Abstract:
An aerodynamic fairing system for an airship having a substantially spherical balloon portion includes an inflatable fairing that is attachable to the balloon portion, and a fairing actuation mechanism that selectively inflates and deploys the fairing after lift-off, and deflates and retracts the fairing before landing. The actuation mechanism includes an inflation/deflation mechanism and a deployment/retraction mechanism that cooperate to deploy and inflate the fairing, and to deflate and retract the fairing. The fairing includes a substantially conical, inflatable tail section tapering from a wide forward end to a narrow aft end, and a collapsible annular collar connecting the forward end of the tail section to the balloon portion. The inflation/deflation mechanism includes a fan system in the tail section, and the deployment/retraction mechanism includes a plurality of cables attached between the tail section and a plurality of winches mounted on the balloon portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit, under 35 U.S.C. §119(e), of co-pending provisional application No. 60/710,786; filed Aug. 24, 2005, the disclosure of which is incorporated herein by reference. 

   FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   The present invention relates to powered lighter-than-air aircraft or airships. More specifically, it relates to an aerodynamic fairing for an airship that is selectively deployable and retractable while the craft is aloft. 
   Powered lighter-than-air aircraft, or airships, have been in existence for more than a century. Typically, such aircraft fall into two major classes: dirigibles and blimps. The major difference between the two is that in the former, the inflatable chambers or balloons are supported in a rigid framework or support structure, while the latter lack a rigid support structure. In both types, the overall shape of the craft typically resembles a cigar, i.e., elongate, with a circular cross-section, a rounded bow or nose, and a stern or tail that is tapered or pointed. This elongate shape provides greater aerodynamic efficiency as compared with, for example, a spherical shape, allowing greater altitude, speed, and endurance (due to improved fuel efficiency) for a given propulsion system. These advantages are achieved, however, at some cost in the efficiency of the distribution of internal and external gas pressures, thereby requiring a more complex pressurization system that would be necessary in a spherical craft. Furthermore, a spherical craft would simplify ground operations, by requiring a smaller landing/lift-off area without the need for a mooring pylon. 
   It would therefore be advantageous to provide an airship that combines, to the greatest extend possible, the aerodynamic advantages of a conventional, elongate airship with the above-mentioned advantages of a spherical craft. To this end, the prior art has proposed various types of aerodynamic structures and fitting that can be attached to an airship or balloon to improve its aerodynamic efficiency. Nevertheless, it would be a great improvement in airship technology to provide an aerodynamic structure that can be attached to a spherical craft and that can be easily deployed and retracted while the craft is aloft, so that the craft can lift off and land in the manner of a spherical balloon, while greatly increasing aerodynamic efficiency while the craft is in flight. 
   SUMMARY OF THE INVENTION 
   Broadly, the present invention, in one aspect, is an aerodynamic fairing system for an airship comprising a substantially spherical balloon, wherein the system includes an inflatable fairing that is attachable to the balloon, and a fairing actuation mechanism for selectively inflating and deploying the fairing after lift-off and deflating and retracting the fairing before landing. More specifically, the actuation mechanism includes an inflation/deflation mechanism and a deployment/retraction mechanism that cooperate to deploy and inflate the fairing after lift-off, and to deflate and retract the fairing before landing. 
   In another aspect, the present invention is a powered airship, comprising a substantially spherical balloon containing a lighter-than-air gas (e.g., helium), an inflatable fairing attached to the balloon, a fairing actuation mechanism for selectively inflating and deploying the fairing after lift-off and deflating and retracting the fairing before landing. More specifically, the actuation mechanism includes an inflation/deflation mechanism and a deployment/retraction mechanism that cooperate to deploy and inflate the fairing after lift-off, and to deflate and retract the fairing before landing. 
   In either of the above-described aspects of the invention, the fairing comprises an inflatable, substantially conical, tail section that is removably attached to the balloon by an annular collar. The inflation/deflation mechanism comprises at least one inflation/deflation fan, and preferably two or more inflation/deflation fans. Each fan is operable in an inflation mode to inflate the tail section to a desired pressure in a fully inflated configuration, and in a deflation mode to deflate the tail section. The deployment/retraction mechanism comprises a plurality of cables, each of which is spooled on a winch secured to the balloon, and each of which has a distal end secured to the tail section. 
   To deploy the fairing, the inflation/deflation fans are operated in the inflation mode while the winches on the balloon are operated in a deployment mode to spool out the chords as the tail section inflates to a fully inflated configuration. To retract the fairing, the process is reversed: The fans are operated in a deflation mode to deflate the tail section while the winches are operated in a retraction mode to reel in the chords, thereby collapsing and retracting the tail section as it deflates. 
   The fairing system of the present invention improves the aerodynamic efficiency of the airship by increasing the ratio of the length of the airship to its maximum diameter (i.e., the “fineness ratio”). The fineness ratio is inversely proportional to the coefficient of drag (C D ). Thus, a spherical balloon has a fineness ratio of 1.0, which corresponds to a C D  of 0.2. By adding a tail section to the balloon, the present invention increases the fineness ratio to about 2.0, yielding a C D  of about 0.03. With the coefficient of drag so reduced, the speed and endurance of the airship are markedly increased. 
   As will be more apparent from the detailed description that follows, the present invention provides an airship that can lift off and land substantially in the manner of a spherical balloon, but that possesses aerodynamic qualities and advantages similar to those of a conventional, elongate airship while in powered flight. This combination of the advantages of a spherical craft and an elongate craft is achieved with a fairing system that can be attached to almost any spherical airship, and that can be conveniently and easily deployed after lift-off, retracted before landing, and removed after landing. These and other attributes, characteristics, and advantages of the present invention will be readily understood and appreciated from the detailed description that follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an airship with a fairing system in accordance with a preferred embodiment of the present invention, wherein the tail section of the fairing system is in its deployed and inflated configuration; 
       FIG. 2  is an exploded perspective view of the airship of  FIG. 1 , showing the tail section and the attachment collar of the fairing system of the present invention, separated from the main balloon portion of the airship; 
       FIG. 3  is a front elevational view of the airship of  FIG. 1 ; 
       FIG. 4  is a side elevational view of the airship of  FIG. 1 ; 
       FIG. 5  is a bottom plan view of the airship of  FIG. 1 ; 
       FIG. 6  is a cross-sectional view taken along line  6 — 6  of  FIG. 3 ; 
       FIG. 7  is an enlarged, detailed view of the area within the dashed circle designated by the numeral  7  in  FIG. 6 ; 
       FIG. 8  is an enlarged, detailed view of the area within the dashed circle designated by the numeral  8  in  FIG. 6 ; 
       FIG. 9  is an enlarged, detailed view of the area within the dashed circle designated by the numeral  9  in  FIG. 6 ; 
       FIG. 10  is an elevational view of a portion of the interior side wall of the tail section of the airship of  FIG. 1 , taken along line  10 — 10  of  FIG. 6 ; 
       FIG. 11  is an enlarged, detailed view of the area within the dashed circle designated by the numeral  11  in  FIG. 6 ; 
       FIG. 12  is a cross-sectional view taken along line  12 — 12  of  FIG. 6 ; 
       FIG. 13  is an elevational view of a portion of the exterior surface of the balloon portion of the airship of  FIG. 1 , taken along line  13 — 13  of  FIG. 6 ; 
       FIG. 14  is an elevational view of a portion of the forward interior surface of the tail section of the airship of  FIG. 1 , taken along line  14 — 14  of  FIG. 6 ; and 
       FIGS. 15–19  are schematic views of the airship of  FIG. 1 , showing the transition of the tail section and collar of the fairing system from a fully deployed configuration to a fully retracted and collapsed configuration. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, an airship  10  having a fairing system in accordance with the present invention is shown. The airship  10  comprises a main balloon portion  12  and a fairing system that, in turn, comprises an inflatable, substantially conical tail section  14  and a substantially annular attachment collar  16 . The balloon portion  12  is equipped with a propulsion system comprising a plurality of motor-driven propellers  18 , each mounted on a propeller pylon  20  fixed to a support  22  on the outer surface of the balloon portion  12 . The pylon supports  22 , in turn, are mounted on a mounting ring  24  ( FIG. 6 ) that encircles the equatorial circumference of the balloon portion  12 . In a preferred embodiment, as illustrated, there are four propellers  18 , two on each side of the balloon portion  12 , but the total number of propellers may be greater than four or as few as two. 
   The annular collar  16  has a substantially frustoconical configuration, with a first or forward circumference that is slightly smaller than the circumference of the balloon portion  12 , and a second or aft circumference that is somewhat smaller than the forward circumference thereof. Thus, the forward part of the collar  16  fits around the balloon portion  12  just aft of the engine mounting ring  24 . The collar  16  is made of a lightweight, durable, moisture-proof fabric, preferably a urethane-coated nylon, such as the fabric marketed under the trademark “NORLITE 50” by North Sails North America (www.na.northsails.com). As shown in  FIGS. 6 and 7 , the collar  16  is removably attached to the balloon portion  12  by a first or forward fastening ring  26 , which advantageously comprises mating rings of hook-and-loop fasteners, such as those marketed under the trademark VELCRO®, respectively attached to the adjoining surfaces of the balloon  12  and the collar  16 . A first or forward cinch strap  28  may advantageously be removably fastened around the forward fastening ring  26  to provide a more secure attachment of the collar  16  to the balloon portion  12 . 
   The inflatable tail section  14  is, when fully inflated, substantially conical in form, tapering from a substantially circular forward end  30 , having a circumference substantially equal to the aft or second circumference of the collar  16 , to a blunt or rounded apex at its rear-most or aft end  32 . Also, when the tail section  14  is fully inflated, its forward end  30  bulges slightly outward, presenting an arcuate forward surface. 
   The tail section  14  is an inflatable gas chamber or envelope that is advantageously formed of the same material as the collar  16 , as described above. An inner liner (not shown) of a gas impermeable material, such as urethane, may optionally be provided. The tail section  14  is designed to be inflated to a suitable pressure by a plurality of reversible, electrically-powered inflation/deflation fans  34  that are built into passages  36  in the tail section. The fans  34  are operable in an inflation mode to inflate the tail section  14  to a suitable pressure, which, in an exemplary embodiment of the invention, is about 6.35 mm H 2 O. The fans  34  are operable in reverse to operate in a deflation mode when it is desired to deflate the tail section  14 . The passages  36  include conventional gating or valving mechanisms (not shown) to close the passages  36  when the fans  34  are not in use. The fans  34  are preferably run by DC motors (not shown), which are powered by a DC power source  38  contained in the balloon portion  12 , as shown in  FIG. 6 . Current from the power source  38 , and control signals from a control unit (not shown) in the balloon portion  12 , are conducted to the fan motors by suitable cables  40  (one of which is shown in  FIG. 6 ), that may advantageously be run through one or more fabric sleeves  42  that may be sewn into the material of the collar  16 , as also shown in  FIG. 6 . 
   As shown in  FIGS. 6 and 8 , the tail section  14  is removably attached to the collar  16  by a second or aft fastening ring  44 , which advantageously comprises mating rings of hook-and-loop fasteners, such as those marketed under the trademark VELCRO®, respectively attached to the adjoining surfaces of the collar  16  and the tail section  14 . A second or aft cinch strap  46  may advantageously be removably fastened around the aft fastening ring  44  to provide a more secure attachment of the tail section  14  to the collar  16 . When the tail section  14  is attached to the collar  16  and is fully inflated, as shown in  FIG. 6 , the arcuate forward surface of the forward end  30  of the tail section  14  abuts against the spherical balloon portion  12 . In a preferred embodiment of the invention, the inflation pressure of the tail section  14  is measurably less than that of the balloon portion  12 , and therefore the abutment of the two components will result in a slight compression of the forward surface of the tail section  14 . This compression produces a tensile force in the collar  16  that helps hold the tail section  14  in place. 
   The airship  10  further includes a fairing deployment/retraction mechanism, comprising at least one pair of longitudinal retraction cables  48 , each driven by an electrically-powered main winch  50  mounted on the balloon portion on or near one of the pylon supports  22 . Each of the longitudinal retraction cables  48 , preferably nylon ropes or their equivalent, is run from one of the main winches  50  to an aft cable anchor  52  sewn into the tail section  14  at the aft end  32  thereof, as shown in  FIG. 9 . Specifically, a first end of each longitudinal retraction cable  48  is spooled onto its respective one of the main winches  50 , and the longitudinal cable  48  is passed through an associated longitudinal fabric sleeve  53  that extends along the surface the collar  16  and the tail section  14 , with the second end being attached to its associated aft cable anchor  52 . The main winches  50  are operable in a deployment mode to spool out the longitudinal retraction cables  48 , and in a retraction mode to reel them in, as explained in detail below. Preferably there are two pairs of main winches  50 , one pair on each side of the balloon portion  12 . 
   The deployment/retraction mechanism further comprises a circumferential retraction cable  54  that is connected by a linking cable segment  56  to a ventral winch  58  mounted on the surface of the balloon portion  12 , as best shown in  FIG. 5 . The circumferential retraction cable  54  is enclosed in a circumferential sleeve  59  that encircles the tail section  14 , while the linking cable segment  56  passes through a longitudinal ventral sleeve  61  that extends along the surface of the collar  16  and the tail section  14 . The circumferential retraction cable  54 , with its linking cable segment, operates as a “noose,” as explained below, to collapse the tail section  14  radially when the ventral winch  58  is operated in a retraction mode to reel in the linking cable segment  56 , and to allow the radial expansion of the tail section  14  when the ventral winch  58  is operated in a deployment mode to spool out the linking cable segment  56 . 
   The deployment/retraction mechanism may also advantageously include a plurality of elastic chords, such as “bungee” chords, secured between the balloon portion  12  and the tail section  14  to assist in the retraction process. Specifically, as shown in  FIG. 6 , a plurality of diagonal elastic chords  60  may be secured between the exterior of the balloon portion  12  and the interior of the tail section  14 . Each of the elastic chords  60  has a first end secured to a first anchor  62  ( FIG. 10 ) that is fastened to the interior of the tail section  14 , and a second anchor  64  ( FIG. 13 ) fastened to the exterior of the balloon portion  12 . Each of the chords  60  passes through a chord passage structure  66  ( FIG. 14 ) sewn into the tail section  14 , each of the chord passage structures  66  comprising an elastomeric membrane  68  having a slit  70  that resiliently closes around the chord  60  passing through it, so as to effect a nearly airtight seal around the chord  60 . 
   In operation, the airship  10  lifts off much as a conventional spherical balloon, with the tail section  14  and collar  16  in a collapsed and retracted configuration ( FIG. 19 ). After lift-off, the fans  34  are operated in their inflation mode, and the main winches  50  and the ventral winch  58  are operated in their deployment mode, spooling out the longitudinal retraction cables  48  and the linking cable segment  56  of the circumferential retraction cable  54 , respectively. With the longitudinal cables  48  spooling out, and the circumferential cable  54  being loosened by the spooling out of the linking cable segment  56 , the resultant slack in the cables  48 ,  54  allows the tail section  14  to be expanded by inflation (against the elastic forces exerted by the chords  60 ) until the tail section  14  and the collar  16  assume their fully deployed configuration ( FIG. 15 ). Once the desired backpressure is registered in the inflation system (by conventional pressure sensors, not shown, appropriately located in the tail section  14 ), the fans  34  are shut off (or operated intermittently in a pressure-maintenance mode), and any excess slack in the cables  48 ,  54  is taken up by their respective winches  50 ,  58 . In the fully deployed configuration of  FIG. 15 , the airship  10  is ready for powered flight, with the tail section  14  providing an aerodynamic efficiency that is much improved over that of a spherical balloon, as discussed above. 
   When the airship  10  is ready to land, the fans are operated in their deflation mode, while the winches  50 ,  58  are operated in their retraction mode to reel in the longitudinal cable  48  and to tighten (radially contract) the circumferential cable  54 . At the same time, the elastic chords  60  exert a retraction force that urges the tail section  14  toward the balloon portion  12 . Thus, as shown in  FIGS. 16 ,  17 , and  18 , the tail section  14  and the collar  16  are drawn toward the balloon portion  12  and are collapsed against it, until the fully retracted configuration shown in  FIG. 19  is achieved. Thus, the airship  10  may land in the manner of a conventional spherical balloon. 
   While a preferred embodiment of the invention has been described above, in conjunction with the drawings, it is to be understood that this embodiment is exemplary only, and represents the best mode currently contemplated for practicing the invention. A number of variations and modifications may suggest themselves to those skilled in the pertinent arts, and equivalent structures and elements will be found for many of the elements and structures described with particularity herein will. For example, the present invention will be readily adaptable to airships having a variety of propulsions systems. In addition, the system of cables, winches and chords described above for deploying and retracting the fairing components (the collar  16  and tail section  14 ) is by way of example only, and other equivalent structures for performing the deployment/retraction function will suggest themselves to those skilled in the pertinent arts. These and other variations and modifications are considered to be within the spirit and scope of the present invention, as defined in the claims that follow.