned below the cargo hold that is configured to selectively open to load and/or unload cargo from a bottom portion of the fuselage. Loading and/or unloading the cargo through the bottom cargo door may automate and/or expedite the loading and/or unloading process. For example, for loading cargo, the aircraft may vertically land or hover over the cargo, with the bottom cargo door being configured to engage and lift, or scoop, the cargo into the cargo hold. For unloading cargo, the aircraft may vertically lift away from the cargo so that it falls out of the aircraft under its own weight due to gravity (without requiring user intervention) when the bottom cargo door is opened. 
       FIGS. 1-3  schematically illustrate an aircraft  10 , according the present disclosure.  FIG. 1  schematically illustrates aircraft  10  at a high-level, and  FIGS. 2-3  illustrate additional optional elements, features, and/or configurations of aircraft  10 . In particular,  FIG. 2  schematically illustrates different rotor positions of aircraft  10  in examples where aircraft  10  includes rotors that are configured to tilt, and  FIG. 3  schematically illustrates various loading and/or unloading structures that are optionally included in aircraft  10 , such as when it is configured as a cargo aircraft. Because  FIGS. 1-3  all illustrate various features, elements, and/or configurations of aircraft  10 , they will be described collectively herein. For convenience, specific reference may be made to particular figure(s), where appropriate. 
     In the figures, a forward (“FWD”) direction of aircraft  10  is schematically represented and corresponds to the forward direction of flight of aircraft  10  when configured for horizontal flight (e.g., in a cruise mode, as discussed herein). Herein, such positional terms as “forward,” “front,” “rearward,” “rear,” “in front of,” “behind,” etc. are with respect to the designated forward direction of flight of aircraft  10 . For example, a first structure that is described as being behind a second structure is positioned rearward of the second structure relative to the forward direction of flight of the aircraft. Similarly, a first structure that is described as being in front of a second structure is positioned forward of the second structure relative to the forward direction of flight of the aircraft. 
     As schematically illustrated in  FIGS. 1-3 , aircraft  10  includes an airframe  20 , one or more pusher rotors  100  supported by airframe  20 , and one or more puller rotors  120  supported by airframe  20 . Because aircraft  10  includes rotors, aircraft  10  also may be referred to as a rotorcraft. In some examples, aircraft  10  is configured to take off and land vertically, and, in some such examples, aircraft  10  may be referred to as vertical take-off and landing (VTOL) aircraft. In some examples, aircraft  10  is configured to be an autonomous delivery vehicle, and, in some such examples, aircraft  10  may be referred to as unmanned aircraft. In some examples, aircraft  10  is an electric aircraft. 
     Airframe  20  includes one or more wings  70  and, in some examples, a fuselage  22 . In some examples, one or more wings  70  include a forward set of wings  76  and/or an aft set of wings  78  (also referred to herein as “rearward set of wings  78 ”). When included, aft set of wings  78  is positioned behind forward set of wings  76 , more proximate a rear end of aircraft  10 . 
     One or more wings  70  comprise aerodynamic surfaces that are configured to generate lift. In some examples, and as described in greater detail below, one or more wings  70  also are configured to support one or more pusher rotors  100  and/or one or more puller rotors  120 . As one such example, forward set of wings  76  is configured to support (e.g., structurally support, retain, and/or otherwise hold in place) one or more pusher rotors  100  at a trailing edge thereof, and/or rearward set of wings  78  is configured to support one or more puller rotors  120  at a leading edge thereof. As examples, the one or more pusher rotors and/or the one or more puller rotors are connected to, coupled to, mounted to, attached to, and/or otherwise supported by the wings via a mechanical linkage  160  (e.g., mounting structures, fasteners, etc.), illustrated in  FIG. 2 . 
     In some examples, one or more wings  70  include tips  71  (optionally including winglets), a leading edge  72 , and a trailing edge  73 . One or more wings  70  are configured to generate lift when air flows around (i.e., over and under) one or more wings  70 . In flight, leading edge  72  is configured to face forward (i.e., face the direction of motion of aircraft  10  and/or face oncoming airflow), and trailing edge  73  is configured to face rearward (i.e., face away from the direction of motion of aircraft  10  and/or face away from oncoming airflow). 
     When fuselage  22  is included in airframe  20 , one or more wings  70  are coupled to, connected to, and/or otherwise supported by fuselage  22 . In such examples, one or more wings  70  extend outward from fuselage  22  and terminate at tips  71  (which also may be referred to as wing tips). Further, one or more wings  70  include one or more right-side wings  74  that extend to the right of fuselage  22  and one or more left-side wings  75  that extend to the left of fuselage (i.e., from an opposite side of fuselage  22 ). Thus, in examples where one or more wings  70  include forward set of wings  76  and rearward set of wings  78 , one or more wings  70  include four wings. In particular, forward set of wings  76  and rearward set of wings  78  each include one of the one or more right-side wings and one of the one or more left-side wings. 
     Unlike conventional push-pull aircraft, one or more puller rotors  120  of aircraft  10  are positioned behind (rearward of) one or more pusher rotors  100 . One or more pusher rotors  100  and one or more puller rotors  120  comprise rotor blades that are configured to spin and/or rotate to generate thrust. One or more pusher rotors  100  and/or one or more puller rotors  120  include at least two, at least three, at least four, at least five, and/or at least six or more rotor blades. In the example of  FIG. 4 , each of the rotors include two rotor blades. In some examples, one or more pusher rotors  100  are mirror images of one or more puller rotors  120  and are configured to generate thrust in an opposite direction to one or more puller rotors  120  when rotated in the same direction. 
     By including one or more puller rotors  120  behind one or more pusher rotors  100 , the one or more puller rotors and the one or more pusher rotors may be positioned farther from the front and rear ends of airframe  20  than conventional push-pull aircraft, closer to a middle of aircraft  10 . In some examples, one or more pusher rotors  100  are positioned at least partially behind forward set of wings  76  (i.e., such that the one or more pusher rotors extend behind trailing edge  73  of the forward set of wings), and one or more puller rotors  120  are positioned at least partially in front of rearward set of wings  78  (i.e., such that the one or more puller rotors extend in front of leading edge  72  of the rearward set of wings). In this way, the wings may provide a physical and visual barrier to the rotors, thereby restricting inadvertent contact with the rotors by persons. 
     In some examples, one or more pusher rotors  100  are positioned behind leading edge  72  of forward set of wings  76  such that one or more pusher rotors  100  do not extend forward of leading edge  72  of forward set of wings  76 . In some further such examples, one or more pusher rotors  100  are fully positioned behind forward set of wings  76 , such that one or more pusher rotors  100  do not overlap with forward set of wings  76  and are positioned behind trailing edge  73  of forward set of wings  76  (i.e., the one or more pusher rotors do not extend forward of the trailing edge of the forward set of wings). 
     In some examples, one or more puller rotors  120  are positioned forward of trailing edge  73  of rearward set of wings  78  such that one or more puller rotors  120  do not extend rearward of trailing edge  73  of rearward set of wings  78 . In some further such examples, one or more puller rotors  120  are fully positioned in front of rearward set of wings  78 , such that one or more puller rotors  120  do not overlap with rearward set of wings  78  and are positioned forward of leading edge  72  of rearward set of wings  78  (i.e., the one or more puller rotors do not extend rearward of the leading edge of the rearward set of wings). 
     In the above examples, the one or more pusher rotors and/or the one or more puller rotors are fully included and/or contained within a footprint (i.e., perimeter) of airframe  20 . That is, the one or more pusher rotors and/or the one or more puller rotors do not extend past the footprint of airframe  20 . In some such examples, the one or more pusher rotors and/or the one or more puller rotors are set in from (spaced away from) the perimeter of a rectangular prismatic volume that encloses the airframe  20 . For example, the one or more pusher rotors and the one or more puller rotors are included and/or positioned in-between the forward set of wings and the rearward set of wings, as illustrated in the example of  FIG. 1 . In the above examples therefore, the wings may shield and/or protect a user from the rotors, thereby further reducing the chances that a user may come into contact with one or more of the rotors. 
     In some examples, aircraft  10  includes one, two, three, four, five, and/or six or more pusher rotors  100  and/or puller rotors  120 . In  FIG. 1 , aircraft  10  is schematically represented as including at least one pusher rotor  100  and at least one puller rotor  120 ; however, six additional optional rotors are illustrated in dashed lines to schematically illustrate that, in some examples, more than one pusher rotor  100  and/or more than puller rotor  120  may be included. In some examples where multiple pusher rotors  100  and/or multiple puller rotors  120  are included, the rotors are positioned on opposite sides of fuselage  22 . For example, when aircraft  10  includes two pusher rotors and two puller rotors, one of the pusher rotors and one of the puller rotors are positioned on the right-hand side of the aircraft (to the right of the fuselage) and the other rotors are positioned on the left-hand side of the aircraft (to the left of the fuselage). As another example, when aircraft  10  includes four pusher rotors and four puller rotors, two of the pusher rotors and two of the puller rotors are positioned on the right-hand side of the aircraft and the other rotors are positioned on the left-hand side of the aircraft. 
     In some examples where multiple pusher rotors  100  and/or multiple puller rotors  120  are included, the rotors are evenly spaced from one another and/or evenly spaced from fuselage  22 . Additionally or alternatively, two or more (and in some such examples, all) of pusher rotors  100  are aligned with one another at the same point on longitudinal axis  16  (forward of one or more puller rotors  120 ) such that the two or more pusher rotors are neither forward nor rearward of one another. Additionally or alternatively, two or more (and in some such examples, all) puller rotors  120  are aligned with one another at a point on longitudinal axis  16  rearward of one or more pusher rotors  100  such that the two or more pusher rotors are neither forward nor rearward of one another. 
     In some examples, one or more pusher rotors  100  and/or one or more puller rotors  120  are coupled and/or otherwise connected to one or more wings  70  by mechanical linkage  160 . Thus, as illustrated in  FIG. 2 , aircraft  10  optionally includes mechanical linkages  160 . When included, mechanical linkages  160  are configured to mechanically couple and/or otherwise connect one or more pusher rotors  100  and/or one or more puller rotors  120  to one or more wings  70 . In particular, mechanical linkages  160  are configured to mechanically couple and/or otherwise connect one or more pusher rotors  100  to forward set of wings  76  and/or one or more puller rotors  120  to rearward set of wings  78 . As examples, mechanical linkages comprise one or more of mounting structures, fasteners, rods, gears, pulleys, chains, etc. 
     In some examples (as illustrated in  FIG. 2 ), one or more pusher rotors  100  and/or one or more puller rotors  120  are configured to tilt. That is, a rotational axis  110  of one or more pusher rotors  100  and/or a rotational axis  130  of one or more puller rotors  120  is/are configured to tilt, rotate, and/or pivot relative to airframe  20 , and more specifically, relative to a longitudinal axis  16  of aircraft  10 . Tilting one or more pusher rotors  100  and/or one or more puller rotors  120  changes a direction of the thrust generated by the one or more pusher rotors and/or the one or more puller rotors when the one or more pusher rotors and/or the one or more puller rotors are powered on. 
     In particular, at constant power, tilting rotational axis  110  of one or more pusher rotors  100  toward parallel with longitudinal axis  16 , increases an amount of horizontal thrust and decreases an amount of vertical thrust generated by one or more pusher rotors  100 . Conversely, at constant power, tilting rotational axis  110  of one or more pusher rotors  100  away from parallel toward longitudinal axis  16 , reduces the amount of horizontal thrust and increases the amount of vertical thrust generated by one or more pusher rotors  100 . Similarly, at constant power, tilting rotational axis  130  of one or more puller rotors  120  toward parallel with longitudinal axis  16 , increases the amount of horizontal thrust and decreases the amount of vertical thrust generated by the one or more puller rotors  120 . Conversely, at constant power, tilting rotational axis  130  of one or more puller rotors  120  away from parallel to longitudinal axis  16 , reduces the amount of horizontal thrust and increases the amount of vertical thrust generated by the one or more puller rotors  120 . 
     In some examples, one or more pusher rotors  100  are configured to tilt between a vertical thrusting push position  102  (illustrated with solid lines in  FIG. 2 ) and a horizontal thrusting push position  104  (illustrated with dash-dot lines in  FIG. 2 ) and/or one or more puller rotors  120  are configured to tilt between a vertical thrusting pull position  122  (illustrated with solid lines in  FIG. 2 ) and a horizontal thrusting pull position  124  (illustrated with dash-dot lines in  FIG. 2 ). When powered on, one or more pusher rotors  100  are configured to generate at least some thrust in a positive vertical direction (opposite gravity) in vertical thrusting push position  102 . In some such examples, one or more pusher rotors  100  are configured to generate thrust in a direction orthogonal to longitudinal axis  16 . In such examples, rotor blades of one or more pusher rotors  100  are oriented in a horizontal position, parallel to longitudinal axis  16 , in vertical thrusting push position  102 . Similarly, when powered on, one or more puller rotors  120  are configured to generate at least some thrust in the positive vertical direction (opposite gravity) in the vertical thrusting pull position  122 . In some such examples, one or more puller rotors  120  are configured to generate thrust in a direction orthogonal to longitudinal axis  16 . In such examples, rotor blades of one or more puller rotors  120  are oriented in a horizontal position, parallel to longitudinal axis  16 , in vertical thrusting pull position  122 . 
     When powered on, one or more pusher rotors  100  are configured to generate at least some thrust in a forward horizontal direction (orthogonal to gravity) in horizontal thrusting push position  104 . In some such examples, one or more pusher rotors  100  are configured to generate thrust in a direction parallel to longitudinal axis  16 . In such examples, rotor blades of one or more pusher rotors  100  are oriented in a vertical position, orthogonal to longitudinal axis  16 , in horizontal thrusting push position  104 . Similarly, when powered on, one or more puller rotors  120  are configured to generate at least some thrust in the forward horizontal direction (orthogonal to gravity) in the horizontal thrusting pull position  124 . In some such examples, one or more puller rotors  120  are configured to generate thrust in a direction parallel to longitudinal axis  16 . In such examples, rotor blades of one or more puller rotors  120  are oriented in a vertical position, parallel to longitudinal axis  16 , in horizontal thrusting pull position  124 . 
     In some such examples, one or more pusher rotors  100  and/or one or more puller rotors are configured to tilt when transitioning between a hover mode and a cruise mode since the thrust direction changes when transitioning between these two modes. In particular, in the hover mode, aircraft  10  is configured to only generate thrust in a direction orthogonal to longitudinal axis  16  (e.g., the rotational axes are oriented orthogonal to longitudinal axis  16  and/or the rotor blades are oriented parallel to longitudinal axis  16 ), and in the cruise mode, aircraft  10  is configured to only generate thrust in a direction parallel to longitudinal axis  16  (e.g., the rotational axes are oriented parallel to longitudinal axis  16  and/or the rotor blades are oriented orthogonal to longitudinal axis  16 ). Thus, aircraft  10  is configured to tilt at least one of the pusher rotors and/or at least one of the puller rotors when transitioning between the hover mode and the cruise mode. In some examples, aircraft  10  also is configured to generate thrust in both the horizontal and vertical positions when transitioning between the hover mode and the cruise mode. For example, after gaining altitude in the hover mode, aircraft  10  enters a transition mode in which aircraft  10  continues to gain altitude (i.e. climb) while also beginning to move horizontally towards the cruise mode. Additionally or alternatively, aircraft  10  enters a transition mode while descending when exiting the cruise mode in which aircraft  10  continues to move horizontally but also begins to lose altitude. 
     In some examples, one or more pusher rotors  100  and one or more puller rotors  120  face opposite directions and/or are oriented in opposite directions. This orientation of the rotors is at least partially the result of positioning the one or more pusher rotors forward of the one or more puller rotors. For example, to generate forward thrust, one or more pusher rotors  100  face rearwards in horizontal thrusting push position  104  and/or one or more puller rotors  120  face forwards in horizontal thrusting pull position  124 . Thus, in such examples, the one or more pusher rotors and the one or more puller rotors are oriented in opposite directions, facing one another. In some examples, the rotational axes of both one or more pusher rotors  100  and one or more puller rotors  120  (rotational axis  110  and rotational axis  130 , respectively) are configured to rotate in the same direction to perform the same type of thrust adjustment. For example, rotational axis  110  of one or more pusher rotors  100  and rotational axis  130  of one or more puller rotors  120  are configured to rotate in the same direction (a first rotational direction) when both one or more pusher rotors  100  and one or more puller rotors  120  are tilted to increase vertical thrust and decrease horizontal thrust. Correspondingly, rotational axis  110  and rotational axis  130  are both configured to rotate in a second rotational direction that is opposite to the first rotational direction, when both of one or more pusher rotors  100  and one or more puller rotors  120  are tilted to decrease vertical thrust and increase horizontal thrust. 
     However, in some examples, one or more pusher rotors  100  and one or more puller rotors  120  are configured to tilt in opposite directions. In particular, one or more pusher rotors  100  are configured to tilt in an opposite direction to one or more puller rotors  120  to perform the same type of change in thrust direction (e.g., to increase horizontal thrust and decrease vertical thrust or decrease horizontal thrust and increase vertical thrust). Again, this opposite tilt configuration may be at least partially the result of the opposite orientations of the pusher and puller rotors and/or the positioning of the one or more pusher rotors forward of the one or more puller rotors. For example (as illustrated in  FIG. 2 ), because one or more pusher rotors  100  are oriented downwards relative to their associated mechanical linkage  160  to generate positive vertical lift, the one or more pusher rotors are configured to tilt upward to increase horizontal thrust and decrease vertical thrust. Conversely, because one or more puller rotors  120  are oriented upwards relative to their associated mechanical linkage  160  to generate positive vertical lift, the one or more puller rotors are configured to tilt downward to increase horizontal thrust and decrease vertical thrust. Correspondingly, one or more pusher rotors  100  are configured to tilt downward to decrease horizontal thrust and increase vertical thrust, and one or more puller rotors  120  are configured to tilt upward to increase horizontal thrust and decrease vertical thrust. 
     In some examples, one or more pusher rotors  100  and one or more puller rotors  120  are vertically offset from one another. As one such example (as illustrated in  FIG. 2 ), when one or more pusher rotors  100  are in vertical thrusting push position  102  and one or more puller rotors  120  are in vertical thrusting pull position  122 , one or more pusher rotors  100  are positioned vertically below one or more puller rotors  120 . However, in another example, when one or more pusher rotors  100  are in vertical thrusting push position  102  and one or more puller rotors  120  are in vertical thrusting pull position  122 , one or more pusher rotors  100  are positioned vertically above one or more puller rotors  120 . As another such example, when one or more pusher rotors  100  are in horizontal thrusting push position  104  and one or more puller rotors  120  are in horizontal thrusting pull position  124 , rotational axis  110  of one or more pusher rotors  100  are positioned vertically below rotational axis  130  of one or more puller rotors  120 . However, in another example (as illustrated in  FIG. 2 ), when one or more pusher rotors  100  are in horizontal thrusting push position  104  and one or more puller rotors  120  are in horizontal thrusting pull position  124 , rotational axis  110  of one or more pusher rotors  100  are positioned vertically above rotational axis  130  of one or more puller rotors  120 . 
     By vertically offsetting the one or more pusher rotors and the one or more puller rotors in the horizontal thrusting positions (where the rotor blades of the one or more pusher rotors and the one or more puller rotors are vertically oriented), such as during the cruise mode, the rearward rotors (the one or more puller rotors  120 ) may operate less in the disturbed air of the forward rotors (the one or more pusher rotors  100 ), thereby increasing the efficiency and thrust output of the one or more puller rotors. 
     In some examples, one or more pusher rotors  100  and/or one or more puller rotors  120  are configured to tilt independently of one another. Additionally or alternatively, one or more of the one or more pusher rotors are configured to tilt independently of one another. In some such examples, each of the one or more pusher rotors is configured to be individually tilted, such that all of the one or more pusher rotors are configured to tilt independently of one another. Additionally or alternatively, one or more of the one or more puller rotors are configured to tilt independently of one another. In some such examples, each of the one or more puller rotors is configured to be individually tilted, such that all of the one or more puller rotors are configured to tilt independently of one another. 
     Because at least one of one or more pusher rotors  100  and/or at least one of one or more puller rotors  120  are configured to tilt, aircraft  10  may take off and land vertically and transition between horizontal and vertical flying. 
     In some examples, one or more pusher rotors  100  and/or one or more puller rotors  120  are configured to be selectively adjusted (e.g., tilted, powered, and/or otherwise operated). For example, one or more pusher rotors  100  and/or one or more puller rotors  120  are configured to be adjusted (e.g., tilted, powered on, powered off, etc.) by a control system. In some such examples, aircraft  10  optionally includes a control system  190  that is configured to selectively adjust various electrically powered components of aircraft  10 , including the one or more pusher rotors and/or the one or more puller rotors. 
     When included, control system  190  includes a controller  191  including a processing unit  192  and a memory unit  194 . Memory unit  194  is configured to store computer-readable instructions and processing unit  192  is configured to execute the stored computer-readable instructions to perform various computing functions. For example, processing unit  192  is configured to execute the computer-readable instructions stored in memory unit  194  to tilt the one or more pusher rotors and/or the one or more puller rotors. 
     Memory unit  194  comprises non-volatile (also referred to herein as “non-transitory”) memory  196  (e.g., ROM, PROM, and EPROM) and optionally includes volatile (also referred to herein as “transitory”) memory  198  (e.g., RAM, SRAM, and DRAM). Processing unit  192  comprises integrated circuits including one or more of field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), digital signal processors (DSPs), microprocessors, microcontrollers, programmable array logic (PALs), and complex programmable logic devices (CPLDs). 
     As will be described in greater detail below, controller  191  is programmed to execute various methods, such as the methods schematically represented in  FIGS. 6 and 7 . In some examples, memory unit  194  is configured to store computer-readable instructions for performing the methods, and processing unit  192  is configured to execute the methods responsive to various inputs. As just one example, processing unit  192  is configured to tilt at least one of the one or more pusher rotors and/or at least one of the one or more puller rotors to adjust the thrust direction (i.e., selectively adjust the relative amount of vertical and horizontal thrust) of aircraft  10 . As another example, processing unit  192  is configured to vary the thrust output of the one or more pusher rotors and/or the one or more puller rotors by varying an amount of power (e.g., electrical power) supplied to the one or more pusher rotors and/or the one or more puller rotors. 
     Aircraft  10  optionally includes one or more motors  164  and/or one or more tilt mechanisms  162  that, in some examples, are configured to be selectively adjusted and/or otherwise controlled by control system  190 . When included, one or more motors  164  are configured to rotate one or more pusher rotors  100  and/or one or more puller rotors  120  about rotational axis  110  and rotational axis  130 , respectively. In some examples, controller  191  is programmed to selectively adjust an amount of thrust generated by one or more pusher rotors  100  and/or one or more puller rotors  120  by adjusting operation of one or more motors  164 . As an example, controller  191  is programmed to adjust a torque output of one or more motors  164  (to selectively adjust the thrust output of the one or more pusher rotors and/or the one or more puller rotors) by adjusting an amount of electrical power supplied to one or more motors  164  (e.g., via pulse width modulation) by a power source  146 . 
     When included, one or more tilt mechanisms  162  are configured to tilt one or more pusher rotors  100  and/or one or more puller rotors  120 . In some examples, controller  191  is programmed to selectively tilt one or more pusher rotors  100  and/or one or more puller rotors  120  by adjusting operation of one or more tilt mechanisms  162 . As an example, controller  191  is programmed to send electrical command signals (via a wired and/or wireless connection with the one or more tilt mechanisms) that encode for a desired pivot angle of rotational axis  110  and/or rotational axis  130 . 
     The one or more tilt mechanisms comprise one or more of an electromechanical, pneumatic, and hydraulic tilt actuator that is configured to be electronically controlled by controller  191 . As examples, one or more tilt mechanisms  162  comprise one or more of a ring-and-pinion, piston-and-bell crank, ball-screw, harmonic drive, multi-link geometry, and/or harmonic drive gearbox. 
     In some examples, one of the one or more motors and/or one of the one or more tilt mechanisms is/are included for each of the one or more pusher rotors and/or each of the one or more puller rotors. Thus, in some such examples, aircraft  10  includes the same number of tilt mechanisms and/or motors as rotors (e.g., both pusher and puller rotors). 
     In some examples, one or more motors  164  and/or one or more tilt mechanisms  162  are included and/or otherwise positioned between one or more wings  70  and one or more pusher rotors  100  and/or one or more puller rotors  120 . In some such examples, one or more motors  164  and/or one or more tilt mechanisms  162  are included as part of mechanical linkage  160 . In particular, one or more motors  164  and/or one or more tilt mechanisms  162  may form a portion of the mechanical linkage that couples and/or otherwise connects one or more pusher rotors  100  and/or one or more puller rotors  120  to one or more wings  70 . 
     Aircraft  10  optionally includes longitudinal crossbars  90 . When included, longitudinal crossbars  90  are configured to extend lengthwise between forward set of wings  76  and rearward set of wings  78 . In some examples, longitudinal crossbars  90  extend between tips  71  of forward set of wings  76  and rearward set of wings  78 . 
     In some examples, longitudinal crossbars  90  are positioned outboard of one or more pusher rotors  100  and/or one or more puller rotors  120  (i.e., farther from fuselage  22  than one or more pusher rotors  100  and/or one or more puller rotors  120 ). In some such examples, one or more pusher rotors  100  and/or one or more puller rotors  120  do not extend past longitudinal crossbars  90 . In some further such examples, one or more pusher rotors  100  and/or one or more puller rotors  120  are spaced away from longitudinal crossbars  90 , more proximate to fuselage  22 . 
     In some examples, longitudinal crossbars  90  include a right-side longitudinal crossbar  92  that extends between one or more right-side wings  74  and a left-side longitudinal crossbar  94  that extends between one or more left-side wings  75 . In such examples, one or more pusher rotors  100  and/or one or more puller rotors  120  are included in-between the longitudinal crossbars. Including longitudinal crossbars  90  outboard of one or more pusher rotors  100  and/or one or more puller rotors  120  may reduce the chance that the rotors come into contact with persons and/or foreign objects. That is, longitudinal crossbars  90  may shield persons and/or foreign objects from the one or more pusher rotors and/or the one or more puller rotors. Additionally or alternatively, longitudinal crossbars  90  may form at least a portion of the perimeter of the aircraft (with one or more wings  70  and/or fuselage  22  forming the other portions of the perimeter of the aircraft). As discussed above, positioning one or more pusher rotors  100  and/or one or more puller rotors  120  within, inwardly spaced away from, and/or inwardly spaced farther away from the perimeter of the aircraft, reduces the likelihood that the rotors may come into contact with persons and/or foreign objects. Additionally, longitudinal crossbars  90 , when present, increase the stiffness of airframe  20  and eliminates the need for cantilevers, often present in prior art designs and which are prone to vibration issues. 
     Aircraft  10  optionally includes landing gear  140 . When included, landing gear  140  is configured support airframe  20  above ground  210  (also referred to herein as landing surface  210 ) during and/or after landing. In some examples, landing gear  140  extends from underneath one or more wings  70 . Additionally or alternatively, landing gear  140  extends from underneath fuselage  22 . In some examples, landing gear  140  includes two landing gears, three landing gears, four landing gears, five landing gear, and/or six or more landing gears. In some such examples, landing gear  140  includes four landing gears, two on forward set of wings  76  and two on rearward set of wings  78  that are positioned on opposite sides of fuselage  22 . Positioning landing gear  140  farther from fuselage  22  creates a wider base for which to support airframe  20 . In this way, landing gear  140  may provide more stability when on ground  210 , and/or may support heavier airframes than landing gear of conventional aircraft. 
     In some examples, landing gear  140  is configured to orient airframe  20  at a pitch angle relative to ground  210 . That is, when on ground  210 , the longitudinal axis of airframe  20  is configured to be at an angle with respect to ground. As an example, airframe  20  may be configured to be in a nose-down attitude with respect to ground  210  or may be configured to be a nose-up attitude with respect to ground  210 . In one such example (an example of which is illustrated in  FIG. 5 ), front landing gear  142  is configured to be shorter than rear landing gear  144 , such that front end  23  of fuselage  22  is closer to ground  210  than rear end  24  of fuselage  22 . Such a nose-down stance, in combination with the center of gravity of aircraft  10 , for example, may improve liftoff characteristics, stability during liftoff, etc. 
     In some examples, landing gear  140  is configured to be retracted and/or extended. In some such examples, a length of landing gear  140  is configured to be adjusted. For example, a length of front landing gear  142  is configured to be adjusted relative to a length of rear landing gear  144  depending on a center of gravity of aircraft  10  and/or other flight parameters. Adjusting the relative lengths of the front and rear landing gear may change the attitude of aircraft  10  with respect to ground  210  and may improve liftoff characteristics, stability during liftoff, etc. by compensating for the effects of changes in the center of gravity (such as changes in cargo weight, cargo positioning within fuselage  22 , etc.) and/or other flight parameters (e.g., wind speed, wind direction, etc.). In some examples of aircraft  10 , landing gear  140  includes wheels or other mechanisms that facilitate maneuvering of aircraft  10  on the ground, including taxiing, for example. In some such examples, the wheels are passive permitting personnel to manually translate the aircraft along the ground, while in other examples, the wheels are powered and may be controlled to translate the aircraft along the ground. 
     In some examples, aircraft  10  includes one or more loading and/or unloading structures that are configured to facilitate loading and/or unloading of cargo  200  into and/or from aircraft  10 . When included, loading and/or unloading structures include one or more of a cargo door  30 , a ramp structure  40 , a cargo unloading door  50  and/or associated motorized door opening mechanism  58 , and a conveyor system  170 . Although aircraft  10  is described as including one or more pusher rotors  100  and one or more puller rotors  120 , it should be appreciated that in some examples, aircraft  10  includes one or more of the loading and/or unloading structures without including both one or more pusher rotors  100  and one or more puller rotors  120 . That is, in some examples, aircraft  10  includes one or more of the loading and/or unloading structures and either one or more pusher rotors  100  or one or more puller rotors  120 . In sum, the loading and/or unloading structures may be included in rotorcraft generally, not just push-pull rotorcraft. 
     In some examples, fuselage  22  comprises a cargo hold  28  that is configured to store cargo  200 . Cargo  200  includes one or more of packages, products, goods, and raw materials. In some such examples, cargo hold  28  comprises at least a portion of the hollow interior of fuselage  22  defined by a skin of fuselage  22 . In some examples, cargo hold  28  is positioned behind ramp structure  40  and/or cargo door  30 . Additionally or alternatively, cargo hold  28  is positioned above (at a vertically higher position than) cargo unloading door  50 . 
     When included, ramp structure  40  is configured to provide a passageway for cargo  200  to advance between cargo door  30  and cargo hold  28 . As examples, ramp structure  40  is configured to permit cargo  200  to slide, roll, and/or otherwise advance between cargo door  30  and cargo hold  28 . Ramp structure  40  comprises an angled surface  42 , also referred to herein as inclined surface  42 . Angled surface  42  is at an incline relative to a floor of cargo hold  28  and is at a decline relative to cargo door  30 . That is, angled surface  42  extends vertically upward when progressing forward along fuselage  22  (toward front end  23 ) and extends vertically downward when progressing rearward along fuselage  22  (towards rear end  24 ). In some examples, cargo door  30  is positioned forward of cargo hold  28 , and thus, in such examples, cargo  200  is configured to advance rearwards and downwards on ramp structure  40  when being loaded into cargo hold  28  from cargo door  30 , and/or is configured to advance forwards and upwards on ramp structure  40  when being unloaded from cargo hold  28  through cargo door  30 . 
     In some examples, ramp structure  40  is positioned between cargo door  30  and cargo hold  28 . In some such examples, ramp structure  40  is positioned forward of cargo hold  28 . Additionally or alternatively, ramp structure  40  is positioned below and/or behind cargo door  30 . 
     In some examples, ramp structure  40  extends from cargo hold  28  to cargo door  30  and/or a top  25  of fuselage  22 . In some further such examples, ramp structure  40  extends from the front and bottom of cargo hold  28  up to the front of cargo door  30 . However, in other such examples, ramp structure  40  stops short of one or more of cargo door  30 , top  25  of fuselage  22 , and/or cargo hold  28 . Stated slightly differently, in such examples, ramp structure  40  extends partially between cargo hold  28  and cargo door  30 . 
     When included, conveyor system  170  is configured to advance cargo  200  into, out of, and/or within fuselage  22 . As one example, conveyor system  170  is configured to advance cargo  200  into fuselage  22  via cargo door  30 . In another example, conveyor system  170  is configured to advance cargo  200  out of fuselage  22  via cargo door  30 . As yet another example, conveyor system  170  is configured to advance cargo  200  along ramp structure  40 . In one such example, conveyor system  170  is configured to advance cargo rearwards and downwards along ramp structure  40  towards cargo hold  28  (e.g., when loading cargo  200  onto aircraft  10 ). Additionally or alternatively, conveyor system  170  is configured to advance cargo upwards and forwards along ramp structure  40  towards cargo door  30  (e.g., when unloading cargo  200  from aircraft  10 ). 
     Conveyor system  170  includes one or more of a roller conveyor, belt conveyor, chain conveyor, and/or other suitable conveyor. In particular, conveyor system  170  includes a conveyance medium  172  that is configured to hold and/or carry cargo  200  (e.g., via frictional forces between conveyance medium  172  and cargo  200 ) and an actuator  174  that is configured to advance, rotate, and/or otherwise move conveyance medium  172 . In some examples, actuator  174  comprises an electric motor. In some examples, conveyance medium  172  comprises one or more of rollers, chains, and belts. Thus, when conveyance medium  172  comprises a belt, conveyor system  170  may be referred to as a conveyor belt. 
     In some examples, conveyor system  170  is included in and/or coupled to ramp structure  40 . As an example, ramp structure  40  includes conveyor system  170  and conveyor system  170  forms angled surface  42 . In another example conveyor system  170  is positioned above and/or on top of angled surface  42  and/or is coupled to angled surface  42 . In some examples, conveyor system  170  extends between cargo hold  28  and cargo door  30 . In other examples, conveyor system  170  extends partially between cargo hold  28  and cargo door  30 . In yet further examples, conveyor system  170  extends past cargo door  30 , out of fuselage  22  and/or into cargo hold  28 . 
     In some examples, conveyor system  170  is configured to be one or more of retracted, extended, and/or repositioned. As examples, conveyor system  170  is configured to retract and/or advance towards cargo hold  28  during flight such that conveyor system  170  is fully included within fuselage  22  during flight and is configured to extend and/or advance forwards, out of fuselage  22  through cargo door  30  after landing to receive and/or deliver cargo  200  from and/or to the outside of aircraft  10 . 
     In yet further examples, conveyor system  170  is an external structure not included in aircraft  10  that is temporarily inserted into fuselage  22  during loading and/or unloading of cargo  200  to facilitate the loading and/or unloading process. 
     When included, cargo door  30  is configured to selectively open to receive and/or unload cargo  200  through an upper forward portion of fuselage  22 . In some examples, cargo door  30  is configured to be adjusted (e.g., pivoted) between a cargo-door closed position  31  and a cargo-door open position  32 . As illustrated in  FIG. 3 , in the cargo-door open position, an opening is formed in fuselage  22  at the upper forward portion of fuselage  22  that permits cargo  200  to pass into and/or out of fuselage  22 . In some examples, in cargo-door closed position  31 , cargo door  30  is configured to be flush with fuselage  22  and close, seal, and/or otherwise enclose the interior of fuselage  22 . In some such examples, when cargo door  30  is in cargo-door closed position  31 , cargo  200  cannot exit fuselage  22  via cargo door  30  because cargo door  30  is closed. 
     In some examples, cargo door  30  is configured to pivot upward when adjusted towards the cargo-door open position  32 . In some such examples, a front end of cargo door  30  is configured to pivot upwards and rearwards when the cargo door is adjusted towards the cargo-door open position  32 . In some examples, cargo door  30  is configured to pivot at least  80  degrees, such as when adjusting between cargo-door open position  32  and cargo-door closed position  31 . In some such examples, cargo door  30  is configured to pivot at least  90  degrees. 
     In some examples, cargo door  30  is configured to be manually adjusted between cargo-door open position  32  and cargo-door closed position  31  (e.g., by a user). In other examples, cargo door  30  is configured to be electronically adjusted by controller  191 . For example, cargo door  30  includes an actuator that is configured to selectively pivot cargo door  30  responsive to control signals received from controller  191 . In yet further examples, cargo door  30  includes a passive device that is configured to selectively pivot cargo door  30  responsive to manual adjustment of a locking mechanism. As an example, the locking mechanism includes a latch that, when released manually by a user, permits a compressed spring and/or hydraulic cylinder to expand and pivot the cargo door. 
     In some examples, cargo door  30  is included in at least a portion of the upper forward portion of the fuselage  22 . In some examples, at the forward portion of the fuselage in which cargo door  30  is included, cargo door  30  is at least partially included at a top  25  of forward portion of fuselage  22 . That is, cargo door  30  extends to a top of a cross-section of the fuselage in which the cargo door is included. In some examples, cargo door  30  is positioned above (at a vertically higher position) than a floor of cargo hold  28 . Thus, in such examples, cargo door  30  is configured to receive and/or unload the cargo from a position vertically higher than the cargo hold. Including cargo door  30  at the upper forward portion of fuselage  22  may facilitate and expedite loading and/or unloading of cargo  200  when cargo  200  is being loaded from, and/or unloaded to, a position vertically higher than the aircraft (e.g., such as when being loaded by a user). In this way, cargo door  30  may enable easier and/or faster loading and/or unloading of aircraft  10 . 
     As discussed above, cargo door  30  is positioned at a forward portion of fuselage  22 . In some examples, cargo door  30  is included in a front half of fuselage  22 . In some such examples, cargo door  30  is included in a front third of fuselage  22 . In some examples, cargo door  30  extends to front end  23  of fuselage  22 . However, in other examples, cargo door  30  is positioned behind front end  23  of fuselage  22 . That is, in such examples, a front end of cargo door  30  is positioned behind front end  23  of fuselage  22  such that cargo door  30  does not extend all the way to front end  23  of fuselage  22 . 
     When included, cargo unloading door  50  is configured to selectively open to unload cargo  200  through a bottom  26  of fuselage  22 . In some examples, cargo unloading door  50  is configured to be adjusted (e.g., pivoted) between a cargo-unloading-door closed position  51  and a cargo-unloading-door open position  52 . As illustrated in  FIG. 3 , in the cargo-unloading-door open position, an opening is formed in fuselage  22  at the bottom of fuselage  22  that permits cargo  200  to pass into and/or out of fuselage  22 . In some examples, in cargo-unloading-door closed position  51 , cargo unloading door  50  is configured to be flush with fuselage  22  and close, seal, and/or otherwise enclose the interior of fuselage  22  (e.g., cargo hold  28 ). In some such examples, when cargo unloading door  50  is in cargo-unloading-door closed position  51 , cargo  200  cannot exit fuselage  22  via cargo unloading door  50  because cargo unloading door  50  is closed. 
     In some examples, cargo unloading door  50  is configured to pivot downward when adjusted towards the cargo-unloading-door open position  52 . In some examples, cargo unloading door  50  is configured to pivot at least  80  degrees, such as when adjusting between cargo-unloading-door open position  52  and cargo-unloading-door closed position  51 . In some such examples, cargo unloading door  50  is configured to pivot at least  90  degrees. 
     In some examples, cargo unloading door  50  comprises a set of double doors that are configured to open downwards and outwards (away from fuselage  22 ) in opposite directions. For example, cargo unloading door  50  comprises a first cargo unloading door  54  and a second cargo unloading door  56 . A rear end of first cargo unloading door  54  is configured to pivot downwards and forwards when adjusting toward cargo-unloading-door open position  52  and second cargo unloading door  56  is configured to pivot downwards and rearwards when adjusting toward cargo-unloading-door open position  52 .  1   
     In some examples, cargo unloading door  50  is configured to be electronically adjusted by controller  191 . In some such examples, aircraft  10  includes motorized door opening mechanism  58  that is configured to selectively adjust the cargo unloading door between the cargo-unloading-door closed position and the cargo-unloading-door open position. In particular, motorized door opening mechanism  58  is configured to selectively pivot cargo unloading door  50  responsive to control signals received from controller  191 . When included, motorized door opening mechanism  58  comprises an electric motor  60  and a power transfer structure  62  that is configured to transfer and/or convert rotational energy output by electric motor  60  to adjust (e.g., pivot) cargo unloading door  50 . As an example, power transfer structure  62  includes one or more gears  64 . In some such examples, one or more gears  64  include a worm gear  66  and one or more wheel gears  68 . In some examples, one or more wheel gears  68  comprise quarter-wheel gears. As worm gear  66  rotates, worm gear  66  causes wheel gears  68  to pivot and/or rotate. One or more wheel gears  68  in turn may be in a locked rotational engagement with cargo unloading door  50  such that rotation and/or pivoting of wheel gears  68  causes cargo unloading door  50  to pivot. A same and/or similar motorized door opening mechanism may additionally or alternatively be utilized to open and/or close cargo door  30 . 
     In other examples, cargo unloading door  50  is configured to be manually adjusted between cargo-unloading-door open position  52  and cargo-unloading-door closed position  51  (e.g., by a user). In yet further examples, cargo unloading door  50  includes a passive device that is configured to selectively pivot cargo unloading door  50  responsive to manual adjustment of a locking mechanism. As an example, the locking mechanism includes a latch that, when released manually by a user, permits a compressed spring and/or hydraulic cylinder to expand and pivot the cargo unloading door. 
     In some examples, cargo unloading door  50  is included below cargo door  30  (i.e., at a vertically lower position on fuselage  22  than cargo door  30 ). In some such examples, in the portion of fuselage  22  in which it is included, cargo unloading door  50  extends to bottom  26  of fuselage  22  and/or is at least partially included on bottom  26  of fuselage  22 . Thus, in such examples, cargo unloading door  50  extends to the bottom cross-section of fuselage  22  in which cargo unloading door  50  is included. In some examples, cargo unloading door  50  is included below (at a vertically lower position than) cargo hold  28 . In some such examples, cargo unloading door  50  is included directly below and/or underneath cargo hold  28 , such that upon opening of cargo unloading door  50 , cargo  200  in cargo hold  28  is configured to drop out of aircraft  10  onto landing surface  210 . 
     Additionally or alternatively, cargo unloading door  50  is positioned rearward (behind) cargo door  30 . As one such example, cargo unloading door  50  is positioned at an intermediate portion of fuselage  22 , behind the upper forward portion of fuselage  22  where cargo door  30  is included, and/or behind ramp structure  40 . 
     In this way, cargo unloading door  50  may facilitate faster and/or easier unloading of cargo  200  from aircraft  10 . As an example, when cargo unloading door  50  is positioned directly underneath cargo hold  28 , cargo  200  may be unloaded from aircraft  10  without requiring any user intervention. Upon opening of cargo unloading door  50 , cargo  200  may fall out of cargo hold  28  and onto landing surface  210  under the force of gravity alone. As another example, when motorized door opening mechanism  58  is included, cargo unloading door  50  may be opened without requiring user intervention. Thus, the entire unloading process, from door opening to cargo extraction may be entirely automated. 
     In some examples where landing gear  140  is included in aircraft  10 , cargo unloading door  50  is shorter than landing gear  140  and/or otherwise does not extend below landing gear  140  when in cargo-unloading-door open position  52 . In this way, cargo unloading door  50  may not come into contact with landing surface  210 . 
     In some examples, aircraft  10  includes power source  146 . When included, power source  146  is configured to supply electrical power to aircraft  10 , and in particular, to the electrically powered devices of aircraft  10 , such as one or more of controller  191 , tilt mechanism  162 , one or more motors  164 , actuator  174 , and electric motor  60 . As an example, power source  146  comprises a battery. In such examples, the battery comprises a rechargeable battery (such as a lithium-ion battery) and/or a disposable battery. 
     In some examples, power source  146  is configured to retain cargo  200  in cargo hold  28  and/or otherwise restrict movement of cargo  200  out of cargo hold  28 . As an example, power source  146  is included forward of cargo hold  28  and is configured to restrict forward movement of cargo  200  from cargo hold  28 . Additionally or alternatively, power source  146  is positioned and/or included above and/or on top of ramp structure  40  and/or conveyor system  170 . As one such example, power source  146  is positioned above and/or on top of angled surface  42  of ramp structure  40 . In some such examples, power source  146  is positioned and/or included in-between angled surface  42  and cargo door  30  (e.g., directly underneath cargo door  30 ). Including power source  146  underneath cargo door  30  makes power source  146  more accessible to a user, enabling faster and/or easier charging, refueling, etc., and/or replacement, of power source  146 . This may be particularly useful when power source  146  is a rechargeable battery, where charging and/or replacement of power source  146  occurs more frequently. 
     Including ramp structure  40  and/or power source  146  forward of cargo hold  28  may restrict and/or prevent drift of cargo  200  during flight, particularly forward drift of cargo  200 . Reducing such cargo shifting during flight may help aircraft  10  maintain more stable flight and/or may otherwise improve flight characteristics. 
     Further positioning ramp structure  40  and/or power source  146  forward of cargo hold  28  and/or positioning cargo hold  28  in the intermediate section of fuselage  22  may shift the center of gravity of aircraft  10  forward as compared to conventional aircraft and/or may improve flight characteristics. That is, because of the positioning of one or more of cargo hold  28  (and cargo  200  in cargo hold  28 ), ramp structure  40 , and/or power source  146 , aircraft  10  may have a more forward center of gravity as compared to conventional delivery aircraft which may improve flight characteristics. Moreover, by having such structures as ramp structure  40  and/or power source  146  positioned forward of cargo hold  28 , when cargo  200  is present, the location of the ramp structure  40  and/or power source  146  counterbalances the weight of cargo  200 , resulting in a desired center of gravity for aircraft  10 . 
     In some examples, power source  146  is configured to be selectively coupled to aircraft  10  via mating coupling mechanisms in the power source and the aircraft. As an example, power source  146  includes a first coupling mechanism  148 , and aircraft  10  includes a second coupling mechanism  180  that is configured to selectively engage with first coupling mechanism  148  to couple power source  146  to aircraft  10 . First coupling mechanism  148  and second coupling mechanism  180  may comprise any suitable releasable coupling mechanism such as frictional and/or magnetic type releasable coupling mechanisms. 
     As one example, first coupling mechanism  148  and second coupling mechanism  180  comprise a pin and socket arrangement, where second coupling mechanism  180  comprises a socket, and first coupling mechanism  148  comprises one or more pins and springs. In one such example, when a user carries power source  146  (e.g., by a top handle), the upward force provided by the user is configured to hyperextend the pins, which in turn pulls the pins inwards away from and/or out of the socket (thereby decoupling power source  146  from aircraft  10 ). When the user sets power source  146  down and/or otherwise releases the handle, the spring retracts and/or compresses, pushing the pins outward into the socket (thereby coupling power source  146  to aircraft  10 ). However, first coupling mechanism  148  and second coupling mechanism  180  comprise other frictional releasable locking mechanism in other examples, such as one or more of friction fits, latches, threaded engagements, bayonet locks, and/or other pin and socket arrangements. 
     In some examples, ramp structure  40  includes second coupling mechanism  180  and power source  146  is configured to be selectively coupled to ramp structure  40  and/or conveyor system  170 . In such examples, power source  146  rests on top of ramp structure  40  and/or conveyor system  170 . In other examples, cargo door  30  includes second coupling mechanism  180  and power source  146  is configured to be selectively coupled to cargo door  30 . In some such examples, power source  146  rests on top of (and physically touches and/or otherwise contacts) ramp structure  40  and/or conveyor system  170  when cargo door  30  is in cargo-door closed position  31 . In other such examples, power source  146  is spaced away from (above) ramp structure  40  and/or conveyor system  170  when cargo door  30  is in cargo-door closed position  31 . However, in other examples, other structures in aircraft  10 , such as fuselage  22 , additionally and/or alternatively include second coupling mechanism  180  and are configured to be selectively coupled to cargo door  30 . 
     In some examples, power source  146  is configured to be selectively electrically connected to aircraft  10  (and specifically to the one or more electrically powered devices of aircraft  10 ) via electrical connections included in the power source and the aircraft. As an example, power source  146  includes a first electrical connector  147 , and aircraft  10  includes a second electrical connector  178  that is configured to selectively electrically connect (e.g., via a wired and/or wireless connection) with first electrical connector  147 , to enable power source  146  to supply power to the electrically powered devices of aircraft  10 . 
     In some examples, ramp structure  40  includes second electrical connector  178  and ramp structure  40  is configured to electrically connect with power source  146  to provide power to aircraft  10 . In another example, conveyor system  170  includes second electrical connector  178  and conveyor system  170  is configured to electrically connect with power source  146  to provide power to aircraft  10 . In another example, cargo door  30  includes second electrical connector  178  and cargo door  30  is configured to electrically connect with power source  146  to provide power to aircraft  10 . However, in other examples, other structures in aircraft  10 , such as fuselage  22 , additionally or alternatively include second electrical connector  178  and are configured to selectively electrically connect with power source  146  to provide power to aircraft  10 . 
     In some examples, aircraft  10  comprises an unmanned, autonomous vehicle, such as a delivery vehicle for cargo  200 . In some examples, aircraft  10  is entirely an electrically powered aircraft. In other examples, aircraft  10  is a hybrid aircraft. 
     In some examples, aircraft  10  is at most 20 meters (m) in length, 15 m in length, 10 m in length, 5 m in length, 4 m in length, 3 m in length, 2 m in length, and/or 1 m in length. In some examples, aircraft  10  is at most 20 m in width, 15 m in width, 10 m in width, 5 m in width, 4 m in width, 3 m in width, 2 m in width, and/or 1 m in width. 
     Turning now to  FIGS. 4-5 , non-exclusive examples of aircraft  10  are illustrated. Where appropriate, the reference numerals from the schematic illustrations of  FIGS. 1-3  are used to designate corresponding parts of the examples of  FIGS. 1-3 ; however, the examples of  FIGS. 4-5  are non-exclusive and do not limit aircraft  10  to the illustrated embodiments of  FIGS. 4-5 . That is, aircraft  10  are not limited to the specific embodiments of  FIGS. 4-5 , and aircraft  10  may incorporate any number of the various aspects, configurations, characteristics, properties, etc. of aircraft  10  that are illustrated in and discussed with reference to the schematic representations of  FIGS. 1-3  and/or the embodiments of Figs.  FIGS. 4-5  as well as variations thereof, without requiring the inclusion of all such aspects, configurations, characteristics, properties, etc. For the purpose of brevity, each previously discussed component, part, portion, aspect, region, etc. or variants thereof may not be discussed, illustrated, and/or labeled again with respect to the examples of  FIGS. 4-5 ; however, it is within the scope of the present disclosure that the previously discussed features, variants, etc. may be utilized with the examples of  FIGS. 4-5 . 
     As seen in  FIG. 4 , aircraft  410  is an example of an aircraft  10 . Aircraft  410  comprises forward set of wings  76  and rearward set of wings  78 . Further, aircraft  410  comprises eight total rotors, four of one or more pusher rotors  100  and four of one or more puller rotors  120 . Each of one or more pusher rotors  100  and each of one or more puller rotors  120  of aircraft  410  includes two rotor blades. Aircraft  410  additionally includes four of landing gear  140 , one off each of the wings. Longitudinal crossbars  90  extend between forward set of wings  76  and rearward set of wings  78 , outboard of all of the rotors. Thus, all of the rotors of aircraft  410  are included between the wings and the longitudinal crossbars. In some examples, aircraft  410  additionally includes a tail  420 . 
     As seen in  FIG. 5 , aircraft  510  is an example of an aircraft  10 .  FIG. 5  illustrates a side view of aircraft  510  with internal components of aircraft  510  illustrated in dotted lines. For example, power source  146 , cargo  200 , and ramp structure  40  are illustrated in dotted lines. As illustrated, power source  146  restricts and/or prevents forward movement of cargo  200 . Further, front landing gear  142  of aircraft  510  is shorter than rear landing gear  144 . Aircraft  510  additionally includes tail  420 . 
       FIGS. 6-7  schematically provide flowcharts that represent illustrative, non-exclusive examples of methods according to the present disclosure. In  FIGS. 6-7 , some steps are illustrated in dashed boxes indicating that such steps may be optional or may correspond to an optional version of a method according to the present disclosure. That said, not all methods according to the present disclosure are required to include the steps illustrated in solid boxes. The methods and steps illustrated in  FIGS. 6-7  are not limiting and other methods and steps are within the scope of the present disclosure, including methods having greater than or fewer than the number of steps illustrated, as understood from the discussions herein. 
       FIG. 6  schematically provides flowcharts of methods  600  for loading and/or unloading an aircraft (e.g., aircraft  10 ), and  FIG. 7  schematically provides flowcharts of methods for loading and/or unloading cargo (e.g., cargo  200 ) from the aircraft. 
     Methods  600  include loading cargo into a fuselage (e.g., fuselage  22 ) of the aircraft through an upper forward portion of the fuselage at  602 . In some examples, loading the cargo at  602  includes one or more of opening a cargo door (e.g., cargo door  30 ) positioned at the upper forward portion of the fuselage at  604 , advancing cargo rearward and downward toward a cargo hold (e.g., cargo hold  28 ) at  606 , and closing the cargo door at  608 . In examples, where aircraft includes more than one cargo door, the cargo door through which cargo is loaded at  602  is referred to herein as first cargo door (e.g., cargo door  30 ). 
     The opening the cargo door at  604  includes opening the cargo door to create an opening in the upper forward portion of the fuselage. After the opening the cargo door at  604 , the loading at  602  optionally includes inserting the cargo into the aircraft through the opening in the upper forward portion of the fuselage. 
     Advancing the cargo rearward and downward at  606  optionally includes pushing, sliding, rolling, and/or otherwise advancing the cargo rearward and downward towards the cargo hold. In some such examples, the advancing the cargo rearward and downward towards the cargo hold includes pushing, sliding, rolling, and/or otherwise advancing the cargo on an angled surface (e.g., angled surface  42 ) of a ramp structure (e.g., ramp structure  40 ) towards and/or into the cargo hold. In some examples, the advancing at  606  includes powering a conveyor system (e.g., conveyor system  170 ) to advance the cargo rearward and downward towards and/or into the cargo hold. In some such examples, the advancing at  606  includes advancing the cargo via the conveyor system such that the cargo is advanced rearward and downward on the conveyor system. In some examples, the advancing at  606  is performed after the opening at  604 . 
     At  620 , methods  600  optionally include loading a power source (e.g., power source  146 ) into the fuselage in front of the cargo in the cargo hold. In some examples, the loading the power source at  620  is performed after the advancing the cargo rear and downward at  606 , but before the closing the cargo door at  608 . As an example, methods  600  include the advancing the cargo into the cargo hold at  606 , the loading the power source in front of the cargo at  620 , and then the closing the cargo door at  608 . In some examples, the loading the power source at  620  includes mechanically coupling and/or electrically connecting the power source to the aircraft. As one such example, the loading at  620  includes mechanically coupling the power source to the ramp structure. In another example, the loading at  620  includes mechanically coupling the power source to the cargo door. In yet another example, the loading at  620  includes mechanically coupling the power source to the fuselage. In some examples, the loading the power source at  620  includes positioning and/or placing the power source above and/or on top of the ramp structure, and in front of the cargo hold. 
     At  640 , methods  600  optionally include unloading the cargo from the aircraft. In some examples, the unloading at  640  includes unloading the cargo through the upper forward portion of the fuselage at  642 . In some such examples, the unloading at  642  includes opening the cargo door to create the opening in the upper forward portion of the fuselage. 
     In some examples, the unloading at  640  includes extracting the cargo from the aircraft through the opening in the upper forward portion of the fuselage. In some such examples, the extracting includes pulling the cargo upwards and forwards out of the cargo hold. In some examples, the extracting is performed after opening the first cargo door. In some such examples, the pulling comprises sliding the cargo upwards and forwards out of the cargo hold on a ramp structure. In some further such examples, the extracting the cargo from the cargo hold further comprises powering the conveyor system and advancing the cargo upwards and forwards towards the cargo door and away from the cargo hold via the conveyor system. 
     Unloading the cargo at  640  optionally includes unloading the cargo through a bottom (e.g., bottom  26 ) of the fuselage via a second cargo door (e.g., cargo unloading door  50 ) at  644 . In some examples, unloading the cargo through the bottom of the fuselage at  644  includes opening the second cargo door (also referred to herein as “cargo unloading door”) positioned on the bottom of the fuselage. In some examples, the opening the cargo unloading door comprises powering a motorized door opening mechanism (e.g., motorized door opening mechanism  58 ). 
     In some examples, methods  600  are performed by a user to load and/or unload the aircraft. However, the aircraft, specifically a controller (e.g., controller  191 ) of the aircraft may perform one or more of methods  600 , such as the powering of the conveyor system and/or the opening of the cargo unloading door. 
     Methods  700  include receiving cargo (e.g., cargo  200 ) through a first cargo door (e.g., cargo door  30 ) positioned on a top (e.g., top  25 ) of a fuselage of an aircraft at  702 , and unloading the cargo through a second cargo door (e.g., cargo unloading door  50 ) positioned on a bottom (e.g., bottom  26 ) of the fuselage of an aircraft (e.g., aircraft  10 ) at  712 . In some examples, the receiving cargo through the first cargo door optionally includes opening the first cargo door to create an opening through which to receive the cargo. Thus, in some such examples, opening the cargo door is performed prior to receiving the cargo. In some examples, the cargo is received in a cargo hold (e.g., cargo hold  28 ) after being received through the first cargo door. As an example, the receiving the cargo through the first cargo door at  702  optionally includes powering on a conveyor system (e.g., conveyor system  170 ) to advance the cargo rearwards and downwards from the first cargo door into the cargo hold. 
     In some examples, unloading the cargo at  708  optionally includes unloading the cargo through the first cargo door at  710 . Additionally or alternatively, the unloading at  708  includes the unloading the cargo through the second cargo door positioned on a bottom portion of the aircraft at  712 . In some such examples, the unloading the cargo through the second cargo door at  712  includes opening the second cargo door at  714 . The opening the second cargo door at  714  optionally includes powering a motorized door opening mechanism (e.g., motorized door opening mechanism  58 ). In some examples, the opening the second cargo door at  714  includes dropping the cargo out of the cargo hold. In particular, upon opening the second cargo door, the cargo is configured to drop out of the cargo hold onto a landing surface (e.g., landing surface  210 ). 
     Methods  700  optionally include keeping the second cargo door open and lifting off from the landing surface after unloading the cargo through the second cargo door at  704 . In some examples, methods  700  include closing the second cargo door after the aircraft has lifted off the landing surface. 
     Methods  700  optionally include landing on the landing surface at  706 . In some examples, the aircraft lands on the landing surface prior to receiving the cargo at  702 . In some examples, the aircraft lands on the landing surface prior to unloading the cargo at  708 . In this way, the cargo may be loaded into and/or unloaded from the aircraft after the aircraft has landed. 
     In some examples, methods  700  are performed by the aircraft. In some such examples, methods  700  are performed by a control system (e.g., control system  190 ) including a controller (e.g., controller  191 ). As explained above, the controller may include computer-readable instructions stored in non-transitory memory (e.g., non-transitory memory  196 ) for performing one or more of methods  700  and the controller may include a processor (e.g., processing unit  192 ) that is configured to execute the computer-readable instructions to perform one or more of methods  700 . Some methods  700  are performed autonomously. For example, the control system may cause the aircraft&#39;s guidance, navigation, and/or control by controlling actuation of flight control surfaces such as rotors and tilting mechanisms. The control system may be equipped with a navigation system (such as GPS or INS (inertial navigation system)) or other sensors to execute the navigation of the aircraft (i.e. travel from point A to B). Other sensors, such as LiDAR or cameras may be used to assist in situational awareness of the aircraft as it travels. 
     A controller may be any suitable device or devices that are configured to perform the functions of the controller discussed herein. For example, the controller may include one or more of an electronic controller, a dedicated controller, a special-purpose controller, a personal computer, a special-purpose computer, a display device, a logic device, a memory device, and/or a memory device having non-transitory computer readable media suitable for storing computer-executable instructions for implementing aspects of systems and/or methods according to the present disclosure. 
     Additionally or alternatively, a controller may include, or be configured to read, non-transitory computer readable storage, or memory, media suitable for storing computer-executable instructions, or software, for implementing methods or steps of methods according to the present disclosure. Examples of such media include CD-ROMs, disks, hard drives, flash memory, etc. As used herein, storage, or memory, devices and media having computer-executable instructions as well as computer-implemented methods and other methods according to the present disclosure are considered to be within the scope of subject matter deemed patentable in accordance with Section 101 of Title 35 of the United States Code. 
     Illustrative, non-exclusive examples of inventive subject matter according to the present disclosure are described in the following enumerated paragraphs: 
     A. An aircraft ( 10 ), comprising: 
     an airframe ( 20 ) comprising one or more wings ( 70 ); 
     one or more pusher rotors ( 100 ) supported by the airframe ( 20 ); and 
     one or more puller rotors ( 120 ) supported by the airframe ( 20 ). 
     A1. The aircraft ( 10 ) of paragraph A, wherein the one or more puller rotors ( 120 ) are positioned behind the one or more pusher rotors ( 100 ). 
     A2. The aircraft ( 10 ) of any of paragraphs A-A1, wherein the aircraft ( 10 ) is configured to take off and land vertically. 
     A2.1. The aircraft ( 10 ) of paragraph A2, wherein the aircraft ( 10 ) is configured to selectively adjust an amount of vertical thrust and/or an amount of horizontal thrust by tilting at least one of the one or more pusher rotors ( 100 ) and/or at least one of the one or more puller rotors ( 120 ). 
     A3. The aircraft ( 10 ) of paragraph A2.1, wherein a rotational axis ( 110 ) of the at least one of the one or more pusher rotors ( 100 ) is configured to be selectively tilted towards a longitudinal axis ( 16 ) of the aircraft ( 10 ) to increase horizontal thrust and/or reduce vertical thrust, and wherein the at least one of the one or more pusher rotors ( 100 ) is configured to be selectively tilted away from the longitudinal axis ( 16 ) to reduce horizontal thrust and/or increase vertical thrust. 
     A4. The aircraft ( 10 ) of paragraph A3, wherein the at least one of the one or more pusher rotors ( 100 ) is configured to be selectively tilted between a vertical thrusting push position ( 102 ) and a horizontal thrusting push position ( 104 ). 
     A5. The aircraft ( 10 ) of paragraph A4, wherein the at least one of the one or more pusher rotors ( 100 ) generates thrust in an upward vertical direction in the vertical thrusting push position ( 102 ) and generates thrust in a forward horizontal direction in the horizontal thrusting push position ( 104 ). 
     A6. The aircraft ( 10 ) of any of paragraphs A4-A5, wherein the one or more pusher rotors ( 100 ) face downwards in the vertical thrusting push position ( 102 ) and face rearward in the horizontal thrusting push position ( 104 ). 
     A7. The aircraft ( 10 ) of any of paragraphs A2.1-A6, wherein the at least one of the one or more pusher rotors ( 100 ) is configured to tilt when the aircraft ( 10 ) is transitioning between a hover mode and a cruise mode. 
     A8. The aircraft ( 10 ) of any of paragraphs A2.1-A7, wherein the at least one of the one or more pusher rotors ( 100 ) is configured to be individually tilted such that when two or more of the pusher rotors ( 100 ) are configured to be tilted, the two or more of the pusher rotors ( 100 ) are configured to be tilted independently of one another. 
     A9. The aircraft ( 10 ) of any of paragraphs A3-A8, wherein a rotational axis ( 130 ) of the at least one of the one or more puller rotors ( 120 ) is configured to be selectively tilted towards the longitudinal axis ( 16 ) of the aircraft ( 10 ) to increase horizontal thrust and/or reduce vertical thrust, and wherein the at least one of the one or more puller rotors ( 120 ) is configured to be selectively tilted away from the longitudinal axis ( 16 ) to reduce horizontal thrust and/or increase vertical thrust. 
     A10. The aircraft ( 10 ) of paragraph A9, wherein the at least one of the one or more puller rotors ( 120 ) is configured to be selectively tilted between a vertical thrusting pull position ( 122 ) and a horizontal thrusting pull position ( 124 ). 
     A11. The aircraft ( 10 ) of paragraph A10, wherein the at least one of the one or more puller rotors ( 120 ) generates thrust in an upward vertical direction in the vertical thrusting pull position ( 122 ) and generates thrust in a forward horizontal direction in the horizontal thrusting pull position ( 124 ). 
     A12. The aircraft ( 10 ) of any of paragraphs A10-A11, wherein the one or more puller rotors ( 120 ) face upwards in the vertical thrusting pull position ( 122 ) and face forwards in the horizontal thrusting pull position ( 124 ). 
     A13. The aircraft ( 10 ) of any of paragraphs A8-A12 when depending from paragraph A7, wherein the at least one of the one or more puller rotors ( 120 ) is configured to tilt when the aircraft ( 10 ) is transitioning between the hover mode and the cruise mode. 
     A14. The aircraft ( 10 ) of any of paragraphs A9-A13, wherein the at least one of the one or more puller rotors ( 120 ) is configured to be individually tilted such that when two or more of the puller rotors ( 120 ) are configured to be tilted, the two or more of the puller rotors ( 120 ) are configured to be tilted independently of one another. 
     A15. The aircraft ( 10 ) of any of paragraphs A9-A14 when depending from any of paragraphs A3-A8, wherein the at least one of the one or more pusher rotors ( 100 ) is configured to be tilted independently of the at least one of the one or more puller rotors ( 120 ). 
     A16. The aircraft ( 10 ) of paragraph A15, wherein the at least one of the one or more pusher rotors ( 100 ) is configured to tilt in an opposite rotational direction to the at least one of the one or more puller rotors ( 120 ). 
     A17. The aircraft ( 10 ) of any of paragraphs A15-A16 when depending from any of paragraphs A2-A14, wherein, when transitioning to the cruise mode, the at least one of the one or more pusher rotors ( 100 ) is configured to tilt vertically upwards and the at least one of the one or more puller rotors ( 120 ) is configured to tilt vertically downwards. 
     A18. The aircraft ( 10 ) of any of paragraphs A-A17, wherein the one or more wings ( 70 ) comprise a forward set of wings ( 76 ) and an aft set of wings ( 78 ). 
     A19. The aircraft ( 10 ) of paragraph A18, wherein the one or more pusher rotors ( 100 ) extend behind a trailing edge ( 73 ) of the forward set of wings ( 76 ), and wherein the one or more puller rotors ( 120 ) extend in front of the leading edge ( 72 ) of the aft set of wings ( 78 ). 
     A20. The aircraft ( 10 ) of any of paragraphs A18-A19, wherein the one or more pusher rotors ( 100 ) and the one or more puller rotors ( 120 ) are positioned between the forward set of wings ( 76 ) and the aft set of wings ( 78 ). 
     A21. The aircraft ( 10 ) of any of paragraphs A18-A20 when depending from any of paragraphs A10-A16, wherein the one or more pusher rotors ( 100 ) are positioned behind the forward set of wings ( 76 ) in the horizontal thrusting push position ( 104 ) and wherein the one or more puller rotors ( 120 ) are positioned in front of the aft set of wings ( 78 ) in the horizontal thrusting pull position ( 124 ). 
     A22. The aircraft ( 10 ) of paragraph A21, wherein the one or more pusher rotors ( 100 ) are positioned behind a trailing edge ( 73 ) of the forward set of wings ( 76 ) and wherein the one or more puller rotors ( 120 ) are positioned in front of a leading edge ( 72 ) of the aft set of wings ( 78 ). 
     A23. The aircraft ( 10 ) of any of paragraphs A-A22, wherein the one or more pusher rotors ( 100 ) and the one or more puller rotors ( 120 ) are positioned such that they are vertically offset from one another. 
     A24. The aircraft ( 10 ) of paragraph A23 when depending from any of paragraphs A4-A6 and any of paragraphs A10-A12, wherein when the one or more pusher rotors ( 100 ) are in the vertical thrusting push position ( 102 ) and the one or more puller rotors ( 120 ) are in the vertical thrusting pull position ( 122 ), the one or more pusher rotors ( 100 ) are located at a vertically lower position than the one or more puller rotors ( 120 ). 
     A25. The aircraft ( 10 ) of paragraph A24, wherein when the one or more pusher rotors ( 100 ) are in the horizontal thrusting push position ( 104 ) and the one or more puller rotors ( 120 ) are in the horizontal thrusting pull position ( 124 ), the one or more pusher rotors ( 100 ) are located at a vertically higher position than the one or more puller rotors ( 120 ). 
     A26. The aircraft ( 10 ) of any of paragraphs A-A25, further comprising landing gear ( 140 ). 
     A27. The aircraft ( 10 ) of paragraph A26, when depending from any of paragraphs A18-A22, wherein the landing gear ( 140 ) comprises front landing gear ( 142 ) that is coupled to the forward set of wings ( 76 ). 
     A28. The aircraft ( 10 ) of any of paragraphs A26-A27 when depending from any of paragraphs A18-A22, wherein the landing gear ( 140 ) comprises rear landing gear ( 144 ) that is coupled to the aft set of wings ( 78 ). 
     A29. The aircraft ( 10 ) of paragraph A28 when depending from paragraph A27, wherein the rear landing gear ( 144 ) is longer than the front landing gear ( 142 ). 
     A30. The aircraft ( 10 ) of any of paragraphs A18-A29, further comprising longitudinal crossbars ( 90 ) that extend lengthwise between the forward set of wings ( 76 ) and the aft set of wings ( 78 ). 
     A31. The aircraft ( 10 ) of paragraph A30, wherein the longitudinal crossbars ( 90 ) are positioned outboard of the one or more pusher rotors ( 100 ) and the one or more puller rotors ( 120 ) such that the one or more pusher rotors ( 100 ) and the one or more puller rotors ( 120 ) are positioned between the longitudinal crossbars ( 90 ). 
     A32. The aircraft ( 10 ) of any of paragraphs A30-A31, wherein the longitudinal crossbars ( 90 ) extend between tips ( 71 ) of the forward set of wings ( 76 ) and the aft set of wings ( 78 ). 
     A33. The aircraft ( 10 ) of any of paragraphs A30-A32, wherein the longitudinal crossbars ( 90 ) comprise a right-side longitudinal crossbar ( 92 ) and a left-side longitudinal crossbar ( 94 ). 
     A34. The aircraft ( 10 ) of any of paragraphs A-A33, wherein the aircraft ( 10 ) is an unmanned electric aircraft. 
     A35. A method of operating the aircraft of any of paragraphs A-A34, comprising: 
     operating the aircraft ( 10 ) in a/the hover mode by tilting the one or more pusher rotors ( 100 ) relative to the airframe ( 20 ) to a/the vertical thrusting push position ( 102 ) and tilting the one or more puller rotors ( 120 ) relative to the airframe ( 20 ) to a/the vertical thrusting pull position ( 122 ); and 
     operating the aircraft ( 10 ) in a/the cruise mode by tiling the one or more pusher rotors ( 100 ) relative to the aircraft ( 10 ) to a/the horizontal thrusting push position ( 104 ) and tiling the one or more puller rotors ( 120 ) relative to the aircraft ( 10 ) to a/the horizontal thrusting pull position ( 124 ). 
     A36. The method of paragraph A35, further comprising the method of any of paragraphs C-D4. 
     B. An aircraft ( 10 ), comprising: 
     a fuselage ( 22 ) comprising a cargo hold ( 28 ) configured to store cargo ( 200 ); 
     a cargo door ( 30 ) configured to selectively open to receive the cargo ( 200 ) through an upper forward portion of the fuselage ( 22 ); and 
     a ramp structure ( 40 ) included within the fuselage ( 22 ), wherein the ramp structure ( 40 ) is configured to provide a passageway for the cargo ( 200 ) to advance between the cargo door ( 30 ) and the cargo hold ( 28 ). 
     B1. The aircraft ( 10 ) of paragraph B, wherein the cargo door ( 30 ) is configured to selectively open to unload the cargo ( 200 ) through the upper forward portion of the fuselage ( 22 ). 
     B2. The aircraft ( 10 ) of any of paragraphs B-B1, wherein the cargo door ( 30 ) is configured to receive and/or unload the cargo ( 200 ) from a position vertically higher than the cargo hold ( 28 ). 
     B3. The aircraft ( 10 ) of any of paragraphs B-B2, wherein the cargo door ( 30 ) is included in at least a portion of the upper forward portion of the fuselage ( 22 ). 
     B4. The aircraft ( 10 ) of any of paragraphs B-B3, wherein the cargo door ( 30 ) extends to a top of a cross-section of the fuselage ( 22 ) in which the cargo door ( 30 ) is included. 
     B5. The aircraft ( 10 ) of any of paragraphs B-B4, wherein the cargo door ( 30 ) is included in a front half of the aircraft ( 10 ). 
     B6. The aircraft ( 10 ) of paragraph B5, wherein the cargo door ( 30 ) is included in a front third of the aircraft ( 10 ). 
     B7. The aircraft ( 10 ) of any of paragraphs B-B6, wherein the cargo door ( 30 ) is positioned behind a front end ( 23 ) of the fuselage ( 22 ). 
     B8. The aircraft ( 10 ) of any of paragraphs B-B7, wherein the cargo door ( 30 ) is configured to be adjusted between a cargo-door closed position ( 31 ) and a cargo-door open position ( 32 ). 
     B9. The aircraft ( 10 ) of paragraph B8, wherein the cargo door ( 30 ) is configured to pivot upward when adjusted towards the cargo-door open position ( 32 ). 
     B10. The aircraft ( 10 ) of any of paragraphs B8-B9, wherein the cargo door ( 30 ) is configured to pivot at least 80 degrees. 
     B11. The aircraft ( 10 ) of any of paragraphs B-B10, wherein the ramp structure ( 40 ) is positioned in front of the cargo hold ( 28 ). 
     B12. The aircraft ( 10 ) of any of paragraphs B-B11, wherein the ramp structure ( 40 ) is positioned below the cargo door ( 30 ). 
     B13. The aircraft ( 10 ) of any of paragraphs B-12, wherein the ramp structure ( 40 ) is positioned between the cargo door ( 30 ) and the cargo hold ( 28 ). 
     B14. The aircraft ( 10 ) of any of paragraphs B12-B13, wherein the ramp structure ( 40 ) extends to the cargo door ( 30 ) of the aircraft ( 10 ). 
     B15. The aircraft ( 10 ) of any of paragraphs B-B14, wherein the ramp structure ( 40 ) is fully included within the fuselage ( 22 ). 
     B16. The aircraft ( 10 ) of any of paragraphs B-B15, wherein, when the cargo ( 200 ) is advanced along the ramp structure ( 40 ) towards the cargo hold ( 28 ), the ramp structure ( 40 ) is configured to lower the cargo ( 200 ) in the fuselage ( 22 ). 
     B17. The aircraft ( 10 ) of any of paragraphs B-B16, wherein the ramp structure ( 40 ) includes an inclined surface ( 42 ). 
     B18. The aircraft ( 10 ) of paragraph B17, wherein the inclined surface ( 42 ) slopes downwards from the cargo door ( 30 ) to the cargo hold ( 28 ). 
     B19. The aircraft ( 10 ) of any of paragraphs B-B18, wherein the ramp structure ( 40 ) is configured to permit the cargo ( 200 ) to slide into the cargo hold ( 28 ). 
     B20. The aircraft ( 10 ) of any of paragraphs B-B19, further comprising a conveyor system ( 170 ) configured to advance the cargo ( 200 ) rearwards towards the cargo hold ( 28 ). 
     B21. The aircraft ( 10 ) of paragraph B20, wherein the conveyor system ( 170 ) extends between the cargo door ( 30 ) and the cargo hold ( 28 ). 
     B22. The aircraft ( 10 ) of any of paragraphs B20-B21, wherein the conveyor system ( 170 ) is electrically powered. 
     B23. The aircraft ( 10 ) of any of paragraphs B20-B22, wherein the conveyor system ( 170 ) comprises a conveyor belt. 
     B24. The aircraft ( 10 ) of any of paragraphs B20-B23, wherein the ramp structure ( 40 ) comprises at least a portion of the conveyor system ( 170 ). 
     B25. The aircraft ( 10 ) of any of paragraphs B-B24, further comprising a cargo unloading door ( 50 ) configured to selectively open to unload the cargo ( 200 ) through a bottom ( 26 ) of the fuselage ( 22 ). 
     B26. The aircraft ( 10 ) of paragraph B25, wherein the cargo unloading door ( 50 ) is included at a vertically lower position on the fuselage ( 22 ) than the cargo door ( 30 ). 
     B27. The aircraft ( 10 ) of any of paragraphs B25-B26, wherein the cargo unloading door ( 50 ) is configured to selectively open to unload the cargo ( 200 ) through an intermediate portion of the bottom ( 26 ) of the fuselage ( 22 ). 
     B28. The aircraft ( 10 ) of any of paragraphs B25-B27, wherein the cargo unloading door ( 50 ) is configured to selectively open to drop the cargo ( 200 ) out of the cargo hold ( 28 ) to a landing surface ( 210 ). 
     B29. The aircraft ( 10 ) of any of paragraphs B25-B28, wherein the cargo unloading door ( 50 ) is positioned directly underneath the cargo hold ( 28 ). 
     B30. The aircraft ( 10 ) of any of paragraphs B25-B29, wherein the cargo unloading door ( 50 ) is positioned behind the cargo door ( 30 ). 
     B31. The aircraft ( 10 ) of any of paragraphs B25-B30, wherein the cargo unloading door ( 50 ) extends to a bottom of an unloading door cross-section of the fuselage ( 22 ) in which the cargo unloading door ( 50 ) is included. 
     B32. The aircraft ( 10 ) of any of paragraphs B25-B31, wherein the cargo unloading door ( 50 ) is configured to be adjusted between a cargo-unloading-door closed position ( 51 ) and a cargo-unloading-door open position ( 52 ). 
     B33. The aircraft ( 10 ) of any of paragraphs B25-B32, wherein the cargo unloading door ( 50 ) comprises a set of double doors ( 54  and  56 ). 
     B34. The aircraft ( 10 ) of paragraph B33 when depending from paragraph B32, wherein the double doors ( 54  and  56 ) are configured to pivot in opposite rotational directions. 
     B35. The aircraft ( 10 ) of any of paragraphs B32-B34, further comprising a motorized door opening mechanism ( 58 ) that is configured to selectively adjust the cargo unloading door ( 50 ) between the cargo-unloading-door closed position ( 51 ) and the cargo-unloading-door open position ( 52 ). 
     B36. The aircraft of any of paragraphs B-B35, further comprising a power source ( 146 ). 
     B37. The aircraft ( 10 ) of paragraph B36, wherein the power source ( 146 ) comprises a battery. 
     B38. The aircraft ( 10 ) of any of paragraphs B36-B37, wherein the ramp structure ( 40 ) comprises a power source connector that is configured to selectively electrically connect to the power source ( 146 ) to provide electrical power to the aircraft ( 10 ). 
     B39. The aircraft ( 10 ) of any of paragraphs B36-B38, wherein the power source ( 146 ) is configured to be selectively mechanically coupled to the fuselage ( 22 ). 
     B40. The aircraft ( 10 ) of any of paragraphs B36-B39, wherein the power source ( 146 ) is positioned forward of the cargo hold ( 28 ). 
     B41. The aircraft ( 10 ) of paragraph B40, wherein the power source ( 146 ) is configured to be selectively coupled to the ramp structure ( 40 ). 
     B42. The aircraft ( 10 ) of any of paragraphs B36-B41, wherein the power source ( 146 ) is configured to retain the cargo ( 200 ) in the cargo hold ( 28 ). 
     B43. The aircraft ( 10 ) of any of paragraphs A-A34, further comprising the subject matter of any of paragraphs B-B41. 
     C. A method ( 600 ) for loading cargo ( 200 ) on to an aircraft ( 10 ), the method ( 600 ) comprising: 
     loading ( 602 ) cargo ( 200 ) into a fuselage ( 22 ) of the aircraft ( 10 ) through an upper forward portion of the fuselage ( 22 ). 
     C1. The method ( 600 ) of paragraph C, wherein the loading ( 602 ) comprises opening ( 604 ) a first cargo door ( 30 ) included in the upper forward portion of the fuselage ( 22 ) to create an opening in the upper forward portion of the fuselage ( 22 ). 
     C2. The method ( 600 ) of paragraph C1, wherein, after the opening ( 604 ) the first cargo door ( 30 ), the loading further comprises inserting the cargo ( 200 ) into the aircraft ( 10 ) through the opening in the upper forward portion of the fuselage ( 22 ). 
     C3. The method ( 600 ) of any of paragraphs C-C2, wherein the loading ( 602 ) further comprises advancing ( 606 ) the cargo ( 200 ) downwards and rearwards towards and/or into a cargo hold ( 28 ) of the aircraft ( 10 ). 
     C4. The method ( 600 ) of paragraph C3, wherein the advancing ( 606 ) the cargo ( 200 ) downwards and rearwards towards and/or into the cargo hold ( 28 ) comprises sliding the cargo ( 200 ) towards and/or into the cargo hold ( 28 ). 
     C5. The method ( 600 ) of any of paragraphs C3-C4, wherein the advancing ( 606 ) the cargo ( 200 ) downwards and rearwards towards and/or into the cargo hold ( 28 ) further comprises powering a conveyor system ( 170 ). 
     C6. The method ( 600 ) of any of paragraphs C-C5, further comprising unloading ( 640 ) the cargo ( 200 ) from the aircraft ( 10 ). 
     C7. The method ( 600 ) of paragraph C6, wherein the unloading ( 640 ) comprises unloading ( 642 ) the cargo ( 200 ) through the upper forward portion of the fuselage ( 22 ). 
     C8. The method ( 600 ) of paragraph C7 when depending from any of paragraphs C1-C5, wherein the unloading ( 640 ) comprises the opening ( 604 ) the first cargo door ( 30 ) to create the opening in the upper forward portion of the fuselage ( 22 ). 
     C9. The method ( 600 ) of paragraph C8, wherein, after the opening ( 604 ) the first cargo door ( 30 ), the unloading ( 640 ) further comprises unloading ( 642 ) the cargo ( 200 ) from the aircraft ( 10 ) through the opening in the upper forward portion of the fuselage ( 22 ). 
     C10. The method ( 600 ) of any of paragraphs C6-C9, wherein the unloading ( 640 ) further comprises pulling the cargo ( 200 ) upwards and forwards out of the cargo hold ( 28 ). 
     C11. The method ( 600 ) of paragraph C10, wherein the pulling comprises sliding the cargo ( 200 ) upwards and forwards out of the cargo hold ( 28 ). 
     C12. The method ( 600 ) of any of paragraphs C10-C11 when depending from paragraph C5, wherein the pulling further comprises powering the conveyor system ( 170 ). 
     C13. The method ( 600 ) of any of paragraphs C-C12, wherein the unloading ( 640 ) further comprises unloading ( 644 ) the cargo ( 200 ) through a bottom ( 26 ) of the fuselage ( 22 ). 
     C14. The method ( 600 ) of paragraph C13, wherein the unloading ( 644 ) the cargo ( 200 ) through the bottom ( 26 ) of the fuselage ( 22 ) comprises opening a cargo unloading door ( 50 ) positioned on the bottom ( 26 ) of the fuselage ( 22 ). 
     C15. The method ( 600 ) of paragraph C14, wherein the opening the cargo unloading door ( 50 ) comprises powering a motorized door opening mechanism ( 58 ). 
     C16. The method ( 600 ) of any of paragraphs C-C15, further comprising loading ( 620 ) a power source ( 146 ) into the fuselage ( 22 ). 
     C17. The method ( 600 ) of paragraph C16, wherein the loading ( 620 ) the power source ( 146 ) is performed after the loading ( 602 ) the cargo ( 200 ) on to the aircraft ( 10 ). 
     C18. The method ( 600 ) of any of paragraphs C16-C17, wherein the loading ( 620 ) the power source ( 146 ) further comprises coupling the power source ( 146 ) to one or more of the fuselage ( 22 ) and a ramp structure ( 40 ) positioned forward of the cargo hold ( 28 ). 
     D. A method ( 700 ) for loading and/or unloading cargo ( 200 ) onto and/or from an aircraft ( 10 ), the method ( 700 ) comprising: 
     receiving ( 702 ) cargo ( 200 ) through a first cargo door ( 30 ) positioned on a top ( 25 ) of a fuselage ( 22 ) of the aircraft ( 10 ); and 
     unloading ( 712 ) the cargo ( 200 ) through a cargo unloading door ( 50 ) positioned on a bottom ( 26 ) of the fuselage ( 22 ) of the aircraft ( 10 ). 
     D1. The method ( 700 ) of paragraph D, further comprising landing ( 706 ) on a landing surface ( 210 ) prior to the receiving ( 702 ) the cargo ( 200 ). 
     D2. The method ( 700 ) of any of paragraphs D-D1, further comprising opening the first cargo door ( 30 ) prior to the receiving the cargo ( 200 ). 
     D3. The method ( 700 ) of any of paragraphs D-D2, wherein the unloading ( 712 ) comprises opening ( 714 ) the cargo unloading door ( 50 ). 
     D4. The method ( 700 ) of paragraph D3, further comprising maintaining ( 716 ) the cargo unloading door ( 50 ) open and lifting off from the landing surface ( 210 ) after unloading ( 708 ) the cargo ( 200 ). 
     E. A method of enhancing operational efficiency of an aircraft ( 10 ), comprising: 
     using pusher rotors ( 100 ) and puller rotors ( 120 ), wherein the puller rotors ( 120 ) are positioned rearward of the pusher rotors ( 100 ) relative to an airframe ( 20 ) of the aircraft ( 10 ). 
     E1. The method of paragraph E1, further comprising the method of any of paragraphs C-D4. 
     E2. The method of any of paragraphs E-E1, wherein the aircraft ( 10 ) is the aircraft ( 10 ) of any of paragraphs A-B43. 
     F. The use of the aircraft ( 10 ) of any of paragraphs A-B43. 
     As used herein, the terms “adapted” and “configured” mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms “adapted” and “configured” should not be construed to mean that a given element, component, or other subject matter is simply “capable of” performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function. It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, subject matter that is recited as being configured to perform a particular function may additionally or alternatively be described as being operative to perform that function. 
     As used herein, the term “and/or” placed between a first entity and a second entity means one of (1) the first entity, (2) the second entity, and (3) the first entity and the second entity. Multiple entries listed with “and/or” should be construed in the same manner, i.e., “one or more” of the entities so conjoined. Other entities optionally may be present other than the entities specifically identified by the “and/or” clause, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising,” may refer, in one example, to A only (optionally including entities other than B); in another example, to B only (optionally including entities other than A); in yet another example, to both A and B (optionally including other entities). These entities may refer to elements, actions, structures, steps, operations, values, and the like. 
     The various disclosed elements of apparatuses and steps of methods disclosed herein are not required to all apparatuses and methods according to the present disclosure, and the present disclosure includes all novel and non-obvious combinations and subcombinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define independent inventive subject matter that is separate and apart from the whole of a disclosed apparatus or method. Accordingly, such inventive subject matter is not required to be associated with the specific apparatuses and methods that are expressly disclosed herein, and such inventive subject matter may find utility in apparatuses and/or methods that are not expressly disclosed herein.