USOO9623954B2

(12) United States Patent (10) Patent No.: US 9,623,954 B2 Kempshall (45) Date of Patent: Apr. 18, 2017

(54) HYBRID LIGHTER-THAN-AIR VEHICLE B64C3/14: B64C 2001/0045; B64C3/00; B64C 1/064; B64C 220 1/105; B64C (71) Applicant: Scott R. Kempshall, St. Petersburg, FL 25/56; B64C 3/44; B64C 3/56 (US) USPC ...... 244/5 (72) Inventor: Scott R. Kempshall, St. Petersburg, FL S ee appl1cauonlication Illefile fIor completelet searcnh historv.n1story (US) (56) References Cited (73) Assignee: Hyalta Aeronautices, Inc., St. U.S. PATENT DOCUMENTS Petersburg, FL (US) 3,907,218 A 9, 1975 Miller (*) Notice: Subject to any disclaimer, the term of this 3.913,871 A 10, 1975 Miller patent is extended or adjusted under 35 3,970,270 A 7, 1976 Pittet, Jr. U.S.C 154(b) bV 166 davs 3,976,265 A 8, 1976 Doolittle M YW- y yS. 3,993,268 A 11/1976 Moore 4,052,025 A 10, 1977 Clark et al. (21) Appl. No.: 14/341,184 4,085,912 A 4/1978 Slater 4,102,519 A 7/1978 Crosby, Jr. (22) Filed: Jul. 25, 2014 4,261,534 A 4, 1981 Roselli 4,366,936 A 1/1983 Ferguson (65) Prior Publication Data 4,482,110 A 1 1/1984 Crimmins, Jr. (Continued) US 2016/OO23748 A1 Jan. 28, 2016 Primary Examiner — Valentina Xavier (51) Int. Cl. Assistant Examiner — George Andonyan B64B I/20 (2006.01) (74) Attorney, Agent, or Firm — Nicholas Pfeifer; Smith B64C 3/44 (2006.01) & Hopen, P.A. B64B I/08 (2006.01) B64B I/4 (2006.01) (57) ABSTRACT B64C3/54 (2006.01) The present invention is a variable geometry lighter-than-air B64B I/58 (2006.01) (LTA) that is adapted to morph its shape from a FO3D 9/00 (2016.01) symmetric cross-section buoyant craft to an asymmetric (52) U.S. Cl. lifting body and even to a symmetric Zero lift configuration. CPC ...... B64C3/44 (2013.01); B64B I/08 The basic structure is a semi rigid airship with movable (2013.01); B64B I/14 (2013.01); B64B I/58 longerons. Movement of the longerons adjusts the camber of (2013.01); B64C3/54 (2013.01); F03D 9/002 the upper and/or lower Surfaces to achieve varying shapes of (2013.01); B64B 2201/00 (2013.01); F05B the lifting-body. This transformation changes both the lift 2240/921 (2013.01); Y02E 10/725 (2013.01) and drag characteristics of the craft to alter the flight (58) Field of Classification Search characteristics. The transformation may be accomplished CPC ...... B64B 1/00; B64B 2201/00; B64B 1/20; while the craft is airborne and does not require any ground B64B 1/06; B64B 1/58; B64B 1/14: Support equipment. B64B 1/26: B64C 1/34; B64C 39/10: B64C 3/30; B64C 2700/6273; B64C 3/10; 12 Claims, 16 Drawing Sheets

136 4 14 136 US 9,623.954 B2 Page 2

(56) References Cited U.S. PATENT DOCUMENTS 4497,272 A 2/1985 Veazey 4,695,012 A 9, 1987 Lindenbaum 4,779,825 A 10, 1988 Sams 5,005,783 A 4/1991 Taylor 5,823,468 A * 10/1998 Bothe ...... B64B 1.08 244, 12.3 2004/0084565 A1 5/2004 Albrecht ...... B64B 1/20 244/5 2011 0163198 A1* 7, 2011 Leaver ...... B64C 27.20 244/12.1 * cited by examiner U.S. Patent Apr. 18, 2017 Sheet 1 of 16 US 9,623,954 B2

124

136

FIG. I. U.S. Patent Apr. 18, 2017 Sheet 2 of 16 US 9,623,954 B2

FIG. 2

FIG. 3 U.S. Patent Apr. 18, 2017 Sheet 3 of 16 US 9,623,954 B2

136

120

FIG. 4B U.S. Patent Apr. 18, 2017 Sheet 4 of 16 US 9,623,954 B2

U.S. Patent Apr. 18, 2017 Sheet S of 16 US 9,623,954 B2

3. 5 U.S. Patent Apr. 18, 2017 Sheet 6 of 16 US 9,623,954 B2

U.S. Patent US 9,623,954 B2

U.S. Patent Apr. 18, 2017 Sheet 8 of 16 US 9,623,954 B2

U.S. Patent US 9,623,954 B2

§101H U.S. Patent Apr. 18, 2017 Sheet 10 of 16 US 9,623,954 B2

U.S. Patent Apr. 18, 2017 Sheet 11 of 16 US 9,623,954 B2

U.S. Patent Apr. 18, 2017 Sheet 12 of 16 US 9,623,954 B2

U.S. Patent Apr. 18, 2017 Sheet 13 of 16 US 9,623,954 B2

FIG. 14A

FIG. I.4B U.S. Patent Apr. 18, 2017 Sheet 14 of 16 US 9,623,954 B2

U.S. Patent Apr. 18, 2017 Sheet 15 of 16 US 9,623,954 B2

112 110 112

102 108 102

|- s—- FIG. I 74

112 112 102 102 - 110 S -108 110 - FIG. 17B U.S. Patent Apr. 18, 2017 Sheet 16 of 16 US 9,623,954 B2

FIG. 18

r-107 112 110 108 112 = H(s) = FIG. 19

107

108 110 112 112 "1 FIG. 20

107-N 147 112 7 112

FIG 21 US 9,623,954 B2 1. 2 HYBRD LIGHTER-THAN-AR VEHICLE U.S. Pat. No. 4,102,519 to Edward L. Crosby, Jr. teaches a variable lift inflatable airfoil. However, this invention lacks BACKGROUND OF THE INVENTION internal moveable structures, which prevent the airfoil from achieving multiple configurations. Additionally, the airfoil 1. Field of the Invention 5 lacks a propulsion system and/or control Surfaces. This invention relates, generally, to aircrafts. More spe Accordingly, what is needed is an improved variable cifically, it relates to aircrafts convertible between lighter geometry aircraft having a simple, moveable internal struc than-air and heavy-than-air configurations. ture to easily convert the aircraft between an LTA configu 2. Brief Description of the Prior Art Lighter-Than-Air (LTA) aircrafts have some characteris- 10 ration and an HTA configuration. However, in view of the art tics not shared with Heavier-Than-Air (HTA) aircrafts in considered as a whole at the time the present invention was that they can maintain altitude without moving in a medium made, it was not obvious to those of ordinary skill in the field and can do so as long as buoyancy is maintained. LTA of this invention how the shortcomings of the prior art could aircrafts use low-density gas, such as helium or hydrogen to be overcome. float in higher density air. These aircrafts usually employ 15 All referenced publications are incorporated herein by one or more gasbags filled with low-density gas to create a reference in their entirety. Furthermore, where a definition or buoyancy force that offsets the weight of the aircraft. The use of a term in a reference, which is incorporated by downside of LTA aircrafts is their large size, which is reference herein, is inconsistent or contrary to the definition accompanied by large drag characteristics, preventing them of that term provided herein, the definition of that term from traveling at higher speeds. The current speed record for 20 provided herein applies and the definition of that term in the an LTA aircraft is 112 Km/hr (69.6 mph). reference does not apply. HTA aircrafts use Newton's third law and Bernoulli’s While certain aspects of conventional technologies have principle to achieve flight. These aircrafts are generally fixed been discussed to facilitate disclosure of the invention, wing or rotor wing aircraft. In either case, part or parts of the Applicant in no way disclaims these technical aspects, and structure (e.g., wing, rotors, propellers, , and control 25 it is contemplated that the claimed invention may encompass Surfaces) have a characteristic shape called an airfoil. Air one or more of the conventional technical aspects discussed foils are generally asymmetric in cross-section with the herein. upper Surface having a greater length than the lower Surface. The present invention may address one or more of the This causes air moving across the upper Surface to travel problems and deficiencies of the prior art discussed above. faster than the air traveling across the lower Surface causing 30 a pressure decrease on the upper Surface resulting in lift. However, it is contemplated that the invention may prove Lift can also be achieved/altered by altering the angle of useful in addressing other problems and deficiencies in a attack (AoA) of an airfoil relative to the oncoming airflow. number of technical areas. Therefore, the claimed invention Increased AoA causes mass deflection resulting in lift (New should not necessarily be construed as limited to addressing tons third law). Generally, increasing AoA increases lift 35 any of the particular problems or deficiencies discussed until the angle reaches a point at which the airflow separates herein. from the Surface of the airfoil causing aerodynamic stall. In this specification, where a document, act or item of Regardless of means for creating lift, an HTA requires a knowledge is referred to or discussed, this reference or wing-like structure moving through a fluid. Movement discussion is not an admission that the document, actor item requires a power Source and no power source can last 40 of knowledge or any combination thereof was at the priority indefinitely. Therefore, the HTA aircrafts can only maintain date, publicly available, known to the public, part of com flight for limited periods of time. Even powerless gliders mon general knowledge, or otherwise constitutes prior art have duration limits as they trade airspeed for altitude under the applicable statutory provisions; or is known to be gained from thermal lift. The limitation in flight time of an relevant to an attempt to solve any problem with which this HTA aircraft, however, is compensated by low drag char- 45 specification is concerned. acteristics and thus, high-speed flight. The clear tradeoff between LTA and HTA aircrafts is BRIEF SUMMARY OF THE INVENTION speed verse indefinite flight. An ideal aircraft would have the ability of an LTA to hover, or station-keep, for extended The long-standing but heretofore unfulfilled need for an periods for observation or surveillance roles and also the 50 improved variable geometry aircraft having simple, move ability of an HTA to operate at high-speeds. This can able internal structure to easily convert the aircraft between theoretically be achieved through an aircraft convertible a lighter-than-air configuration and a heavier-than-air con between an LTA and an HTA configuration. Currently, there figuration is now met by a new, useful, and nonobvious exist hybrid convertible aircrafts, but none that provide a invention. unique combination of attributes of both a fixed wing 55 The novel structure includes a convertible design having aircraft and a LTA craft allowing for indefinite mission a lighter-than-air configuration and a heavier-than-air con durations, low energy station keeping, and the ability to dash figuration with a flexible envelope in communication with a at relatively high velocities. base structure. The flexible envelope has a and U.S. Pat. No. 5,005,783 to James D. Taylor teaches a a creating a chord line. The aircraft also has a variable geometry airship capable of converting between a 60 span extending from a port side wingtip to a starboard side LTA and HTA airship. However, the airship is operationally wingtip. The lighter-than-air configuration has a span that is complex and does not extend the operating range Sufficiently less than the span of the aircraft when in the heavier-than-air to be practical as shown in Table 1. Along with multiple configuration. other pitfalls, the shape and design of this airship prevents The base structure includes a central core, a port side the airship from transforming into both a symmetric neutral 65 outrigger, and a starboard side outrigger. In an embodiment, lift configuration and a negative lift configuration, thereby the novel structure further includes moveable longerons, and reducing the effectiveness of the airship. length adjusting envelope expansion arms (also referred to US 9,623,954 B2 3 4 as "slack managers') for varying the span of the aircraft. In flexible envelope overcomes the bias force, resulting from a certain embodiment, the aircraft may include a propulsion the transition of the moveable longerons towards a more system. vertical orientation, thereby reducing the length and arc of In addition to the central core running along a central the envelope expansion arm. Contrastingly, the expanded longitudinal axis of the aircraft, the base structure includes position is achieved when the tension force in the flexible a leading edge extending in a direction perpendicular to envelope is overcome by the bias force, resulting from the and in communication with the central core, a trailing edge transition of the moveable longerons to a more horizontal Strut extending in a direction perpendicular to and in com orientation, thereby increasing the length and arc of the munication with the central core. The port side outrigger envelope expansion arm. Due to the positioning of the extends in a direction parallel to the central core and is in 10 envelope expansion arms, the span of the aircraft is directly communication with the , and the starboard side out affected by the transition between the retracted position and rigger extends in a direction parallel to the central core and the extended position. in communication with the struts. Additionally, the base In a certain embodiment, the envelope expansion arm is structure is in communication with the moveable longerons an anisotropic beam having two or more composite rods and the envelope expansion arms. 15 The moveable longerons include upper and lower lon with cross members extending between the rods. The cross gerons. The upper longerons are in communication with the members are designed to have a predetermined spring flexible envelope and an upper translation assembly. In an constant embedded into the structure. One of the composite embodiment, the upper translation assembly has an extended rods is pivotally attached to the aircraft and one or more of configuration where the moveable longerons are in a high the composite rods are anchored against the pivot structure camber orientation and a retracted configuration where the to provide a source of the tension. upper moveable longerons are in a low camber orientation. The novel structure further includes a structural connec In transitioning to the retracted configuration, the upper tion point to connect the base structure with the moveable translation assembly pulls the upper moveable longerons longerons and the envelope expansion arms. The structural inward towards the central longitudinal axis of the aircraft to connection point has a first fixed connection attached to an decrease aircraft thickness. In transitioning to the extended 25 outrigger, a second fixed connection attached to a strut, a configuration, the upper translation assembly pushes (or first pivoting connection attached to one of the upper move pulls in the case of the strap type translation assembly) the able longeron, a second pivoting connection attached to one moveable longerons outward away from the central longi of the lower moveable longeron, and a third pivoting con tudinal axis of the aircraft to place the upper moveable nection attached to one of the envelope expansion arms. longerons in a more vertical orientation, which increases the 30 In an embodiment, the aircraft uses a gas storage and aircraft thickness, compared to longeron's orientation in the retrieval system adapted to house, distribute, and retrieve retracted configuration. lighter-than-air gas. This system allows the aircraft to easily Similarly, the lower longerons are in communication with convert between a lighter-than-air configuration and a the flexible envelope and a lower translation assembly. The lower translation assembly has an extended configuration heavier-than-air configuration multiple times without having where the moveable longerons are in a high camber orien 35 to refill on gas. tation and a retracted configuration where the lower move In an embodiment, the aircraft includes a propulsion able longerons are in a low camber orientation. In transi system that includes an electrical generator system adapted tioning to the retracted configuration, the lower translation to convert wind energy into electrical energy while the assembly pulls the lower moveable longerons inward aircraft is in the lighter-than-air configuration. In a certain towards a central longitudinal axis of the aircraft to decrease 40 embodiment, flexible solar panels are attached to an exterior aircraft thickness. In transitioning to the extended configu Surface of the envelope to retrieve and convert Solar energy ration, the lower translation assembly pushes the moveable into electrical energy to extend mission time. longerons outward away from the central longitudinal axis In an embodiment, the aircraft has a payload hard point of the aircraft to place the lower moveable longerons in a attached to the lower translation assembly to facilitate the more vertical orientation, which increases the aircraft's 45 attachment and management of external payloads in addition thickness, compared to longeron's orientation in the to payloads attached internally to the core structure. retracted configuration. These and other important objects, advantages, and fea The upper and lower moveable longerons each include a tures of the invention will become clear as this disclosure port side longeron and a starboard side longeron, wherein proceeds. each longeron has a generally airfoil or arc shape and a 50 The invention accordingly comprises the features of con predetermined length that extends in generally the same struction, combination of elements, and arrangement of parts direction as the central longitudinal axis of the aircraft. Moreover, the moveable longerons are in a generally vertical that will be exemplified in the disclosure set forth hereinafter orientation when in the high camber position and in an acute and the scope of the invention will be indicated in the claims. angle orientation when in the low camber position. The length-adjusting envelope expansion arms comprise 55 BRIEF DESCRIPTION OF THE DRAWINGS of a port side envelope expansion arm and a starboard side envelope expansion arm. Each arm has a generally arc For a fuller understanding of the invention, reference shape, is Subjected to a bias force attempting to force each should be made to the following detailed description, taken arm in a direction away from the central longitudinal axis of in connection with the accompanying drawings, in which: the aircraft resulting in an increased arc shape, and is in 60 FIG. 1 is a perspective view of a certain embodiment of communication with the flexible envelope. Additionally, the present invention in an LTA configuration. each envelope expansion arm has a retracted position and an FIG. 2 is a perspective view of an embodiment of the expanded position, where in the retracted position, the present invention in a negative lift configuration. length and arc of the envelope expansion arm is at a FIG. 3 is a side view of an embodiment of the present minimum and in the expanded position, the length and are 65 invention shown in a positive lift configuration. of the envelope expansion arm is at a maximum. The FIG. 4A is a side view of the present invention in an LTA retracted position is achieved when a tension force in the configuration. US 9,623,954 B2 5 6 FIG. 4B is a front view of the present invention in an LTA through a medium to create Bernoulli lift, changing the configuration. angle of attack, or providing vertical thrust. FIG. 5A is a side view of the present invention in the dash Lighter-Than-Air Configuration: is a configuration of the configuration. aircraft that has a buoyancy to weight ratio greater than 1:1. FIG. 5B is a perspective view of the present invention in Longeron: is a structural member of the aircraft. the dash configuration. Outrigger: is a rod or bar forming part of a framework and FIG.5C is a front view of the present invention in the dash designed to resist compression that extends in generally the configuration. same direction as the longitudinal axis of the aircraft. FIG.5D is a bottom perspective view the present inven Payload Hard Point: is an attachment point for payloads tion in the dash configuration. 10 or instruments carried on the aircraft. FIG. 6 is a captured output for a symmetric airfoil with Propulsion System: is a system capable of moving the high thickness as a percentage of chord that was achieved aircraft through a medium. using FoilSim software. Strut: is a rod or bar forming part of a framework and FIG. 7 is a captured output for a symmetric airfoil with designed to resist compression. low thickness as a percentage of chord that was achieved 15 The present invention is a variable geometry aircraft using FoilSim software. capable of morphing its shape from a buoyant craft having FIG. 8 is a captured output for an asymmetric airfoil with a symmetric cross-section to an asymmetric lifting body low thickness as a percentage of chord that was achieved configuration or to a low camber symmetric shape. The using FoilSim software. convertibility of the present invention provides a unique FIG. 9 is a perspective view of a certain embodiment of combination of attributes of both a fixed wing HTA aircraft the present invention illustrating the location of reinforce and a LTA aircraft allowing indefinite mission durations, low ment layers. energy station keeping and the ability to glide or dash at FIG. 10 is a perspective view of a certain embodiment relatively high Velocities when equipped with a propulsion showing the configuration of internal panels used to create system (the term “dash herein refers to this high speed compartmentalized gas bladders. mode where the aircraft has a symmetric, low coefficient of FIG. 11 is a perspective view of a certain embodiment of 25 drag configuration). Additionally, the aircraft is highly por the present invention showing the internal structural com table by folding into a transportable configuration, light ponents of the aircraft. weight, relatively silent in operation, inexpensive to produce FIG. 12 is a rear perspective view of the starboard side of and operate, and has a unique structure that allows it to a certain embodiment of the present invention showing the operate even if the gas envelope is penetrated. Although internal structural components of the aircraft. 30 there are numerous other aircraft technologies, this device FIG. 13 is an exploded view of a certain embodiment of can operate across a number of operating envelopes and a structural connection point. performs multiple roles very well without significant com FIG. 14A is a top view of the internal base structure of a promise (see Table 1 below). This ability is facilitated by the certain embodiment of the present invention. unique internal structural elements of the aircraft. FIG. 14B is a top view of the internal base structure of a 35 certain embodiment of the present invention shown in a TABLE 1. folded configuration. FIG. 15 is a certain embodiment of the envelope expan Table 1: Aircraft Comparison sion arm. FIG. 16 is a perspective view of a certain embodiment of Velocity Range Operating Operational the upper translation assembly. 40 Aircraft (kts) Cost Complexity Duration FIG. 17A is front view of a certain embodiment of the Rotorf VTOL 0-115 (217*) High High Low Fixed Wing SO- Low-High Low-Med Low upper translation assembly in an extended configuration. LTA 0-30 (60*) Low Low-Med High FIG. 17B is front view of a certain embodiment of the Hybrid LTA** 0-40 High High Me upper translation assembly in a retracted configuration. Present O-200 Low Low High FIG. 18 is a front view of a certain embodiment of the 45 Invention lower translation assembly, having a payload hard point, while in an extended orientation. World Record FIG. 19 is a top view of FIG. 18. **Only viable recorded device defined in Patent 5,005,783 FIG. 20 is a front view of the lower translation assembly Table 1 above illustrates that the present invention fills a shown in FIG. 18 while in a retracted orientation. 50 unique performance niche in that, with low complexity and FIG. 21 is a bottom view of FIG. 20. high reliability, a unique and broad range of performance DETAILED DESCRIPTION OF THE feats can be achieved. The unique design features of the INVENTION present design, taken in combination, make it an improve ment on the technology for LTA aircraft, hybrid LTA aircraft, In the following detailed description of the preferred 55 and fixed wing flying bodies, especially as applied to embodiments, reference is made to the accompanying draw unmanned vehicles. ings, which form a part thereof, and within which are shown The present invention includes a flexible envelope enclos by way of illustration specific embodiments by which the ing a variable rigid inner structure. The envelope may invention may be practiced. It is to be understood that other include internal bladders adapted to contain low-density embodiments may be utilized and structural changes may be 60 buoyant gas, Such as Helium. made without departing from the scope of the invention. In an embodiment, the novel structure includes a central, Glossary of Claim Terms tubular core containing a propulsion system. The propulsion Envelope: is a lightweight flexible material. system is preferably an electric ducted fan motor. An Chord Line: is a straight line extending between the embodiment may include several cores depending on the leading edge and trailing edge of the envelope. 65 size of the aircraft and the mission requirements. In an Heavier-Than-Air Configuration: is a configuration of the embodiment, Such as a non-powered glider version, the aircraft that cannot maintain altitude without moving core(s) serves as the structural backbone for the envelope US 9,623,954 B2 7 8 while also acting as gas tank(s). The core further provides extended configuration, the moveable longerons are in a attachment points for additional equipment and may serve as generally vertical orientation, as shown in FIGS. 1 and 17A, a lead component in adjusting the aircraft's chord length. which increases the camber and affects the lift and drag The core(s) can also serve as a key structural base for a characteristics of the aircraft. When the translation assembly dual outrigger configuration to Support the leading and 5 is in a retracted position, the moveable longerons are pulled trailing edges. The two outriggers are preferably generally inwards towards the longitudinal axis of the aircraft, as parallel to the core and attach at the ends of the leading and shown in FIGS. 2, 5B, 5D, and 17B, which decreases trailing edge struts. The outriggers provide structure as well camber and thickness. as an attachment point for mounting the moveable lon The additional structural components contributing to the gerons. 10 present invention's Superior functionality include cylindrical The moveable longerons are adapted to pivot between a core 114 extending the length of the aircraft in the longitu more vertical orientation and more horizontal orientation dinal direction. In addition to the core, is a rigid, preferably such that the camber and thickness of the aircraft can be rectangular, base structure. The base structure includes lead altered based on flight needs. The chamber adjustment ing and trailing edge struts, collectively denoted by refer assemblies (also referred to as translation assemblies) can be 15 ence numeral 116, connected to outrig mounted both above and below the core of the aircraft such gers, which are collectively denoted by reference numeral that both the top and bottom surfaces of the aircraft are 118. The design also includes envelope expansion arms (also variable. referred to as "slack managers') 120 having an adjustable When the aircraft is in the LTA configuration—typically length and a generally arc shape. There is preferably one a large buoyant shape, the craft has all of the traditional envelope expansion arm along the port side of the aircraft characteristics of a blimp for station keeping or slow speed and one along the starboard side of the aircraft where each flight. By adjusting the shape of the lower surface to achieve is capable of extending outward away from the central an airfoil shape, the craft can augment the buoyancy by longitudinal axis of the aircraft to alter the span of the aircraft. As shown in FIGS. 1-5, flexible envelope 122 creating aerodynamic lift to increase its duration of flight or encloses the base structure, envelope expansion arms, and act as a conventional unpowered glider. Finally, by reshap 25 longerons. ing both the upper and lower Surfaces, the craft can achieve The moveable longerons, envelope expansion arms, and a relatively low drag configuration for high velocity (in flexible envelope allow the aircraft to operate in various excess of 200 km/hr for smaller aircraft sizes) to rapidly configurations. The position of the longerons is not limited reposition itself or fly high Velocity missions. In a certain to the fully extended or fully retracted position. Rather, the embodiment, the design includes a leading edge shield to 30 longerons can be configured in any state of extension to protect the envelope in high velocity flight. achieve optimal aerodynamic performance to meet a par The aircraft includes one or more gas containers coupled ticular mission's requirements. At one extreme, the lon to a gas delivery and preferably retrieval system. The gas gerons can be positioned to transform the aircraft into a delivery system fills the internal volume of the flexible symmetric buoyant configuration, as is typical for LTA envelope with lighter than air gas, while the retrieval system 35 aircraft, and shown in FIGS. 1, 4, and 5. This configuration is adapted to recover any gas already contained in the includes both upper translation assembly 106 and lower internal volume of the flexible envelope. These two systems translation assembly 107 in the fully extended position to allow for easy transformation between the LTA and HTA place moveable upper longerons 102 and lower longerons configurations. 104 in a generally vertical orientation. The non-linear arc 40 shape of the longerons increases the thickness of the aircraft Example of the Present Invention when in a more vertical orientation. As shown in FIG. 1, an embodiment of the present Another possible configuration is a negative lift configu invention, generally denoted by reference numeral 100, ration, as shown in FIG. 2. The configuration is achievable includes flexible envelope 122 with movable longerons 102, by retracting upper translation assembly 106 and extending 104. Aircraft 100 has two moveable upper longerons 102 lower translation assembly 107. Likewise, the aircraft can and two moveable lower longerons 104. The movement of 45 achieve a positive lift configuration, as shown in FIG. 3, by the longerons adjusts the camber and thickness of the upper extending upper translation assembly 106 and retracting and/or lower surfaces to achieve differing body shapes. The lower translation assembly 107. longerons are non-linear, preferably having an arc shape. In The truly innovative and functionally distinct orientation addition, the longerons preferably have a fixed length to found in no other LTA to HTA convertible aircraft, is the decrease complexity of the aircraft, however, length-adjust 50 dash configuration. As shown in FIGS. 5A-5D, the dash ing longerons are considered. The length of the longerons configuration is an approximately symmetric HTA configu extends preferably in a direction generally parallel to the ration achieved when both upper translation assembly 106 longitudinal axis of the aircraft. and lower translation assembly 107 are in the retracted The movement of the longerons and therefore camber position. In this position, the upper and lower moveable transformation can be accomplished while the craft is air 55 longerons 106, 107 are pulled inwardly towards core 114 borne and does not require any ground Support equipment. where they reside in a more horizontal orientation to sub The transformation changes both the lift and drag charac stantially reduce the thickness and camber of the aircraft. teristics of the craft to alter the flight characteristics. In a The variability of the aircraft imposes several require certain embodiment, only the upper or only the lower ments on flexible envelope 122. For example, flexible enve longerons are moveable to decrease the complexity and 60 lope 122 must be flexible to accommodate the shape mor weight of the aircraft. phing capability, have a very low permeability to Helium, Moveable upper longerons 102 and moveable lower lon and be lightweight. As a result, the envelope is preferably gerons 104 are each in communication with upper transla made from a plastic sheet material. This material is prone to tion assembly 106 and lower translation assembly 107. two negative features that will affect the performance of the respectively. The translation assemblies each include motor 65 LTA in the dash configuration and impact performance 108 (see FIGS. 16-21), gear assembly 110, and extendable overall. One is flutter of the envelope, which increases drag arms 112. When the translation assembly is in a fully and causes aerodynamic instability. The second is the pos US 9,623,954 B2 9 10 sibility of penetration of the envelope by airborne hazards tion in Table 2 is used to calculate the amount of force (such as insects, birds, or debris) at the high speeds. The required to move a body through a viscous medium. This is possibility of penetration may be avoided by the installation used to derive the motor size to achieve the required speed; of leading edge shields 127 that are hinged on the leading thus driving other factors such as weight, power, envelope edge strut and can expand or contract with the movement of 5 size, etc. The initial calculation is to determine the minimum the envelope. See FIG.1. Additionally, mechanical stops can motor output required to achieve the desired maximum dash be installed to reflect the shape of the leading edge in the velocity of 230 mph at a cruise altitude of 10,000 feet MSL. dash configuration to remove the possibility of flutter at high Using the desired dash speed shown in Table 2 below, the speeds. resultant drag force, or the required motor output to over Stability and Control Components " come that drag. is determined. Using a mathematical simu Aircraft 100 also includes flight stability and control lation tool (FoilSim)g is availabler from9. NASA, the C for components, such as 124 (which may be substituted- various configurations of the aircraft from a large chord to by an / configuration), vertical 125, length rati ll chord to length ration is calculated. A 126, leading edge shield 127, and propulsion system engt rat1O to a Small Chord to engt. ration 1S Calculated. AS 128. The pair of rear-mounted elevons 124 perform the 15 S" " Table 3, the drag force exhibited by a low chord to function of both elevators and to control pitch and length ratio with a highly symmetric profile yields the lowest roll. Both are controlled via servos and a microprocessor C, and therefore, the lowest motor size to achieve the mounted to the core assembly. Yaw control/directional sta- desired speeds. The model output corresponding to this bility is provided through rudder 126 mounted to vertical performance is shown in FIG. 7. These values are high Stabilizer 125. 20 lighted in the Drag Coefficient section of Table 3 for each of An embodiment may include rudder 126 configured to three configurations shown in FIGS. 6, 7, and 8. Also project into the ducted fan airstream to provide a degree of highlighted in the Drag Force and Required Motor Output thrust vectoring for very low speed flight and low velocity sections of Table 3 are the best performance conditions for maneuvering. It is envisioned that the larger sizes of this the LTA dash mode. It is apparent that the maximum LTA LTA would employ thrust vectoring entirely as its method of 25 speed in the highly buoyant configuration (high thickness to directional control for certain applications. Thrust vectoring chord length ratios) will be nowhere near those achieved in with multiple motors and larger sizes would significantly the dash configuration. FIGS. 6 and 7 show the output for reduce the Weight of the aircraft and provide Superior two of the symmetric configurations examined using the myths E. over conventional control Surfaces. FoilSim simulation program. FIG. 8 shows how C. ircraft Performance - ... " increases in the asymmetric configuration while also expe Due to the variable geometry capabilities, the aircraft will riencing a corresponding increase in the coefficient of lift havea high a Coefficientrange of performance of Drag (C) characteristics seen in the spanningdirigible fromcon- (C).C, ). The ddata showsh thathat in thisthi configuration,fi significantignifi aerodynamic lift can be achieved by this design at 0 degree configuration.figuration to a The relatively lift characteristics low C, seen will in alsothe varyflying from wing a 35 AOA. Hiigher lift performanceperf can beb achievedhieved at higherhi lift neutral symmetric configuration to a positive lift or AoA. negative lift airfoil shape to Suit mission requirements. These configurations can be changed dynamically while TABLE 2 airborne to suit mission needs. The driving requirement for Desired speed in knots: 200 kys = 102.88 m/sec the aircraft is the desired dash Speed of approximately 200 40 Fr-5(C) p.sv2 A. Assume Altitude of 10000 ft and speed of 250 kts for Small aircraft sizes. The assessment of performance kts and structural characteristics has been completed for three Altitude 10000 ft = 3048 m different configurations of craft defined by the length or Speed 230 ph-209 its 370 km/hr. chord of the aircraft and the span of the central, airfoil 102.88. w Velocitycharacteristic (m/sec); and drivesin this themodel, motor this size. is an input shapedh portionh endof theof thcraft, whichft excludes the half blimp 45 O413S Pair Density of Air:sa. is a function of atmospheric Snape on each end O Ca. conditions and varies as shown in Table 1 Dash Speed Calculation: Table A. Surface Area (m) A novel characteristic of this aircraft is the speed at which Table CD Coefficient of Drag: using FoilSim III the aircraft is capable of traveling when in the dash con figuration and powered by a propulsion system. The equa TABLE 3 10000 Ft Standard Lapse Chord Drag Coefficient (Co)

Thickness 10 12 14 16 18 2O

Chord (m) 1 Camber O O.O11 O.O15 O.019 O.O22 O.O23 O.O24 (% of FIG. 2 FIG. 1 Span (m) 1 Chord) 1 O.O16 O.O2 O.O24 O.O27 O.O29 O.O3 2 O.O3 O.O34 O.O38 O.O41 O.043 O.O45 3 O.OS2 O.OS6 O.O6 O.O63 O.06S O.066 FIG. 3 Chord (m) 2 O O.O1 O.O14 O.O17 O.O2 O.O21 O.O22 Span (m) 2 1 O.O15 O.019 O.O23 O.O2S O.O27 O.O28 2 O.O29 O.O33 O.O37 O.O39 O.041 O.043 3 O.OS1 O.OS4 O.OS8 O.061 O.063 O.064 US 9,623,954 B2

TABLE 3-continued Chord (m) 4 O O.O1 O.O13 O.O16 O.018 O.O2 O.O21 Span (m) 4 1 O.O15 O.O18 O.O21 O.O24 O.O2S O.O26 2 O.O29 O.O32 O.036 O.O38 O.04 O.O41 3 O.OS O.OS4 0.057 O.O59 O.061 O.O63 10000 Ft Standard Lapse Chord Drag Force (N)

Thickness 10 12 14 16 18 2O

Chord (m) 1 Camber O 24.1 32.8 41.6 48.1 S.O.3 52.5 Span (m) 1 (% of 1 33.O 43.8 52.5 59.1 63.5 65.6 Chord) 2 65.6 744 83.2 89.7 94.1 98.5 3 113.8 122.5 131.3 137.9 1422 1444 Chord (m) 2 O 87.5 122.5 148.8 175.1 1838 1926 Span (m) 2 1 131.3 166.3 2013 218.8 236.3 245.1 2 253.8 288.9 323.9 3414 358.9 376.4 3 446.4 472.7 507.7 S34.O 551.5 S60.2 Chord (m) 4 O 3SO.1 455.2 S60.2 630.2 700.3 735.3 Span (m) 4 1 525.2 630.2 735.3 840.3 875.3 910.3 2 1015.4 1120.4 126O.S 133 O.S 14OO.S 1435.5 3 1750.7 1890.7 1995.8 2O65.8 2135.8 22O5.8 10000 Ft Standard Lapse Chord Required Motor Output (gmf) 1N = 1.02 kgF = .225 lbf

Thickness 10 12 14 16 18 2O

Chord (m) 1 Camber O 2455.3 3348.1 4241.0 4910.6 S133.8 53.57.0 Span (m) 1 (% of 1 3571.4 4464.2 53.57.0 6026.7 6473.1 6696.3 Chord) 2 6696.3 7589.1 8482.O 9151.6 9598.O 100444 3 11606.9 12499.7 13392.6 14062.2 145086 14731.8 Chord (m) 2 O 8928.4 12499.7 15178.3 17856.8 18749.6 19642.5 Span (m) 2 1 13392.6 16963.9 20535.3 22321.0 24106.7 24999.5 2 25892.3 29463.7 3303S.O 34820.7 366.064 38.392.1 3 4S534.8 48213.3 51784.7 54463.2 36248.9 57.141.7 Chord (m) 4 O 35713.6 46427.6 57141.7 64284.4 71427.1 74998.5 Span (m) 4 1 53.570.3 64284.4 74998.5 85.712.5 89.283.9 92.855.3 2 103569.3 114283.4 128568.8 135711.S 142854.2 146425.6 3 178567.8 192853.2 203567.3 21071 O.O 217852.7 224995.4

Propulsion System and flexible material, to increase the serviceable life of the The motor size and number of motors are derived for each 40 envelope. In an embodiment, the reinforcement layer is also of the three configurations to determine if commercially added at the leading edge and under the translation assem available Electronic Ducted Fan (EDF) motors can be used blies to improve tear resistance at possible impact areas from in the design. The data in Table 3 proves that a single 3000 outside debris. gmfmotor is sufficient to achieve the desired velocity for the FIG. 10 shows internal panels that create separate gas 1-meter-by-1-meter sized aircraft. This size motor is readily 45 bladders within the envelope. The internal panels act as available for Radio Control (RC) aircraft. For larger size flexible walls creating four independent chambers. The craft, the number of core units would be increased to provide internals panels include top panel 131, bottom panel 132, the required thrust. This assessment shows that two core starboard panel 133, and port panel 134. Top panel 131 runs units of roughly the same size as above will propel a between the outriggers 118 and rests on the central core 114, 2-meter-by-2-meter design. Larger motors or core combi- 50 both of which are not shown to aid in clearly identifying the nations of four motors would be required for the 4-meter internal panels. Bottom panel 132 also rims between the by-4-meter design. In an embodiment, any number and type outriggers 118, but is located under the central core 114. of motors may be used as is known to a person having Both the port and starboard panels 134 and 133 run between ordinary skill in the art. the top and bottom longerons 102, 104 on the respective Envelope 55 sides of the aircraft. The panels are preferably made from the In an embodiment, the envelope includes an internal same material as the envelope, however any lightweight reinforcement layer and a secondary containment bag to flexible and airtight material known to a person having facilitate Helium recovery. The moveable structural compo ordinary skill in the art may be used. These panels aid in the nents of the aircraft raise concerns regarding structural recovery of the low-density gas used in the LTA configura members rubbing on a fairly thin plastic Surface and ulti- 60 tion. The partition bladders also reduce the possibility of mately causing the envelope to fail. Therefore, an embodi catastrophic gas loss if the envelope integrity is compro ment includes reinforcement layers 130 located in areas mised. In conjunction with the individual bladders, the likely to experience increased wear and tear from the move aircraft also includes gas containers Sufficient for one or able internal structure of the aircraft. FIG. 9 illustrates the more refills and a gas recovery pump system. approximate areas on envelope 122 requiring the addition of 65 Base Structure reinforcement layers 130. Reinforcement layers 130 are As shown in FIG. 11, the base structure of the aircraft made of Mylar or some other wear resistant, lightweight, includes a preferably rectangular frame made up of leading US 9,623,954 B2 13 14 and trailing edge Struts 116 connected to port and starboard envelope expansion arm 120 in turn transferring the tension outriggers 118. The structure also includes envelope expan onto the envelope; thereby removing slack in the dash sion arms 120, which extend outward from the base structure configuration. on the port and starboard sides in a generally planar direction As shown in FIGS. 14A and 14B, an embodiment with respect to the base structure. A pair of moveable 5 includes strut-core connection points 140 that pivotally longerons—one moveable upper longeron 102 and one connect struts 116 to core 114. Along with pivoting core moveable lower longeron 104, is located on both the port Support member connection points 137, strut-core connec and starboard sides of the aircraft. The longerons 102 and tion points 140 allow the base structure of the aircraft to fold 104 and envelope expansion arms 120 are connected at two to a more compact orientation and improve transportability 10 of the aircraft. FIG. 14 also illustrate how an embodiment structural connection points 136 located on each side of the includes slideable outrigger-support member connection aircraft where the outriggers and struts are connected. Lon points 139 instead of the support member connection at the gerons 102 and 104 are moveable such that the longerons structural connection point. Slideable outrigger-support may be forced in towards core 114 of the aircraft as seen on member connection point 139 slides along outrigger 118 to the port side of the aircraft in FIG. 11. As the longerons 15 aid in folding the aircraft. move towards a more horizontal position, slack would be FIG. 15 provides an embodiment of envelope expansion created in the envelop if it were not for the envelope arm 120. On the smaller sized aircraft, tubes of the appro expansion arms. Envelop expansion arms 120, are under a priate diameter telescope to permit the removal of slack in constant bias force directed away from core 114 and the flexible envelope to enable high speed flight with mini lengthen/extend outward in the direction of the bias force, 20 mum envelope flutter. The tension is provided by spring which in turn keeps envelope 122 taught. The envelope loading features on the structural connection points 136 that expansion arms ultimately increase the span of the aircraft as connect envelope expansion arms 120, as discussed above. seen in FIG. 5C. On larger versions, however, the telescoping tube design is FIG. 11 also illustrates, on the starboard side of the likely be less effective than the use of a unique anisotropic aircraft, the orientation of longerons 102 and 104 and 25 beam design as shown in FIG. 15. The anisotropic beam envelope expansion arm 120 when the starboard translation includes two or more composite rods (preferably a three-rod assembly transitions to an expanded configuration. This configuration) with spring steel cross members embedded configuration includes longerons 102 and 104 in a generally into the structure. The spring constant (controlled by mate vertical orientation, which results in the envelope forcing rial and length) will be varied across the length of the beam 30 to provide variable tension on the envelope based on the envelope expansion arm 120 towards core 114 to overcome pressure on the envelope. One or more of the composite rods the predetermined bias force of envelope expansion arm will interface with the pivot joint assembly at both ends to 120. provide the source of the tension while the other rod(s) will In an embodiment, as shown in FIG. 12, the base structure be anchored against the pivot structure. Any twisting or may include an additional support member 138. Support 35 translation of the rods relative to each other is prevented by member 138 is included to increase the rigidity of the base the spring steel cross members. The design allows different structure and may be connected to the base structure at any spring constants to be used along the length of the structure location known to a person having ordinary skill in the art, by adjusting the stiffness and lengths of the cross members such that the structure improves rigidity. Multiple support so that pressure on the envelope at the tips and trailing edge members may be included depending on aircraft configura- 40 can be significantly reduced while pressure at the leading tion. It should be noted that the base structure would include edge can be maintained. This feature provides Superior support structure 138 on both the port and starboard sides of tension control with a lightweight structure and significantly the aircraft, but FIG. 12 is limited to the starboard section of reduces envelope flutter in the dash mode. the aircraft to reduce clutter. As illustrated in FIG. 15, the cross section of envelope Also illustrated in FIG. 12 is the open space between core 45 expansion arm 120 is preferably triangular in shape with two 114 and outrigger 118. This open space allows for the rods 144 fixed to cross member trusses (made up of cross storage of the additional systems that will likely be used in members 142) and a third rod 146 slidably attached to the operation. The additional systems are preferably mounted to cross member trusses. This unique assembly provides enve the side of core 114 and may include, but are not limited to lope expansion arm 120 with varying length capabilities batteries, computation devices including the navigation sys- 50 while also allowing for varying structural Support depending tem, control computer, battery charger and control device, on the strength of the individual cross member trusses navigation, servo motors, internal payload elements and located along the length of envelope expansion arm 120. structural components for the envelope. Translation Assembly Referring now to FIG. 13, an embodiment of structural Referring to FIG. 16, an embodiment of upper translation connection point 136 includes five connection excluding a 55 assembly 106 includes motor 108, gear assembly 110, and connection for an additional Support member. The connec extendable arms 112. In an embodiment, the center of gear tions of moveable longerons 102 and 104 and the connection assembly 110 is attached to the envelope to aid in maintain for envelope expansion arm 120 are pivoting connections, ing proper envelope positioning. As shown in FIG. 17A, such as ball joints. Strut 116 and outrigger 118 connections extendable arms 112 are attached to upper moveable lon are preferably fixed connections. The pivoting connections 60 gerons 102 and when upper translation assembly 106 is in for moveable longerons 102 and 104 and envelope expan the extended configuration, upper moveable longerons 102 sion arm 120 aid in the convertibility of the aircraft. The are in a generally vertical orientation. Contrastingly, FIG. fixed connections of strut 116 and outrigger 118 aid in the 17B shows upper translation assembly 106 in the retracted rigidity of the base structure to improve the aircraft's ability configuration, with the moveable longerons 102 pulled to operate under the typical forces and stresses associated 65 inwardly towards motor 108. with flight. In an embodiment, the connection for envelope Referring now to FIGS. 18-21, an embodiment includes expansion arm 120 is spring loaded to produce tension on payload hard points 147 on translation assemblies 106 and US 9,623,954 B2 15 16 107. Most commonly, the hard point would be located on the starboard side of the aircraft and a second envelope lower translation assembly. FIGS. 18 and 19 show lower expansion arm located at least partially on a port side translation assembly 107 in the extended configuration and of the aircraft. FIGS. 20 and 21 show the translation assembly in the 2. The aircraft of claim 1, wherein the base structure retracted configuration. Payload hard points 147 provide an 5 includes a central core extending generally parallel to a attachment structure for securing payloads to the aircraft. In central longitudinal axis of the aircraft, a leading edge Strut an embodiment, payload hard point 147 on lower translation extending in a direction perpendicular to and in communi assembly 107 is externally located with respect to the cation with the central core, a trailing edge Strut extending envelope. In this embodiment, extendable arms 112 are in in a direction perpendicular to and in communication with communication with lower moveable longerons inside of the 10 envelope while payload hard point 147 extends downwards the central core, a port side outrigger extending in a direction and out of the envelope allowing certain payloads to be parallel to the central core and in communication with the attached outside of the envelope. leading and trailing edge Struts, and a starboard side outrig An embodiment of the aircraft may be equipped with ger extending in a direction parallel to the central core and flexible solar panels mounted to the upper exterior surface of 15 in communication with the leading and trailing edge struts. the envelope to extended on station performance. This 3. The aircraft of claim 2, further including the flexible allows the aircraft to remain in the LTA configuration and envelope sealing around a perimeter of an open front end of hover while the system batteries are recharged. Energy the core and also sealing around a perimeter an open back recovery through the motor, when equipped, is also available end of the core creating an open fluidic passage through the while in buoyant mode if turned into an oncoming airstream. flexible envelope via the central core. The advantages set forth above, and those made apparent 4. The aircraft of claim 1, further comprising a structural from the foregoing description, are efficiently attained. Since connection point having a first fixed connection attached to certain changes may be made in the above construction an outrigger, a second fixed connection attached to a strut, a without departing from the scope of the invention, it is first pivoting connection attached to one of the upper lon intended that all matters contained in the foregoing descrip 25 geron rods, a second pivoting connection attached to one of tion or shown in the accompanying drawings shall be the lower longeron rods, and a third pivoting connection interpreted as illustrative and not in a limiting sense. attached to one of the envelope expansion arms. It is also to be understood that the following claims are 5. The aircraft of claim 3, further including a propulsion intended to cover all of the generic and specific features of system secured within the central core. Such that the pro the invention herein described, and all statements of the 30 pulsion system receives incoming air through the open front Scope of the invention that, as a matter of language, might end of the core to generate thrust, which exits the open back be said to fall therebetween. end of the core. 6. The aircraft of claim 1, wherein the pair of upper What is claimed is: longeron rods includes a port side longeron rod and a 1. An aircraft comprising: 35 starboard side longeron rod and the pair of lower longeron a flexible envelope that encloses a base structure, a pair of rods includes a port side lower longeron rod and a starboard upper longeron rods and a pair of lower longeron rods side lower longeron rod. with each longeron rod pivotally connected to the base 7. The aircraft of claim 1, wherein the envelope expansion structure, and a pair of envelope expansion arms; arm is an anisotropic beam including two or more composite each upper longeron rod in the pair of upper longeron rods 40 rods with cross members having a predetermined spring further including a curved shape extending between a constant embedded into the structure, one of the composite fore end and an aft end with a vertex at the local rods is pivotally attached to the aircraft and one or more of maximum of the curved shape, wherein the curved the composite rods is anchored against the pivot structure to shape extends away from a lateral axis of the aircraft to provide a tension force. support the flexible envelope; 45 8. The aircraft of claim 1, further including a span that each upper longeron rod in the pair of upper longeron rods increases when the envelope expansion arms are in an further including being in communication with an expanded position and decreases when the envelope expan upper translation assembly, the upper translation sion arms are in a retracted position. assembly adapted to pivot the upper longeron rod, 9. The aircraft of claim 1, further comprising a lighter thereby moving the vertex of the upper longeron rod 50 than-air configuration, the lighter-than-air configuration towards or away from the lateral axis of the aircraft to including: alter a thickness of the aircraft; each of the upper longeron rods is positioned so that each each lower longeron rod in the pair of lower longeron rods respective vertex is a maximum distance from the further including a curved shape extending between a lateral axis of the aircraft, and each of the lower fore end and an aft end with a vertex at a local 55 longeron rods is positioned so that each respective maximum of the curved shape, wherein the curved Vertex is a maximum distance from the lateral axis of shape extends away from the lateral axis of the aircraft the aircraft, thereby increasing the thickness of the to support the flexible envelope; aircraft; and each lower longeron rod in the pair of lower longeron rods each envelope expansion arm is in a retracted position and further including being in communication with a lower 60 the span of the aircraft is at a minimum value. translation assembly, the lower translation assembly 10. The aircraft of claim 1, further comprising a gas adapted to pivot the lower longeron rod, thereby mov storage and retrieval system adapted to house, distribute, and ing the vertex of the lower longeron rod towards or retrieve lighter-than-air gas. away from the lateral axis of the aircraft to alter the 11. The aircraft of claim 1, further including a propulsion thickness of the aircraft; and 65 system having an electrical generator system adapted to the pair of envelope expansion arms including a first convert wind energy into electrical energy while the aircraft envelope expansion arm located at least partially on a is in a lighter-than-air configuration. US 9,623,954 B2 17 18 12. The aircraft of claim 1, wherein each envelope expan sion arm further includes: an adjustable length; a biasing member imparting a constant bias force directed away from the longitudinal axis of the aircraft to increase the length of each envelope expansion arm which in turn increases the span of the aircraft; a retracted position in which the length of the envelope expansion arm is at a minimum value and an expanded position in which the length of the envelope expansion 10 arm is at a maximum value; the retracted position is achieved when a tension force in the flexible envelope overcomes the constant bias force that results from pivoting the vertices of the upper and lower longerons away from the lateral axis of the 15 aircraft; and the expanded position is achieved when the tension force in the flexible envelope is overcome by the constant bias force that results from pivoting the vertices of the upper and lower longerons towards the lateral axis of 20 the aircraft.