Abstract:
An airship system having a flexible envelope and at least one bladder positioned therein is described. The bladder(s) provide an impervious barrier between the gas within the bladder(s) and the air exterior to the bladder(s). The envelope includes longitudinal and hoops straps weaved together in a criss-cross manner. The envelope also includes rings positioned thereon that include truss members for receiving struts for removably coupling the airship to another airship. A tri-hull delta dirigible system is also described, comprising three airships coupled together using struts and arranged in an equilateral triangle formation. The tri-hull delta dirigible system has a similar lift capacity (volume) as a conventional large mono-hull dirigible, while minimizing the detrimental bending in the center of the conventional mono-hull dirigible.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application 61/372,286 filed on Aug. 10, 2010, entitled “Tri-Hull Airship”, and is hereby fully incorporated by reference herein for all purposes. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to cargo airships. More particularly, the present invention is directed to a dirigible suitable for the long haul of heavy cargo. 
     BACKGROUND 
     Conventional airships, or dirigibles, are used in a variety of applications, including heavy cargo, surveillance, transportation, and observation. Conventional dirigibles typically include a single hull, or singlet, having an ellipsoid body, or envelope, and a frame. Generally, the efficiency of the dirigibles is dependent on the weight to volume ratio of the singlet. Conventional dirigibles are typically known to be efficient based on their weight to volume ratio, however, the body of singlet has been known to buckle upon lifting of heavy cargo. To eliminate the problem of buckling, additional framing can be added to the upper portion of the body for added strength. However, the additional framing results in the weight of the singlet to increase, thereby requiring an increase in the size of the singlet to maintain efficiency. As a result, conventional single-hull dirigibles having the additional framing and weight would result in the size of the singlet being unfeasibly too large, and could potentially buckle due to its size even with the additional framing. Dual-hull dirigibles also are not feasible options for heavy cargo lift, as they are incredibly unstable since the load would be positioned between the two hulls and any difference in size or weight between the two hulls could cause the dirigible to rotate or invert. 
     Therefore, a need exists for an improved dirigible that is stable and able to withstand long haul of heavy cargo without buckling. 
     SUMMARY 
     The present invention satisfies the above-referenced need by providing an airship having a bladder positioned therein. In one aspect of the invention, the airship includes an outer envelope having a nose end, a tail end opposing the nose end, and a cavity therein. At least two segments having a gas, such as helium gas, are positioned within the cavity of the outer envelope. The segments provide an impervious air barrier for containing the gas therein. The segments can include two or more bladders or a single bladder having multiple sections. In certain embodiments, the segments are constructed from biaxially-oriented polyethylene terephthalate multi-layer films. 
     In another aspect of the invention, the airship includes an outer envelope having a nose end, a tail end opposing the nose end, and a cavity therein. The outer envelope also includes longitudinal and hoop straps that are weaved together in a criss-cross manner. The airship can include multiple rings around the envelope, whereby the longitudinal straps are coupled to each ring by metal hoops. The longitudinal and hoop straps can be constructed from liquid crystalline polymer fibers. At least one bladder having a gas, such as helium gas, is positioned within the cavity of the outer envelope. The bladder(s) provide an impervious air barrier for containing the gas therein. 
     In yet another aspect of the invention, a dirigible of the present invention includes three airships coupled together forming a tri-hull delta configuration. The three airships are positioned parallel to each other along the length of each airship, and are arranged at the apex of an equilateral triangle when coupled together. The airships each include multiple rings that include truss members for coupling to struts, the struts being removably coupled to each airship. In certain embodiments, each ring includes a V-shaped truss member for receiving ends of two struts at a 60 degree angle, and two linear truss member for receiving struts removably therein. Accordingly, the airships can be removably coupled to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description, in conjunction with the accompanying drawings briefly described as follows. 
         FIG. 1A  is a perspective view of a single hull for a dirigible, according to an exemplary embodiment 
         FIG. 1B  is a side cross-sectional view of the single hull of  FIG. 1A , with the bladders removed, according to an exemplary embodiment. 
         FIG. 1C  is an exploded view of the single hull of  FIG. 1A , according to an exemplary embodiment. 
         FIG. 2A  is a perspective view of a ring for surrounding the body of a single hull, according to an exemplary embodiment. 
         FIG. 2B  is a side cross-sectional view of the ring of  FIG. 2A , according to an exemplary embodiment. 
         FIG. 3A  is a partial front view of a body of a single hull coupled to a ring, according to an exemplary embodiment. 
         FIG. 3B  is a partial side view of the body coupled to the ring of  FIG. 3A , according to an exemplary embodiment. 
         FIG. 4A  is a perspective view of a tri-hull dirigible, according to an exemplary embodiment. 
         FIG. 4B  is a side cross-sectional view of the tri-hull dirigible of  FIG. 4A , according to an exemplary embodiment. 
     
    
    
     While the present disclosure is susceptible to various modifications and alternative forms, specific example embodiments thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific example embodiments is not intended to limit the disclosure to the particular forms disclosed herein, but on the contrary, this disclosure is to cover all modifications and equivalents as defined by the appended claims. 
     DETAILED DESCRIPTION 
     The present invention is directed to a dirigible suitable for long haul of heavy cargo. Generally, the dirigible includes a singlet having multiple bladders positioned within, and can have an exterior formed of longitudinal and hoop straps intersecting, or criss-crossing, together. In certain exemplary embodiments, the dirigible includes three singlets coupled together using struts in an equilateral triangular formation. The invention may be better understood by reading the following description of non-limitative, exemplary embodiments with reference to the attached drawings wherein like parts of each of the figures are identified by the same reference characters. 
       FIG. 1A  is a perspective view of a singlet, or hull,  100  for a dirigible,  FIG. 1B  is a side cross-sectional view of the singlet  100  with bladders  116  removed, and  FIG. 1C  is an exploded view of the singlet  100 , according to an exemplary embodiment. Referring to  FIGS. 1A-1C , the singlet  100  includes a generally ellipsoid-shaped soft inflatable envelope or body  102  having a nose end  102   a , a tail end  102   b  opposing the nose end  102   a , and a length L extending from the nose end  102   a  to the tail end  102   b . In certain exemplary embodiments, the tail end  102   b  of the ellipsoid is about 40 percent (%) longer than the front. A nose section  104  is coupled to the nose end  102   a  of the body  102 , and a tail section  106  is coupled to the tail end  102   b  of the body  102 . In certain exemplary embodiments, the nose section  104  and the tail section  106  are constructed from any rigid structural material, such as molded graphite. In certain alternative embodiments, the nose section  104  and the tail section  106  may be constructed from aluminum or titanium, or a composite having a carbon fiber reinforcement. In certain exemplary embodiments, the nose section  104  and tail section  106  provide a means for attaching to longitudinal straps of the body  102 . The singlet  100  also includes rings  200  ( FIGS. 2A-2B ) circumferentially surrounding the body  102 . In certain exemplary embodiments, the singlet  100  includes four rings  200  spaced apart along the length L of the body  102 . In certain exemplary embodiments, each ring  200  is constructed from any rigid structural material, such as a honeycomb graphite epoxy. In certain alternative embodiments, the rings  200  may be constructed from aluminum or titanium, or a composite having a carbon fiber reinforcement. In certain exemplary embodiments, the rings  200  provide a means for attaching to longitudinal straps  302  of the body  102 , as described further with respect to  FIGS. 3A and 3B  below. In certain embodiments, the rings  200  also provide a means for attaching struts  404  ( FIGS. 4A-4B ) for securing the singlet  100  to another singlet. In certain exemplary embodiments, the struts  114  extend from an interior cavity  118  of body  102  to the exterior. 
     Referring to  FIGS. 1B and 1C , the singlet  100  includes a plurality of bladders  116  positioned within the interior cavity  118  of the body  102  to create separate sections within the body  102 . Generally, each bladder  116  is filled with helium gas. In certain exemplary embodiments, the bladders  116  are constructed from a multi-layer impervious film, such as biaxially-oriented polyethylene terephthalate (boPET) multi-layer films. In certain embodiments, the bladders  116  are constructed from a reinforced Mylar®-based laminate, and offers gas permeability, strength and resistance to surface scratches. In certain exemplary embodiments, six flexible cylindrical bladders  116  are positioned within the interior cavity  118 , and take the shape allowed by the straps that form the body  102 . In certain alternative embodiments, a single bladder having a plurality of separate sections therein can be included. Generally, the bladders  116  form an impervious air barrier between the helium gas inside and the outside air. The bladders  116  divide the body  102  into separate volumes, and ensure that if there were to be a leak in one volume or section, the entire singlet  100  would not be subject to failure. In certain exemplary embodiments, the bladders  116  are configured to retain the helium gas, while the straps of the body  102  form the load-bearing component of the singlet  100  and take on the tensile load. In certain exemplary embodiments, the bladders  116  when placed together are sized to be about 10 percent (%) larger than the body  102 . In certain exemplary embodiments, the longitudinal straps  302  and hoop straps  304  ( FIGS. 3A-3B ) form the load bearing component of the singlet  100  while the bladders  116  only retain gas on the interior, but takes no tensile load. In certain exemplary embodiments, the singlet  100  is about 552 feet (ft) long with a largest external body diameter of about 110 ft, and a total weight of about 50 tons. In certain exemplary embodiments, the singlet  100  is designed to carry a 60 ton cargo. 
       FIG. 2A  is a perspective view of the ring  200  surrounding the body  102  of the singlet  100 , and  FIG. 2B  is a side cross-sectional view of the ring  200 , according to an exemplary embodiment. Referring to  FIGS. 2A and 2B , the rings  200  provide a conformal shape to the soft skin of the body  102  ( FIGS. 1A-1C ) and the modular bladder  116  ( FIGS. 1A ,  1 C) construction. In certain exemplary embodiments, the three rings  200  proximate to the nose end  102   a  have a constant diameter reflecting the tailored cylindrical region both for load distribution and ease of manufacturing. The rings  200  also can serve as reinforcement sites to attach an engine (not shown) as well as provide passage and support for iso-truss members. In certain exemplary embodiments, the ring  200  includes a carbon fiber reinforced epoxy resin system  202  having a nonmetallic honeycomb Nomex® core  204 . The system  202  can be constructed from a cured graphite epoxy laminate. In certain exemplary embodiments, the core  204  can be constructed from Hexcel&#39;s HexWeb HRH-10 having a density of about 4 pounds per cubic feet (lb/ft3), and having a core thickness of about 4 inches (in). In certain embodiments, the ratio of a radius R to a thickness t of the ring  200  is about 165. In certain embodiments, the ring  200  can be fabricated by joining flat panels together. In certain exemplary embodiments, the ring  200  includes panels having a width w of about 2 ft, which circumscribe the ring  200  having a radius R of about 55 ft. 
     In certain exemplary embodiments, methods of fabricating the ring  200  include curing the system  202  separately either in autoclave or out-of-autoclave through vacuum assisted resin transfer molding (VARTM). The system  202  can then be bonded to the Nomex® core on a frame scaffold (circular arc mandrel) to create the ring shape. This system is clamped until cured at room temperature and then removed. The number of panels to be joined together can depend on length of each panel. For instance, if the length of each panel is about 8 ft, then about 43 panel segments are needed to be joined together with adhesively bonded doublers per ring  200 . 
       FIG. 3A  is a partial front view of the body  102  ( FIGS. 1A-1C ) coupled to the ring  200  ( FIGS. 2A-2B ), and  FIG. 3B  is a partial side view of the body  102  coupled to the ring  200 , according to an exemplary embodiment. The body  102  includes a series of longitudinal straps  302  and hoop straps  304  arranged in a criss-cross or weave pattern. In certain embodiments, metal loops  310  are attached to the ring  200 , and the longitudinal straps are inserted into the metal loops  310  to ultimately couple the longitudinal straps  302  to the ring  200 . In certain exemplary embodiments, the straps  302 ,  304  are constructed from a high-strength, durable woven material. Suitable examples of high-strength, durable woven materials include a liquid crystalline polymer fiber with high creep, ultraviolet (UV) and moisture resistance, such as Vectran®. In certain exemplary embodiments, the strength of the hoop straps  304  varies by the location along the length L of the body  102 . In certain exemplary embodiments, the strength of a hoop strap  304  at a center of the body  102  is greater than the strength of a hoop strap  304  at an end of the body  102 . 
       FIG. 4A  is a perspective view of a tri-hull delta dirigible  400 , and  FIG. 4B  is a side cross-sectional view of the tri-hull dirigible  400 , according to an exemplary embodiment. Referring to  FIGS. 4A and 4B , the tri-hull dirigible  400  includes three ellipsoid singlets  100   a ,  100   b ,  100   c , collectively referred to herein as singlets  100  ( FIGS. 1A-1C ), coupled together using struts  404 . The singlets  100  are positioned such that they are parallel to each other along its length, and are arranged at the apex of an equilateral triangle when coupled together. In certain exemplary embodiments, each singlet  100  is coupled to its adjacent hull using three struts  404  and a plurality of cross-tie cables  406  between the struts  404 . The cross-tie cables  406  are attached between the struts  404  to serve as a shear-tie between the struts  404  to prevent fore and aft relative motion of the three singlets  100 . The triangular design of the dirigible  400  allows for a much more stable configuration when compared to a dual-hull design. The dirigible  400  can also include a gondola  410 , or control car, coupled to the bottom singlet  100   c . The gondola  410  generally houses the pilot, crew, and passengers (not shown) of the dirigible  400 . Four propulsion systems  416  are also included. Each of the top two singlets  100   a ,  100   b  includes a propulsion system  416 , and the other two propulsion systems  416  are coupled to the bottom singlet  100   c  on either side of the gondola  410 . The propulsion systems  416  and the gondola  410  are each attached with their own fixtures through the three rings  200  proximate the nose end  102   a  and the struts  404 . Generally, the tri-hull dirigible  400  configuration reduces the overall dimensions of a single hull dirigible of the same volume and lift capacity. The three shorter singlets  100  attached through struts  404  also offer better performance and flexibility to tailor hauling range and cargo capacity when compared to conventional dirigibles. 
     Referring to  FIG. 4B , the diagonal struts  404  generally experience compression while the horizontal struts  404  undergo tensile loads. In certain exemplary embodiments, each of the struts  404  has an external radius of about eight inches and a length of about 285 feet, thus resulting in an aspect ratio (length/diameter) of about 213. For the buckling driven diagonal struts  404 , the ratio of the radius to wall thickness is about 16, while the radius to wall thickness for the horizontal struts  404  that are tensile load critical is about 53, reflecting the high tensile strength capacity of carbon-reinforced polymers. In certain exemplary embodiments, each of the rings  200  includes three metal reinforced holes  430  along its circumference for one V-shaped truss member  432  and two linear truss members  434  to pass through. In each of the V-shaped truss members  432 , two struts  404  are coupled thereto at approximately 60degrees relative to each other. In certain exemplary embodiments, the struts  404  are separable and are joined together to the truss members  434  at joints  438  using a bolted connection or other specially designed fitting, and can be disconnected at the joints  438  to separate the singlets  100  from each other. Accordingly, the tri-hull dirigible  400  can readily be separated into a dual-hull or a single-hull, or singlet  100 , to accommodate smaller cargo loads. 
     Therefore, the invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiment disclosed above is illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those having ordinary skill in the art and having the benefit of the teachings herein. While numerous changes may be made by those having ordinary skill in the art, such changes are encompassed within the spirit of this invention defined in the claims. It is therefore evident that the particular illustrative embodiments disclosed herein may be altered or modified and all such variations are considered within the scope and spirit of the claimed invention.