Patent Publication Number: US-2007114325-A1

Title: Tailboom-stabilized VTOL aircraft

Description:
BACKGROUND OF THE INVENTION  
      Vertical Takeoff and Landing (VTOL) aircraft have long been considered desirable because of their ability to hover in flight and transition in and out of flight without a runway, in addition to flying in a horizontal direction. The aircraft&#39;s lift unit or units have propulsors (e.g., rotor, tiltable jet engines) that develop an aggregate aerial motive force. This aerial motive force can be viewed as the combination of a vertical (i.e., countering gravity) and horizontal (i.e., parallel to ground) vector passing through a single point herein called the “center of lift.” For a VTOL aircraft to be stable and controllable in hover or vertical flight, the vertical vector of its aerial motive force must pass through its center of mass.  
      Conventional single-rotor helicopters satisfy this requirement by having their center of mass directly below the rotor. (The number of rotors is typically considered the number of rotor axes, irrespective of whether a given “rotor” contains a single set of blades or a pair of counter-rotating sets.) However, that configuration prevents such an aircraft from tilting its rotor for axial flow in horizontal flight with lift developed by a fixed wing. Instead, it must rely on the rotor&#39;s own inefficient lift in edgewise airflow, with only enough rotor clearance available for a slight tilt to develop some horizontal airspeed.  
      As a compromise, aircraft have been developed that include tiltable rotors on opposite wingtips. This configuration has significant drawbacks, perhaps primarily that the prospect of blade interference with a centerline fuselage limits the diameter of paired co-planar rotors to less than half that of a comparable single rotor. The use of paired smaller diameter rotors hurts efficiency, resulting in a hovering propulsive force that is less than 70% of what a single rotor would produce for comparable engine power, but with over 40% greater downwash velocity.  
      Accordingly, it would be desirable to have a VTOL aircraft that could employ a single rotor for stable vertical flight and hover as well as efficient axial airflow in horizontal flight with lift provided by a fixed wing. It would also be desirable to have a VTOL aircraft, regardless of the type of lift unit employed, with improved control over transition between horizontal flight and vertical or hovering flight.  
     SUMMARY OF THE INVENTION  
      A flying craft according to vanous aspects of the present invention includes a substantially rigid suspension structure having a first end and a second end, a lift unit, and a payload unit. The lift unit includes a nacelle (typically housing one or more engines) and a tailboom, and pivotally couples to the first end of the suspension structure. A payload unit couples to the structure&#39;s second end. Thus the tailboom can pivotally couple with respect to the payload unit, which advantageously permits the tailboom to assume an orientation desirable for a particular mode of flight.  
      According to a particularly advantageous aspect of the invention, the lift unit can employ a rotor as a propulsion subsystem to provide an aerial motive force. In a mode of flight where such force is predominantly countering gravity (vertical flight or hover), the tailboom can hang from the lift unit in an orientation substantially parallel to the suspension structure and minimizing resistance to downwash from the lift unit. During a mode of flight in which the rotor (or other suitable propulsion subsystem) provides an aerial motive force predominantly parallel to the ground (horizontal flight), the tailboom can be orthogonal to the suspension structure, extending rearward in an orientation where it can develop pitching and yawing moments to control and stabilize horizontal flight.  
      In a method of the invention, a payload unit pivotally couples to a lift unit having a propulsion subsystem (e.g., a rotor) and tailboom such that the tailboom and payload unit are free to independently pivot with respect to the lift unit about parallel axes. The lift unit operates in multiple modes during the method. In a first mode, the propulsion subsystem provides an aerial motive force that predominantly counters gravity. In other words, the force has a vertical vector that is larger than any combination of horizontal vectors, given a normal frame of reference with respect to the ground. During at least a portion of this first mode, the tailboom latches to the payload unit in a substantially vertical orientation. At some point with lift provided by a fixed wing, the lift unit transitions to a second mode in which its propulsion subsystem provides an aerial motive force that is predominantly parallel to the ground, i.e., with a smaller vertical vector than combined horizontal vectors. During at least a portion of this second mode, the tailboom is released from the payload unit and is allowed to pivot independently of the payload unit. When released, the tailboom can assume the rearward-extending orientation desirable for horizontal flight.  
      The above summary does not include an exhaustive list of all aspects of the present invention. Indeed, the inventor contemplates that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the detailed description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a flying craft according to various aspects of the present invention in transition between vertical and horizontal modes of flight.  
       FIG. 2  is an exploded perspective view of the flying craft of  FIG. 1 .  
       FIG. 3  is a perspective view of the flying craft of  FIG. 1  in a stowed configuration.  
       FIG. 4  is a perspective view of the flying craft of  FIG. 1  in a deployed configuration before operation of the lift unit.  
       FIG. 5  is a perspective view of the flying craft of  FIG. 1  during initial operation of the lift unit.  
       FIG. 6  is a perspective view of the flying craft of  FIG. 1  during operation of the lift unit hovering above a payload to be transported.  
       FIG. 7  is a perspective view of the flying craft of  FIG. 1  during operation of the lift unit in a vertical mode of flight with the payload of  FIG. 6  in transit.  
       FIG. 8  is a perspective view of the flying craft of  FIG. 1  during operation of the lift unit in a horizontal mode of flight with the payload of  FIG. 6  in transit.  
       FIG. 9  including  FIGS. 9A and 9B  is a cut-away side view of a fastener on the payload unit of the flying craft of  FIG. 2  with the tailboom latched to, and released from, the payload unit.  
       FIG. 10  including  FIGS. 10A, 10B , and  10 C, is a schematic side view of the flying craft of  FIG. 1  during horizontal flight and two stages of transition to vertical flight. 
    
    
     DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS  
      A VTOL flying craft according to various aspects of the present invention employs a tailboom to facilitate efficient, stable flight in both vertical and horizontal modes. As may be better understood with reference to  FIG. 1 , for example, one such flying craft  100  includes a suspension structure  110 , a payload unit  130 , and a lift unit  120  that includes a nacelle  128  and a tailboom  140 . One end  113  of suspension structure  110  pivotally couples to lift unit  120  while an opposite end  115  pivotally couples to payload unit  130 . Lift unit  120  further includes an aerodynamic lift structure  150 .  
      A lift unit according to various aspects of the invention includes any heavier-than-air structure suitable for developing an aerial motive force including an upward component without exerting a corresponding force on any external supporting structure or relying on aerostatic buoyancy. A lift unit can develop such a force from a suitably configured propulsion subsystem, an aerodynamic lift structure, or both. As illustrated in the exploded perspective view of  FIG. 2 , for example, lift unit  120  includes both a rotor  200  mounted on a hub  126  (which extends from one end of nacelle  128 ) and an aerodynamic lift structure  150 .  
      In accordance with various aspects of the invention, a nacelle is a structure, typically having an aerodynamically streamlined outer shell, that serves as a central point of pivotal attachment between a lift unit and a suspension structure, and between a tailboom and other portions of a lift unit. A nacelle typically includes one or more engines, a gearbox, and other structure that the lift unit can employ to drive a propulsion subsystem. However, a nacelle can suitably omit some or all of such structure if desired, e.g., where the propulsion subsystem employs a rotor with tip-mounted jet engines on its blades. As used herein, the term “nacelle” includes an overall structure consisting not just of the outer shell that is typically but not necessarily employed for protection and aerodynamics, but also whatever internal structure is employed to pivotally couple the lift unit to the suspension structure and pivotally couple the tailboom to the remainder of the lift unit.  
      A rotor, which is a particularly advantageous type of propulsion subsystem, can include any configuration of airfoil blades mounted on a hub in a configuration suitable for the blades to rotate on an axis about the hub and thereby generate an aerial motive force parallel to the axis. For example, rotor  200  consists substantially of two sets  210 ,  220  of rotor blades. Set  210  consists of blades  212 ,  214 ,  216  while set  220  consists of blades  222 ,  224 ,  226 . Blade sets  210 ,  220  are independently rotatable about hub  126 , a configuration that permits the sets to rotate in opposite directions and thus neutralize the moment they individually generate about the axis passing through nacelle  128  and hub  126 . Separate turboshaft engines in nacelle  128  drive blade sets  210 ,  220  of rotor  200 .  
      Any structure suitable for supporting a set of rotor blades for rotation about an axis can be employed as a hub. For example, hub  126  includes a pair of coaxial torsional shafts (not shown) and two sets  310 ,  320  ( FIG. 3 ) of latchable pivot couplings. Each torsional shaft couples mechanical energy from a gear box driven by an engine or engines (not shown) inside lift unit nacelle  128  to rotor blade sets  210 ,  220 .  
      Many other types of propulsion subsystems can be suitably employed to develop an aerial motive force including an upward component, including those employed by embodiments 10, 100, 200, and 1600 of commonly owned, co-pending patent application Ser. No. 09/976,348, filed Oct. 12, 2001 by the same inventor as the present application, which is incorporated by reference and referred to herein as the &#39;348 application.  
      Lift structure  150  includes wing panels  152 ,  154 , which pivotally couple to opposite sides of a fixed central airfoil portion  141  of tailboom  140 . Wing panels  152 ,  154  include partial span flaps  155 ,  156  that can deploy for increased lift during transition between vertical and horizontal modes of flight. An aerodynamic lift structure according to various aspects of the invention is not limited to exemplary wing panels  152 ,  154  but can be any structure suitable for developing a significant upward aerodynamic force, as appropriate for the particular aircraft&#39;s purposes, upon passing horizontally through a fluid medium, typically ambient air. Examples of other aerodynamic lift structures include those employed by embodiments 10, 100, 200, and 6800 of the &#39;348 application.  
      Rotor  200  acts in a gyrodynamically neutral fashion while generating an aerial motive force, powered by a suitable converter of fuel (or any other suitable source of stored energy, e.g., a battery) into mechanical energy. With such neutrality, an aircraft has improved pitch and yaw control in vertical flight. Gyrodynamic theory predicts that a gyroscope, when acted upon by a moment, will move through an angular displacement at a right angle to the applied moment. One method to neutralize this effect is to place a second gyroscope on the same axis as the first gyroscope, with the gyroscopes spinning at the same rate in opposite directions. Employing this method, the operation of blade set  220  rotating counter to blade set  210  is for practical purposes gyrodynamically neutral. Unlike a gyroscopic rotor comprised of a single set of blades, a gyrodynamically neutral system does not distort the effects of pitching and yawing moments. Freedom from such distortion improves pitch and yaw control.  
      As may be better understood with reference to  FIG. 2 , tailboom  140  of exemplary flying craft  100  pivotally couples to lift unit  120 , at about the midpoint of the upper side of lift unit nacelle  128 , by mechanical structure not shown. Suitable structure for such coupling includes, for example, a hinge at the leading edge of central airfoil  141 .  
      Pivotal coupling between tailboom  140  and lift unit  120  is not strictly necessary for tailboom  140  to have the desirable capability of orienting in the vertical direction for vertical flight and extending horizontally for horizontal flight because tailboom  140  is free to pivot (together with lift unit  120 ) with respect to payload unit  130 . However, tailboom  140  is capable of various orientations with respect to rotor  200  when pivotally coupled to lift unit  120 . As illustrated in  FIG. 1 , for example, tailboom  140  can extend mostly horizontal from lift unit  120  when rotor  200  ( FIG. 2 ) is oriented somewhat vertically but producing a mostly horizontal air stream due to horizontal flight of craft  100 . Another benefit of pivotal coupling between tailboom  140  and lift unit  120  is that, as illustrated in  FIGS. 3-4 , nacelle  128  can be oriented vertically alongside payload unit  130  with tailboom  140  and suspension structure  110  oriented substantially horizontal between nacelle  128  and payload unit  130 .  
      Lift unit  120  includes landing gear  229  ( FIG. 2 ) that supports lift unit  120  when craft  100  is in a stowed configuration, as further discussed below with reference to  FIG. 3 . Landing gear  229  can be, e.g., a set of wheels having sufficient dimensions and structural integrity to support weight of lift unit  120 , or a fixed structure designed to fit into a mated receptacle.  
      A suspension structure according to various aspects of the invention includes any structure suitable for suspending a payload unit from a lift unit. For example, suspension structure  110  includes a pair of tensile members  112 ,  114  that are fabricated from suitable materials (e.g., carbon graphite) in a suitable structural configuration (e.g., extruded hollow-core piping with aerodynamic cross-section, optionally including fuel pipes and mechanical and/or electrical power and control cables) to suspend payload unit  130  and payload  190  from lift unit  120  during all expected flight conditions of craft  100 .  
      In exemplary flying craft  100 , lift unit  120  couples to payload unit  130  through a suspension structure  110  that is rigid. Rigidity of tensile members  112 ,  114  helps maintain structural integrity of craft  100  in its stowed and initial deployment configurations. As discussed below, those configurations are illustrated in  FIGS. 3 and 4 , respectively. Suspension structures according to various aspects of the invention can have many advantageous variations, as may be better understood with reference to paragraph 96 (yaw control) and paragraphs 104-105, 107, 111-112, 128-130, and 135 (damped elastic structure) of the &#39;348 application.  
      Advantageously, a suspension structure of a vertical lift flying craft according to various aspects of the invention can pivotally couple to a lift unit about one axis while being constrained from rotation about the two orthogonal axes. By permitting rotation about one axis and restricting rotation about the others, such a configuration permits movement of a suspended payload unit within a common plane with the lift unit while preventing the payload unit from substantial lateral deviations outside that plane. For example, bearings  127  at end  115  of suspension structure  110  permit fore and aft movement of payload unit  130  but restrict sideways movement. Thus, the plane of permissible movement is parallel to the direction of horizontal flight, and flying craft  100  enjoys roll stability as a result.  
      As illustrated in  FIG. 2 , lift unit  120  has bearings  127  mounted on sides of its nacelle  128  that pivotally couple to the top ends of tubes  112 ,  114 . In addition, payload unit  130  includes bearings  137  that pivotally couple to the bottom terminations of tubes  112 ,  114 . Thus lift unit  120  suspension pivotally couples to end  115  of suspension structure  110 , while payload unit  130  pivotally couples to the opposite end  113  of suspension structure  110 .  
      Pivoting between structural members, in accordance with various aspects of the invention, employs any type of structure that permits axial rotation between two members while transferring lateral forces from one member to another. One example of such structure is a conventional bearing that includes a first member that is (or includes) at least one shaft and a second member coupled to the first member such that the shaft is free to rotate but not move laterally with respect to the second member. Another example is shown as element 102 in FIG. 4 of the &#39;348 application and accompanying text. Other types of pivot structures include ball-and-socket arrangements and lengths of flexible cable.  
      Exemplary payload unit  130  further includes: a roof  132  with fairings  131  on each side; a crew compartment  134 ; upper truss members  136 ; lower truss members  135 ; a forward end cap  138 ; an aft end cap  139 ; and a payload stabilizing structure  133 . The weight of a 20-foot standard cargo container is carried from the four comers of its base, through the lower truss members  135 , to the upper truss members  136 , and up through the suspension structure  110  ( FIGS. 6-8 ). Crew compartment  134  includes a clear canopy for pilot visibility and suitable seating, controls, and environmental comfort systems (not shown) for one or more crew members. Truss members  135  and  136  can fold upward and into fairings  131  in the underside of roof  132  when not in use.  
      Some of the many possible alternative embodiments that can be constructed and operate according to various aspects of the invention include unmanned flying craft of any suitable size (e.g., smaller than a typical human), manned or unmanned flying craft dimensioned to carry more than one cargo container as payload, flying craft configured to carry a number of passengers, and flying craft containing a payload that is an integral part of its payload unit or carried inside an enclosure of the payload unit.  
      An exemplary method for flying craft  100  to transport payload  190  may be better understood with reference to the sequence of FIGS.  3 - 4 - 5 - 6 - 7 - 1 - 8 .  
       FIG. 3  illustrates flying craft  100  (with a partially cut-away view of wing panel  152 ) before any flight takes place in the exemplary method. Sets  310 ,  320  of latchable pivot couplings are mounted between the blades of sets  210 ,  220 , respectively, and hub  126  so that the blades can orient parallel to tailboom  140  for the compact stowage configuration illustrated. In an exemplary configuration, rotor  200  ( FIG. 2 ) has a radius of about 40 ft. while tailboom  140  and suspension structure  110  each have a length of about 40 ft. The benefit of these dimensions is apparent when it is noted that craft  100  rests in a diagonal “corner-to-corner” orientation on a standard naval weapons elevator  330  measuring 44 by 50 ft. Lift unit  120  rests on the support surface (elevator  330 ) alongside payload unit  130 , and is held upright by tailboom  140 , which is pivotally latched to the payload unit  130 .  
      Another benefit arises from the radius of rotor  200  being slightly less than the length of suspension structure  110 . In that case, the rotor can advantageously mount close to the pivotal coupling (nacelle  128 ). As illustrated in  FIG. 8 , in that case, operating rotor  200  sweeps nearly the largest possible area, and thus has the greatest possible efficiency, without tips of the rotor blades hitting payload unit  130  in a horizontal mode of flight.  
       FIG. 4  illustrates flying craft  100  after deployment from the stowed configuration of  FIG. 3  but with lift unit  120  not yet operational, still supported by landing gear  229  and held upright by tailboom  140 . Blades  212 ,  214 ,  216  and blades  222 ,  224 ,  226  are fully deployed, the blades of each set extending equispaced about hub  126 . As would be expected for a counter-rotating coaxial rotor, blades in the two sets have opposite chord profiles, an example of which  FIG. 4  illustrates with blades  214 ,  220 . Wing panels  152 ,  154  hang from their pivotal attachments to central airfoil  141  at their lowest gravitational potential. Payload stabilizing structure  133  is tilted rearward, ready to hang down at the back of payload unit  130  to stabilize it during horizontal flight.  
      The method of operation of flying craft  100  proceeds, as may be better understood with reference to  FIG. 5 , with lift unit  120  moving away from support surface  420  and about payload unit  130  in an arc  510  until it begins to suspend payload unit  130 . This initial motion of lift unit  120  is made possible in the exemplary embodiment by pivotal coupling between payload unit  130  and end  113  of suspension structure  110  and pivotal coupling between tailboom  140  and lift unit  120 . When tailboom  140  is latched to payload unit  130  during this motion, as is preferred, tailboom  140  contributes to the structural integrity of the mechanical connection between lift unit  120  and payload  130  as lift unit  120  moves in arc  510 . (The overall structure is akin to a parallelogram.)  
       FIG. 6  illustrates flying craft  100  hovering above payload  190  with lift unit  120  operating in the vertical mode, generating a predominantly gravity-countering aerial motive force. Tailboom  140  is suitably latched to payload unit  130  in a substantially vertical orientation. The deviation of tailboom  140  from vertical is only about five degrees in the configuration of  FIG. 6 . In this configuration, tailboom  140  can cooperate with suspension structure  110  to support any forces of lift unit  120  that push down on or shear across payload  190  when craft  100  descends onto it. At that point, upper support trusses  136  rotate to extend from recesses in roof  132 . When payload unit  130  is to contact a sensitive external load such as containerized fuel, both flying craft  100  and the external load can be grounded before payload unit  130  contacts the load.  
      In an alternative method, craft  100  can rest on or suspend from a suitable support before taking off, in a position similar to that shown in  FIGS. 4-6 , allowing payload  190  to be mounted on payload unit  130  before craft  100  begins flight. FIGS. 27-32, 41-45, and 50-52 of the &#39;348 application illustrate examples of such structure.  
      End caps  138 ,  139  include aerodynamic streamlining structure suitable for the fore and aft ends, respectively, of payload  190 . Any structure suitable for decreasing wind resistance of payload  190  during horizontal flight of flying craft  100  can be employed. For example, end caps  138 ,  139  can be fabricated from elastic sheets reinforced by internal ribs. Alternatives include inflatable structures filled with compressed air from an internal pump or ambient air collected in a way that exploits pressure differential between moving and still fluid bodies.  
      Any suitable type of fastener can be employed to latch a tailboom to a payload unit in accordance with various aspects of the invention. Such a fastener can be located near the end of the tailboom, making mechanical connection directly to the payload unit. Alternatively, the fastener can be at or near a pivot point between the tailboom and payload unit. As may be better understood with reference to  FIGS. 9A and 9B , flying craft  100  employs a faster  900  at the aft end of crew compartment  134  on payload unit  130 .  
      Fastener  900  includes an overhanging pedestal  910 , which can attach with suitable fasteners, integral construction, etc. to (1) roof  132  of payload unit  130  ( FIG. 2 ) at bottom  912  of pedestal  910 , or (2) the aft end of crew compartment  134  at back side  914  of pedestal  910 , or (3) both. Pedestal  910  supports a cam  920  that is ratchet-mounted on a shaft  930 , which mounts athwart payload unit  130 . Cam  920  readily moves clockwise, from the orientation illustrated in  FIG. 9A  (nubs extending downward and aft) to the orientation illustrated in  FIG. 9B  (nubs extending forward and downward). A ratchet (not shown) prevents cam  920  from moving counterclockwise except when a suitable actuator (not shown) releases cam  920 .  
      As illustrated  FIG. 7 , the bottom end of tailboom  140  includes a crosspiece  720  that connects aft ends of empennage booms  142 ,  144  together. In latching operation of fastener  900 , as illustrated in the sequence of  FIGS. 9A-9B , crosspiece  720  pushes cam  920  in a clockwise direction and secures between a downward-pointing nub of cam  920  and an interior wall of pedestal  910 . When thus secured, crosspiece  720  keeps tailboom  140  latched to payload unit  130 . An actuator (not shown) can release cam  920 , under computer or operator control, to rotate counterclockwise about shaft  930  and release tailboom  140  from payload unit  130 , thereby allowing tailboom  140  to pivot independently of payload unit  130 .  
      Regardless of the particular type of fastener employed, latching the tailboom to the payload unit fixes it in an orientation substantially parallel to suspension structure  110 . This configuration prevents the tailboom from repeatedly banging against the payload unit during lateral movements of the flying craft. It also permits suspension structure  110  and tailboom to mechanically cooperate in supporting forces of the lift unit when the tailboom is resting on a surface. Furthermore, with a forward center of gravity in payload  190 , pivotally latched tail  140  is pushed up towards lift unit  120 . A limit on forward center of gravity of an acceptable payload can be imposed to assure sufficient rotor pitch-up control authority in vertical flight mode, balancing the nose-down moment produced by pivotally latched tailboom  140 .  
      When the tailboom is not latched to the payload unit, it can be left free to rotate, within an angular range, about a rotational axis that is orthogonal to an axis passing through the first and second ends of suspension structure  110 . Exemplary lift unit  120  includes an actuator (not shown) that is coupled via tilt boom  143  to pivot tailboom  140  with respect to nacelle  128 . As may be better understood with reference to  FIGS. 11-13 . Another benefit of pivotal coupling between tailboom  140  and lift unit  120 , discussed below with reference to the sequence of FIGS.  10 A- 10 B- 10 C, is that an actuator (not shown) at the couple can effect tilt of rotor  120  and initiate a transition from horizontal to vertical flight.  
      As discussed above with reference to  FIG. 10C , flying craft  100  can move horizontally even in a vertical mode of flight, though not with the efficiency and speed of horizontal flight mode. For example,  FIG. 7  illustrates flying craft  100  in a vertical mode of flight with payload  190  attached to payload unit  130 , and with craft  100  moving horizontally at a modest speed. During the vertical mode of flight, tailboom  140  can hang from lift unit  120  in an orientation substantially parallel to suspension structure  110 , as illustrated in  FIG. 6 . This configuration minimizes resistance to downwash from lift unit  120 .  
      Payload stabilizing structure  133  hangs down at the aft end of payload unit  130 , in a position to interact with an airstream resulting from forward motion of craft  100  (represented by arrow  710 ) and thus stabilize pitch and yaw of payload unit  130 , e.g., as discussed below. The airstream also pushes back (a) tailboom  140 , which at this point may freely pivot with respect to payload unit  130 , and (b) wing panels  152 ,  154  of aerodynamic lift structure  150 , which thus begin to assume an operating position extending substantially orthogonal from tailboom  140 . Advantageously, no actuator is needed to move wing panels  152 ,  154  into position, though one can be employed if desired.  
       FIG. 1  illustrates flying craft  100  during transition between the vertical mode of flight illustrated in  FIG. 7  and the horizontal mode of flight illustrated in  FIG. 8 . At this point, aerodynamic lift structure  150  is fully in its operating position and is developing a substantial portion of the lifting force generated by lift unit  120 . In a particular example, horizontal speed at transition is about 122 knots.  
       FIG. 8  illustrates flying craft  100  in a fully horizontal mode of flight. In this mode, aerodynamic lift structure  150  efficiently generates most of the lifting force from lift unit  120  to keep craft  100  airborne. Except for minor upward force from any slight upward pitch of lift unit  120 , rotor  200  serves strictly as a horizontal propulsion device to (a) pull aerodynamic lift structure  150  through the air so that structure  150  can generate lift and (b) move flying craft  100  to its destination. In a particular example, horizontal speed in horizontal flight mode is about 312 knots.  
      As discussed above, lift unit  120  couples to suspension structure  110  pivotally around bearings (not shown) at upper end  115  of suspension structure  110 . Consequently, lift unit  120  can assume either a vertical or horizontal orientation. Flying craft  100  can thus operate in a vertical mode of flight in which lift unit  120  generates a vertical aerial motive force predominantly opposing gravity, or a horizontal mode of flight in which lift unit  120  generates an aerial motive force predominantly parallel to the ground.  FIG. 1  illustrates flying craft  100  in a transition between the two modes.  
      During the vertical mode of flight, tailboom  140  can be substantially orthogonal to suspension structure  110 , as illustrated in  FIG. 8 . In that configuration, tailboom  140  extends rearward in an orientation where it can develop pitching and yawing moments to control and stabilize horizontal flight and where it can counteract a moment produced by aerodynamic lift structure  150 .  
      A tailboom according to various aspects of the invention includes any structure suitable for interacting with an airstream at one end to develop a moment about an opposite end. Interaction with an airstream can take place passively, with movable control surfaces or fixed airfoils. Alternatively or in addition, airstream interaction can employ one or more active generators of aerial motive force, e.g., a tail rotor. As may be better understood with reference to  FIG. 2 , for example, tailboom  140  is of a type that employs vertical stabilizers with rudders and a horizontal tail to passively interact with an airstream, which results from downwash produced by rotor  200  or horizontal flight of craft  100 , or both.  
      A control surface according to various aspects of the invention includes any stabilizer, aileron, elevator, rudder, tail, or trimming device that can be suitably employed to influence roll, pitch, or yaw of a flying craft. For example, tailboom  140  includes vertical stabilizers  146 ,  148  with rudders  145 ,  147  and a horizontal tail  149  mounted atop vertical stabilizers  146 ,  148 . Tail  149  has an elevator  410  ( FIG. 4 ) with a 30% chord partially spanning it. Tailboom  140  further includes two empennage booms  142  ( FIG. 2 ) and  144  ( FIG. 4 ) to which vertical stabilizers  146 ,  148 , respectively, are attached.  
      The operation of tailboom  140  to counteract moment produced by aerodynamic lift structure  150  may be better understood with reference to  FIG. 8 , which illustrates flying craft  100  in horizontal flight. Wings  152 ,  154  of aerodynamic lift structure  150  (best seen in  FIG. 2 ) generate lift due to forward motion of craft  100 , which results from aerial motive force from lift unit  120  that is predominantly parallel to the ground (not shown). As with the aerial motive force that lift unit  120  generates in hover, lifting force from aerodynamic lift structure  150  can be viewed as a vertical vector  810  passing through a point herein called the “center of lift.” This point is displaced slightly aft of end  115  of suspension structure  110 , where lift unit  120  pivotally couples to suspension structure  110 .  
      The weight of payload unit  130  with captured payload  190  imparts a downward force  820  on suspension structure  110 , which lifting force from aerodynamic lift structure  150  opposes to keep craft  100  airborne. The horizontal displacement between the center of lift from structure  150  and the pivot point of end  115  of suspension structure  110  results in a moment  830  about the point, which acts to pitch craft  100  downward.  
      Elevator  410 , located on horizontal tail  149  of tailboom  140  and illustrated in  FIG. 4 , can orient slightly upward or downward (e.g., plus or minus 20 degrees) with respect to tail  149 . To counteract the downward-pitching moment from aerodynamic lift structure  150 , elevator  410  can orient upward and interact with the airstream resulting from forward motion of craft  100  to develop an opposing, upward-pitching moment  840 .  
      As may be better understood with reference to the sequence of FIGS.  10 A- 10 B- 10 C, flying craft  100  can employ an actuator (not shown) at the pivotal couple (not shown) between tailboom  140  and nacelle  128  to tilt rotor  200  and transition from a horizontal mode of flight (as in  FIGS. 8, 10A ) to a vertical mode of flight with some horizontal velocity (as in  FIGS. 7, 10C ). During the horizontal mode of flight ( FIG. 10A ), tail  149  of tailboom  140  advantageously interacts with the airstream from horizontal motion of flying craft  100  to counteract a downward-pitching moment from aerodynamic lift structure  150  with an upward-pitching moment of its own, as discussed above.  
      To initiate a transition to vertical flight mode, the actuator applies a counterclockwise (from the observer of  FIG. 10B ′ sperspective) moment to tailboom  140  relative to nacelle  128  while elevator  410  ( FIG. 4 ) adjusts slightly to increase its upward-pitching moment. The result is that tailboom  140  maintains its orientation with respect to the ground (not shown) and nacelle  128  rotates clockwise with respect to tailboom  140 , bringing rotor  200  into a vertical orientation. As illustrated in  FIG. 10C , flying craft  100  can move in a horizontal direction in vertical flight mode with rotor  200  tilted slightly forward and tailboom  140  trailing behind where tail  149  can influence pitch and rudders  145 ,  147  ( FIG. 2 ) can influence yaw.  
      In the schematic view of  FIG. 10 , nacelle  128  can also be understood as the center of gravity of craft  100 . The aerial motive force normal to the plane of rotor  200  passes through this center of gravity. Nacelle  128  is preferably locked under aerodynamic lift structure  150  when wing panels  152 ,  154  ( FIG. 2 ) are at 10% mean aerodynamic chord.  
      Advantageously, payload unit  130  imparts lateral stability to flying craft  100  by suspending from lift unit  120  with rotation restricted about one axis. In this suspended configuration, payload  190  increases the moment of inertia in the plane that includes parallel members  112 ,  114  ( FIG. 2 ). As a result, suspended payload  190  increases stability about the axis normal to that plane.  
      The force of gravity tends to position payload unit  130  beneath lift unit  120 , which lowers the center of gravity and increases pendular stability. This behavior conforms to accepted aircraft design theory, which holds that pendular stability (also known as lateral stability or roll stability) increases for “high wing” airplanes having a low center of gravity. Contrary to some conventional teachings, enhancement of pitch stability of lift unit  120  is not primarily due to the addition of suspension structure  110  and payload unit  130 . Instead, the mass of payload unit  130  is believed to behave in pitch like a point mass at the axis of rotation. Pitch stability and control of lift unit  120  are thus unaffected by the addition of suspension structure  110  and payload unit  130 , while roll or pendular stability in horizontal flight ( FIG. 9 ) and yaw stability in vertical flight ( FIG. 8 ) increase.  
      Various particular features of exemplary flying craft  100  may be better understood with reference to the labeled paragraphs below. In variations where the benefits of these particular features are not required, they may be suitably omitted or modified while retaining the benefits of the various aspects of the invention discussed above. With possible exceptions, structural elements not introduced with a reference numeral are not illustrated in the drawings. Those structural features referenced by number are illustrated in  FIG. 2  unless otherwise indicated.  
      PAYLOAD UNIT—Payload unit  130  is optimized to capture and streamline exemplary payload  190 , which is a 20-foot MILVAN container. Payload unit  130  can be reconfigured in flight to capture and partially streamline a 40-foot ISO container. A winch is located below crew compartment  134  for attaching slung cargo. A special MILVAN with containerized fuel, fuel pump, and streamlined bottom can be provided for a self-deployment ferrying operation. The aircraft portion of a recovery assist system is located on either side of payload unit  130  at suspension structure  110  attachment points. Payload unit  130  may also be operated without having an external load.  
      CREW COMPARTMENT—Crew compartment  134  holds one pilot, having dimensions of 4 foot height, 4 foot depth, and 3 foot width. The entire monocoque crew compartment is mounted to payload unit  130  by oleo struts for shock absorption upon landing, and can be jettisoned for emergency egress including parachute recovery with positive buoyancy for ocean recovery. Crew compartment  134  then becomes a self-contained recovery module. Provisions for a remote co-pilot are also provided.  
      GENERAL FLIGHT CONTROLS—Flying craft  100  permits single pilot operation from either crew compartment  134  or a remote operator&#39;s console. Control moments are generated by means of rotor and fixed surface controls, with rotor cyclic control phased out as craft  100  converts from a vertical to a horizontal mode of flight. The conversion and power management systems are designed for straightforward cockpit procedures. All normal and emergency procedures can be controlled by a single pilot.  
      COCKPIT CONTROLS—The cockpit controls indude a longitudinal/lateral stick, a collective-type power lever, and pedals for both the pilot and the remote operator. The throttles contain levers that control flaps  155 ,  156  and a blade-pitch governor hand-wheel for manual override of the rotor governor. A three-position switch on the power lever controls the nacelle conversion angle.  
      ROTOR CONTROLS—In vertical flight mode, pitching moments arise from application of longitudinal cyclic pitch change to blades of rotor  200 , and rolling moments from applying lateral cyclic pitch change. Upward or downward movement of the power lever simultaneously increases or decreases engine power and rotor blade collective pitch to provide vertical thrust control. Differential rotor collective pitch generates yawing moments in vertical flight mode and rolling moments in horizontal flight mode.  
      FIXED CONTROLS—Elevator  410  ( FIG. 4 ) is active in all flight modes. During conversion from a vertical to a horizontal mode of flight, the desired control response is achieved by phasing out the cyclic pitch control as aerodynamic lift structure  150  offloads the rotor, and by phasing differential collective from pedal control to the lateral stick control. Wing panels  152 ,  154  have partial span flaps  155 ,  156 , respectively, for increased lift during conversion.  
      FLIGHT MODE CONVERSION—The conversion system is mounted to the gearbox and active only during conversion between vertical and horizontal flight modes. The system engages with tilt boom  143  to pull nacelle  128  underneath aerodynamic lift structure  150  for horizontal mode, or to gradually release nacelle  128  for vertical mode. The force is provided by redundant linear actuators having hydraulic motors and electrically-powered servo valves. The conversion system disengages with tilt boom  143  when not active. In the event of conversion system failure, an automatic mechanical damper temporarily engages with tilt boom  143  to modulate movement of nacelle  128  into vertical mode.  
      POWER MANAGEMENT—A power management cockpit control consists of a pair of throttles and a power lever. The collective stick-type power levers are located to the left of the pilot and have the same sense of motion as a conventional helicopter collective stick. Following engine start and checkout, each throttle lever is hooked to the power lever. Then, in vertical flight mode, power lever motion simultaneously changes the power setting of the rotors. In horizontal flight mode, however, the power lever only controls. power setting of the engines as the collective pitch input is phased out as a function of nacelle tilt angle. In addition, power management is simplified by the automatic inputs of a rotor collective pitch governor which adjusts to maintain the rotor rpm selected by the pilot.  
      POWER PLANT—Two Rolls-Royce AE  1107  turboshaft engines and a co-axial gearbox are located in nacelle  128 , which is of the centerline type. The co-axial gearbox provides function similar to the gearbox in the Kamov Ka-32A helicopter. Total engine rating is 12,300 HP and transmission rating is 10,209 HP.  
      PAYLOAD UNIT YAW STABILIZATION SUBSYSTEM—Yawing sensors are mounted to suspension structure  110  to provide control information. A feedback loop converts yawing strain on suspension structure  110  into a correcting moment at rudders of payload stabilizing structure  133 , thereby aligning payload unit  130  with lift unit  120  and preventing yaw divergence. The pilot may override the yaw stabilization subsystem with pedal control, or disable it at lower airspeeds with well-behaved external loads.  
      LIFT UNIT GUST AND LOAD ALLEVIATION SYSTEM—During ground mode operations, lift unit  120  is automatically controlled to minimize stress on latched tailboom  140 . Strain sensors mounted on payload unit  130  at the latching fastener measure roll and yaw moments exerted by payload unit  130  on tailboom  140 . A feedback loop to the rotor controls creates an equivalent moment at rotor  200 , releasing strain from tailboom  140 . For high sea states with a rolling deck, rotor  200  follows the rotation of grounded payload unit  130  without stressing tailboom  140 . The pilot may disable lift unit  120  gust and load alleviation system for light external loads, or for calm air with a stable deck.  
      ROTOR RPM GOVERNOR—The rotor RPM governor can be used in all modes to simplify power management. It is a closed loop system that maintains a pilot-selected RPM by controlling collective blade pitch. In vertical flight mode, the collective pitch inputs from the RPM governor are superimposed on the collective pitch inputs from the power lever and the differential collective pitch inputs from the control stick. In horizontal flight mode, the primary collective pitch input comes from the RPM governor as required to maintain pilot selected RPM. This results from the fact that during transition the collective pitch inputs from the power lever are phased out, and only a small amount of differential collective pitch inputs from the control stick are retained in horizontal flight mode for roll control. The pilot can manually override the RPM governor.  
      FUEL SYSTEM—Fuel is supplied to the engines by a lightweight, crash resistant, 4,000 pound capacity fuel cell contained in fixed central airfoil portion  141 . Gravity refueling is accomplished through a filler cap. External fuel is supplied by a special 24,000 pound fuel capacity MILVAN shaped container. Redundant, electrically driven boost pumps located at the lowest point of the container deliver fuel up through a hose in the left side of suspension structure  110  to a fuel cell in engine nacelle  128 . Alternatively, fuel may be pumped using ambient air collected in a way that exploits pressure differential between moving and still fluid bodies. The interface between the special MILVAN and payload unit  130  has quick release fuel connections and quick release electrical connections. The hose in suspension structure  110  has pivoting connections on both ends to allow free pivotal movement at nacelle  128  and at payload unit  130 .  
      HYDRAULIC SYSTEM—Flying craft  100  has three independent transmission driven hydraulic systems. The pump for each system is geared to the rotor side of the transmission clutch so that full hydraulic power can be provided with both engines shut down, as long as the rotors are turning within the normal speed range. The hydraulic systems power the cyclic control, collective control, RPM governor, elevator, and heat exchanger blower.  
      ELECTRICAL SYSTEM—The electrical system consists of dual DC and AC electrical subsystems with sufficient capacity to accommodate peak load requirements with one engine out. A battery is connected to each DC bus during normal operation. The batteries provide self-contained engine-start capability. DC power is delivered to payload unit  130  through a distribution bus within the right side of suspension structure  110 . AC power at payload unit  130  is supplied by two solid-state inverters.  
      ENVIRONMENTAL CONTROL SYSTEM—The environmental control system provides heating, ventilation, air conditioning, window defogging, and crew breathing oxygen for crew compartment  134 . Heating is provided by electric powered heaters. An ambient air-inlet valve enables the introduction of unconditioned air for fresh air ventilation of crew compartment  134 . An electrically powered inlet fan provides the required airflow at all flight conditions. Noise and vibration control structure or equipment can be included as desired.  
      MONOCOQUE STRUCTURES—Wing panels  152 ,  154 , vertical stabilizers  146 ,  148 , rudders  145 ,  147 , horizontal tail  149 , elevator  410  ( FIG. 4 ), and payload stabilizing structure  133 , and crew compartment  134  are of conventional monocoque construction. Booms  142 ,  143 ,  144  are made of rigid tubular metal. Suspension structure  110  is made of high tensile strength composites. Payload unit  130  has high tensile strength upper and lower truss members  136 ,  135  for holding payload  190  ( FIG. 6 ) and lightweight aerodynamic end caps  138 ,  139  for enveloping payload  190  in a streamlined shape.  
      LANDING GEAR—Payload  190  provides its own landing gear. When no load is attached, payload unit  130  supports itself without any special landing gear requirements. Nacelle  128  includes biped landing gear  127  which provides support in rest mode and absorbs shocks in the event of gusts or deck movement while near rest mode. Each leg is rated to support 15,000 pounds.  
      TAIL BOOM AND SUSPENSION STRUCTURE LATCHES—During ground mode and vertical flight mode, tailboom  140  is latched to payload unit  130  at fastener  910  ( FIGS. 9A, 9B ). Transition to forward flight, i.e., horizontal flight mode, begins with shaft  720  released from fastener  910  and tailboom  140  free to rotate with the airstream. When not engaged, fastener  910  reverts to a capture state, as illustrated in  FIG. 9A . In the reverse transition from horizontal to vertical flight mode, fastener  910  recaptures tailboom  140 . Suspension structure  110  can freely pivot with respect to payload unit  130  at bearings  137  ( FIG. 2 ), but its angle with respect to payload unit  130  can be fixed when shaft  720  is released and freed again when the tail latching engages.  
      PAYLOAD UNIT—Payload unit  130  is comprised of load carrying members and aerodynamic members. Pivoting support trusses  136 ,  136  carry the load from the lower corners of the ISO container (payload  190  of  FIG. 6 ) to suspension structure  110 . The aerodynamic members are the roof  132 , payload stabilizing structure  133 , sides, and end caps  138 ,  139 . End caps  138 ,  139  have a pivotal attachment to the lower end of lower truss members  135 , and a screw jack attachment to roof  132 . As the screw jack rotates, the end cap translates over the roof edge and rotates upper support truss members  136 . Each one of end caps  138 ,  139  has latches for holding the ISO container corners. The jack screws and latches are electrically actuated. Accordion siding can unfold with the rotating support truss members  136 . In operation ( FIG. 6 ), flying craft in vertical flight mode lowers payload unit  130  onto payload  190 . Then the screw jacks rotate to lower end caps  138 ,  139 , truss members  135 ,  136 , and siding onto payload  190 . Latches hold end caps  138 ,  139  and members  136  to the comers of the ISO container. After the container is secure, craft  100  lifts and transitions to cruise, i.e., horizontal flight mode ( FIG. 8 ), as end caps  138 ,  139  inflate to a streamlined shape. Flying craft  100  carries payload  190  to its destination and reverses the operation to release payload  190  and rotate end caps  138 ,  139  into a horizontal position for the return flight. Payload unit  130  may be reconfigured in flight to accommodate either a 20-foot or a 40-foot ISO container. Truss members  135  and  136  overlap one another may be extended or retracted in flight. For oversize load operations, a cargo net may be snugged up to the payload unit  130  by the integrated wench. The aircraft portion of the recovery assist system deploys two messenger cables from either side of payload unit  130  at end  113  of suspension structure  110  (attachment points) for recovery onto a container or down to the deck of a ship. Flying craft  100  may self-deploy using a special streamlined MILVAN fuel container.  
      ROTOR—Disk area of rotor  200  is 5,026 square feet. In vertical flight mode, the rotor disk plane is parallel with the roof  132  of payload unit  130 . In horizontal flight mode, the rotor centerline is fixed at 10 degrees below centerline of aerodynamic lift structure  150 , thus providing axial thrust with wing panels  152 ,  154  near maximum lift coefficient. In horizontal flight, the tips of blades in sets  210 ,  220  should clear payload unit  130  by about 1.5 feet. The tips of blades in set  210  and should clear wing panels  152 ,  154  by about nine feet.  
      STRUCTURAL CONFIGURATION AND MATERIALS—The entire craft (again, only in a particular embodiment) has a maximum gross weight of about 74,000 pounds. Three important structural components are the booms  142 ,  143 ,  144 , tailboom  140  as a whole, and suspension structure  110 . Tailboom  140  provides structural support during take-off and landing. During transition from rest mode to grounded vertical flight mode, tailboom  140  is latched to payload unit  130 . Suspension structure  110  provides tensile support in opposition to the compressive support of tailboom  140 , which together form a rigid cantilever arm about the roll axis to absorb rolling and yawing moments due to wind gusts or ship deck movement. Suspension structure  110  provides sufficient tensile strength to support a 37,000 pound payload in vertical flight mode at 150 knots, and support a 30,000 pound payload in horizontal flight mode at 350 knots with appropriate safety margin. The tilt boom has sufficient tensile strength to pull the gearbox underneath the wing during transition to horizontal flight mode, and sufficient rigidity in combination with the booms  142 ,  143 ,  144  to prevent rotor whirl-induced tail flutter. Payload unit  130  has trusses  135 ,  136  of sufficient tensile strength to hold a 40-foot ISO container weighing 37,000 pounds, and sufficient toughness to withstand the impact of lowering the container onto a sea state  5  deck. In horizontal flight mode, fixed central airfoil portion  141  locks down to both the gearbox and folding wing panels  152 ,  154  for increased structural integrity.  
      AUTOROTATION—Rotor  200  has low disk loading and thus can be operated in autorotation mode for reduced descent rate emergency landing. In the event that all power is lost, flying craft  100  can automatically revert to autorotation mode. Blades  212 - 226  of rotor  200  revert to autorotation pitch, a failsafe conversion damper engages, locks of wing panels  152 ,  154  release, and elevator  410  ( FIG. 4 ) rotates up. The oleo struts supporting crew compartment  134  and supporting biped landing gear  127  can be fabricated to withstand the autorotation sink rate at design gross weight.  
      ENGINE SAFETY—Blade sets  210 ,  220  are driven by center mounted engines of proven high reliability. A co-axial gearbox connecting the pair of engines to the pair of blade sets  210 ,  220  allows either engine to power both blade sets in the event of an engine failure. Overrunning clutches in the engine speed reduction gearing can automatically disconnect a failed engine from the drive system, thus allowing the effective use of available power. Single engine performance, stability, and control are similar to two engine operation at low power settings because of the co-axial gearbox in nacelle  128 . Horizontal flight mode and transition can be performed as normal, but single engine hover (vertical flight mode) is then limited to low payload weights. The conversion mechanism is simple and engages natural aerodynamic forces. In the event of complete loss of power, conversion from horizontal to vertical flight mode with autorotation is automatically achieved.  
      SYSTEM SAFETY—Appropriate levels of hydraulic system and electrical system redundancy and safety are included in the design of the aircraft. A pilot caution and warning system can provide visual and/or audible indications of detectable system malfunctions, such as hydraulic system pressure loss, rotor control discrepancies, engine fire, latch failure, etc. Instrumentation will be incorporated to monitor loads and positions at critical locations (such as control linkages, control surfaces, etc.) during flight.  
      Other particular features of exemplary flying craft  100  and variations in the better understood with reference to the contents of www.baldwintechnology.com, which is incorporated herein by reference.  
     PUBLIC NOTICE REGARDING THE SCOPE OF THE INVENTION AND CLAIMS  
      The inventor considers various elements of the aspects and methods recited in the claims filed with the application as advantageous, perhaps even critical to certain implementations of the invention. However, the inventor regards no particular element as being “essential,” except as set forth expressly in any particular claim. For example, a claim calling for an aerodynamic lift structure but not for pivotally coupled wing panels reads on flying craft employing any suitable type of aerodynamic lift structure (e.g., single fixed wing, fabric free wing) regardless of whether the system employs such wing panels or not.  
      While the invention has been described in terms of preferred embodiments and generally associated methods, the inventor contemplates that alterations and permutations of the preferred embodiments and methods will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings. For example, a hub employing a pair of blade pitch control rods surrounding a central shaft, or other open structure, can substitute for hub  126  of  FIG. 2 .  
      Additional structure can be included, or additional processes performed, while still practicing various aspects of the invention claimed without reference to such structure or processes. For example, a rotor can be of a “variable geometry” type that works well in both vertical and horizontal modes of flight, as disclosed in published U.S. patent application Ser. No. 2002/0098087 filed Jan. 23, 2001 by Yuriy and in U.S. Pat. No. 6,019,578 issued Feb. 1, 2000 to Hager et al. and U.S. Pat. No. 6,578,793 issued Jun. 17, 2003 to Byrnes et al., all of which are incorporated herein by reference. (Patents and patent applications incorporated herein by reference may themselves incorporate documents by reference, and such documents are also incorporated herein by reference.) Another example of a “variable geometry” rotor employs blades having multi-element airfoils. The blades include flaps that can extend from to increase surface area during slower vertical-mode operation and retract to permit efficient high-velocity operation in horizontal flight mode, where the rotor is called upon to generate efficient axial thrust. Furthermore, wing panels  152 ,  154  may be removed to lighten the lift unit and increase payload weight for short haul flights in vertical flight mode.  
      Accordingly, neither the above description of preferred exemplary embodiments nor the abstract defines or constrains the invention. Rather, the issued claims variously define the invention. Each variation of the invention is limited only by the recited limitations of its respective claim, and equivalents thereof, without limitation by other terms not present in the claim.  
      In addition, aspects of the invention are particularly pointed out in the claims using terminology that the inventor regards as having its broadest reasonable interpretation; the more specific interpretations of 35 U.S.C. § 112(6) are only intended in those instances where the terms “means” or “steps” are actually recited. For example, the term “ground” is broadly used herein to indicate a portion of the earth&#39;s surface (or, conceivably, the surface of an extraterrestrial body) that is beneath a flying craft, regardless of whether the surface is actually dry land or a body of water. As another example, the term “orthogonal” is used to indicate that two structures are oriented substantially 90° from each other, without requiring an exactly perpendicular orientation or intersection of any axes of the structures.  
      The words “comprising,” “induding,” and “having” are intended as open-ended terminology, with the same meaning as if the phrase “at least” were appended after each instance thereof. A clause using the term “whereby” merely states the result of the limitations in any claim in which it may appear and does not set forth an additional limitation therein. Both in the claims and in the description above, the conjunction “or” between alternative elements means “and/or,” and thus does not imply that the elements are mutually exclusive unless context or a specific statement indicates otherwise.