Abstract:
An airship ( 100 ) for conveyance through a fluid medium in a selected direction of travel. The airship includes a hull adapted to contain a lifting medium therein, wherein the hull ( 108 ) includes a first section having a width which varies along the selected direction of travel, the width increasing from a bow of the hull to a maximum width and decreasing from the maximum width to a tail section of the first section; and a second section coupled to the first section and having a width which varies along the selected direction of travel, the width increasing from a leading edge of the second section to a maximum width and decreasing from the maximum width to a stern of the hull.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation of application Ser. No. 10/389,014, filed Mar. 12, 2003, now U.S. Pat. No. 6,837,458, issued on Jan. 4, 2005, the disclosure of which is hereby expressly incorporated by reference. 

   FIELD OF THE INVENTION 
   The present invention pertains to airships, and more particularly, to airships utilizing a lifting gas as a lifting source. 
   BACKGROUND OF THE INVENTION 
   Airships have long been known and used as a means of conveyance, surveillance, and entertainment. In one common form of an airship, an elongate ellipsoidal shaped bladder is used to suspend a gondola housing crew, equipment, etc., thereunder. This airship is a non-rigid lighter than air craft commonly referred to as a “blimp.” Although previously developed airships are effective in accomplishing their intended purpose, they are not without their problems. For instance, in ellipsoidal airships, many attachment mechanisms are coupled to the exterior of the ellipsoidal lift bladder to couple the lifting force of the bladder to the gondola. These attachment mechanism increase the drag of the airship, thus decreasing its efficiency. 
   Further, propulsion sources are exposed to the main air stream, thus increasing drag. Further still, the airship has a horizontally oriented lifting bladder defining a large footprint. Such a large footprint increases storage costs and the potential for an accident, as well as increasing landing and takeoff area space requirements. Inasmuch as the lifting bag is horizontally oriented, large forces are required to turn the airship since the horizontal arrangement of the lifting bladder increases the moment of inertia of the airship about a vertical axis. Thus, larger control surfaces, which develop large amounts of drag, are needed. Further, steerage is sluggish due to the large moment of inertia. 
   In the ellipsoidal airship, altitude changes are instigated by manipulating the pitch of the airship. For instance, to rise in altitude, the bow of the airship is elevated relative to the stern, thus providing a tilted attitude of the airship, causing an awkward and uncomfortable environment onboard the airship. Ellipsoidal airships also use semi-rigid to rigid lift bladder designs that are heavy and expensive, wherein loss of balloon pressure often causes severe safety issues. Further, the propulsion sources are often located adjacent to or attached to the gondola. This causes significant safety concerns for manned gondolas, and exposes any occupants to unpleasant noise and vibration. 
   Also, in ellipsoidal airships, the outer skin is typically laminated to enhance the rigidity of the outer skin and to aid in retaining the lifting gas therein. This results in a heavy and expensive outer skin. Further still, previously developed airships only use a single lifting bladder, causing significant safety issues should the single lifting bladder become punctured. Further, the breakdown of the airship requires the dumping of the lifting gas from the lifting bladder, since the lifting bladder is non-removably attached to the gondola. Also, if the propulsion fails in the previously developed ellipsoidal airship, steerage is lost and the airship will drift at the whims of the wind, an inherently dangerous situation. 
   SUMMARY OF THE INVENTION 
   An airship for conveyance through a fluid medium in a selected direction of travel is provided. The airship includes a hull adapted to contain a lifting medium therein. The hull includes a first section having a width which varies along the selected direction of travel, the width increasing from a bow of the hull to a maximum width and decreasing from the maximum width to a tail section of the first section. The hull also includes a second section coupled to the first section and having a width which varies along the selected direction of travel, the width increasing from a leading edge of the second section to a maximum width and decreasing from the maximum width to a stern of the hull. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of one embodiment of an airship formed in accordance with one embodiment of the present invention; 
       FIG. 2  is a perspective view of a series of lift bladders suitable for use in the airship depicted in  FIG. 1 ; 
       FIG. 3  is a cross-sectional view of the airship depicted in  FIG. 1  the cross-sectional cut taken through Section  3 — 3  of  FIG. 1 ; 
       FIG. 4  is a schematic of an outer skin suitable to enshroud the lift bladders depicted in  FIG. 2 ; 
       FIG. 5  is a perspective schematic of the lower portion of the covering depicted in  FIG. 4  showing first and second enclosed spaces; and 
       FIG. 6  is a side view of a structural frame suitable for use in the airship depicted in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1–6  illustrate an airship  100  formed in accordance with one embodiment of the present invention. Referring to  FIG. 1 , the airship  100  generally includes a lift assembly  102 , a propulsion system  104 , a control system  106 , a hull  108 , and a structural frame  110 . The lift assembly  102  includes a plurality of lift bladders  112  coupled to the structural frame  110  and covered by an outer skin  146  to form the hull  108 . The lift bladders  112  are filled with a suitable lifting gas, such as helium, hot air, a partial vacuum, etc., to provide sufficient lift to the airship  100 . The propulsion and control systems  104  and  106  allow the airship  100  to be selectively maneuvered by either a remote or onboard user, all of which will be described in further detail below. The preferred direction of travel is indicated by an arrow identified by reference numeral  111 . 
   Referring to  FIGS. 1 and 2 , the lifting assembly  102  includes a plurality of lift bladders  112 . In the illustrated embodiment, five lift bladders  112 A,  112 B,  112 C,  112 D, and  112 E are utilized. Each lift bladder  112  includes an outer skin  113  defining an elongate hollow cylindrical inner cavity adapted to receive a suitable lifting gas therein. The outer skin  113  of each of the illustrated lift bladders  112  is formed from a flexible material resistant to lifting gas migration therethrough, such as synthetic fabrics, one suitable example being a polyester film sold under the trademark MYLAR®, manufactured by DuPont Teijin Films, U.S. Limited Partnership, Barley Mill Plaza, Bldg. 27, Lancaster Pike &amp; Route 141, P.O. Box 80027, Wilmington, Del. 19880-0027, USA. The fabric may be metalized to improve gas retention within the lift bladder  112 . 
   The height and width of each lift bladder  112  is selected to provide a desired lifting force to the airship. More specifically, for a greater lifting force, i.e. cargo carrying capacity, lift bladders  112  having increased heights and/or widths are selected. Moreover, by increasing the heights and/or widths of the lift bladders  112 , the lifting gas carrying capacity of the lift bladders  112  is increased, causing a resultant increase in the cargo carrying capacity of the lifting bladders  112 . 
   Referring now to  FIG. 3 , the diameters of each of the lift bladders  112  are sized to assist in providing an advantageous shape to the hull  108  of the airship  100 . More specifically, the hull  108  of the airship  100  is shaped to resemble a carangifoil adapted for carangiform locomotion. The hull  108  includes a leading section  114  substantially formed by lift bladders  112 A and  112 B, and a trailing section  116 , substantially formed by lift bladders  112 C,  112 D, and  112 E. The leading section  114  has a blunt or rounded nose  118  defined by the curvature of lift bladder  112 A and a rounded trailing edge  120  defined by the curvature of lift bladder  112 B. The trailing section  116  has a rounded nose  122  defined by the curvature of lift bladder  112 C, and a pointed trailing edge  124  defined by a tail section  126 , the shape of the tail section  126  defined by the structural frame as will be discussed in further detail below. 
   The shape of the airship  100  is thus formed by selectively choosing the diameters of each lift bladder  112 .More specifically, it has been found that the leading lift bladders  112 A and  112 C of each leading section  114  and  116  may have a suitable diameter that may be determined by dividing the height of lift bladder  112 A or  112 C by a number between about 3.3 and about 6.7, with a preferred value of approximately 5. 
   A suitable diameter for lift bladder  112 D may be determined by dividing the diameter of lift bladder  112 A or  112 C by a number equal to about 2. A suitable diameter for lift bladder  112 E may be determined by dividing the diameter of lift bladder  112 A or  112 C by a number equal to about four. 
   The diameter of lift bladder  112 B may be selected depending on the desired handling characteristics of the airship.Moreover, it has been found that by decreasing the diameter of lift bladder  112 B, the handling characteristics of the airship  100  can be improved, however, due to the smaller diameter of lift bladder  112 B, the lifting capacity of the airship  100  is decreased. Likewise, by increasing the diameter of lift bladder  112 B, the handling characteristics of the airship  100  are slightly decreased, however the lifting capacity of the airship  100  is increased. 
   More specifically, for the preferred embodiment, a suitable diameter of lift bladder  112 B may be approximated by taking the diameter of lift bladder  112 D and adding about one to about three inches, with a preferred diameter selected by adding about two inches to the diameter of lift bladder  112 D. Alternately, the width of the second bladder may be calculated by multiplying the width of the first bladder by a number between about 0.4 and 0.6, with a preferred value of 0.5, and adding about one to three inches, with a preferred value of two inches. 
   For increased lift, at the price of a slight decline in maneuverability, the diameter of lift bladder  112 B may be approximated by multiplying the diameter of lift bladder  112 E by a number between about 0.3 and about 0.7, with a preferred number of approximately 0.5, and adding the diameter of lift bladder  112 B. Alternately, the width of the second bladder may be calculated by multiplying the width of the first bladder by a number between about 0.5 and 0.7, with a preferred value of 0.625. 
   For even further increased lift, at the price of a more pronounced decline in maneuverability, the diameter of lift bladder  112 B may be approximated by taking the diameter of lift bladder  112 D and adding the diameter of lift bladder  112 E multiplied by a number between about 0.7 and 1.3, with a preferred value of 1. Alternately, the width of the second bladder may be calculated by multiplying the width of the first bladder by a number between about 0.6 and about 0.9, with a preferred value of 0.75. 
   Adjacent and aft of lift bladder  112 E is the tail section  126 . The tail section  126  in the illustrated embodiment is a non-buoyant compartment formed by the outer skin  146  engaging the structural frame of the airship  100 . The tail section  126  is defined as the portion of the airship  100  extending aft of lift bladder  112 E to the aft most structure of the stern  130  of the airship  100  (excluding any fin or rudder structures), which in the illustrated embodiment is a stern post  128 . The longitudinal length of the tail section  126  is measured from the aft most portion of lift bladder  112 E to the stern post  128 . The longitudinal length of the tail section  126  is approximated by multiplying the diameter of lift bladder  112 E by a number between about 0.5 and about 1.5, with a preferred value of about 1 (wherein the longitudinal length of the tail section  126  equals the diameter of lift bladder  112 E.) 
   Referring to  FIGS. 1 and 5 , the detailed description will now focus upon the control system  106 . The control system  106  includes an optional tail fin  132 , optional spinner thruster  134 , and the propulsion system  104 . The tail fin  132  is pivotally coupled to the structural frame  110  at the stern  130  of the airship  100  adjacent to the stern post  128 . The tail fin  132  is rotatable about a vertically oriented axis to selectively control the yaw of the airship  100 . In the illustrated embodiment, the tail fin  132  is of about the same height as lift bladder  112 E. The width of a suitable tail fin  132  may be approximated by dividing the diameter of lift bladder  112 E by a number between about 1.5 and about 2.5, with a preferred number of about 2. The operation of the tail fin  132  is well known in the art and substantially identical to that of a rudder of a waterborne ship or airplane, and therefore will not be described further herein for the sake of brevity. 
   The control system  106  includes the spinner thruster  134 . The spinner thruster  134  is operable to create side thrusts upon the airship  100  as to induce yaw, and to a lesser extent roll, to the airship. More specifically, the spinner thruster  134  is adapted to selectively create thrust oriented perpendicular to the centerline of the airship  100  by rotating a propeller  135  about an axis located perpendicular to the centerline of the airship  100 . Inasmuch as the spinner thruster  134  is located in the stern  130  of the airship  100 , any thrust produced by the spinner thruster  134  tends to rotate the airship  100  about a vertical axis passing through the center of mass of the airship  100 . Thus, the spinner thruster  134  acts substantially similar to a stern thruster of a waterborne ship. Further, inasmuch as the spinner thruster  134  is located below a horizontal axis passing through the center of mass of the airship  100 , any thrust produced by the spinner thruster  134  also tends to cause the airship  100  to roll. In the illustrated embodiment, the diameter of the spinner thruster  134  may be approximated as about the diameter of lift bladder  112 E. 
   Although the spinner thruster  134  is located below a horizontal axis passing through the center of mass of the airship  100 , it should be apparent to those skilled in the art that the spinner thruster  134  may be located in alternate locations. For instance, the spinner thruster  134  may be located above or on the horizontal axis passing through the center of mass of the airship  100 . 
   Further, the spinner thruster  134  in the illustrated embodiment may be pivotally coupled to the structural frame  110  of the airship  100  to allow the thrust axis of the spinner thruster  134  to be selectively oriented relative to the airship  100 . Moreover, the spinner thruster  134  is coupled to the airship  100  by a gimbal  155 , such that the spinner thruster  134  may rotate about at least one axis of rotation. In the illustrated embodiment, the spinner thruster  134  is gimbaled so as to rotate about a first axis located parallel to the centerline of the airship  100 . Thus, the thrust axis of the spinner thruster  134  may be selectively oriented to provide side thrust (i.e. left or right thrust), lift thrust, and downward thrust, and combinations thereof. Alternately, the spinner thruster  134  may be gimbaled so as to rotate about a second axis located perpendicular to the first axis, such that the spinner thruster  134  may also provide forward thrust and reverse thrust. 
   The spinner thruster  134  and the tail fin  132  of the control system  106  both permit the airship  100  to turn. Thus, the spinner thruster  134  and the tail fin  132  are redundant in some sense, although it should be noted that the spinner thruster  134  may be used to turn the airship  100  even without the passage of air across the airship  100 , wherein the tail fin  132  requires the passage of air across the airship  100  for operation. Thus, it should be apparent to those skilled in the art that either the spinner thruster  134  or the tail fin  132  may be eliminated without disabling the airship  100  from turning. Further, if turning is not a required characteristic of the airship  100 , then both the spinner thruster  134  and the tail fin  132  may be eliminated. 
   The propulsion system  104  includes a propulsion source  136 . The propulsion source  136  may be any well known propulsion source, a few suitable examples being an electrical or fuel powered propeller, or a jet, turbine, or rocket engine. The propulsion source  136  in the illustrated embodiment is pivotally coupled to the structural frame  110  of the airship  100  to allow the thrust axis of the propulsion source  136  to be selectively oriented relative to the airship  100 . Moreover, the propulsion source  136  is coupled to the airship  100  by a gimbal  154 , such that the propulsion source  136  may rotate about at least one axis of rotation. In the illustrated embodiment, the propulsion source  136  is gimbaled so as to rotate about a first axis located perpendicular to the centerline of the airship  100 . Thus, the thrust axis of the propulsion source  136  may be selectively oriented to provide forward thrust, reverse thrust, lift thrust, and downward thrust, and combinations thereof. 
   Alternately, the propulsion source  136  may be gimbaled so as to rotated about a second axis located perpendicular to the first axis, such that the propulsion source  136  may also provide side thrust. 
   In the airship  100  of the illustrated embodiment, the propulsion source  136  may be located either below lift bladder  112 B as shown in the illustrated embodiment, or above lift bladder  112 B at a location indicated by reference numeral  156 . Alternately, tandem propulsion sources may be utilized with a propulsion source positioned both below and above lift bladder  112 B. If the propulsion source  136  is located above lift bladder  112 B, lift bladder  112 B is shortened in length approximately the diameter of lift bladder  112 B to accommodate the propulsion source  136 . More specifically, the height of lift bladder  112 B is shortened such that the propulsion source  136  may be placed behind, and not above, lift bladder  112 A, such that the propulsion source  136  is mounted in the slipstream behind lift bladder  112 A to minimize drag. 
   The positioning of the propulsion source  136  in the upper location  156 , and positioning of the spinner thruster  134  in an upper location, is preferred in instances wherein the airship  100  is designed to convey humans, as the upper location  156  may provide increased safety by removing the propulsion source from proximity to any occupants. Although specific locations of propulsions sources have been described for the illustrated embodiment, it should be apparent to those skilled in the art that alternate locations of the propulsion sources are within the spirit and scope of the present invention. The lower propulsion source  136  is preferably placed behind, and not below, a forward enclosed space  150  (which will be described in further detail below) such that the propulsion source  136  is mounted in the slipstream behind the forward enclosed space  150  to minimize drag. 
   Referring now to  FIG. 6  and focusing on the structural frame  110  of the airship, the structural frame  110  provides a skeletal framework to tie the various components of the airship  100  together. In the illustrated embodiment, the structural frame  110  includes a lower keel  138  and an upper keel  140  spaced from the lower keel  138 . Both the lower and upper keels  138  and  140  are intersected by the centerline of the airship  100  and are oriented parallel to one another in a generally horizontal orientation. Extending between the lower and upper keels  138  and  140  are a plurality of vertically oriented frame members  142 . The vertical frame members  142  are disposed in the stern  130  of the airship, and more particularly are disposed in the tail section  126  of the airship. The vertical members  142  are coupled to horizontally oriented stringers  144  to provide additional rigidity to the structural frame  110 . The vertical members  142  and the stringers  144  provide the skeletal framework for forming of the shape of the tail section  126 . 
   Referring to  FIGS. 5 and 6 , the upper and lower keels  138  and  140 , in addition to providing rigidity to the airship  100 , provide accessible and convenient locations for securing equipment thereto. For instance, in the illustrated embodiment, both the propulsion source  136  and the spinner thruster  134  are coupled to the lower keel  138 . Likewise, if an upper propulsion source  136  is desired, the upper keel  140  provides a suitable mounting location for securing the propulsion source  136  and the spinner thruster  134  at a location elevated above the lower keel  138 . Further, additional equipment or frame members may be mounted to the lower and upper keels  138  and  140  as desired. For instance, in the illustrated embodiment, a pair of landing wheels  158  are coupled to the lower keel  138  in proximity to the distal ends of the lower keel  138 . 
   Referring to  FIGS. 3–5 , the detailed description will now focus upon the hull  108 . The hull  108  is defined by an outer skin  146  that enshrouds the lift bladders  112 . The outer skin  146  is formed from a flexible covering, such as an organic or synthetic fabric. In one working embodiment, the outer skin  146  is formed from rip-stop nylon. 
   The outer skin  146  enshrouds lift bladders  112 A and  112 B to form the forward or leading section  114 , and enshrouds lift bladders  112 C,  112 D, and  112 E, and the tail section  126 , to form the trailing section  116 . The outer skin  146  extends down from the lift bladders  112  and couples to the lower keel  138 . A substantial portion or all of the lift generated by the lift bladders  112  is transferred to the outer skin  146 , which then transfers the lift to the lower keel  138 . The upper keel is attached to the upper portion (i.e. the top) of the outer skin  146 . The upper keel may provide solely stability to the lift bladders  112 , tying the top portions of the lift bladders  112  to the structural frame  110 . Alternately, the upper keel may be designed to absorb a portion of or all of the lift generated by the lift bladders  112 . 
   The outer skin  146  is further utilized to form substantially enclosed spaces directly underneath the lift bladders  112 . More specifically, as stated above, the outer skin  146  extends down from the lift bladders  112  to the lower keel  138 . Inasmuch as the lower keel  138  is spaced from the bottom end surfaces  148  (See  FIG. 2 ) of the lift bladders  112 , a forward enclosed space  150  and an aft enclosed space  152  are formed. The forward enclosed space  150  is defined by the outer skin  146 , the bottom end surfaces  148  (See  FIG. 2 ) of lift bladders  112 A and  112 B, and the lower keel  138 . The aft enclosed space  152  is defined by the outer skin  146 , the bottom end surfaces  148  of lift bladders  112 C,  112 D, and  112 E, and the lower keel  138 . The enclosed spaces  150  and  152  may be designed to accommodate equipment, cargo and/or passengers as desired by a user. 
   Although the illustrated embodiment depicts enclosed spaces located above the lower keel  138 , it should be apparent to those skilled in the art that enclosed spaces may be located in other locations, such as below the lower keel  138 , or above or below the upper keel  140 . Further, although the illustrated embodiment depicts the enclosed spaces as having a specific shape, it should be apparent to those skilled in the art that the enclosed spaces may take alternate forms, such to be angled, flat, domed, or otherwise shaped to accommodate the needs of the end user. 
   Although the illustrated embodiment depicts an airship utilizing five lift bladders, it should be apparent to those skilled in the art that any number of lift bladders  112  may be used without departing from the spirit and scope of the present invention, including any number greater than one. Further, although the illustrated embodiment depicts the lift bladders as having a cylindrical shape, it should be apparent to those skilled in the art that the lift bladders may be shaped in other forms, such as a shape that more closely matches that of the shape of the hull, such that there is no void located between adjacent lift bladders, or such that the airship is substantially formed from a single lift bladder, the lift bladder closely matching the shape of the hull. 
   While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.