Patent Application
20160023748
1. Field of the Invention
This invention relates, generally, to aircrafts. More specifically, it relates to aircrafts convertible between lighter-than-air and heavy-than-air configurations.
2. Brief Description of the Prior Art
Lighter-Than-Air (LTA) aircrafts have some characteristics not shared with Heavier-Than-Air (HTA) aircrafts in that they can maintain altitude without moving in the medium and can do so as long as buoyancy is maintained. LTA aircraft uses low-density gas, such as helium or hydrogen to float in the higher density air. These aircrafts usually employ one or more gasbags filled with the low-density gas to create a buoyancy force that offsets the weight of the aircraft. The downside is that LTA aircrafts are large in size, which is accompanied by large drag characteristics, preventing them from traveling at higher speeds. The current record speed for an LTA aircraft is 112 Km/hr (69.6 mph).
HTA aircrafts use Newton's third law and Bernoulli's principle to achieve flight. HTA crafts generally are either fixed wing or rotor wing aircraft. In either case, part or parts of the structure (e.g., wing, rotors, propellers, fuselage, and control surfaces) have a characteristic shape called an airfoil. Airfoils are generally asymmetric in cross-section with the distance across the upper surface longer than the distance across the lower surface. This causes air moving across the upper surface to travel faster than that traveling across the lower surface causing the pressure on the upper surface to decrease resulting in lift. Lift can also be altered for an airfoil by altering the angle of attack (AoA) relative to the oncoming airflow. Increased AoA causes mass deflection resulting in lift (Newton's third law). Generally, increasing AoA increases lift to an angle at which the airflow separates from the surface of the airfoil causing a condition of aerodynamic stall (at which lift decreases abruptly).
Regardless of how lift is created, an HTA requires a wing-like structure moving through a fluid. Movement requires a power source and no power source is indefinite. Therefore, the HTA aircrafts can only maintain flight for limited periods of time. Even powerless gliders have duration limits as they trade airspeed for altitude gained from thermal lift. However, one of the benefits includes low drag characteristics and thus, high-speed flight.
Any body traveling through a fluid (air in this case) also interacts with the air molecules creating both friction and turbulence, resulting in aerodynamic drag. For a fixed wing aircraft to fly, (change attitude and altitude in the fluid medium) a balance of forces must be achieved with the thrust (motive force of the body through the medium) exceeding the drag and lift exceeding the force of gravity.
The clear tradeoff between LTA and HTA aircrafts is speed verse indefinite flight. The added benefit of an LTA to hover, or station-keep, for extended periods is a significant capacity for observation or surveillance roles. The ideal aircraft would include both indefinite flight and high speed capabilities. This can theoretically be achieved through an aircraft convertible between an LTA and an HTA configuration. Currently, there exist hybrid convertible aircrafts, but none that provide a unique combination of attributes of both a fixed wing aircraft and a LTA craft allowing indefinite mission durations, low energy station keeping, and the ability to dash at relatively high velocities.
U.S. Pat. No. 5,005,783 to James D. Taylor teaches a variable geometry airship capable of converting between a LTA and HTA airship. However, the airship is operationally complex and does not extend the operating range sufficiently to be practical as shown in Table 1. Along with multiple other pitfalls, the shape and design of this airship prevents the airship from transforming into both a symmetric neutral lift configuration and a negative lift configuration, thereby reducing the effectiveness of the airship.
U.S. Pat. No. 4,102,519 to Edward L. Crosby, Jr. teaches a variable lift inflatable airfoil. However, this invention lacks internal moveable structures, which prevent the airfoil from achieving multiple configurations. Additionally, the airfoil lacks a propulsion system and control surfaces.
Accordingly, what is needed is an improved variable geometry aircraft having simple, moveable internal structure to easily convert the aircraft between a lighter-than-air configuration and a heavier-than-air configuration. However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the field of this invention how the shortcomings of the prior art could be overcome.
All referenced publications are incorporated herein by reference in their entirety. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein, is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicant in no way disclaims these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein.
The present invention may address one or more of the problems and deficiencies of the prior art discussed above. However, it is contemplated that the invention may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the claimed invention should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.
The long-standing but heretofore unfulfilled need for an improved variable geometry aircraft having simple, moveable internal structure to easily convert the aircraft between a lighter-than-air configuration and a heavier-than-air configuration is now met by a new, useful, and nonobvious invention.
The novel structure includes a convertible design having a lighter-than-air configuration and a heavier-than-air configuration along with a propulsion system and a flexible envelope enclosing a base structure, moveable longerons, and length-adjusting envelope expansion arms.
The base structure includes a central core running along a central longitudinal axis of the aircraft, a leading edge strut extending in a direction perpendicular to and in communication with the central core, a trailing edge strut extending in a direction perpendicular to and in communication with the central core, a port side outrigger extending in a direction parallel to the central core and in communication with struts, and a starboard side outrigger extending in a direction parallel to the central core and in communication with struts. Additionally, the base structure is in communication with the moveable longerons and the envelope expansion arms.
The moveable longerons include upper and lower longerons. The upper longerons are in communication with the flexible envelope and an upper translation assembly. The upper translation assembly has an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the upper moveable longerons are in a low camber orientation. In transitioning to the retracted configuration, the upper translation assembly pulls the upper moveable longerons inward towards the central longitudinal axis of the aircraft to decrease aircraft thickness. In transitioning to the extended configuration, the upper translation assembly pushes the moveable longerons outward away from the central longitudinal axis of the aircraft to place the upper moveable longerons in a more vertical orientation, which increases the aircraft thickness, compared to longeron's orientation in the retracted configuration.
Similarly, the lower longerons are in communication with the flexible envelope and a lower translation assembly. The lower translation assembly has an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the lower moveable longerons are in a low camber orientation. In transitioning to the retracted configuration, the lower translation assembly pulls the lower moveable longerons inward towards a central longitudinal axis of the aircraft to decrease aircraft thickness. In transitioning to the extended configuration, the lower translation assembly pushes the moveable longerons outward away from the central longitudinal axis of the aircraft to place the lower moveable longerons in a more vertical orientation, which increases the aircraft's thickness, compared to longeron's orientation in the retracted configuration.
The upper and lower moveable longerons each include a port side longeron and a starboard side longeron, wherein each longeron has a generally arc shape and a predetermined length that extends in generally the same direction as the central longitudinal axis of the aircraft. Moreover, the moveable longerons are in a generally vertical orientation when in the high camber position and in an acute angle orientation when in the low camber position.
The length-adjusting envelope expansion arms comprise of a port side envelope expansion arm and a starboard side envelope expansion arm. Each arm has a generally arc shape, is subjected to a bias force attempting to force each arm in a direction away from the central longitudinal axis of the aircraft resulting in an increased arc shape, and is in communication with the flexible envelope. Additionally, each envelope expansion arm has a retracted position and an expanded position, where in the retracted position, the length and arc of the envelope expansion arm is at a minimum and in the expanded position, the length and arc of the envelope expansion arm is at a maximum. The retracted position is achieved when a tension force in the flexible envelope overcomes the bias force, resulting from the transition of the moveable longerons towards a more vertical orientation, thereby reducing the length and arc of the envelope expansion arm. Contrastingly, the expanded position is achieved when the tension force in the flexible envelope is overcome by the bias force, resulting from the transition of the moveable longerons to a more horizontal orientation, thereby increasing the length and arc of the envelope expansion arm. Due to the positioning of the envelope expansion arms, the span of the aircraft is directly affected by the transition between the retracted position and the extended position.
In a certain embodiment, the envelope expansion arm is an anisotropic beam having two or more composite rods with cross members extending between the rods. The cross members are designed to have a predetermined spring constant embedded into the structure. One of the composite rods is pivotally attached to the aircraft and one or more of the composite rods are anchored against the pivot structure to provide a source of the tension.
The novel structure further includes a structural connection point to connect the base structure with the moveable longerons and the envelope expansion arms. The structural connection point has a first fixed connection attached to an outrigger, a second fixed connection attached to a strut, a first pivoting connection attached to one of the upper moveable longeron, a second pivoting connection attached to one of the lower moveable longeron, and a third pivoting connection attached to one of the envelope expansion arms.
Moreover, the aircraft uses a gas storage and retrieval system adapted to house, distribute, and retrieve lighter-than-air gas. This system allows the aircraft to easily convert between a lighter-than-air configuration and a heavier-than-air configuration multiple times without having to refill on gas. Furthermore, the aircraft has a propulsion system that includes an electrical generator system adapted to convert wind energy into electrical energy while the aircraft is in the lighter-than-air configuration. In a certain embodiment, flexible solar panels are attached to an exterior surface of the envelope to retrieve and convert solar energy into electrical energy to extend mission time. In addition, the aircraft has a payload hard point attached to the lower translation assembly to facilitate the attachment and management of external payloads in addition to payloads attached internally to the core structure.
These and other important objects, advantages, and features of the invention will become clear as this disclosure proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the disclosure set forth hereinafter and the scope of the invention will be indicated in the claims.
For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part thereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.
Envelope: is a lightweight flexible material.
Heavier-Than-Air Configuration: is a configuration of the aircraft that cannot maintain altitude without moving in the medium or changing the angle of attack.
Lighter-Than-Air Configuration: is a configuration of the aircraft that can maintain altitude without moving in the medium.
Longeron: is a structural member of the aircraft.
Outrigger: is a rod or bar forming part of a framework and designed to resist compression that extends in generally the same direction as the longitudinal axis of the aircraft.
Payload Hard Point: is an attachment point for payloads or instruments carried on the aircraft.
Propulsion System: is a system capable of moving the aircraft through a medium.
Strut: is a rod or bar forming part of a framework and designed to resist compression.
The present invention is a variable geometry aircraft capable of morphing its shape from a buoyant craft having a symmetric cross-section to an asymmetric lifting body configuration or to a low camber symmetric shape. The convertibility of the present invention provides a unique combination of attributes of both a fixed wing aircraft and a LTA aircraft allowing indefinite mission durations, low energy station keeping and the ability to dash at relatively high velocities (the term “dash” herein refers to this high speed mode where the aircraft has a symmetric zero lift configuration). Additionally, the aircraft is highly portable by folding into a transportable configuration, relatively silent in operation, low cost to produce and operate, and has a unique structure that allows it to operate even if the gas envelope is penetrated. Although there are numerous other aircraft technologies, this device can operate across a number of operating envelopes and perform multiple roles very well without significant compromise (See Table 1 below). This ability is facilitated by the unique internal structural elements of the aircraft.
Table 1 above illustrates that the present invention fills a unique performance niche in that, with low complexity and highly reliable, a unique and broad range of performance feats can be achieved (Note: VTOL stands for vertical takeoff and landing). Furthermore, other Hybrid LTAs (e.g., U.S. Pat. No. 5,005,783) are too operationally complex, and do not extend the operating range sufficiently to be practical. No such designs have ever proceeded beyond the present invention. The unique design features of the present design, taken in combination, make it an improvement on the technology for LTA craft, hybrid LTA craft, and fixed wing flying bodies, especially as applied to unmanned vehicles.
The aircraft has a flexible envelope with a variable rigid inner structure. The envelope has internal bladders adapted to contain low-density buoyant gas. The gas is preferably Helium, however any low-density gas known to a person having ordinary skill in the art is considered. The novel structure includes a central, tube shaped core or cores (depending on size and mission requirements) containing a ducted fan motor, preferably electric, to which all of the other elements electrically attach (power, payload and craft structure). The core(s) use a dual outrigger configuration to support the leading and trailing edges. The two outriggers are generally parallel to the core and attach at the end of the leading and trailing edge members. The outriggers provide structure as well as the mounting for the moveable longerons. The longerons are articulated to adjust the camber and thickness of the aircraft based on flight needs by chamber adjustment assemblies (also referred to as translation assemblies) preferably mounted above and below the core of the aircraft. Payloads are mounted internally to the sides of the core and/or to the translation assembly. This unique structure presents a design that can achieve a range of performances in altitude, payload, and airspeed at a far lower cost and complexity than any existing aircraft of any class.
When the aircraft converts to an LTA configuration—a large buoyant shape, the craft has all of the traditional characteristics of a blimp or rigid airship for station keeping or slow speed flight. By adjusting the shape the lower surface to achieve an airfoil shape, the craft can augment the buoyancy by creating aerodynamic lift to increase its duration of flight. Finally, by reshaping both the upper and lower surfaces, the craft can achieve a relatively low drag configuration for high velocity (in excess of 200 km/hr) to rapidly reposition itself or fly high velocity missions. In a certain embodiment, the design includes a leading edge shield to protect the envelope in high velocity flight.
As shown in
The movement of the longerons and therefore camber-transformation can be accomplished while the craft is airborne and does not require any ground support equipment. The transformation changes both the lift and drag characteristics of the craft to alter the flight characteristics. In a certain embodiment, only the upper or only the lower longerons are moveable to decrease complexity and weight of the aircraft.
Moveable upper longerons 102 and moveable lower longerons 104 are each in communication with upper translation assembly 106 and lower translation assembly 107, respectively. The translation assemblies each include motor 108 (See
The additional structural components contributing to the present invention's superior functionality include cylindrical core 114 extending the length of the aircraft in the longitudinal direction. Surrounding the core is a rigid, preferably rectangular, base structure comprising leading and trailing edge struts 116 connected to port and starboard outriggers 118. The design also includes envelope expansion arms 120 having an adjustable length and a generally arc shape. There is preferably one envelope expansion arm along the port side of the aircraft and one along the starboard side of the aircraft where each is capable of extending outward away from the central longitudinal axis of the aircraft to alter the span of the aircraft. Enclosing the base structure, envelope expansion arms, and longerons is flexible envelope 122.
Also provided in
The moveable longerons, envelope expansion arms, and flexible envelope allow the present invention to operate in various configurations. As shown in
The dash configuration is unique for a partially rigid LTA aircraft. Since the envelope must be flexible to accommodate the shape morphing capability and have very low permeability to Helium while being lightweight, the envelope is preferably made from a plastic sheet material. This material is prone to two negative features that will affect the performance of the LTA in the dash configuration and impact performance overall. One is flutter of the envelope, increasing drag and causing aerodynamic instability. The second is the possibility of penetration of the envelope by airborne hazards (such as insects, birds, debris) at the high speeds. The possibility of penetration is avoided by the installation of leading edge shields that are hinged on the leading edge strut and can expand or contract with the movement of the envelope. Additionally, mechanical stops can be installed to reflect the shape of the leading edge in the dash configuration to remove the possibility of flutter at high speeds.
Due to the variable geometry of the aircraft, it will have a range of performance characteristics from that of a high Coefficient of Drag (CD) dirigible performance to a relatively low CD flying wing configuration. The lift characteristics will also vary from a lift neutral symmetric configuration to a positive lift or negative lift airfoil shape to suit mission requirements. These configurations can be changed dynamically while airborne to suit mission needs. The driving requirement for the device is the desired dash speed of approximately 200 kts. The assessment of performance and structural characteristics has been completed for three different configurations of craft defined by the length or chord of the aircraft and the span of the central, airfoil shaped portion of the craft or span, which excludes the half blimp shape on each end of the craft.
A novel characteristic of this aircraft is the speed at which the aircraft is capable of traveling when in the dash configuration. The equation in Table 2 is used to calculate the amount of force required to move a body through a viscous medium. This is used to derive the motor size to achieve the required speed; thus driving other factors such as weight, power, envelope size etc. The initial calculation is to determine the minimum motor output required to achieve the desired maximum dash velocity of 230 mph at a cruise altitude of 10,000 ft. MSL. Using the desired dash speed shown in Table 2 below, the resultant drag force or the required motor output to overcome that drag is determined. Using a mathematical simulation tool (SimFoil) available from NASA, the CD for various configurations of the aircraft from a large chord to length ratio to a small chord to length ration is calculated. As seen in Table 3, the drag force exhibited by a low chord to length ratio with a highly symmetric profile yields the lowest CD and therefore, the lowest motor size to achieve the desired speeds. The model output corresponding to this performance is shown in
The motor size and number of motors are derived for each of the three configurations to determine if commercially available Electronic Ducted Fan (EDF) motors can be used in the design. The data in Table 3 proves that a single 3000 gmf motor is sufficient to achieve the desired velocity for the 1-meter-by-1-meter configuration. This size motor is readily available for Radio Control (RC) aircraft. For larger size craft, the number of core units would be increased to provide the required thrust. This assessment shows that two core units of roughly the same size as above will propel a 2-meter-by-2-meter design. Larger motors or core combinations of four motors would be required for the 4-meter-by-4-meter design, but still feasible. In a certain embodiment, any number of motors and any type of motors may be used as is known to a person having ordinary skill in the art.
In a certain embodiment, the envelope is comprised of an outer gas containment bag (or envelope), internal reinforcement layer and a secondary containment bag to facilitate Helium recovery. With elements of the LTA structure movable, there is a concern that structural members rubbing on a fairly thin plastic surface could contribute to failure of the envelope. Therefore, a certain embodiment includes reinforcement layers 130 located in areas likely to experience increased wear and tear from the moveable internal structure of the aircraft.
As shown in
In a certain embodiment, as shown in
Also illustrated in
As shown in
On larger versions, the telescoping tube design will likely be less effective than the use of a unique anisotropic beam design used to both provide tension on the envelope and to maintain the leading edge shape of the wing extensions. This design is detailed in
The cross section of envelope expansion arm 120 is preferably triangular in shape with two rods 144 fixed to cross member trusses (made up of cross members 142) and a third rod 144 slidably attached to the cross member trusses. This unique assembly provides envelope expansion arm 120 with varying length capabilities while also allowing for varying structural support depending on the strength of the individual cross member trusses located along the length of envelope expansion arm 120.
In a certain embodiment, translation assemblies 106 and 107 have payload hard points 146. Most commonly, the hard point would be located on the lower translation assembly.
In a certain embodiment requiring extended on station performance, the aircraft is equipped with flexible solar panels mounted to the upper exterior surface of the envelope. This allows the aircraft to remain in the LTA configuration and hover while the system batteries are recharged. Energy recovery through the motor is also available while in buoyant mode if turned into the oncoming airstream.
The advantages set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.
